{"title":"Explore Scientific Filters","description":"\u003cp\u003eExplore Scientific telescope filters help astronomers improve contrast, suppress unwanted light and reveal more detail in the Moon, planets and deep-sky objects. Shop 1.25-inch and 2-inch astronomy filters in Canada, including UHC, OIII, CLS and H-Beta nebula filters, neutral-density Moon filters, and narrowband H-Alpha and SII filters for visual astronomy and astrophotography.\u003c\/p\u003e\u003cp\u003eNot sure which telescope filter you need? Choose UHC or OIII for enhanced nebula contrast, CLS for broader light-pollution reduction, H-Beta for select emission nebulae, or a neutral-density filter for more comfortable lunar observing. Explore the collection and find the right Explore Scientific filter for your telescope, eyepiece or imaging setup.\u003c\/p\u003e","products":[{"product_id":"uhc-filter-2","title":"Explore Scientific 2-inch UHC Nebula Filter","description":"\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003eOne of the most important obstacles for the exploration of the night sky is the brightening of the night sky by artificial lights, such as streetlights. The night sky is not really dark in the vicinity of towns or cities, which reduces the visibility of objects bejond the solar systems enourmously. Depending on the type of the celestial object it is possible to increase the contrast dramatically by blocking the annoying artifical light. \u003c\/span\u003e\u003cdiv\u003e\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003e\u003cbr\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003eThe Explore Scientific UHC filter uses a characteristic property of the so called emmission nebulae. Those objects glow in special colors, the so called emmission lines. Those emmission lines are linked to chemical elements - in this case hydrogen at 486nm and 656nm, plus oxygen at 496nm and 501nm. \u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003e\u003cbr\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003eThe Explore Scientific UHC nebula filter blocks all other colors (and thereby nearly all of the artificial light) and only the emmission line of the hydrogen and oxygen can pass the filter. The result is astonishing: suddenly nebulae are visible at locations that were completely empty without filters. In suburbian skies for example the Owl-nebula M97, the Veil-nebula Ngc 6992 or even the bright Dumbell-nebula M27are not clearly visible.\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003e\u003cbr\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\n\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003eBy using this filter you can see the nebulae and their structures without problems. A must for every visual observer. The Explore Scientific nebula filters come with a individual test certificate - your guarantee to receive a premium filter.\u003c\/span\u003e   \u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003e\u003cbr\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"color: rgb(50, 50, 50); font-family: Arial, Helvetica, sans-serif; font-size: 12px; line-height: 16.2px; background-color: rgb(255, 255, 255);\"\u003e UHC Nebula Filter. Range from 458nm to 508nm with peak at 488nm. Peak transmission 96.7%\u003c\/span\u003e\u003c\/div\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":44013255852143,"sku":"310210","price":184.2,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/0310210_PAC_small__35622.jpg?v=1766550360"},{"product_id":"h-beta-filter-2","title":"Explore Scientific 2-inch H-Beta Nebula Filter","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThe Explore Scientific H-Beta is a 2.0-inch nebula filter built around a single emission line. Explore Scientific quotes 94.5% transmission across a 478nm to 496nm passband, peaking at 489nm. Everything outside that narrow window is blocked, which includes almost the whole spectrum of artificial lighting.\u003c\/p\u003e\n\u003cp\u003e489nm is where hydrogen-beta sits — the second line of the Balmer series, emitted by ionised hydrogen throughout the interstellar medium. A filter this narrow throws away the sky and keeps the nebula, and the result on the right target is a rise in contrast that no amount of aperture on its own produces.\u003c\/p\u003e\n\u003cp\u003eIt is a 2.0-inch filter, so it threads into 2-inch eyepieces, 2-inch diagonals and standard filter wheels.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eObservers working under light-polluted skies\u003c\/strong\u003e on hydrogen-emission nebulae, where blocking everything outside 478–496nm removes most of the sky glow along with it.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eObservers with real aperture:\u003c\/strong\u003e a passband this narrow removes a great deal of light, and the objects it serves are faint to start with. The more aperture behind it, the more it delivers.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePeople chasing the classic H-beta targets:\u003c\/strong\u003e the Horsehead and the California Nebula are the two objects most often cited as needing this filter specifically, and both emit strongly at hydrogen-beta.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eObservers who already own an oxygen-III or narrowband filter\u003c\/strong\u003e and want to cover the emission line those do not favour.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eImagers building a filter set\u003c\/strong\u003e where a discrete hydrogen-beta channel is part of the plan.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e94.5% quoted transmission\u003c\/strong\u003e at the passband — a high figure, which matters enormously when the filter is deliberately discarding most of the incoming light.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e478nm to 496nm passband, peaking at 489nm:\u003c\/strong\u003e an 18nm window centred on the hydrogen-beta line.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBlocks essentially everything outside the passband,\u003c\/strong\u003e including mercury, sodium and most LED street lighting, which fall well away from 489nm.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e2.0-inch format,\u003c\/strong\u003e compatible with 2-inch eyepieces, 2-inch diagonals and standard filter wheels.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSingle-line design:\u003c\/strong\u003e unlike a broadband light-pollution filter that passes several regions, this one isolates a single emission line, which is what produces the contrast gain.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eVisual observing of hydrogen-emission nebulae from suburban and light-polluted sites.\u003c\/li\u003e\n\u003cli\u003eThe Horsehead, the California Nebula and other objects traditionally associated with H-beta.\u003c\/li\u003e\n\u003cli\u003eAdding a discrete hydrogen-beta channel to an existing narrowband filter set.\u003c\/li\u003e\n\u003cli\u003eComparative observing, where switching between an oxygen-III and an H-beta filter shows which part of a nebula emits where.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eFits 2-inch eyepieces and 2-inch diagonals,\u003c\/strong\u003e threading into the base of the barrel in the usual way, and it fits standard 2-inch filter wheels.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTelescopes with 1.25-inch focusers\u003c\/strong\u003e use the 1.25-inch version of the filter rather than this one; we stock both sizes.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePairs naturally with a low-power, wide-field eyepiece.\u003c\/strong\u003e Large emission nebulae benefit from field as much as from contrast, so a long-focal-length 2-inch eyepiece is the usual partner.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eComplements rather than replaces an oxygen-III filter.\u003c\/strong\u003e The two isolate different emission lines and favour different objects, which is why many observers carry both.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFilter stacking\u003c\/strong\u003e is possible mechanically, though combining two narrow filters leaves very little light through. One at a time is how these are normally used.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eGood to Know Before You Order\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eAn H-beta filter is a specialist instrument, not a general improvement.\u003c\/strong\u003e On star clusters, galaxies, the Moon and the planets it simply dims the view, because those objects emit across the spectrum rather than at 489nm. It earns its place on a specific and short list of targets.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIt works best behind aperture.\u003c\/strong\u003e An 18nm passband discards most of the light reaching the telescope, so the same filter that transforms the view in a large instrument may show very little in a small one. Tell us your aperture and we will give you a straight answer about what to expect.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThe view goes dark and monochrome.\u003c\/strong\u003e That is the filter doing exactly what it is designed to do, and letting your eyes readapt for a few minutes after fitting it is part of using it well.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eExplore Scientific publishes no specification table for this filter.\u003c\/strong\u003e Substrate, thickness, thread pitch and coating count are absent from the table below rather than estimated. If a physical dimension matters for your filter wheel or drawer, ask and we will measure the item we hold in stock.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIt is a 2.0-inch filter.\u003c\/strong\u003e A telescope with a 1.25-inch focuser takes the smaller version instead, which we also carry.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eFrequently Asked Questions\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003eIs it difficult to set up?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo — it threads onto the base of a 2-inch eyepiece barrel or into a 2-inch diagonal or filter wheel, and that is the whole of the installation. There is nothing to align or adjust, and it takes about fifteen seconds in the dark once you have done it once.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat does it actually do?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt passes light between 478nm and 496nm, peaking at 489nm, and blocks the rest. Because hydrogen-beta emission falls inside that window and street lighting does not, the nebula stays and the sky glow largely goes.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhich objects is it for?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNebulae that emit strongly at hydrogen-beta. The Horsehead and the California Nebula are the two most commonly named, and it is worth trying on other emission nebulae to see how they respond.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs it the same as an oxygen-III or a light-pollution filter?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo. An oxygen-III filter isolates a different pair of lines and suits a different set of objects; a broadband light-pollution filter passes much more of the spectrum and gives a gentler effect on a wider range of targets. The H-beta is the narrowest and most specialised of the three.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWill it help with galaxies?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eGalaxies emit across the whole spectrum, so a filter that blocks all but 18nm of it dims them. A broadband light-pollution filter is the more useful tool there, and we stock those.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan I use it for imaging?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eYes — a 2-inch H-beta filter fits standard filter wheels, and the narrow passband works the same way for a sensor as for an eye. Exposures run longer, which is the expected cost of a narrow bandpass.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eIn short: a 2.0-inch hydrogen-beta filter passing 478nm to 496nm at a quoted 94.5% transmission, peaking at 489nm — a narrow, specialised filter that lifts a short list of emission nebulae out of a bright sky. If you would like help deciding whether an H-beta, an oxygen-III or a broadband filter suits the objects and the aperture you work with, tell us what you observe and we will give you our honest recommendation.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":44013257097327,"sku":"310230","price":200.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/0310200_PAC_small__83292.jpg?v=1766550367"},{"product_id":"cls-fliter-2","title":"Explore Scientific 2-inch CLS Light Pollution Reduction Nebula Filter","description":"\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003e\u003cspan style=\"font-size: 13px; font-family: 'Source Sans Pro', sans-serif;\"\u003eOne of the most important obstacles for the exploration of the night sky is the brightening of the night sky by artificial lights, such as streetlights. The night sky is not really dark in the vicinity of towns or cities, which reduces the visibility of objects beyond the solar systems enormously. \u003c\/span\u003e\u003c\/span\u003e\u003cdiv\u003e\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003e\u003cbr\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"font-family: \" source sans pro sans-serif font-size: background-color: rgb\u003eThe Explore Scientific CLS nebula filter blocks those colors and thereby increases contrast - the light ot the celestial objects can pass the filter. The result is astonishing: suddenly objects are visible at locations that were completely empty without filters. In suburban skies for example the large galaxy M101, the Veil-nebula Ngc 6992 or even the bright Dumbbell-nebula M27 are not clearly visible. By using this filter you can see the nebulae and their structures. \u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003e\u003cbr\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\n\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003eThe Explore Scientific nebula filters come with a individual test certificate - your guarantee to receive a premium filter.\u003c\/span\u003e  \u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003e\u003cbr\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"color: rgb(50, 50, 50); font-family: Arial, Helvetica, sans-serif; font-size: 12px; line-height: 16.2px; background-color: rgb(255, 255, 255);\"\u003eExplore Scientific 2\" CLS City Light Pollution Reduction Filter. Range from 436nm to 536nm with peak at 488nm. Peak transmission 98.3%\u003c\/span\u003e\u003c\/div\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":44013257850991,"sku":"310220","price":162.99,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/0310220_PAC_small__15891.jpg?v=1766550373"},{"product_id":"oxygen-iii-2-filter","title":"Explore Scientific 2-inch Oxygen III (OIII) Nebula Filter","description":"\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003e\u003cspan style=\"font-size: 13px; font-family: 'Source Sans Pro', sans-serif;\"\u003eOne of the most important obstacles for the exploration of the night sky is the brightening of the night sky by artificial lights, such as streetlights. The night sky is not really dark in the vicinity of towns or cities, which reduces the visibility of objects beyond the solar systems enormously. Depending on the type of the celestial object it is possible to increase the contrast dramatically by blocking the annoying artificial light. The Explore Scientific O-III filter uses a characteristic property of the so called emission nebulae.\u003c\/span\u003e\u003c\/span\u003e\u003cdiv\u003e\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003e\u003cspan style=\"font-size: 13px; font-family: 'Source Sans Pro', sans-serif;\"\u003e\u003cbr\u003e\u003c\/span\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003e\u003cspan style=\"font-size: 13px; font-family: 'Source Sans Pro', sans-serif;\"\u003eThose objects glow in special colors, the so called emission lines. Those emission lines are linked to chemical elements - in this case oxygen. The Explore Scientific O-III nebula filter blocks all other colors (and thereby nearly all of the artificial light) and only the two emission lines of the oxygen can pass the filter. \u003c\/span\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003e\u003cspan style=\"font-size: 13px; font-family: 'Source Sans Pro', sans-serif;\"\u003e\u003cbr\u003e\u003c\/span\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\n\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003e\u003cspan style=\"font-size: 13px; font-family: 'Source Sans Pro', sans-serif;\"\u003eThe result is astonishing: suddenly nebulae are visible at locations that were completely empty without filters. In suburbian skies for example the veil nebula NGC 6992 is almost not visible with a 200mm telescope. By using this filter you can see the nebula and its structures without problems. The Explore Scientific nebula filters come with a individual test certificate - your guarantee to receive a premium filter.\u003c\/span\u003e\u003c\/span\u003e   \u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"color: rgb(50, 50, 50); font-family: Arial, Helvetica, sans-serif; font-size: 12px; line-height: 16.2px; background-color: rgb(255, 255, 255);\"\u003e\u003cbr\u003e\u003c\/span\u003e\u003c\/div\u003e\u003cdiv\u003e\u003cspan style=\"color: rgb(50, 50, 50); font-family: Arial, Helvetica, sans-serif; font-size: 12px; line-height: 16.2px; background-color: rgb(255, 255, 255);\"\u003eExplore Scientific 2\" Oxygen-III Nebula Filter. Range from 483nm to 511nm with peak at 496nm. Peak transmission 96.7%. \u003c\/span\u003e\u003c\/div\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":44013258375279,"sku":"310200","price":184.2,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/0310200_PAC_small__91034.jpg?v=1766550379"},{"product_id":"neutral-density-0-9-2-filter","title":"Explore Scientific 2-inch ND 0.9 Neutral Density Moon Filter with 13 Percent Transmission","description":"\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003eThe neutral density filter transmits light uniformly across the entire visual spectrum. It serves as an excellent filter to reduce glare and irradiation when observing the Moon with any telescope 4\"(10.2cm) and larger. The ND96 filter may also be employed in the splitting of close double stars where one of the binary pair significantly exceeds the other in brightness.\u003c\/span\u003e\u003cbr style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003e\u003cbr style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003e\u003cspan style=\"font-family: 'Source Sans Pro', sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);\"\u003eColor Filter #ND96 Moon Filter (0.9 density; 13% transmission)\u003c\/span\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":44013259292783,"sku":"310240","price":73.67,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/2moon_2_1__31188.jpg?v=1766550385"},{"product_id":"explore-scientific-1-25-inch-cls-light-pollution-reduction-filter","title":"Explore Scientific 1.25-inch CLS Light Pollution Reduction Nebula Filter","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific CLS Nebula Filter is a 1.25-inch light pollution reduction filter intended for general deep sky observing from skies that are not truly dark. Explore Scientific describes it as a general-purpose light-pollution reduction filter for a broad range of deep sky objects, and publishes a wavelength range of 436nm to 536nm with peak transmission at 488nm and a transmission rate of 98.3 per cent. That passband sits directly over the blue-green region where the strongest visual emission lines of nebulae live, so the light you want arrives with very little loss while a good deal of the sky glow around it is held back. It is item 310225 and threads into the barrel of any standard 1.25-inch eyepiece.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThis filter is for the observer whose sky is the limiting factor rather than the telescope. If you are working from a driveway in a town or a suburb, the problem is rarely resolution or aperture; it is that the background of the field is grey instead of black, and faint extended objects simply do not have enough contrast against it to register. A CLS filter attacks that directly. Rather than making the object brighter, it darkens the field around it, and the object separates from the background because the ratio between the two has changed.\u003c\/p\u003e\u003cp\u003eIt is also the sensible first filter for someone who is not ready to commit to a narrowband set. A dedicated O-III or H-beta filter is a far more aggressive tool and will show you a small number of targets spectacularly while making most of the sky unusable. The CLS is deliberately broader. You can leave it in the eyepiece and star hop, work through an evening of Messier objects, and keep enough field stars visible to know where you are.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003ePublished wavelength range of 436nm to 536nm, covering the blue-green band where the brightest visual nebula emission occurs\u003c\/li\u003e\n\u003cli\u003ePeak transmission at 488nm, close to the O-III doublet that carries most of the visible signal in planetary and emission nebulae\u003c\/li\u003e\n\u003cli\u003ePublished transmission rate of 98.3 per cent at peak, so very little of the wanted light is given up to the coating\u003c\/li\u003e\n\u003cli\u003eStandard 1.25-inch filter thread, compatible with the great majority of 1.25-inch eyepieces and diagonals\u003c\/li\u003e\n\u003cli\u003eThreaded cell that stacks with other standard 1.25-inch filters if you want to combine effects\u003c\/li\u003e\n\u003cli\u003eBroadband rather than line-specific behaviour, so field stars remain visible and star hopping stays practical\u003c\/li\u003e\n\u003cli\u003eWorks with any focal ratio and requires no power, batteries or adapters\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eA light pollution reduction filter is an interference filter, not a piece of tinted glass. Alternating thin layers of material with different refractive indices are deposited on the substrate, and their thicknesses are chosen so that reflections within the stack cancel at some wavelengths and reinforce at others. The result is a transmission curve that can be shaped, in this case to pass the 436nm to 536nm region efficiently and to reject a good deal of what falls outside it. The wavelengths that mercury and older sodium street lighting throw into the sky sit largely outside that window, while the emission lines that make nebulae visible sit inside it. Because the filter subtracts rather than adds, the whole field including the target does get dimmer in absolute terms; what improves is contrast, and contrast is what the eye actually uses to detect faint extended detail. It is worth understanding that this is a physical wavelength selection, which is also why the filter cannot help with light that arrives at the same wavelengths as your target.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eVisual observing of emission and planetary nebulae from suburban or town skies\u003c\/li\u003e\n\u003cli\u003eGeneral deep sky sweeping where you want a darker background without losing field stars\u003c\/li\u003e\n\u003cli\u003eOutreach and public nights under compromised lighting, where the improvement is easy for a newcomer to see\u003c\/li\u003e\n\u003cli\u003eA first light pollution filter for an observer who is not yet ready for narrowband\u003c\/li\u003e\n\u003cli\u003eReducing the visual impact of moonlight-brightened sky on brighter nebulae\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe filter uses the standard 1.25-inch filter thread found on the barrel of most 1.25-inch eyepieces, and it can equally be threaded into many 1.25-inch star diagonals and camera nosepieces. A small number of eyepieces have unusually deep or recessed barrels and can be awkward to thread by hand, and a very small number of older or specialised barrels are not threaded at all. If you are unsure whether it will thread into a particular eyepiece, contact our team in Bolton with the model and we will confirm it before you order. If you also observe with 2-inch eyepieces, note that this filter will not fit them and a 2-inch version is a separate item.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. Beyond that, set expectations honestly on performance. A CLS filter gives its best results on emission and planetary nebulae. Galaxies, globular clusters and open clusters shine by broadband starlight, and any filter that removes part of the spectrum removes part of their light too, so the gain on those targets ranges from slight to none. The filter also cannot do anything about modern broad-spectrum white LED street lighting, which puts energy right across the visible band including inside the passband. Nothing is included beyond the filter itself in its case; eyepieces, diagonals and adapters are separate.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eWill this make faint objects brighter?\u003c\/strong\u003e No, and no filter can. It removes unwanted light, so the whole view including the target gets slightly dimmer. What increases is the contrast between the object and the sky background, and that is what determines whether you can see faint detail at all.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it for astrophotography?\u003c\/strong\u003e You can thread it into a 1.25-inch camera nosepiece and it will help under light pollution, though it is designed and specified as a visual filter. Imagers working seriously under light pollution usually move to narrowband filters matched to their sensor and optical train.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it work on galaxies?\u003c\/strong\u003e Only marginally. Galaxy light is broadband continuum, so it is attenuated along with the sky glow. The honest answer is that this filter earns its place on nebulae.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it fit my 2-inch eyepieces?\u003c\/strong\u003e No. This is the 1.25-inch version and threads only into 1.25-inch barrels. Ask us about the 2-inch size if that is what your eyepieces use.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eIf your observing site is bright and your nebula views are washed out, a broadband light pollution filter is the least expensive change that will visibly help. The CLS is an easy filter to live with because it is gentle enough to leave in place all evening. Contact our team in Bolton if you would like help deciding between this and a narrowband filter for your sky and your telescope.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958533185647,"sku":"310225","price":117.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/0310225_PAC.jpg?v=1785960458"},{"product_id":"explore-scientific-1-25-inch-nd-0-9-neutral-density-moon-filter","title":"Explore Scientific 1.25-inch ND 0.9 Neutral Density Moon Filter with 13 Percent Transmission","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThis is the Explore Scientific ND96 neutral density filter in the 1.25-inch size, item 310245, supplied at an optical density of 0.9. Explore Scientific publishes a transmission figure of 13 per cent and describes the filter as transmitting light uniformly across the entire visual spectrum. In practice that means it takes roughly seven eighths of the light out of the view without tinting it, which is exactly what you want when the problem is simply too much brightness. The vendor recommends it for reducing glare and irradiation when observing the Moon with any telescope of 4 inches (10.2cm) aperture and larger, and notes its usefulness in splitting close double stars where one member of the pair is far brighter than the other.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eAnyone who has put a 6-inch or 8-inch telescope on a gibbous Moon knows the problem this solves. The Moon is not a faint object; through a decent aperture it is dazzling, and the dazzle is not just uncomfortable. Once the eye is flooded, it loses the ability to discriminate subtle tonal differences, and irradiation, the tendency of a very bright area to visually bleed into the dark area beside it, softens the terminator and washes out the low-contrast detail on crater floors and mare surfaces. You end up seeing a brilliant white disc rather than a landscape. Cutting the brightness back lets the eye work in a comfortable range again, and detail that was always in the image becomes visible.\u003c\/p\u003e\u003cp\u003eThe second job is double stars. When a bright primary sits close to a much fainter companion, the glare halo around the primary can simply swallow the companion. Dimming both by the same factor shrinks that halo and often lifts the secondary clear of it, which is why experienced double star observers keep a neutral density filter in the case even when the Moon is nowhere in the sky.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eOptical density of 0.9, giving a published transmission of 13 per cent across the visual spectrum\u003c\/li\u003e\n\u003cli\u003eNeutral by design, so lunar and planetary colour and albedo relationships are preserved rather than tinted\u003c\/li\u003e\n\u003cli\u003eStandard 1.25-inch filter thread that fits the barrel of most 1.25-inch eyepieces and many diagonals\u003c\/li\u003e\n\u003cli\u003eRecommended by Explore Scientific for telescopes of 4 inches (10.2cm) aperture and larger\u003c\/li\u003e\n\u003cli\u003eUseful on unequal double star pairs where glare from the primary hides the companion\u003c\/li\u003e\n\u003cli\u003eThreads onto other 1.25-inch filters if you want to stack density or combine with a colour filter\u003c\/li\u003e\n\u003cli\u003eEntirely passive, with no power, adapters or maintenance required\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eOptical density is a base-ten logarithmic measure of attenuation. A density of 0.9 corresponds to ten raised to the power of minus 0.9, which is about 0.126, or the 13 per cent that Explore Scientific publishes. Expressed another way, the filter costs you a little over two magnitudes of brightness. The important word in the name is neutral: the attenuation is intended to be flat with wavelength, so red, green and blue are reduced by the same proportion. That is what separates a neutral density filter from a coloured or so-called moon filter with a green cast, which changes the apparent tone of what you are looking at. Because lunar and planetary observing depends heavily on reading subtle albedo differences, keeping the response flat matters more than it might sound. The other reason density is chosen rather than simply stopping down the aperture is resolution. An aperture mask reduces brightness but also reduces the resolving power and increases the diffraction pattern, whereas a neutral density filter leaves the full aperture and its full resolution intact and only removes light.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eLunar observing near first and last quarter through to full, especially with 4-inch and larger telescopes\u003c\/li\u003e\n\u003cli\u003eSplitting close double stars where the components differ significantly in brightness\u003c\/li\u003e\n\u003cli\u003eTaming brightness on Venus, which is dazzling and largely featureless at full aperture\u003c\/li\u003e\n\u003cli\u003eComfortable extended lunar sessions and public viewing, where eye fatigue is a real limit\u003c\/li\u003e\n\u003cli\u003eStacking with a second filter when the Moon is full and a single density is not enough\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe cell uses the common 1.25-inch filter thread and screws into the barrel of the great majority of 1.25-inch eyepieces, as well as many 1.25-inch star diagonals and camera nosepieces. Because the front of the cell is also threaded, you can stack this filter with another neutral density or with a colour filter, though every additional glass surface adds a little scatter, so stack only when you need to. If you use 2-inch eyepieces, this filter will not fit them and you will want the 2-inch equivalent. If you are unsure whether your particular eyepiece barrel is threaded, send us the model and our team in Bolton will confirm before you order.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. Two other things are worth stating plainly. First, this is not a solar filter and must never be used to look at the Sun. Neutral density filters of this type are eyepiece filters, and no eyepiece filter is safe for solar observing; solar work requires a certified full aperture filter fitted at the front of the telescope. Second, 0.9 is a moderate density. On a full Moon through a large aperture some observers still find it bright and prefer to stack a second filter or step up to a variable polarising filter that can be dialled continuously. Only the filter and its case are included.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eHow much does it actually dim the view?\u003c\/strong\u003e To about 13 per cent of the unfiltered brightness, a little over two magnitudes. That is a substantial cut and it is the right order of magnitude for the Moon in a 4-inch to 10-inch telescope.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it add a colour cast?\u003c\/strong\u003e It is designed not to. The attenuation is intended to be uniform across the visual spectrum, which is why it is called neutral density and why it suits lunar and planetary work where subtle tonal differences carry the detail.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it to look at the Sun?\u003c\/strong\u003e No, under no circumstances. Use only a properly certified full aperture solar filter for the Sun. Contact us if you need advice on safe solar equipment.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs it useful in a small telescope?\u003c\/strong\u003e Explore Scientific recommends it for apertures of 4 inches and larger. In a 60mm or 80mm refractor the Moon is usually manageable without it, although a full Moon can still be bright enough to justify one.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eA neutral density filter is a small, inexpensive accessory that makes the single most-observed object in the sky far more rewarding to look at, and it earns its keep again on tight, unequal double stars. At 0.9 density it is a sensible general-purpose choice for most amateur apertures. Contact our team in Bolton if you would like help choosing between a fixed density like this one and a variable polarising filter.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958567460975,"sku":"310245","price":42.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310245.jpg?v=1785960535"},{"product_id":"explore-scientific-1-25-inch-sulphur-ii-12nm-nebula-filter","title":"Explore Scientific 1.25-inch Sulphur II 12nm Narrowband Nebula Filter","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific 1.25-inch S-II Nebula Filter is a narrowband interference filter with a 12 nm passband centred on the ionised sulphur emission line at 672 nm. Explore Scientific states the design goal plainly: block the rest of the spectrum, and with it almost all artificial light, so that only the sulphur emission from the nebula reaches your eyepiece or sensor. It is supplied in a standard 1.25-inch threaded cell, and like every filter in this Explore Scientific narrowband range it arrives with an individual test report for the specific piece of glass in the cell.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eS-II is the difficult member of the usual narrowband trio. In most emission nebulae the ionised sulphur signal is considerably weaker than hydrogen-alpha, and it is frequently weaker than doubly ionised oxygen as well. That changes how you should think about bandpass. Going narrower always buys contrast, because the sky background falls roughly in proportion to the width of the passband while the emission line itself passes through intact. It also costs you, though: a narrower filter is less tolerant of a converging light cone, less tolerant of focus and temperature drift, and it makes an already faint subject fainter on the chip. With S-II you are starting from a weak signal, so 12 nm is the sensible default rather than a compromise.\u003c\/p\u003e\u003cp\u003eThis is the filter to reach for if you are assembling your first mapped-colour narrowband set, if you image at f\/4 to f\/6 where a very narrow band begins to shift and lose effective transmission across the field, or if you are working with a 200 mm or smaller aperture and cannot realistically commit twenty-minute subframes to the weakest channel of a three-channel project. It suits 1.25-inch filter wheels and sensors up to roughly Four Thirds or small APS-C format. If your rig is fast and modest in aperture, the extra photons the 12 nm passband lets through will do more for your final image than the extra sky rejection of a 6.5 nm filter would.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e12 nm passband, wide enough to keep the weak S-II signal usable on modest apertures and fast optics\u003c\/li\u003e\n\u003cli\u003eCentred on the ionised sulphur emission line at 672 nm, deep in the red\u003c\/li\u003e\n\u003cli\u003eInterference coatings reject the rest of the visible spectrum, including the mercury and sodium vapour lines that dominate urban skyglow\u003c\/li\u003e\n\u003cli\u003eStandard 1.25-inch threaded cell that fits eyepiece barrels, camera nosepieces and 1.25-inch filter wheels\u003c\/li\u003e\n\u003cli\u003eIndividual test report for your specific filter included in the scope of delivery\u003c\/li\u003e\n\u003cli\u003eBuilt for the sulphur channel of narrowband imaging, with useful contrast on bright planetary nebulae in larger visual apertures\u003c\/li\u003e\n\u003cli\u003eExplore Scientific positions the S-II filter specifically at urban observers and astrophotographers fighting a brightened sky\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eAn interference filter of this kind works through thin-film physics rather than absorption. Many alternating layers of high and low refractive index material are deposited on the substrate, and light at the design wavelength reflects between those layers in phase and is transmitted, while everything else interferes destructively and is rejected. The consequence worth understanding is that the passband is defined for light arriving perpendicular to the coating. As the angle of incidence rises, the effective optical thickness of each layer falls and the whole passband shifts toward the blue. In the converging beam of a fast telescope the edge rays arrive at a meaningful angle, so part of your light cone sees a passband that no longer sits on 672 nm. A 12 nm window has enough margin to absorb that shift at ordinary imaging speeds, which is exactly why it remains a practical choice for f\/4 and f\/5 systems where a much narrower filter would start to lose transmission toward the edge of the field.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eThe sulphur channel of mapped-colour narrowband imaging on emission nebulae\u003c\/li\u003e\n\u003cli\u003eSupernova remnants such as the Veil, where S-II structure is genuinely distinct from hydrogen\u003c\/li\u003e\n\u003cli\u003ePlanetary nebulae, where sulphur often traces the outer shells\u003c\/li\u003e\n\u003cli\u003eImaging from suburban and urban sites, or under moonlight, when broadband work is not an option\u003c\/li\u003e\n\u003cli\u003eContrast work on bright planetary nebulae visually, with generous aperture\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe cell uses the standard 1.25-inch filter thread, so it screws into the bottom of a conventional 1.25-inch eyepiece barrel, into a 1.25-inch camera nosepiece, or into the carousel of a 1.25-inch filter wheel. It will not fit a 2-inch wheel or an unmounted 31 mm or 36 mm filter drawer without an adapter, and mounted 1.25-inch filters are too thick for many slim internal drawers. If you are building a full narrowband set, keep it within the same Explore Scientific 1.25-inch family so that your exposure planning stays consistent from channel to channel. If you are unsure whether your particular filter wheel, off-axis guider or backfocus budget will take a mounted 1.25-inch filter, contact our team in Bolton and we will confirm the fit before you order.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. Beyond that, be realistic about visual use: at 672 nm the dark-adapted eye is already well down its sensitivity curve, and on all but the brightest planetary nebulae in a large aperture this behaves as a photographic filter. Explore Scientific does not publish a peak transmission figure, a substrate specification or a full blocking range for this filter, so we will not quote numbers we cannot source; the individual test report in the box gives the measured curve for the filter you receive. Explore Scientific lists the filter and that test report as the scope of delivery, so no eyepiece, nosepiece, filter wheel or adapter is included.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eWill I see anything through this filter visually?\u003c\/strong\u003e On a large aperture and a bright planetary nebula, sometimes. In general, no. S-II sits deep in the red where the dark-adapted eye is least sensitive, and a 12 nm window passes very little total light. Treat it as an imaging filter and use an O-III or broadband nebula filter for visual work.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhy choose 12 nm rather than the 6.5 nm version?\u003c\/strong\u003e Because sulphur is faint. The narrower filter darkens the sky background further, but it also demands longer subframes, more aperture and a slower light cone to hold its passband. If you image at f\/4 to f\/6, or your total integration per target is a few hours rather than tens of hours, the 12 nm filter will usually give you the cleaner sulphur channel.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it work with a one-shot colour camera or a DSLR?\u003c\/strong\u003e It will pass light, but only the red-sensitive photosites contribute, so most of your sensor sits idle and the Bayer array costs you further transmission. Narrowband filters of this kind are built around monochrome cameras.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow much sensor will it cover?\u003c\/strong\u003e A mounted 1.25-inch filter typically offers a clear aperture near 27 mm, which comfortably covers Four Thirds and smaller sensors. On APS-C and larger, expect vignetting and step up to the 2-inch version.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eThe 12 nm S-II is the version of this filter that keeps the weakest narrowband channel practical for ordinary apertures, ordinary exposure budgets and fast optics. If you are building a 1.25-inch narrowband set and want sulphur data you can actually stretch, this is the sensible place to start. Contact us and we will help you match it to your camera, wheel and focal ratio.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958583418991,"sku":"310115","price":179.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310115_2.jpg?v=1785960578"},{"product_id":"explore-scientific-2-inch-variable-polarizing-filter","title":"Explore Scientific 2-inch Variable Polarizing Filter with Continuously Adjustable Brightness","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific 2-inch Variable Polarizing Filter, item 310250, is a two-element polarising filter that lets you set image brightness continuously rather than in fixed steps. Explore Scientific publishes a light transmission range of 40 per cent down to 1 per cent, adjusted simply by rotating the two halves of the housing against one another. The cell is black anodised aluminium with a 2-inch filter thread on both the inside and the outside, and the optical elements are described as highly parallel optical glass. A dust cover is supplied. Explore Scientific positions it as a universally applicable filter for lunar, planetary and solar observing, particularly behind a Herschel wedge or on large apertures where brightness needs to come down to a comfortable level.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThis is the filter for the observer who is tired of swapping fixed densities. Brightness at the eyepiece is a moving target: the Moon changes by several magnitudes between a thin crescent and full, a 12-inch reflector delivers far more light than a 4-inch refractor at the same magnification, and the eyepiece you reach for at the end of the session may be four times faster than the one you started with. A fixed neutral density filter is chosen for one of those situations and is wrong for the others. Here you leave the filter in place and turn the ring until the view looks right, then keep turning as conditions change.\u003c\/p\u003e\u003cp\u003eIt also earns its place with anyone doing white-light solar work behind a Herschel wedge. A wedge dumps the great majority of the solar energy out of the back, but what reaches the eyepiece is still bright, and because a wedge outputs strongly polarised light, a polarising filter behind it is the accepted way to trim the remaining brightness smoothly to a comfortable working level.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eContinuously variable transmission from a published 40 per cent down to 1 per cent\u003c\/li\u003e\n\u003cli\u003eAdjustment by rotating the two halves of the housing, so brightness can be set at the eyepiece without unthreading anything\u003c\/li\u003e\n\u003cli\u003eStandard 2-inch filter thread on both the inside and the outside of the cell, so it can be sandwiched between accessories or carry a second filter\u003c\/li\u003e\n\u003cli\u003eBlack anodised aluminium housing, which suppresses internal reflections as well as resisting handling wear\u003c\/li\u003e\n\u003cli\u003eHighly parallel optical glass elements, so the filter does not introduce wedge error into the converging beam\u003c\/li\u003e\n\u003cli\u003eWell suited to Herschel wedge solar work, where the output is already polarised\u003c\/li\u003e\n\u003cli\u003eDust cover included\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eThe filter is a pair of linear polarisers mounted in the two rotating halves of the cell. Starlight and reflected sunlight arriving at the telescope are effectively unpolarised, so the first element passes only the component aligned with its own axis, which is why the maximum transmission is around 40 per cent rather than anything close to 100. The second element then acts on light that is already polarised, and the fraction it passes follows the square of the cosine of the angle between the two axes. With the axes parallel you are at maximum transmission; as you rotate towards 90 degrees the transmission falls away steeply, reaching the published 1 per cent at the crossed position. The practical consequence is that the adjustment is not linear across the rotation. Most of the useful range sits in a fairly narrow band of rotation near the crossed end, so a small movement there makes a large difference to brightness. It is worth knowing that both elements are neutral in intent rather than coloured, so the view darkens without taking on the green cast that older single-element moon filters were known for, although a slight warming is normal with polarising material.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eLunar observing across all phases, where the required attenuation changes night to night\u003c\/li\u003e\n\u003cli\u003ePlanetary work on bright targets such as Venus, and on Jupiter in a large aperture\u003c\/li\u003e\n\u003cli\u003eWhite-light solar observing behind a Herschel wedge, to trim the residual brightness smoothly\u003c\/li\u003e\n\u003cli\u003eAny large-aperture telescope where the Moon is uncomfortable to look at even through a fixed density filter\u003c\/li\u003e\n\u003cli\u003ePublic observing sessions where the same telescope has to suit many pairs of eyes in a short time\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe cell carries the standard 2-inch filter thread and screws into the barrel of most 2-inch eyepieces, and into many 2-inch star diagonals and adapters. Because the thread is doubled, inside and outside, you can also mount it between two components of a 2-inch train or thread another 2-inch filter onto it. Note that access matters here: you have to be able to reach the cell to rotate it, so mounting it deep inside a diagonal where your fingers cannot get to it defeats the purpose. Most observers thread it onto the eyepiece barrel or the front of the diagonal for that reason. This is the 2-inch version and will not fit 1.25-inch eyepieces. If you want to confirm it will work in a particular diagonal or focuser arrangement, contact our team in Bolton with the models and we will check it for you.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. On safety, be clear about what the solar reference means: this filter is used behind a Herschel wedge or another certified solar filter that has already removed the dangerous energy. A polarising filter at the eyepiece is never itself a solar filter and must not be used to view the Sun on its own. Also note that a 2-inch filter cell adds physical length and a little weight to the eyepiece end, which can matter on a delicately balanced mount, and that the adjustment being non-linear takes a session or two to get a feel for. What is included is the filter and a dust cover; eyepieces, diagonals and wedges are separate.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eHow dark can it actually go?\u003c\/strong\u003e Explore Scientific publishes a range of 40 per cent down to 1 per cent transmission. At the dark end that is a reduction of about four magnitudes, which is more than enough for a full Moon in a large aperture.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhy is the maximum only 40 per cent?\u003c\/strong\u003e Because a single linear polariser can only pass the component of unpolarised light aligned with its axis, so about half is lost before the second element does anything. That is inherent to how polarisers work, not a shortcoming of this filter.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it with a Herschel wedge?\u003c\/strong\u003e Yes, and that is one of its intended uses. The wedge does the safety work and the polariser trims the remaining brightness. Never point a telescope at the Sun without a purpose-made solar device fitted correctly.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it fit 1.25-inch eyepieces?\u003c\/strong\u003e No. This is the 2-inch version. Ask us if you need the smaller size instead.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eIf you observe the Moon and planets regularly and own more than one eyepiece, a variable polariser replaces a drawer full of fixed densities and gives you exactly the brightness you want at any moment. The dual 2-inch threading and anodised aluminium cell make it easy to work into an existing train. Contact our team in Bolton if you would like help deciding where in your optical train to fit it.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958592036975,"sku":"310250","price":200.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310250_1.jpg?v=1785960605"},{"product_id":"explore-scientific-77mm-slim-dark-sky-filter-for-camera-lenses","title":"Explore Scientific 77mm Slim Dark Sky Filter for Camera Lenses with 4mm Low Profile Mount","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific Dark Sky Filter, item 310260, is a 77mm screw-in filter made for camera lenses rather than telescopes. Explore Scientific describes it as a universally applicable dark sky filter for photo lenses, particularly suited to increasing contrast in aurora and deep-sky photography. The substrate is a special optical glass containing neodymium oxide, which absorbs strongly in a narrow band centred on the 590nm sodium line while passing 550nm green and 630nm red at over 90 per cent. The frame is black anodised aluminium with a construction height of just 4mm, a slim profile chosen specifically so the filter does not vignette on wide-angle lenses.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThis is for the photographer shooting nightscapes, aurora and wide-field Milky Way frames from anywhere within reach of town lighting. The problem it addresses is specific and quite different from what a telescope filter deals with. A camera sensor records colour through red, green and blue channels, and the yellow of sodium vapour street lighting and greenhouse lighting lands across both the red and the green channels at once. Once that has happened, the skyglow is entangled with exactly the colours you are trying to record, the red of hydrogen emission and the green of aurora, and no amount of work in post-processing separates them cleanly. Blocking the sodium line at the point of capture keeps the channels distinct so the red and green in your image mean something.\u003c\/p\u003e\u003cp\u003eIt is also the practical answer for anyone who does not want to modify their camera. Clip-in interference filters that sit between lens and camera body mean disassembly, careful handling near the sensor, and a filter that only fits one body. This one threads onto the front of the lens like any other 77mm filter, goes on and off in seconds, and moves between bodies freely, which makes it realistic for time-lapse work and for travel where you are shooting on the move.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eBlocks the 590nm yellow sodium line, suppressing sodium vapour street lighting and greenhouse lighting\u003c\/li\u003e\n\u003cli\u003eTransmits over 90 per cent at 550nm green and 630nm red, the bands that carry aurora and hydrogen emission signal\u003c\/li\u003e\n\u003cli\u003eSlim 4mm construction height, chosen to avoid vignetting on wide-angle lenses\u003c\/li\u003e\n\u003cli\u003eStandard 77mm filter thread, so it fits directly on the front of a 77mm lens with no camera modification\u003c\/li\u003e\n\u003cli\u003eSpecial optical glass with neodymium oxide, an absorption glass rather than an interference coating\u003c\/li\u003e\n\u003cli\u003eBlack anodised aluminium frame, which resists handling wear and limits internal reflection off the ring\u003c\/li\u003e\n\u003cli\u003eNatural night sky colour reproduction, with the correction confined to a narrow band rather than a broad cast\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eThe important engineering decision here is absorption rather than interference. An interference filter builds its passband from stacked thin-film layers, and the wavelength at which those layers cancel depends on the angle at which the light crosses them. Light entering the corner of a fast wide-angle lens arrives at a very different angle from light down the centre, so an interference filter mounted in front of such a lens shifts its passband across the frame and produces uneven colour. Neodymium oxide glass works differently. The neodymium ion has an absorption band that sits over the yellow region near 590nm, and because that absorption is a property of the material itself rather than of a layer structure, it behaves the same regardless of the angle of incidence. That is what makes the filter usable in front of a 14mm or 24mm lens where an interference filter would not be. The 4mm frame height serves the same goal from the mechanical side: a standard filter ring intrudes into the field of a very wide lens and darkens the corners, so the mount is cut down to keep clear of it.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eAurora photography, where separating green and red emission from yellow skyglow is the whole battle\u003c\/li\u003e\n\u003cli\u003eWide-field Milky Way and nightscape work from suburban or semi-rural sites\u003c\/li\u003e\n\u003cli\u003eNight sky time-lapse sequences, where a screw-in filter can stay on the lens for hours unattended\u003c\/li\u003e\n\u003cli\u003eWide-field imaging of emission nebulae with a camera lens on a star tracker\u003c\/li\u003e\n\u003cli\u003eGeneral night photography where sodium lighting is casting an orange wash over the scene\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe filter fits any lens with a 77mm front filter thread directly. Lenses with smaller threads can use it with an inexpensive step-up ring, though on the widest lenses a step-up ring reintroduces the very intrusion into the field that the slim mount was designed to avoid, so test for vignetting at your widest focal length and largest aperture before you rely on it. Some ultra-wide and fisheye lenses have bulbous front elements with no filter thread at all and cannot take a front filter of any kind. Slim frames also vary in whether they carry a front thread for stacking or for a lens cap, so if you need to keep a cap or hood on top, contact our team in Bolton and we will confirm what this frame will accept before you order. It works with any camera body, mirrorless or DSLR, modified or unmodified.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. On performance, be realistic about what a sodium-line filter can and cannot do. It is aimed at one specific pollutant. Broad-spectrum white LED street lighting, which now dominates in many municipalities, emits right across the visible band and cannot be notched out this way, so under LED-lit skies the improvement is modest. Under older sodium lighting it is substantial. The filter also removes some light, which means slightly longer exposures, and like any front-mounted glass it can produce ghosting if a bright lamp is in or just outside the frame. Custom white balance is worth setting with the filter fitted. The filter is supplied on its own; step-up rings, caps and hoods are separate.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eWill it vignette on my wide-angle lens?\u003c\/strong\u003e The 4mm slim frame is designed specifically to avoid that, and it is the reason to choose this filter over a standard-height one. On extremely wide lenses, and particularly if you add a step-up ring, test a frame at your widest setting to be sure.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it need a modified camera?\u003c\/strong\u003e No. It threads onto the front of the lens and works with any standard camera body, which is the main practical advantage over clip-in filters that sit in front of the sensor.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it help under white LED street lights?\u003c\/strong\u003e Only a little. Neodymium glass targets the yellow sodium line near 590nm. LED lighting is broadband and there is no narrow band to remove, so the honest answer is that this filter is at its best where sodium lighting still dominates.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it on a telescope?\u003c\/strong\u003e Not directly. It is built around a 77mm photographic thread for camera lenses. For telescope work, ask us about the light pollution filters made in 1.25-inch and 2-inch astronomical cells.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eIf you photograph aurora or wide-field night skies near sodium-lit towns, this filter fixes a problem at capture that is genuinely difficult to fix afterwards, and the slim mount means you can use it on the wide lenses that matter most for that work. It is a simple screw-in accessory with no camera modification involved. Contact our team in Bolton if you would like help matching it to your lens set or choosing step-up rings.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958629032047,"sku":"310260","price":186.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310260_1.jpg?v=1785960691"},{"product_id":"explore-scientific-1-25-inch-sulphur-ii-6-5nm-nebula-filter","title":"Explore Scientific 1.25-inch Sulphur II 6.5nm Narrowband Nebula Filter","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThis is the tighter of the two 1.25-inch sulphur filters Explore Scientific builds: a narrowband interference filter with a 6.5 nm passband sitting on the ionised sulphur emission line at 672 nm. Explore Scientific describes the effect in blunt terms, noting that with the filter in place fog becomes visible in places that appear completely empty without one. The filter comes in a standard 1.25-inch threaded cell and is supplied with an individual test report measured on the actual filter you receive rather than a generic curve for the product line.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eHalving the passband does something specific and worth being precise about. The emission line you want is a few tenths of a nanometre wide, so narrowing the window from 12 nm to 6.5 nm passes essentially the same nebular signal while cutting the continuum sky background you collect alongside it by close to half. In a background-limited exposure that is a real gain in signal-to-noise, and it is why this filter keeps working on nights when a 12 nm filter is already struggling: near a gibbous or full moon, under a bright suburban dome, or on targets low enough to sit in the worst of the light dome.\u003c\/p\u003e\u003cp\u003eThe bill comes due elsewhere. Sulphur is the faintest of the three lines normally mapped in narrowband work, and a tighter filter is more sensitive to the angle at which light strikes it. That combination means this filter wants a slower light cone, roughly f\/5 and above, a camera with low read noise so that long subframes are not wasted, and an owner willing to spend real integration time on the sulphur channel: ten to twenty minute subframes and several hours per session are normal here, not exceptional. Choose it if you already know your way around narrowband processing, if your sky is genuinely bright and you need the extra rejection more than the extra photons, or if you image with enough aperture that the faintness of S-II is not the limiting factor. If you are still on a fast small refractor and short exposures, the 12 nm sibling is the better tool.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e6.5 nm passband, roughly half the sky background of a 12 nm filter for the same nebular signal\u003c\/li\u003e\n\u003cli\u003eCentred on the ionised sulphur emission line at 672 nm\u003c\/li\u003e\n\u003cli\u003eDeep rejection of the rest of the visible spectrum, including mercury and sodium vapour street lighting\u003c\/li\u003e\n\u003cli\u003eMounted in a standard 1.25-inch threaded cell for eyepiece barrels, nosepieces and 1.25-inch filter wheels\u003c\/li\u003e\n\u003cli\u003eIndividual test report for the specific filter supplied, included with the product\u003c\/li\u003e\n\u003cli\u003eSuited to planetary nebulae, emission nebulae and supernova remnants, the three families Explore Scientific names for this filter\u003c\/li\u003e\n\u003cli\u003eHolds contrast in moonlight where wider narrowband filters begin to lose it\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eThe passband of a dielectric interference filter is set by the optical thickness of its coating layers, and that optical thickness depends on the path a ray takes through them. Light arriving square to the surface sees the design thickness; light arriving at an angle sees a different one, and the whole transmission curve slides toward shorter wavelengths. The shift is not large in absolute terms, but it is measured against the width of your window. A ray tilted enough to move the band by two nanometres is a minor nuisance in a 12 nm filter and a significant loss of transmission in a 6.5 nm one, because the 672 nm line you are trying to record is now sitting on the shoulder of the curve rather than at its peak. This is the physical reason narrower filters are usually specified with a focal ratio limit, and why 6.5 nm is best matched to systems around f\/5 and slower rather than to fast astrographs.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eSulphur data for mapped-colour narrowband imaging from bright suburban and urban sites\u003c\/li\u003e\n\u003cli\u003eImaging through moonlight, when the sky background rather than the target sets your limit\u003c\/li\u003e\n\u003cli\u003eSupernova remnants and planetary nebulae where sulphur structure is the point of the exercise\u003c\/li\u003e\n\u003cli\u003eLong-integration projects on emission nebulae where the sulphur channel needs the most help\u003c\/li\u003e\n\u003cli\u003eMonochrome cameras on 1.25-inch filter wheels with sensors up to about Four Thirds format\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eStandard 1.25-inch filter threads mean this screws directly into a 1.25-inch camera nosepiece, an eyepiece barrel, or the carousel of a 1.25-inch filter wheel. It is not a match for 2-inch wheels or for the unmounted 31 mm and 36 mm formats used in many larger wheels, and the extra thickness of a mounted cell can matter in tight backfocus arrangements with an off-axis guider. If you already own the matching Explore Scientific hydrogen-alpha filter at a different bandwidth, be aware that mixing widths across a set means each channel reaches a given depth at a different rate, which complicates exposure planning more than it complicates processing. Send us your imaging train and our team in Bolton will confirm the fit and the spacing before you order.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. Two other things are worth saying plainly. First, this is not a visual filter in any practical sense: 6.5 nm at 672 nm leaves far too little light for the dark-adapted eye. Second, Explore Scientific does not publish peak transmission, substrate or out-of-band blocking figures on the product page, so we do not repeat numbers we cannot verify. The individual test report packed with the filter is the authoritative measurement for your copy. The scope of delivery is the filter and that report; camera, wheel, adapters and spacers are not included.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eIs 6.5 nm always better than 12 nm?\u003c\/strong\u003e No. It is better when the sky background is what limits you, which is most urban and moonlit nights. It is worse when the target itself is what limits you, which is what happens on a fast small aperture with short subframes on a faint line like sulphur. Match the filter to your bottleneck.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat focal ratio can I use it at?\u003c\/strong\u003e Explore Scientific does not publish a limit, but the physics of interference coatings means that below roughly f\/4 the passband shift across a converging beam starts to cost you real transmission at 672 nm. Around f\/5 and slower this filter is comfortable. If you are near the boundary, contact us and we will talk through your specific optics.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow long should my subframes be?\u003c\/strong\u003e Longer than you are used to. With a cooled monochrome camera, ten to twenty minutes per subframe on the sulphur channel is a reasonable starting point, and expect to need more total integration on S-II than on hydrogen-alpha for the same target.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes the test report matter?\u003c\/strong\u003e It is genuinely useful. It tells you where the centre wavelength of your particular filter landed and how the transmission curve is shaped, which is the information you need if you are ever troubleshooting a weak channel.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eThe 6.5 nm S-II is the version for imagers whose enemy is the sky, not the clock: it trades photons for contrast and rewards patience, aperture and a moderate focal ratio. If you are already producing usable sulphur data and want it cleaner under a brighter sky, this is the upgrade. Contact us if you would like a second opinion on whether your rig will make the most of it.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958658752623,"sku":"310125","price":193.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310125_2.jpg?v=1785960770"},{"product_id":"explore-scientific-1-25-inch-h-alpha-12nm-nebula-filter","title":"Explore Scientific 1.25-inch Hydrogen-Alpha 12nm Narrowband Nebula Filter","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific 1.25-inch H-Alpha Nebula Filter has a 12 nm passband and is built to pass the hydrogen emission line at 656.3 nm while rejecting everything else. Explore Scientific is direct about the intended use: this is a filter developed for astrophotography, aimed squarely at imagers working near cities, and the company notes it blocks almost all the light from mercury and sodium vapour lamps. It comes mounted in a standard 1.25-inch threaded cell with an individual test report for the filter in the box.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eHydrogen-alpha is the loud one. In an emission nebula it is normally the strongest of the three lines narrowband imagers work with, often by a wide margin, and that single fact changes the whole calculation around bandpass. Because the signal is strong, you do not need to squeeze the window down to get a usable result, and a 12 nm passband gives you something more valuable on modest equipment: tolerance. Tolerance of a fast light cone, where the passband shifts as rays strike the coating off-axis. Tolerance of shorter subframes, because the target is bright enough that you are not waiting forever to climb out of the read noise. Tolerance of nights that are less than ideal, since the streetlight emission that ruins broadband work sits at 589 nm and below, comfortably outside this window.\u003c\/p\u003e\u003cp\u003eThat makes this the natural first narrowband filter for someone with a 1.25-inch filter wheel and a small monochrome sensor, for an f\/4 or f\/5 Newtonian where a 3 nm filter would be a poor match, or for anyone who wants a hydrogen luminance layer to blend into an existing colour image. It is also the honest choice if your total time per target is one or two nights rather than one or two months. If you routinely image from a genuinely bright site through a full moon and you already own a slower scope and a patient temperament, the tighter 7 nm hydrogen-alpha filters will pull the background down further; for everyone else, 12 nm is the width that gets a good image out of ordinary conditions.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e12 nm passband on the hydrogen emission line at 656.3 nm, in the red\u003c\/li\u003e\n\u003cli\u003eExplore Scientific states it blocks almost all light from mercury and sodium vapour street lighting\u003c\/li\u003e\n\u003cli\u003eWide enough to stay well behaved in fast light cones around f\/4 to f\/5\u003c\/li\u003e\n\u003cli\u003eStandard 1.25-inch threaded cell for nosepieces, eyepiece barrels and 1.25-inch filter wheels\u003c\/li\u003e\n\u003cli\u003eIndividual test report for the specific filter included with the product\u003c\/li\u003e\n\u003cli\u003eExplore Scientific specifies it for astrophotography rather than visual observing\u003c\/li\u003e\n\u003cli\u003eRecords red emission nebulae to their full extent in photographs where an unfiltered exposure shows mostly skyglow\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eA narrowband filter is not tinted glass. It is a stack of dielectric layers whose thicknesses are chosen so that light near 656 nm reflects back and forth between them in phase and emerges, while every other wavelength interferes with itself and is turned back. The reason this matters for a 12 nm filter specifically is that the window's width is what buys you angular tolerance. The transmission curve moves toward the blue as the angle of incidence increases, and in a converging beam the edge of your light cone is always arriving at an angle. With 12 nm of width the shift produced by an f\/4 or f\/5 cone still leaves 656.3 nm sitting near the top of the curve across the whole field, so the centre and the corners of the frame record the same signal. Narrow that window enough and the corners start to see a filter that is no longer tuned to hydrogen, which shows up as an unevenly illuminated frame that no amount of flat-fielding fixes properly.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eThe hydrogen channel of mapped-colour narrowband imaging on emission nebulae\u003c\/li\u003e\n\u003cli\u003eHydrogen-alpha luminance layers blended into broadband colour images\u003c\/li\u003e\n\u003cli\u003eImaging emission nebulae and supernova remnants from urban and suburban back gardens\u003c\/li\u003e\n\u003cli\u003eContinuing to collect useful data through moonlight, when broadband imaging is finished for the night\u003c\/li\u003e\n\u003cli\u003eFast Newtonians and small refractors at f\/4 to f\/6 with monochrome cameras\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe cell carries the usual 1.25-inch filter thread, so it will thread into a 1.25-inch camera nosepiece, the barrel of a 1.25-inch eyepiece, or a 1.25-inch filter wheel carousel. It is not intended for 2-inch focusers or for wheels built around unmounted 31 mm and 36 mm discs. If your imaging train is tight on backfocus, remember that a mounted filter adds a few millimetres of glass in the optical path and shifts focus slightly rearward, which is worth accounting for when you set your spacing to a field flattener. This is also the filter most people pair first with a matching Explore Scientific O-III and S-II in the same 1.25-inch format when they are building a full narrowband set. Tell us what camera and wheel you are running and our team in Bolton will confirm the fit.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. It is also worth repeating that Explore Scientific specifies this filter for photographic use. Visually, a 12 nm window in the deep red passes far too little light for the dark-adapted eye to do much with, and you should not buy this expecting an eyepiece filter. Explore Scientific does not publish peak transmission, substrate or blocking specifications for the filter, so we do not quote figures we cannot source; the enclosed test report is the measurement that applies to your copy. The scope of delivery is the filter and its report, with no adapters, wheel or camera included.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eCan I use this with an unmodified DSLR?\u003c\/strong\u003e You can, but the result will disappoint you. The internal cut filter in a stock camera is designed to attenuate exactly the deep red region where hydrogen-alpha sits, so you lose most of the signal before it reaches the sensor. A modified or astronomy-specific camera is the right partner for this filter, and a monochrome camera is better still.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhy start with hydrogen-alpha rather than O-III or S-II?\u003c\/strong\u003e Because it is the strongest line and the most forgiving. You will get a usable image from a single night with H-alpha long before you get one with sulphur, and the technique you learn on this filter transfers directly to the others.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs 12 nm too wide for a light-polluted sky?\u003c\/strong\u003e Not for hydrogen. The window at 656 nm sits clear of the sodium and mercury emission that dominates urban skyglow, so a 12 nm filter already removes the great majority of what a broadband exposure suffers from. A tighter filter reduces the remaining continuum background further, which matters most under a bright moon.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it vignette on my sensor?\u003c\/strong\u003e A mounted 1.25-inch filter usually offers a clear aperture near 27 mm, which is comfortable for Four Thirds and smaller chips. Larger sensors want the 2-inch version of this filter.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eIf you are taking your first serious step into narrowband imaging with a 1.25-inch wheel and a small sensor, the 12 nm hydrogen-alpha is the filter that gives you the most result for the least demanded of your equipment. It is forgiving of fast optics, short subframes and imperfect nights in a way the tighter filters are not. Contact us and we will help you slot it into your imaging train.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958684409967,"sku":"310135","price":154.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310135_2.jpg?v=1785960832"},{"product_id":"explore-scientific-2-inch-sulphur-ii-12nm-nebula-filter","title":"Explore Scientific 2-inch Sulphur II 12nm Narrowband Nebula Filter","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific 2-inch S-II Nebula Filter is a 12 nm narrowband filter tuned to the ionised sulphur emission line at 672 nm, mounted in a 2-inch cell. Explore Scientific explains the principle behind it directly: emission nebulae glow in specific colours tied to specific chemical elements, and this filter blocks all the other colours, and with them almost all artificial light, letting only the sulphur emission through. Each filter ships with an individual test report for that particular piece of glass.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThe reason to buy this rather than the 1.25-inch version is aperture, and the reason to buy 12 nm rather than 6.5 nm is what a large aperture does to a narrowband filter. On a big sensor the light reaching one corner of the frame arrives at the filter with a different angle and a different range of angles than the light landing at the centre. Because an interference coating shifts its passband toward the blue as the angle of incidence increases, that means the corners of a full-frame chip are effectively looking through a slightly different filter than the middle. With a 12 nm window there is enough room either side of 672 nm to absorb that variation, and your corners and your centre record the sulphur line at comparable efficiency. Tighten the window and the difference starts to appear in the data as a radial falloff that is not a vignette and does not calibrate out cleanly.\u003c\/p\u003e\u003cp\u003eSo this is the sulphur filter for someone running a full-frame or large APS-C monochrome camera in a 2-inch filter wheel or drawer, or for an observer with a large-aperture visual instrument who wants to try sulphur contrast on bright planetary nebulae through a 2-inch diagonal. It also suits fast, wide astrographs where both the focal ratio and the field size are working against a narrow band at once. Given that sulphur is already the faintest of the commonly mapped lines, the extra photons a 12 nm window collects are worth more here than the additional background suppression a 6.5 nm filter would provide, unless your sky is exceptionally bright.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e2-inch mounted cell, sized for full-frame sensors, 2-inch filter wheels and 2-inch diagonals\u003c\/li\u003e\n\u003cli\u003e12 nm passband centred on the ionised sulphur emission line at 672 nm\u003c\/li\u003e\n\u003cli\u003eRejects the remainder of the visible spectrum, including the artificial light that dominates an urban sky\u003c\/li\u003e\n\u003cli\u003eBandwidth chosen to stay consistent from field centre to corner across a large sensor\u003c\/li\u003e\n\u003cli\u003eIndividual test report for the filter you receive, included in the scope of delivery\u003c\/li\u003e\n\u003cli\u003eExplore Scientific names planetary nebulae, emission nebulae and supernova remnants as its targets\u003c\/li\u003e\n\u003cli\u003eUsable both photographically and, on large apertures, for visual contrast work on the brightest planetaries\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eThe 672 nm passband is produced by a multilayer dielectric coating, and its behaviour depends on geometry as much as on chemistry. Each layer is a fraction of a wavelength thick, and the interference condition that defines the transmission peak depends on the optical path a ray takes through the stack. Rays arriving perpendicular to the surface see the design condition. Rays arriving at an angle satisfy the same condition at a shorter wavelength, so the peak migrates blueward. In a 2-inch filter placed in a converging beam ahead of a large sensor, the angle of incidence varies systematically across the aperture of the filter, which is why the 12 nm width is the practical choice at this size: it is broad enough that the whole illuminated area of the coating still delivers the sulphur line near peak transmission. A wider window does admit slightly more sky continuum, but with a line as faint as S-II, uniform transmission across the field is usually the more valuable property.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eSulphur data for mapped-colour narrowband imaging on full-frame and large APS-C monochrome cameras\u003c\/li\u003e\n\u003cli\u003eWide-field emission nebula work with fast astrographs and short focal lengths\u003c\/li\u003e\n\u003cli\u003eSupernova remnants where the sulphur structure diverges from the hydrogen structure\u003c\/li\u003e\n\u003cli\u003eImaging from suburban and urban sites where broadband work is not practical\u003c\/li\u003e\n\u003cli\u003eVisual contrast work on bright planetary nebulae through a 2-inch diagonal with generous aperture\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe cell is threaded to the standard 2-inch filter thread, so it screws into the barrel of a 2-inch eyepiece, into a 2-inch nosepiece or star diagonal, and into most 2-inch filter wheels. It does not fit wheels that take unmounted 36 mm or 50.8 mm discs, and its cell thickness is worth checking against tight filter drawers before you commit. If you already own the 1.25-inch Explore Scientific narrowband filters, note that a 2-inch cell will not step down without an adapter, and that the mounted glass adds a small amount of optical path that shifts focus rearward, which matters when you are setting the spacing between a field flattener and your sensor. If you are unsure whether your wheel, drawer or diagonal will take a mounted 2-inch filter, contact our team in Bolton with the model and we will confirm it.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. Also worth setting expectations on: sulphur is the weakest of the three lines most narrowband imagers work with, so this channel will always need more integration time than hydrogen-alpha to reach the same depth, whatever the bandpass. Explore Scientific does not publish peak transmission, substrate material or a full out-of-band blocking range for this filter, and we will not invent those numbers; the individual test report supplied with the filter carries the measured curve for your copy. The delivery is the filter and that report, with no diagonal, wheel, adapter or camera included.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eDo I actually need a 2-inch filter?\u003c\/strong\u003e If your sensor is larger than about Four Thirds, or your filter wheel and drawer are built around 2-inch threads, yes. A 1.25-inch filter in front of an APS-C or full-frame chip will vignette the corners noticeably. If you are running a small mono camera, the 1.25-inch version does the same optical job for less.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs this usable visually?\u003c\/strong\u003e On a large aperture and a bright planetary nebula it can show real structure, and Explore Scientific does mention urban observers alongside astrophotographers for the S-II line. But 672 nm is deep in the red where the dark-adapted eye is weakest, so treat visual use as a bonus rather than the purpose.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhy not go to 6.5 nm for more contrast?\u003c\/strong\u003e Because on a big sensor, a fast beam, and the faintest of the three lines, you would be paying twice: once in signal and once in field uniformity. The 6.5 nm version rewards slower optics, smaller fields and long integration. This one is the more forgiving instrument.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it work with a colour camera?\u003c\/strong\u003e Only inefficiently. Bayer-array cameras dedicate roughly a quarter of their photosites to red, and the colour filters themselves attenuate what reaches them. Narrowband work of this kind belongs to monochrome sensors.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eThis is the sulphur filter for a large sensor and a fast telescope, where uniform transmission across a wide field matters more than the last decibel of background rejection. It fits standard 2-inch threads, ships with its own measured test report, and behaves predictably from centre to corner. Contact us if you would like help deciding between this and the 6.5 nm version for your particular optics.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958705905775,"sku":"310110","price":249.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310110_2.jpg?v=1785960889"},{"product_id":"explore-scientific-2-inch-sulphur-ii-6-5nm-nebula-filter","title":"Explore Scientific 2-inch Sulphur II 6.5nm Narrowband Nebula Filter","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThis is the most specialised sulphur filter Explore Scientific offers in the 2-inch format: a 6.5 nm passband centred on the ionised sulphur emission line at 672 nm, in a mounted 2-inch cell. Explore Scientific describes the result as amazing for revealing nebulae in light-polluted urban areas, and frames the filter's job as absorbing interfering emission lines to deliver more contrast and detail for urban observers and astrophotographers. As with the rest of the range, an individual test report for the specific filter is part of the scope of delivery.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eEverything in narrowband imaging is a negotiation between contrast and signal, and this filter sits at one extreme of it. Halving the passband relative to a 12 nm filter roughly halves the sky continuum you accumulate in a given exposure while leaving the nebular emission line untouched, so the target sits on a darker background and the contrast in the raw subframe is visibly better. That is exactly what you want when the sky itself is the problem: a white-zone back garden, a rising moon, a target that never climbs out of the light dome to the south.\u003c\/p\u003e\u003cp\u003eWhat you should be clear-eyed about is that this filter stacks the two hardest conditions in the range on top of each other. Sulphur is the weakest of the three lines commonly mapped in narrowband work, and 6.5 nm is the tightest window Explore Scientific puts on it. The result is a filter that demands things of your setup rather than accommodating it: enough aperture that the sulphur channel is not hopeless, a focal ratio around f\/5 or slower so the passband does not drift off the line in a steep light cone, a cooled monochrome camera with low read noise so that fifteen or twenty minute subframes actually pay, and a project measured in tens of hours rather than a single clear night. Buy it if you are already producing decent S-II data with a wider filter and you have decided the sky background is what stands between you and a better image. If you are still fighting for signal rather than fighting the sky, the 12 nm 2-inch version is the more sensible instrument.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e6.5 nm passband, the narrowest sulphur window in the Explore Scientific 2-inch range\u003c\/li\u003e\n\u003cli\u003eCentred on the ionised sulphur emission line at 672 nm\u003c\/li\u003e\n\u003cli\u003eRoughly half the sky background of a 12 nm filter for the same nebular signal\u003c\/li\u003e\n\u003cli\u003eMounted 2-inch cell suited to large sensors, 2-inch filter wheels and 2-inch diagonals\u003c\/li\u003e\n\u003cli\u003eBlocks the artificial light that dominates urban skies, including sodium and mercury vapour lighting\u003c\/li\u003e\n\u003cli\u003eIndividual test report for your specific filter included\u003c\/li\u003e\n\u003cli\u003eIntended for planetary nebulae, emission nebulae and supernova remnants\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eThe narrower the window, the more the geometry of your optical system matters. A dielectric interference filter defines its passband for light arriving perpendicular to the coating, and the transmission curve moves toward shorter wavelengths as the angle of incidence grows. In a 2-inch filter feeding a large sensor there are two separate contributors to that angle: the convergence of the beam, set by your focal ratio, and the field position, since light destined for a corner of a full-frame chip crosses the filter differently from light headed for the centre. Both effects push the passband away from 672 nm. In a 12 nm filter that drift eats into the margin. In a 6.5 nm filter, with only about three nanometres either side of the peak to spare, the same drift can move the sulphur line onto the shoulder of the curve, where transmission falls away. The practical consequence is that this filter belongs on moderate focal ratios and rewards a well-collimated, well-spaced imaging train, and it is why the enclosed test report showing where your filter's centre wavelength actually landed is more than a nicety here.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eDeep sulphur channels for mapped-colour imaging from heavily light-polluted sites\u003c\/li\u003e\n\u003cli\u003eMulti-night and multi-season projects on emission nebulae where S-II is the limiting channel\u003c\/li\u003e\n\u003cli\u003eImaging through moonlight, when sky background rather than target brightness sets the floor\u003c\/li\u003e\n\u003cli\u003eSupernova remnants and planetary nebulae photographed with large monochrome sensors\u003c\/li\u003e\n\u003cli\u003eModerate focal ratio refractors and reflectors with 2-inch filter wheels or drawers\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eStandard 2-inch filter threads let this screw into a 2-inch nosepiece, a 2-inch star diagonal, the barrel of a 2-inch eyepiece, or most 2-inch filter wheels. It is not a fit for wheels designed around unmounted 36 mm or 50.8 mm discs, and the mounted cell is thicker than an unmounted disc, so check the clearance in a filter drawer before ordering. Mounted glass in the light path also shifts focus slightly rearward, which is worth allowing for when you set the distance between a field flattener or reducer and your sensor. If you are matching this to a hydrogen-alpha and an O-III filter, keeping the whole set at a similar bandwidth makes your exposure planning far easier to reason about. Our team in Bolton will confirm fit against your specific wheel or drawer if you send us the model.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. Two honest caveats beyond that. This is not a visual filter: a 6.5 nm window at 672 nm passes far too little light for the eye, whatever your aperture. And Explore Scientific does not publish peak transmission, substrate specification or an out-of-band blocking range for this filter, so we do not quote figures we cannot source. The measured curve for your individual filter comes with it in the box. The delivery is the filter and that report; no wheel, adapter, diagonal or camera is included.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eHow does this differ from the 12 nm 2-inch S-II?\u003c\/strong\u003e Same line, same format, roughly half the window. You get a darker sky background and better raw contrast, and you pay for it with a filter that is less tolerant of fast optics, large fields and short exposures. The 12 nm is the general-purpose filter; this one is a specialist for bright skies and long projects.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat focal ratio does it want?\u003c\/strong\u003e Explore Scientific does not publish a limit. As a working guide, around f\/5 and slower is comfortable, and below roughly f\/4 the passband shift across the beam begins to cost you meaningful transmission at 672 nm. If your system sits near that boundary, contact us and we will work through it with you.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow much total integration should I plan for?\u003c\/strong\u003e More than you would for hydrogen-alpha, typically by a factor of two or three on the same target. Sulphur is faint and a tight window is unforgiving, so treat this as a channel you build up across several nights.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it cover a full-frame sensor?\u003c\/strong\u003e The 2-inch format is the right choice for large chips, though as with any filter placed in a converging beam close to the sensor, keep an eye on transmission uniformity in the corners at fast focal ratios.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eThe 6.5 nm 2-inch S-II is the filter you buy when the sky is the obstacle and you have the aperture, the focal ratio and the patience to meet its terms. It rewards long integration and a well-sorted imaging train, and it will out-contrast a wider filter on any night with a bright background. If you want to talk through whether your rig is the right home for it, contact us and we will give you a straight answer.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958724976751,"sku":"310120","price":297.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310120_2.jpg?v=1785960948"},{"product_id":"explore-scientific-2-inch-h-alpha-12nm-nebula-filter","title":"Explore Scientific 2-inch Hydrogen-Alpha 12nm Narrowband Nebula Filter","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific 2-inch H-Alpha Nebula Filter pairs a 12 nm passband on the hydrogen emission line with a mounted 2-inch cell, so it covers large sensors and drops straight into 2-inch wheels, drawers and diagonals. Explore Scientific presents it as an answer to artificial light: it passes the hydrogen emission and blocks the interfering wavelengths, including the mercury and sodium vapour lighting that makes deep-sky work from a town so difficult. Explore Scientific specifies it for astrophotography, and each filter is supplied with an individual test report.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThis is the filter that stays in the wheel. Hydrogen-alpha is the brightest of the lines narrowband imagers work with, and 12 nm is a generous window, so the combination produces usable signal fast. That has a practical consequence that is easy to overlook when you are comparing bandpass numbers on a page: because the target is bright through this filter, you can work in three to five minute subframes rather than fifteen or twenty. Short subframes mean a satellite trail or a gust of wind costs you one frame instead of a quarter of an hour, and it means you can integrate meaningfully on a night that only offers ninety clear minutes. Under a 12 nm hydrogen window that is a real image; under a 3 nm sulphur window it is a test frame.\u003c\/p\u003e\u003cp\u003eThe 2-inch format is what makes it a wide-field instrument. On a full-frame or large APS-C monochrome camera behind a short focal length astrograph, you are covering several degrees of sky, and the light heading for the corners crosses the filter at a very different angle from the light heading for the centre. A wide passband is what keeps those two regions transmitting the hydrogen line equally, so mosaics stitch cleanly and gradients are genuinely sky gradients rather than filter artefacts. Choose this if you shoot wide fields at f\/4 to f\/6, if you build mosaics, if you want a hydrogen luminance layer for broadband colour work, or if you simply want the narrowband filter that asks the least of your mount, your sky and your available hours. If your sky is bright enough that the residual background under 12 nm is still what limits you, step to the 7 nm version instead.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e12 nm passband on the hydrogen emission line at 656.3 nm\u003c\/li\u003e\n\u003cli\u003eMounted 2-inch cell for full-frame and large APS-C sensors, 2-inch wheels and 2-inch diagonals\u003c\/li\u003e\n\u003cli\u003eExplore Scientific states it blocks almost all mercury and sodium vapour lamp light\u003c\/li\u003e\n\u003cli\u003eWide enough to transmit evenly from field centre to corner on short focal length astrographs\u003c\/li\u003e\n\u003cli\u003eStrong enough signal to work in short subframes, which limits the cost of a spoiled frame\u003c\/li\u003e\n\u003cli\u003eIndividual test report for the specific filter included in the scope of delivery\u003c\/li\u003e\n\u003cli\u003eRecords red emission nebulae to their full extent in photographs taken from bright sites\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eThe passband comes from a dielectric interference stack rather than from dye or absorption glass, and the property that governs its behaviour in a real telescope is angular sensitivity. The interference condition that defines peak transmission is satisfied at progressively shorter wavelengths as light strikes the coating further from perpendicular, so the whole curve shifts blueward with angle. In a 2-inch filter mounted close to a large sensor, the range of angles present across the filter is set both by the focal ratio and by how far off-axis a given ray is headed. A 12 nm window is broad enough that even the most steeply inclined rays in an f\/4 cone at the corner of a full-frame chip still see 656.3 nm well inside the flat part of the transmission curve. That is the whole argument for a wider band at this aperture: it is not that narrower filters are worse in principle, it is that the geometry of a fast, wide system uses up the margin a narrow filter does not have.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eWide-field hydrogen-alpha imaging on emission nebulae and supernova remnants\u003c\/li\u003e\n\u003cli\u003eMulti-panel mosaics, where consistent transmission across the frame matters most\u003c\/li\u003e\n\u003cli\u003eHydrogen luminance layers blended into broadband colour images\u003c\/li\u003e\n\u003cli\u003eContinuing to collect data through moonlight and from urban and suburban sites\u003c\/li\u003e\n\u003cli\u003eFast astrographs and Newtonians at f\/4 to f\/6 with large monochrome sensors\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe cell uses the standard 2-inch filter thread and will screw into a 2-inch camera nosepiece, a 2-inch star diagonal, the barrel of a 2-inch eyepiece, or the carousel of most 2-inch filter wheels. It is not compatible with wheels built for unmounted 36 mm or 50.8 mm discs, and the mounted cell may be too thick for some slim filter drawers, so check that clearance first. Adding a mounted filter to the light path shifts focus slightly rearward, which matters when you are dialling in the spacing between a reducer or field flattener and your sensor. This filter is the usual first purchase in a 2-inch narrowband set, with matching Explore Scientific narrowband filters available in the same format. Send us the model of your wheel or drawer and our team in Bolton will confirm the fit before you order.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. It is also worth being plain that Explore Scientific develops these hydrogen-alpha filters for photography, not for the eyepiece; a 12 nm window in the deep red gives the dark-adapted eye very little to work with, and you should not buy it as a visual nebula filter. Explore Scientific does not publish transmission, substrate or blocking figures on the product page, so we do not repeat numbers we cannot verify. The measured curve for your particular filter is in the enclosed test report. Delivery consists of the filter and that report, with no camera, wheel, diagonal or adapter included.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eShould I buy this or the 7 nm 2-inch hydrogen-alpha?\u003c\/strong\u003e Ask what limits your images. If it is the sky background, because you are shooting from a bright site or through a full moon, the 7 nm filter will help. If it is field size, focal ratio or available clear hours, the 12 nm filter will produce better data, and it is the more forgiving filter on fast optics.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it visually?\u003c\/strong\u003e Not productively. Explore Scientific developed the hydrogen-alpha line of filters for astrophotography. For visual nebula observing, an O-III or a broadband nebula filter is the correct tool.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it work with a colour camera?\u003c\/strong\u003e Poorly. Only the red photosites of a Bayer sensor contribute, and their own colour filters attenuate the signal further. A monochrome camera gets the full benefit.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow long should my subframes be?\u003c\/strong\u003e Considerably shorter than for the fainter lines. Many imagers find three to five minutes per subframe sufficient with this filter on a cooled monochrome camera, which is one of its practical advantages over a narrower window.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eThe 2-inch 12 nm hydrogen-alpha is the workhorse of a large-format narrowband set: bright, forgiving, even across a wide field, and productive on nights that would defeat a tighter filter. It is the one most imagers use the most. Contact us if you would like help deciding between this and the 7 nm version for your optics and your sky.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958752960623,"sku":"310130","price":242.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310130_2.jpg?v=1785961005"},{"product_id":"explore-scientific-2-inch-h-alpha-7nm-nebula-filter","title":"Explore Scientific 2-inch Hydrogen-Alpha 7nm Narrowband Nebula Filter","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific 2-inch H-Alpha Nebula Filter with a 7 nm passband is the tighter of the company's two 2-inch hydrogen filters. Explore Scientific describes what it does without hedging: it blocks all other colours and nearly all artificial light, letting through only the hydrogen emission lines, and the effect is that structure appears in photographs where an unfiltered frame looks empty. The company developed it exclusively for astrophotography and calls it a must for urban astrophotographers, noting that it is especially effective when the sky is slightly brightened. It is mounted in a 2-inch cell and supplied with an individual test report.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThe argument for narrowing the band is different for hydrogen than it is for sulphur or oxygen, and it is worth understanding why. Narrowing the window from 12 nm to 7 nm cuts the continuum background you collect by roughly forty percent while the emission line, which is a fraction of a nanometre wide, passes through as strongly as before. The image gets darker overall and the nebula does not, which is the entire point. The reason this is a comfortable trade with hydrogen specifically, and an uncomfortable one with sulphur, is that hydrogen-alpha is normally the strongest line in an emission nebula by a considerable margin. You have signal to spend, so spending some of it on contrast is a reasonable bargain rather than a sacrifice.\u003c\/p\u003e\u003cp\u003eThat makes this the hydrogen filter for people whose limiting factor is the sky rather than the target. If you image from a genuinely bright suburban or urban site, if you want to keep working within a few days of full moon, or if you are shooting targets that sit low over a city light dome, the 7 nm window keeps the background down where the 12 nm filter starts to fill in. It suits full-frame and large APS-C monochrome cameras in 2-inch wheels and drawers, and it is at its best on systems around f\/5 and slower, where the angular spread across a converging beam is modest enough that the tighter passband stays parked on 656.3 nm from centre to corner. On a very fast wide-field astrograph, or on nights where you only get an hour of sky, the 12 nm version will still serve you better.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e7 nm passband on the hydrogen emission line at 656.3 nm\u003c\/li\u003e\n\u003cli\u003eAround forty percent less continuum sky background than a 12 nm filter for the same nebular signal\u003c\/li\u003e\n\u003cli\u003eMounted 2-inch cell for full-frame and large APS-C sensors and 2-inch filter wheels\u003c\/li\u003e\n\u003cli\u003eBlocks mercury and sodium vapour lamp emission, the dominant components of urban skyglow\u003c\/li\u003e\n\u003cli\u003eExplore Scientific developed it exclusively for astrophotography and recommends it for brightened skies\u003c\/li\u003e\n\u003cli\u003eNarrow enough to hold contrast through moonlight, wide enough to stay practical on moderate focal ratios\u003c\/li\u003e\n\u003cli\u003eIndividual test report for your specific filter included in the scope of delivery\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eThe transmission window is produced by a dielectric interference coating, and its two most important behaviours both follow from the same physics. First, the band is defined at normal incidence: light striking the coating at an angle satisfies the interference condition at a shorter wavelength, so the passband shifts toward the blue as the beam converges or as a ray heads for the edge of the field. Second, the size of that shift is the same in nanometres regardless of how wide your window is, which means it costs you proportionally more the tighter the filter. Seven nanometres is a well-judged compromise for a 2-inch filter: it leaves roughly three and a half nanometres of margin either side of the hydrogen line, enough that a moderate light cone and a large sensor still see the line near peak transmission, while removing a substantial slice of the background that a 12 nm filter admits. Push much narrower than this in a 2-inch cell close to a big chip and you begin trading real corner transmission for background suppression you may not need.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eHydrogen-alpha imaging from light-polluted urban and suburban sites\u003c\/li\u003e\n\u003cli\u003eWorking through moonlit periods when broadband and wider narrowband filters lose contrast\u003c\/li\u003e\n\u003cli\u003eEmission nebulae, supernova remnants and hydrogen-rich star-forming regions on large sensors\u003c\/li\u003e\n\u003cli\u003eHigh-contrast hydrogen luminance layers for blending into broadband colour images\u003c\/li\u003e\n\u003cli\u003eModerate focal ratio refractors and reflectors with 2-inch filter wheels or drawers\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe cell carries the standard 2-inch filter thread and screws into a 2-inch nosepiece, a 2-inch star diagonal, a 2-inch eyepiece barrel or the carousel of most 2-inch filter wheels. Wheels and drawers designed around unmounted 36 mm or 50.8 mm discs will not take a mounted cell, and slim drawers may not have the clearance, so it is worth confirming that before you order. Any mounted filter adds glass to the optical path and moves focus slightly rearward, which is a detail worth accounting for in the spacing between a reducer or field flattener and your sensor. If you are pairing this with sulphur and oxygen filters, remember that hydrogen tolerates a tighter window better than the other two lines do, so a mixed-bandwidth set is a defensible choice rather than an error, provided you plan your exposures accordingly. Our team in Bolton will confirm fit against your wheel, drawer or diagonal if you send us the model.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. Beyond that: Explore Scientific is explicit that this filter was developed for astrophotography alone, and a 7 nm window in the deep red is of no practical use at the eyepiece. Explore Scientific also does not publish peak transmission, substrate details or a full out-of-band blocking specification for this filter, so we do not quote numbers we cannot source; the individual test report in the box gives the measured curve for the filter you receive. Delivery is the filter and that report, with no camera, wheel, adapter or diagonal included.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eWhy is 7 nm sensible for hydrogen when 6.5 nm is demanding for sulphur?\u003c\/strong\u003e Because the underlying signal is different. Hydrogen-alpha is usually much the strongest line in an emission nebula, so you can afford to trade some throughput for background suppression. Sulphur is the weakest, so the same trade leaves you scraping for signal. Bandwidth choices should follow line strength, not just the number on the box.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I image through a full moon with this?\u003c\/strong\u003e Within reason, yes, provided the moon is not close to your target. The narrower window is exactly what keeps moonlit continuum out of the frame, and it is the main reason to choose this over the 12 nm version.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs it too narrow for my f\/4 astrograph?\u003c\/strong\u003e Explore Scientific does not publish a focal ratio limit. As a practical guide, 7 nm is comfortable around f\/5 and slower and starts to lose corner transmission on very fast systems with large sensors. If you are near that boundary, contact us with your optics and sensor size and we will give you our honest read.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it need a monochrome camera?\u003c\/strong\u003e It works best with one. On a Bayer-array colour camera only the red photosites see the hydrogen line, and their own dyes cost you further transmission, so you are paying for a premium filter and using a quarter of your sensor.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eThis is the hydrogen filter for imagers fighting a bright sky: tight enough to suppress the background that ruins urban and moonlit frames, but sitting on a line strong enough to absorb the cost. On a moderate focal ratio and a large monochrome sensor it is the version that produces the cleanest hydrogen data. Contact us if you would like help choosing between it and the 12 nm filter for your site and your optics.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958771114095,"sku":"310140","price":311.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310140_2.jpg?v=1785961061"}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/collections\/apibagtgx__57136.jpg?v=1786027399","url":"https:\/\/ontariotelescope.com\/collections\/explore-scientific-filters.oembed","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}