{"product_id":"zwo-ha-7nm-narrowband-filter","title":"ZWO H-alpha 7nm Narrowband Filter","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThe \u003cstrong\u003eZWO H-alpha 7nm Narrowband Filter\u003c\/strong\u003e passes a \u003cstrong\u003e7 nm\u003c\/strong\u003e band centred on the hydrogen-alpha line at \u003cstrong\u003e656 nm\u003c\/strong\u003e and rejects effectively everything else. Peak transmission is around \u003cstrong\u003e90%\u003c\/strong\u003e, off-band rejection is \u003cstrong\u003eOD3 (below 0.1%)\u003c\/strong\u003e, and infrared from \u003cstrong\u003e700–1100 nm is cut\u003c\/strong\u003e. Every size is polished to \u003cstrong\u003e1\/4 wavefront on both surfaces\u003c\/strong\u003e.\u003c\/p\u003e\n\u003cp\u003eAvailable in \u003cstrong\u003ethree sizes — 1.25\" mounted, 36 mm unmounted, and 2\" mounted\u003c\/strong\u003e. Each is a \u003cstrong\u003esingle filter\u003c\/strong\u003e, not a set. Which one you need is decided by your sensor, not your telescope — see the sizing guidance below before ordering.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eChoosing the Right Size\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThis is the only decision that really matters here, and it is the one most often got wrong. \u003cstrong\u003eA filter too small for your sensor vignettes the corners, and no amount of processing recovers it\u003c\/strong\u003e — the cell wall is a physical obstruction.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e1.25\" mounted — for sensors up to about 4\/3\":\u003c\/strong\u003e ASI1600, ASI294, ASI533 and similar. Threaded cell, fits 1.25\" filter wheels and any standard 1.25\" thread. 1.9 mm glass. \u003cstrong\u003eWill vignette APS-C and full-frame\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e36 mm unmounted — for APS-C and smaller:\u003c\/strong\u003e ASI2600MM, ASI294MM and similar. Bare glass, no cell and no thread, so the full 36 mm is clear aperture. Fits the ZWO 36 mm EFW (7×36 mm). 2 mm glass. \u003cstrong\u003eWill not cover full-frame\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e2\" mounted — for sensors up to full-frame:\u003c\/strong\u003e ASI6200MM, ASI2400 and similar. Threaded cell, fits 2\" filter wheels, drawers, and any standard 2\" (M48) thread\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eIf you are between sizes, size up. The cost difference is far smaller than the cost of re-buying.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThis is a good match if you image \u003cstrong\u003eemission nebulae with a monochrome camera\u003c\/strong\u003e from a light-polluted site. A 7 nm passband rejects mercury vapour, sodium vapour, and atmospheric skyglow almost entirely — which is why narrowband work is productive on nights when broadband imaging is not, including with the Moon up.\u003c\/p\u003e\n\u003cp\u003eIt is also the standard first step \u003cstrong\u003ebeyond LRGB\u003c\/strong\u003e: blending a mono H-alpha channel into RGB data sharpens nebular structure while keeping colour natural. H-alpha is the filter most imagers buy first, because it is where emission nebulae are brightest and where narrowband beats broadband by the widest margin.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e656 nm centre wavelength, 7 nm bandpass:\u003c\/strong\u003e targets the hydrogen-alpha emission line where most nebulae radiate strongest\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFWHM 7 ± 0.5 nm:\u003c\/strong\u003e a tight, specified passband rather than a nominal figure\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eApproximately 90% peak transmission\u003c\/strong\u003e at the H-alpha line, with 80% as the floor\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOD3 off-band blocking:\u003c\/strong\u003e under 0.1% transmission outside the passband — this is what kills light pollution\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIR cut from 700–1100 nm:\u003c\/strong\u003e keeps infrared from bloating stars, so no separate UV\/IR-cut filter is needed behind it\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e1\/4 wavefront both surfaces:\u003c\/strong\u003e fine-polished, so the filter does not degrade star shapes in a converging beam\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThree sizes:\u003c\/strong\u003e 1.25\" mounted (1.9 mm glass), 36 mm unmounted (2 mm), and 2\" mounted\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\u003e\n\u003cstrong\u003eEmission nebulae\u003c\/strong\u003e — Orion, Lagoon, Eagle, North America, Rosette\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePlanetary nebulae and supernova remnants\u003c\/strong\u003e — the Ring, Dumbbell, Helix, and the Veil\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSHO \/ Hubble-palette imaging\u003c\/strong\u003e combined with the matching S-II and O-III 7 nm filters\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eHa-enhanced LRGB\u003c\/strong\u003e, blending H-alpha into RGB to lift structural detail without shifting colour\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eImaging under moonlight or heavy light pollution\u003c\/strong\u003e, where broadband work is not viable\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\u003eMonochrome cameras only.\u003c\/strong\u003e A one-shot-colour camera or DSLR has a Bayer matrix, so only the red-sensitive pixels see H-alpha — you lose most of your resolution and most of your light\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e36 mm is unmounted:\u003c\/strong\u003e no cell and no thread. It cannot be screwed into a filter drawer or nosepiece — it is retained by M2 screws in a filter wheel recess, and those screws ship with the ZWO 36 mm EFW\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e1.25\" and 2\" are mounted:\u003c\/strong\u003e threaded cells that fit filter wheels, drawers, and standard filter threads\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThird-party wheels:\u003c\/strong\u003e ZWO specifies filter thickness between 1.5 mm and 3.0 mm for its wheels\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOrientation:\u003c\/strong\u003e ZWO advises that on the current Mark II filters the \u003cstrong\u003ecoated side should face the telescope\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBackfocus:\u003c\/strong\u003e glass in a converging beam shifts focus by roughly one third of its thickness — about 0.6–0.7 mm here. Include it in your 55 mm sum, and use the same thickness in every wheel slot so focus does not shift between channels\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSold singly.\u003c\/strong\u003e For all three channels, the S-II and O-III filters are separate products, or buy the 2\" SHO set\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eImportant Limitations\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eNot for one-shot-colour cameras or DSLRs.\u003c\/strong\u003e This is a monochrome imaging filter. On a colour sensor the Bayer matrix wastes most of the signal\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSize must match your sensor.\u003c\/strong\u003e 1.25\" vignettes APS-C and full-frame; 36 mm will not cover full-frame. This is a physical obstruction, not a coating issue\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUnmounted 36 mm glass must be handled by the edges.\u003c\/strong\u003e There is no cell protecting the coating, and a fingerprint on a narrowband coating is a real problem\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNarrowband does not brighten nebulae — it raises contrast\u003c\/strong\u003e by darkening the sky. Expect longer sub-exposures, not brighter ones\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNot a general light-pollution filter.\u003c\/strong\u003e It passes one 7 nm band. Stars and galaxies, which emit broadband, largely disappear\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNot for visual observing.\u003c\/strong\u003e A 7 nm H-alpha band is far too dark for the eye\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eA filter wheel and monochrome camera are required\u003c\/strong\u003e and sold separately\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\u003eWhich size do I need?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eMatch it to your sensor, not your telescope. Up to about 4\/3\" (ASI1600, ASI294, ASI533), the 1.25\" is fine. APS-C and smaller (ASI2600MM), the 36 mm unmounted. Up to full-frame (ASI6200MM), the 2\". Buying 1.25\" for an APS-C camera vignettes the corners permanently.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat is the difference between mounted and unmounted?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eA mounted filter sits in a threaded cell you can screw into things. An unmounted filter is bare glass held by screws in a filter wheel. The 36 mm is unmounted precisely because a cell has walls, and walls block the corners of a big sensor.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs this good for beginners?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt is a sound first narrowband filter if you already have a monochrome camera and a filter wheel. If you image with a one-shot-colour camera, this is not your next purchase — a dual-band filter is.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWill it work with my ASI2600MC or my DSLR?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNot effectively. Those are colour sensors. Only the red pixels respond to H-alpha, so you throw away roughly three quarters of your resolution. Use a mono camera, or a duo-band filter designed for colour sensors.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhy is my H-alpha image so dark?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThat is the filter working. It rejects over 99.9% of the spectrum. Narrowband raises contrast by darkening the background, not by brightening the target — so plan on longer subs.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan I image with the Moon up?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eYes, and that is much of the point. A 7 nm passband rejects moonlight and light pollution well enough that narrowband nights are the ones a broadband imager writes off.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhich way round does it go?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eZWO advises that on the Mark II filters the coated side should face the telescope.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDo I need a UV\/IR-cut filter as well?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo. This filter cuts 700–1100 nm itself, so infrared will not bloat your stars through it.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes it change my backfocus?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eSlightly. Glass shifts focus by roughly a third of its thickness — about 0.6–0.7 mm depending on size. What matters more is using the same thickness across every wheel slot so focus does not jump between channels.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat do I need for the Hubble palette?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eAll three: this H-alpha, plus the S-II 7 nm at 672 nm and the O-III 7 nm at 500 nm. Map them to R, G, and B in processing.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs one filter included, or three?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eOne. Each size option is a single H-alpha filter. The S-II and O-III are separate products.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eIn short: a 7 nm H-alpha filter at 656 nm with roughly 90% peak transmission, OD3 blocking, and 1\/4 wavefront polish — the first narrowband filter most mono imagers buy, and the one that makes light-polluted and moonlit nights productive. Pick the size from your sensor: 4\/3\" takes 1.25\", APS-C takes 36 mm, full-frame takes 2\".\u003c\/p\u003e","brand":"ZWO Optical","offers":[{"title":"1.25\" mounted","offer_id":53804730679407,"sku":"Ha7nm1.25","price":164.0,"currency_code":"CAD","in_stock":true},{"title":"36mm unmounted","offer_id":53804730712175,"sku":"Ha7nmD36","price":214.0,"currency_code":"CAD","in_stock":true},{"title":"2\" mounted","offer_id":53804730744943,"sku":"Ha7nmD2","price":316.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/08fd46e15c0f7c733a032a761034763d.webp?v=1784084878","url":"https:\/\/ontariotelescope.com\/products\/zwo-ha-7nm-narrowband-filter","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}