{"title":"Explore Scientific Focusing","description":"\u003cp\u003eEvery Explore Scientific focusing product we carry — focusers, motors, controllers and the adapters and brackets that go with them. Part of \u003ca href=\"\/collections\/focusers\"\u003eFocusers\u003c\/a\u003e.\u003c\/p\u003e","products":[{"product_id":"explore-scientific-adapter-for-fffr507x-00-to-2-5-hex-focuser","title":"Explore Scientific Adapter for FFFR507X-00 0.7x Corrector to 2.5-Inch Hex Focuser","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThis is the Explore Scientific mechanical adapter that joins the FFFR507X-00 3-inch 0.7x field flattener and focal reducer to a 2.5-inch hex focuser. It carries no optical elements of its own. Its entire job is to hold two components of different diameters concentric, square to the optical axis, and at whatever spacing the corrector was designed for — which, in an imaging train, is the difference between round stars in the corners and elongated ones.\u003c\/p\u003e\n\u003cp\u003eThe FFFR507X-00 is a 3-inch corrector, sized for the larger focusers fitted to Explore Scientific's bigger refractors. A 2.5-inch hex focuser has a smaller drawtube, so on its own the corrector has nothing to seat against. The adapter is the interface that makes that pairing mechanically possible.\u003c\/p\u003e\n\u003cp\u003eExplore Scientific does not publish a specification table for this item — no dimensions, no thread callouts, no weight and no optical path length. Everything below that is not in their data is stated as unpublished rather than estimated, and we are glad to take a specific question to our Explore Scientific contact on your behalf.\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\u003eOwners of the FFFR507X-00 3″ 0.7x corrector\u003c\/strong\u003e who want to use it on a telescope fitted with a 2.5-inch hex focuser rather than a 3-inch one.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eImagers assembling a fixed, repeatable optical train,\u003c\/strong\u003e where a purpose-made adapter is more rigid and more concentric than a stack of general-purpose rings.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAnyone who has changed focusers or telescopes\u003c\/strong\u003e and needs to carry an existing corrector across to the new setup.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eObservers troubleshooting corner star shapes,\u003c\/strong\u003e where a mechanical mismatch in the train is one of the usual causes.\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\u003ePurpose-built interface:\u003c\/strong\u003e made specifically for the FFFR507X-00 to 2.5-inch hex focuser pairing rather than adapted from a generic ring.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMechanical only:\u003c\/strong\u003e no lenses and no coatings, so it introduces no aberrations of its own and needs no cleaning regime beyond keeping the mating faces clean.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eConcentricity and squareness:\u003c\/strong\u003e the two functions that matter in an adapter. A part machined for a specific pair holds the corrector on-axis more reliably than a chain of step rings does.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFixed geometry:\u003c\/strong\u003e a single machined part contributes one known length to the train rather than the accumulated tolerance of several stacked components.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart of the Explore Scientific accessory line,\u003c\/strong\u003e so the mating dimensions are drawn from the same drawings as the focuser and the corrector it joins.\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\u003eFitting the FFFR507X-00 3-inch 0.7x reducer and flattener onto a 2.5-inch hex focuser.\u003c\/li\u003e\n\u003cli\u003eBuilding a deep-sky imaging train that reduces focal length and flattens the field in one component.\u003c\/li\u003e\n\u003cli\u003eMoving an existing corrector between telescopes with different focuser sizes.\u003c\/li\u003e\n\u003cli\u003eReplacing an improvised stack of step rings with a single machined interface.\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\u003eCorrector side:\u003c\/strong\u003e made for the Explore Scientific FFFR507X-00, the 3-inch 0.7x field flattener and focal reducer.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFocuser side:\u003c\/strong\u003e made for the 2.5-inch hex focuser.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSpacing matters downstream of it.\u003c\/strong\u003e A reducer and flattener has a designed distance from its rear surface to the sensor, and that distance is set by the parts that follow the adapter — the camera, the filter wheel, any spacer rings. If you send us the camera and any filter wheel or off-axis guider you plan to use, we will work through the spacing with you.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFilters in the train add optical path.\u003c\/strong\u003e Glass in the light path shifts focus slightly, which is one of the more common reasons a train that measures correctly still does not quite deliver. It is straightforward to allow for once it is accounted for.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eExplore Scientific publishes no thread specification, length or weight\u003c\/strong\u003e for this adapter, so those rows read as unpublished below. For a specific figure, ask us and we will take it to our Explore Scientific contact before you commit to an order.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOther correctors:\u003c\/strong\u003e this part is specified for the FFFR507X-00. If you have a different flattener or reducer in mind, send us the model and we will look at whether the interface suits it.\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\u003eIt is a mechanical adapter, not a corrector.\u003c\/strong\u003e The optical work is done by the FFFR507X-00; this part positions it. Both are needed for the pairing, and we can supply them together.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eExplore Scientific publishes no specification table for it.\u003c\/strong\u003e No dimensions, thread callouts, optical path length or weight appear on their product page, so the table below records those rows as unpublished rather than estimated. If a figure decides the purchase for you, ask and we will get it from our Explore Scientific contact first.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBack-focus is the specification that governs the result.\u003c\/strong\u003e The adapter contributes a fixed length; the remainder of the distance to the sensor comes from spacers and from the camera itself. Sending us the full list of what sits behind the corrector is the quickest way to get that right the first time.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIt is a narrow-purpose part.\u003c\/strong\u003e It exists for one corrector and one focuser size, which is precisely why it fits well. For any other combination, we would rather check the fit with you than have the wrong part arrive.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNothing else is required to use it\u003c\/strong\u003e beyond the corrector and the focuser it was made for — there is no separate clamp, ring or tool involved.\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 is a single machined part that goes between the corrector and the focuser and then stays there. There is nothing to align, collimate or calibrate on the adapter itself. The one job that repays a few minutes is measuring the spacing from the back of the corrector to your camera sensor, and we will happily work that out with you.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes it contain any glass?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo. It is purely mechanical, so it adds no aberrations, no reflections and no light loss of its own.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat does the FFFR507X-00 do?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt is a 3-inch field flattener and 0.7x focal reducer. It flattens the curved focal plane that a refractor naturally produces, so stars stay round toward the corners of a sensor, and it shortens the effective focal length to 0.7 of its native value — a wider field and a faster focal ratio at the same time.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWill it change my back-focus?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eAny component in the train contributes length, and this one is no exception. Explore Scientific does not publish its optical path length, so we are not going to quote a figure. Send us the parts list for your train and we will work the spacing through with you.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes it fit other Explore Scientific focusers?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt is specified for the 2.5-inch hex focuser. If your telescope has a different focuser, send us the model and we will check the interface for you before you order.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs a camera adapter included?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo. This part joins the corrector to the focuser; the connection from the corrector to your camera is a separate item, chosen to suit the camera and the spacing your train needs.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan I use it for visual observing?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe FFFR507X-00 it supports is an imaging corrector, so the pairing is aimed at cameras. It is mechanically harmless in a visual train, though there is little for it to do there.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eIn short: a mechanical adapter that lets the Explore Scientific FFFR507X-00 3-inch 0.7x flattener and reducer sit on a 2.5-inch hex focuser, with no optics of its own and one job to do properly. Explore Scientific publishes no dimensions for it, so if you would like exact figures before you order, or help laying out the spacing between the corrector and your camera, send us the list of what is in your imaging train and we will map it out with you.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":44013400981615,"sku":"510366","price":138.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/ES_0510366_2_3000x__04467.jpg?v=1766553257"},{"product_id":"explore-scientific-rack-and-pinion-focuser-2-extension-tube","title":"Explore Scientific ESRPEXT2 1.5-Inch Extension Tube for 2-Inch Rack and Pinion Focusers","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThis is an Explore Scientific extension tube for the 2-inch rack-and-pinion focusers fitted to their ED APO telescopes, carried under item number ESRPEXT2. It adds 1.5 inches of additional travel to the focuser, which lets an imaging or visual train reach focus in configurations that would otherwise run past the end of the focuser's native range.\u003c\/p\u003e\n\u003cp\u003eIt is a plain machined tube. There is no glass in it, no moving part and no electronics — it sits between the focuser and whatever follows it, and its only job is to place that equipment 1.5 inches further back.\u003c\/p\u003e\n\u003cp\u003eEvery telescope brings light to focus a fixed distance behind the focuser flange. A visual eyepiece in a diagonal usually lands inside the focuser's travel comfortably; a camera, a binoviewer, a filter wheel or a long adapter stack often does not, and the focuser reaches the end of its outward travel before the image is sharp. An extension tube moves the whole train outward by a known amount so that focus falls back inside the range the focuser actually has.\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\u003eOwners of Explore Scientific ED APO telescopes with 2-inch rack-and-pinion focusers,\u003c\/strong\u003e which is the fitment this tube is specified for.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAnyone whose focuser runs out of outward travel\u003c\/strong\u003e before an image comes to focus — the classic symptom being a focuser racked fully out with the stars still soft.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBinoviewer users:\u003c\/strong\u003e a binoviewer consumes a large amount of light path, and reaching focus with one is a common reason to add a fixed extension.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eImagers assembling a train:\u003c\/strong\u003e when the sum of camera, filter wheel, spacers and adapter comes up short of the required distance, a fixed extension is the simplest way to make up the difference.\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\u003eAdds 1.5 inches of travel\u003c\/strong\u003e to the focuser's native range.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMade for 2-inch rack-and-pinion focusers\u003c\/strong\u003e on Explore Scientific ED APO telescopes.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMachined tube with no optical elements:\u003c\/strong\u003e nothing in the light path to add aberration, reflection or colour.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNo moving parts:\u003c\/strong\u003e a fixed spacer holds its length exactly, which is what makes it predictable in an imaging train where spacing is arithmetic.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eItem number ESRPEXT2,\u003c\/strong\u003e the designation to quote when checking fitment against a particular telescope.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSupplied on its own\u003c\/strong\u003e — the vendor lists no additional included accessories with it.\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\u003eReaching focus with a binoviewer, which typically needs more light path than a single eyepiece.\u003c\/li\u003e\n\u003cli\u003eAdding length to an imaging train that falls short of the required backfocus distance.\u003c\/li\u003e\n\u003cli\u003eRestoring focus after a diagonal has been removed from a visual setup, which shortens the path considerably.\u003c\/li\u003e\n\u003cli\u003eGiving a camera enough standoff from the focuser that the focuser is not working at the very end of its travel, where a rack-and-pinion is least well supported.\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\u003eFitment:\u003c\/strong\u003e specified for the 2-inch rack-and-pinion focusers used on Explore Scientific ED APO telescopes. If you are unsure which focuser your tube carries, send us the model and we will check it.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eLength added:\u003c\/strong\u003e 1.5 inches, which is 38.1mm. That is the figure to use when adding up an imaging train.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDirection of the change:\u003c\/strong\u003e an extension pushes the focus point outward. Where a setup already reaches focus with the drawtube well in, adding this tube pushes it further out and may take some setups past their inward range instead — which is why extensions are added to trains that come up short rather than as a default.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOptical effect:\u003c\/strong\u003e none of its own. There is no glass, so it changes distance and nothing else.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFilters:\u003c\/strong\u003e the vendor does not publish a filter thread for this tube, so that row is absent from the specifications rather than estimated.\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\u003eThe vendor lists this item under two names.\u003c\/strong\u003e Explore Scientific titles it a 1.5-inch extension tube while the part is catalogued as the 2-inch rack-and-pinion focuser extension — the 2 inches refers to the focuser it fits and the 1.5 inches to the travel it adds. Item number ESRPEXT2 identifies it either way.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eExplore Scientific publishes no dimensional or weight specification for this part.\u003c\/strong\u003e Outer diameter, thread type, material and mass are not given, so those rows are absent below rather than estimated. If a specific figure decides the purchase for you, ask us and we will put the question to our Explore Scientific rep.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAn extension solves a shortfall, not a surplus.\u003c\/strong\u003e Where a train already focuses with room to spare, adding length works against you. The useful check is whether the focuser currently runs out of outward travel before the image sharpens.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAny extension adds a joint to the light path.\u003c\/strong\u003e With a heavy camera on the end, that additional cantilever is worth accounting for in how the train is supported — keeping the heaviest item as close to the focuser as the spacing allows is the usual approach.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFitment is worth checking once rather than guessing.\u003c\/strong\u003e Send us your telescope model and the accessories going behind it and we will tell you whether this is the right part before it ships.\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 or slots into the 2-inch rack-and-pinion focuser and the eyepiece, diagonal or camera goes on after it. There is nothing to adjust, align or calibrate, and refocusing after fitting it is the only step.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eHow much length does it add?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e1.5 inches, which is 38.1mm.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWill it degrade the image?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThere is no glass in it, so it introduces no aberration of its own. What it changes is the distance between the focuser and everything behind it.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eHow do I know whether I need one?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe usual sign is a focuser racked all the way out with the image still soft — the focus point is falling behind where the drawtube can reach. Send us a list of what is in your train and we will work out whether 1.5 inches is the right amount.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes it work with a binoviewer?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eBinoviewers are one of the common reasons to add a fixed extension, because they consume a substantial amount of light path. Whether 1.5 inches is enough depends on the particular binoviewer, so send us the model and we will check.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWill it fit a focuser from another brand?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eIt is specified for Explore Scientific 2-inch rack-and-pinion focusers. Other 2-inch focusers vary in how they accept accessories, so tell us what you have and we will look at it before you order.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eIn short: a simple machined extension that adds 1.5 inches of travel to the 2-inch rack-and-pinion focusers on Explore Scientific ED APO telescopes, with no glass and nothing to adjust — the straightforward fix when a camera, binoviewer or adapter stack pushes focus beyond the focuser's reach. Send us your telescope and the accessories behind it and we will tell you whether this is the piece that closes the gap.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":44013540311151,"sku":"ESRPEXT2","price":54.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/ESRPEXT2_Bottom_1800x1800__39608.jpg?v=1766555687"},{"product_id":"explore-scientific-3-inch-self-centering-focuser","title":"Explore Scientific 3-inch Self-Centering Focuser for 152mm and 165mm Refractors","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific 3-inch Self-Centering Focuser is a heavy-duty replacement focuser for large refractors, rated to lift 17 lb of imaging equipment. It uses a helical rack-and-pinion mechanism with a 9:1 reduction running on stainless steel ball bearings, gives 84.5 mm (3.32 inches) of draw tube travel, and passes a full 3-inch clear aperture through a 14-baffle draw tube. It weighs 5.7 lb including the 3-inch to 2-inch twist-lock adapter.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThis is an upgrade part for someone running a large refractor whose original focuser flexes or slips under a loaded imaging train — camera, filter wheel, off-axis guider and flattener together can easily pass 10 lb. It suits imagers chasing round stars in the corners, and visual observers using heavy 2-inch and 3-inch eyepieces where sag shifts the focal plane.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e17 lb lifting capacity for heavy imaging trains\u003c\/li\u003e\n\u003cli\u003eSelf-centering compression attachment that grips without pulling the optical axis off centre\u003c\/li\u003e\n\u003cli\u003e9:1 reduction ratio on stainless steel ball bearings and shaft for fine focus control\u003c\/li\u003e\n\u003cli\u003e84.5 mm of draw tube travel with a 76.2 mm (3-inch) clear interior diameter\u003c\/li\u003e\n\u003cli\u003e14 internal baffles to suppress stray light across a large image circle\u003c\/li\u003e\n\u003cli\u003eM82 x 1.25 draw tube thread\u003c\/li\u003e\n\u003cli\u003eCompatible with electric focusers for automated and remote focusing\u003c\/li\u003e\n\u003cli\u003e3-inch to 2-inch twist-lock adapter included\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eOptical and Mechanical Design\u003c\/h2\u003e\u003cp\u003eA self-centering compression mechanism spreads its grip evenly around the accessory barrel rather than pushing from one side, which keeps a camera square to the optical axis — the difference shows as consistent star shapes across the frame instead of one soft corner. The 3-inch clear aperture matters for large sensors: a narrower draw tube vignettes the corners of a full-frame chip regardless of how good the objective is. Fourteen baffles line that clear path to keep scattered light out of the image.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eReplacing the stock focuser on a 120 mm or larger refractor carrying a full imaging train\u003c\/li\u003e\n\u003cli\u003eFull-frame and large-format astrophotography where a 3-inch clear path prevents corner vignetting\u003c\/li\u003e\n\u003cli\u003eRemote and automated imaging with an electric focuser fitted\u003c\/li\u003e\n\u003cli\u003eVisual observing with heavy 2-inch eyepieces\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eExplore Scientific specifies this focuser for their refractors 120 mm and larger, and offers custom back cells on request for other brands of refractor 120 mm and larger. Two notes from the manufacturer worth reading before ordering: the FPL53-165CF telescopes require a new back cell adapter, and the TED15208CF does not — the focuser fits its back cell directly. If your telescope is another brand, contact us with the model and we will confirm what back cell you need before anything ships.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eBack cell fit is the thing to settle first, and it is a one-line question we are glad to answer — tell us your telescope model and we will tell you exactly what is required. Explore Scientific lists two dedicated back-cell versions of this focuser for the FCD100-127-CF and the white-tube ED127; those are separate part numbers and we are confirming their details with the manufacturer. The published weight of 5.7 lb includes the supplied 3-inch to 2-inch adapter.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eIs it difficult to fit?\u003c\/strong\u003e On a telescope with a matching back cell it is a straightforward swap with hand tools. The work is in confirming the back cell beforehand, not in the installation.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it hold my camera and filter wheel?\u003c\/strong\u003e A 17 lb rating covers essentially any amateur imaging train, including a large cooled camera with a filter wheel and off-axis guider.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I motorise it?\u003c\/strong\u003e Yes — Explore Scientific lists it as compatible with electric focusers, so it suits automated focus routines and remote operation.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it work with 2-inch accessories?\u003c\/strong\u003e Yes. The 3-inch to 2-inch twist-lock adapter is included in the box.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eA 3-inch focuser with a 17 lb capacity, 9:1 fine focus and a fully baffled clear aperture — the part that stops a good large refractor being limited by its focuser. Send us your telescope model and we will confirm the back cell you need.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53956018372719,"sku":"ES-FOC3","price":1177.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/ES-FOC3_1.jpg?v=1785953782"},{"product_id":"explore-scientific-2-inch-dual-speed-rack-pinion-focuser-apo","title":"Explore Scientific 2-inch Dual-Speed Rack and Pinion Focuser for Apochromatic Refractors","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific Rack \u0026amp; Pinion Focuser is a dual-speed 2-inch focuser for apochromatic refractors, combining a coarse focus knob with 10:1 micro-focusing for fine adjustment. It comes with a 1.25-inch compression ring eyepiece adapter, and three set screws hold an eyepiece, adapter or barrelled accessory securely in place. Explore Scientific publishes a weight of 2.0 lb, a 2-inch diameter and a length of 120.7 mm.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThis suits an observer or imager who wants finer focus control than a single-speed focuser allows. At high magnification and at fast focal ratios the depth of focus is small enough that a coarse knob overshoots; a 10:1 reduction gives you the resolution to land on best focus and stay there. It is equally useful as a replacement for a worn focuser and as an upgrade to a working but coarse one.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eDual-speed operation with both a coarse focus knob and 10:1 micro-focusing knobs\u003c\/li\u003e\n\u003cli\u003eLarge knurled dials that stay easy to grip in cold weather or with gloves on\u003c\/li\u003e\n\u003cli\u003eThree set screws securing eyepieces, adapters and barrelled accessories\u003c\/li\u003e\n\u003cli\u003e1.25-inch compression ring eyepiece adapter included\u003c\/li\u003e\n\u003cli\u003e2-inch barrel accepting the full range of 2-inch eyepieces and accessories\u003c\/li\u003e\n\u003cli\u003e2.0 lb, 120.7 mm long\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eOptical and Mechanical Design\u003c\/h2\u003e\u003cp\u003eA rack-and-pinion mechanism drives the draw tube through a toothed rack, and the 10:1 reduction stage gears that motion down so a full turn of the fine knob moves the tube a tenth as far as the coarse knob would. That is the whole point at f\/6 and faster, where the range of acceptable focus is a fraction of a millimetre. The 1.25-inch adapter uses a compression ring rather than a screw pressing directly on the barrel, so eyepiece barrels are not marked or pushed off axis.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eReplacing or upgrading the focuser on an apochromatic refractor\u003c\/li\u003e\n\u003cli\u003eHigh-magnification lunar, planetary and double star observing\u003c\/li\u003e\n\u003cli\u003eAstrophotography where focus needs to be set precisely and repeatably\u003c\/li\u003e\n\u003cli\u003eAny setup where the existing focuser is too coarse to reach best focus reliably\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThis focuser is specified by Explore Scientific for their apochromatic refractors. It takes 2-inch accessories directly and 1.25-inch accessories through the included compression ring adapter. Explore Scientific also offers rack-and-pinion extension tubes if your imaging train or diagonal needs more back focus to reach a sharp image. Because focuser fit depends on the back cell of your particular telescope, send us the model and we will confirm compatibility before shipping.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eFit varies by telescope back cell, so a quick check with us saves a return — tell us the make and model and we will confirm. The included adapter covers 1.25-inch eyepieces, so an existing eyepiece set in either barrel size works from day one. If you reach the end of the draw tube travel without hitting focus, an extension tube is the usual remedy and we stock them.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eIs it difficult to fit?\u003c\/strong\u003e On a matching back cell it is a hand-tool job. Confirming your telescope's back cell first is the important part, and we are happy to do that with you.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat does dual-speed actually change?\u003c\/strong\u003e The 10:1 knob moves the draw tube a tenth as far per turn as the coarse knob, so you can settle on exact focus instead of rocking back and forth past it.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use 1.25-inch eyepieces?\u003c\/strong\u003e Yes. The 1.25-inch compression ring adapter is included.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it hold a camera?\u003c\/strong\u003e It handles a light imaging train. For a heavy cooled camera with a filter wheel on a large refractor, the 3-inch self-centering focuser is the better match at a 17 lb rating.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eA dual-speed 2-inch focuser with 10:1 fine control, a 1.25-inch adapter in the box and knobs you can work with gloves on. A straightforward improvement in focus precision on an apochromatic refractor. Send us your telescope model and we will confirm the fit.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53956050944111,"sku":"FOCEDAPO-RP","price":415.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/pinion_focuser_1_7e1c6252-dc40-461b-8557-dbd73c8183f1.jpg?v=1785953886"},{"product_id":"explore-scientific-half-inch-extension-tube-2-inch-rack-and-pinion-focuser","title":"Explore Scientific Half-Inch Extension Tube for 2-inch Rack and Pinion Focusers","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\n\u003cp\u003eThis is Explore Scientific's extension tube for their 2-inch rack and pinion focusers, catalogued as item ESRPEXT1. Explore Scientific describe it in a single line on their own product page: it adds half an inch to the 2-inch rack and pinion focusers fitted to their ED APO telescopes. It is a short, fixed-length spacer that sits in the focuser's optical train and moves the focal plane outwards, and it is the standard remedy when an accessory stack cannot quite reach focus on one of those refractors.\u003c\/p\u003e\n\n\u003ch2\u003eWho It's For\u003c\/h2\u003e\n\u003cp\u003eEvery telescope has a fixed amount of back focus, and every accessory you put behind the focuser spends some of it. A star diagonal, a camera with a long flange distance, a filter wheel, an off-axis guider, a binoviewer, or a field flattener each add optical path, and at some point you run the focuser all the way in and the star image is still not sharp. The opposite problem happens too: you rack the drawtube almost fully out to reach focus, which is exactly where a rack and pinion focuser is least rigid and most prone to sag with a heavy camera hanging off it.\u003c\/p\u003e\n\u003cp\u003eA short extension tube solves both. Adding half an inch of fixed spacing shifts the whole focus range outwards so the drawtube can sit closer to the middle of its travel, where it is well supported and the pinion has good engagement. That is a small change on paper and a large one at the eyepiece: better mechanical stiffness, less differential flexure across a long exposure sequence, and a focuser that is not fighting its own end stops. If you have ever found that a particular diagonal and eyepiece combination will not come to focus on your ED APO while a shorter one will, this is the part you were missing.\u003c\/p\u003e\n\n\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eAdds half an inch of fixed spacing to the optical train, per Explore Scientific's published description.\u003c\/li\u003e\n\u003cli\u003eDesigned by Explore Scientific specifically for their own 2-inch rack and pinion focusers.\u003c\/li\u003e\n\u003cli\u003eIntended for the ED APO refractor range that ships with those focusers.\u003c\/li\u003e\n\u003cli\u003eFixed length, with no moving parts, threads to work loose, or clamping mechanism to introduce slop.\u003c\/li\u003e\n\u003cli\u003eShort enough to shift the focus range without meaningfully increasing the cantilevered load on the drawtube.\u003c\/li\u003e\n\u003cli\u003eExplore Scientific item number ESRPEXT1.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eMechanical Design\u003c\/h2\u003e\n\u003cp\u003eAn extension tube does nothing optically. It has no glass in it and it does not change focal length, focal ratio, or image scale. What it changes is geometry. The focal plane of a refractor sits a fixed distance behind the objective, and the focuser's job is to place your eyepiece or sensor at that plane. The drawtube can only travel so far in each direction, so the set of accessory stacks that can reach focus is bounded at both ends. Inserting a rigid half-inch spacer between the focuser and the accessory adds a constant to the optical path, which translates the entire usable focus window outwards by that same half inch. Anything that previously needed the drawtube racked further in than it could go now falls inside the range. The trade-off is symmetric and worth knowing: the same half inch comes off the other end, so a short-path accessory that used to focus with the drawtube nearly fully out may no longer reach focus with the extension fitted. This is why extensions are treated as a per-configuration part rather than something you leave in permanently.\u003c\/p\u003e\n\n\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eRecovering focus with a long-path accessory stack such as a binoviewer, filter wheel, or off-axis guider.\u003c\/li\u003e\n\u003cli\u003eMoving the drawtube back towards the middle of its travel for better rigidity under an imaging load.\u003c\/li\u003e\n\u003cli\u003eFine-tuning spacing when a diagonal and eyepiece combination will not quite come to focus.\u003c\/li\u003e\n\u003cli\u003eBuilding out a repeatable imaging train where a fixed spacer is preferable to a variable one.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\n\u003cp\u003eExplore Scientific state that this extension is for their 2-inch rack and pinion focusers on their ED APO telescopes. They do not publish a list of specific telescope or focuser model numbers on the product page, nor do they publish the fitting's thread or barrel dimensions, so we cannot promise a fit on a third-party focuser or on an Explore Scientific focuser of a different type such as their dual-speed Crayford units. If you tell our team in Bolton which telescope and which focuser you have, we will confirm compatibility with you before it ships rather than have you guess. It is also worth working out how much extra spacing you actually need first, because extensions are only useful in the right length and stacking two short ones is rarely as rigid as fitting one of the correct size.\u003c\/p\u003e\n\n\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\n\u003cp\u003eOne point of honesty about the naming. This item is listed in some catalogues, including the vendor price sheet we work from, as a 1-inch extension tube, but Explore Scientific's own live product page for item ESRPEXT1 describes it as adding half an inch and titles it as a half-inch extension. We have written this listing to the figure the manufacturer currently publishes. If the exact optical length is critical to your imaging train, contact us before ordering and we will measure the part in hand and confirm it for you. Beyond that, this is the extension tube alone with no adapters, compression rings, or spacers included, and it is a spacer rather than a focuser upgrade, so it will not add travel or improve the feel of an existing focuser. Explore 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.\u003c\/p\u003e\n\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eWill this let my camera reach focus?\u003c\/strong\u003e It will if the reason you cannot focus is that your accessory stack is too short and the drawtube is already racked fully out, or if you need to shift the focus window outwards. If you are running out of inward travel instead, an extension makes the problem worse rather than better. Tell us your imaging train and we will work out which direction you need to go.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes it fit a Crayford or a third-party focuser?\u003c\/strong\u003e Explore Scientific specify it for their own 2-inch rack and pinion focusers only, and they do not publish the fitting dimensions, so we cannot confirm a fit on anything else. Ask us with your focuser model and we will check.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWill it degrade the image?\u003c\/strong\u003e No. There is no glass in an extension tube, so it introduces no aberration of its own. The only optical consideration is that it changes where the focal plane sits relative to your focuser travel.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan I stack two of them?\u003c\/strong\u003e Mechanically you can, but each additional joint is another place for tilt and flexure to creep in, which matters for imaging. If you need more than half an inch, we would rather find you a single spacer of the right length.\u003c\/p\u003e\n\n\u003ch2\u003eBottom Line\u003c\/h2\u003e\n\u003cp\u003eA half-inch spacer is a small part that quietly fixes a frustrating problem, letting a stubborn accessory stack come to focus and keeping the drawtube in the stiffer part of its travel. Explore Scientific publish very little about it beyond its purpose, so if the exact length or the fit on your particular focuser matters, contact us and we will confirm both before you order.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958600720495,"sku":"ESRPEXT1","price":41.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/ESRPEXT1_Side.jpg?v=1785960632"}],"url":"https:\/\/ontariotelescope.com\/collections\/focusers-explore-scientific.oembed","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}