{"product_id":"explore-scientific-0-8x-focal-reducer-f5-to-f7-refractors","title":"Explore Scientific 0.8x Focal Reducer for f\/5 to f\/7 Refractors with 55mm Back Spacing","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific ES-FR0.8x is a two-element 0.8x focal reducer made for refractors working between roughly f\/5 and f\/7. It multiplies your telescope's focal length by 0.8, which shortens the focal length, speeds up the focal ratio and widens the field your camera records. Explore Scientific gives two worked examples: a 480mm f\/6 refractor becomes 384mm at f\/4.8, and a 714mm f\/7 refractor becomes 571mm at f\/5.6. It threads into a standard 42mm T-ring and works at 55mm of back spacing, plus or minus 2mm, which is the same nominal spacing used by most T-ring and camera combinations in astrophotography.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThis is for the imager who likes their refractor but wants more sky in the frame and shorter exposures to get it. A reducer solves a framing and speed problem: the target does not fit, or it fits so tightly that there is nothing left for composition, or the sub-exposures are long enough that guiding errors and satellite trails start eating your night. Dropping from f\/6 to f\/4.8 collects the same signal in noticeably less time, and the wider field turns large emission nebulae and open clusters from crops into portraits.\u003c\/p\u003e\u003cp\u003eIt is worth being blunt about what this is not. A focal reducer and a coma corrector are not interchangeable, and buying one when you needed the other leaves you with the wrong tool entirely. A coma corrector fixes off-axis coma, the seagull-shaped stars at the edge of the frame that fast Newtonian reflectors produce, and it does not meaningfully widen your field. This reducer is the opposite errand: it is for refractors, it changes focal length and focal ratio, and it is about framing and exposure time rather than repairing a specific aberration of a mirror telescope. If you shoot with a fast Newtonian, you want a coma corrector. If you shoot with an f\/5 to f\/7 refractor and want a wider, faster field, you want this.\u003c\/p\u003e\u003ch2\u003eKey Features and Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e0.8x reduction factor, shortening focal length and speeding the focal ratio by the same proportion\u003c\/li\u003e\n\u003cli\u003eTwo-element optical design\u003c\/li\u003e\n\u003cli\u003eBack spacing of 55mm, plus or minus 2mm, the standard working distance for most T-ring and camera stacks\u003c\/li\u003e\n\u003cli\u003eAccepts a standard 42mm T-ring, so it drops into the usual imaging train rather than demanding proprietary adapters\u003c\/li\u003e\n\u003cli\u003eIntended for refractors in the f\/5 to f\/7 range\u003c\/li\u003e\n\u003cli\u003eExplore Scientific publishes worked conversions of 480mm to 384mm, taking f\/6 to f\/4.8, and 714mm to 571mm, taking f\/7 to f\/5.6\u003c\/li\u003e\n\u003cli\u003eListed by Explore Scientific for the ES-ED0806-02, ES-ED10207-02, FCD100-0806-02, FCD100-10207-02 and FCD100-10207-CF-01 telescopes\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eOptical Design\u003c\/h2\u003e\u003cp\u003eA focal reducer sits in the converging light cone behind the objective and adds negative-to-positive optical power that brings the focus in closer, shortening the effective focal length. Because the aperture has not changed, a shorter focal length means a smaller focal ratio number, and the image scale on the sensor shrinks by the same 0.8 factor, so more sky lands on the same chip. The illumination per square millimetre of sensor rises as the square of the change in focal ratio, which is why a 0.8x reducer is often described as making a telescope roughly one and a half times faster in exposure terms. The 55mm back spacing is not a suggestion. Reducers only deliver their designed correction at one working distance, and drifting away from it changes the effective reduction and pushes stars in the corners out of round. Explore Scientific quotes a tolerance of plus or minus 2mm, which is tight enough that you should measure your spacers rather than estimate them. The two-element construction keeps the glass count and the light loss low, and it also keeps the reducer short enough not to swallow an unreasonable amount of your focuser's back focus.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eWide-field deep-sky imaging with an f\/5 to f\/7 apochromatic or ED refractor\u003c\/li\u003e\n\u003cli\u003eShortening exposure times on faint, extended targets such as large emission nebulae\u003c\/li\u003e\n\u003cli\u003eFraming large objects that do not fit the native field of your refractor\u003c\/li\u003e\n\u003cli\u003eReducing the demand on your guiding by cutting sub-exposure length\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eExplore Scientific lists this reducer for its ES-ED0806-02, ES-ED10207-02, FCD100-0806-02, FCD100-10207-02 and FCD100-10207-CF-01 refractors, and describes it more generally as suiting f\/5 to f\/7 refractors. You will need a 42mm T-ring for your camera body, and you will need to build the imaging train so that the sensor sits 55mm behind the reducer, which usually means the T-ring plus one or more spacer rings depending on your camera's flange distance. Cooled astronomy cameras with built-in filter drawers and off-axis guiders complicate that arithmetic, so it is worth working out the numbers before you order. Send us your telescope and camera model and our team in Bolton will confirm the spacing you need and whether this reducer suits your particular optical train.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eNo T-ring, spacers or camera adapters are included, and Explore Scientific does not publish a packing list for this item. This reducer is designed for refractors in a specific focal ratio band, and it is not a coma corrector for Newtonian reflectors, nor is it a substitute for one. The 55mm spacing tolerance of plus or minus 2mm is worth respecting, and if your back focus budget is already tight you should confirm the numbers before committing. 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\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eWill this correct coma in my Newtonian?\u003c\/strong\u003e No. Coma is an off-axis aberration of the parabolic mirror in a reflector and needs a coma corrector. This is a focal reducer for refractors, and it changes focal length and field width rather than repairing coma.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat does 55mm back spacing actually mean?\u003c\/strong\u003e It is the distance from the reducer's shoulder to your camera's sensor. Get it right and the correction is as designed. Drift outside the plus or minus 2mm tolerance and the reduction factor shifts and corner stars start to elongate.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it visually?\u003c\/strong\u003e It is designed and specified as an imaging accessory working to a 42mm T-ring at a defined sensor distance, so visual use is not what Explore Scientific specifies for it. If you want a wider visual field, a longer focal length eyepiece is the simpler answer.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it work on telescopes outside the f\/5 to f\/7 range?\u003c\/strong\u003e Explore Scientific specifies f\/5 to f\/7 refractors and names five of its own models. Outside that band the correction may not hold across the field. Ask us and we will check your telescope against the specification.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eIf you image with an f\/5 to f\/7 refractor and keep running out of frame, this two-element 0.8x reducer widens the field and speeds the system in one step, using standard 42mm T-ring threads and 55mm back spacing. Just make sure a reducer is what your telescope needs, because a fast Newtonian wants a coma corrector instead. Contact our team in Bolton and we will confirm the fit and the spacing for your setup.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958593970287,"sku":"ES-FR0.8x","price":193.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/ES-FR0.8X_1_7c74a6f1-4013-4ce6-9df0-3c958a8967b3.jpg?v=1785960612","url":"https:\/\/ontariotelescope.com\/products\/explore-scientific-0-8x-focal-reducer-f5-to-f7-refractors","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}