{"product_id":"askar-131f-0-74-focal-reducer","title":"Askar 131F 0.74× Focal Reducer","description":"\u003ch2\u003eAskar 131F 0.74× Focal Reducer — For the Askar 131F Flat-Field Astrograph\u003c\/h2\u003e\n\n\u003cp\u003eThe \u003cstrong\u003eAskar 131F 0.74× Reducer\u003c\/strong\u003e is a dedicated focal reducer designed exclusively for the Askar 131F Flat-Field astrograph. It reduces the 131F’s native f\/7.5 focal ratio down to f\/5.6, shortening the effective focal length from 983mm to 733.6mm. This delivers a wider field of view and significantly faster exposures — roughly 80% of the original exposure time — making it particularly valuable for capturing large nebulae, expansive star fields, faint emission structures, and fast-moving or time-sensitive celestial events.\u003c\/p\u003e\n\n\u003cp\u003eIn addition to reducing the focal ratio, the reducer incorporates built-in field-flattening correction that eliminates field curvature across the 44mm full-frame image circle. Stars remain sharp and round from the centre of the frame to the corners, with no additional flattener required at the reduced focal ratio.\u003c\/p\u003e\n\n\u003cp\u003eThe optical design uses a triplet lens group for smooth, well-corrected reduction across the full field. The standard back focus distance is 55mm measured from the M48×0.75 male thread. Both ends of the reducer body feature M72×1 threads. The package includes M54×0.75 and M48×0.75 adapter rings for direct connection to the 131F’s photographic extension tube, and the rear adapter ring has a built-in M48×0.75 standard 2\" filter thread for direct filter installation. The body is precision CNC-machined and ships with protective metal thread caps on both ends.\u003c\/p\u003e\n\n\u003ch2\u003eWho Is This Product Best For?\u003c\/h2\u003e\n\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eAskar 131F owners\u003c\/strong\u003e who image large nebulae, emission regions, or wide star fields and want a broader field of view without changing telescopes.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eImagers in light-polluted skies\u003c\/strong\u003e who benefit from the faster f\/5.6 ratio to shorten sub-exposure times.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eNarrowband and broadband filter users\u003c\/strong\u003e who want the faster ratio for more efficient filter imaging.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eAstrophotographers\u003c\/strong\u003e who want to switch between the native f\/7.5 (for tighter framing) and f\/5.6 (for wider field) without buying a second telescope.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eWhy Choose the Askar 131F 0.74× Reducer?\u003c\/h2\u003e\n\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eDedicated design\u003c\/strong\u003e — optically optimized specifically for the 131F, not a generic reducer. Delivers consistent correction across the full 44mm image circle at the reduced ratio.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBuilt-in field flattening\u003c\/strong\u003e — no additional flattener needed at f\/5.6; the reducer handles both reduction and correction simultaneously.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFaster imaging\u003c\/strong\u003e — f\/5.6 vs f\/7.5 means roughly 44% less exposure time needed for the same signal level.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eWider field\u003c\/strong\u003e — 733.6mm focal length vs 983mm gives approximately 26% more field width in each direction.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eStandard back focus\u003c\/strong\u003e — 55mm from M48 thread eliminates guesswork; direct adapter connections included in the box.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFilter-ready rear\u003c\/strong\u003e — built-in M48×0.75 thread accepts standard 2\" astronomy filters without an additional adapter.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCNC precision body with dust caps\u003c\/strong\u003e — professional-grade build quality with protective metal end caps.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\n\n\u003cul\u003e\n  \u003cli\u003eWide-field deep-sky nebula imaging with the Askar 131F\u003c\/li\u003e\n  \u003cli\u003eLarge emission and reflection nebulae (Orion, Rosette, North America, etc.)\u003c\/li\u003e\n  \u003cli\u003eGalaxy groups and clusters requiring wider framing\u003c\/li\u003e\n  \u003cli\u003eNarrowband and broadband filter imaging in light-polluted sites\u003c\/li\u003e\n  \u003cli\u003eTime-lapse or short-exposure widefield astrophotography\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\n\n\u003cp\u003e\u003cstrong\u003eCompatible telescope:\u003c\/strong\u003e Askar 131F Flat-Field only. Not designed for use with any other telescope.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eConnection:\u003c\/strong\u003e The 131F’s photographic extension tube connects directly to the reducer via the included M54×0.75 or M48×0.75 adapter rings. Both end threads on the reducer body are M72×1.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eBack focus:\u003c\/strong\u003e 55mm from the base of the M48×0.75 male thread. No additional spacing calculation required when using the supplied adapters.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eFilter compatibility:\u003c\/strong\u003e The built-in rear M48×0.75 thread accepts standard 2\" (48mm) astronomy filters directly.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eCamera compatibility:\u003c\/strong\u003e Works with any camera system that connects via the included M54 or M48 adapter rings — DSLRs with T-rings, and dedicated astronomy cameras with M54 or M48 nose threads.\u003c\/p\u003e\n\n\u003ch2\u003eImportant Limitations\u003c\/h2\u003e\n\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003e131F only\u003c\/strong\u003e — this reducer is not compatible with the 91F, 111F, or any other telescope. Each F Series model has its own dedicated reducer.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eNot for visual observing\u003c\/strong\u003e — focal reducers are imaging-only accessories and are not used with eyepieces.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e55mm back focus must be respected\u003c\/strong\u003e — using spacers or adapters that change the back focus distance from the specified 55mm will degrade corner star quality.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\n\u003cp\u003e\u003cstrong\u003eWhat does the 0.74× reducer do to the 131F?\u003c\/strong\u003e\u003cbr\u003eIt reduces the focal length from 983mm to 733.6mm and the focal ratio from f\/7.5 to f\/5.6, giving a wider field of view and faster exposures.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eDoes it work on the 91F or 111F?\u003c\/strong\u003e\u003cbr\u003eNo. Each F Series telescope has its own dedicated reducer. The 91F uses the 0.75× Reducer and the 111F uses the 0.74× Reducer — both are different products.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eDo I still need a field flattener at f\/5.6?\u003c\/strong\u003e\u003cbr\u003eNo. The reducer has field-flattening correction built in and covers the full 44mm image circle with sharp stars to the corners.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eWhat is the back focus distance?\u003c\/strong\u003e\u003cbr\u003e55mm measured from the base of the M48×0.75 male thread on the rear of the reducer.\u003c\/p\u003e\n\n\u003ch2\u003eOur Recommendation\u003c\/h2\u003e\n\n\u003cp\u003eAt Ontario Telescope and Accessories, we consider the \u003cstrong\u003eAskar 131F 0.74× Reducer\u003c\/strong\u003e a worthwhile companion purchase for any 131F owner who does wide-field deep-sky imaging. The improvement in field width and exposure speed is significant, and the fact that it handles both reduction and field flattening in one unit keeps the imaging train simple. If you own a 131F and shoot large nebulae or work under moderate light pollution, this reducer will meaningfully expand what you can do with the telescope.\u003c\/p\u003e","brand":"Askar","offers":[{"title":"Default Title","offer_id":53154396668015,"sku":"131F-REDUCER-074X","price":418.6,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/39700a9a-6969-4a4b-bb2c-f65eb7ad5c26.png?v=1779667444","url":"https:\/\/ontariotelescope.com\/products\/askar-131f-0-74-focal-reducer","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}