{"product_id":"takahashi-rd-qb-0-73x-new-reducer-for-baby-q","title":"Takahashi RD-QB 0.73x Reducer for FSQ-85EDX (\"Baby-Q\")","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe RD-QB 0.73x is the current-generation reducer for the FSQ-85EDX, Takahashi's BabyQ Petzval astrograph. Built with four elements in two groups using a newer, highly refractive low-dispersion ED glass, it brings the native 450mm f\/5.3 down to 330mm f\/3.9 while holding a 44mm image circle that covers full-frame sensors.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThis is a good match if you own the FSQ-85EDX and want the widest, fastest field it can deliver — large nebula complexes, Milky Way fields, and wide star clusters on a full-frame sensor.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e0.73x reduction:\u003c\/strong\u003e 450mm f\/5.3 becomes 330mm f\/3.9 on the FSQ-85EDX.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e44mm image circle:\u003c\/strong\u003e covers full-frame digital sensors with the corrected field.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNew ED glass formula:\u003c\/strong\u003e four elements in two groups, an updated design over the earlier QE0.73x reducer with improved field curvature performance.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eM72 x 1 input, M56 x 0.75 output\u003c\/strong\u003e threads, with an internal 58mm filter thread, in a compact 78 x 63mm, 520 g housing.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eOptical \/ Mechanical Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe FSQ-85EDX's four-element Petzval design is already corrected for a wide native field; the RD-QB 0.73x uses the newer low-dispersion ED formula to speed that field up to f\/3.9 while holding the 44mm image circle needed for full-frame coverage. Takahashi positions it as the direct successor to the earlier QE0.73x reducer, with better field curvature control at the same reduction factor.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eWide-field, full-frame deep-sky imaging on the FSQ-85EDX — large nebula complexes, star clusters, and Milky Way fields where a fast, wide, flat field matters more than reach.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eTakahashi publishes this reducer for the FSQ-85EDX.\u003c\/p\u003e\u003ctable\u003e\n\u003ctr\u003e\n\u003cth\u003eTelescope\u003c\/th\u003e\n\u003cth\u003eNative\u003c\/th\u003e\n\u003cth\u003eWith RD QB0.73x\u003c\/th\u003e\n\u003cth\u003eImage circle\u003c\/th\u003e\n\u003cth\u003eBack focus\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFSQ-85EDX\u003c\/td\u003e\n\u003ctd\u003e450mm f\/5.3\u003c\/td\u003e\n\u003ctd\u003e330mm f\/3.9\u003c\/td\u003e\n\u003ctd\u003eΦ44mm\u003c\/td\u003e\n\u003ctd\u003e72.2mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/table\u003e\u003cp\u003eAn internal 58mm filter thread accepts common filter sizes without a separate holder. For spacing this reducer against your camera and filter wheel, see the \u003ca href=\"\/pages\/takahashi-back-focus-guide\"\u003eTakahashi Back Focus Guide\u003c\/a\u003e.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eGood to Know Before You Order\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003e\u003cstrong\u003eSupersedes the earlier QE0.73x reducer:\u003c\/strong\u003e if you are matching this against an older FSQ-85EDX system chart that references the QE0.73x, the resulting focal length and ratio are the same but the internal glass and field curvature performance differ.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eBuilt for imaging, not eyepiece use:\u003c\/strong\u003e the reduced, flattened field has no benefit for visual observing.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eFrequently Asked Questions\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003e\u003cstrong\u003eIs it difficult to set up?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eNo — it threads onto the FSQ-85EDX's M72 x 1 drawtube and presents an M56 x 0.75 output with a fixed 72.2mm back focus.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is it best used for?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eWide-field, full-frame deep-sky imaging on the FSQ-85EDX.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it accept filters?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eYes — a 58mm internal filter thread is built into the unit.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs this the same as the older QE0.73x reducer?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eIt reduces to the same 330mm f\/3.9, but uses a newer ED glass formula with better field curvature control — send us your current setup if you are upgrading and we will confirm compatibility.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe RD-QB 0.73x brings the FSQ-85EDX to a wide, fast 330mm f\/3.9 with a full-frame-covering 44mm image circle and a fixed 72.2mm back focus, at 520 g.\u003c\/p\u003e","brand":"Takahashi","offers":[{"title":"Default Title","offer_id":54047127928943,"sku":"TAK-TKA37580","price":972.4,"currency_code":"CAD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/tka37580-1.jpg?v=1786914575","url":"https:\/\/ontariotelescope.com\/products\/takahashi-rd-qb-0-73x-new-reducer-for-baby-q","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}