{"product_id":"askar-91f-flat-field-refractor","title":"Askar 91F 91mm f\/6.7 Flat-Field Refractor Telescope","description":"\u003ch2\u003eAskar 91F 91mm f\/6.7 Quadruplet Flat-Field Refractor Telescope\u003c\/h2\u003e\n\u003cp\u003eThe \u003cstrong\u003eAskar 91F\u003c\/strong\u003e is a compact 91mm flat-field refractor designed to make high-quality astrophotography straightforward. Its \u003cstrong\u003e609mm focal length and f\/6.7 focal ratio\u003c\/strong\u003e provide a versatile field of view for imaging nebulae, galaxies, star clusters, and other deep-sky targets.\u003c\/p\u003e\n\u003cp\u003eAt the heart of the 91F is a \u003cstrong\u003equadruplet air-spaced APO optical system with one ED glass element\u003c\/strong\u003e. Unlike a conventional refractor that requires a separate field flattener, the 91F incorporates its field correction into the telescope itself. The result is a \u003cstrong\u003e44mm image circle suitable for full-frame cameras\u003c\/strong\u003e without the need to purchase an additional flattener or precisely configure a traditional 55mm backfocus spacing. Attach your imaging train, reach focus, and you're ready to image.\u003c\/p\u003e\n\u003ch3\u003eBuilt for Astrophotography\u003c\/h3\u003e\n\u003cp\u003eThe 91F pairs its flat-field optical system with a substantial \u003cstrong\u003e3\" rack-and-pinion focuser\u003c\/strong\u003e featuring dual-speed adjustment and \u003cstrong\u003e1:10 fine focusing\u003c\/strong\u003e. A built-in \u003cstrong\u003e360° graduated camera rotator\u003c\/strong\u003e makes framing your target easy without disturbing the rest of the imaging train.\u003c\/p\u003e\n\u003cp\u003eThe telescope provides both \u003cstrong\u003eM54 and M48 threaded imaging connections\u003c\/strong\u003e, with an M48 filter thread available for standard 2\" filters.\u003c\/p\u003e\n\u003ch3\u003eCompact, Versatile Design\u003c\/h3\u003e\n\u003cp\u003eAt approximately \u003cstrong\u003e8.6 lb (3.92 kg) for the OTA\u003c\/strong\u003e, the 91F offers enough aperture for serious imaging while remaining manageable for portable astrophotography setups. A retractable dew shield keeps the telescope compact for transport, while the included tube rings, carrying handle, and \u003cstrong\u003e230mm Vixen-style dovetail plate\u003c\/strong\u003e make it ready to mount.\u003c\/p\u003e\n\u003cp\u003eThe 91F isn't limited to imaging. Included \u003cstrong\u003e1.25\" and 2\" visual connections\u003c\/strong\u003e allow it to serve as a capable visual refractor as well.\u003cbr\u003e\u003cbr\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0327\/2569\/6648\/files\/ASKAR-91F-FEATURES.jpg?v=1787782958\" alt=\"\"\u003e\u003cbr\u003e\u003c\/p\u003e\n\u003ch3\u003eKey Features\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003e91mm aperture\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003e609mm focal length\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003ef\/6.7 focal ratio\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003eQuadruplet air-spaced APO optical design\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003eOne ED glass element\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003eIntegrated flat-field correction — \u003cstrong\u003eno separate field flattener required\u003c\/strong\u003e\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003e44mm image circle for full-frame astrophotography\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003e3\" dual-speed rack-and-pinion focuser\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003e1:10 fine-focus adjustment\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003eBuilt-in 360° graduated camera rotator\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003eM54 and M48 imaging connections\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003e1.25\" and 2\" visual compatibility\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003eRetractable dew shield\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003e230mm Vixen-style dovetail plate\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003eOTA weight: 3.92 kg \/ approximately 8.6 lb\u003c\/p\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eWhat's Included\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003eAskar 91F optical tube\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003ePair of tube rings\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003eCarrying\/accessory handle\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003e230mm Vixen-style dovetail plate\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003ePhotographic adapter set\u003c\/p\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cp\u003e1.25\" \/ 2\" visual adapter\u003c\/p\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eSpecifications\u003c\/h3\u003e\n\u003ctable\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eSpecification\u003c\/th\u003e\n\u003cth\u003eAskar 91F\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eAperture\u003c\/td\u003e\n\u003ctd\u003e91mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Length\u003c\/td\u003e\n\u003ctd\u003e609mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Ratio\u003c\/td\u003e\n\u003ctd\u003ef\/6.7\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOptical Design\u003c\/td\u003e\n\u003ctd\u003eQuadruplet air-spaced APO\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eED Glass\u003c\/td\u003e\n\u003ctd\u003e1 element\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eImage Circle\u003c\/td\u003e\n\u003ctd\u003e44mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocuser\u003c\/td\u003e\n\u003ctd\u003e3\" dual-speed rack-and-pinion\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFine Focus\u003c\/td\u003e\n\u003ctd\u003e1:10\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocuser Travel\u003c\/td\u003e\n\u003ctd\u003e30mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCamera Rotator\u003c\/td\u003e\n\u003ctd\u003e360° graduated\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eImaging Threads\u003c\/td\u003e\n\u003ctd\u003eM54x0.75 \/ M48x0.75\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOTA Weight\u003c\/td\u003e\n\u003ctd\u003e3.92 kg \/ 8.6 lb\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eWeight with Rings \u0026amp; Dovetail\u003c\/td\u003e\n\u003ctd\u003e4.52 kg \/ 10 lb\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eDovetail\u003c\/td\u003e\n\u003ctd\u003e230mm Vixen-style\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c\/p\u003e","brand":"Askar","offers":[{"title":"Default Title","offer_id":50241852637441,"sku":"ASKAR-91F","price":999.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0327\/2569\/6648\/files\/4a0aa511-087e-46a0-897a-b099e77a876e_png.webp?v=1787782232","url":"https:\/\/starizona.com\/products\/askar-91f-flat-field-refractor","provider":"Starizona","version":"1.0","type":"link"}