{"product_id":"askar-0-75x-reducer-for-91f","title":"Askar 91F 0.75x Reducer","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eReduces focal ratio to a fast f\/5\u003c\/li\u003e\n\u003cli\u003e0.75x reduction factor for wider fields of view\u003c\/li\u003e\n\u003cli\u003eTriplet optical design provides field-flattening correction\u003c\/li\u003e\n\u003cli\u003eStandard 55mm back focus from the M48 thread\u003c\/li\u003e\n\u003cli\u003eLightweight 0.3kg construction\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section-center\"\u003e\n\u003ch2\u003eAskar 91F 0.75x Reducer\u003c\/h2\u003e\n\u003cp\u003eThe Askar 91F 0.75x Reducer transforms its dedicated telescope into a faster, wider imaging system, shortening the native focal length to 455mm and the focal ratio to a rapid f\/5. This triplet reducer is engineered to provide full-frame, field-flattened correction while maintaining a standard 55mm back focus for seamless integration with your existing M48-threaded imaging train.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eFaster f\/5 Imaging: The 0.75x Optical Advantage\u003c\/h3\u003e\n\u003cp\u003eBy decreasing the focal ratio to f\/5, this 0.75x reducer significantly cuts down required exposure times, allowing you to gather more signal on faint targets in less time. The wider field of view is ideal for capturing large-scale celestial objects that would otherwise be too expansive for the telescope's native field, such as the Andromeda Galaxy (M31) or the entire Veil Nebula complex.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eTriplet Design with 55mm Back Focus for Full-Frame Sensors\u003c\/h3\u003e\n\u003cp\u003eThe air-spaced triplet optical design not only reduces the focal length but also acts as a dedicated field flattener, ensuring sharp, point-like stars across a full-frame sensor. It establishes a standard 55mm back focus distance from its M48 male thread, simplifying the connection to DSLRs, mirrorless cameras, and dedicated astronomy cameras with common spacers.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eIntegrated Filter Thread:\u003c\/strong\u003e A built-in M48x0.75 thread allows you to mount 2-inch filters directly into the reducer, placing them securely within the optical path without needing a separate filter drawer.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSecure Connection:\u003c\/strong\u003e The reducer attaches to the Askar 91F focuser via a robust M59*1 thread, ensuring a rigid, tilt-free connection for imaging.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCNC Machining:\u003c\/strong\u003e The entire housing is CNC-machined for precision and durability, and includes threaded metal dust caps for protection when not in use.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eImaging with the Askar 91F: Native vs. f\/5 Reduced\u003c\/h3\u003e\n\u003cp\u003eThis reducer offers a critical choice for astrophotographers. Using the Askar 91F at its native focal length provides higher magnification, perfect for framing smaller galaxies or planetary nebulae where image scale is paramount. Attaching the 0.75x reducer is the superior option for large emission nebulae and star clusters, where its light-gathering speed and wider perspective are essential for capturing the entire object in a single frame.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat does the 91F 0.75x Reducer do for my Askar 91F telescope?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe 91F 0.75x Reducer shortens your telescope's focal ratio to a faster f\/5 and focal length to 455mm. This provides two main benefits: a \u003cstrong\u003ewider field of view\u003c\/strong\u003e to fit larger objects in the frame, and \u003cstrong\u003eshorter exposure times\u003c\/strong\u003e to capture faint details more efficiently.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I connect the Askar 91F 0.75x Reducer to my camera?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe reducer provides a standard \u003cstrong\u003e55mm back focus\u003c\/strong\u003e from the base of its M48 male thread. This is a common standard for most astronomy cameras and DSLRs with the appropriate T-ring. You simply add or remove M48 spacers until the distance from the reducer's flange to your camera sensor is exactly 55mm.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use 2-inch filters with the 91F 0.75x Reducer?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. The reducer has a built-in M48x0.75 female thread on the camera side, allowing you to directly screw in standard 2-inch astronomy filters. This is convenient for using light pollution or narrowband filters without needing a separate filter wheel or drawer.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the Askar 91F 0.75x Reducer also a field flattener?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes, it is. The triplet optical design is engineered to provide field-flattening correction specifically for the Askar 91F telescope. This ensures that stars remain sharp and round across the entire image, even at the edges of a full-frame sensor.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhich targets benefit most from the 91F 0.75x Reducer?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThis reducer is ideal for large deep-sky objects that require a wide field of view. Excellent targets include the \u003cstrong\u003eNorth American Nebula (NGC 7000)\u003c\/strong\u003e, the \u003cstrong\u003eAndromeda Galaxy (M31)\u003c\/strong\u003e, and large star-forming regions like the Heart and Soul Nebulae (IC 1805 and IC 1848).\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhen should I *not* use the 91F 0.75x Reducer with my Askar 91F?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYou should image without the reducer when your target is small and requires maximum image scale. For example, most galaxies like the Whirlpool Galaxy (M51), smaller planetary nebulae like the Ring Nebula (M57), or any planetary imaging would be better suited to the telescope's native, longer focal length.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ctable class=\"DAV-specifications\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eReduction Factor\u003c\/td\u003e\n\u003ctd\u003e0.75x\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eResulting Focal Length\u003c\/td\u003e\n\u003ctd\u003e455mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eResulting Focal Ratio\u003c\/td\u003e\n\u003ctd\u003ef\/5\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOptical Design\u003c\/td\u003e\n\u003ctd\u003eTriplet, Air-Spaced\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBack Focus\u003c\/td\u003e\n\u003ctd\u003e55mm (from M48 thread base)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTelescope Side Thread\u003c\/td\u003e\n\u003ctd\u003eM59*1\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCamera Side Thread\u003c\/td\u003e\n\u003ctd\u003eM48x0.75 (Male)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFilter Thread\u003c\/td\u003e\n\u003ctd\u003eM48x0.75 (Female, for 2\" filters)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eWeight\u003c\/td\u003e\n\u003ctd\u003e0.3kg\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/askar-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eAskar 1-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Askar","offers":[{"title":"Default Title","offer_id":52851336904989,"sku":"ASK-ASKAR91R","price":199.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Askar-91F-0-75x-Reducer-1_234100f2-15d6-4254-a83f-7aaf11c45959.jpg?v=1788401763","url":"https:\/\/davidastro.com\/fr-eu\/products\/askar-0-75x-reducer-for-91f","provider":"David Astro","version":"1.0","type":"link"}