{"product_id":"askar-131f","title":"Askar 131F Flat-Field APO Refractor","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003e131mm Aperture\u003c\/li\u003e\n\u003cli\u003ef\/7.5 Focal Ratio\u003c\/li\u003e\n\u003cli\u003eQuadruplet Air-Spaced APO Optical Design\u003c\/li\u003e\n\u003cli\u003eIncludes one ED Glass Element\u003c\/li\u003e\n\u003cli\u003e44mm Full-Frame Image Circle\u003c\/li\u003e\n\u003cli\u003eIntegrated Field Flattener\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\u003eDownloads\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 131F Flat-Field APO Refractor\u003c\/h2\u003e\n\u003cp\u003eThe Askar 131F Flat-Field refractor combines a 131mm aperture with a 983mm focal length in a native f\/7.5 optical system designed for serious astrophotography. Its quadruplet air-spaced APO objective, which includes one ED glass element, delivers a flat, color-corrected 44mm image circle without the need for an external flattener. With a gross weight of 9.4kg including rings and dovetail plate, this telescope integrates optical correction directly into the design, simplifying your 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\u003e131mm f\/7.5 Quadruplet APO: Color-Free, Flat-Field Imaging\u003c\/h3\u003e\n\u003cp\u003eThe core of the 131F is its advanced quadruplet objective lens. This design uses four air-spaced elements, including one ED (Extra-low Dispersion) glass element, to aggressively suppress chromatic aberration. Unlike standard doublets or triplets, this configuration corrects for color fringing and field curvature across the 44mm image circle, producing pinpoint stars on a dark background without requiring additional corrective optics.\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\u003e44mm Image Circle: Full-Frame Ready, No Flattener Required\u003c\/h3\u003e\n\u003cp\u003eThe defining feature of the Askar 131F is its \"self-flattening\" optical system. This eliminates the most common point of failure and complexity in imaging setups: calculating and achieving the correct back focus for a separate flattener. The 44mm image circle fully illuminates full-frame sensors, and with the included M48 and M54 adapters, you can directly attach your camera, focus, and begin imaging immediately.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eNo Additional Purchases:\u003c\/strong\u003e The integrated flattener means you save the cost and weight of a separate optical corrector.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eZero Back Focus Calculation:\u003c\/strong\u003e Simply attach your camera via the appropriate adapter and use the 30mm of focuser travel to achieve a sharp, flat field.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFilter Integration:\u003c\/strong\u003e The M54 to M48 adapter includes standard M48x0.75 filter threads, allowing you to easily add 2-inch filters to your imaging train.\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\u003e9.4kg Gross Weight: Robust Mechanics and 30mm Focuser Travel\u003c\/h3\u003e\n\u003cp\u003eEngineered for stability, the Askar 131F weighs 9.4kg when fully assembled with its included tube rings, handle, and 300mm Losmandy-style dovetail plate. The OTA itself has a net weight of 7.9kg and a variable length from 878mm to 1026mm depending on the adapter used and dew shield position. High-quality CNC machining ensures precise alignment, while the robust focuser provides 30mm of travel for fine-tuning focus with a variety of cameras.\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\u003eAskar 131F vs. Triplet APOs: The Integrated Flattener Advantage\u003c\/h3\u003e\n\u003cp\u003eWhile many high-end refractors use a triplet objective, they almost always require an additional field flattener or reducer\/flattener for astrophotography. This introduces complexity, potential tilt, and critical back focus spacing requirements that must be met with precision spacers.\u003c\/p\u003e\n\u003cp\u003eThe Askar 131F's quadruplet design incorporates that correction into the main optical tube. This provides a significant advantage: you get a guaranteed flat field optimized for the telescope's native 983mm focal length without any extra components or calculations. While a triplet with a separate flattener might offer more flexibility with reducers, the 131F delivers perfect out-of-the-box performance for full-frame imaging at its designed focal ratio.\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 is the main advantage of the Askar 131F's self-flattening design?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe primary advantage is simplicity and reliability. You do not need to purchase a separate field flattener or calculate the precise 55mm (or other) back focus distance. The Askar 131F's quadruplet optics deliver a flat 44mm image circle right out of the box, eliminating a major source of frustration in astrophotography.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat size camera sensors will the Askar 131F's 44mm image circle cover?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe 44mm image circle is large enough to fully illuminate \u003cstrong\u003efull-frame sensors\u003c\/strong\u003e (typically 43.3mm diagonal) found in cameras like the ZWO ASI6200 or Sony A7 series. It will also easily cover smaller APS-C and Micro Four Thirds sensors with no vignetting.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the Askar 131F perform on large deep-sky objects like the Andromeda Galaxy (M31)?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe 983mm focal length provides excellent image scale for resolving detail in medium-to-large targets. When paired with a full-frame camera, the Askar 131F can frame the entirety of the Andromeda Galaxy (M31) or the North American Nebula (NGC 7000), capturing these expansive objects with sharp stars from edge to edge.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat kind of mount is required for the Askar 131F's 9.4kg weight?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eFor imaging, a mount with a payload capacity of at least 40-50 lbs (18-22 kg) is recommended. The total weight of the Askar 131F is 9.4kg (about 20.7 lbs), and you must also account for your camera, guide scope, and other accessories. A mount like the Sky-Watcher EQ6-R Pro or Celestron CGX would be a suitable choice.\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 Askar 131F?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. The included photographic adapter set contains an M54-to-M48 adapter that is threaded to accept standard \u003cstrong\u003eM48x0.75 (2-inch) filters\u003c\/strong\u003e. This allows you to easily incorporate narrowband or light pollution filters into your imaging train.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eDoes the Askar 131F need a separate dew heater?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eLike all refractors, the objective lens is exposed to the night air and can collect dew. While the extendable dew shield (which increases the total length to 963mm or 1026mm) helps, using a dedicated dew heater strip around the objective is highly recommended for all-night imaging sessions, especially in humid conditions.\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\u003eAperture\u003c\/td\u003e\n\u003ctd\u003e131mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Length\u003c\/td\u003e\n\u003ctd\u003e983mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Ratio\u003c\/td\u003e\n\u003ctd\u003ef\/7.5\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eObjective Lens\u003c\/td\u003e\n\u003ctd\u003eQuadruplet air-spaced APO (including one ED glass)\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 Travel\u003c\/td\u003e\n\u003ctd\u003e30mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eNet Weight (OTA only)\u003c\/td\u003e\n\u003ctd\u003e7.9kg\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eGross Weight (with rings \u0026amp; plate)\u003c\/td\u003e\n\u003ctd\u003e9.4kg\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTotal Length (Contracted)\u003c\/td\u003e\n\u003ctd\u003e878mm (with 1.25\" adapter) \/ 941mm (with photo adapter)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTotal Length (Stretched)\u003c\/td\u003e\n\u003ctd\u003e963mm (with 1.25\" adapter) \/ 1026mm (with photo adapter)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eRear-End Adapters\u003c\/td\u003e\n\u003ctd\u003eM78×1 to M54×0.75, M54×0.75 to M54×0.75, M54×0.75 to M48×0.75\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFilter Thread\u003c\/td\u003e\n\u003ctd\u003eM48×0.75 (on M54-M48 adapter)\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\u003cli class=\"DAV-grid-item\"\u003e\u003ca href=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Askar_131F_Flat-Field_Manual.pdf\" target=\"_blank\"\u003e\u003csvg class=\"DAV-img-box\" viewbox=\"0 0 512 512\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"\u003e\u003cpath d=\"M0 64C0 28.7 28.7 0 64 0L224 0l0 128c0 17.7 14.3 32 32 32l128 0 0 144-208 0c-35.3 0-64 28.7-64 64l0 144-48 0c-35.3 0-64-28.7-64-64L0 64zm384 64l-128 0L256 0 384 128zM176 352l32 0c30.9 0 56 25.1 56 56s-25.1 56-56 56l-16 0 0 32c0 8.8-7.2 16-16 16s-16-7.2-16-16l0-48 0-80c0-8.8 7.2-16 16-16zm32 80c13.3 0 24-10.7 24-24s-10.7-24-24-24l-16 0 0 48 16 0zm96-80l32 0c26.5 0 48 21.5 48 48l0 64c0 26.5-21.5 48-48 48l-32 0c-8.8 0-16-7.2-16-16l0-128c0-8.8 7.2-16 16-16zm32 128c8.8 0 16-7.2 16-16l0-64c0-8.8-7.2-16-16-16l-16 0 0 96 16 0zm80-112c0-8.8 7.2-16 16-16l48 0c8.8 0 16 7.2 16 16s-7.2 16-16 16l-32 0 0 32 32 0c8.8 0 16 7.2 16 16s-7.2 16-16 16l-32 0 0 48c0 8.8-7.2 16-16 16s-16-7.2-16-16l0-64 0-64z\" fill=\"#0047a7\"\u003e\u003c\/path\u003e\u003c\/svg\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eDownload Manual\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/a\u003e\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003e131F OTA\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eTube Rings\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1 Pair\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eHandle\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003e300mm Losmandy Dovetail Plate\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003ePhotographic Adapter Set\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\u003ca href=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Askar_131F_Flat-Field_Manual.pdf\" target=\"_blank\"\u003e\u003csvg class=\"DAV-img-box\" viewbox=\"0 0 512 512\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"\u003e\u003cpath d=\"M0 64C0 28.7 28.7 0 64 0L224 0l0 128c0 17.7 14.3 32 32 32l128 0 0 144-208 0c-35.3 0-64 28.7-64 64l0 144-48 0c-35.3 0-64-28.7-64-64L0 64zm384 64l-128 0L256 0 384 128zM176 352l32 0c30.9 0 56 25.1 56 56s-25.1 56-56 56l-16 0 0 32c0 8.8-7.2 16-16 16s-16-7.2-16-16l0-48 0-80c0-8.8 7.2-16 16-16zm32 80c13.3 0 24-10.7 24-24s-10.7-24-24-24l-16 0 0 48 16 0zm96-80l32 0c26.5 0 48 21.5 48 48l0 64c0 26.5-21.5 48-48 48l-32 0c-8.8 0-16-7.2-16-16l0-128c0-8.8 7.2-16 16-16zm32 128c8.8 0 16-7.2 16-16l0-64c0-8.8-7.2-16-16-16l-16 0 0 96 16 0zm80-112c0-8.8 7.2-16 16-16l48 0c8.8 0 16 7.2 16 16s-7.2 16-16 16l-32 0 0 32 32 0c8.8 0 16 7.2 16 16s-7.2 16-16 16l-32 0 0 48c0 8.8-7.2 16-16 16s-16-7.2-16-16l0-64 0-64z\" fill=\"#0047a7\"\u003e\u003c\/path\u003e\u003c\/svg\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eDownload Manual\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/a\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\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":52851331236125,"sku":"ASK-ASAPO131F","price":1999.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Askar-131F-Flat-Field-1_466f55e4-2cbf-413b-ab14-1372829037b5.jpg?v=1788401697","url":"https:\/\/davidastro.com\/en-int\/products\/askar-131f","provider":"David Astro","version":"1.0","type":"link"}