{"product_id":"askar-backfocus-adjuster","title":"Askar M54\/M48 Backfocus Adjuster","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eProvides ±2mm of fine backfocus adjustment\u003c\/li\u003e\n\u003cli\u003eTotal optical length adjustable from 16mm to 20mm\u003c\/li\u003e\n\u003cli\u003eHigh-precision 0.05mm increments\u003c\/li\u003e\n\u003cli\u003eAvailable with M54 or M48 male camera-side threads\u003c\/li\u003e\n\u003cli\u003eCNC machined with laser-etched reference scale\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 M54\/M48 Backfocus Adjuster\u003c\/h2\u003e\n\u003cp\u003eThe Askar M54\/M48 Backfocus Adjuster provides a critical ±2mm of fine-tuning for your imaging train, allowing you to dial in spacing between 16mm and 20mm. Each increment on the laser-etched scale corresponds to a 0.05mm adjustment, ensuring you can achieve perfect star shapes across the entire frame. Available in two versions with either M54 or M48 male threads, this CNC-machined adjuster is the solution for eliminating stubborn backfocus errors.\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\u003eEliminate Spacing Errors with 0.05mm Precision Control\u003c\/h3\u003e\n\u003cp\u003ePerfect backfocus is non-negotiable for achieving sharp stars corner-to-corner, but tiny errors from filter thicknesses or manufacturing tolerances can compromise your results. This adjuster provides a total of 4mm of travel, adjustable in 0.05mm increments, allowing you to methodically find the exact spacing your flattener or reducer requires. The CNC-machined body includes a clear, printed scale for repeatable settings and two locking screw holes to fix the position once you've achieved perfect focus.\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\u003eAn M54 Input with 2 Output Options: M54 or M48\u003c\/h3\u003e\n\u003cp\u003eBoth versions of the Askar Backfocus Adjuster feature a female M54x0.75 thread on the telescope side, making them compatible with a wide range of modern correctors. The choice depends on your camera-side connection. Select the M54 male thread version for full-frame cameras and native M54 accessories, or the M48 male thread version to connect to the common 2-inch filter thread standard found on most dedicated astronomy cameras and filter wheels.\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\"\u003eHow do I use the Askar Backfocus Adjuster to find the correct spacing?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eStart with your theoretically correct backfocus distance, accounting for the adjuster's minimum 16mm length. Take a test image and examine the star shapes in the corners. Rotate the adjuster in small, \u003cstrong\u003e0.05mm increments\u003c\/strong\u003e and take new test images until the corner stars are perfectly round. Once set, use the two fixing screws to lock the position.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhich version of the Askar Backfocus Adjuster do I need?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eBoth versions accept an \u003cstrong\u003eM54x0.75 female\u003c\/strong\u003e thread from your telescope or corrector. The choice depends on the next item in your imaging train:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eM54 Version:\u003c\/strong\u003e Choose this if your camera, OAG, or filter wheel has female M54 threads.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eM48 Version:\u003c\/strong\u003e Choose this if your camera or filter wheel uses the standard male M48 (2-inch filter) thread.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eMy flattener needs 55mm of backfocus, but my train is 53.5mm. Can the Askar Adjuster fix this?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo, the Askar Backfocus Adjuster cannot fill a gap that large on its own. Its adjustment range is 16mm to 20mm. You would first need to add extension tubes to get close to the required 55mm, and then use the adjuster to fine-tune the final millimeter or two with its ±2mm range.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I lock the position on the Askar Backfocus Adjuster?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe adjuster features two holes for fixing screws. Once you have rotated the barrel to the desired backfocus distance, you can insert and tighten small screws (not included) into these holes to prevent any further rotation, securing your setting for the rest of your imaging session.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill the Askar M54 Adjuster help with elongated stars on my full-frame camera when imaging M31?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes, most likely. Elongated stars in the corners of a full-frame sensor, especially on a large target like the Andromeda Galaxy (M31), are a classic sign of incorrect backfocus. The Askar M54 adjuster is ideal for this, allowing you to make tiny, precise changes to the spacing until those corner stars become sharp and round.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat is the minimum optical path length of the Askar Backfocus Adjuster?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe minimum optical path length added by the adjuster is \u003cstrong\u003e16mm\u003c\/strong\u003e when it is fully retracted. It can be extended up to a maximum of \u003cstrong\u003e20mm\u003c\/strong\u003e.\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\u003eFront Thread (Telescope Interface)\u003c\/td\u003e\n\u003ctd\u003eM54x0.75 Female\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eRear Thread (Camera Interface)\u003c\/td\u003e\n\u003ctd\u003eM54x0.75 Male or M48x0.75 Male (model dependent)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eNominal Thickness\u003c\/td\u003e\n\u003ctd\u003e18mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eAdjustment Range\u003c\/td\u003e\n\u003ctd\u003e±2mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTotal Optical Path\u003c\/td\u003e\n\u003ctd\u003e16mm - 20mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eAdjustment Precision\u003c\/td\u003e\n\u003ctd\u003e0.05mm per increment\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eConstruction\u003c\/td\u003e\n\u003ctd\u003eCNC Machined Aluminum\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eLocking Mechanism\u003c\/td\u003e\n\u003ctd\u003e2x Fixing Screw Holes\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_M54-M48_Backfocus_Adjuster_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\"\u003eAskar M54\/M48 Backfocus Adjuster\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_M54-M48_Backfocus_Adjuster_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":52851345326365,"sku":"ASK-ASKARBA48","price":199.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Askar-M54-M48-Backfocus-Adjuster-1_fbaf3b22-71f1-4061-807a-daaef6d9090f.jpg?v=1788401884","url":"https:\/\/davidastro.com\/products\/askar-backfocus-adjuster","provider":"David Astro","version":"1.0","type":"link"}