{"product_id":"zwo-m54-extension-21mm","title":"ZWO M54 Extension - 21mm","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eAdds precisely 21mm of optical path length\u003c\/li\u003e\n\u003cli\u003eM54x0.75 male and female threads for secure connections\u003c\/li\u003e\n\u003cli\u003ePrevents vignetting with full-frame sensors\u003c\/li\u003e\n\u003cli\u003eMachined from black anodized aluminum to reduce reflections\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\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\u003eZWO M54 Extension - 21mm\u003c\/h2\u003e\n      \u003cp\u003eThe ZWO M54 Extension Tube adds exactly 21mm of optical path length, providing a critical spacing solution for achieving perfect 55mm back focus with full-frame cameras. Machined from a single piece of black anodized aluminum, this 21mm extender ensures a rigid, tilt-free connection in your M54 imaging train, preventing flexure that can compromise edge-of-field star shapes.\u003c\/p\u003e\n    \u003c\/div\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"DAV-bg-light\"\u003e\n    \u003cdiv class=\"DAV-section\"\u003e\n      \u003ch3\u003eAchieve 55mm Back Focus with Full-Frame Cameras\u003c\/h3\u003e\n      \u003cp\u003eMost field flatteners and coma correctors require a precise sensor distance of 55mm to deliver sharp stars across the frame. This 21mm extension is a key component in the ZWO ecosystem for reaching that standard. When combined with a ZWO full-frame camera (which typically has 17.5mm of back focus) and a ZWO 16.5mm extension, this 21mm piece completes the 55mm requirement without stacking multiple, less stable adapters.\u003c\/p\u003e\n    \u003c\/div\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"DAV-bg-light\"\u003e\n    \u003cdiv class=\"DAV-section\"\u003e\n      \u003ch3\u003eSecure M54 Threading for Large-Sensor Payloads\u003c\/h3\u003e\n      \u003cp\u003eThe ZWO 21mm Extension uses M54x0.75 threads on both its male and female ends. This large-diameter connection provides a more rigid and stable optical train than the older M48 standard, which is critical when supporting the weight of a filter wheel and a heavy, cooled camera. The wider M54 aperture also prevents vignetting on large sensors, ensuring the corrected light cone from your optics reaches the entire sensor without being clipped at the edges.\u003c\/p\u003e\n      \u003cul\u003e\n        \u003cli\u003e\n\u003cstrong\u003eSolid, Single-Piece Construction:\u003c\/strong\u003e Eliminates the potential for optical tilt that can occur when stacking multiple shorter, thinner adapters to achieve the same distance.\u003c\/li\u003e\n        \u003cli\u003e\n\u003cstrong\u003eInternal Matte-Black Finish:\u003c\/strong\u003e The interior of the extension tube is anodized and baffled to absorb stray light, preventing internal reflections from reducing image contrast.\u003c\/li\u003e\n        \u003cli\u003e\n\u003cstrong\u003eSeamless Integration:\u003c\/strong\u003e Designed to thread directly and securely onto other ZWO M54 components like filter wheels, off-axis guiders, and camera tilt adapters for a reliable, repeatable setup.\u003c\/li\u003e\n      \u003c\/ul\u003e\n    \u003c\/div\u003e\n  \u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eWhy do I need the ZWO M54 21mm Extension?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eYou need this 21mm extension to achieve the standard \u003cstrong\u003e55mm back focus\u003c\/strong\u003e required by most flatteners and correctors, especially when using a ZWO full-frame camera. It provides a precise, solid spacer that prevents optical tilt and ensures sharp stars across your entire image.\u003c\/p\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eHow does this 21mm extension fit into a standard ZWO full-frame imaging train?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eA typical ZWO full-frame setup to achieve 55mm back focus consists of the camera's native 17.5mm back focus, a 16.5mm M54 extension, and this 21mm M54 extension. The total (17.5mm + 16.5mm + 21mm) equals 55mm, the ideal distance for most optical correctors.\u003c\/p\u003e\n  \u003c\/div\u003e\n    \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eWill the ZWO M54 21mm extension cause vignetting with my full-frame camera?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eNo. The M54 thread standard has a larger diameter than M48, specifically to accommodate the light cone required by full-frame (36mm x 24mm) sensors. This 21mm extension maintains that clear aperture, preventing the clipping of light that can cause vignetting.\u003c\/p\u003e\n  \u003c\/div\u003e\n    \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eIs the ZWO M54 21mm extension made of plastic or metal?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eThe ZWO M54 21mm Extension is precision CNC-machined from a single piece of \u003cstrong\u003eaircraft-grade aluminum\u003c\/strong\u003e. It is then black anodized to increase durability and minimize internal reflections.\u003c\/p\u003e\n  \u003c\/div\u003e\n    \u003cdiv class=\"DAV-accordion\"\u003e\n    \u003ch3 class=\"DAV-accordion-Q\"\u003eCan I thread a 2-inch filter into this ZWO 21mm extension?\u003c\/h3\u003e\n  \u003c\/div\u003e\n  \u003cdiv class=\"DAV-accordion-A\"\u003e\n    \u003cp\u003eThis specific M54-to-M54 extension does not have filter threads. ZWO produces other adapters, often with an M54-to-M48 conversion, that are designed to accept 2-inch (M48x0.75) filters. This piece is designed purely for adding 21mm of spacing while maintaining a robust M54 connection.\u003c\/p\u003e\n  \u003c\/div\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n  \u003ctable class=\"DAV-specifications\"\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n\u003ctd\u003eOptical Length\u003c\/td\u003e\n\u003ctd\u003e21mm\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eMale Thread\u003c\/td\u003e\n\u003ctd\u003eM54x0.75\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eFemale Thread\u003c\/td\u003e\n\u003ctd\u003eM54x0.75\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eMaterial\u003c\/td\u003e\n\u003ctd\u003eAluminum\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eFinish\u003c\/td\u003e\n\u003ctd\u003eBlack Anodized\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n  \u003cul class=\"DAV-grid\"\u003e\n    \u003cli class=\"DAV-grid-item\"\u003e\n      \u003cdiv\u003e\n        \u003cp class=\"DAV-item-title\"\u003eZWO 21mm M54 to M54 Extension Tube\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\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/zwo-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eZWO 2-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":50843678540061,"sku":"ZWO-M54-M54-21","price":18.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/ZWOM54-M54-21.jpg?v=1768507587","url":"https:\/\/davidastro.com\/fr-us\/products\/zwo-m54-extension-21mm","provider":"David Astro","version":"1.0","type":"link"}