{"product_id":"zwo-m54-extension-16-5mm","title":"ZWO M54 Extension - 16.5mm","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003eOptical Length: 16.5mm\u003c\/li\u003e\n\u003cli\u003eConnection Side 1: M54x0.75 Male Thread\u003c\/li\u003e\n\u003cli\u003eConnection Side 2: M54x0.75 Female Thread\u003c\/li\u003e\n\u003cli\u003eMaterial: Anodized Aluminum\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\u003ePrecision Back Focus for ZWO Full-Frame Systems — The M54 Extension 16.5mm\u003c\/h2\u003e\n\u003cp\u003eThe ZWO M54 Extension 16.5mm tube is a purpose-built spacer designed to solve one of the most critical steps in astrophotography: achieving the standard 55mm back focus distance for full-frame ZWO imaging systems. This is not just a generic spacer. It is the specific component required to bridge the gap between a ZWO 2” Filter Wheel (M54) and a full-frame camera like the ASI6200 or ASI2400, completing the optical train with mechanical rigidity and precise spacing.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-section-container\"\u003e\n\u003cdiv class=\"DAV-section-img\"\u003e\n\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/ZWO-M54-Cameras-55mm-Backfocus.jpg?v=1778870039\" alt=\"Diagram showing the ZWO M54 16.5mm Extension in a 55mm back focus imaging train.\"\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-section-text\"\u003e\n\u003ch3\u003eAchieve the Critical 55mm Back Focus Distance\u003c\/h3\u003e\n\u003cp\u003eMost field flatteners and coma correctors require a sensor distance of exactly 55mm to deliver sharp stars across the frame. The ZWO M54 Extension 16.5mm is a key part of the ZWO system solution. When combined with a ZWO full-frame camera (17.5mm back focus) and a ZWO 21mm M54 spacer, this 16.5mm extension provides the final piece, summing to a perfect 55mm. \u003c\/p\u003e\n\u003cp\u003eThis precision eliminates the need for stacking multiple, less-stable adapters. By using a single, solid spacer, you reduce the potential for optical tilt that can ruin an otherwise perfect image, especially with the demanding tolerances of large, full-frame sensors. It simplifies your setup and provides a reliable, repeatable connection every time you assemble your gear.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-section-container\"\u003e\n\u003cdiv class=\"DAV-section-text\"\u003e\n\u003ch3\u003eSecure M54 Threading for Full-Frame Payloads\u003c\/h3\u003e\n\u003cp\u003eThe ZWO M54 Extension uses M54x0.75 threads on both its male and female ends. This larger diameter provides a more rigid and stable connection than the older M48 standard, which is critical when supporting the weight of a filter wheel and a heavy, cooled full-frame camera. The wider aperture also helps prevent vignetting on large sensors, ensuring the light cone from the corrector reaches the entire sensor without being clipped.\u003c\/p\u003e\n\u003cp\u003eThe male M54 thread connects directly to the filter wheel or camera tilt adapter, while the female side connects to your corrector or off-axis guider. This creates a seamless, all-ZWO train where every component is designed to work together mechanically, preserving the integrity of your optical alignment throughout a long imaging session.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-section-img\"\u003e\n\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/ZWOM54-M54-16.5.jpg?v=1768507530\" alt=\"Close-up of the M54 threads on a ZWO adapter.\"\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eInternal Light Baffling for Maximum Contrast\u003c\/h3\u003e\n\u003cp\u003eThe interior of the extension tube is machined with a matte-black, anodized finish. This surface treatment is designed to absorb stray light that might otherwise reflect off internal surfaces and reduce image contrast. While a small component, its contribution to a clean final image is significant, preventing faint, off-axis light from scattering and washing out the delicate details in nebulae and galaxies.\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\u003eA Note on System Compatibility\u003c\/h3\u003e\n\u003cp\u003eThis extension is engineered as part of the ZWO ecosystem for achieving 55mm back focus. Its 16.5mm length is highly specific to the optical path lengths of ZWO's own cameras and filter wheels. If you are using components from other manufacturers, you must measure your required spacing carefully, as this part may not be the correct length for a mixed-brand imaging train. It represents a trade-off: perfect integration within the ZWO system in exchange for less universal applicability.\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\u003eLightweight and Durable Construction\u003c\/h3\u003e\n\u003cp\u003eMachined from aircraft-grade aluminum, the adapter adds minimal weight to the imaging train. This helps reduce the overall load on your focuser and mount, which is always a consideration with heavy full-frame systems. \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\"\u003eWhich ZWO cameras need the 16.5mm M54 extension for 55mm back focus?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThis spacer is designed for ZWO full-frame cameras like the ASI6200, ASI2400, and ASI2600 when used with the ZWO 2\" EFW (20mm path length). The camera's 17.5mm sensor depth plus the 20mm EFW and this 16.5mm spacer totals 54mm, achieving the 55mm standard when threaded onto a corrector.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs this the right spacer if I don't use a filter wheel?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo. If you connect a ZWO full-frame camera (17.5mm back focus) directly to your corrector, you will need a different combination of spacers to reach 55mm, typically a 20mm and a 16.5mm extension combined (or a variable spacer). This 16.5mm piece is specifically for setups that include the 20mm path length of a filter wheel.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWill this M54 extension cause vignetting?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo, the M54 diameter is large enough to pass the full light cone from a 2-inch corrector to a full-frame sensor without clipping the edges. It is the preferred standard over M48 for full-frame imaging to prevent vignetting.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eCan I use this adapter with non-ZWO cameras or filter wheels?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYou can, but only if the total optical path length of your components requires exactly 16.5mm of spacing. You must calculate your back focus needs precisely, as this adapter is not a universal solution and is optimized for the ZWO ecosystem.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eDoes the ZWO M54 Extension 16.5mm add any tilt?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eAs a single, solid-machined component, it is designed to minimize tilt. Using one 16.5mm extension is mechanically more stable and less prone to tilt than stacking multiple smaller spacers to achieve the same distance.\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\u003eProduct Code\u003c\/td\u003e\n\u003ctd\u003eM54-M54-16.5L\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOptical Length\u003c\/td\u003e\n\u003ctd\u003e16.5mm\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\u003eMatte Black Anodized\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\n\u003cimg class=\"DAV-img-box\" alt=\"ZWO M54 Extension - 16.5mm\" src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/ZWOM54-M54-16.5.jpg?v=1768507530\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eZWO M54 to M54 Extension Tube (16.5mm)\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\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":50843662188829,"sku":"ZWO-M54-M54-16.5","price":18.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/ZWOM54-M54-16.5.jpg?v=1768507530","url":"https:\/\/davidastro.com\/fr-us\/products\/zwo-m54-extension-16-5mm","provider":"David Astro","version":"1.0","type":"link"}