{"product_id":"zwo-m54-m48-21-adapter","title":"ZWO M54-M48-21 Adapter","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThe \u003cstrong\u003eZWO M54-M48-21 Adapter\u003c\/strong\u003e is a \u003cstrong\u003e21 mm\u003c\/strong\u003e extender carrying an \u003cstrong\u003eM54 male thread\u003c\/strong\u003e on one end and an \u003cstrong\u003eM48 female thread\u003c\/strong\u003e on the other. Machined from black anodized aluminium, it converts the M54 rear thread found on ZWO's larger cooled cameras to the M48 (2\") filter standard while contributing a known, fixed 21 mm to your imaging train.\u003c\/p\u003e\n\u003cp\u003eIts purpose is arithmetic. Most ZWO cooled cameras are built around a \u003cstrong\u003e55 mm backfocus\u003c\/strong\u003e target, and this adapter exists to fill a 21 mm gap in that sum exactly.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThis is a good match if you run a \u003cstrong\u003eZWO cooled camera with an M54 rear thread\u003c\/strong\u003e and need to reach 55 mm backfocus without stacking a pile of thin spacers, each with its own tolerance.\u003c\/p\u003e\n\u003cp\u003eIt is also useful if you want a \u003cstrong\u003e2\" nosepiece\u003c\/strong\u003e on an M54-threaded camera — the M48 female end accepts a 2\" filter directly, and the barrel drops into a 2\" focuser.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e21 mm optical length:\u003c\/strong\u003e a known, fixed contribution to the backfocus sum — not an adjustable part\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eM54 × 0.75 male thread:\u003c\/strong\u003e mates to the M54 rear thread on ZWO's larger cooled bodies\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eM48 × 0.75 female thread:\u003c\/strong\u003e the 2\" filter standard — threads a 2\" filter straight in\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDoubles as a 2\" nosepiece:\u003c\/strong\u003e the M48 end is a 2\" barrel, so it drops into a standard 2\" focuser\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBlack anodized aluminium:\u003c\/strong\u003e the internal finish suppresses reflections inside the light path\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMechanical only\u003c\/strong\u003e — no optics, no glass, no electrical connection\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eHitting 55 mm backfocus\u003c\/strong\u003e on an M54-threaded ZWO cooled camera where 21 mm is the gap you need to fill\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThreading a 2\" filter directly to the camera\u003c\/strong\u003e when you are not running a filter wheel\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUsing an M54 camera as a 2\" nosepiece assembly\u003c\/strong\u003e in a standard focuser\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReplacing a spacer stack\u003c\/strong\u003e with one machined part, removing the accumulated tolerance of several thin rings\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eCamera side:\u003c\/strong\u003e M54 × 0.75 male — fits ZWO cooled cameras with an M54 rear thread. Confirm your camera's rear thread before ordering; ZWO also uses M42 and M68 across the range\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFilter side:\u003c\/strong\u003e M48 × 0.75 female, the 2\" filter thread\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBackfocus is a sum, not a single number.\u003c\/strong\u003e Your camera's own sensor-to-flange distance, plus this 21 mm, plus any filter wheel, OAG, or filter thickness, must total what your flattener or reducer specifies — usually 55 mm. Work the whole chain out before ordering\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFilters add optical path.\u003c\/strong\u003e A filter in the train shifts focus by roughly one third of its glass thickness. Account for it rather than discovering it at the corners\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNot adjustable.\u003c\/strong\u003e If you need a different length, ZWO makes M54 extenders in other sizes — including 16.5 mm and 21 mm M54-to-M54 versions\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMechanical adapter only\u003c\/strong\u003e — no electronic communication with the camera\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eImportant Limitations\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eThis is a spacer, not a corrector.\u003c\/strong\u003e It does not flatten a field, reduce a focal ratio, or fix star shapes. If your corners are poor, spacing is only one of the possible causes\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWrong length means bad corners.\u003c\/strong\u003e Backfocus tolerance on a fast flattener is typically a millimetre or so. Being 21 mm out because you guessed the chain will show as elongated or misshapen corner stars\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFixed 21 mm.\u003c\/strong\u003e It cannot be shortened, and shimming it longer defeats the point of a machined part\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eM54 male only.\u003c\/strong\u003e It will not thread to an M42 or M68 camera without a further adapter\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNo filter, no optics, and no camera included.\u003c\/strong\u003e This is a bare aluminium adapter\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eFrequently Asked Questions\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003eWhat is this adapter actually for?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eReaching 55 mm backfocus on an M54-threaded ZWO cooled camera. It contributes a fixed, known 21 mm so the chain adds up, and converts M54 to the M48 2\" filter thread on the way.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan I thread a 2\" filter into it?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eYes. The M48 × 0.75 female end is the 2\" filter standard.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan I use it as a 2\" nosepiece?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eYes — the M48 end is a 2\" barrel, so it drops into a standard 2\" focuser. That makes it a practical way to put an M54 camera into a visual-style focuser.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhich cameras does this fit?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eZWO cooled cameras with an M54 rear thread. Check your specific model first — ZWO uses M42, M54, and M68 across the line, and the wrong one simply will not thread.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eHow do I work out whether I need 21 mm?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eAdd your camera's sensor-to-flange backfocus, this adapter's 21 mm, and anything else in the chain — filter wheel, OAG, filter glass. The total needs to match what your flattener or reducer calls for. If the sum is not 55 mm, this is not the right length.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes the filter I put in it change my spacing?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eYes. Glass in a converging beam shifts focus by roughly a third of its thickness. Include it in the sum.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs this good for beginners?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe part is simple to fit — it threads on. The hard bit is the arithmetic, not the assembly. If you are unsure of your chain, work the numbers out before ordering rather than buying spacers and hoping.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eMy corner stars are still bad after fitting this. Why?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eSpacing is one cause of poor corners; sensor tilt and an optic that does not cover your sensor are the others. If your total backfocus is right and the corners are still wrong, look at tilt next.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eIn short: a 21 mm M54 male to M48 female adapter in black anodized aluminium — the part that closes a 21 mm gap in a 55 mm backfocus chain and gives you a 2\" filter thread and nosepiece at the same time. Work out your full chain before ordering; the length is fixed and the tolerance is tight.\u003c\/p\u003e","brand":"ZWO Optical","offers":[{"title":"Default Title","offer_id":53804616613999,"sku":"M54-M48-21","price":32.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/62bf1edb36141f114521ec4bb4175579_2023-10.jpg?v=1784084346","url":"https:\/\/ontariotelescope.com\/products\/zwo-m54-m48-21-adapter","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}