{"product_id":"takahashi-fc-fs-multi-flattener-1-04x-field-flattener","title":"Takahashi FC\/FS Multi-Flattener 1.04x Field Flattener","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe FC\/FS Multi-Flattener 1.04x is Takahashi's universal field flattener for the FC and FS doublet refractor families. It replaces the separate model-specific flatteners Takahashi previously sold: one optic now covers the whole range, with a telescope-specific CA ring setting the correct spacing for each tube.\u003c\/p\u003e\u003cp\u003eTwo elements in one group, 40 mm long, 60 mm across and 110 g. It threads M56 x 0.75 female on the telescope side and presents M52 x 0.75 male to your camera adapter, with 40 mm of backfocus behind it. The 1.04x factor means focal length moves only slightly — a 355 mm FS-60CB becomes 370 mm — so this is a corrector, not a focal-length changer.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThis is what you need if you image with an FC or FS doublet and your stars go elongated toward the corners of the frame. At prime focus these telescopes have a curved field; the flattener corrects it and gives a 44 mm flat circle on the shorter tubes — enough to cover APS-C completely and most of full frame.\u003c\/p\u003e\u003cp\u003eIf you observe visually with an eyepiece, this has no application in that train. It corrects a photographic field for a sensor.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eTwo elements in one group:\u003c\/strong\u003e a cemented pair that corrects field curvature without adding measurable chromatic error of its own.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e1.04x magnification factor:\u003c\/strong\u003e focal length and focal ratio shift only marginally — the point is the flat field, not a speed change.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e44 mm corrected image circle\u003c\/strong\u003e on FS-60CB, FC-76D, FC-100D, FC-50, FC-65, FC-76 and FS-78; \u003cstrong\u003e40 mm\u003c\/strong\u003e on FC-100DL, FC-60, FC-100, FC-125, FS-102, FS-128 and FS-152.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eM56 x 0.75 female in, M52 x 0.75 male out:\u003c\/strong\u003e standard Takahashi interfaces on both faces.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e40 mm backfocus:\u003c\/strong\u003e the distance from the rear thread to the sensor, which your camera adapter stack must total.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e110 g and 40 mm long:\u003c\/strong\u003e adds almost nothing to focuser load or train length.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOne optic, whole family:\u003c\/strong\u003e replaces the older per-telescope flatteners; the CA ring does the model-specific work.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eOptical Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eA doublet refractor focuses a curved surface, not a plane. Stars at the centre of the frame come to focus in front of the stars at the corners, so a flat sensor cannot record both sharply at once — which is why uncorrected short refractors show round stars in the middle and elongated ones at the edges.\u003c\/p\u003e\u003cp\u003eThe MFL 1.04x introduces the opposite curvature. Two elements in a single group bend the focal surface flat across the working circle while adding only 4% to the focal length. Because it is a corrector rather than a reducer, it does not compress the image or brighten the field — an FS-60CB goes from 355 mm at f\/5.9 to 370 mm at f\/6.2, and the corners come into line with the centre.\u003c\/p\u003e\u003cp\u003eWhat makes it universal is that the optical correction is common to the FC and FS doublets while only the required spacing differs. Takahashi puts that difference in the CA ring rather than in the glass, so a single flattener covers telescopes from 50 mm to 152 mm of aperture.\u003c\/p\u003e\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/takahashi-fc-fs-mfl-104x-flattener-dimensional-diagram.png?v=1786907633\" alt=\"Dimensional diagram of the Takahashi FC\/FS MFL 1.04x field flattener showing M56x0.75 input thread, M52x0.75 output thread, 40 mm backfocus and 40 mm overall length\" style=\"max-width:100%;height:auto;\"\u003e\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eDeep-sky imaging with a DSLR, mirrorless or cooled astro camera\u003c\/strong\u003e on any current FC or FS doublet.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAPS-C and full-frame coverage:\u003c\/strong\u003e the 44 mm circle covers APS-C entirely and reaches most of a full-frame corner.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReplacing an older model-specific flattener\u003c\/strong\u003e when you own more than one FC or FS tube and want one corrector for both.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWide-field mosaics\u003c\/strong\u003e where edge star shape has to match between panels.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe flattener and the CA ring are bought together — the ring is what sets the metal back distance for your particular telescope. Takahashi publishes the pairing:\u003c\/p\u003e\u003ctable\u003e\n\u003ctr\u003e\n\u003cth\u003eTakahashi part\u003c\/th\u003e\n\u003cth\u003eCA ring\u003c\/th\u003e\n\u003cth\u003eTelescope\u003c\/th\u003e\n\u003cth\u003eMetal back distance\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTKA20203\u003c\/td\u003e\n\u003ctd\u003eCA-60C\u003c\/td\u003e\n\u003ctd\u003eFS-60CB\u003c\/td\u003e\n\u003ctd\u003e87.5 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTKA18203\u003c\/td\u003e\n\u003ctd\u003eCA-76\u003c\/td\u003e\n\u003ctd\u003eFC-76D, FC-76, FS-78\u003c\/td\u003e\n\u003ctd\u003e75.0 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTKA19203\u003c\/td\u003e\n\u003ctd\u003eCA-100\u003c\/td\u003e\n\u003ctd\u003eFC-100D, FC-100\u003c\/td\u003e\n\u003ctd\u003e71.2 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTKA01203\u003c\/td\u003e\n\u003ctd\u003eCA-50\u003c\/td\u003e\n\u003ctd\u003eFC-50\u003c\/td\u003e\n\u003ctd\u003e84.0 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTKA03203\u003c\/td\u003e\n\u003ctd\u003eCA-65\u003c\/td\u003e\n\u003ctd\u003eFC-60, FC-65\u003c\/td\u003e\n\u003ctd\u003e78.0 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTKA07203\u003c\/td\u003e\n\u003ctd\u003eCA-125\u003c\/td\u003e\n\u003ctd\u003eFC-100DL, FS-102, FC-125\u003c\/td\u003e\n\u003ctd\u003e69.2 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTKA24203\u003c\/td\u003e\n\u003ctd\u003eCA-128\u003c\/td\u003e\n\u003ctd\u003eFS-128, FS-152\u003c\/td\u003e\n\u003ctd\u003e66.2 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/table\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eCamera side:\u003c\/strong\u003e M52 x 0.75 male, with 40 mm of backfocus to the sensor. Your camera adapter, filter drawer and spacers together need to total that 40 mm.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFilters count:\u003c\/strong\u003e a filter in the light path adds roughly one third of its thickness to the optical path. A 2 mm filter shifts focus by about 0.7 mm, which comes out of the spacer stack.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eNot compatible with the FOA-60 or SKY90.\u003c\/strong\u003e Both use different optical designs. The FOA-60 has its own 0.93x flattener; ask us and we will point you to the right part.\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eIf you tell us your telescope, camera and any filters you use, we will work out the spacer stack with you and confirm the CA ring before you order.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eGood to Know Before You Order\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eThe CA ring is a separate purchase.\u003c\/strong\u003e The flattener does not include one, and it will not reach correct spacing without the ring matched to your telescope. The table above names it; we stock the range.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThis is a photographic corrector.\u003c\/strong\u003e It has no application in a visual train with an eyepiece.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBackfocus is 40 mm from the rear thread.\u003c\/strong\u003e The corner star shape follows how closely your adapter stack hits that figure, and the diagram above gives you the reference distances to measure against.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThe corrected circle depends on the telescope.\u003c\/strong\u003e 44 mm on the shorter tubes, 40 mm on the longer ones — the list above tells you which applies. A full-frame sensor has a 43.3 mm diagonal, so full-frame corners are covered on the 44 mm group and just short on the 40 mm group.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIt does not fit the FOA-60 or SKY90.\u003c\/strong\u003e Those telescopes take their own correctors.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eFrequently Asked Questions\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003e\u003cstrong\u003eIs it difficult to set up?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eIt threads on directly — the CA ring goes on the telescope, the flattener onto the ring, and your camera adapter behind it. The work is in getting the 40 mm backfocus right on the camera side, and that is arithmetic rather than trial and error: add up your adapter, filter drawer and spacers to 40 mm. Send us your camera and filter setup and we will do the sum with you.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it change my focal length?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eSlightly. The 1.04x factor takes a 355 mm FS-60CB to 370 mm and f\/5.9 to f\/6.2. It is a flattener, not a reducer.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhich CA ring do I need?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eThe table above pairs every FC and FS telescope with its ring and metal back distance. For an FS-60CB it is the CA-60C, Takahashi part TKA20203.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it cover a full-frame sensor?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eOn the 44 mm group — FS-60CB, FC-76D, FC-100D, FC-50, FC-65, FC-76, FS-78 — yes, a full-frame diagonal of 43.3 mm sits inside the corrected circle. On the 40 mm group the extreme corners fall outside it.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it with a filter in the train?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eYes. Allow for the focus shift a filter introduces — about a third of its thickness — when you build the spacer stack to 40 mm.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is the difference between this and the older flatteners?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eTakahashi previously sold a flattener per telescope. This one optic covers the whole FC and FS doublet range, with the CA ring handling the model-specific spacing.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it work on my FOA-60?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eNo — the FOA-60 and SKY90 use different optical designs. The FOA-60 takes the dedicated 0.93x flattener.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eIn short: one 110 g corrector that flattens the field across the whole FC and FS doublet range, giving a 44 mm circle on the shorter tubes and 40 mm on the longer ones, at 40 mm of backfocus. Pair it with the CA ring for your telescope and it does its job — and we will confirm which ring and what spacing before you order.\u003c\/p\u003e","brand":"Takahashi","offers":[{"title":"Default Title","offer_id":54046965858415,"sku":"TAK-TKA00582","price":303.16,"currency_code":"CAD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/TKA00582_1.jpg?v=1786907709","url":"https:\/\/ontariotelescope.com\/products\/takahashi-fc-fs-multi-flattener-1-04x-field-flattener","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}