{"product_id":"takahashi-fc-100dc-f-7-4-steinheil-fluorite-doublet-apo-refractor-ota-visual-model","title":"Takahashi FC-100DC f\/7.4 Steinheil Fluorite Doublet APO Refractor OTA, Visual Model","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe FC-100DC is Takahashi's 100 mm Steinheil fluorite doublet apochromat, sold here as the Visual model — the crown element leads in this design rather than following, a configuration Takahashi has used specifically for its 100 mm fluorite refractors. At 740 mm focal length and f\/7.4 it runs 815 mm long with a 30 mm drawtube extension, and weighs 2.7 kg.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThis is a good match if visual observing is the main use — lunar, planetary and double-star work at 100 mm aperture, where the Steinheil doublet's colour correction and light throughput matter more than field width. It suits observers stepping up from a 60 or 76 mm apochromat who want a noticeably brighter, higher-resolution view, and anyone who wants a single well-corrected tube for the moon and planets without the added elements of a larger triplet. Takahashi also sells this objective as the FC-100DF, an imaging-oriented configuration in a different tube; this Visual model is built around eyepiece use.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eSteinheil fluorite doublet:\u003c\/strong\u003e two elements in two groups, with the fluorite crown element leading the light path — a Takahashi design choice specific to its 100 mm doublets.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e740 mm at f\/7.4:\u003c\/strong\u003e 100 mm aperture with meaningfully more light grasp and resolution than a 60–76 mm refractor.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e161 mm of back focus:\u003c\/strong\u003e room for a diagonal or a straightforward imaging train.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e30 mm drawtube extension\u003c\/strong\u003e on a rack-and-pinion focuser.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e2.7 kg:\u003c\/strong\u003e substantial but still manageable on a mid-sized equatorial mount.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eOptical \/ Mechanical Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eMost doublet apochromats use a Fraunhofer layout, with the ED or fluorite element behind the crown glass. Takahashi's 100 mm fluorite doublets instead use a Steinheil configuration, with the fluorite crown element in front. Combined with fluorite's anomalous partial dispersion, the arrangement is what Takahashi credits for the FC-100 series' colour correction and contrast at this aperture — clean planetary and lunar detail without the residual violet fringing that limits achromats at 100 mm.\u003c\/p\u003e\u003cp\u003eHard multicoatings protect the fluorite surfaces, and the 161 mm of back focus is enough for the FC\/FS MFL 1.04x flattener to reach focus at 760 mm and f\/7.6, correcting to a 44 mm image circle if imaging is added to the visual use this model is built around.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eLunar and planetary observing:\u003c\/strong\u003e at 740 mm and f\/7.4, where the 100 mm aperture resolves finer detail than a smaller refractor.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDouble-star splitting:\u003c\/strong\u003e the Steinheil doublet's colour correction shows clearly on close, bright pairs.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCasual deep-sky visual observing:\u003c\/strong\u003e star clusters and brighter nebulae benefit from the extra aperture over a 60–76 mm scope.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOccasional imaging:\u003c\/strong\u003e with the FC\/FS MFL 1.04x flattener at 760 mm and f\/7.6, for those who want to photograph the moon or planets without switching to the dedicated FC-100DF.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe FC-100DC's system chart, plus its Extender-Q and Extender-C2X charts, are in the Downloads tab and list the adapters and distances Takahashi publishes for each configuration. Our \u003ca href=\"\/pages\/takahashi-back-focus-guide\"\u003eTakahashi Back Focus Guide\u003c\/a\u003e collects the same figures for the whole range.\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBack focus:\u003c\/strong\u003e 161 mm at prime focus.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eField flattener:\u003c\/strong\u003e FC\/FS MFL 1.04x — 760 mm, f\/7.6, 44 mm circle, 71.2 mm back focus.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMount:\u003c\/strong\u003e sold as an OTA — no mount, rings or dovetail included. At 2.7 kg it suits mid-sized equatorial mounts.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eRelated model:\u003c\/strong\u003e the FC-100DF shares this objective in a tube built around imaging rather than visual use, with a different back focus and reducer options.\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eIf you are weighing this Visual model against the imaging-oriented FC-100DF, send us how you plan to use it and we will help you choose.\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\u003eThis is an optical tube assembly.\u003c\/strong\u003e Mount, tripod, rings, dovetail, diagonal, eyepiece and finder are sold separately.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThis is the Visual model.\u003c\/strong\u003e It is built around eyepiece use; the FC-100DF is Takahashi's dedicated imaging configuration of the same objective, in a different tube.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eA flat field for imaging needs the MFL 1.04x flattener.\u003c\/strong\u003e At prime focus the field curves, as on any doublet refractor.\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\u003eNo — at prime focus it is a diagonal and eyepiece and you are observing. The system chart in the Downloads tab lists parts and distances if you add a flattener for imaging.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is it best used for?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eVisual observing of the moon, planets and double stars at 100 mm aperture. It can image with the MFL 1.04x flattener, but the FC-100DF is Takahashi's dedicated model for that use.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is the difference between this and the FC-100DF?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eSame 100 mm Steinheil fluorite doublet objective, different tube and intended use — this Visual model is built for eyepiece observing; the DF is configured for astrophotography with its own back focus and reducer options.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat does Steinheil mean, and why does it matter?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eIt describes which element leads the light path — the fluorite crown element sits in front here, rather than behind the flint element as in a Fraunhofer doublet. Takahashi uses this layout specifically on its 100 mm fluorite doublets.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it for astrophotography?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eWith the FC\/FS MFL 1.04x flattener, yes, at 760 mm and f\/7.6 across a 44 mm corrected circle — though the FC-100DF is the model built specifically for that purpose.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eIn short: a 100 mm Steinheil fluorite doublet apochromat at 740 mm and f\/7.4, with 161 mm of back focus, built as a visual instrument for lunar, planetary and double-star observing.\u003c\/p\u003e","brand":"Takahashi","offers":[{"title":"Default Title","offer_id":54047058591855,"sku":"TAK-TFK10010","price":2902.9,"currency_code":"CAD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/TFK10010_FC-100DC_1.jpg?v=1786912049","url":"https:\/\/ontariotelescope.com\/products\/takahashi-fc-100dc-f-7-4-steinheil-fluorite-doublet-apo-refractor-ota-visual-model","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}