{"product_id":"takahashi-fc-100dz-100mm-f-8-fluorite-doublet-refractor-ota","title":"Takahashi FC-100DZ 100mm f\/8 Fluorite Doublet Refractor OTA","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe FC-100DZ is Takahashi's 100 mm fluorite doublet apochromat, the newest member of the FC-100D family. At 800 mm focal length and f\/8, it retracts to 770 mm and extends to 840 mm through a variable-length dew shield and tube assembly, weighing 3.7 kg. Back focus at prime is 225 mm, and the doublet uses a fluorite element paired with high-index, low-dispersion glass rather than the Steinheil pairing of the DC and DF.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThis is a good match if you want the latest revision of Takahashi's 100 mm fluorite doublet line, with reduced blue halo compared to the FC-100D and compatibility with the existing FC-100 accessory range — flatteners, reducers and adapters already built for the DC and DF fit here too. It suits visual observers after clean, high-contrast lunar and planetary views, and imagers who reduce to 530 mm at f\/5.3 with the FC-35RD for wider framing.\u003c\/p\u003e\u003cp\u003eTell us your camera and sensor size and we will confirm which reducer or flattener gets you the field you want.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eFluorite doublet, refined design:\u003c\/strong\u003e two elements in two groups, pairing fluorite with high-index, low-dispersion glass for reduced blue halo relative to the FC-100D.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e800 mm at f\/8:\u003c\/strong\u003e in a 770–840 mm variable-length tube, 95 mm across (124 mm dew shield).\u003c\/li\u003e\n\u003cli\u003e\u003cstrong\u003e2.7-inch rack-and-pinion focuser, single-speed.\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e225 mm of back focus\u003c\/strong\u003e at prime focus — ample room for a full imaging or visual train.\u003c\/li\u003e\n\u003cli\u003e\u003cstrong\u003e63 mm of drawtube extension.\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCompatible with existing FC-100 accessories:\u003c\/strong\u003e the same flatteners, reducers and adapters built for the FC-100DC and FC-100DF fit this tube.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eOptical \/ Mechanical Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe objective pairs a fluorite element with a high-index, low-dispersion glass element in a two-element air-spaced doublet — a refinement over the Steinheil FC-100DC\/DF pairing that Takahashi states cuts blue halo by roughly half. In practice that means tighter colour correction at the same 100 mm aperture and f\/8 focal ratio, with the retractable dew shield collapsing the 840 mm tube to 770 mm for transport.\u003c\/p\u003e\u003cp\u003eThe FC\/FS MFL 1.04x flattener brings the system to 820 mm at f\/8.2 with a 44 mm corrected circle at 71.2 mm back focus, and the FC-35RD 0.66x reducer shortens it to 530 mm at f\/5.3, also 44 mm, at 68.8 mm back focus — the same conversion lenses used across the FC-100D family.\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 800 mm and f\/8, with reduced chromatic error over the earlier FC-100D.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDeep-sky imaging at native focal length:\u003c\/strong\u003e 800 mm for medium-sized targets.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWide-field imaging:\u003c\/strong\u003e with the FC-35RD 0.66x reducer at 530 mm and f\/5.3, a 44 mm corrected circle.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFlat-field imaging:\u003c\/strong\u003e with the FC\/FS MFL 1.04x flattener at 820 mm and f\/8.2.\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eBack focus at prime is 225 mm, dropping to 71.2 mm with the MFL 1.04x flattener or 68.8 mm with the FC-35RD reducer. Because the FC-100DZ shares its rear cell with the DC and DF, existing FC-100 flatteners, reducers and adapters fit directly. Takahashi's system charts for the base configuration, the FC-35RD reducer and the EX-Q 1.6x extender are in the Downloads tab, and 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\u003eFlattener:\u003c\/strong\u003e FC\/FS MFL 1.04x, 820 mm at f\/8.2, 44 mm circle, 71.2 mm back focus.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReducer:\u003c\/strong\u003e FC-35RD 0.66x, 530 mm at f\/5.3, 44 mm circle, 68.8 mm back focus.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eExtender:\u003c\/strong\u003e EX-Q 1.6x extends the focal length for planetary and lunar imaging — system chart in the Downloads tab.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMount:\u003c\/strong\u003e sold as an OTA — no mount, rings, dovetail, diagonal or eyepiece included. At 3.7 kg plus accessories, a mount rated for 8–10 kg of total payload is a reasonable starting point.\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eIf you already own FC-100DC or FC-100DF accessories and are not sure they carry over, send us the part numbers and we will confirm.\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, rings, dovetail, diagonal, eyepiece and finder are all sold separately.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eA flat field needs a corrector.\u003c\/strong\u003e At prime focus the field curves; the MFL 1.04x flattener corrects it across 44 mm.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBack focus changes with each conversion lens.\u003c\/strong\u003e 225 mm at prime, 71.2 mm with the flattener, 68.8 mm with the reducer — the system charts in the Downloads tab list the exact parts.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThe tube length varies with the dew shield position.\u003c\/strong\u003e 770 mm retracted, 840 mm extended — worth accounting for in a case or travel bag.\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 with a diagonal and eyepiece it is straightforward. Imaging trains take more care because spacing changes with each conversion lens, and the published system charts name the exact parts — send us your camera and we will confirm the train with you.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is it best used for?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eLunar and planetary observing with reduced chromatic error, and deep-sky imaging at 800 mm native or wider with the FC-35RD reducer.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow is this different from the FC-100DC and FC-100DF?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eA refined optical prescription — fluorite paired with high-index, low-dispersion glass rather than the Steinheil pairing — with roughly half the blue halo of the FC-100D, while remaining compatible with the same accessory range.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDo existing FC-100 accessories fit?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eYes — the flatteners, reducers and adapters built for the FC-100DC and FC-100DF fit the FC-100DZ's rear cell directly.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat mount does it need?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eAt 3.7 kg before accessories, most mid-weight mounts handle it once a diagonal or camera is added. Tell us your setup and we will confirm the total payload.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhen should this not be the choice?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eFor wide-field imaging without a reducer — native f\/8 is a long native ratio for large nebulae, though the FC-35RD reducer addresses that at 530 mm and f\/5.3.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eIn short: a 100 mm fluorite doublet apochromat at 800 mm and f\/8, with 225 mm of back focus at prime and 63 mm of drawtube extension, weighing 3.7 kg. It reduces to 530 mm at f\/5.3 or flattens to 820 mm at f\/8.2 depending on the conversion lens, and it shares its accessory range with the rest of the FC-100D family.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eOptical Diagram Reports\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eTakahashi publishes a spot diagram for the FC-100DZ at prime focus, showing star images across the field at the design wavelengths.\u003c\/p\u003e\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/FC-100DZ_spots.png?v=1786911643\" alt=\"Takahashi FC-100DZ 100mm fluorite doublet spot diagram at prime focus\" style=\"max-width:100%;height:auto;\"\u003e\u003c\/p\u003e","brand":"Takahashi","offers":[{"title":"Default Title","offer_id":54047054004335,"sku":"TAK-TFK10310","price":4418.7,"currency_code":"CAD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/TFK10310_FC-100DZ_1.jpg?v=1786911938","url":"https:\/\/ontariotelescope.com\/products\/takahashi-fc-100dz-100mm-f-8-fluorite-doublet-refractor-ota","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}