{"product_id":"takahashi-cca-250-250mm-f-5-tri-focal-corrected-cassegrain-astrograph","title":"Takahashi CCA-250 250mm f\/5 Tri-Focal Corrected Cassegrain Astrograph","description":"\u003ch3\u003e\u003cstrong\u003eProduct Overview\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe CCA-250 replaces Takahashi's Baker-Ritchey-Chrétien BRC-250 as their flagship astrograph. It is a 250 mm aperture instrument working at 1250 mm and f\/5 natively, built in carbon fibre, with electric focus driven by a moving secondary mirror rather than a conventional drawtube.\u003c\/p\u003e\u003cp\u003eThe \"tri-focal\" name describes its three working configurations: \u003cstrong\u003ef\/5 native, f\/3.9 with the reducer, and f\/8\u003c\/strong\u003e. That range covers wide-field deep-sky work at one end and high-resolution imaging at the other, from a single optical tube.\u003c\/p\u003e\u003cp\u003eThe optical performance figures are the headline: a \u003cstrong\u003e2 micron RMS spot radius on axis\u003c\/strong\u003e, and an \u003cstrong\u003eØ88 mm image circle\u003c\/strong\u003e spanning 4° of sky, 60% illuminated at its edge. Limiting stellar magnitude is 14.5.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThis is a good match if you are equipping an observatory or a permanent pier and want one instrument that covers wide-field and high-resolution imaging without changing telescopes. The 88 mm image circle suits large-format sensors, and the computer-controlled focus fits a rig that runs unattended.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e250 mm aperture at f\/5:\u003c\/strong\u003e 1250 mm native focal length.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eThree focal ratios:\u003c\/strong\u003e f\/5 native, f\/3.9 with reducer, f\/8.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eØ88 mm image circle:\u003c\/strong\u003e 4° of sky, 60% illuminated at the edge — well beyond full-frame.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e2 micron RMS spot radius on axis:\u003c\/strong\u003e the on-axis optical performance figure Takahashi publishes.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eInternal moving-secondary electric focus:\u003c\/strong\u003e computer-controlled over USB, with no external drawtube to flex.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCarbon fibre tube:\u003c\/strong\u003e holds focus across temperature changes better than metal.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBack focus 155.4 mm to 193.9 mm\u003c\/strong\u003e with the CAA removed.\u003c\/li\u003e\n\u003cli\u003e\u003cstrong\u003eLimiting stellar magnitude 14.5.\u003c\/strong\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003e\u003cstrong\u003eOptical \/ Mechanical Design\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eTwo design choices set this instrument apart from a conventional Cassegrain astrograph. The first is focusing by moving the secondary mirror internally rather than racking a drawtube: nothing outside the tube moves, so a heavy camera train never loads a focuser, and there is no drawtube flexure to introduce tilt as the telescope tracks. The focus motor is computer-controlled over USB, which is what makes automated focus runs practical on a rig that images unattended.\u003c\/p\u003e\u003cp\u003eThe second is carbon fibre. An aluminium tube changes length as it cools through the night, and on a fast f\/5 system the depth of focus is shallow enough that thermal drift shows up in the stars. Carbon fibre's low coefficient of expansion largely removes that, which matters more here than it would on a slower instrument.\u003c\/p\u003e\u003cp\u003eThe Ø88 mm image circle is the figure that justifies the rest. A full-frame sensor spans 43 mm diagonally, so 88 mm leaves the entire frame well inside the well-corrected field, with room for medium-format sensors too. Combined with a 2 micron on-axis RMS spot, the system is resolving finer detail than most sensors will sample at 1250 mm.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eObservatory-based deep-sky astrophotography across a wide range of targets: extended nebulae and galaxy fields at f\/3.9, general deep-sky work at f\/5, and small galaxies and planetary nebulae at f\/8. Also usable visually.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eThe back focus range is \u003cstrong\u003e155.4 mm to 193.9 mm\u003c\/strong\u003e with the camera angle adjuster removed — generous, and enough to accommodate a filter wheel and off-axis guider in the train. The f\/3.9 configuration requires the matching reducer, which is a separate item. We stock the CCA-250 reducer and the camera angle adjuster; tell us your camera, filter wheel and guiding arrangement and we will map the full train and its spacing with you before you order.\u003c\/p\u003e\u003cp\u003eThe optical tube is supplied without a mount. At 50.16 lb before a camera train, it wants a substantial equatorial mount — we can go through mount options with you.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eGood to Know Before You Order\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003e\u003cstrong\u003eMount not included:\u003c\/strong\u003e this is an optical tube assembly. The tube alone is 50.16 lb, and the camera, filter wheel and guider add to that, so the mount is a significant part of the decision. We are happy to work through it with you.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eThe reducer is separate:\u003c\/strong\u003e f\/5 and f\/8 are available from the tube as supplied; f\/3.9 needs the matching reducer, which we stock.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eFocus is computer-controlled:\u003c\/strong\u003e the electric moving-secondary focuser connects over USB to control software. That is a strength for automated imaging, and it does mean a computer is part of the setup rather than an optional extra.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eSize:\u003c\/strong\u003e 34.25″ long and 12.05″ in outside diameter — an observatory or permanent-pier instrument rather than something to carry to a dark site.\u003c\/p\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\u003eThe optics need no collimation fuss from you in normal use, and focus is handled by software rather than by hand. The demanding parts are the mount and the pier, which is true of any instrument this size — and we will help you specify both.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat are the three focal ratios?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003ef\/5 native at 1250 mm, f\/3.9 with the reducer, and f\/8.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat sensor size will it cover?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eThe Ø88 mm image circle covers full-frame with a wide margin and reaches into medium format.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow much back focus do I have to work with?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003e155.4 mm to 193.9 mm with the CAA removed — room for a filter wheel and off-axis guider.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes it need a computer?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eThe electric focuser is computer-controlled over USB, so yes for focusing.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it visually?\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003eYes — Takahashi describes it as a visual as well as a photographic instrument, though the design priorities are photographic.\u003c\/p\u003e\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\u003cp\u003eA 250 mm carbon fibre astrograph working at f\/3.9, f\/5 and f\/8, with an 88 mm image circle and computer-controlled internal focus — an observatory instrument built to cover most of deep-sky imaging from one tube.\u003c\/p\u003e","brand":"Takahashi","offers":[{"title":"Default Title","offer_id":54086147801199,"sku":"TAK-TCK25010","price":22011.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/tck25010_2.jpg?v=1787329293","url":"https:\/\/ontariotelescope.com\/products\/takahashi-cca-250-250mm-f-5-tri-focal-corrected-cassegrain-astrograph","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}