{"product_id":"orion-optics-uk-ag8-optical-tube-assembly-only","title":"Orion Optics UK AG8 f\/3.8 Astrograph OTA","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003e200mm (8-inch) Primary Mirror\u003c\/li\u003e\n\u003cli\u003e760mm Focal Length\u003c\/li\u003e\n\u003cli\u003eExtremely Fast f\/3.8 Focal Ratio\u003c\/li\u003e\n\u003cli\u003e45mm Corrected Flat Field Circle\u003c\/li\u003e\n\u003cli\u003eCarbon Fibre Sandwich Tube Construction\u003c\/li\u003e\n\u003cli\u003e3\" Ceres Rack and Pinion Focuser with 10:1 Reduction\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- more --\u003e\n\u003cul class=\"tabs\"\u003e\n\u003cli class=\"active\"\u003eDescription\u003c\/li\u003e\n\u003cli\u003eFAQ\u003c\/li\u003e\n\u003cli\u003eSpecifications\u003c\/li\u003e\n\u003cli\u003eIn the Box\u003c\/li\u003e\n\u003cli\u003eWarranty\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cul class=\"tabs-content\"\u003e\n\u003cli class=\"active\"\u003e\n\u003cdiv\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section-center\"\u003e\n\u003ch2\u003eOrion Optics UK AG8 f\/3.8 Astrograph OTA\u003c\/h2\u003e\n\u003cp\u003eThe Orion Optics UK AG8 Optical Tube Assembly is a dedicated imaging instrument, combining a fast 200mm f\/3.8 primary mirror with a 4-lens ED corrector to produce a 45mm flat image circle. Its 760mm focal length frames large deep-sky targets, while the carbon fibre sandwich tube construction maintains focus stability at a low weight of approximately 6kg. With tight stellar spot sizes of just 4.1µm on-axis and 8.1µm at the edge of the field, the AG8 delivers sharp, coma-free stars across full-frame sensors.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eFast f\/3.8 Optics: The 200mm Primary and 4-Lens Corrector\u003c\/h3\u003e\n\u003cp\u003eThe AG8 is built for speed. The 200mm primary mirror operates at a native f\/3.8, drastically reducing exposure times compared to f\/5 or f\/6 systems and allowing you to capture more data in a single night. This aggressive focal ratio is managed by an integrated 4-lens ED corrector, which eliminates off-axis coma and produces a flat field, ensuring that stars remain pinpoint across the entire frame.\u003c\/p\u003e\n\u003cp\u003eThe 90mm secondary mirror provides even illumination over the 45mm image circle, a necessary design choice for a fast, wide-field astrograph. While this large central obstruction compromises some contrast for high-resolution planetary viewing, it is an essential trade-off for achieving the bright, wide-field performance required for deep-sky imaging.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eAstrograph Engineering: Carbon Fibre Tube and 3\" Ceres Focuser\u003c\/h3\u003e\n\u003cp\u003eAn imaging platform must be mechanically rigid and thermally stable. The AG8's tube is constructed from a carbon fibre sandwich material, which has a near-zero coefficient of thermal expansion. This prevents the 760mm focal length from shifting as temperatures drop overnight, keeping your images perfectly focused. The entire optical tube weighs only approximately 6kg, placing less demand on your equatorial mount.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e3\" Ceres Focuser:\u003c\/strong\u003e This heavy-duty rack and pinion focuser provides a rigid, flex-free connection for your imaging train. The 10:1 fine-focus knob allows for precise adjustments, critical for achieving sharp focus at f\/3.8.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e9-Point Mirror Cell:\u003c\/strong\u003e The primary mirror rests on a CNC machined, 9-point flotation cell that provides uniform support without introducing astigmatism or other optical distortions.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eFull-Frame Imaging: A 45mm Flat Field with 8.1µm Edge Spots\u003c\/h3\u003e\n\u003cp\u003eThe AG8 is designed to illuminate large sensors without compromise. The optical system delivers a fully corrected, flat image circle of 45mm in diameter, easily covering full-frame (36x24mm) and many medium-format CMOS and CCD sensors. This allows you to capture vast targets like the North American Nebula (NGC 7000) or the Andromeda Galaxy (M31) in a single frame.\u003c\/p\u003e\n\u003cp\u003eThe optical correction is quantified by the stellar spot sizes. On-axis, stars are focused to a tight 4.1µm, and even at the extreme edge of the 45mm field, the spot size is only 8.1µm. This ensures that whether your guide star is in the center or the corner of your off-axis guider, the stars in your final image are round and sharp.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eActive Thermal Control: 3 Integrated Cooling Fans\u003c\/h3\u003e\n\u003cp\u003eRapidly cooling the 200mm primary mirror to match the ambient air temperature is crucial for achieving the best image sharpness. The AG8 includes three controllable fans integrated into the rear mirror cell. By actively circulating air across the back of the mirror, you can dramatically reduce the cooling time, minimizing tube currents and ensuring your telescope is ready for imaging almost immediately after setup.\u003c\/p\u003e\n\u003cdiv class=\"DAV-bg-light\"\u003e\n\u003cdiv class=\"DAV-section\"\u003e\n\u003ch3\u003eComparing the Optical Grades\u003c\/h3\u003e\n\u003cp\u003eThe images below show the same view of Saturn captured through the included Professional grade and the optional Ultra (Lambda\/10 PV) upgrade, under identical conditions -- a visual illustration of the difference in contrast and fine detail the upgrade delivers.\u003c\/p\u003e\n\u003cdiv class=\"DAV-comparison-grid\"\u003e\n\u003cdiv class=\"DAV-comparison-item\"\u003e\n\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Orion-Optics-UK-Saturn-1_6-PV.jpg\" alt=\"Saturn viewed through 1\/6 PV Professional grade optics\"\u003e\n\u003cp\u003e1\/6 PV (Professional)\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-comparison-item\"\u003e\n\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Orion-Optics-UK-Saturn-1_10-PV.jpg\" alt=\"Saturn viewed through the Ultra (Lambda\/10 PV) grade optics upgrade\"\u003e\n\u003cp\u003eLambda\/10 PV (Ultra)\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat kind of camera sensor is the Orion Optics UK AG8 designed for?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe AG8 is optimized for large-format sensors. Its integrated corrector produces a \u003cstrong\u003e45mm flat image circle\u003c\/strong\u003e, which is large enough to fully illuminate full-frame sensors (36mm x 24mm) and many popular APS-C and smaller medium-format astronomy cameras without vignetting or distorted stars at the edges.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the f\/3.8 focal ratio of the AG8 affect my imaging?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eAn f\/3.8 focal ratio is extremely fast, allowing the telescope to gather light much more quickly than systems with higher f-ratios. This means you can achieve the same image brightness with significantly shorter sub-exposure times, reducing the demands on your mount's tracking accuracy and allowing you to collect more data on a target in a single session.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the 3\" Ceres focuser on the AG8 strong enough for a heavy camera and filter wheel?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. The \u003cstrong\u003e3\" Ceres Rack and Pinion focuser\u003c\/strong\u003e is a heavy-duty unit designed specifically to handle the weight and leverage of modern imaging trains. Its rack and pinion design prevents the slippage and flexure common with Crayford-style focusers when under heavy load, ensuring your camera, filter wheel, and off-axis guider remain perfectly aligned.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat is the benefit of the AG8's carbon fibre tube?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe AG8's \u003cstrong\u003ecarbon fibre sandwich tube\u003c\/strong\u003e provides two main advantages for astrophotography. First, it has an extremely low thermal expansion coefficient, meaning it won't shrink or expand significantly with temperature changes, which keeps the focus stable throughout the night. Second, it has a high stiffness-to-weight ratio, resulting in a rigid tube that weighs only \u003cstrong\u003eapprox. 6kg\u003c\/strong\u003e.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow will the AG8 perform when imaging the Andromeda Galaxy (M31) with a full-frame DSLR?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe AG8 is an excellent choice for this target. Its \u003cstrong\u003e760mm focal length\u003c\/strong\u003e provides a good image scale for capturing detail in M31's dust lanes and star-forming regions. More importantly, the \u003cstrong\u003e45mm corrected image circle\u003c\/strong\u003e will fully cover your full-frame sensor, allowing you to capture the galaxy and its satellite companions, M32 and M110, in a single, wide, flat field.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat back focus distance do I need to maintain for the AG8's corrector?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe Orion Optics UK AG8 requires a precise spacing from the corrector to your camera sensor to achieve its specified image quality. You must maintain a back focus distance of \u003cstrong\u003e79mm\u003c\/strong\u003e from the mounting flange of the corrector to the focal plane (your camera's sensor).\u003c\/p\u003e\n\u003c\/div\u003e\n\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the AG8 available in a higher optical grade?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe AG8 ships with Orion Optics UK's Professional (1\/6 PV) hand-figured optics as standard, each supplied with its own Zygo interferometer test report. For imagers who want the tightest possible star images, an Ultra (Lambda\/10 PV) hand-figured optics upgrade is available, further reducing the spot sizes across the field.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ctable class=\"DAV-specifications\"\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eAperture\u003c\/td\u003e\n\u003ctd\u003e200mm (8\")\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Length\u003c\/td\u003e\n\u003ctd\u003e760mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Ratio\u003c\/td\u003e\n\u003ctd\u003ef\/3.8\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCorrected Image Circle\u003c\/td\u003e\n\u003ctd\u003e45mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSpot Size (On-Axis)\u003c\/td\u003e\n\u003ctd\u003e4.1µm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSpot Size (Field Edge)\u003c\/td\u003e\n\u003ctd\u003e8.1µm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBack Focus Distance\u003c\/td\u003e\n\u003ctd\u003e79mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocuser\u003c\/td\u003e\n\u003ctd\u003e3\" Ceres Rack and Pinion with 10:1 Reduction\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCorrector Design\u003c\/td\u003e\n\u003ctd\u003e4-lens ED\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSecondary Mirror Size\u003c\/td\u003e\n\u003ctd\u003e90mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMirror Cell\u003c\/td\u003e\n\u003ctd\u003eCNC machined aluminum, 9-point suspension\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCooling System\u003c\/td\u003e\n\u003ctd\u003e3 controllable fans\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTube Material\u003c\/td\u003e\n\u003ctd\u003eCarbon fibre sandwich\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTube Diameter\u003c\/td\u003e\n\u003ctd\u003e255mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTube Length\u003c\/td\u003e\n\u003ctd\u003e635mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTube Weight\u003c\/td\u003e\n\u003ctd\u003eApprox. 6kg\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMounting Hardware\u003c\/td\u003e\n\u003ctd\u003eCNC machined aluminum cradles \u0026amp; dovetail\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003cul class=\"DAV-grid\"\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/orion-optics-uk-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eOrion Optics UK 1-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Orion Optics UK","offers":[{"title":"Professional (1\/6 PV)","offer_id":52942359200029,"sku":"OOUK-AG8-OPTICAL-TUBE-ASSEMBLY-ONLY","price":7586.0,"currency_code":"CAD","in_stock":true},{"title":"Ultra (Lambda\/10 PV)","offer_id":52942359232797,"sku":"OOUK-AG8-OPTICAL-TUBE-ASSEMBLY-ONLY-2","price":7720.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/Orion-Optics-UK-Logo_39d816cf-1a11-40e9-8b68-941f5ac4ae6f.jpg?v=1789606569","url":"https:\/\/davidastro.com\/products\/orion-optics-uk-ag8-optical-tube-assembly-only","provider":"David Astro","version":"1.0","type":"link"}