{"title":"William Optics Ultra-Cat","description":"\u003cp\u003eThe William Optics Ultra-Cat line, listed by aperture. Part of \u003ca href=\"\/collections\/william-optics-telescopes\"\u003eWilliam Optics Telescopes\u003c\/a\u003e.\u003c\/p\u003e","products":[{"product_id":"william-optics-ultra-cat-131-astrograph-ai-optimized-example","title":"William Optics Ultra-Cat 131 Astrograph","description":"\u003cp\u003eThe \u003cstrong\u003eWilliam Optics Ultra-Cat 131\u003c\/strong\u003e is a premium large-aperture astrograph designed for serious deep-sky astrophotographers who want a fast, flat-field imaging telescope for high-resolution wide-field work. It combines a 131mm aperture, 648mm focal length, fast f\/4.9 focal ratio, and advanced 5-element Petzval optical design for sharp, detailed astrophotography with large camera sensors.\u003c\/p\u003e\n\u003cp\u003eThis telescope is best suited for experienced astrophotographers using cooled astronomy cameras, full-frame cameras, APS-C cameras, Micro Four Thirds cameras, or medium-format imaging systems. It is a strong choice for imaging nebulae, galaxies, star fields, mosaics, and large deep-sky targets where edge-to-edge star quality and a large corrected image circle matter.\u003c\/p\u003e\n\u003ch2\u003eWho Is the William Optics Ultra-Cat 131 Best For?\u003c\/h2\u003e\n\u003cp\u003eThe Ultra-Cat 131 is ideal for advanced backyard imagers, serious deep-sky astrophotographers, and observatory users who want a high-performance imaging refractor\/astrograph with a large corrected field. It is especially well suited to imagers who use full-frame or larger camera sensors and want a telescope that can support demanding astrophotography setups.\u003c\/p\u003e\n\u003cp\u003eChoose the William Optics Ultra-Cat 131 if you want a premium 131mm f\/4.9 Petzval astrograph for deep-sky imaging with full-frame or medium-format cameras. It is designed to help astrophotographers capture wide-field objects with excellent correction, strong contrast, and sharp stars across a large imaging area.\u003c\/p\u003e\n\u003ch2\u003eWhy Choose the Ultra-Cat 131?\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eAdvanced 5-element Petzval optical design:\u003c\/strong\u003e Produces a flat imaging field without requiring a separate field flattener.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eLarge 60mm image circle:\u003c\/strong\u003e Supports full-frame and medium-format camera systems for expansive astrophotography compositions.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFast f\/4.9 focal ratio:\u003c\/strong\u003e Helps reduce exposure time compared with slower refractors while maintaining premium image quality.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e131mm aperture:\u003c\/strong\u003e Provides more light-gathering performance than smaller portable astrographs.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWIFD internal focuser:\u003c\/strong\u003e William Optics Internal Focuser Design helps maintain balance and stability in demanding imaging trains.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIntegrated sensor tilt correction:\u003c\/strong\u003e Helps fine-tune the imaging plane for sharper stars across the frame.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDesigned for serious imaging systems:\u003c\/strong\u003e A strong fit for cooled astronomy cameras, large sensors, filter wheels, and permanent or semi-permanent astrophotography setups.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eDeep-sky astrophotography\u003c\/li\u003e\n\u003cli\u003eWide-field nebula imaging\u003c\/li\u003e\n\u003cli\u003eGalaxy and star-field imaging\u003c\/li\u003e\n\u003cli\u003eFull-frame astrophotography\u003c\/li\u003e\n\u003cli\u003eMedium-format astrophotography\u003c\/li\u003e\n\u003cli\u003eAdvanced backyard imaging systems\u003c\/li\u003e\n\u003cli\u003ePermanent or semi-permanent observatory setups\u003c\/li\u003e\n\u003cli\u003eHigh-end imaging refractor\/astrograph systems\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003eCamera and Accessory Compatibility\u003c\/h2\u003e\n\u003cp\u003eThe Ultra-Cat 131 is designed for medium-format, full-frame, APS-C, and Micro Four Thirds camera systems. It includes M68, M54, and M48 camera adapter support and works with common camera mount ecosystems including Canon EF, Canon RF, Nikon F, Nikon Z, Sony E, Pentax K, Micro Four Thirds, and Fuji X.\u003c\/p\u003e\n\u003cp\u003eFor astrophotographers comparing large imaging refractors, the Ultra-Cat 131 is a strong option when the priority is a fast, corrected Petzval design with a large image circle and support for modern large-sensor cameras.\u003c\/p\u003e\n\u003ch2\u003eImportant Limitation\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Ultra-Cat 131 is an \u003cstrong\u003eastrophotography-only telescope\u003c\/strong\u003e. It is not intended for visual observing and should not be chosen by customers looking for eyepiece viewing, casual visual astronomy, or a beginner visual telescope. It should be recommended to customers whose primary goal is deep-sky imaging, not visual observation.\u003c\/p\u003e\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003ch3\u003eIs the William Optics Ultra-Cat 131 good for beginners?\u003c\/h3\u003e\n\u003cp\u003eThe Ultra-Cat 131 is best suited for experienced astrophotographers or serious imagers building a high-end deep-sky imaging system. Beginners can use it, but they should already be comfortable with equatorial mounts, guiding, camera spacing, focusing, and image processing.\u003c\/p\u003e\n\u003ch3\u003eCan the Ultra-Cat 131 be used for visual observing?\u003c\/h3\u003e\n\u003cp\u003eNo. The Ultra-Cat 131 is designed specifically for astrophotography and is not intended for visual observing with eyepieces.\u003c\/p\u003e\n\u003ch3\u003eWhat type of astrophotography is the Ultra-Cat 131 best for?\u003c\/h3\u003e\n\u003cp\u003eIt is best for deep-sky astrophotography, including nebulae, galaxies, star fields, mosaics, and large-format imaging with full-frame or medium-format cameras.\u003c\/p\u003e\n\u003ch3\u003eDoes the Ultra-Cat 131 need a field flattener?\u003c\/h3\u003e\n\u003cp\u003eNo. Its 5-element Petzval optical design is built to provide a flat image field without an additional flattener.\u003c\/p\u003e\n\u003ch3\u003eWhat camera formats work with the Ultra-Cat 131?\u003c\/h3\u003e\n\u003cp\u003eThe Ultra-Cat 131 supports medium-format, full-frame, APS-C, and Micro Four Thirds camera systems.\u003c\/p\u003e\n\u003ch2\u003eOur Recommendation\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Ultra-Cat 131 is best for experienced astrophotographers looking for a premium 131mm f\/4.9 Petzval astrograph for deep-sky imaging with full-frame or medium-format cameras. It is a strong choice for imagers who want a fast, corrected optical system with a large image circle and excellent support for advanced camera setups. This telescope is not intended for visual observing.\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/williamoptics.com\/cdn\/shop\/files\/Diagram_UltraCat-131_SD.jpg?v=1771925443\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/williamoptics.com\/cdn\/shop\/files\/Diagram_UltraCat-131_LA.jpg?v=1765448234\"\u003e\u003c\/p\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":53153887912047,"sku":"T-C-131BR-AI-DEMO","price":7559.99,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/ultra-cat-131-perspective-1.jpg?v=1779637072"},{"product_id":"william-optics-ultra-cat-56","title":"William Optics Ultra-Cat 56","description":"\u003cp\u003eThe \u003cstrong\u003eWilliam Optics Ultra-Cat 56\u003c\/strong\u003e is a compact 56mm f\/4.8 Petzval astrograph designed for portable wide-field deep-sky astrophotography. With a 269mm focal length, advanced 5-element Petzval optical design, and a 50mm image circle, it is built for astrophotographers who want a small, travel-friendly imaging telescope that can still support serious camera systems.\u003c\/p\u003e\n\n\u003cp\u003eThis telescope is designed for imaging large nebulae, star fields, Milky Way regions, mosaics, and wide deep-sky targets where a short focal length and corrected field are important. It is especially useful for travel imaging rigs, lightweight equatorial mounts, and astrophotographers who want a high-quality refractor\/astrograph that is easier to transport than larger aperture systems.\u003c\/p\u003e\n\n\u003ch2\u003eWho Is This Product Best For?\u003c\/h2\u003e\n\u003cp\u003eThe Ultra-Cat 56 is best for astrophotographers who want a premium compact astrograph for ultra-wide-field imaging. It is a strong fit for portable setups, travel-friendly astrophotography, and users working with full-frame, APS-C, or Micro Four Thirds cameras. It can also be used in advanced imaging setups where a short 269mm focal length is preferred.\u003c\/p\u003e\n\n\u003cp\u003eThis product is well suited to intermediate and experienced imagers who understand equatorial mounts, camera connection, focusing, guiding, and image processing. Beginners can use it as part of a planned astrophotography system, but it is not a visual observing telescope.\u003c\/p\u003e\n\n\u003ch2\u003eWhy Choose This Product?\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCompact 56mm aperture:\u003c\/strong\u003e Ideal for portable astrophotography and lightweight imaging systems.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFast f\/4.8 optics:\u003c\/strong\u003e Helps capture deep-sky objects efficiently with shorter exposure times.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e269mm focal length:\u003c\/strong\u003e Excellent for wide nebulae, star fields, large targets, and mosaic work.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e5-element Petzval design:\u003c\/strong\u003e Produces a flat image field without requiring a separate flattener.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e50mm image circle:\u003c\/strong\u003e Supports full-frame, APS-C, and Micro Four Thirds cameras, with medium-format compatibility noted by the manufacturer.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eWIFD internal focuser:\u003c\/strong\u003e Helps maintain balance and stable focusing for astrophotography.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eIntegrated tilt adjustment and rotator:\u003c\/strong\u003e Helps fine-tune camera alignment and image framing.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003ePortable deep-sky astrophotography\u003c\/li\u003e\n  \u003cli\u003eWide-field nebula imaging\u003c\/li\u003e\n  \u003cli\u003eMilky Way region imaging\u003c\/li\u003e\n  \u003cli\u003eLarge star fields and dark nebulae\u003c\/li\u003e\n  \u003cli\u003eTravel astrophotography setups\u003c\/li\u003e\n  \u003cli\u003eFull-frame, APS-C, and Micro Four Thirds imaging systems\u003c\/li\u003e\n  \u003cli\u003eLightweight mount and grab-and-go imaging rigs\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\n\u003cp\u003eThe Ultra-Cat 56 includes camera adapter support for M54 and M48 connections and is designed for common camera mount ecosystems including Canon EF, Canon RF, Nikon F, Nikon Z, Sony E, Pentax K, Micro Four Thirds, and Fuji X. It is compatible with electronic automatic focusing systems and uses a WIFD rack-and-pinion focuser for stable, precise imaging.\u003c\/p\u003e\n\n\u003cp\u003eThe telescope uses a Vixen to Arca-Swiss style dovetail arrangement, making it well suited to compact astrophotography setups. As with any imaging telescope, customers should confirm camera adapter needs, focusing accessories, guiding setup, and mount capacity before purchase.\u003c\/p\u003e\n\n\u003ch2\u003eImportant Limitations\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Ultra-Cat 56 is an \u003cstrong\u003eastrophotography-only telescope\u003c\/strong\u003e. It is not intended for visual observing and should not be recommended to customers looking for eyepiece viewing, casual visual astronomy, or a general beginner telescope. It is best selected by customers whose primary goal is wide-field imaging.\u003c\/p\u003e\n\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003ch3\u003eIs the William Optics Ultra-Cat 56 good for beginners?\u003c\/h3\u003e\n\u003cp\u003eIt can be used by a beginner who is building a dedicated astrophotography system, but it is best for users who already understand mounts, cameras, focusing, and image capture. It is not a beginner visual telescope.\u003c\/p\u003e\n\n\u003ch3\u003eWhat type of astrophotography is the Ultra-Cat 56 best for?\u003c\/h3\u003e\n\u003cp\u003eThe Ultra-Cat 56 is best for portable wide-field deep-sky imaging, including large nebulae, star fields, Milky Way regions, and mosaic projects.\u003c\/p\u003e\n\n\u003ch3\u003eDoes the Ultra-Cat 56 need a field flattener?\u003c\/h3\u003e\n\u003cp\u003eNo. Its 5-element Petzval optical design is built to provide a flat field without a separate field flattener.\u003c\/p\u003e\n\n\u003ch3\u003eWhat camera formats work with the Ultra-Cat 56?\u003c\/h3\u003e\n\u003cp\u003eThe Ultra-Cat 56 is optimized for full-frame, APS-C, and Micro Four Thirds sensors, with manufacturer-noted compatibility for medium-format imaging setups.\u003c\/p\u003e\n\n\u003ch3\u003eCan the Ultra-Cat 56 be used for visual observing?\u003c\/h3\u003e\n\u003cp\u003eNo. The Ultra-Cat 56 is designed specifically for astrophotography and does not support visual observing.\u003c\/p\u003e\n\n\u003ch2\u003eOur Recommendation\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Ultra-Cat 56 is a strong choice for astrophotographers who want a premium, compact, wide-field Petzval astrograph for portable deep-sky imaging. Choose it for travel-friendly astrophotography, large nebulae, star fields, and full-frame or APS-C imaging setups. Do not choose this telescope if your main goal is visual observing.\u003c\/p\u003e\n\n\u003ch2\u003eOptical Diagram Reports\u003c\/h2\u003e\n\u003cp\u003eThe following optical report graphics are provided for customers who want to review the telescope’s spot diagram, longitudinal aberration, MTF, and relative illumination performance.\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-56-spot-diagram.jpg?v=1779641844\" alt=\"William Optics Ultra-Cat 56 spot diagram optical report\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-56-longitudinal-aberration.jpg?v=1779641851\" alt=\"William Optics Ultra-Cat 56 longitudinal aberration optical report\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-56-mtf-diagram.jpg?v=1779641857\" alt=\"William Optics Ultra-Cat 56 MTF optical report\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-56-relative-illumination.jpg?v=1779641862\" alt=\"William Optics Ultra-Cat 56 relative illumination optical report\"\u003e\u003c\/p\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":53153910128751,"sku":"T-C-56BR","price":1957.2,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-56-perspective-1.jpg?v=1779641709"},{"product_id":"william-optics-ultra-cat-76","title":"William Optics Ultra-Cat 76","description":"\u003cp\u003eThe \u003cstrong\u003eWilliam Optics Ultra-Cat 76\u003c\/strong\u003e is a high-performance 76mm f\/4.8 Petzval astrograph designed for wide-field deep-sky astrophotography. With a 365mm focal length, 5-element advanced Petzval optical system, and 50mm image circle, it is built for sharp flat-field imaging with full-frame, APS-C, and Micro Four Thirds cameras.\u003c\/p\u003e\n\u003ch2\u003eWho Is This Product Best For?\u003c\/h2\u003e\u003cp\u003eBest for astrophotographers who want a compact but serious imaging refractor for nebulae, star fields, large deep-sky targets, travel imaging, and full-frame camera setups.\u003c\/p\u003e\n\u003ch2\u003eWhy Choose This Product?\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e5-element Petzval optics:\u003c\/strong\u003e Flat imaging field with no separate flattener required.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e50mm image circle:\u003c\/strong\u003e Supports full-frame, APS-C, and Micro Four Thirds cameras.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFast f\/4.8 focal ratio:\u003c\/strong\u003e Helps capture deep-sky targets efficiently.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWIFD focuser:\u003c\/strong\u003e Stable internal focusing with EAF compatibility.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eWide-field deep-sky astrophotography\u003c\/li\u003e\n\u003cli\u003eNebula and star-field imaging\u003c\/li\u003e\n\u003cli\u003eFull-frame astrophotography\u003c\/li\u003e\n\u003cli\u003ePortable imaging systems\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe Ultra-Cat 76 includes M54 and M48 camera adapters and supports common camera mount ecosystems including Canon EF, Canon RF, Nikon F, Nikon Z, Sony E, Pentax K, Micro Four Thirds, and Fuji X.\u003c\/p\u003e\n\u003ch2\u003eImportant Limitations\u003c\/h2\u003e\u003cp\u003eThis telescope is designed specifically for astrophotography and does not support visual observation.\u003c\/p\u003e\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003ch3\u003eDoes the Ultra-Cat 76 need a flattener?\u003c\/h3\u003e\u003cp\u003eNo. The Petzval optical design provides a flat field without a separate field flattener.\u003c\/p\u003e\u003ch3\u003eWhat camera formats work with the Ultra-Cat 76?\u003c\/h3\u003e\u003cp\u003eIt supports full-frame, APS-C, and Micro Four Thirds cameras, with medium-format compatibility noted by William Optics.\u003c\/p\u003e\u003ch3\u003eCan it be used visually?\u003c\/h3\u003e\u003cp\u003eNo. It is an astrophotography-only telescope.\u003c\/p\u003e\n\u003ch2\u003eOur Recommendation\u003c\/h2\u003e\u003cp\u003eThe William Optics Ultra-Cat 76 is a strong choice for astrophotographers who want a premium compact 76mm f\/4.8 Petzval astrograph for full-frame wide-field deep-sky imaging. Choose it for nebulae, star fields, and portable imaging rigs. Do not choose it for visual observing.\u003c\/p\u003e\n\u003ch2\u003eOptical Diagram Reports\u003c\/h2\u003e\u003cp\u003eThe following optical report graphics are provided for customers reviewing spot diagram, longitudinal aberration, MTF, and relative illumination performance.\u003c\/p\u003e\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-76-spot-diagram.jpg?v=1779642249\" alt=\"William Optics Ultra-Cat 76 spot diagram optical report\"\u003e\u003c\/p\u003e\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-76-longitudinal-aberration.jpg?v=1779642256\" alt=\"William Optics Ultra-Cat 76 longitudinal aberration optical report\"\u003e\u003c\/p\u003e\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-76-mtf-diagram.jpg?v=1779642262\" alt=\"William Optics Ultra-Cat 76 MTF optical report\"\u003e\u003c\/p\u003e\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-76-relative-illumination.jpg?v=1779642269\" alt=\"William Optics Ultra-Cat 76 relative illumination optical report\"\u003e\u003c\/p\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":53153911996527,"sku":"T-C-76BR","price":3033.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-76-perspective-1.jpg?v=1779642198"},{"product_id":"william-optics-ultra-cat-108-wifd","title":"William Optics Ultra-Cat 108 WIFD","description":"\u003cp\u003eThe \u003cstrong\u003eWilliam Optics Ultra-Cat 108 WIFD\u003c\/strong\u003e is a premium 108mm f\/4.8 Petzval astrograph designed for serious deep-sky astrophotography with full-frame and medium-format camera systems. With a 518mm focal length, 60mm image circle, and advanced 5-element optical design, it is built for imagers who want high-end correction, fast optics, and a large imaging field.\u003c\/p\u003e\n\n\u003cp\u003eThis telescope is designed for nebulae, galaxies, star fields, mosaics, and large-format deep-sky imaging where sharp stars across the frame are important. Its Petzval design eliminates the need for a separate field flattener, simplifying the imaging train for advanced astrophotography setups.\u003c\/p\u003e\n\n\u003ch2\u003eWho Is This Product Best For?\u003c\/h2\u003e\n\u003cp\u003eThe Ultra-Cat 108 WIFD is best for experienced astrophotographers, observatory users, and advanced backyard imagers who want a premium large-sensor astrograph. It is especially well suited to full-frame and medium-format cameras, cooled astronomy cameras, filter wheels, electronic focusers, and semi-permanent imaging systems.\u003c\/p\u003e\n\n\u003ch2\u003eWhy Choose This Product?\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003e108mm aperture:\u003c\/strong\u003e Strong light-gathering performance for serious deep-sky imaging.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFast f\/4.8 focal ratio:\u003c\/strong\u003e Helps reduce exposure time compared with slower refractors.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e5-element Petzval optics:\u003c\/strong\u003e Produces a corrected flat field without requiring a separate flattener.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e60mm image circle:\u003c\/strong\u003e Supports full-frame and medium-format imaging systems.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eWIFD internal focuser:\u003c\/strong\u003e Helps maintain stability with heavy cameras and accessories.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eIntegrated tilt corrector and rotator:\u003c\/strong\u003e Helps optimize framing and corner-to-corner sharpness.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003eDeep-sky astrophotography\u003c\/li\u003e\n  \u003cli\u003eFull-frame and medium-format astrophotography\u003c\/li\u003e\n  \u003cli\u003eNebula, galaxy, and star-field imaging\u003c\/li\u003e\n  \u003cli\u003eWide-field and mid-focal-length imaging\u003c\/li\u003e\n  \u003cli\u003eAdvanced backyard and observatory imaging systems\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\n\u003cp\u003eThe Ultra-Cat 108 WIFD includes M68, M54, and M48 camera adapter support and works with common camera mount ecosystems including Canon EF, Canon RF, Nikon F, Nikon Z, Sony E, Pentax K, Micro Four Thirds, and Fuji X. It is compatible with electronic automatic focusing systems and is designed for demanding imaging trains.\u003c\/p\u003e\n\n\u003ch2\u003eImportant Limitations\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Ultra-Cat 108 WIFD is an astrophotography-focused telescope. It should be recommended to customers building a serious imaging system rather than customers looking for a simple visual observing telescope.\u003c\/p\u003e\n\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003ch3\u003eIs the Ultra-Cat 108 WIFD good for beginners?\u003c\/h3\u003e\n\u003cp\u003eIt is best suited to experienced astrophotographers or serious beginners who are building a dedicated imaging system and understand mounts, cameras, guiding, focusing, and image processing.\u003c\/p\u003e\n\u003ch3\u003eWhat type of astrophotography is it best for?\u003c\/h3\u003e\n\u003cp\u003eIt is best for deep-sky astrophotography, including nebulae, galaxies, star fields, mosaics, and full-frame or medium-format imaging.\u003c\/p\u003e\n\u003ch3\u003eDoes it need a field flattener?\u003c\/h3\u003e\n\u003cp\u003eNo. The 5-element Petzval design provides a flat field without a separate field flattener.\u003c\/p\u003e\n\u003ch3\u003eWhat camera formats work with it?\u003c\/h3\u003e\n\u003cp\u003eThe Ultra-Cat 108 WIFD supports medium-format, full-frame, APS-C, and Micro Four Thirds imaging systems.\u003c\/p\u003e\n\n\u003ch2\u003eOur Recommendation\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Ultra-Cat 108 WIFD is a strong choice for astrophotographers who want a premium 108mm f\/4.8 Petzval astrograph with a large 60mm image circle for full-frame or medium-format deep-sky imaging. Choose it when image quality, large-sensor support, and a simplified flat-field optical system are priorities.\u003c\/p\u003e\n\n\u003ch2\u003eOptical Diagram Reports\u003c\/h2\u003e\n\u003cp\u003eThe following optical report graphic is provided for customers reviewing the Ultra-Cat 108 WIFD optical design and field performance.\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/Diagram_UltraCat-108_1__47751.jpg?v=1766570880\" alt=\"William Optics Ultra-Cat 108 WIFD optical diagram report\"\u003e\u003c\/p\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":53153927954543,"sku":"L-C108-WIFD","price":5517.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-cat-108-perspective-1.jpg?v=1779643045"},{"product_id":"william-optics-ultra-flat-132-0-79x-reducer","title":"William Optics Ultra Flat 132 0.79x Reducer","description":"\u003cp\u003eThe \u003cstrong\u003eWilliam Optics Ultra Flat 132\u003c\/strong\u003e is a 0.79x reducer-flattener built as the matched corrector for the William Optics Fluorostar 132. It is a three-element, three-group design with a 137.5 mm optical length, an M92 x 1 telescope-side thread, and an M54 x 0.75 camera-side thread. On the Fluorostar 132 it delivers a corrected image circle of 43.2 mm at 55 mm of backfocus, and it weighs 1096 g.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThis is a good match if you already own — or are ordering — a Fluorostar 132 and intend to image with it. It is the corrector that pairs with that telescope, so the decision is less about choosing between flatteners and more about whether you want the 0.79x reduced configuration rather than the native focal length.\u003c\/p\u003e\n\u003cp\u003eIt suits a deep-sky imaging rig running a full-frame or APS-C camera. Setting it up is refreshingly direct: the supplied PVC gasket sets the 55 mm spacing on the Fluorostar 132, so there is no adjustment ring to dial in and no trial-and-error before your first session.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003e0.79x reduction:\u003c\/strong\u003e multiplies the native focal length and focal ratio of the Fluorostar 132 by 0.79. Because focal ratio scales linearly and light-gathering per unit area scales with its square, the reduced configuration collects roughly 1.6x more light per unit time (1 \/ 0.79²) than the native configuration.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e3 groups, 3 elements:\u003c\/strong\u003e a three-element corrector group, each element air-spaced as its own group.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e137.5 mm optical length:\u003c\/strong\u003e the corrector's own contribution to the imaging train, before your camera spacing. This is a long assembly — nearly twice the optical length of the Ultra Flat 156 — so account for it when planning the train.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eM92 x 1 x 6.5 mm telescope thread:\u003c\/strong\u003e threads directly to the Fluorostar 132 focuser drawtube — no push-fit, no adapter.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eM54 x 0.75 x 4 mm camera thread:\u003c\/strong\u003e the camera-side interface from which 55 mm of backfocus is measured.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e43.2 mm corrected image circle:\u003c\/strong\u003e on the Fluorostar 132, covering a full-frame sensor (43.3 mm diagonal).\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e1096 g:\u003c\/strong\u003e plan your focuser load and any rotator or filter wheel accordingly.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eOptical \/ Mechanical Design\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eA reducer-flattener does two jobs at once. Fast refractors of this aperture project a field that is curved rather than flat — stars that focus sharply at the centre fall progressively out of focus toward the edges, because the natural focal surface is a shallow bowl rather than a plane, and your sensor is a plane. The corrector group flattens that surface onto the sensor. The 0.79x element compresses the image scale at the same time, shortening the effective focal length and lowering the focal ratio, which shortens the exposure needed for a given signal.\u003c\/p\u003e\n\u003cp\u003eThe three-element, three-group construction is what allows both corrections to be made without reintroducing colour error at the edges. The consequence is that spacing tolerance drives corner star quality: the design is computed for one specific separation between the M54 thread and your sensor. Under-space it and corner stars elongate radially; over-space it and they elongate tangentially. The centre of the frame looks fine either way, which is why the corners are the place to check your work — and why the supplied gasket, which sets the spacing for you on the Fluorostar 132, is worth using as directed.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003eDeep-sky astrophotography with a Fluorostar 132 in its reduced 0.79x configuration\u003c\/li\u003e\n  \u003cli\u003eFull-frame and APS-C cooled camera imaging where a flat field to the corners is required\u003c\/li\u003e\n  \u003cli\u003eWider framing than the Fluorostar 132 delivers natively — larger nebulae, extended galaxy fields\u003c\/li\u003e\n  \u003cli\u003eShorter sub-exposures at the same signal level, useful under mediocre guiding or shorter imaging windows\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eWilliam Optics publishes this corrector as the match for the \u003cstrong\u003eFluorostar 132\u003c\/strong\u003e. On the Fluorostar 132 it requires \u003cstrong\u003e55 mm of backfocus\u003c\/strong\u003e and needs \u003cstrong\u003eno adjustment\u003c\/strong\u003e — set the spacing with the supplied PVC gasket as directed. Backfocus is measured from the M54 x 0.75 camera-side thread to your sensor plane, and the total must account for every component in the train: filter drawer or filter wheel, off-axis guider, rotator, and the camera's own sensor-to-flange distance.\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/Flattener_back_focus-04.jpg?v=1784224665\" alt=\"William Optics flattener back focus diagram showing the 55 mm spacing measured from the M54 camera-side thread of the Ultra Flat 132\" style=\"max-width:100%;height:auto;\"\u003e\u003c\/p\u003e\n\u003cp\u003eThe telescope side is \u003cstrong\u003eM92 x 1\u003c\/strong\u003e, threading straight to the Fluorostar 132. The camera side is \u003cstrong\u003eM54 x 0.75\u003c\/strong\u003e; most cooled astronomy cameras present an M48 or T2 interface, so confirm what your specific camera and filter hardware need to reach M54 and budget that adapter's optical length within the 55 mm figure — not on top of it. If you are not sure what your train adds up to, send us your camera and filter setup and we will work it out with you.\u003c\/p\u003e\n\u003cp\u003eWilliam Optics also publishes a back focus adjustment guide for the Ultra Flat series. If you are matching a different William Optics telescope, contact us before ordering — the Fluorostar 156 uses the \u003ca href=\"\/products\/william-optics-ultra-flat-156-0-79x-reducer\"\u003eUltra Flat 156\u003c\/a\u003e, and the Fluorostar 132 is also listed as compatible with the FLAT 68III, FLAT 7A, and FLAT 8 correctors at their own respective reduction factors.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eGood to Know Before You Order\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eImaging accessory:\u003c\/strong\u003e this is an optical corrector for astrophotography. It has no application in a visual train with an eyepiece.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMatched to the Fluorostar 132:\u003c\/strong\u003e the 43.2 mm image circle and 55 mm backfocus are the figures William Optics publishes for that telescope. Other William Optics refractors pair with their own correctors — if you are matching a different model, get in touch and we will confirm the right one.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eSpacing matters:\u003c\/strong\u003e corner star shape depends on hitting the 55 mm backfocus. On the Fluorostar 132 the supplied PVC gasket sets it, with no further adjustment needed.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCamera-side adapter:\u003c\/strong\u003e the corrector presents M54 x 0.75, while most cooled cameras and filter wheels use M48 or T2. An adapter is usually needed and is sold separately — its optical length counts toward the 55 mm, not on top of it. We can help you identify the right one for your camera.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eSensor coverage:\u003c\/strong\u003e the 43.2 mm corrected circle on the Fluorostar 132 covers a full-frame sensor (43.3 mm diagonal). William Optics lists this corrector for APS-C and full frame.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eOptical length:\u003c\/strong\u003e at 137.5 mm this is a long corrector — worth checking against your focuser travel and any dew shield or clearance constraints.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eFrequently Asked Questions\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003eWhat telescope does this work with?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eWilliam Optics lists it as the matched corrector for the Fluorostar 132, with a 43.2 mm image circle at 55 mm backfocus and no adjustment required.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs it difficult to set up?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo. On the Fluorostar 132 it threads straight to the M92 drawtube and the supplied PVC gasket sets the 55 mm spacing for you — there is no adjustment ring to dial in and no trial-and-error. The main thing to get right is the total distance from the M54 thread to your sensor, and we are happy to check that with you before you order.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan I use it for visual observing?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo. It is a reducer-flattener for imaging. It has no place in a visual train.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat backfocus do I need?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e55 mm, measured from the M54 x 0.75 camera-side thread to your sensor plane. Use the supplied PVC gasket as directed; the Fluorostar 132 pairing requires no further adjustment.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWill it cover a full-frame sensor?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eYes. The published corrected image circle on the Fluorostar 132 is 43.2 mm, and a full-frame sensor has a 43.3 mm diagonal — so the corrected field is sized to full frame. William Optics lists the camera format as APS-C and full frame.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat is the difference between this and the Ultra Flat 156?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eBoth are 0.79x correctors, but they are computed for different telescopes: the Ultra Flat 132 is matched to the Fluorostar 132 and the Ultra Flat 156 to the Fluorostar 156. They also differ mechanically — 137.5 mm optical length here versus 75.5 mm on the 156. They are not interchangeable.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDo I need any additional adapters?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eVery likely on the camera side. The corrector presents M54 x 0.75; most cooled cameras and filter wheels use M48 or T2. Any adapter you add consumes part of the 55 mm backfocus budget. Tell us what camera you are running and we will point you to the right adapter.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes it change my focal length?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eYes — it multiplies the native focal length and focal ratio of the Fluorostar 132 by 0.79, which widens the field and shortens the exposure needed for a given signal.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eIn short: the matched 0.79x reducer-flattener for the Fluorostar 132. It threads on at M92, presents M54 to your camera, needs 55 mm of backfocus with the supplied gasket, and delivers a flat 43.2 mm field sized to a full-frame sensor. Spacing is the one figure worth measuring carefully — the corners are where it shows.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eOptical Diagram Reports\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eWilliam Optics publishes measured diagram reports for the Ultra Flat 132 on the Fluorostar 132. These show the corrected performance across the field rather than a marketing claim about it.\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/FLT-132_Flat132-Diagram-1.jpg?v=1784224665\" alt=\"William Optics Ultra Flat 132 optical test diagram report for the Fluorostar 132 imaging system\" style=\"max-width:100%;height:auto;\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/FLT-132_Flat132-Diagram-2.jpg?v=1784224665\" alt=\"William Optics Ultra Flat 132 spot diagram report showing corrected star images across the 43.2 mm image circle\" style=\"max-width:100%;height:auto;\"\u003e\u003c\/p\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":53154243149935,"sku":"P-FLAT132","price":1474.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-flat-132.jpg?v=1779654809"},{"product_id":"william-optics-ultra-flat-156-0-79x-reducer","title":"William Optics Ultra Flat 156 0.79x Reducer","description":"\u003cp\u003eThe \u003cstrong\u003eWilliam Optics Ultra Flat 156\u003c\/strong\u003e is a 0.79x reducer-flattener built as the matched corrector for the William Optics Fluorostar 156. It is a three-element, three-group design with a 75.5 mm optical length, an M92 x 1 telescope-side thread, and an M54 x 0.75 camera-side thread. On the Fluorostar 156 it delivers a corrected image circle of 43.2 mm at 55 mm of backfocus, and it weighs 1202 g.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eWho It's For\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eThis is a good match if you already own — or are ordering — a Fluorostar 156 and intend to image with it. It is the corrector that pairs with that telescope, so the decision is less about choosing between flatteners and more about whether you want the 0.79x reduced configuration rather than the native focal length.\u003c\/p\u003e\n\u003cp\u003eIt suits a permanent or semi-permanent deep-sky imaging rig running a full-frame or APS-C camera. At 1202 g on top of a 156 mm refractor, this is not a travel-weight combination. Setting it up is refreshingly direct: the supplied PVC gasket sets the 55 mm spacing on the Fluorostar 156, so there is no trial-and-error to work through before your first session.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eKey Features \u0026amp; Design\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003e0.79x reduction:\u003c\/strong\u003e multiplies the native focal length and focal ratio of the Fluorostar 156 by 0.79. Because focal ratio scales linearly and light-gathering per unit area scales with its square, the reduced configuration collects roughly 1.6x more light per unit time (1 \/ 0.79²) than the native configuration.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e3 groups, 3 elements:\u003c\/strong\u003e a three-element corrector group, each element air-spaced as its own group.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e75.5 mm optical length:\u003c\/strong\u003e the corrector's own contribution to the imaging train, before your camera spacing.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eM92 x 1 x 6.5 mm telescope thread:\u003c\/strong\u003e threads directly to the Fluorostar 156 focuser drawtube — no push-fit, no adapter.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eM54 x 0.75 x 4 mm camera thread:\u003c\/strong\u003e the camera-side interface from which 55 mm of backfocus is measured.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e43.2 mm corrected image circle:\u003c\/strong\u003e on the Fluorostar 156, covering a full-frame sensor (43.3 mm diagonal).\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e1202 g:\u003c\/strong\u003e plan your focuser load and any rotator or filter wheel accordingly.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eOptical \/ Mechanical Design\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eA reducer-flattener does two jobs at once. Fast refractors of this aperture project a field that is curved rather than flat — stars that focus sharply at the centre fall progressively out of focus toward the edges, because the natural focal surface is a shallow bowl rather than a plane, and your sensor is a plane. The corrector group flattens that surface onto the sensor. The 0.79x element compresses the image scale at the same time, shortening the effective focal length and lowering the focal ratio, which shortens the exposure needed for a given signal.\u003c\/p\u003e\n\u003cp\u003eThe three-element, three-group construction is what allows both corrections to be made without reintroducing colour error at the edges. The consequence is that spacing tolerance drives corner star quality: the design is computed for one specific separation between the M54 thread and your sensor. Under-space it and corner stars elongate radially; over-space it and they elongate tangentially. The centre of the frame looks fine either way, which is why the corners are the place to check your work — and why the supplied gasket, which sets the spacing for you on the Fluorostar 156, is worth using as directed.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eRecommended Uses\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003eDeep-sky astrophotography with a Fluorostar 156 in its reduced 0.79x configuration\u003c\/li\u003e\n  \u003cli\u003eFull-frame and APS-C cooled camera imaging where a flat field to the corners is required\u003c\/li\u003e\n  \u003cli\u003eWider framing than the Fluorostar 156 delivers natively — larger nebulae, extended galaxy fields\u003c\/li\u003e\n  \u003cli\u003eShorter sub-exposures at the same signal level, useful under mediocre guiding or shorter imaging windows\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eCompatibility and Accessory Notes\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eWilliam Optics publishes this corrector as the match for the \u003cstrong\u003eFluorostar 156\u003c\/strong\u003e. On the Fluorostar 156 it requires \u003cstrong\u003e55 mm of backfocus\u003c\/strong\u003e and needs \u003cstrong\u003eno adjustment\u003c\/strong\u003e — set the spacing with the supplied PVC gasket as directed. Backfocus is measured from the M54 x 0.75 camera-side thread to your sensor plane, and the total must account for every component in the train: filter drawer or filter wheel, off-axis guider, rotator, and the camera's own sensor-to-flange distance.\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/Flattener_back_focus-02.jpg?v=1784220246\" alt=\"William Optics flattener back focus diagram showing the 55 mm spacing measured from the M54 camera-side thread of the Ultra Flat 156\" style=\"max-width:100%;height:auto;\"\u003e\u003c\/p\u003e\n\u003cp\u003eThe telescope side is \u003cstrong\u003eM92 x 1\u003c\/strong\u003e, threading straight to the Fluorostar 156. The camera side is \u003cstrong\u003eM54 x 0.75\u003c\/strong\u003e; most cooled astronomy cameras present an M48 or T2 interface, so confirm what your specific camera and filter hardware need to reach M54 and budget that adapter's optical length within the 55 mm figure — not on top of it. If you are not sure what your train adds up to, send us your camera and filter setup and we will work it out with you.\u003c\/p\u003e\n\u003cp\u003eWilliam Optics also publishes a back focus adjustment guide for the Ultra Flat series. If you are unsure which corrector matches a different William Optics telescope, contact us before ordering — the Fluorostar 132 uses the \u003ca href=\"\/products\/william-optics-ultra-flat-132-0-79x-reducer\"\u003eUltra Flat 132\u003c\/a\u003e, and the Fluorostar 156 is also listed as compatible with the FLAT 68III, FLAT 7A, and FLAT 8 correctors at their own respective reduction factors.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eGood to Know Before You Order\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eImaging accessory:\u003c\/strong\u003e this is an optical corrector for astrophotography. It has no application in a visual train with an eyepiece.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMatched to the Fluorostar 156:\u003c\/strong\u003e the 43.2 mm image circle and 55 mm backfocus are the figures William Optics publishes for that telescope. Other William Optics refractors pair with their own correctors — if you are matching a different model, get in touch and we will confirm the right one.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eSpacing matters:\u003c\/strong\u003e corner star shape depends on hitting the 55 mm backfocus. On the Fluorostar 156 the supplied PVC gasket sets it, with no further adjustment needed.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCamera-side adapter:\u003c\/strong\u003e the corrector presents M54 x 0.75, while most cooled cameras and filter wheels use M48 or T2. An adapter is usually needed and is sold separately — its optical length counts toward the 55 mm, not on top of it. We can help you identify the right one for your camera.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eSensor coverage:\u003c\/strong\u003e the 43.2 mm corrected circle on the Fluorostar 156 covers a full-frame sensor (43.3 mm diagonal). Medium-format sensors are larger than that circle.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eWeight:\u003c\/strong\u003e at 1202 g it is worth accounting for in your focuser load and mount payload once the camera is attached.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003e\u003cstrong\u003eFrequently Asked Questions\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003eWhat telescope does this work with?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eWilliam Optics lists it as the matched corrector for the Fluorostar 156, with a 43.2 mm image circle at 55 mm backfocus and no adjustment required.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIs it difficult to set up?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo. On the Fluorostar 156 it threads straight to the M92 drawtube and the supplied PVC gasket sets the 55 mm spacing for you — there is no adjustment ring to dial in and no trial-and-error. The main thing to get right is the total distance from the M54 thread to your sensor, and we are happy to check that with you before you order.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCan I use it for visual observing?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eNo. It is a reducer-flattener for imaging. It has no place in a visual train.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat backfocus do I need?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e55 mm, measured from the M54 x 0.75 camera-side thread to your sensor plane. Use the supplied PVC gasket as directed; the Fluorostar 156 pairing requires no further adjustment.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWill it cover a full-frame sensor?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe published corrected image circle on the Fluorostar 156 is 43.2 mm. A full-frame sensor has a 43.3 mm diagonal, so the corrected field is sized to full frame. Larger medium-format sensors are outside that circle.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWhat is the difference between this and the Ultra Flat 132?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eBoth are 0.79x correctors, but they are computed for different telescopes: the Ultra Flat 132 is matched to the Fluorostar 132 and the Ultra Flat 156 to the Fluorostar 156. They are not interchangeable.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDo I need any additional adapters?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eVery likely on the camera side. The corrector presents M54 x 0.75; most cooled cameras and filter wheels use M48 or T2. Any adapter you add consumes part of the 55 mm backfocus budget. Tell us what camera you are running and we will point you to the right adapter.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eDoes it change my focal length?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eYes — it multiplies the native focal length and focal ratio of the Fluorostar 156 by 0.79, which widens the field and shortens the exposure needed for a given signal.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eBottom Line\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eIn short: the matched 0.79x reducer-flattener for the Fluorostar 156. It threads on at M92, presents M54 to your camera, needs 55 mm of backfocus with the supplied gasket, and delivers a flat 43.2 mm field sized to a full-frame sensor. Spacing is the one figure worth measuring carefully — the corners are where it shows.\u003c\/p\u003e\n\n\u003ch3\u003e\u003cstrong\u003eOptical Diagram Reports\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cp\u003eWilliam Optics publishes measured diagram reports for the Ultra Flat 156 on the Fluorostar 156. These show the corrected performance across the field rather than a marketing claim about it.\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/FLT-156_Flat156-Diagram-1.jpg?v=1784220248\" alt=\"William Optics Ultra Flat 156 optical test diagram report for the Fluorostar 156 imaging system\" style=\"max-width:100%;height:auto;\"\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/FLT-156_Flat156-Diagram-2.jpg?v=1784220246\" alt=\"William Optics Ultra Flat 156 spot diagram report showing corrected star images across the 43.2 mm image circle\" style=\"max-width:100%;height:auto;\"\u003e\u003c\/p\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":53154243870831,"sku":"P-FLAT156","price":1474.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/william-optics-ultra-flat-156.jpg?v=1779654823"}],"url":"https:\/\/ontariotelescope.com\/collections\/wo-ultracat.oembed","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}