{"product_id":"william-optics-t-c-131br","title":"William Optics Ultra-Cat 131 f\/4.9 Petzval Astrograph","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003e131mm Aperture\u003c\/li\u003e\n\u003cli\u003e648mm Focal Length (f\/4.9)\u003c\/li\u003e\n\u003cli\u003e5-Element Advanced Petzval Optical Design\u003c\/li\u003e\n\u003cli\u003e60mm Flat-Field Image Circle\u003c\/li\u003e\n\u003cli\u003ePatented WIFD Internal Focuser\u003c\/li\u003e\n\u003cli\u003e13.97 kg Total Weight\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\u003eWilliam Optics Ultra-Cat 131 f\/4.9 Petzval Astrograph\u003c\/h2\u003e\n\u003cp\u003eThe William Optics Ultra-Cat 131 combines a massive 131mm aperture with a fast f\/4.9 focal ratio, delivering exceptional light-gathering power for serious deep-sky imagers. Its 5-element Petzval optical system produces a completely flat 60mm image circle without an external flattener, fully illuminating medium-format sensors. With a native 648mm focal length and a total weight of 13.97 kg, this astrograph is engineered for capturing vast, high-resolution celestial portraits with pinpoint stars from edge to edge.\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\u003eFlagship 131mm Petzval Optics: A 60mm Flat-Field Image Circle\u003c\/h3\u003e\n\u003cp\u003eThe optical core of the Ultra-Cat 131 is an advanced 5-element Petzval design featuring two Super ED elements, one ED element, and one Lanthanum element. This sophisticated configuration eliminates the need for a separate field flattener, correcting for field curvature and chromatic aberration natively to produce a perfectly flat 60mm image circle. This allows you to place your medium-format or full-frame sensor anywhere within the field and achieve sharp, perfectly formed stars.\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\u003ePatented WIFD Focuser: 20mm of Zero-Shift Internal Focus\u003c\/h3\u003e\n\u003cp\u003eWilliam Optics' patented WIFD (William Optics Internal Focuser Design) provides 20mm of precise focus travel without any external drawtube movement. By moving the optics internally, the system completely avoids the balance shifts, flexure, and vignetting common with traditional focusers. This robust design maintains perfect optical alignment and rigidity, even when loaded with heavy imaging trains, and is fully compatible with electronic auto-focusers (EAF).\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\u003eObservatory-Grade Build: 13.97 kg of Stability and Broad Camera Support\u003c\/h3\u003e\n\u003cp\u003eEngineered for thermal stability and mechanical rigidity, the Ultra-Cat 131 weighs in at a substantial 13.97 kg with all accessories. It ships with robust mounting rings and a Losmandy-style dovetail plate for secure attachment to observatory-class mounts. The package includes a comprehensive set of M68, M54, and M48 camera adapters and a Sensor Tilt Xterminator (STX-R), ensuring you can achieve perfect sensor alignment with virtually any Canon, Nikon, Sony, or dedicated astronomy camera.\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\u003eUltra-Cat 131 vs. 106mm Refractors: The Aperture Advantage\u003c\/h3\u003e\n\u003cp\u003eWhen compared to premium 106mm refractors, the Ultra-Cat 131's primary advantage is its sheer light-gathering power and field coverage. The difference in aperture provides a significant boost in signal for faint deep-sky targets.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eLight Gathering:\u003c\/strong\u003e The 131mm objective collects over 50% more light than a 106mm objective, allowing you to capture fainter details in the same exposure time or significantly shorten your sub-exposures.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eImage Circle:\u003c\/strong\u003e The Ultra-Cat's native 60mm flat image circle dwarfs the 44mm circle typical of full-frame-corrected 106mm scopes, providing superior illumination and vignetting control for large sensors.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIntegrated Design:\u003c\/strong\u003e While many refractors require a separate, carefully spaced flattener, the Ultra-Cat 131's Petzval design is inherently corrected, simplifying your imaging train and eliminating a potential source of tilt and error.\u003c\/li\u003e\n\u003c\/ul\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\"\u003eHow does the Ultra-Cat 131's 60mm image circle benefit imaging the Andromeda Galaxy (M31) with a full-frame camera?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe Andromeda Galaxy is a massive target. The Ultra-Cat 131's 648mm focal length and 60mm image circle allow you to frame the entire galaxy, including its faint outer arms and satellite galaxies M32 and M110, on a full-frame sensor with excellent illumination and sharp stars right to the corners of the frame. A smaller image circle would introduce significant vignetting, darkening the edges and losing crucial detail.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat class of mount is required for the 13.97 kg total weight of the Ultra-Cat 131?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eWith a total weight of 13.97 kg (30.8 lbs), plus the weight of your camera, guide scope, and other accessories, you will need a robust equatorial mount with a payload capacity of at least 50-60 lbs (22-27 kg) for reliable astrophotography. Mounts in the Sky-Watcher EQ6-R Pro, iOptron CEM60\/70, or Losmandy G11 class are recommended for stable, long-exposure imaging with the Ultra-Cat 131.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eDo I need a separate field flattener for the Ultra-Cat 131?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo. The Ultra-Cat 131 uses an advanced 5-element Petzval optical design that has field flattening built-in. It produces a perfectly flat 60mm image circle without the need for any additional flattener or reducer, simplifying your imaging train.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the WIFD internal focuser on the Ultra-Cat 131 improve imaging sessions?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe WIFD (William Optics Internal Focuser Design) offers two key advantages. First, because only internal optical elements move, the overall length of the telescope never changes. This keeps the balance point constant, preventing tracking errors as you cross the meridian. Second, it eliminates drawtube sag, a common problem with heavy cameras on traditional focusers, ensuring your sensor remains perfectly orthogonal to the light path.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the f\/4.9 focal ratio of the Ultra-Cat 131 fast enough for narrowband imaging of targets like the Elephant's Trunk Nebula (IC 1396)?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eAbsolutely. An f\/4.9 focal ratio is considered very fast for astrophotography. This speed allows you to collect a strong signal with narrowband filters (like H-alpha, OIII, and SII) in a fraction of the time it would take with a slower f\/7 or f\/8 system, making it ideal for capturing deep, high-contrast images of emission nebulae like IC 1396.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat is the purpose of the included Sensor Tilt Xterminator (STX-R) with the Ultra-Cat 131?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe Sensor Tilt Xterminator (STX-R) is a precision tilt adapter. It allows you to make minute adjustments to the angle of your camera sensor relative to the telescope's optical axis. This is crucial for achieving perfectly sharp stars across a large, flat field, as it corrects for any slight tilt that may exist in your camera or focuser.\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\u003eOptical Design\u003c\/td\u003e\n\u003ctd\u003e5-Element Advanced Petzval\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eLens Elements\u003c\/td\u003e\n\u003ctd\u003eSuper ED Glass x2, ED Glass x1, Lanthanum Glass x1, X-Element x1\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eDiameter\u003c\/td\u003e\n\u003ctd\u003e131 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Length\u003c\/td\u003e\n\u003ctd\u003e648 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Ratio\u003c\/td\u003e\n\u003ctd\u003ef\/4.9\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eImage Circle\u003c\/td\u003e\n\u003ctd\u003e60 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocuser\u003c\/td\u003e\n\u003ctd\u003eWIFD Rack \u0026amp; Pinion Internal Focuser, EAF Compatible\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocuser Travel\u003c\/td\u003e\n\u003ctd\u003e0-20 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFlattener Required\u003c\/td\u003e\n\u003ctd\u003eNo\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSupported Camera Formats\u003c\/td\u003e\n\u003ctd\u003eMedium Format, Full Frame, APS-C, M4\/3\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSupported T-Mounts\u003c\/td\u003e\n\u003ctd\u003eCanon EF, RF; Nikon F, Z; Sony E; Pentax K; MFT (M4\/3); FUJI X\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eDovetail Type\u003c\/td\u003e\n\u003ctd\u003eLosmandy\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTube Length (Retracted\/Extended)\u003c\/td\u003e\n\u003ctd\u003e650 mm - 785.5 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOTA Weight\u003c\/td\u003e\n\u003ctd\u003e11.3 kg \/ 24.91 lbs\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTotal Weight\u003c\/td\u003e\n\u003ctd\u003e13.97 kg \/ 30.8 lbs\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\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eUltra-Cat 131 Main Tube\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eBahtinov Mask Focus Aid Cap\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eSensor Tilt Xterminator (STX-R)\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eM68, M54, and M48 Camera Adapters\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eMounting Rings \u0026amp; Handle Bar\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eLosmandy-Style Dovetail Plate\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eSoft Padded Carry Case\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eAllen Key Set \u0026amp; Wrench\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\n\u003ca href=\"https:\/\/davidastro.com\/pages\/william-optics-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eWilliam Optics 2-Year Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"William Optics","offers":[{"title":"Default Title","offer_id":52853689057565,"sku":"WO-T-C-131BR","price":5398.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/WilliamOptics-Ultra-Cat-131-1_4421596a-b1ce-428f-84ff-326b3a644d9a.jpg?v=1788457750","url":"https:\/\/davidastro.com\/en-eu\/products\/william-optics-t-c-131br","provider":"David Astro","version":"1.0","type":"link"}