{"product_id":"zwo-ff131-apo-131mm-quadruplet-refractor","title":"ZWO FF131-APO 131mm Quadruplet Refractor F\/7.5","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003e131mm Aperture\u003c\/li\u003e\n\u003cli\u003e983mm Focal Length (f\/7.5)\u003c\/li\u003e\n\u003cli\u003e4-Element Petzval Optical Design\u003c\/li\u003e\n\u003cli\u003e3-inch Dual-Speed Rack \u0026amp; Pinion Focuser\u003c\/li\u003e\n\u003cli\u003e20.7 lb. Optical Tube Assembly 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\u003eDownloads\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\u003eZWO FF131-APO 131mm Quadruplet Refractor F\/7.5\u003c\/h2\u003e\n\u003cp\u003eThe ZWO FF131-APO's 131mm (5.15\") aperture and 983mm focal length are built on a 4-element optical design for high-contrast imaging of demanding deep-sky targets. This f\/7.5 system features a rigid 3\" dual-speed focuser and weighs 20.7 lbs, providing a stable platform for full-frame cameras without requiring additional field flatteners.\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\u003eFlat-Field Quadruplet Optics at 983mm\u003c\/h3\u003e\n\u003cp\u003eThe 4-element Petzval optical design delivers a corrected image circle without the need for an external flattener or complex back-focus calculations. This simplifies your imaging train, allowing you to attach a camera and achieve sharp stars across the entire field, as long as the focuser can reach its target. The 983mm focal length provides the ideal image scale for resolving details in smaller targets like the Whirlpool Galaxy (M51) or the Dumbbell Nebula (M27) with modern CMOS 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\u003e3-inch Rack \u0026amp; Pinion Focuser\u003c\/h3\u003e\n\u003cp\u003eTo support heavy imaging loads, the FF131-APO is equipped with a 3\" rack and pinion focuser. Its large diameter prevents vignetting on full-frame sensors and provides the rigidity needed to hold a filter wheel and camera without flexure. The dual-speed mechanism allows for coarse adjustments to find the general focus point, followed by fine 1:10 adjustments to achieve critical sharpness.\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\u003eZWO FF131-APO vs. the 110mm FF110-APO\u003c\/h3\u003e\n\u003cp\u003eThe primary advantage of the smaller FF110-APO is its lower weight (14.9 lbs), making it compatible with lighter-duty mounts. The FF131-APO, at 20.7 lbs, requires a more substantial mount but delivers significantly more light-gathering power and resolution from its 131mm aperture. Its 983mm focal length also yields a tighter image scale than the FF110's 766mm, resolving finer details on distant galaxies and nebulae.\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\u003eImaging-Ready Design at 20.7 lbs\u003c\/h3\u003e\n\u003cp\u003eThe FF131-APO's 20.7 lb. tube weight is a key factor in mount selection, requiring a platform in the EQ6-R, AM5, or a higher payload class for stable, unguided imaging. ZWO includes essential mounting hardware right in the box to integrate the OTA into your setup. The package contains a set of mounting rings, a Vixen-style dovetail plate, and two findershoes, providing attachment points for guide scopes, finder scopes, or an ASIAIR controller.\u003c\/p\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\"\u003eDo I need a field flattener for the ZWO FF131-APO?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo. The ZWO FF131-APO uses a 4-element Petzval optical design that has a built-in flattener. You do not need to purchase an additional flattener or calculate any back-focus spacing; as long as you can reach focus, the field will be flat.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat kind of mount is required for the 20.7 lb ZWO FF131-APO?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eDue to its 20.7 lb. weight, the ZWO FF131-APO requires a medium to heavy-duty equatorial mount for astrophotography. For reliable tracking, a mount with a payload capacity of at least 35-40 lbs is recommended, such as a Sky-Watcher EQ6-R Pro, ZWO AM5, or a larger class of mount.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the FF131-APO's 983mm focal length perform on targets like the Whirlpool Galaxy (M51)?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe 983mm focal length is excellent for medium-to-small deep-sky objects. On a target like the Whirlpool Galaxy (M51), it provides enough image scale to resolve individual dust lanes and star-forming regions, especially when paired with cameras that have small pixels (under 4µm).\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the ZWO FF131-APO a good choice for a portable setup?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eAt 20.7 lbs for the optical tube alone, plus the required heavy-duty mount, the ZWO FF131-APO is generally considered a backyard or observatory-class instrument rather than a \"grab-and-go\" portable setup. While transportable, it requires more effort to set up than smaller refractors.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the ZWO FF131-APO compare to the smaller FF110-APO?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe FF131-APO offers a 20% increase in aperture over the 110mm model, resulting in higher resolution and the ability to capture fainter detail. It also has a longer focal length (983mm vs. 766mm), making it better suited for smaller targets. The main trade-off is weight; the FF131-APO is nearly 6 lbs heavier and requires a more robust mount.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow do I attach a full-frame camera to the FF131-APO's 3\" focuser?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe ZWO FF131-APO includes a photography extension tube with standard M48x0.75 and M54x0.75 male threads. You connect this to the focuser's drawtube, and then attach your camera using the appropriate T-ring or adapter for your camera's bayonet or thread size.\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\u003eSKU\u003c\/td\u003e\n\u003ctd\u003eZWO-FF131-APO\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eModel\u003c\/td\u003e\n\u003ctd\u003e131 mm APO Refractor\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSeries\u003c\/td\u003e\n\u003ctd\u003eZWO Refractors\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOptical Design\u003c\/td\u003e\n\u003ctd\u003eApochromatic Refractor\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eAperture\u003c\/td\u003e\n\u003ctd\u003e131mm (5.15\")\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Length\u003c\/td\u003e\n\u003ctd\u003e983 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Ratio\u003c\/td\u003e\n\u003ctd\u003ef\/7.5\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOptical Elements\u003c\/td\u003e\n\u003ctd\u003e4 (Quadruplet)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocuser\u003c\/td\u003e\n\u003ctd\u003e3\" Rack \u0026amp; Pinion\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocuser Speed\u003c\/td\u003e\n\u003ctd\u003eDual Speed\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOTA Weight\u003c\/td\u003e\n\u003ctd\u003e20.7 lb.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMount Type\u003c\/td\u003e\n\u003ctd\u003eNo Mount - OTA Only\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eElectronics\u003c\/td\u003e\n\u003ctd\u003eNone\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\"\u003eZWO 131 mm APO Refractor OTA\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\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 1 Pair\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\"\u003eVixen 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\"\u003eFindershoes\u003c\/p\u003e\n\u003cp class=\"DAV-item-subtitle\"\u003e× 2\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\"\u003ePhotography Extension 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\"\u003eWarranty Card\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\"\u003eInspection Card\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\"\u003eUser Manual\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\u003cul class=\"DAV-grid\"\u003e\n\u003cli class=\"DAV-grid-item\"\u003e\u003ca href=\"https:\/\/www.zwoastro.com\/software\/\" target=\"_blank\"\u003e\u003csvg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" viewbox=\"0 0 640 512\" class=\"DAV-img-box\"\u003e\u003cpath fill=\"#0047a7\" d=\"M128 32C92.7 32 64 60.7 64 96l0 256 64 0 0-256 384 0 0 256 64 0 0-256c0-35.3-28.7-64-64-64L128 32zM19.2 384C8.6 384 0 392.6 0 403.2C0 445.6 34.4 480 76.8 480l486.4 0c42.4 0 76.8-34.4 76.8-76.8c0-10.6-8.6-19.2-19.2-19.2L19.2 384z\"\u003e\u003c\/path\u003e\u003c\/svg\u003e\n\u003cdiv\u003e\n\u003cp class=\"DAV-item-title\"\u003eDownload ZWO Software\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/a\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/li\u003e\n\u003cli\u003e\u003ca href=\"https:\/\/davidastro.com\/pages\/zwo-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eZWO 2-Year Warranty\u003c\/a\u003e\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":51858498519325,"sku":"ZWO-FF131-APO","price":1999.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/ZWO-FF131-APO-Quadruplet-Refractor-1.jpg?v=1781058960","url":"https:\/\/davidastro.com\/fr-us\/products\/zwo-ff131-apo-131mm-quadruplet-refractor","provider":"David Astro","version":"1.0","type":"link"}