{"product_id":"zwo-ff90-apo-90mm-quadruplet-refractor","title":"ZWO FF90-APO 90mm Quadruplet Refractor F\/6.8","description":"\u003cul class=\"DAV-feature-list\"\u003e\n\u003cli\u003e90mm Aperture\u003c\/li\u003e\n\u003cli\u003e609mm Focal Length (f\/6.8)\u003c\/li\u003e\n\u003cli\u003e4-Element Quadruplet Optical Design\u003c\/li\u003e\n\u003cli\u003e3\" Dual-Speed Rack \u0026amp; Pinion Focuser\u003c\/li\u003e\n\u003cli\u003e9.97 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 FF90-APO 90mm Quadruplet Refractor F\/6.8\u003c\/h2\u003e\n\u003cp\u003eThe ZWO FF90-APO refractor integrates a 90mm objective and a 609mm focal length into a self-flattening optical design for wide-field astrophotography. Its 4-element quadruplet lens system corrects for field curvature across a full-frame sensor without requiring a separate flattener, and the entire 9.97 lb. optical tube is managed by a rigid 3\" dual-speed focuser.\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\u003eSelf-Flattening 4-Element Optics at f\/6.8\u003c\/h3\u003e\n\u003cp\u003eThe core of the FF90 is its 4-element Petzval-like optical design, which provides a flat, corrected field of view without the need for additional accessories or complex back-focus calculations. This simplifies your imaging train significantly; as long as you can reach focus, the star field will be sharp edge-to-edge. At a focal ratio of f\/6.8, you acquire deep signal on targets like the Eagle Nebula (M16) or the Triangulum Galaxy (M33) with shorter sub-exposure times than a slower instrument would require.\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 Focuser for a 9.97 lb. OTA\u003c\/h3\u003e\n\u003cp\u003eTo prevent flexure with modern imaging cameras and filter wheels, the FF90 is equipped with a 3\" rack \u0026amp; pinion focuser. This large-format focuser provides a rigid, stable platform for your equipment, while the 10:1 dual-speed mechanism allows for the fine adjustments necessary to achieve critical focus. The entire optical tube assembly weighs 9.97 lb., making it a stable and manageable payload for a wide range of mid-sized equatorial mounts.\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 FF90 vs. ZWO FF70: Aperture and Image Scale\u003c\/h3\u003e\n\u003cp\u003eWhen choosing between ZWO's quadruplet refractors, the primary difference is light-gathering ability and image scale. The FF70 is lighter and offers a wider true field of view, making it ideal for the largest nebulae. The FF90, however, has a distinct advantage in light grasp and resolution with its 90mm aperture. Its 609mm focal length also provides greater magnification, framing smaller deep-sky objects more effectively than the shorter focal length FF70. The trade-off is weight; the FF90 weighs 9.97 lb., requiring a more substantial mount than the 5.5 lb. FF70.\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 FF90 APO?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eNo. The ZWO FF90 APO uses a \u003cstrong\u003e4-element quadruplet\u003c\/strong\u003e optical design that is \"self-flattening.\" This means you do not need to purchase a separate field flattener or calculate a precise back-focus distance. Simply attach your camera and focus.\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 9.97 lb. ZWO FF90 APO?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eFor astrophotography, a mount should typically carry no more than 50-60% of its maximum rated payload capacity. With an optical tube weight of \u003cstrong\u003e9.97 lb.\u003c\/strong\u003e, plus the weight of your camera and guide scope, a mount in the 25-30 lb payload class (like a Celestron AVX, Sky-Watcher HEQ5, or ZWO AM3) would be a stable platform.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eHow does the ZWO FF90 APO perform on the Triangulum Galaxy (M33)?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe ZWO FF90's \u003cstrong\u003e609mm focal length\u003c\/strong\u003e is an excellent match for medium-to-large galaxies like M33. Paired with a full-frame or APS-C sensor, it will frame the entire galaxy and its spiral arms with room to spare, while the \u003cstrong\u003e90mm aperture\u003c\/strong\u003e is sufficient to resolve its brighter HII regions and star-forming areas.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eWhat adapters are needed to connect a full-frame camera to the ZWO FF90?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eThe ZWO FF90 includes a photography extension tube with standard M54 and M48 male threads, which are common connection sizes for full-frame cameras and filter wheels. You will likely only need a standard M48 T-ring for your specific camera brand (e.g., Canon, Nikon, Sony) to connect directly.\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 ZWO FF90's 4-element design over a standard doublet?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eA standard doublet refractor requires a separate field flattener accessory to correct for field curvature, which introduces potential spacing errors and extra cost. The ZWO FF90's integrated \u003cstrong\u003e4-element\u003c\/strong\u003e system corrects for chromatic aberration and field curvature simultaneously, resulting in a simpler, more rigid imaging train with sharp stars across the entire frame by design.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion\"\u003e\n\u003ch3 class=\"DAV-accordion-Q\"\u003eIs the ZWO FF90 APO suitable for visual astronomy?\u003c\/h3\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"DAV-accordion-A\"\u003e\n\u003cp\u003eYes. While designed for imaging, the FF90 is also an excellent visual instrument. Its \u003cstrong\u003e90mm aperture\u003c\/strong\u003e and apochromatic optics provide high-contrast, color-free views of the Moon, planets, and bright deep-sky objects. You will need a 2\" or 1.25\" star diagonal and eyepieces, which are not included.\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-FF90-APO\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\u003eNumber of Elements\u003c\/td\u003e\n\u003ctd\u003e4 (Quadruplet)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eAperture\u003c\/td\u003e\n\u003ctd\u003e90mm (3.54\")\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Length\u003c\/td\u003e\n\u003ctd\u003e609 mm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFocal Ratio\u003c\/td\u003e\n\u003ctd\u003ef\/6.8\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\u003e9.97 lb.\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\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\u003eOTA Only - No Electronics\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 90 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× 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\"\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 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\n\u003ca href=\"https:\/\/davidastro.com\/pages\/zwo-warranty-policy\" rel=\"noopener\" target=\"_blank\"\u003eZWO 2-Year Limited Warranty\u003c\/a\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"ZWO","offers":[{"title":"Default Title","offer_id":51858442977565,"sku":"ZWO-FF90-APO","price":999.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0753\/5280\/1565\/files\/ZWO-FF90-APO-Quadruplet-Refractor-1.jpg?v=1781058596","url":"https:\/\/davidastro.com\/fr-us\/products\/zwo-ff90-apo-90mm-quadruplet-refractor","provider":"David Astro","version":"1.0","type":"link"}