ZWO 131mm Quad APO Refractor

ZWO FF131 APO Flat-Field Apochromatic Refractor *Focus can be achieved within a back focus range of 42–73 mm, measured from the M54–M48 interface shoulder. Main Features Flexible Connectivity for Multiple Configurations Uniqueness Four-Element Optical Design The FF131 APO features a four-element, fully air-spaced apochromatic optical design. All four elements work together to deliver a flat imaging field without the need for an additional field flattener. One ED (extra-low dispersion) glass element is incorporated to effectively reduce chromatic aberration, resulting in improved color correction and image clarity. 44 mm Image Circle — Full-Frame Support With a 44 mm image circle, the FF131 APO fully supports full-frame sensors and a wide range of imaging setups. It delivers sharp star fields with excellent edge-to-edge performance, ensuring consistent image quality across the entire frame. Native Flat-Field Design The FF131 APO features a native flat-field optical design, eliminating the need for an additional field flattener. No complex back focus calculations or spacing adjustments are required—simply attach your imaging setup and start capturing once focus is achieved. Convenient Design Coarse & fine focus adjustment Equipped with a rigid 3-inch rack-and-pinion focuser, the FF131 APO offers precise control with a 1:10 coarse & fine focus adjustment mechanism. A built-in 360° rotator at the rear allows for smooth and accurate camera angle adjustments. Retractable Dew Shield  The FF131 APO features a retractable dew shield, reducing overall length for improved portability. Precision CNC machining and a high-quality painted finish, combined with an internal anti-reflection coating, help minimize stray light and enhance image contrast. Quick-Release Mounting Rings The mounting rings are detachable, allowing for quick and easy setup or teardown of the telescope. Photography Extension Tube The FF131 APO is designed for seamless integration with modern imaging systems, and includes a standard four-section photographic extension tube with a 2-inch filter thread. Rear adapters in both M48x0.75 and M54x0.75 formats are also included, making it easy to connect a wide range of cameras, filters, and astrophotography accessories for a clean, flexible setup right out of the box. Performance Optical Layout Star Field Map Product Diagram Specifications What's in the Box?