ZWO FF131 APO Flat-Field 131mm Apochromatic Refractor

ZWO Flat-Field APO Series FF131 APO. Flat field, built in. A 131 mm f/7.5 four-element apochromatic refractor with a native flat field and a 44 mm full-frame image circle. The flagship of the FF series, with 983 mm of focal length and serious light grasp for deep-sky imaging. Explore the design View specifications 131 mm aperture four-element air-spaced APO 983 mm focal length f/7.5 44 mm image circle full-frame coverage 7.9 kg optical tube 9.4 kg with rings and dovetail ZWO FF Series Designed as an astrograph first. Every FF series telescope is built around a native flat field, so the optics, focuser and rear interfaces all serve one goal: clean stars across the whole sensor. Attach your camera, reach focus, start imaging. No flattener. No spacing maths. Optics Four elements, fully air-spaced. The FF131 APO uses a four-element, fully air-spaced apochromatic design in which all four elements work together to form the image. One ED (extra-low dispersion) glass element reduces chromatic aberration for cleaner colour correction and sharper stars. Native flat field Flat to the edge. No flattener. The flat imaging field is generated by the optical design itself, so there is no field flattener to buy and no back focus calculations to get right. Once focus is achieved, you are ready to capture. Full-frame support 44 mm image circle. A 44 mm corrected image circle fully covers full-frame sensors, with sharp star fields and consistent illumination from centre to corner. Smaller APS-C and dedicated astronomy sensors have generous headroom. Focusing 1:10 dual-speed control. A rigid 3″ rack-and-pinion focuser offers precise control, and the 1:10 coarse and fine adjustment makes critical focus easy to hit. A built-in 360° rotator at the rear sets your framing without disturbing focus. Build Retractable dew shield. The dew shield retracts to shorten the tube for packing and travel. Precision CNC machining, a high-quality painted finish and an internal anti-reflection coating keep stray light down and image contrast up. Connectivity Adapters in the box. A four-section photography extension tube with a 2″ filter thread is included, along with rear adapters in M48×0.75 and M54×0.75 standards. The quick-release mounting rings detach in seconds for fast setup and teardown. Quadruplet optics Four elements. One flat field. All four air-spaced elements work together to form the image, with one ED glass element controlling chromatic aberration for clean colour correction and tight, well-defined stars. Optical layout The light path, end to end. The optical layout delivers a corrected, flat field at the sensor with no additional optics in the imaging train. What leaves the objective arrives at your camera, flat. Full-frame ready 44 mm image circle. Full-frame sensors are covered corner to corner with sharp star fields and consistent illumination, and smaller sensors sit comfortably inside the sweet spot. Critical focus Coarse and fine, 1:10. The rigid 3″ rack-and-pinion focuser moves heavy imaging trains smoothly, and the 1:10 fine knob gives you the resolution to land exact focus on a star. Framing 360° of rotation. A built-in rotator at the rear lets you set the camera angle for perfect framing without unthreading anything or disturbing focus. Field-ready build Quick-release rings. Retractable dew shield. The mounting rings detach in seconds for fast setup and teardown, and the dew shield slides back to shorten the tube for transport. CNC machining and an internal anti-reflection coating keep contrast high. In the box Photography extension tube. A four-section photographic extension tube with a 2″ filter thread is included, plus M48×0.75 and M54×0.75 rear adapters, connecting cameras, filters and accessories cleanly out of the box. Aperture and reach 131 mm of light grasp, 983 mm of reach. The flagship of the FF series pulls in the most light and resolves the finest detail of the range, and the 983 mm focal length frames smaller targets tightly. The optical tube weighs 7.9 kg, or 9.4 kg with the handle, mounting rings and dovetail plate fitted. Flexible connectivity One telescope. Three configurations. Pair the FF131 APO with ZWO ASI astronomy cameras, attach a DSLR or mirrorless body, or drop in a diagonal and eyepiece for visual observing. Focus is reached within a back focus range of 42–73 mm, measured from the M54–M48 interface shoulder. Visual accessories are available separately. Every detail, considered. Four-element, fully air-spaced apochromatic design with one ED glass element. Native flat-field design, no separate field flattener or spacing adjustments required. 44 mm image circle with full-frame sensor support and edge-to-edge sharpness. 3″ rack-and-pinion focuser with 1:10 coarse and fine adjustment. Built-in 360° rotator for precise camera angle adjustment. Retractable dew shield with internal anti-reflection coating for higher contrast. Quick-release mounting rings for fast setup and teardown. Four-section photography extension tube with 2″ filter thread plus M48×0.75 and M54×0.75 rear adapters included. Specifications. Optics Effective aperture 131 mm Focal length 983 mm Focal ratio f/7.5 Objective type Four-element air-spaced APO (including one ED element) Image circle 44 mm Integrated field flattener design Yes Focuser and rotation Focuser 3″ rack-and-pinion, 1:10 coarse and fine adjustment Camera rotator Built-in, 360° Back focus Back focus range 42–73 mm, measured from the M54–M48 interface shoulder Maximum rear connection length (focuser retracted) Imaging mode 73 mm (from the M48×0.75 male thread) 91 mm (from the M54×0.75 male thread) Observation mode 131 mm (from the 1.25″ interface) 142 mm (from the 2″ interface) Minimum rear connection length (focuser retracted) Imaging mode 42 mm (from M48×0.75 male thread) 60 mm (from M54×0.75 male thread) Observation mode 100 mm (from 1.25″ interface) 111 mm (from 2″ interface) Dimensions and weight Overall length 878 mm (1.25″ interface retracted) 941 mm (photography extension tube retracted) 963 mm (1.25″ interface, dew shield extended) 1026 mm (photography extension tube, dew shield extended) Telescope body weight 7.9 kg Standard configuration weight 9.4 kg (including handle, mounting rings and dovetail plate) Interfaces Rear interfaces M78×1 – 55 mm extension adapter M78×1 – M54×0.75 M54×0.75 – M54×0.75 M54×0.75 – M48×0.75 (built-in M48×0.75 filter thread) In the box FF131 APO optical tube With handle, mounting rings and dovetail plate Photography extension tube Four-section, with 2″ filter thread, M48×0.75 and M54×0.75 rear adapters Documentation User manual, inspection sheet, warranty card Built to last a lifetime. Australian warranty Full local cover Ships from Sydney From local stock Expert advice From working astronomers 40+ years In Australian astronomy