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ZWO FF131 131/983 APO Refractor OTA
ZWO FF131 APO — 131 mm flat-field refractor A 983 mm, f/7.5 optical tube for astrophotography and visual observing. Its four air-spaced elements include ED glass for colour correction. The native flat field covers a 44 mm image circle without a separate flattener.
Focus and framing The 3-inch rack-and-pinion focuser has 1:10 fine adjustment. A 360° rear rotator sets camera orientation. ZWO specifies an imaging focus range of 42–73 mm from M54–M48 shoulder; this is a usable focusing range, rather than a fixed reducer-spacing requirement.
Camera connections M48 × 0.75 and M54 × 0.75 interfaces accommodate imaging trains. The photographic extension accepts a 2-inch threaded filter. Eyepiece interfaces support visual use.
Handling and installation A retractable dew shield shortens the tube for transport. Detachable rings support mounting. Body weight is 7.9 kg; the standard configuration with handle, rings and dovetail weighs 9.4 kg.
ZWO FF131 manufacturer specifications
Compatibility notes Native flat field design does not require an added flattener; the imaging train must still fit the available focus travel and interface.
Additional specifications Focuser size inches 3 Camera rotator degrees 360 Mounting rings Detachable Length visual retracted (mm) 878 Length imaging retracted (mm) 941 Length visual extended (mm) 963 Length imaging extended (mm) 1026
Reference
93005
Data sheet
Aperture (mm)
131
Applications
Astrophotography and visual observing
Dew shield
Retractable
External field flattener required
No
Filter thread
M48 × 0.75 (2-inch)
Fine focus ratio
1:10
Focal length (mm)
983
Focal ratio
7.5
Focuser type
Rack and pinion, dual speed
Image circle (mm)
44
Imaging focus range
42–73 mm from M54–M48 shoulder
Maximum optical path m48 (mm)
73
Maximum optical path m54 (mm)
91
Maximum visual path 1 25 inch (mm)
131
Maximum visual path 2 inch (mm)
142
Optical design
Four-element air-spaced apochromat; one ED element
Rear adapter threads
M78 × 1 with 55 mm extension; M78 × 1 → M54 × 0.75; M54 × 0.75 → M54 × 0.75; M54 × 0.75 → M48 × 0.75
Standard weight (kg)
9.4
Standard weight includes
Handle, mounting rings and dovetail plate
Telescope body weight (kg)
7.9
Telescope model
FF131 APO
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ZWO FF131 APO — 131 mm flat-field refractor A 983 mm, f/7.5 optical tube for astrophotography and visual observing. Its four air-spaced elements include ED glass for colour correction. The native flat field covers a 44 mm image circle without a separate flattener.
Manufacturer model: ZWO FF131 131/983 APO Refractor OTA · Specifications checked against manufacturer data on 2026-11-03