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
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.
These specifications describe the telescope component only. Native flat field design does not require an added flattener; the imaging train must still fit the available focus travel and interface. Package mount/tripod specifications are not inferred from telescope data.
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
93005
Fiche technique
Diamètre (mm)
131
Applications
Astrophotography and visual observing
Pare-buée
Retractable
Aplanisseur de champ externe requis
No
Filetage de filtre
M48 × 0.75 (2-inch)
Démultiplication de la mise au point fine
1:10
Focale (mm)
983
Rapport F/D
7.5
Type de porte-oculaire
Rack and pinion, dual speed
Cercle image (mm)
44
Plage de mise au point en imagerie
42–73 mm from M54–M48 shoulder
Chemin optique max. M48 (mm)
73
Chemin optique max. M54 (mm)
91
Chemin visuel max. 1,25" (mm)
131
Chemin visuel max. 2" (mm)
142
Formule optique
Four-element air-spaced apochromat; one ED element
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
