ZWO FF90 APO — 90 mm flat-field refractor A 609 mm, f/6.8 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 FF90 90/609 APO Refractor OTA · Specifications checked against manufacturer data on 2026-11-03
A 609 mm, f/6.8 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 45–75 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 3.92 kg; the standard configuration with handle, rings and dovetail weighs 4.52 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)
513
Length imaging retracted (mm)
550
Length visual extended (mm)
599
Length imaging extended (mm)
636
93003
Fiche technique
Diamètre (mm)
90
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)
609
Rapport F/D
6.8
Type de porte-oculaire
Rack and pinion, dual speed
Cercle image (mm)
44
Plage de mise au point en imagerie
45–75 mm from M54–M48 shoulder
Chemin optique max. M48 (mm)
75
Chemin optique max. M54 (mm)
93
Chemin visuel max. 1,25" (mm)
112
Chemin visuel max. 2" (mm)
122
Formule optique
Four-element air-spaced apochromat; one ED element
ZWO FF90 APO — 90 mm flat-field refractor A 609 mm, f/6.8 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 FF90 90/609 APO Refractor OTA · Specifications checked against manufacturer data on 2026-11-03
