William Optics GreyCat 91 WIFD OTA — 91 mm Petzval astrograph The 5-element optical system provides a 448 mm focal length at f/4.9, with a 55 mm image circle. Its Petzval design does not require an external field flattener.
Manufacturer model: William Optics GreyCat 91 WIFD OTA · Specifications checked against manufacturer data on 2026-11-03
William Optics GreyCat 91 WIFD OTA — 91 mm Petzval astrograph
The 5-element optical system provides a 448 mm focal length at f/4.9, with a 55 mm image circle. Its Petzval design does not require an external field flattener.
Focus and camera alignment
The WIFD rack-and-pinion focuser provides 36 mm travel and 1:10 fine adjustment. A camera rotator controls framing, while a sensor tilt adjuster allows sensor alignment. The lens cover incorporates a Bahtinov focusing mask.
Imaging connections
Tilt adjuster; camera rotator; M63 to M48 and M63 to M54 adapters. The M48 adapter incorporates an internal filter thread. Petzval focus depends on the complete camera train remaining within the telescope's focusing range.
Size and mounting
The tube length is 556 mm. OTA weight is 4.72 kg and the manufacturer lists 6.3 kg total weight. The mounting plate is Vixen-style PV-LII.
William Optics specifies two Super ED elements, one ED element, one lanthanum element and one X-element in the five-element optical system. The internal focuser moves the focusing mechanism within the telescope, while the rear tilt and rotation adjustments support sensor alignment and framing.
Compatibility notes
Petzval focus range must accommodate the complete imaging train; do not interpret recommended camera spacing as an exact flattener backfocus. Confirm supplied adapters and revision.
Additional specifications
Maximum m48 backspacing (mm)
60.8
Maximum m54 backspacing (mm)
65.8
88166
Technische Daten
Öffnung (mm)
91
Kameraadapter
Tilt adjuster; camera rotator; M63 to M48 and M63 to M54 adapters
Kameraformat
Full frame, APS-C and Micro Four Thirds; medium format needs additional adapter
Kamerarotation
Camera angle rotator
Elektronischer Fokus
ZWO EAF compatible; use the manufacturer installation guide for the selected EAF model.
Externer Bildfeldebner erforderlich
No
Untersetzung Feinfokus
1:10
Brennweite (mm)
448
Öffnungsverhältnis
4.9
Okularauszug
WIFD rack-and-pinion
Auszugsweg (mm)
36
Fokussiermaske
Bahtinov mask incorporated in lens cover
Bildkreis (mm)
55
M48-Filterinnengewinde
Yes
Linsenelemente
2 Super ED, 1 ED, 1 lanthanum and 1 X-element (5 elements total)
Montageplatte
Vixen-style PV-LII
Optisches Design
5-element Petzval
Tubusgewicht (kg)
4.72
Sensor-Tilt-Einstellung
Sensor tilt adjuster
Gesamtgewicht (kg)
6.3
Tubuslänge (mm)
556
Sie nutzen dieses Produkt? Teilen Sie Ihre Erfahrung mit anderen Astronomen.
Kommentare (0)
Aktuell keine Kunden-Kommentare
Ihre Bewertung der Rezension kann nicht gesendet werden
Kommentar melden
Möchten Sie diesen Kommentar wirklich melden?
Meldung gesendet
Ihre Meldung wurde übermittelt und wird durch einen Moderator geprüft.
Ihre Meldung kann nicht gesendet werden
Eigenen Kommentar verfassen
Bewertung gesendet
Ihr Kommentar wurde gespeichert und wird sofort nach Freigabe durch einen Moderator angezeigt.
William Optics GreyCat 91 WIFD OTA — 91 mm Petzval astrograph The 5-element optical system provides a 448 mm focal length at f/4.9, with a 55 mm image circle. Its Petzval design does not require an external field flattener.
Manufacturer model: William Optics GreyCat 91 WIFD OTA · Specifications checked against manufacturer data on 2026-11-03
