William Optics UltraCat 131 WIFD — 131 mm Petzval astrograph The 5-element optical system provides a 648 mm focal length at f/4.9, with a 60 mm image circle. Its Petzval design does not require an external field flattener.
Manufacturer model: William Optics UltraCat 131 WIFD · Specifications checked against manufacturer data on 2026-11-03
The 5-element optical system provides a 648 mm focal length at f/4.9, with a 60 mm image circle. Its Petzval design does not require an external field flattener.
The WIFD rack-and-pinion focuser provides 20 mm travel and 1:10 fine adjustment. A camera rotator controls framing, while the Sensor Tilt Xterminator allows sensor alignment. The lens cover incorporates a Bahtinov focusing mask.
STX-R tilt adjuster / rotator; M79 to M68, M54 and M48 adapters. Petzval focus depends on the complete camera train remaining within the telescope's focusing range.
The tube length is 650–785.5 mm. OTA weight is 11.3 kg and the manufacturer lists 13.97 kg total weight. The mounting plate is 400 mm Losmandy-style.
William Optics manufacturer manual
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.
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.
Data sheet
William Optics UltraCat 131 WIFD — 131 mm Petzval astrograph The 5-element optical system provides a 648 mm focal length at f/4.9, with a 60 mm image circle. Its Petzval design does not require an external field flattener.
Manufacturer model: William Optics UltraCat 131 WIFD · Specifications checked against manufacturer data on 2026-11-03
