The mighty Ultra-Cat 131 is finally here! 30th Anniversary Limited Edition will be shipping beginning in March, with a standard edition soon to follow.

The Ultra-Cat 131 · 30th Anniversary Edition is a commemorative refractor celebrating three decades of William Optics craftsmanship and innovation. Built upon the acclaimed five-element advanced Petzval optical design, this limited edition of 30 units worldwide combines uncompromising astrophotography performance with a symbolic anniversary finish.

Featuring a unique laser-engraved emblem of a cat embracing “30” ,personally hand-signed by founder William Yang on the lens cover, and accompanied by a 30th Anniversary Certificate, the Ultra-Cat 131 is not only a professional imaging instrument but also a collector’s piece that honors the Cat series legacy.

Key Features:

Advanced 5-Element Petzval Design
Eliminates field curvature, providing sharp, flat-field images without requiring additional flatteners.

60mm Superior Image Circle
Fully supports full-frame and medium-format cameras for wide-field and detailed astrophotography, outperforming standard 106mm telescopes.

F/4.9 Fast Optics
Offers exceptional light-gathering capability for vibrant deep-sky photography.

WIFD (William’s Internal Focuser Design)
Patented internal focuser ensures precise, stable, and hassle-free imaging, avoiding balance issues and eliminating vignetting.

Anti-Shrink Lens Cell Technology
Minimizes thermal expansion and contraction, maintaining perfect optical alignment in any environment.

Sensor Tilt Corrector
Integrated and patented design eliminates distortion, optimizing sharpness and detail for professional-level results.

Built-In Patented Bahtinov Mask
Simplifies focusing for pinpoint precision, a feature that sets it apart from competitors.

Patented Handle Bar Design
Combines ergonomic usability with enhanced portability.

Lens Type

5-Element Advanced Petzval

Lens Elements

Super ED Glass x2 ED Glass x1 Lanthanum Glass x1 X-Element x1

Focal Length

648 mm

Diameter

131 mm

Focal Ratio

f/4.9

Image Circle

60 mm

Focuser

WIFD R&P Focuser Compatible with EAF

Focuser Travel

0-20 mm

Adapter Included

Sensor Tilt Xterminator Rotator M68, M54, M48 Camera Adapters

Optional Flattener

No Flattener Required

T-Mount Support

Canon EF, RF Nikon F, Z Sony E Pentax K MFT (M4/3) FUJI X

Camera Format

Medium Format Full Frame APS-C M4/3

Dovetail Type

Losmandy

Tube Length

650 mm - 785.5 mm

OTA Weight

9.95 kg / 21.94 lbs