William Optics Ultra-Cat 131

The William Optics Ultra-Cat 131 is the flagship of the Ultra-Cat series, representing the pinnacle of wide-field astrophotography performance. Built around a large-aperture 131mm apochromatic optical system and an advanced 5-element Petzval design, it delivers extraordinary light-gathering power, exceptional color correction, and razor-sharp stars across an expansive, flat image circle.

Designed for serious astrophotographers and observatories alike, the Ultra-Cat 131 combines a fast focal ratio with uncompromising optical precision, enabling stunning deep-sky detail, rich contrast, and immersive wide-field compositions. Its premium mechanical construction, thermal stability, and flagship-level engineering set a new benchmark for large-format astrophotography systems.

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 Xterminator
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.

Personalized Laser Engraving
Free customization for direct purchases, adding a personal touch to your telescope.

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 (STX-R) 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

11.3 kg / 24.91 lbs

Total Weight

13.97 kg / 30.8 lbs

Diagram Reports;

                                    What's in the box

Main Tube

Bahtinov Cap

M48, M54, M68
Adapter with Wrench

Losmandy Plate

Mounting Ring & Handle bar

Riser Blocks

Soft Carry Case

Allen Key Set