William Optics Ultra-Cat 76

William Optics Ultra-Cat 76

Description

The William Optics Ultra-Cat 76 is a premium apochromatic refractor built for astrophotographers seeking uncompromising performance. Its advanced 5-element Petzval optical design (2× Super ED, 1× ED, 1× Lanthanum, 1× X-element) ensures excellent chromatic correction and naturally flat-field images. Unlike many refractors, no field flattener is required: stars remain pinpoint to the very edge of the frame.

With a focal length of 365 mm and a fast f/4.8 focal ratio, the Ultra-Cat 76 excels in deep-sky imaging, capturing faint objects in shorter exposures. The large 50 mm image circle fully supports full-frame, APS-C, M4/3, and even medium-format sensors, making it highly versatile.

The patented WIFD (William’s Internal Focuser Design) rack-and-pinion focuser ensures precise, stable focusing with no flexure or vignetting, and is fully EAF-compatible. Integrated Sensor Tilt Xterminator (STX) and rotator eliminate sensor tilt issues, guaranteeing uniform sharpness across the frame.

Thermal stability is achieved via Anti-Shrink Lens Cell technology, maintaining perfect optical alignment under varying temperatures. A patented Bahtinov mask, integrated in the lens cap, allows quick and accurate focusing.

Compact (363–415 mm tube length) and portable (3.81 kg OTA, 4.98 kg total), the Ultra-Cat 76 combines robust anodized aluminum construction with an ergonomic patented handle. It comes with M54 and M48 adapters, and supports multiple camera mounts: Canon EF/RF, Nikon F/Z, Sony E, Pentax K, Fuji X, and MFT.

Technical specifications

• Optical design: 5-element Petzval apochromatic quintuplet

• Aperture: 76 mm

• Focal length: 365 mm

• Focal ratio: f/4.8

• Optical elements: 2× Super ED, 1× ED, 1× Lanthanum, 1× X-element

• Image circle: 50 mm

• Flattener: Not required

• Supported formats: Full Frame, APS-C, M4/3, Medium Format (compatible)

• Focuser: WIFD internal rack-and-pinion, EAF compatible

• Focus travel: 0–20 mm (scale to 21 mm)

• Tilt adjustment: Integrated Sensor Tilt Xterminator + rotator

• Thermal design: Anti-Shrink Lens Cell

• Focus aid: Built-in patented Bahtinov mask

• Tube length: 363–415 mm

• OTA weight: 3.81 kg

• Total weight: 4.98 kg

• Accessories included: M54 and M48 adapters, patented handle, Bahtinov mask

• Camera mounts: Canon EF/RF, Nikon F/Z, Sony E, Pentax K, Fuji X, MFT

• Finish: Robust anodized aluminum