William Optics Ultra-Cat 76
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William Optics Ultra-Cat 76
The William Optics Ultra-Cat 76 is a high-performance 76 mm apochromatic refractor optimized for wide-field astrophotography. With a 5-element Petzval design, fast f/4.8 ratio, and a 50 mm image circle, it delivers sharp, flat images across full-frame and medium-format sensors.
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
William Optics Ultra-Cat 76
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William Optics Ultra-Cat 76
The William Optics Ultra-Cat 76 is a high-performance 76 mm apochromatic refractor optimized for wide-field astrophotography. With a 5-element Petzval design, fast f/4.8 ratio, and a 50 mm image circle, it delivers sharp, flat images across full-frame and medium-format sensors.