William Optics Apochromatic refractor AP 76/365 UltraCat 76 WIFD (87765)

William Optics Apochromatic Refractor AP 76/365 UltraCat 76 WIFD (87765)

The UltraCat 76 is a premium 76 mm apochromatic refractor developed for astrophotographers who demand outstanding image sharpness and accurate color reproduction. It combines advanced optical engineering with a compact and robust design, making it ideal for wide-field imaging.

Featuring a sophisticated 5-element Petzval optical system with Super ED and lanthanum glass, the telescope achieves exceptional correction of chromatic aberration. With its fast focal ratio of f/4.8, it delivers bright, sharp, and flat-field images across a fully corrected 50 mm image circle. It is optimized for full-frame, APS-C, and Micro Four Thirds sensors, and also supports medium format cameras for expansive astrophotography.

The integrated optical corrector eliminates the need for an additional field flattener, simplifying setup and ensuring consistent performance.

Advanced Technologies and Features

• 5-element Petzval design with integrated field correction

• Super ED and lanthanum glass for precise color accuracy

• Fully corrected 50 mm image circle

• Anti-Shrink Lens Cell technology to maintain alignment under temperature changes

• Built-in Bahtinov mask for precise focusing

• Sensor Tilt Xterminator (STX) with integrated rotator to eliminate sensor tilt

The William Optics Internal Focus Design (WIFD) integrates a patented internal focusing mechanism directly into the main tube. This design ensures high mechanical stability and supports even large, heavy cooled cameras without flexure. Since the focusing movement is internal, no external extension is visible.

Users benefit from dual-speed fine focusing similar to a conventional focuser, without the typical issues associated with rear-mounted systems, such as vignetting. An integrated position indicator window allows quick and accurate reading of the focus scale. The focuser is compatible with ZWO EAF electronic focus motors.

Optical Specifications

• Optical design: Refractor, apochromat

• Aperture: 76 mm

• Focal length: 365 mm

• Focal ratio: f/4.8

• Resolving power: 1.82 arcseconds

• Limiting magnitude: 11.2

• Light gathering power: 120x

• Maximum useful magnification: 152x

• Fully corrected field: 50 mm

• Lens coating: Multi-coated

• Lens design: Triplet with integrated corrector

Tube and Construction

• Tube material: Aluminium

• Tube weight: 4.98 kg

• Tube length: 415 mm

• Carrying length: 363 mm

• Series: Cat

Focuser and Mechanics

• Internal focuser

• Adjustment range: 20 mm

• Rotatable focuser

• Integrated tilt adapter

Included Accessories

• Integrated corrector

• Bahtinov focusing mask

• Dew shield

• Vixen-style prism rail

• UniGuide 32 mm finder scope

• Carry case

• Optical tube assembly only (no mount included)

Application

• Astrophotography: Excellent performance

• Nebulae and galaxies: Yes

• Moon and planets: Yes

• Solar observation: Only with appropriate solar filter

• Nature observation: No

• Recommended for advanced users

• Not specifically intended for permanent observatory installation