William Optics Apochromatic refractor AP 56/269 UltraCat 56 WIFD (88286)

William Optics Apochromatic Refractor AP 56/269 UltraCat 56 WIFD (88286)

The UltraCat 56 is a compact, high-performance 56 mm apochromatic refractor developed for astrophotographers who require outstanding sharpness and true color reproduction. Despite its small size, it delivers professional-level optical performance for wide-field imaging.

The telescope features an advanced 5-element Petzval optical design incorporating Super ED and lanthanum glass. With a fast focal ratio of f/4.8, it produces exceptionally sharp, 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 is also compatible with medium format cameras for expansive wide-field astrophotography.

The integrated optical design eliminates the need for an additional field flattener, simplifying setup and reducing extra components.

Advanced Optical and Mechanical Features

• 5-element Petzval design for a naturally flat field

• Super ED and lanthanum glass for excellent color correction

• Fully corrected 50 mm image circle

• Anti-Shrink Lens Cell technology to minimize thermal expansion effects and maintain precise optical alignment

• Integrated Bahtinov mask for accurate and convenient focusing

• Sensor Tilt Xterminator (STX) with built-in rotator for precise sensor alignment and uniform sharpness

The William Optics Internal Focus Design (WIFD) incorporates a patented internal focusing mechanism combined with premium optics. The focusing movement is built directly into the main tube, leaving no external mechanical extension. This design supports even large and heavy cooled cameras without compromising stability or image quality.

Users benefit from dual-speed fine focusing controls similar to a traditional focuser, but without the limitations of rear-mounted focusers, such as vignetting. A built-in position indicator window allows quick and precise reading of the numerical scale. The focuser is compatible with ZWO EAF electronic focusers.

Optical Specifications

• Optical design: Refractor, apochromat

• Aperture: 56 mm

• Focal length: 269 mm

• Focal ratio: f/4.8

• Resolving power: 2.46 arcseconds

• Limiting magnitude: 10.5

• Light gathering power: 60x

• Maximum useful magnification: 112x

• Fully corrected field: 50 mm

• Lens coating: Multi-coated

• Lens design: Triplet with integrated corrector

Tube and Construction

• Tube material: Aluminium

• Tube weight: 3.21 kg

• Tube length: 348 mm

• Carrying length: 296 mm

• Series: Cat

Focuser and Connections

• Internal focuser design

• Adjustment range: 30 mm

• Rotatable focuser

• Integrated tilt adapter

• Camera-side threaded connections: M68, M54, M48

Included Accessories

• Integrated corrector

• Bahtinov focusing mask

• Dew shield

• Vixen-style prism rail

• Carry case

• No finder scope

• No mount included (OTA only)

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 setups