[Refurbished] Ultra-Cat 56

The Ultra-Cat 56 is a high-performance 56mm apochromatic refractor, engineered for astrophotographers who demand exceptional portability without sacrificing optical precision, color accuracy, and wide-field performance.

Featuring a 5-element advanced Petzval optical design with super ED and lanthanum glass, paired with a fast f/4.8 focal ratio, the Ultra-Cat 56 delivers razor-sharp, perfectly flat images across a 50mm image circle. With a 269mm focal length, it is optimized for Full Frame, APS-C, and M4/3 sensors, and remains fully compatible with Medium Format cameras, making it an ideal ultra-wide-field imaging platform for deep-sky and large-scale nebula photography.

Key Features:

Advanced 5-Element Petzval Optics
Eliminates field curvature, ensuring sharp, edge-to-edge stars without additional flatteners.

50mm Large Image Circle
Fully supports Full Frame cameras, APS-C and M4/3 sensors for optimal performance. Compatible with Medium Format.

Fast f/4.8 Optics
Superior light-gathering capability, enabling deep-sky imaging with shorter exposure times.

WIFD (William Optics Internal Focuser Design)
Patented internal rack-and-pinion focuser ensures stable and precise focusing.
No vignetting or balance issues — ideal for astrophotography.
Compatible with EAF (Electronic Automatic Focuser) for precision focus control.

Sensor Tilt Xterminator (STX) & Rotator
Integrated tilt adjuster eliminates sensor misalignment, ensuring uniform image sharpness.

No Flattener Required
The optical design naturally corrects field curvature, simplifying setup.

Anti-Shrink Lens Cell Technology
Reduces thermal expansion effects, maintaining perfect optical alignment in any climate.

Patented Bahtinov Mask for Focusing
Built-in focusing aid ensures pinpoint star sharpness with ease.

Premium Build & Ergonomic Design
Lightweight yet robust (4.31 kg / 9.5 lbs) construction with a sleek anodized finish.
Patented handle bar design for enhanced portability and ease of use.

Versatile Camera Compatibility
Supports Canon EF, RF, Nikon F,Z, Sony E, Pentax K, MFT, and FUJI X mounts.