William Optics Apochromatic 56/269 mm Refractor Ultra-Cat 56 WIFD

William Optics Apochromatic Refractor AP 56/269 UltraCat WIFD

With a 5-element advanced Petzval optical design, including super ED and lanthanum glass, and a fast f/4.8 focal ratio, this telescope delivers stunningly sharp, flat-field images across its 50 mm image circle. Optimized for full frame, APS-C, and M4/3 sensors, it also offers limited compatibility with medium format cameras for outstanding wide-field astrophotography.

The UltraCat astrograph at a glance

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

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

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

WIFD (William 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 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.

No Flattener Required
The Petzval 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.

Sensor Tilt Xterminator (STX) & Rotator
Integrated tilt adjuster eliminates sensor misalignment, ensuring uniform image sharpness. The adjustment is not complicated:

1. Locate the pair of diagonally opposing screws corresponding to the affected corners.
2. Use 2 mm hex key to release (turn clockwise) the STX knob near the corner where the sensor is too far.
3. Push out (turn counterclockwise) the opposite knob accordingly.

Do not touch the Auto Tension Screws. It may disrupt balance or cause loosening.

Make small adjustments - turn each knobs only about 1/8 turn at a time, and avoid rotating any knob beyond a full 360°.

Use gentle pressure when turning - overtightening may affect collimation or introduce unwanted stress.

4. After each adjustment, perform a test exposure to check the star shape and alignment. Fine-tune as needed until the stars are round and sharp across the entire frame.

Tips & Notice

Perform adjustments in a stable environment - wait for your optics and sensor to cool, and avoid large temperature fluctuations during testing.

Typical tilt tuning takes 2-4 test exposures. Final adjustment needs may vary depending on your camera, filters, and backfocus configuration.

Tilt does not require frequent adjustment. Once properly set, it should remain stable unless major components (e.g., camera, tilt plate, or spacing) are changed.

Lock the CAA knob before adjusting tilt to ensure consistent and accurate results.

Do not overload the STX adjusters - keep constant load under 4 kg and impact load under 2 kg to preserve mechanical precision.

Superb focusing
The William Optics Internal Focus Design (WIFD) is an innovative and revolutionary design that combines a precise (patented) internal focusing mechanism with the highest quality optics available, offering the ultimate apochromatic refractor for astrophotography. Designed from the ground up to handle even the largest, heaviest, cooled cameras, this optics is uncompromising in its quality. The focuser movement is integrated into the main tube, so no adjustments are visible from the outside.

The user can enjoy the benefits of a conventional focuser with two fine focus controls without having to worry about the limitations normally found with conventional rear-mounted focusers (vignetting). The integrated position indicator window on the focuser allows instant verification of the graduated numerical display.

The focusing mechanics can be adjusted:




The focussing system is compatible with ZWO´s EAF
The installation can be done by the user, there are detailed and illustrated instructions:

- Telescope
- Camera adapters
- Dust cap with Bahtinov mask
- Tube rings
- Handle bar with integrates finder base
- Dovetail bar
- Bag

Safety informations: PDF Download