WILLIAM OPTICS ULTRA-CAT 131 f/4.9 REFRACTOR

The William Optics UltraCat 131 is a high performance 131mm apochromatic refractor designed for astrophotographers who demand top-tier performance. Featuring a 5-element advanced Petzval optical design and a fast f/4.9 focal ratio, it delivers breathtaking edge-to-edge clarity and vivid details, making it perfect for capturing expansive celestial views. Its robust build, exceptional optics, and innovative features redefine the standard for astrophotography.

Innovative 5-Element Petzval Design

Eliminates field curvature, providing sharp, flat-field images without requiring additional flatteners. This advanced system achieves a flawless spot diagram across a medium-format image circle.

This new system does NOT have specific requirement for the backfocus, however the focus travel distance can effect the ability to find the focus if there is too much space between the telescope and the acquisition device. 

60mm Superior Image Circle

Fully supports full-frame and medium-format cameras for wide-field and detailed astrophotography, outperforming standard ~130mm telescopes. 

Extra-Low dispersion ED Glasses

The Ultra-Cat 131 has two Super ED glass elements, one standard ED glass element, one lanthanum element and one X-element with advanced fully multi-coated, to deliver sharp and vibrant images with true colours, reducing chromatic aberration.

F/49 Fast Optics

Offers exceptional light-gathering capability for vibrant deep-sky photography.

WIFD (William’s Internal Focuser Design)

Patented internal centre balanced focuser ensures precise, stable, and hassle-free imaging, avoiding balance issues and eliminating vignetting. The WIFD system solves the issue of tube tilt caused by the excessive weight of accessories and cameras.

With its its precise internal sliding and balanced rigid, structure the Ultra-Cat 131 prevents image shift and weight limits for photographic equipment. 

The Rack & Pinion designed for the WIFD provide accurate and smooth focusing for both imaging and visual observation. Fine-tuning can be achieved thanks to 1:10 fine focuser.

Temperature can be immediately checked with the gauge installed in one of the knobs.

Anti-Shrink Lens Cell Technology

Minimizes thermal expansion and contraction, maintaining perfect optical alignment in any environment.

Sensor Tilt Corrector

The Sensor Tilt Xterminator (STX) allows to adjust the tilt without removing the camera. With its integrated and patented design eliminates distortion, optimizing sharpness and detail for professional-level results. This new system is an evolution of the old 4 pull-in and 8 push-out screws, with a more efficient 4 pull-in and 4 tension screws mechanism makes easier and effortless any correction.

Camera Rotator

As with all William Optics refractors, the Ultra-Cat 131 comes with a camera rotator built-in and integrated with the Sensor Tilt Xterminator. Smooth and precise control over adjustments are provided by an oil-sealed mechanism and the laser-engraved angle scale allows easy repeatability.

Built-In Patented Bahtinov Mask

The dust cap has an integrated Bahtinov Mask to simplify focusing for pinpoint precision, a feature that reduces the equipment needed, saving space. The mask is made in a high-transparent optical acrylic (PMMA) cut with precision laser, for a better transmission of the light and more accurate focus..  

Mounting Solutions

The Ultra-Cat 131 is equipped with finder-style saddle handle allowing easy installation of guide/finder scopes, control computers and other accessories. It combines ergonomic usability with enhanced portability. 

Diagram Report

SPECIFICATIONS

Items included

• Ultra-Cat 131
• Lens cover with Bahtinov mask and cover
• M68 to M48, M54 adapter with dust cap
• Handle bar with mini-Vixen-style mounting base
• Mounting rings with Losmandy-style dovetail
  
• William Optics bag for Ultra-Cat 131
• Allen key set

Instruction Tilt Adjuster (STX)

Installing EAF