William Optics UltraCat 56 f/4.8 WIFD

5-Element Petzval Optics: A Flat 50mm Image Circle at f/4.8

The UltraCat 56's optical system is engineered to deliver a perfectly flat field across its entire 50mm image circle, eliminating the need for a separate field flattener. This 5-element Petzval design incorporates two Super ED glass elements, one ED element, and one Lanthanum element to achieve apochromatic color correction, rendering stars as sharp points with no distracting chromatic aberration.

The fast f/4.8 focal ratio significantly reduces exposure times, allowing you to gather more signal on faint, expansive targets like the Andromeda Galaxy (M31) or the Rho Ophiuchi cloud complex in a single session. This combination of a wide, flat field and fast optics makes the UltraCat 56 an ideal instrument for full-frame and APS-C DSLR or dedicated astronomy cameras.

WIFD Focuser: 30mm of Travel with Integrated Rotation & Tilt

At the heart of the imaging train is the William Optics Internal Focus Design (WIFD), a robust rack-and-pinion mechanism that moves the lens elements internally. This design provides 30mm of precise focus travel without any external tube extension, preventing focuser sag and maintaining perfect balance, which is critical when using an electronic autofocuser (EAF).

• Integrated Rotator: The included 360° rotator allows for effortless camera framing without loosening any threaded connections, preserving optical alignment.
• Sensor Tilt Adjuster: A built-in tilt adapter lets you fine-tune your camera's sensor plane to be perfectly orthogonal to the optical axis, ensuring sharp stars across the entire frame.
• Bahtinov Mask Cap: The lens cap features an integrated Bahtinov mask, providing a simple and highly accurate tool for achieving critical focus every time.

2.56 kg Portability with Vixen/Arca-Swiss Compatibility

Engineered for imagers on the go, the UltraCat 56 OTA weighs only 2.56 kg (5.64 lbs). This low weight makes it an excellent match for portable tracking mounts and simplifies setup and transport for field use. The entire package, including rings and dovetail, comes in at a mere 3.21 kg.

The instrument includes a dual-function dovetail plate that is compatible with both traditional Vixen-style saddles and modern Arca-Swiss tripod heads, offering maximum mounting flexibility. The patented William Optics handle bar not only provides a secure grip but also serves as a mounting point for guide scopes or other accessories, while the included soft carry case protects the telescope during travel and storage.

UltraCat 56 vs. RedCat 51: Aperture and Image Circle

While the RedCat 51 has established itself as a benchmark for ultra-portable astrographs, the UltraCat 56 offers key advantages for imagers seeking more light-gathering power and wider field coverage.

• RedCat 51 Advantage: The RedCat 51 is slightly smaller, lighter, and has a proven track record as one of the most popular portable imaging refractors available.
• UltraCat 56 Advantage: The UltraCat 56 features a larger 56mm aperture compared to the RedCat's 51mm, providing a 20% increase in light-gathering area. Its 50mm image circle is also significantly larger than the RedCat's 44mm circle, offering superior illumination and less vignetting for full-frame and larger sensors.