William Optics UltraCat 56 WIFD f/4.8 Astrograph

A 5-element full-frame astrograph that sharpens the corners of the RedCat formula

The William Optics UltraCat 56 is a 56mm f/4.8 apochromatic astrograph for wide-field deep-sky imaging. Its 5-element advanced Petzval design (2 Super ED, 1 ED, 1 lanthanum and 1 special X-element) produces a flat 50mm image circle with no separate flattener, so it covers full-frame, APS-C and Micro Four Thirds sensors. With a 269mm focal length it frames the Andromeda Galaxy, the North America Nebula and large Milky Way star fields, and the whole scope weighs just 7.08 lbs with its ring, handle and dovetail.

It's the step up from the popular RedCat 51: William Optics reports a 41% smaller RMS spot size in the far corners of a full-frame sensor, for tighter stars edge to edge on today's high-megapixel cameras. The UltraCat 56 is on display in our Denver store.

Why imagers choose the UltraCat 56

• Sharper corners on full frame: a fifth lens element tightens star images at the edge of the 50mm image circle, where 4-element designs start to soften.
• No flattener to buy or space: the flattening is built in. Set your camera at the recommended 55mm (±3mm) of back focus.
• Fast f/4.8 optics: collect signal quickly on short summer nights or between clouds.
• WIFD internal focuser: a rack-and-pinion focuser that moves the optics inside the sealed tube, so your camera never shifts or sags. The knob removes to fit an electronic autofocuser.
• Sensor Tilt Xterminator and rotator: fix sensor tilt from the side and frame targets without removing the camera.
• Built-in Bahtinov mask: the lens cap doubles as a focusing mask.

Field of view with popular cameras

With an APS-C camera, the Andromeda Galaxy, the Veil Nebula complex or the Heart Nebula fit in one frame. Full frame reaches for huge regions like the Rho Ophiuchi clouds or the Orion's Belt region with the Horsehead and Flame Nebulae.

What you'll need to complete your setup

• A mount: at 7.08 lbs, the UltraCat 56 suits a strain-wave mount like the Sky-Watcher Wave 100i or ZWO AM5N. With a light camera, a GoTo tracker like the Star Adventurer GTi can carry it for travel.
• A camera: a cooled astronomy camera such as the ZWO ASI2600MC Pro or ASI533MC Pro, or a DSLR or mirrorless camera. Use the included M48 adapter with a wide M48 T-ring for your camera, such as the Canon EF, Canon RF, Nikon F, Nikon Z or Sony E T-mounts.
• Autofocus (optional): the WIFD focuser accepts an electronic focuser such as the ZWO EAFN or EAF Pro.
• Guiding (optional): a small guide scope like the UniGuide 32 mounts on the handle bar.

Compare the William Optics Cat astrographs

Looking for the lightest option? The RedCat 51 is 1.8 lbs lighter and less expensive, with a 4-element design that's excellent on APS-C sensors.

Why buy from Mile High Astronomy

• No surprise import duties: our price includes all import duties. Telescopes ordered directly from overseas are often listed without duties, which are then billed separately before delivery.
• Ships from the US: your UltraCat 56 ships from our Denver store, not from overseas.
• Expert help from astrophotographers: we can help you choose a mount, camera and focuser for your setup, and we're here to help after the sale.

What's in the box

• William Optics UltraCat 56 WIFD f/4.8 astrograph with Sensor Tilt Xterminator and camera angle rotator
• Bahtinov mask cap for precise focusing
• M48 and M54 camera adapters, with adapter wrench
• Mounting ring and handle bar
• 210mm dual Vixen / Arca-Swiss dovetail plate
• Soft carry case
• Allen key set

UltraCat 56 FAQ

Do I need a field flattener?

No. The 5-element Petzval design has the flattening built in. Set your camera sensor 55mm (±3mm) behind the telescope using the included adapters and the right T-ring or spacers.

UltraCat 56 or RedCat 51?

Choose the UltraCat 56 if you image with a full-frame or high-megapixel camera and want the tightest stars in the corners, plus a little more aperture and focal length. The RedCat 51 is lighter, less expensive and excellent on APS-C and smaller sensors.

UltraCat 56 or UltraCat 76?

Both have the same 5-element design and 50mm image circle. The UltraCat 76 has 84% more light-gathering area and a 365mm focal length for a closer view of each target, but weighs almost 4 lbs more and needs a larger mount.

What mount do I need?

Plan for about 7 lbs for the telescope with its ring, handle and dovetail, plus your camera and guiding gear. A compact strain-wave mount like the Wave 100i or ZWO AM5N is an ideal match.

Can I add an electronic focuser?

Yes. The focus knob removes so an electronic focuser like the ZWO EAFN can drive the WIFD focuser directly. Installation steps are in the online manual.

Can I see one before I buy?

Yes. The UltraCat 56 is on display in our Denver store.

Optical performance

Specifications

Online manual: back focus, tilt adjustment, electronic focuser installation and mounting.