William Optics UltraCat 108 WIFD f/4.8 Astrograph

A 108mm medium-format astrograph with a 60mm flat field

The William Optics UltraCat 108 (also written Ultra-Cat 108) is a 108mm f/4.8 apochromatic astrograph with a 518mm focal length. Its 5-element advanced Petzval design (2 Super ED, 1 ED, 1 lanthanum and 1 special X-element) produces a flat 60mm image circle with no separate flattener, large enough for medium format, full-frame, APS-C and Micro Four Thirds sensors. It's built for imagers who want the reach for galaxy groups and nebula detail without giving up a fast focal ratio.

Why imagers choose the UltraCat 108

• A 60mm image circle: covers 44 x 33mm medium format sensors, and gives full-frame cameras sharp, evenly illuminated corners.
• 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 with 108mm of aperture: 518mm of focal length at a speed that keeps total integration times short.
• WIFD internal focuser: a rack-and-pinion focuser that moves the optics inside the sealed tube, so heavy cameras and filter wheels never shift or sag. 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.
• Anti-shrink lens cell: designed to hold optical alignment through large temperature swings, a real help on Colorado nights.
• Built-in Bahtinov mask: the lens cap doubles as a focusing mask.

Field of view with popular cameras

With an APS-C camera, the Elephant's Trunk Nebula, the Pelican Nebula or Markarian's Chain fill the frame. Full frame takes in the whole North America Nebula or the Leo Triplet with plenty of surrounding sky.

North America Nebula by DavesView, with a ZWO ASI6200MM Pro full-frame camera

IC 1396, the Elephant's Trunk Nebula, by Yungshih Lee, with a ZWO ASI2600MM Pro

Markarian's Chain with M87 and M88 by Yungshih Lee, with a ZWO ASI2600MC Duo

LDN 43, the Cosmic Bat Nebula, by Yungshih Lee, with a ZWO ASI2600MC Duo

What you'll need to complete your setup

• A mount: the UltraCat 108 weighs 21.12 lbs with its rings, handle and dovetail. With a camera and guiding gear, plan for a mount like the ZWO AM5N or Sky-Watcher Wave 150i, or a mid-size German equatorial mount.
• A camera: a cooled astronomy camera such as the ZWO ASI2600MM Pro or ASI2600MC Pro, a full-frame or medium format astronomy camera, or a DSLR or mirrorless camera. M48, M54 and M68 camera adapters are included.
• Autofocus (optional): the WIFD focuser accepts an electronic focuser such as the ZWO EAFN or EAF Pro.
• Guiding (optional): the handle bar's mini Vixen base takes a UniGuide 50 guide scope (sold separately, and shown in some photos).

Compare the William Optics Cat astrographs

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 108 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 108 WIFD f/4.8 astrograph with Sensor Tilt Xterminator and camera angle rotator
• Bahtinov mask cap for precise focusing
• M79 to M68, M79 to M54 and M79 to M48 camera adapters
• Mounting rings and handle bar with mini Vixen base
• Vixen-style dovetail plate
• Soft carry case
• Allen key set

The UniGuide 50 guide scope shown in some photos is not included.

UltraCat 108 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 spacers.

Will it cover a medium format camera?

Yes. The 60mm image circle covers a 44 x 33mm medium format sensor, and M68, M54 and M48 adapters are included for large-sensor cameras and filter wheels.

UltraCat 108 or Cat 91?

The UltraCat 108 has 41% more light-gathering area, a longer 518mm focal length and a larger 60mm image circle. The Cat 91 is about 7 lbs lighter and frames a little wider, and fits on smaller mounts.

UltraCat 108 or UltraCat 131?

The UltraCat 131 has more aperture and a 648mm focal length for smaller targets, but weighs about 31 lbs and needs a heavy-duty mount. The UltraCat 108 is the more portable choice with the same 60mm image circle.

What mount do I need?

Plan for about 21 lbs for the telescope with its rings, handle and dovetail, plus your camera, filter wheel and guide scope. A harmonic mount like the ZWO AM5N or Wave 150i, or a German equatorial mount in the 30 to 45 lb payload class, is a good match. If the focuser knobs touch your mount's saddle, loosen the rings slightly and rotate the tube for clearance.

Can I add an electronic focuser?

Yes. The WIFD focuser accepts an electronic focuser like the ZWO EAFN. Installation steps are in the online manual.

Optical performance

Specifications

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