William Optics MiniCat 51 WIFD f/3.5 Astrograph

A 5-pound f/3.5 astrograph for the widest, fastest deep-sky fields

The William Optics MiniCat 51 WIFD f/3.5 is a 51mm, 178mm focal length astrograph made for wide-field astrophotography. Its 6-element Petzval design, with 2 Super ED elements and lanthanum glass, gives a flat field with no separate flattener. William Optics' patented WIFD focuser moves the optics inside the sealed tube instead of pushing a drawtube in and out, so a heavy camera doesn't tilt as you focus. The tube is just 210mm long, and the whole scope with its ring, handle and dovetail weighs 2.29kg (5.05lb), light enough for a star tracker.

Key specs: 51mm aperture · 178mm focal length · f/3.5 · 6-element Petzval with 2 Super ED elements · 43.2mm image circle · no flattener needed · WIFD rack-and-pinion focuser, EAF compatible · 2.29kg (5.05lb) total

The MiniCat 51 is on display in our Denver store, so you can see it in person before you buy.

What you can image

• Large nebula regions: the Heart and Soul Nebulae together, the North America and Pelican Nebulae with the stars around Deneb, and the Rosette with the Cone Nebula and Christmas Tree Cluster.
• Orion: the Orion Nebula, the Running Man and the Horsehead and Flame Nebulae in one frame.
• Galaxies in context: the Andromeda Galaxy with M32 and M110 and plenty of sky around it.
• Comets and the Milky Way: the wide field and fast optics are well suited to bright comets with long tails and to star fields in Cygnus, Sagittarius and Scorpius.

How it works

No flattener to space: the flattening is built into the 6-element design. William Optics recommends 55mm (±3mm) from the camera adapter to the sensor, and the focuser's 28mm of travel covers back spacing from about 30mm to 58mm. Use the included M48 adapter with a wide M48 T-ring for a DSLR or mirrorless camera, or the right spacers for an astronomy camera.

Focusing: turn the large knob on the WIFD rack-and-pinion focuser and read the position in the scale window on top of the tube. The focus knob has a built-in thermometer, which helps you know when to refocus as the night cools. The knob removes so an electronic focuser can drive it.

Framing: loosen the rotator to turn the camera to any angle using the degree scale, and use the tilt adjuster if your stars are elongated on one side of the frame.

What to add for the best results

• A mount (required): at 5.05lb with ring, handle and dovetail, the MiniCat rides on the iOptron SkyGuider Pro star tracker or the GoTo Sky-Watcher Star Adventurer GTi. For a full imaging rig with guiding and a cooled camera, a strain-wave mount like the ZWO AM3N with TC40 tripod is a good match.
• A camera (required): an APS-C astronomy camera like the ZWO ASI2600MC Pro or the ASI2600MC Air with built-in ASIAIR, or a 1" camera like the ASI533MC Pro for a tighter field.
• A T-ring for DSLR or mirrorless cameras: William Optics wide M48 T-mounts for Canon EF, Canon RF, Nikon F, Nikon Z, Sony E and Fuji X.
• Autofocus: a ZWO EAFN, with the K-Astec EAF bracket with clutch made for WIFD focusers. Autofocus is especially useful at f/3.5, where the focus zone is narrow.
• Filters: a ZWO M54 2" filter drawer (20mm thick, so it counts toward your 55mm back focus) with a fast-optics dual-band filter like the Colour Magic C 2" duo-band package, which is designed for wider bandpasses at fast focal ratios.
• Guiding and control: the handle's mini Vixen-style base takes a UniGuide 32 guide scope, and an ASIAIR Plus runs the camera, mount and focuser from your phone or tablet.

MiniCat 51 vs. RedCat 51 III vs. RedCat 61

Prefer space gray? The MiniCat 51 SpaceCat is the same telescope in a gray finish. See all William Optics Cat astrographs.

What's in the box

• William Optics MiniCat 51 WIFD f/3.5 astrograph with tilt adjuster and rotator
• Bahtinov mask cap for focusing
• M48 camera adapter (M54 to M48)
• Mounting ring and handle bar with mini Vixen-style base
• Dual-sided dovetail plate
• Soft carry case
• Allen key set

The mount, camera, T-ring and filters are sold separately.

William Optics MiniCat 51 FAQ

Is the MiniCat 51 good for beginners?

Yes, with one caveat. The short focal length is forgiving of small tracking errors, and there's no flattener to space, which makes it a nice first astrograph. The f/3.5 focal ratio makes focus more critical, so use the included Bahtinov cap carefully or add an autofocuser.

MiniCat 51 or RedCat 51?

The MiniCat is faster (f/3.5 vs. f/4.9) and wider (178mm vs. 250mm), so it collects signal about twice as fast on large targets. The RedCat 51 III has a larger 48mm image circle for full-frame cameras and a slightly closer view.

Will it work with a full-frame camera?

William Optics lists full frame as compatible, but recommends APS-C. The 43.2mm image circle matches the full-frame diagonal, so expect some softening and darkening in the far corners. For full frame, the RedCat 51 III or RedCat 61 is a better fit.

Can I use it for visual observing?

No. The MiniCat is an astrograph built for cameras, not eyepieces.

What mount do I need?

For a DSLR or mirrorless camera, a star tracker such as the SkyGuider Pro or Star Adventurer GTi is enough. With a cooled camera, guide scope and filter drawer, step up to a strain-wave mount like the ZWO AM3N.

Can I add an electronic focuser?

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

Can I see one before I buy?

Yes. The MiniCat 51 is on display in our Denver store.

Specifications

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