William Optics Redcat 51 WIFD

An f/4.9 Imaging Platform for Wide-Field Astrophotography

The Redcat 51 WIFD is purpose-built for astrophotography, combining a fast optical system with a rigid, stable focusing mechanism. William Optics' page says it offers hassle-free imaging without the struggle of backfocus, and describes it for both budding astronomers and seasoned astrophotographers.

This telescope simplifies the entire imaging process. A DSLR or mirrorless camera (with a T-mount) or an astronomy camera connects through the included M48 adapter, with no separate flattener to space.

A 4-Element Petzval System with FPL-53 Glass

At the core of the Redcat 51 is a 4-element Petzval-like optical design, William Optics' manual describes it as a unique Petzval design featuring four optical elements, with high-quality FPL-53 glass for superior optical performance.

Because the correction is part of the telescope's own optics, there is no separate flattener to choose or space. The manual's spot diagram shows the design across the field for the 45mm image circle.

51mm Aperture and 250mm Focal Length

The combination of a 51mm aperture and a 250mm focal length makes the Redcat 51 a true wide-field instrument. With a full-frame sensor the field is about 8.2 x 5.5 degrees, which frames large objects such as the Andromeda Galaxy (M31), the whole Veil Nebula complex or the North America Nebula (NGC 7000).

The fast f/4.9 focal ratio allows you to gather a significant amount of light in a short period. That shortens the exposure needed for each sub-frame, which helps on a portable mount.

A 45mm Image Circle for Full-Frame Sensors

The Redcat 51 WIFD has a 45mm image circle, which William Optics' manual calls full frame: it covers a 36mm x 24mm sensor (43.3mm diagonal).

A flat field also helps when you stitch several frames into a mosaic of a large nebula complex or a section of the Milky Way.

WIFD Focuser: Internal Focusing with a 10:1 Fine Knob

This Redcat model is equipped with the William Optics Internal Focus Design (WIFD), a rack-and-pinion focuser that the manual lists as compatible with EAF.

• Focuser tension: the manual shows tension screws (5mm Allen key) to increase focuser tension, and a focuser tension screw that you should not over-tighten and should release when focusing.
• 10:1 Dual-Speed Control: The manual lists a 2 speed 10:1 ratio fine knob, plus a focuser adjusting knob with a thermometer.
• EAF Compatibility: The manual gives six steps: remove the top screw with a 2mm Allen key, release the two inner knob screws, remove the knob, align the bracket screw holes, lock the two set screws on the shaft and tighten both bracket screws. With a motor fitted, do not over-tighten the tension screw.

M48 Connection, Rotator, and Integrated Tilt Adjuster

The manual shows M54 and M48 threads at the camera end, with an M48 filter position and an M48 adapter for the camera mount. A 48 mm T-mount or an M48 astronomy camera connects to it.

The imaging train includes:

• Camera Angle Rotator: A camera angle rotator with a locking screw lets you turn the camera to frame your target.
• Integrated Tilt Adapter: Inside the rotator, under a twist-off cover, is a tilt adapter with alternating push and pull screws for correcting sensor tilt.
• Focuser smoothness: push and pull gear spacing screws (3mm and 2mm Allen keys) adjust smoothness; adjust them only when necessary.

No External Flattener Required

The Redcat 51's four-element Petzval design needs no additional field flattener, which saves an accessory and a spacing step.

Attach your camera to the included M48 adapter and focus.

Visual Observing with the Redcat 51 WIFD

While designed primarily as an astrograph, the Redcat 51 WIFD can also be used for visual observation. At 250mm, eyepieces give low magnifications and wide fields of star clusters and the Milky Way.

William Optics makes a 1.25-inch erecting prism for the Cat 51 WIFD (its price list item D-EP90-125-RC51III; the manual's accessories map listed it as coming soon), which gives a correctly oriented image for daytime use. The short 250mm focal length is not meant for high magnification on planets.

Integrated Rings, Handle, and Vixen-Style Plate

The tube sits in a single mounting ring with a knob, which carries the saddle handle bar on top and the dovetail plate below.

• Saddle Handle Bar: The handle has M4 locking screws and M4 screw holes for a finder bracket; the manual's accessories map shows a red dot sight and the UniGuide 32mm guide scope (M-G32PB-RD, optional).
• 210mm Vixen-Style Dovetail Plate: The manual lists a 210mm Vixen style dovetail plate, which fits Vixen-style saddles and leaves room to slide for balance.
• Bahtinov Mask Cap: The dust cover has a built-in Bahtinov mask (marked patented): fit it, aim at a bright star and adjust the focuser until the diffraction spikes are symmetrical.

A 1.77 kg OTA Ready for Travel

The optical tube weighs 1.77 kg (3.90 lbs) and, with ring, dovetail and saddle, 2.38 kg (5.25 lbs). The tube length is 298mm.

A soft carry case is included for transport and storage.

Operation and Care: From First Light to Long-Term Storage

Proper care is essential for maintaining the optical performance of the Redcat 51. Before storing the telescope after a night of observing, allow it to acclimatize to room temperature with the lens cap off to ensure any dew or moisture evaporates completely. The manual warns that moisture can damage the optical elements. Always store the scope in the included case in a dry, temperature-stable environment.

For your safety, you must follow this solar warning: Never aim the telescope or finder at the Sun without proper solar filters installed on the front of the telescope; doing so for even a moment may permanently damage your vision. Solar eyepiece filters are not considered safe.