William Optics RedCat 51 III WIFD f/4.9 Petzval Refractor Telescope

What Makes the RedCat 51 So Great?

With its premium quality optics, case-included portability, and a Petzval optical design all for under $1000, it's a no-brainer why this telescope has been a best-selling telescope for astrophotographers for years. The RedCat 51 features a focal length of 250mm and a focal ratio of f/4.9, which is perfect for wide field imaging and very forgiving for beginner astrophotographers who may not have top of the line tracking mounts. You can find many of the amazing images taken with the RedCat 51 on AstroBin.

Designed for Wide Field Astrophotography

The RedCat 51's focal length of 250mm is ideal for wide field astrophotography of large nebulae, galaxies, and the Milky Way. The shorter focal length also makes it very forgiving for beginners because it doesn't require as precise of tracking with a mount. Please note that the new WIFD RedCat series telescopes cannot be used visually at this time, but this could change in the future with the addition of accessories.
 

Premium Quality Optics & Petzval Design

Like the previous versions, the RedCat 51 III features FPL-53 glass, which is some of the highest-quality glass available in consumer telescopes today. The RedCat 51 III features four lens elements arranged in a Petzval optical design. A Petzval design has two big benefits. First, the addition of a field flattener is not necessary as it is built into the design. On other telescopes like triplet refractors, a field flattener (added cost) is required for round stars throughout the image. Second, back focus does not need to be precise. This means that you are free to add any accessory in your image train as you'd like, such as a rotator, as long as you can reach focus. No need to conform with 55mm back focus standards like on other telescopes.

What's new about the RedCat 51 III vs. older RedCat 51s?

There are three main differences between the RedCat 51 III and older versions:

1. RedCat 51 III has the same optics as its predecessors, but features a brand new focuser design: the WIFD. William Optics developed this patented focuser design as an improvement to standard drawtube style focusers. They have been replacing all of their existing telescopes to feature this upgraded design. Read on to learn about the WIFD focuser below.
2. As a result of this new focuser design, the RedCat 51 WIFD is also quite a bit heavier than the previous version. This version weighs 5.2 lbs (2.4 kg) vs. the RedCat 51 "U" which weighs 3.9 lbs (1.8 kg) with all accessories (dovetail, tube rings, and saddle) attached.
3. The back of the tilt adapter on the RedCat 51 III now features M54 x 0.75 threads. This means you may remove the M48 adapter and attach M54 accessories, which is the preferred thread size if you are imaging with a full frame sensor camera.
    

Game-Changing WIFD Focuser

If there was one thing to nitpick about earlier versions of the RedCat 51, it would be its helical-style focuser. This focuser design, much like a camera lens, had a rubber ring that wasn't easily compatible with autofocus systems. William Optics recognized this flaw and has given the RedCat 51 III the William Optics Internal Focus Design, or WIFD for short. The WIFD is in the conversation for being the best focuser design in consumer telescopes today.

Instead of the traditional design that extends out the rear of the telescope, the WIFD focuser moves all of the glass lens elements internally. This has multiple benefits — not only does it eliminate vignetting from images, but it also essentially guarantees that there will be no dreaded sensor tilt from the telescope itself. This means that you can add a number of heavy accessories to your imaging train, such as a large filter wheel or rotator, without worrying about sag from the telescope focuser drawtube. Regardless, William Optics has included a tilt adapter built in to the telescope anyway to correct for tilt in case it is caused by other components in your image train. Below is a diagram of how the WIFD focuser works:
 

Out-of-the-box Compatibility with ZWO EAF

Unlike previous versions of the RedCat 51, the WIFD version is compatible with the popular ZWO EAF (electronic automatic focuser) out of the box. This allows for a quick & easy autofocuser solution that enables you to get perfect focus every time, regardless of which operating system you use: PC, Mac, or ASIAIR. You can find instructions on how to install the EAF onto the RedCat 51 III in our Links & Downloads section below.
 

Built-In Filter Drawer

Like previous versions, the RedCat 51 WIFD also features a built-in filter holder. Simply unscrew the M48 adapter (letter P in the diagram below) and thread in your favorite M48 filter. This makes it easy for DSLR & Mirrorless camera owners to add light pollution filters to their image train for better astrophotography images.
 

RedCat 51 III Components

A. Rear Dust Cap (M48)
B. Saddle Handle Bar
C. WIFD Focuser
D. Dew Shield
E. Lens Cover with Bahtinov Mask
F. Front Bahtinov Mask Cover
G. Mounting Ring / Knob
H. Camera Angle Rotator
I. 210mm Dovetail Bar
J. Dual Speed 10:1 Ratio Focus Knob with Fine Focus Control
K. M4 Screw Holes for Finder Bracket
L. M4 Locking Screws on Saddle Handle Bar
M. Camera Angle Rotation Locking Screw
N. M4 Screw Holes for Finder Bracket
O. Focuser Adjusting Knob with Thermometer
P. M48 Adapter (for Camera Mount)

RedCat 51 Specifications

• Optical Design: Petzval (4-element)
• Glass Type: FPL-53
• Focal Length: 250mm
• Aperture: 51mm
• Focal Ratio: f/4.9
• Image Circle: 45mm (full frame)
• Focuser: William Optics Internal Focus Design (WIFD)
• Focuser Compatibility: ZWO EAF
• Tube Length: 298mm
• Dew Shield Circumference: 265mm
• Dew Shield Diameter: 84mm
• Weight of OTA only: 3.90 lbs (1.77 kg)
• Weight of OTA with tube rings, dovetail, & saddle: 5.25 lbs (2.38 kg)