William Optics REDCAT 51 WIFD

William Optics MiniCat 51: the Perfect Wide-Field Astrophotography Telescope

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.

William Optics also offers a 1.25" 90-degree diagonal (sold separately) so you can now use this scope with eyepieces for visual use too. However, please note that depending on the back focus required by an eyepiece, not all 1.25" eyepieces might reach focus. This scope cannot be used with 2" diagonals and eyepieces.

WIFD Focuser: Ideal for Serious Imaging

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:

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.

William Optics 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)
• Soft Carrying Case External Dimensions: 39x25x27 (cm)