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William Optics RedCat 51 f/4.9 Petzval Refracting Telescope

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  • Regular price $698.00

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Accessories Added

  • 51mm f/4.9 Petzval design makes the RedCat 51 the ultimate portable astrophotography telescope
  • Includes a patented Bahtinov Cap to help achieve perfect focus quickly and easily
  • 43mm corrected image circle for use with full-frame cameras


William Optics RedCat 51 f/4.9 Petzval Refracting Telescope

William Optics RedCat 51 Front Body

From the beginning, the goal was to create the best possible design for an affordable, small, lightweight, and fast Apochromatic refactor for astrophotography. The unique optical design includes the highest quality glass for the best possible color correction and flat large image circle. The results is a 51mm objective lens, in a sleek Petzval design, for a full frame image.

Optical Design

51 mm lens, in a sleek Petzval design, using Synthetic Fluoride (FPL53 and FPL51) glass for a full frame flat field image. The optical quality provides exceptional performance at fast focal ratio of f/4.9. The RedCat 51 will out resolve most high resolution DSLR lenses of similar focal lengths.

William Optics RedCat 51 Front Objective

William Optics RedCat 51 Front Objective

William Opticas RedCat 51 Field Rotator

Field Rotator

Inspired by luxury watches, the telescope's filed rotator is laser etched with a  degree indicator. To ensure that you will have the most precise framing possible in a small portable system, the camera can be  rotated to within a degree of accuracy.

Modular Tube Ring

The single tube ring is sturdy enough to hold the optical tube and a large sized DSLR without noticeable flexure. It is modular in the sense that you can add a finder scope or guide camera.

William Opticas RedCat 51 tube Ring

William Optics Redcat 51 Dovetail Bar

All New Dovetail

William Optics has reinvented to the V-style dovetail. Not only will it fit into a vixen style saddle plate, but if it's flipped over it can be attached to any Arca-Swiss style photography tripod head, allowing you to use the telescope for both day and night photography.

Reversible dew shield

To maximize portability, the dew shield on this telescope is reversible. When stored backyards it can shorten the telescope length by approximately 83mm.

William Optics RedCat 51 Invertable Dew Shield

RedCat 51 Bahtinov Cap

Bahtinov Cap

The cap with this telescope not only protects the glass from the elements, but it also has one of these most useful tools when it comes to focusing.

The Bahtinov Cap creates three lines that pass through a bright star. There is a main large line, and a smaller cross-section of two lines making an “X”. The goal is to get the large line centered between the X and centered on the star. As soon as that is done you have perfect focus in as little as 2-3 seconds.


Aperture51 mm (2")
Camera/Eyepiece ConnectionMale 2" Filter/Wide T—Ring (M48x0.75)
Corrected Image Circle43mm
Dawes Limit2.27 arcseconds
Focal Length250 mm
Focal Ratiof/4.9
Free ShippingYes
Glass TypeFPL53
Hightest Magnification102x
Light Gathering Power53x
Limiting Magnitude12.3
Optical DesignPetzval
Tube Diameter80mm
Tube Length225mm
Tube Weight3.2 lbs


RedCat 51 included items