William Optics WhiteCat 51 f/4.9 Petzval Refracting Telescope

  • Telescope tube weight: 3.2 lbs.
  • Focal length: 250 mm (9.85 inches)
  • Focal ratio: f/4.9
  • Aperture: 51 mm (2 inches)
  • Image circle: 43 mm
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  • Regular price $698.00

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William Optics WhiteCat 51 f/4.9 Petzval Refracting Telescope

William Optics WhiteCat 51

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.


William Optics WhiteCat Lens

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 a fast focal ratio of f/4.9. The RedCat 51 will out resolve most high-resolution DSLR lenses of similar focal lengths.


William Optics WhiteCat Back 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.


William Optics WhiteCat 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 Optics WhiteCat 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 WhiteCat Bahtinov Promo

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. Once 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


  • Soft carry case
  • WhiteCat 51 f/4.9
  • M48 Camera Mount
  • Patented Bahtinov Mask

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Stephen G.
United States United States

I’m a dog guy, but love these Cats!

At this moment I am sitting in the warm area of my observatory while a RedCat and a WhiteCat dual imaging system is gathering wonder subs. The images are razor sharp, crisp and detailed. The FOV of these 51mm scopes when coupled with ASI ZWO 1600MM Cooled cameras is perfect for wide field work. As an astrograph, there’s no fuss about back focus distance. The helical focuser is precise, though you do need to make small adjustments to get the provided Bahtinov mask lines properly situated. Love this scope. Admittedly I am a big William Optics fan, with two each of Star 71s and FLT 132s, and a ZS61 as a guide scope. Highly recommend the Cats...get one, or more!