William Optics OPT NightCat 51 | Special Edition

  • ***THIS IS CURRENTLY SOLD OUT*** All previous orders will ship as the manufacturer fulfills orders. This one of a kind, limited edition telescope will never again be available after current orders are completed.

  • If expedited shipping is selected, it will occur after OPT receives the product.

  • Everything you get with the popular RedCat...with a new look!

  • Handle and custom colored soft carry case included.
  • 43 mm image circle perfect for full-frame cameras.

  • 51 mm aperture Petzval refractor.
  • f/4.9 focal ratio allows for fast light-gathering power on this wide-field telescope.
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  • Regular price $778.00

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William Optics OPT NightCat 51 | Special Edition

William Optics RedCat 51 Front Body

Designed to be the best, and looking better than ever, this OPT special edition of the RedCat is an affordable, small, lightweight and fast apochromatic refractor for astrophotography. The unique optical design includes the highest quality glass for the best possible color correction and flat large image circle. The result is a 51 mm objective lens, in a sleek Petzval design, for a full-frame image.

Handle Included!

The included Cat Series handle gives you an easy handle to carry your NightCat. It has a V-Style saddle on top for attaching a guide scope.

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

William Opticas RedCat 51 Field Rotator

Field Rotator

Inspired by luxury watches, the telescope's field 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 fit within a degree of accuracy.

Filter Adapter

 It is now easier to connect your filter to the Filter Adapter.  

Filter Index

The filter index marks let you know the estimated focusing site when you twist the focuser.

Tilt Adjuster

The Tilt Adjuster can adjust the tilt of the image plane.

William Opticas RedCat 51 tube Ring

William Optics Redcat 51 Dovetail Bar

Modular Mounting

The single-tube Cat 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.

New Mounting


William Optics has reinvented the V-style dovetail. Not only will it fit into a V-style saddle plate, but if it's flipped over it can be attached to any Arca-Swiss style photography tripod head. This allows you to use the telescope for both day and night photography. The length of the new mounting plate is 210 mm.


Dew Shield

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

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 the 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 to 3 seconds.


Aperture51 mm (2")
Camera/Eyepiece ConnectionMale M48x0.75
Dawes Limit0.46 arcseconds
Focal Length250 mm
Focal Ratiof/4.9
Free ShippingYes
Glass TypeFPL53 and FPL51
Highest Magnification102x
Light Gathering Power53x
Limiting Magnitude12.3
Optical DesignPetzval
Tube ColorBlack with Blue highlights
Tube Diameter51mm
Tube Weight3.2 lbs


RedCat 51 included items
Customer Reviews
5.0 Based on 1 Reviews
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Canon L glass

While I haven't even seen one of these in the wild, I seriously doubt that it would beat a 200mm Canon L lens which are selling used for a lot less than this scope. A brand new Canon 200 L has f2.8 actually costs less. If you haven't used an f2.8 lens for astro work, you don't know what you're missing. With AF, you could also use the 200 f2.8 lens for terrestrial with lots of filter options. NiteCat 51 is good if you only do astro, but will be interesting to see how this compares to Canon L glass.