The Telescope Authority
Since 1947

View Shopping Cart

Your Cart is Empty

William Optics OPT NightCat 51 | Special Edition


- Read
  • Call for Availability

  • No Longer Available

Add to Wishlist

Got questions? Click for live chat

  • 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.

Product Details

  • 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.

  • specifications

    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
  • included items

    RedCat 51 included items

Product Reviews

Customer Reviews
5.0 Based on 2 Reviews
Write a Review Ask a Question
  • Reviews
  • Questions

Thank you for submitting a review!

Your input is very much appreciated. Share it with your friends so they can enjoy it too!

Filter Reviews:
United States United States
Can't wait!

Ever since I got this there has not been ONE day for viewing--The unit is very well made to perfection works nice with mirrorless camera --auto focuser next project

United States United States
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.