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William Optics RedCat 51II - Upgraded Version


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  • The ultimate portable astrophotography telescope with Bahtinov mask built into the cap for quick and easy focusing.

  • 43 mm image circle is perfect for full-frame cameras in this 51 mm aperture petzval refractor. 
  • The f/4.9 focal ratio allows for fast light-gathering power on this wide-field telescope.
  • Includes the Iconic Soft Cat Carry Case.

Product Details

  • William Optics RedCat 51 Front Body

    The Limited Edition RedCat 51 Upgrade f/4.9 APO 250 mm Telescope!

    Designed to be the best, 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 result is a 51 mm 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 a fast focal ratio of f/4.9. The Limited Edition RedCat 51 Upgrade 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 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.

    Camera Sensor 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 Ring

    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.

    All New Mounting Plate

    William Optics has reinvented 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. This allows you to use the telescope for both day and night photography. The length of the new mounting plate is 210 mm.

    Reversible 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 a perfect focus in as little as 2 to 3 seconds.

  • specifications

    Aperture51 mm (2")
    Camera/Eyepiece ConnectionMale M48x0.75
    Corrected Image Circle43 mm
    Dawes Limit0.46 arcseconds
    Focal Length250 mm
    Focal Ratiof/4.9
    Free ShippingYes
    Glass TypeFPL53 and FPL51
    Highest Magnification102x
    Interfacemini USB 2.0
    Light Gathering Power53x
    Limiting Magnitude12.3
    Optical DesignPetzval
    Tube ColorRed
    Tube Diameter51mm
    Tube Length228mm
    Tube Weight2.9 lb
    Tube Weight3.2 lbs
  • included items

    RedCat 51 included items

Product Reviews

Customer Reviews
5.0 Based on 14 Reviews
5 ★
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Eric K.
United States

Great quality!

I haven’t had too much experience with it yet but this is a beautiful scope and feels very durable. The few photos I’ve taken are stunning and OPT got it to me earlier than expected! Great service!

Andrew F.
United States United States

Love it

Amazing quality. Great captures. Easy setup.

OPT Telescopes William Optics RedCat 51II - Upgraded Version ReviewOPT Telescopes William Optics RedCat 51II - Upgraded Version Review
Cesar G.
Guatemala Guatemala

little big heavenly red cat

It is a work of art, almost an artisanship. I feel comfortable using it these days. Receive a greeting from Quetzaltenango, Guatemala in Central America, 2300 meters above sea level. As there are cloudy days, also cold clear nights. I send a couple of photographs of Selene, one in black and white with a small Meade LPIG camera and the other with a Canon eos Ra. The quality of the lens is good and pretty. It is a basic and simple photography work, which shows a good product

OPT Telescopes William Optics RedCat 51II - Upgraded Version ReviewOPT Telescopes William Optics RedCat 51II - Upgraded Version Review
United States United States

WO RedCat 51 upgraded version

Limited use so far, very sharp on both my Cannon stock 90D and the Ra. Still waiting OPT for my shipment of the T Mount for EOS from WO, but glad I have gotten the lense. I was able to get a mount that is very secure and await an optically clear front lense cover for the 55mm threads to protect the front glass from another well known suppler for the B+W glass. Picked up the saddle as well and both the lense and saddle were included in the carry case. FYI, case still has another cut block that can be removed from the foam block in the case to add additional storage, gave them a 5 Star, be hard pressed to lower

Mike B.
United States United States

RC51 LX review

Excellent experience. Telescope is exactly what salesman described. Don was very helpful with the necessary information to help me make my decision.Scope is well made and easy to use. MB

United States United States

great Tele

Excellent Tele /Photo Lens. used it to shoot the moon last night.