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William Optics RedCat 51LX - 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
    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 ColorRed
    Tube Diameter51mm
    Tube Weight3.2 lbs
  • included items

    RedCat 51 included items

Product Reviews

Customer Reviews
5.0 Based on 7 Reviews
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Filter Reviews:
George J.
United States United States
Work As Advertised

Great product and great service.

OPT Telescopes William Optics RedCat 51LX - Upgraded Version Review
Daniel D.
United States United States
Better late than NEVER

In general, my experience with OPT was stressful, not because OPT but because the backorder situation. They solved my issue rapidly after speaking with one of the managers. Thank you for making this happen in a fast way. Waited for more than 3 months and was able to get it. Once again, thank you OPT.

James C.
United States United States
Well made lens

This lens is all that is advertised. It had great reviews and the reviews are accurate. Well worth the wait.

Ron W.
United States United States

Just received my Red Cat today. Just from unboxing the unit to checking it out it appears to be a work of art ! A well thought out design for Astrophotography. Looking forward to getting it out tonight and giving it a run thru provided the weather permits.

A OPT Telescopes Customer
Robert K.
United States United States
Great Workmanship

I haven’t had it out yet, But I did install a Pegasus Cube V2 stepping motor so I can use auto-focusing. Very easy to do and works perfectly.

Rob P.
United States United States
A great small telescope

I enjoy grab and go astrophotography with camera lenses and small telescopes. The RedCat is small enough to work well with small "camera grade" mounts. Compared to my vintage Nikkor ED 180 and 300 mm lenses, the RedCat gives noticeably improved images. I wanted a travel scope that I could use for visual observation as well as astrophotography. The RedCat can also be converted to use an erecting prism and eyepiece. The quality of construction and finish is outstanding. It was obviously designed by an astrophotographer with evident careful thought to to imaging convenience. The camera style focus is easy and reliable to use and I love the ease with which I can rotate the camera frame. The construction quality, fit and finish strike me as close to that on my Questar, so I have hope that it will last for many decades of reliable use. My only criticism so far is that the procedure for swapping the camera adapter for the image erecting prism requires dealing with allen wrenches and set screws. Not a great idea in the dark. The procedure is also different for the original RedCat and this upgraded model. My first light image was everything I hoped for. I'm looking forward to many beautiful views and images with this scope. Kudos to WO for thinking a bit differently with this new line of scopes.