William Optics RedCat 51LX - Upgraded Version

  • This item has an extensive wait list with the manufacturer and shipments are very limited! Due to high demand for this item, delivery dates are uncertain and can be approximately 4 weeks and up to 2-3 months before your order can be fulfilled.

  • 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.
  • Please note: the Focuser shown in the product images IS NOT INCLUDED with the purchase of this product.
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  • Regular price $748.00

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William Optics RedCat 51LX - Upgraded Version

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 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 ColorRed
Tube Diameter51mm
Tube Weight3.2 lbs


RedCat 51 included items
Customer Reviews
5.0 Based on 5 Reviews
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James C.
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

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
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
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.

United States
Amazing lens

Great. I have just started using it and it’s a piece of art