William Optics RedCat 51 APO f/4.9 Refracting Telescope

63,000.00 excl. 18% GST

  • Telescope Series: William Optics RedCat
  • Optical Design: Refractor
  • Refractor Design: Apochromat (APO)
  • Number of Refractor Elements: 4
  • Aperture: 2″ (51 mm)
  • Focal Ratio: f/4.9
  • Focal Length: 250 mm
  • Focuser Style: Helical
  • OTA Length – Retracted: 8.3″ (210 mm)
  • OTA Weight: 2.9 lb.
  • Image Circle Size: 44 mm

Available on backorder


The William Optics RedCat 51 sports optics made of Ohara FPL53 & FPL51 synthetic fluorite glass for beautiful high contrast, spectacularly sharp results when used in both visual and photographic applications. APO performance means you’ll have virtually zero chromatic aberration. The Petzval design, which consists of four elements in three groups, also known as a Quad, produces a full frame flat field, with a image circle of 44mm.

Thoughtful and Innovative Design

Let’s start at the front and work our way back! The RedCat body is made of a strong aluminum alloy and is anodized a beautiful red for strength and durability. A matching dew/sun shield can be attached when needed and then inverted to store the lens without the additional length the dew shield provides. An aluminum threaded cap protects the optics whenever the RedCat is not in use.

In the middle of the RedCat 51, you will find a nicely designed ring mount that attaches to the reversible base and wraps securely around the body of the lens. A red anodized knob allows you to loosen the ring enough to fully rotate the RedCat 51, and of course, it is also used to lock the ring in place. The “ring” has a flat section that has two 1/4-20 holes spaced far enough to allow the addition of a red dot finder, microphone, or other compatible accessories.

Calibrated Helical Focuser with 360-Degree Rotator

The helical focuser with a focusing index on the RedCat has a focus tension ring that allows you to lock focus or just increase or decrease the drag to your liking. A field rotator is included with this 250 mm lens as well, and every degree is plainly marked…all 360 of them! William Optics says they were inspired by luxury watches when they designed this rotator, but what it means to you is mosaics of large celestial objects or sections of the sky will be much easier!

A filter slot is built into the OTA just after the rotator and accepts 48 mm filters, and the back of the RedCat is fitted with M48 threads. Attach a full-frame (M48) M 4/3, Nikon, Canon, Sony, or Pentax T-ring to the threads and use your DSLR to produce beautiful images. Or, attach a diagonal and eyepiece and turn this 250mm f/4.9 beauty into a telescope or spotting scope.


Model Number L-RC51Ix
Telescope Series William Optics Cat
Focal Ratio f/4.9
Optical Design Refractor
Telescope Aperture 51mm (2″)
Telescope Mount Type No Mount – OTA Only
Type of Electronics OTA Only – No Electronics
Number of Refractor Elements 4 (Quad)
Focal Length (mm) 250 mm
Image Circle 44mm
Focuser Style Helical
Refractor OTA Length – Extended (in.) 12″ (305 mm)
Refractor OTA Length – Retracted (in.) 8.86″ (225 mm)
Telescope OTA Weight (lb.) 3.24 lb. (1.47 kg)


  • Soft carry case
  • RedCat 51mm f/4.0 OTA – Red OTA with Black Accents
  • M48 Camera Threaded Mount (Required 48mm Wide T-Ring sold separately)
  • Patented Bahtinov Mask
  • Dovetail 210mm
  • Mounting Rings


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