William Optics

SpaceCat 51mm f/4.9 Petzval Astrograph - DISCONTINUED

  • Sale
  • Regular price $748.00

Out of stock, but available to order.

Note: As of June 2020, William Optics has discontinued the SpaceCat to focus on production of the RedCat.  

Probably the very sharpest 250mm camera lens you will find!

  • 51mm Doublet ED APO f/4.9 (250mm fl)
  • FPL53 & FPL51 glass 
  • 3.2 lbs tube weight.
  • 44mm imaging circle with a flat field edge to edge for full-frame sensors
  • Dual Vixen and Arca Swiss Dovetail
  • M48 thread to accept wide t-rings/t-mounts


The best value, highest quality 250mm lens you will find for your camera.

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. 

Filter Adapter allows use of 48mm filters. Focusing is made easy with a bahtinov mask integrated into the lens cap. 


Aperture 51 mm (2")
Camera/Eyepiece Connection Male M48x0.75
Dawes Limit 0.46 arcseconds
Focal Length 250 mm
Focal Ratio f/4.9
Glass Type FPL-53 and FPL-51
Highest Useful Magnification 102x
Light Gathering Power 53x
Limiting Magnitude 12.3
Optical Design Petzval
Tube Color Space Grey
Tube Diameter 51mm
Tube Weight 3.2 lbs


  • SpaceCat 51mm Telescope
  • Bahtinov Mask
  • 210mm Dovetail
  • Mount Ring
  • Soft Carry Case