William Optics

RedCat 51 WIFD f/4.9 III


  • Sale
  • Regular price $898.00

Yes, our inventory is accurate!

See It In Person - On Display In Our Showroom!

Qualifies for Free Ground Economy Shipping (CONUS Only)

NEW WIFD Version III RedCat

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

  • Newest version uses the new William Optics Internal Focuser Design (WIFD)
  • 51mm quadruplet ED APO f/4.9 (250mm fl)
  • FPL53 & FPL51 glass 
  • 5.25 lbs weight with rings, dovetail, handlebar.
  • >43mm 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

RedCat 51 WIFD III Manual (pdf)

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 Red
Tube Diameter 84mm
Tube Weight 5.25 lbs
Dew Shield Outer Diameter (for soar filter sizing) 84mm


Note: You may need a riser block to use the RedCat 51 on some dual-saddle mounts. The focuser impacts the plate on the Celestron Advanced VX mount saddle that accepts both CG5 and CGE plates. The focus knob does not impact the Celestron CGX saddle, or the iOptron CEM70 and GEM45 / CEM40 dual-saddle plates. The focuser knob does not impact the SkyWatcher EQ6 and HEQ5 mounts.

  • RedCat 51mm Telescope
  • Bahtinov Mask Cap
  • 210mm Dovetail
  • Upgraded Mount Ring (with cat paw logo)
  • Soft Carry Case