William Optics Flat68III Field Flattener for f/6-7.5 Refractors

William Optics Flat68III Field Flattener for f/6-7.5 Refractors

Due to high demand and global product shortages due to the pandemic, please call for availability.

The WO Flattener 68III is a must-have if you desire a flat field for larger format imaging without focal reduction. It is adjustable for f/6-7.5 refractors. This high-quality accessory has been engineered and CNC machined for usage with WO APO refractors (including those of other make, if possessing a minimum 3" focuser, and if adaptable.)

The design is an airspaced ED doublet utilizing the best Ohara optical glass. The clear aperture of 50mm provides a well-illuminated 45mm imaging circle, intended to cover full size DSLR cameras. The field will be well flattened, realizing tight star images to the frame corners. STM coatings and internal threading/blackening maximize transmission and contrast transfer.

Depending on the telescope focal ratio and its inherent field curvature, the optimized spacing of lens and sensor is achieved by rotating the rear section to the required distance as measured against the built-in printed scale (in millimeters.) Then the locking ring is brought to bear against this rear section, solidly securing the assembly.

The usual superb William Optics anodized finish complements that of our telescopes. Protective covers are included for both ends. Accepts 48mm 'wide' T-rings for your camera (thread size M48x0.75, and sold separately).

Adjust Distance

  • 102GTS: 13.6mm
  • FLT132: 7.7mm
  • Z126: 3.0mm
  • GT153: 2.8mm


  • Focuser mating threads: M92 x 1.0
  • T-mount mating threads: M48 x 0.75
  • Fully-illuminated image circle: ⌀45mm
  • Flattener power: 1:1 (no magnification)

M48 wide T-rings for Canon, Nikon and Sony cameras can be found on our webstore.