PlaneWave CDK20 f/6.8 Optical Tube Assembly The CDK20 f/6.8 is a 508 mm Corrected Dall-Kirkham astrograph with a 3454 mm focal length. Its design has no off-axis coma or astigmatism and a flat field across a 52 mm image circle.
Manufacturer model: PlaneWave CDK20 f/6.8 OTA (200104Q) · Specifications checked against manufacturer data on 2026-11-03
The CDK20 f/6.8 is a 508 mm Corrected Dall-Kirkham astrograph with a 3454 mm focal length. Its design has no off-axis coma or astigmatism and a flat field across a 52 mm image circle.
Construction
Fused silica mirrors and a carbon fibre truss minimise focus shift with temperature. Cooling fans, a Delta-T-ready system and mirror heater pads keep the optics stable and free of dew.
Optical system
Optical design
Corrected Dall-Kirkham
Aperture
508 mm (20")
Focal length
3454 mm
Focal ratio
f/6.8
Central obstruction
39% of primary diameter
Image circle
52 mm
Primary mirror
508 mm optical / 521 mm outer, prolate ellipsoid, fused silica, enhanced aluminium 96%
Secondary mirror
191 mm spherical, fused silica, enhanced aluminium 96%
Corrector lenses
90 mm, broadband AR (<0.5% reflection, 400–700 nm)
PlaneWave CDK20 f/6.8 Optical Tube Assembly The CDK20 f/6.8 is a 508 mm Corrected Dall-Kirkham astrograph with a 3454 mm focal length. Its design has no off-axis coma or astigmatism and a flat field across a 52 mm image circle.
Manufacturer model: PlaneWave CDK20 f/6.8 OTA (200104Q) · Specifications checked against manufacturer data on 2026-11-03
