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.
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 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) |
| Back focus from mounting surface | 224 mm (8.81") |
|---|---|
| OTA length | 1194 mm (47") |
| Weight | 63.5 kg (140 lb) |
| Tube | Carbon fibre truss |
CDK20 f/6.8, not the f/7.7 version (3951 mm) or IRDK20. Optical RMS performance not published on the f/6.8 page.
Data sheet
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
