20 inch CDK Optical Tube Assembly

Part#: 200101

Price: $32,500.00

The PlaneWave Instruments CDK20 is a 20 inch (0.51 m) f/6.8 Corrected Dall-Kirkham Astrograph telescope. The CDK20 has a dual carbon-fiber truss design, with 3 cooling fans ejecting air from the back of the telescope. The CDK20 covers a 52 mm field of view without any field curvature, off-axis coma, or astigmatism. The instrument weight is 140 lbs (64 kg) and comes standard with a back plate retaining ring ready to accept the focuser of your choice.

Also available with Ritchey-Chrétien (RC) optics and Fused Silica glass
   New Fused Silica mirror option available on all  CDK and RC models     200101Q - CDK 20 Fused Silica - $37,000


The CDK (Corrected Dall-Kirkham) Optical Design is an innovative solution for unsurpassed astroimaging quality at an affordable price. The CDK telescope design provides excellent imaging with large format CCD cameras while remaining superb for visual use. The CDK design far exceeds the off-axis performance of most commercial telescope designs including the Ritchey-Chrétien design. This no-compromise design is unique in making the optical alignment forgiving and collimation very easy. This guarantees the user the best possible performance from the telescope. The end result at the image plane of the CDK design is no off-axis coma, no off-axis astigmatism, perfectly flat field (no off-axis defocus). The CDK design will give you pinpoint stars from the center to the corner of the field of view. More about our Optical Design


Carbon Fiber Truss Design Minimizes thermal expansion which causes focus shift with changes in temperature
Dovetail expansion joint Allows for the difference in thermal expansion between carbon fiber and aluminum. The expansion joint allows the aluminum dovetail expand and contract without stressing the carbon fiber lower truss  
Cooling Fans Three cooling fan blow out of the optical tube pulling air though the telescope and pass the primary mirror. This helps the telescope to reach thermal equilibrium quickly. The fans are controlled by a computer if the optional Electronic Focus Accessory (EFA Kit) is purchased.  


Aperture 20 inch (508 mm)
Focal Length 3454 mm (135.98 inch)
Focal ratio F/6.8
Central Obstruction 39% of the Primary Mirror Diameter
Back Focus from Racked in Focuser 5.8 inch (147 mm)
Weight 140 lbs (63.5 kg)
OTA Length 47 inch (1,194 mm)
Upper Cage Carbon Fiber Truss
Lower Cage Carbon Fiber Truss with Carbon Fiber Light Shroud


Diameter 7.5 inch (191mm)
Material Precision Annealed Borosilicate
Shape Spherical
Coating Enhanced Aluminum - 96%


Optical Diameter 20 inch (508 mm)
Outer Diameter 20.5 inch (521 mm)
Shape Prolate Ellipsoid
Material Precision Annealed Borosilicate or Fused SIlica
Coating Enhanced Aluminum - 96%


Diameter 90 mm (3.54 inch)
Number of lenses 2
Coating Broadband AR Coatings (less than .5% reflected from 400 to 700nm)

Crated Shipping Weight 291 lbs   (132.0 kg)
Crate Width 33 inch   (838 mm)
Crate Height 40 inch   (1,016 mm)
Crate Length 65 inch   (1,651 mm)
Ronchi Spacer (200354) This spacer sits in place of a focuser and is used for setting the primary to secondary spacing. It has an 1 .25”  inner diameter and may be used with 1.25” oculars for collimation.
Ronchi Ocular This ocular is a Ronchi screen used for setting the primary to secondary spacing.
Primary Mirror Cover  The Primary Mirror Cover protects the primary mirror.
Printed Instructions  For Collimation and Spacing
12VDC Power Supply (18778)  Provides power for the fans (Not included for European Orders)
Wrench Set (5812A35 )  English Hex Wrenches (European Orders Only)