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CDK20 Optical Tube Assembly (F/7.77)

SKU# 200127Q

Price: $34,000.00


The CDK20 is an innovative telescope for unsurpassed astroimaging, research, or satellite tracking.

  • Additional 1.79″ of backfocus and 497 mm of focal length compared to the standard CDK20 f/6.8 model.
  • f/7.77 and 3951 mm focal length.
  • No coma, no off-axis astigmatism, and no field curvature.
  • Pinpoint stars across a 52mm image circle.
  • Rock solid fused silica mirrors with low thermal expansion.
  • Carbon fiber optical tube assembly for rigidity and fast cooling.
  • Simple secondary mirror collimation thanks to the fixed primary mirror.
  • If you have a standard CDK20 you can order the replaceable lens cell to convert to the f/7.77 model.


Capturing the most stunning astrophotographs possible is something our team is passionate about. From design to manufacture, our goal with the Corrected Dall-Kirkham (CDK) 20″ telescope was centered around performance and ease of use. The CDK20 is an incredible breakthrough in telescope technology and produces no off-axis coma and no off-axis astigmatism. Additionally, the CDK20 provides a perfectly flat field so your astrophotographs will have stunning clarity from corner to corner of the image without field curvature degrading the photos. Offering the simplicity of single-mirror collimation, the stray light control of advanced baffles, structural performance created through finite element analysis (FEA), and decades of telescope design experience, the CDK20 is an exceptional diffraction-limited telescope. CDK20 users can experience pinpoint stars edge-to-edge and a 45 x 45 arcminute field of view when using large 16803 size camera sensors. When equipment fades into the background and simply performs, the astrophotography experience becomes even more fun and rewarding!

Checkout more about our technology and optical design here.


CDK20's Features

Carbon Fiber Truss Design


Minimizes thermal expansion which causes focus shift as temperature changes during an imaging session. Carbon fiber also reaches ambient temperatures quickly and is extremely lightweight and rigid to help ensure excellent imaging data is produced.

3D Printed Baffles


PlaneWave uses digital 3D printing technology to produce lightweight baffle tubes. 3D printers add successive layers of material to construct a baffle system with precision positioned internal stray light baffles to minimize vignetting and maximize image contrast. Quality baffling makes an incredible difference in overall image quality, so we ensured an optimal design was created for our telescopes.

Dovetail Expansion Joint


Allows for the difference in thermal expansion between carbon fiber and aluminum. The expansion joint allows the aluminum dovetail to expand and contract without stressing the carbon fiber lower truss. This results in images that are not distorted due to expansion, or contraction of the optical tube materials.

Delta-T Ready


For added dew prevention, the CDK20 is internally wired with polyimide film heater pads and temperature sensor, which is ready to be controlled with the Delta-T via PlaneWave Interface 3 software.

Cooling Fans


Three fans on the backplate of the optical tube pull air through the telescope and by the primary mirror. Three fans on the side of the optical tube also blow air across the primary to ensure a boundary layer of air does not distort images. These fans help the telescope reach thermal equilibrium quickly, further reducing any distortion in images due to temperature variations. The fans are controlled by a switch on the optical tube, or can be controlled by via PWI3 software if a PlaneWave Electronic Focus Accessory (EFA Kit) is purchased.



Optical System

Aperture20 inch (508 mm)
Focal Length3951 mm (155.55 inch)
Focal ratiof/7.77
Central Obstruction39% of the Primary Mirror Diameter
Back Focus from mounting surface10.61 inch (269.49 mm)
Weight140 lbs (63.5 kg)
OTA Length47 inch (1,194 mm)
Upper CageCarbon fiber truss
Lower CageCarbon fiber truss with carbon fiber light shroud
Optimal Field of View52mm image circle

Secondary Mirror

Diameter7.5 inch (191mm)
MaterialFused silica (quartz)
CoatingEnhanced Aluminum – 96%

Primary Mirror

Optical Diameter20 inch (508 mm)
Outer Diameter20.5 inch (521 mm)
ShapeProlate ellipsoid
MaterialFused silica (quartz)
CoatingEnhanced aluminum – 96%

Lens Group

Diameter90 mm (3.54 inch)
Number of lenses2
CoatingBroadband AR Coatings (less than .5% reflected from 400 to 700nm)
Optical Diameter20 inch (508 mm)

Standard Features

Carbon Fiber Truss DesignMinimizes thermal expansion which causes focus shift with changes in temperature
Dovetail Expansion JointAllows 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 FansThree cooling fans ejecting air from the back of the telescope and four fans blowing across the boundary layer of the mirror surface. 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.


Crated Shipping Weight291 lbs   (132.0 kg)
Crate Width33 inch   (838 mm)
Crate Height33 inch   (838 mm)
Crate Length65 inch   (1,651 mm)

Included Accessories

Primary Mirror CoverTo protect the primary mirror
PlaneWave Thumb DriveContains software and instructions for collimation and spacing the primary to secondary mirror
12VDC Power SupplyProvides power for the fans (Not included for European Orders)
Wrench Set
Standard hex wrenches (European orders only)

Included Items

Included Items

Heating elements for dew preventionThe heating pads on the primary and secondary mirror require the 600195 Delta-T controller sold separately
OTA CoverTo protect the primary mirror and inside of the optical tube
FlashdriveContains software and instructions for collimation and spacing the primary to secondary mirror
Wrench Set (5812A35)Standard hex wrenches (European orders only)



For warranty information please check our Standard Warranty Page.