CDK20 Optical Tube Assembly (F/7.77)
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!
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.
Technical Specifications
Optical System
| Aperture | 20 inch (508 mm) |
| Focal Length | 3951 mm (155.55 inch) |
| Focal ratio | f/7.77 |
| Central Obstruction | 39% of the Primary Mirror Diameter |
| Back Focus from mounting surface | 10.61 inch (269.49 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 |
| Optimal Field of View | 52mm image circle |
Secondary Mirror
| Diameter | 7.5 inch (191mm) |
| Material | Fused silica (quartz) |
| Shape | Spherical |
| Coating | Enhanced Aluminum – 96% |
Primary Mirror
| Optical Diameter | 20 inch (508 mm) |
| Outer Diameter | 20.5 inch (521 mm) |
| Shape | Prolate ellipsoid |
| Material | Fused silica (quartz) |
| Coating | Enhanced aluminum – 96% |
Lens Group
| Diameter | 90 mm (3.54 inch) |
| Number of lenses | 2 |
| Coating | Broadband AR Coatings (less than .5% reflected from 400 to 700nm) |
| Optical Diameter | 20 inch (508 mm) |
Standard Features
| 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 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. |
Shipping
| Crated Shipping Weight | 291 lbs (132.0 kg) |
| Crate Width | 33 inch (838 mm) |
| Crate Height | 33 inch (838 mm) |
| Crate Length | 65 inch (1,651 mm) |
Included Accessories
| Primary Mirror Cover | To protect the primary mirror |
| PlaneWave Thumb Drive | Contains software and instructions for collimation and spacing the primary to secondary mirror |
| 12VDC Power Supply | Provides power for the fans (Not included for European Orders) |
| Wrench Set (5812A35) |
Standard hex wrenches (European orders only) |
In the Box
| Heating elements for dew prevention | The heating pads on the primary and secondary mirror require the 600195 Delta-T controller sold separately |
| OTA Cover | To protect the primary mirror and inside of the optical tube |
| Flashdrive | Contains software and instructions for collimation and spacing the primary to secondary mirror |
| Wrench Set (5812A35) | Standard hex wrenches (European orders only) |
