The new CDK optical design is the innovative solution for unsurpassed astroimaging quality at an affordable price. The purpose of the design is to provide a telescope that will excel at 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. The RMS spot sizes at the edge of a 35mm frame remain smaller than a single pixel on the most advanced CCD cameras available to amateurs today. This no-compromise design is unique in making the optical alignment very forgiving and collimation very easy. This guarantees the user will be sure to get the best performance out of the telescope possible. 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), all the way out to a 52mm image circle. All this means, the stars will be pinpoints from the center of the field of view out to the corner of the field of view. Features and Specifications System | Aperture | 20" (.51m) | | Focal Length | 3454 mm | | Focal ratio | f/6.8 | | Central Obstruction | 39% | | Back Focus | 8.9" from focuser mounting surface, 5.81" from racked in focuser | | Weight | 135 lbs | | OTA Length | 47" | | Upper Cage | Carbon Fiber Truss | | Lower Cage | Carbon Fiber Truss with Carbon Fiber light shroud | | Performance | Optical Performance - Vignetting and Spot Performance | | Dimensions | Overall Dimensions |
Primary Mirror | Diameter | 20.5" | | Aperture | 20" | | Focal ratio | f/3 | | Mounting | Laser Collimated and Permanently Fixed | | Material | Precision Annealed Pyrex | | Shape | Prolate Ellipsoid | | Coating | Enhanced Aluminum - 96% |
Secondary Mirror | Diameter | 7.5" | | Material | Precision Annealed Pyrex | | Shape | Spherical | | Coating | Enhanced Aluminum - 96% |
Lens Group | Diameter | 90mm | | Number of lenses | 2 | | Coating | Broadband AR Coatings (less than .5% from 400 to 700nm) |
Standard Features | Dual Carbon Fiber Truss Design | Minimizes thermal expansion which causes focus shift with changes in temperature | | Carbon Fiber Lower Light Shroud | Protects the primary mirror from damage and from stray light | | 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 | | Dovetail | The CDK20 comes with one of two dovetail designs. The first is the massive PlaneWave dovetail and the second is a dovetail compatible with Software Bisque's Versa Plate, VP dovetail. Both utilize the expansion joint listed above. | | 3.5" Hedrick Focuser | Heavy duty no-slip focuser. The focus tube runs on 5 bearings and is driven by a leadscrew so there is no chance of slipping. It accepts an optional dial indicator and PlaneWave's EFA Kit to control many electronic accessories. The draw tube travel is 1.3". (View picture) (View picture2) Drawing of flange - Drawing of draw tube | | Cooling Fans | Three fans blow filtered air onto the back of the primary mirror to help it quickly equibrate to the ambient temperature. The fans are controlled by a switch on the optical tube or can be controlled by a computer if the optional EFA Kit is purchased. |
Shipping Dimensions and Weight Crate Dimensions: 59" X 32" X 36" Crate Shipping Weight: 291 lbs  shown with optional motorized focuser
CDK20 shown on the Software Bisque Paramount ME
CDK20 shown on the Mathis Instruments MI750 Forkmount 
CDK20 shown on the 10-Micron GM4000 
CDK20 on Celestron CGE Pro Mount 
CDK20 shown on the Celestron CGE Pro | 
ALTERNATIVE PRODUCTS
