PlaneWave - 12.5" CDK Corrected Dall-Kirkham Carbon Fiber Telescope

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-Chretien design. The RMS spot sizes at the edge of a 52mm diameter image circle yield are 12 microns, about the size of a pixel of most CCD cameras.

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 12.5"
Focal Length 2541 mm
Focal ratio f/8
Central Obstruction 39%
Back Focus 10.445" from focuser mounting surface, 7.2" from racked in focuser
Weight 46 lbs
OTA Length 31"
Optical Tube Carbon Fiber
Optical Performance Vignetting Plot - Spot and Diffraction Diagrams
Overall Dimensions Dimensions PDF

Primary Mirror

Diameter 13"
Aperture 12.5"
Focal ratio f/8
Mounting Laser Collimated and Permanentely Fixed
Material Precision Annealed Pyrex
Shape Prolate Ellipsoid
Coating Enhanced Aluminum - 96%

Secondary Mirror

Diameter 4.65"
Material Precision Annealed Pyrex
Shape Spherical
Coating Enhanced Aluminum - 96%

Lens Group

Diameter 70mm
Number of lenses 2
Coating Broadband AR Coatings (less than .5% from 400 to 700nm)
Standard Features

Carbon Fiber Tube 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
2.75" 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 picture 2)
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.

The CDK telescope is a brand new optical design invented by Dave Rowe. The goal of the design is to make an affordable astrographic telescope with a large enough imaging plane to take advantage of the large format CCD cameras of today. Most telescope images degrade as you move off-axis from either coma, off-axis astigmatism, or field curvature. The CDK design suffers from none of these problems. The CDK is coma free, has no off-axis astigmatism, and has a flat field. The design is a simple and elegant solution to the problems posed above. The CDK consists of three components: an ellipsoidal primary mirror, a spherical secondary mirror and a lens group. All these components are optimized to work in concert in order to create superb pinpoint stars across the entire 42mm image plane.