PlaneWave - CDK17 Telescope

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.

The latest member of the CDK family is the CDK17.  The CDK optical design is the innovative solution for unsurpassed astro-imaging
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 35mm full frame remain smaller than
a single pixel of a CCD camera.  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, and a perfectly flat field all the way
out to the edge of 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	 17"
Focal Length	 2939 mm
Focal ratio	 f/6.8
Central Obstruction	 39%
Back Focus	 8.8" from focuser mounting surface, 5.8" from racked in focuser
Weight	 94 lbs
OTA Length 	 37" 
Upper Cage	 Carbon Fiber Truss 
Lower Cage	 Carbon Fiber Truss with Carbon Fiber light shroud
Optical Performance	6.5 micron rms at 21mm and 9.6 micron at 26mm off-axis.  Vignetting and Spot Performance   -   Spot and
Diffraction Diagrams
Overall Dimensions	 Dimensions PDF

Primary Mirror

Diameter	17.75"
Aperture	17"
Focal ratio	f/2.6
Mounting	Laser Collimated and Permanentely Fixed 
Material	Precision Annealed Pyrex
Shape	Prolate Ellipsoid
Coating	Enhanced Multilayer Aluminum - 96%

Secondary Mirror

Diameter	6.25"
Material	Precision Annealed Pyrex
Shape	Spherical
Coating	Enhanced Multilayer Aluminum - 96%

Lens Group

Diameter	90mm
Number of lenses	2
Coating	Broadband AR Coatings (less than .5% per surface from 400 to 700nm)
Standard Features

Carbon Fiber Tube Design	Minimizes thermal expansion which causes focus shift with changes in temperature
Carbon Fiber Lower Light Shroud	Protects the primary mirror from damge 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
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 picture 2)
 Colling Fans	Three fans blow out of the optical tube pulling air though the telescope and by the primary mirror. This helps the
telescope to equilibrate quickly.  The fans are controlled by a switch on the optical tube or can be controlled by a computer if
the optional Electronic Focus Accessory (the EFA Kit) is purchased.