- CDK12.5

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 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.