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PlaneWave Instruments IR DK20 20 inch Infrared Dall-Kirkham Optical Tube Assembly

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Product Description

This is a Dall-Kirkham optical design with coatings that are optimized to transmit in infrared wavelengths.  It is diffraction limited across a 20mm image circle at the focal plane.  There are no refractive lens, only reflective components to the design.  The reflectives coatings are a protected gold which give better than 98% reflectivity from .65 micron (650nm) to 16 micron (16000nm).  This design is ideal for infrared astronomy or LIDAR applications.   The IR DK is available in the three different apertures, 20", 17" and 12.5" 


Aperture 20" (.51m)
Focal Length 3454 mm
Focal ratio f/7
Central Obstruction 39% of the Primary Mirror Diameter
Back Focus 8.9" from focuser mounting surface, 5.81" from racked in focuser
Weight 140 lbs
OTA Length  47" 
Upper Cage Carbon Fiber Truss
Lower Cage Carbon Fiber Truss with Carbon Fiber light shroud

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 Protected Gold Reflective Coating - 98% (.65-16micron)

Secondary Mirror

Diameter 7.5"
Material Precision Annealed Pyrex
Shape Spherical
Coating Protected Gold Reflective Coating - 98% (.65-16micron)

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".
Cooling 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.

Shipping Dimensions and Weight  

Crate Dimensions:  59" X 32" X 36"

Crate Shipping Weight:  291 lbs

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