Site Visit to Planewave



Joe Haberman Standing Next to a CDK17	CDK17 next to "puny" 13-Inch Classical Cass.

Better size representation between the two telescopes (NOTE: The "corrector glass" in the back of the CDK17)	This CDK17 is getting ready to ship

Another view of the two telescopes	Another view of the two telescopes (seems the 13" grew a little?)

This web page details a site visit I made to Joe Haberman's Planewave Instrument's Corporate HQ in Torrance, California on 17 January 2009. Joe was good enough to show me around his well organized facility and compare my old trusty 13" classical cassegrain with their more modern, Dall-Kirkham cassegrains. He had two fully assembled CDK17's (17" aperture DK OTA) as well as most of the mounting paraphernalia needed to mount them on either a AP1200 GTO or Bisque Paramount. Note the large mounting wedge under CDK17. This fits into a special "female" adapter that Planewave makes to mount on Astrophysics, Bisque, or any other german equatorial mount; the fork mounts use a different system. The CDK17 next to Joe is on a special heavy duty Celestron mount. As you can see, the CDK dwarfs the 13-inch classical cassegrain. The primary mirror size in the CDK17 is 17.5" with a useble apeture of 17." The secondary mirror is a relatively small 6.25" and the tube and support struts are all carbon fiber. The focuser assembly was most impressive, and as Mr. Haberman explained, is capable of holding a very large load (say SBIG ST-11K CCD camera with AO-L, etc..) with less then 5 micron (0.005mm) deflection when slewed to across the sky. This 3.5" diameter focuser looks stable enough to handle 10lbs instrument loads (CCD, large filter wheel, AO-L, Rotator...etc) with ease. I was at first thinking about mounting a AP2.7" focuser, but this set-up looks much more robust. Additionally, Joe gave me a quick tour of the grinding/polishing room for the 12.5, 17.5, & 20" blanks. The mirrors they use are "truncated cone" types that have the desirable properties of lightweight with quick cool-down times. These look like excellent systems for an amateur looking to make some great imaging or deep photometry/asteroid work; the system is as fast as F/6.8. Soon to be added accessories are a instrument rotator and thermal control box for secondary (anti-dew) mirror heating. Here is a quick read of the CDK17 specs (as of 2009):

SYSTEM
Aperture	17"(0.43M)
Focal Length	2939mm
Focal Ratio	F/6.8
Central Obstruction	39%
Back Focus	8.8" from Backplate
	5.8" from Racked in Focuser
Instrument (OTA only) Weight	94 lbs
OTA Length	37"
Upper Cage Construction	Carbon Fiber Truss
Lower Cage Construction	Carbon Fiber Truss
	with carbon Fiber Light Shroud
Performance	6.5 micron rms @ 21 mm and
	9.6 micron at 26mm off-axis (λ=730, 585, & 430 nm)
PRIMARY MIRROR
Diameter	17.5"
Aperture	17"
Focal Ratio	F/2.6
Material	Precision Annealed Pyrex
Shape	Prolate Ellipsiod
Coating	Enhanced Multi-layer Aluminum Coatings
SECONDARY MIRROR
Diameter	6.25"
Material	Precision Annealed Pyrex
Shape	Spherical
Coating	Enhanced Multi-layer Aluminum Coatings
LENS GROUP
Diameter	90mm
Number of lenses	Two (2)
Coating	High Transmission Anti-reflective Coatings

Here is a shaded drawing of the OTA from a .PDF diagram on the Planewave Instrument website