PlaneWave CDK20 Astrograph f/6.8 (various versions available)

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PlaneWave CDK20 Astrograph f/6.8 (various versions available)

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€ 41,100.00 Price excl. German VAT tax (19%): € 34,537.82

  • CDK 20 Astrograph, 20 inch with Fused Silica Optics
  • modified to Dall-Kirkham, with fully corrected image field
  • 3.454 mm (f/6,8), 52 mm field of view
  • Delta T Ready, 3,5" Hedrick Focuser and EFA Kit separately available
Important note: This product is not available online. If you are interested, please send us a formal inquiry incl. contact data by email. We shall gladly provide a detailed offer.

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€ 41,100.00 Price excl. German VAT tax (19%): € 34,537.82

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PlaneWave CDK 20"

CDK 20 auf Ascension HR Montierung

The 20" CDK is a revolutionary new telescope optical system that is designed to excel at imaging on large format CCD cameras while remaining an excellent instrument for visual use.

One of the unique features of the CDK design is its ease of collimation and achievable centering tolerance for a telescope of its class. This assures the user will get the best possible performance out of the telescope. The end result is a telescope which is free from off-axis coma, off-axis astigmatism, and curvature of field, yielding a perfectly flat field all the way out to the edge of a 52mm image circle.

The telescope is available in fused silica optics, Ritchey-Chrétien (RC) optics and infrared optimized.

Fused Silicia is a synthetic amorphous silica glass of the highest purity and one of the most transparent glasses made. The optical and thermal properties of fused silica are superior to other types of glass due to its purity. Its transmission and homogeneity exceed those of crystalline quartz without the problems of temperature instability inherent in the crystalline form. Fused Silica has a coefficient of thermal expansion six times lower than Borosilicate (Pyrex) glass, which means that as fused silica cools down, it preserves its shape to a high degree of accuracy. This translates into consistent optical performance and unchanging focus over temperature changes. With its high melting temperature ()~ 1.600 degree Celsius), a very low coefficient of thermal expansion and resistance to thermal shock, fused silica is the material of choice for professional observatories as well as various scientific applications.

Spotdiagramm CDK 20

To the left are two simulations showing the CDK's stunning performance. The first is a diffraction simulation and the second is a spot diagram.

In both simulations the small squares are 9x9 microns, about the size of a CCD pixel. In the diffraction simulation the star images on axis and off-axis are nearly identical. In the spot diagram 21mm off-axis the spot size is an incredible 6 microns RMS diameter. For 26mm off-axis, a 52mm image circle, the RMS spot size is 11 microns. This means the stars across the entire focal plane are going to be pinpoints as small as atmospheric seeing will allow.

The spot diagram was calculated at 720, 585, and 430nm. Many companies show spot diagrams in only one wavelength, however to evaluate chromatic performance multiple wavelengths are required. Both of the simulations take into consideration a flat field, which is a more accurate representation of how the optics would perform on a flat CCD camera chip.


New "state of the art" observatory at the University of Leicester

On December 7, 2009, a Planewave CDK 20, mounted on a Paramount, ME was inaugurated at the University of Leicester, Department of Physics and Astronomy. The complete installation and delivery took place by the company Baader Planetarium, Mammendorf.

Planewave CDK 17 Mallorca Planewave CDK 17 Allsky Kuppel Planewave CDK 17 Allsky Kuppel

Pictures taken by CDK20":

M 27, Dumbbell Nebula
M 27, Dumbbell Nebula
Arp 316, (NGC 3193, 3187, 3189) and NGC 3185
Arp 316, (NGC 3193, 3187, 3189) and NGC 3185
NGC 5139, Omega Centauri
NGC 5139, Omega Centauri
Draco Trio of Galaxies
Draco Trio of Galaxies



Aperture 20 inch (508 mm)
Focal Length 3454 mm(135.98 inch)
Focal ratio f/6.8
Central Obstruction 39% of the Primary Mirror Diameter
Back Focus from Racked in Focuser 5.8 inch (147 mm)
Weight 140 lbs (63.5 kg)
OTA Length 47 inch (1,194 mm)
UpperCage Carbon Fiber Truss
Lower Cage Carbon Fiber Truss with Carbon Fiber Light Shroud
Optimal Field of View 52mm Image Circle



Diameter 7.5 inch (191mm)
Material Precision Annealed Borosilicate
Shape Spherical
Coating Enhanced Aluminum - 96%


Optical Diameter 20 inch (508 mm)
Outer Diameter 20.5 inch (521 mm)
Shape Prolate Ellipsoid
Material Fused Silica
Coating Enhanced Aluminum - 96%



Diameter 90 mm (3.54 inch)
Number of lenses 2
Coating Broadband AR Coatings (less than .5% reflected from 400 to 700nm)



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
Cooling Fans Three cooling fans blow air inside the back of the telescope. This helps the telescope to reach thermal equilibrium quickly. The fans are controlled by a computer if the optional Electronic Focus Accessory (EFA Kit) is purchased.
Delta-T Ready For added dew prevention, the CDK14 is internally wired with polyimide film heater pads and temperature sensor, ready to be controlled with the optional Delta-T controller.
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