PlaneWave CDK17 Astrograph f/6.8 (various versions available)

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PlaneWave CDK17 Astrograph f/6.8 (various versions available)

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€ 25,850.00 Price excl. German VAT tax (19%): € 21,722.69

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  • CDK17" Astrograph, 17 inch with Borosilicate Optics or Fused Silica Optics
  • modified to Dall-Kirkham, with fully corrected image field
  • focal length 2.939 mm (f/8)
  • 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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€ 25,850.00 Price excl. German VAT tax (19%): € 21,722.69

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PlaneWave CDK 17"

The PlaneWave Instruments CDK17 is a 17 inch (0.43 m) f/6.8 Corrected Dall-Kirkham Astrograph telescope. The CDK17 covers a 70 mm field of view without any field curvature, off-axis coma, or astigmatism. The instrument weight is 94 lbs (43 kg) and comes standard with a back plate retaining ring ready to accept the focuser of your choice.

The abbreviation CDK stands for the optical system of the PlaneWave astrographs - a Dall Kirkham Cassegrain with a optical correction unit. More about the Optical Design (CDK).

The PlaneWave CDK17 is available in various types of mirror material. Standard mirror material is borosilicate. The telescope is also available in fused silica optics.

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.

We presented the CDK 17" together with Rick Hedrick, the CEO of CDK, at the ATT 2008 in Essen.

  • Aperture: 17" = 430 mm
  • Focal length: 2.940 mm
  • Focal ratio: f/6.8
  • Obstruction: 49% of the Primary Mirror Diameter
  • Field of View = 70 mm (instead of the normal CDK 17" - 52mm)
  • Figure = diffraction plates of 6.5 mu / 21mm off axis and 9.6 mu / 26mm off axis at 430, - 585 and 730 nanometer wavelength
 
Spotdiagramme für den CDK 17 Widefield Astrographen
 
 

The graphic on the left shows the vignetting and spot diagrams for the CDK 17 Widefield Astrographer depending on the large CCD chips KAF 6303, KAF 11000 and KAF 09000 for the three wavelengths 730, 585 and 430 Nanometer.

The diameter of a star at the edge of the flat field corresponds to the pixel size of current large-format CCD chips and the imaging quality of the optics is limited only by the seeing conditions and the quality of the tracking. The large field of view of 70mm diameter offers enough tolerance for CCD cameras with ever larger chips - also for amateur astronomy.

 

Pictures taken by CDK17":

NGC 6960, Veil Nebula
NGC 6960, Veil Nebula
M 31, The Andormeda Galaxy
M 31, The Andormeda Galaxy
M 81
M 81
NGC 6888, Crescent Nebula
NGC 6888, Crescent Nebula
 

Specifications:

OPTICAL SYSTEM

Aperture 17 inch (432 mm)
Focal Length 2939 mm (115.71 inch)
Focal ratio f/6.8
Central Obstruction 23.7% by surface area; 48.6% of the Primary Mirror Diameter
Back Focus from Mounting Surface 10.24 inch (260 mm)
Back Focus from Racked in Focuser 7.24 inch (184 mm)
Weight 106 lbs (48 kg)
OTA Length 42 inch (1067 mm)
Optical Performance 6.5 micron rms at 21mm and 9.6 micron at 26mm off-axis
UpperCage Carbon Fiber Truss
Lower Cage Carbon Fiber Truss and Light Shroud
Optimal Field of View 70mm Image Circle

 

SECONDARY MIRROR

Diameter 190 mm (7.48 inch)
Material Precision Annealed Pyrex
Shape Spherical
Coating Enhanced Aluminum - 96%

PRIMARY MIRROR

Optical Diameter 17 inch (432 mm)
Outer Diameter 17.5 inch (445 mm)
Shape Prolate Ellipsoid
Material Precision Annealed Borosilicate or Fused Silica
Coating Enhanced Aluminum - 96%

 

LENS GROUP

Diameter 105 mm (4.13 inch)
Number of lenses 2
Coating Broadband AR Coatings (less than .5% reflected 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
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.
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W. Paech 245/09/2018 03/09/201808:28
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A customer review of the 17 inch PlaneWave Astrograph
Dear Mr. Baader,
I am happy to comply with your request and share with you my criteria that led to the purchase of the 17 inch telescope from Planewave, and following my experience with this telescope. Since this was a rather complex topic, please forgive the long text and its extent, which certainly clearly exceeds a "normal" customer judgment.

Decision criterions for the choice of the Planewave astrograph were primarily:

- robust mechanical construction of the whole telescope,
- fixed installation and collimation of primary mirror and field corrector at factory,
- stable secondary mirrorcell,
- easy adjustment of the secondary mirror,
- easy control of distance between the main and secondary mirror withRonchi test,
- good focus stability with slight temperature differences,
- affordable focal reducer available,
- a price difference of about 10.000 Euro to a RC telescope from renowned European or international
manufacters.

To the last point, my following remark: I have not looked into the RC telecopes offered on the amateur market, which are delivered at 16 inches opening and a price below 10,000 euros. Production at this selling price - especially for an RC system - was unimaginable to me. In addition, it is hard to find any reference images taken with these instruments on the Internet, in comparison European - made RCs and PlaneWave telescopes have many international references.

Does that Setup have any disadvantages? Little after almost 4 years of operation:

- the 17" Planewave has an open tube in comparsion to the 12.5 inch and the black "Spantex" cloth against scattering light is often "willing" and shifts easily above the main mirror that is quickly partially obstructed.
- main disadvantage is in my eyes the very short focus travel of the 3.5" electrical Hendrick focuser of just 32mm, but otherwise it works very decently.

I have sent the entire report to Baader Planetarium.
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Thank you, Mr. Paech, for the detailed customer review!

The full review of the 17" PlaneWave Astrograph by Mr. Paech can be found here:

https://www.baader-planetarium.com/en/downloads/dl/file/id/1384/product/3154/customer_review_of_the_17_planewave_astrograph.pdf
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