PlaneWave CDK 17" f/6.8 Astrograph OTA with Fused Silica Optics
PlaneWave CDK 17" f/6.8 OTA (Optical Tube Assembly) with Fused Silica Optics
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- CDK17 Astrograph, 17 inch with Fused Silica Optics
- modified to Dall-Kirkham, with fully corrected image field
- 8" Dovetail bar, focal length 2,940 mm (f/6.8) and 70 mm field of view (instead of the normal CDK 17" - 52mm) without any field curavature, off-axis coma, or astigmatism
- Delta T Ready, (3.5" Hedrick Focuser and EFA Kit available separately)
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.
Due to the relatively low weight of just under 43kg (telescope tube), the CDK17 can be used on one of our medium-to-large mounts - e.g. a Fornax 52, Fornax 100 or Paramount
- 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
The graphic above 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":
|Aperture||17 inch (432 mm)|
|Focal Length||2939 mm (115.71 inch)|
|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|
|Diameter||190 mm (7.48 inch)|
|Material||Precision Annealed Pyrex|
|Coating||Enhanced Aluminum - 96%|
|Optical Diameter||17 inch (432 mm)|
|Outer Diameter||17.5 inch (445 mm)|
|Material||Precision Annealed Borosilicate or Fused Silica|
|Coating||Enhanced Aluminum - 96%|
|Diameter||105 mm (4.13 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.|