PlaneWave CDK 14" Telescope Optical Tube Assembly
- A 14"/0.36m visual and astrographic telescope
- Uses PlaneWave's Corrected Dall-Kirkham (CDK) optical design
- 70mm diameter imaging circle
- No field curvature, off-axis coma, or astigmatism.
- Carbon fibre truss-tube for low thermal expansion, rigidity and weight saving.
- Two optical glass options available
PlaneWave's CDK14 is a 14-inch (0.36 m) aperture f/7.2 telescope that is very well suited for astro-imaging as well as for visual use.
The CDK14 telescope utilises the Corrected Dall-Kirkham (CDK) optical design, developed by Dave Rowe, that provides excellent imaging possibilities with large format CCD cameras, while remaining superb for visual use. The CDK design far exceeds the off-axis performance of most commercial telescope designs including the Ritchey-Chrétien design making the CDK an innovative solution for unsurpassed astro-imaging quality at an affordable price.
The end result, at the image plane of the CDK14, will give you pinpoint stars from the center to the corner of its 70mm field of view without any field curvature, off-axis coma, or astigmatism. The no-compromise optical design is unique in making the optical alignment forgiving and collimation very easy which guarantees the user the best possible performance from the telescope.
The CDK14 features a dual carbon-fibre truss design, with 3 cooling fans blowing air throughout the back of the telescope, The instrument weighs 22kg (48 lbs) and comes as standard with a back plate retaining ring ready to accept the focuser of your choice. The relatively low weight of the CDK14 means it can be used, with additional accessories, on medium sized mounts such as the 10Micron GM2000 (or above) or the Paramount MX+ (and above).
The CDK14 telescope is an open truss tube design for a rigid, but lightweight structure, and for quick thermal cooling. The truss tube utilises a carbon fibre frame which minimises thermal expansion that can cause focus shift with changes in temperature. The carbon fibre truss tube design also promotes quick thermal cooling.
To create the telescope's baffles, Planewave uses digital 3D printing technology. Their 3D printers add successive layers of material to construct a baffle system with precision. These internal stray light baffles minimise vignetting and maximise image contrast.
To mount the CDK14 onto a mount, PlaneWave supplies the CDK with a dovetail bar. The CDK features a dovetail expansion joint that allows for the difference in thermal expansion between carbon fibre and aluminium. This expansion joint allows the aluminium dovetail expand and contract without stressing the carbon fibre lower truss.
To help the primary mirror to cool, there are three cooling fans that blow air inside the back of the telescope. Furthermore, internal diverting fins circulate air flow behind the mirror for even cooling to help the telescope reach thermal equilibrium quickly. The fans are controlled by a computer if the optional Electronic Focus Accessory (EFA Kit) is purchased.
Cooling Fans at the rear of the CDK14
For 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.
The Ritchey Chrétien (RC) optical design has long been "the standard" in high end imaging telescopes due to its use in many professional observatories. The RC is successful in eliminating many of the problems that plague many other optical designs, namely off-axis coma, however the RC design does nothing to eliminate the damaging effects of off-axis astigmatism and field curvature. The RC design is also very difficult, and therefore expensive, to manufacture and optically align.
The CDK design tackles the "off-axis coma problem" by integrating a pair of correcting lenses into a two mirror design. The beauty is that this design also corrects for astigmatism and field curvature. Because the lenses are relatively close to the focal plane (unlike the Schmidt corrector plate found in various Schmidt Cassegrain designs), and because these lenses work together as a doublet, there is no chromatic aberration. The CDK offers a wide aberration-free, flat field of view that allows the user to take full advantage of the very large imaging chip cameras in the market place today.
In the image above, on the left column, the diagram shows a diffraction simulation for 14" CDK optics on the optical axis, and with a distance of 13 and 35mm from the optical axis. The right column shows the calculated spot diagram with small squares being 9 microns wide. 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 increasing-sized sensors.
Having an aberration free telescope design means nothing if the optics cannot be aligned properly. Many Ritchey owners never get to take full advantage of their instrument’s performance because the Ritchey is very difficult to collimate. Aligning the hyperbolic secondary mirror’s optical axis to the optical axis of the primary mirror is critical in the Ritchey design, and the tolerances are unforgiving. The secondary mirror of the CDK design is spherical. It has no optical axis and so the centering tolerance of the CDK secondary mirror is comparatively huge. With the help of some very simple tools, the CDK user will be able to set the secondary spacing, collimate the optics and begin enjoying the full performance potential the instrument has to offer within a few minutes.
There are 2 options available for the type of optical glass used in the CDK14 telescope: Borosilicate and fused Silica:
Below are a few images taken with a CDK14 to show how well they perform.
|Optical Design||Corrected Dall-Kirkham (CDK)|
|Aperture||14 inch (356mm)|
|Focal Length||2563mm (101 inch)|
|Central Obstruction||23.5% by surface area; 48.5% by diameter|
|Back Focus from Mounting Surface||11.09 inch (282 mm)|
|Weight||48 lbs (22 kg)|
|OTA Length||35 inch (889 mm)|
|Optical Performance||3.1 micron RMS at 13mm off-axis; 6.0 micron RMS at 35mm off-axis - Spot Diagram|
|Upper Cage||Carbon Fiber Truss|
|Lower Cage||Carbon Fiber Truss and Light Shroud|
|Optimal Field of View||70mm Image Circle|
|Diameter||165 mm (6.5 inch)|
|Material||Precision Annealed Borosilicate|
|Coating||Enhanced Aluminum - 96%|
|Optical Diameter||14 inches (355.6)|
|Outer Diameter||14.5 inches (468.3mm)|
|Material||Precision Annealed Borosilicate or Fused Silica|
|Coating||Enhanced Aluminum - 96%|
|Diameter||95mm (3.7 inch)|
|Number of lenses||Two|
|Coating||broadband AR Coatings (less than .5% reflected from 400 to 700nm)|
|CDK Optics||The Corrected Dall-Kirkham design yields a perfectly flat field free from off-axis astigmatism, coma and defocus.|
|Carbon Fiber Truss 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.|
|Crated Shipping Weight||225 lbs|
|Crate Width||31 inches|
|Crate Height||26 inches|
|Crate Length||53 inches|
|Ronchi Spacer (600341 & 600344)||This spacer sits in place of a focuser and is used for setting the primary to secondary spacing. It has an 1-1/4 inner diameter and may be used with 1-1/4 oculars for collimation|
|Ronchi Ocular||This ocular is a Ronchi screen used for setting the primary to secondary spacing|
|Primary Mirror Cover||The Primary Mirror Cover protects the primary mirror|
|Planewave Thumb Drive||Containing all documentation and software for collimation and spacing|
|12VDC Power Supply||Provides power for the fans (Not included for European Orders)|
|Wrench Set (5812A35)||English Hex Wrenches (European Orders Only)|
Camera Adapters Diagrams
Drawings & Diagrams
- Collimation and Spacing Instructions for CDK12.5, 14, 17, 20, and 24 (4207)
- Cleaning Optics CDK14/17/20/24 (2807)