PlaneWave Instruments - 12.5" f/8 CDK Telescope
The PlaneWave CDK Optical Design...
PlaneWave CDK Optical Performance...
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. For visual use some amount of field curvature would be allowed since the eye is able to compensate for a curved field. The diffraction simulation was calculated at 585nm. The spot diagram was calculated at 720, 585, and 430nm. Many companies show spot diagrams in only one wavelength, but you cannot see the chromatic performance with only one wavelength.
Comparison: CDK vs Ritchey-Chretien...
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 marketplace today.
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.
In the comparison shown above the drastic difference in performance between the CDK and the RC is apparent. The biggest component that degrades the off-axis performance of the RC is the defocus due to field curvature. In many diagrams shown by RC manufacturers, the diagrams look better than this because they are showing a curved field. This is fine for visual use because the eye can compensate for some amount of curvature of field. But CCD arrays are flat and so in order to evaluate the performance a spot diagrams and/or diffraction simulations requires a flat field as shown in this diagram.
Please note that the charts shown in the above description refer to testing done with the 20" CDK.
PlaneWave 12.5" CDK 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
- 2.75” Hedrick Focuser: Heavy duty no-slip focuser. The focus tube runs on 5 bearings and is driven by a leadscrew so there is no chance of slipping. It accepts an optional dial indicator and PlaneWave’s EFA Kit to control many electronic accessories. The draw tube travel is 1.5".
- Cooling Fans: Three fans blow filtered air onto the back of the primary mirror to help it quickly equibrate to the ambient temperature. The fans are controlled by a switch on the optical tube or can be controlled by a computer if the optional EFA Kit is purchased.
- Typical wait times are 60 days from date of order.
- PlaneWave requires a 50% deposit at the time your order is placed. If you decide to cancel that order, the manufacturer will keep $250 from your deposit.
- This telescope comes with a dovetail. Please let us know the mount you will be using the CDK 12.5" on so that we can get you the proper one.
- We also need to know which CCD camera you will be using so that we can inform you of the proper adapters for your set-up. You can make both of these notations in the "comments" section of the shopping cart, or just give us a call.
- Shipping charges will be quoted separately. Just contact OPT for a shipping quote. The quote will include a shipping crate.
- The image shows optional equipment.
|Telescope Series||Planewave CDK|
|Optical Design||Corrected Dall-Kirkham|
|Mount Type||None - Optical Tube Only|
|Warranty||2 Year Warranty|
|Telescope Focal Length||2541mm|
|Telescope Focal Ratio||f/8|
|Tube Color or Finish||Carbon Fiber|
|Optical Tube Outer Diameter||330mm|
|Length of Optical Tube||31"|
|Optical Tube Weight||46 lbs.|
|Limiting Stellar Magnitude||14.5|
|Highest Useful Magnification||Not supplied by manufacturer|
|OTA Mount Type||N/A|
|Power Adapter Included||DC Cable with Alligator Clips|
- PlaneWave Instruments 12.5" CDK Corrected Dall-Kirkham Carbon Fiber Telescope
- 2.75" Hendrick Focuser
- Losmandy-Style Dovetail
- 2.75" to 2" Adapter (125355)
- Ronchi Spacer (200354)
- Ronchi Ocular
- OTA Cover
- Printed Instructions
- 12VDC Power Supply (18778)