PlaneWave - 12.5" CDK12.5 Corrected Dall-Kirkham Carbon Fiber Telescope

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The 12.5" CDK optical design is the innovative solution for unsurpassed astro imaging quality at an affordable price.

SKU: PLA-125101
Manufactured by:
PlaneWave Instruments

Product Description

 PlaneWave 12.5" CDK Corrected Dall Kirkham Telescope  - 125101

The Planewave CDK optical design is the innovative solution for unsurpassed astroimaging quality at an affordable price. The purpose of the design is to provide a telescope that will excel at imaging 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-Chretien design. The RMS spot sizes at the edge of a 52mm diameter image circle yield are 12 microns, about the size of a pixel of most CCD cameras.

This no-compromise design is unique in making the optical alignment very forgiving and collimation very easy. This guarantees the user will be sure to get the best performance out of the telescope possible. The end result at the image plane of the CDK design is no off-axis coma, no off-axis astigmatism, perfectly flat field (no off-axis defocus), all the way out to a 52mm image circle. All this means, the stars will be pinpoints from the center of the field of view out to the corner of the field of view.


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 inch 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. Focus may be automated through a computer using PlaneWave's EFA Kit add-on. The draw tube travel is 1.3 inch. 
Cooling Fans

Three fans blow out of the optical tube pulling air though the telescope and by the primary mirror. This helps the telescope to reach thermal equilibrium quickly. The fans are controlled by a switch on the optical tube or can be conrolled by a computer if the optional Electronic Focus Accessory (EFA Kit) is purchased.


Diameter 13 inch (330 mm)
Aperture 12.5 inch (318 mm)
Focal ratio f/3
Mounting Laser Collimated and Permanently Fixed
Material Precision Annealed Pyrex
Shape Prolate Ellipsoid
Coating Broadband AR Coatings (less than .5% reflected from 400 to 700nm)



Diameter 4.65 inch (118 mm)
Material Precision Annealed Pyrex
Shape Spherical
Coating Broadband AR Coatings (less than .5% reflected from 400 to 700nm)




Diameter 70 mm (2.76 inch)
Number of lenses 2
Coating Broadband AR Coatings (less than .5% reflected from 400 to 700nm)


2.75" to 2" Adapter (125399)

Adapts the 2.75" inner diameter of the focuser to a standard 2" inner diameter. This adapter is necessary when setting the primary to secondary spacing. The 125399 Visual 2.75" to 2" adapter is an optional accessory that is designed to space a 2" diagonal for visual use.

Ronchi Spacer (200354)

This spacer 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.

OTA Cover

The OTA cover is for closing the front of the tube to protect the primary mirror and the inside of the optical tube.

Printed Instructions

For Collimation and Spacing

12VDC Power Supply (18778)

Provides power for the fans (Not included for European Orders)

Wrench Set (5812A35)

English Hex Wrenches (European Orders Only)



The CDK Optical Design

The CDK [Corrected Dall-Kirkham] telescope is based on an optical design developed by Dave Rowe. The goal of the design is to make an affordable astrographic telescope with a large enough imaging plane to take advantage of the large format CCD cameras of today. Most telescope images degrade as you move off-axis from either coma, off-axis astigmatism, or field curvature.  The CDK design suffers from none of these problems. The CDK is coma free, has no off-axis astigmatism, and has a flat field. The design is a simple and elegant solution to the problems posed above. The CDK consists of three components: an ellipsoidal primary mirror, a spherical secondary mirror and a lens group. All these components are optimized to work in concert in order to create superb pinpoint stars across the entire 52mm image plane.

Optical Performance

Shown 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 9×9 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. This means stars across a 52 mm image circle are going to be pinpoints as small as the atmospheric seeing will allow.

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 Chrétien

The simulations shown compares the optical performance of the CDK design to the Ritchey Chrétien (RC) design. The Ritchey design was popularized as an astroimaging telescope due to its use in many professional observatories. Although very difficult and expensive to manufacture and align, the Ritchey is successful in eliminating many of the problems that plague many other designs, namely off-axis coma. However the Ritchey does nothing to eliminate the damaging effects of off-axis astigmatism and field curvature.

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 Cassigrain 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.

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.

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.


Mechanical Design

High Resolution Axes Encoders


PlaneWave’s A200 German Equatorial Mount comes standard with high-resolution Axis Encoders on both Right Ascension and Declination axes.

The A200 encoder technology is a breakthrough in value for a telescope mount using quality components usually founds in professional equipment costing thousands more.

The A200 uses a non-contact encoder design that offers high speed, reliable operation with zero friction and zero wear.

The encoders sits above a 20 µm thin flexible steel strip, which is gold plated to give high reflectivity and corrosion resistance.  This ensured repeatable, precise results for the  life of your mount.


 Direct Drive Motors

For added precision and accuracy the CDK700 not only uses high resolution encoders, but also employs a Direct Drive motor system.   Direct Drive motors means that there are no gears to cause backlash or periodic error while slewing and tracking. With the high resolution encoders providing the feedback for the direct drive motors, not only will the telescope track without periodic error or have any backlash at all, but the mount will be able to counter against wind gusts. The direct drive motors can move the telescope at incredible speeds for tracking satellites or just to minimize target acquisition time.

The Direct Drive system is composed of 24 coils and 32 neodymium magnets powered by a 3-Phase Axial-Flux Torque Motor.

Combined with a hi-res encoder and stainless steel encoder tape on the circumference, the drive yields 16 million counts per revolution, or  about 0.08 arcsecond resolution.




PlaneWave Interface Software

Behind every great telescope and mount lies a great control program that keeps everything running in Sync. PlaneWave Interface (PWI3) is the one software you will need to monitor and control you CDK inside and out.

PWI3 gives you remote control of you Hedrick focuser, rotating focuser (IRF90), on-board fans and internal dew heaters (optional Delta-T) as well as continually monitoring internal and external temperature sensors.

Now you can focus your focuser, rotate your instrumentation to find a guide star, set your dew heater to turn on at a desired temperature,  all from the comfort of your observatory control room.

No matter if your telescope is in your backyard or being controlled remotely from 1,000 miles away, PWI3 will keep you in control.

PWI Software has a tab to control each device connected to your telescope

















Name PlaneWave - 12.5" CDK12.5 Corrected Dall-Kirkham Carbon Fiber Telescope
Manufacturer PlaneWave Instruments
Model PLA-125101
Aperture 12.5 inch (318 mm)
Backfocus Distance 10.445 inch (265 mm) from focuser mounting surface
Focal Length 2541 mm (100.04 inch)
Focal Ratio f/8
Optical Coatings Broadband AR Coatings (less than .5% reflected from 400 to 700nm)
Optical Tube Carbon Fiber
Optical Tube Length 31"
Primary Mirror 13 inch (330 mm)


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