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PlaneWave Instruments 12.5 inch CDK Optical Tube Assembly

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Product Description

The PlaneWave Instruments CDK12.5 is a 12.5 inch (0.32 m) f/8 Corrected Dall-Kirkham Astrograph telescope. The telescope has a closed carbon fiber tube, with 3 cooling fans ejecting air from the back of the telescope. The CDK12.5 covers a 52 mm field of view without any field curvature, off-axis coma, or astigmatism. The instrument weight is 46 lbs and comes standard with the large capacity 2.75 inch Hedrick focuser.

The CDK (Corrected Dall-Kirkham) Optical Design is an innovative solution for unsurpassed astroimaging quality at an affordable price. The CDK telescope design provides excellent 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-Chrétien design.

This no-compromise design is unique in making the optical alignment forgiving and collimation very easy. This guarantees the user the best possible performance from the telescope. 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). The CDK design will give you pinpoint stars from the center to the corner of the field of view.

More about the CDK optical design.






12.5 inch   (318 mm)

Focal Length

2541 mm   (100.04 inch)

Focal Ratio


Central Obstruction

42% of the Primary Mirror Diameter

Back Focus from Mounting Surface

10.445 inch   (265 mm)

Back Focus from Racked in Focuser

7.2 inch   (183 mm)


46 lbs   (21 kg)

OTA Length

31 inch   (787 mm)

Optical Tube

Carbon Fiber

Optical Performance

Vignetting and Spot Size Plots

Overall Dimensions

Overall Dimensions (PDF)



13 inch   (330 mm)


12.5 inch   (318 mm)

Focal Ratio



Laser Collimated and Permanently Fixed


Precision Annealed Pyrex


Prolate Ellipsoid


Enhanced Aluminum - 96%



4.65 inch   (118 mm)


Precision Annealed Pyrex




Enhanced Aluminum - 96%



70 mm   (2.76 inch)

Number of lenses



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

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. It accepts an optional dial indicator and PlaneWave’s EFA Kit to control many electronic accessories. 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.


Crated Shipping Weight

163 lbs   (74 kg)

Crate Width

23 inch   (584 mm)

Crate Height

31 inch   (787 mm)

Crate Length

41 inch   (1,041 mm)


2.75" to 2" Adapter (125355)

Adap ts 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.

Rochi 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.

Rochi 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)

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