Planewave CDK Reducer – OAG Conversion Kit

(3 customer reviews)


Planewave CDK Reducer – OAG Conversion Kit – Allows using an Off-Axis Guider (OAG) in conjunction with the Planewave 0.66x focal reducer .

The Optec Sagitta OAG will be required

Rouz Astro Carbon Fiber FDM brackets that securely bolt on the OTA

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Planewave CDK Reducer – OAG Conversion Kit – Rouz Astro

The unique Rouz Astro “Fast OAG” turnkey solution is deigned to enable the use of an Off-Axis Guider (OAG) in conjunction with the Planewave 0.66x focal reducer to achieve a fast focal ratio, a much wider field of view, and autoguiding. Coupled with Optec Gemini, precision focus and rotation capability will be added.

FOV gain2 CN    



  • Off-axis guiding
  • Fast focal ratio: f/4.5 ~ f/5.25.
  • Larger field of view: approximately 1.5 degrees
  • High resolution imaging with an image scale of 0.36 ~ 0.47 arcseconds/pixel
  • Mono full-frame camera with filter wheel support
  • Precision focus and instrument rotation
  • Converted back to native in minutes



The majority of these CDK telescopes used sensors like the Kodak 16803 which had large 9 micron pixels and sensors. The resulting native image scale of 0.6~0.7 arcseconds/pixel was in the sweet spot for resolution and good signal to noise ratio buildup.

With today’s modern low noise CMOS cameras like the Sony IMX571 and IMX455, the smaller 3.76 micron pixels often lead to oversampling at a native image scale of about 0.3″/pixel. Oversampling comes at the cost of requiring a lot more integration time to build up high signal to noise ratio. 

The resulting image is much brighter than the native one – about 240%. Image resolution is still very high at 0.37~0.46 arcseconds/pixel (depending on CDK model). Since the system will be oversampling in almost all cases, there is no loss in true resolution. A “larger” image of small targets can be produced simply by upsampling the already sharp reducer image. 

The field of view (FOV) is limited given the smaller sensors. The dedicated Planewave focal reducer allows smaller sensors to capture a much larger field of view, thus reducing the overall cost associated with large cameras, filters, and filter wheels.

Incorporating an OAG into the system means no more guiding and tracking errors regardless of the sub exposure length, type of mount, lack of encoders, or perfect polar alignment.

  guiding2 CN

Performance Test

Performance tests performed on the same night with native vs reduced configuration.

The Soul Nebula was was imaged for 10x600seconds at a longer native focal length with a very fine image scale and then the system was switched to the shorter focal length configuration and the same target was imaged again for 10x600seconds (about 2 hours).


FOV Difference:

FOV Animation Native pipp


Increase in Brightness:

Moving from f/7.2 to f/4.75 increases the brightness over 200%.



Speed – Integration Time:

Having the brighter images with the reducer allows using much less integration time. Below is a comparison 10x600s at native  –vs– 6x600s with the reducer.

Both visual and Pixinsight SNR script verify the results.

SNR 10 vs 6 subs NATIVE10 pipp


What About Loss of Resolution for Imaging Smaller Targets?

Below is side by side of 10x600s at the native focal length, then swapped to the reducer setup on the same night. The object will be smaller but the here we unsampled 150% in Pixinsight and there was no loss in resolution even though the target was much lower by then.

SAme night Animation Native pipp


Resolution Test at Same Altitude:

It didn’t seem fair to compare the reducer images at a lower altitude than the native. Below is a comparison with the reducer images taken the next night at the same altitude of the native images. Also 10 x 600s. To match the image scale, the reducer image was unsampled 150% in Pixinsight. The image is actually sharper with smaller FWHM with the reducer.

Native vs reduced same altitude NATIVE pipp


Dual Focal Length – Native Swap

Dual focal length setup to return back to native in minutes by swapping one part.

This allows the user to swap back to the native focal length configuration in minutes. The procedure involves loosening three set screws, releasing the reducer from the OAG, and replacing the reducer with another custom machined part that maintains the original native focus position.

This component has a dovetail connection that simply plugs into the OAG with the camera on the other end. The focuser and OAG don’t need to be altered. Internal baffles ensure stray light and reflections are eliminated.

Native on OAG





The dedicated Planewave focal reducer only allows 44~47mm of spacing between the reducer and the camera sensor.
With mono-cameras that require a filter wheel, there isn’t enough space to add an OAG as well.
The Rouz Astro Fast-OAG CDK conversion kit was developed after extensive design and testing with several CDKs and focusers. This configuration positions a large OAG before the Planewave reducer to find guide stars for autoguiding the telescope.


Design & Manufacture

The modification calls for several custom CNC machined adapters that position all the optical and mechanical elements at very specific positions.

Extensive testing has been done to compile charts and graphs that allow calculating adapters and spacing that are unique to each Telescope – Focuser – Camera combination.

Each system can be designed with custom components and to fit the users requirements.

Cusrtom Design parts

Tolerances need to be to accurate to the millimeter from the focal reducer’s output flange to the camera sensor. This can be fine tuned by 0.1mm by user.

Distance from the telescope backplate to the input of the reducer is also critical, which in turn varies as the camera spacing is altered.

Furthermore, provisions are needed to position the guide camera at a specific position which is dependent on the other spacing values above.

Guide camera adapters and components are provided with the kit. Some suitable guide cameras are the ZWO ASI174mm or the ASI432MM.

Design sm


  • The recommended Optec Gemini focuser has a very low profile and offers excellent performance as well as instrument rotation ~4inch clear aperture – 0.5inch travel – 20lbs payload
  • The Optec Leo can be used, however that does not offer rotation – smaller clear aperture, 0.35inch travel – 20lbs payload
  • The Planewave IRF90 can work with some telescopes (please confirm)
  • The Standard Hedrick 2.75″ is not suitable for the CDK12.5 conversion kit
  • The Moonlite nitecrawlers are not compatible 
  • The CDK EFA is NOT required
Focuser on 12


Lead Time

Each CDK model has specific spacing requirements, one design does not fit all. Custom adapters are designed, CNC machined and anodized.

All hardware, adapters, and spacers will be provided.

Typical lead time is approximately 3 weeks after the order has been confirmed.

Compatible with Planewave CDK telescopes (CDK 12.5 – CDK14 – CDK17).

Rouz Astro is an Authorized Optec Dealer. Required Optec parts will be supplied with the kit. 


Sample Images

Taken with the Rouz Astro “Fast” OAG imaging train on the CDK14

Feel free to contact us should you have any questions.

3 reviews for Planewave CDK Reducer – OAG Conversion Kit

  1. Laurie Sibbald (

    Went with Rouz Astro’s optical train design for the CDK 14.

    Rouz was extremely helpful and answered many questions about the native/reducer configurations he has come up with.

  2. Claude Baril

    As a client, I’m pleased to say that I had an excellent experience with Rouz himself & all his equipment.
    Rouz is an essential part as a complement in Planewave company’s setup.
    No problem of orthogonality and flexure and no extra weight
    with the OAG instead of a guidescope and it works extremely well !

  3. Randy

    Please accept my thanks in getting the CDK14, Optec and Rouz Astro products here in wonderful condition. I’ve used the CDK14 with its reducer in place and pretty much everything worked the first time.

    Thanks again to all for your wonderful products and excellent customer support. This was a very happy night!

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