Description Planewave CDK Reducer – OAG Conversion Kit The unique Rouz Astro “Fast OAG” turnkey solution is designed to enable the use of an Off-Axis Guider (OAG) in conjunction with the Planewave 0.66x focal reducer. Benefits: Robust Off-axis guiding Fast focal ratio: f/4.5 – f/5.25. Larger field of view: ~1.5 degrees High resolution imaging: 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 Click Here: Astrobin Users Gallery Advantages 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. Robust Guiding 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. Native Vs. “Guided Fast” Comparison 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: 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. Resolution Test at Same Altitude: 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 upsampled 150% in Pixinsight. Image Quality: Star size (FWHM): A typical single exposure, shown below, shows a measured median star size (FWHM) of 4 pixels. With the scale being 0.46 pixels/arcsecond, this means a typical star size is 1.84 arcseconds, just as sharp as the native configuration. The system is limited by seeing blur rather than a lack of image scale. There isn’t much increase as we move off axis, with the corners approaching 4.4 pixels, a 10% increase which is acceptable. Corner Stars: A visual inspection of a single exposure shows the stars in the corners are still reasonably round. The last few millimeters in the extreme corners exhibit slightly deformed stars when viewed at a 1:1 scale. The stars are reproduced very well over the remaining field of view. Mosaic showing a closeup of the stars in the center of the frame and in the corners. This is a single sub. Each square is 10% of the total image size. Vignetting: A flatfield analysis plot below shows the extreme corners (black) have a 40% drop in illumination. This is fully corrected by flatfield calibration and is not evident in the final calibrated images. Illumination of the sensor plotted from maximum brightness (white) to minimum brightness (black). The OAG prism is not blocking any of the incoming light. Field curvature: Testing the field curvature with CCD Inspector shows the curvature at the edges to be 25%, which is a great result that’s only 15% more than the native configuration. Looking at the visual representation below, we can see that the overall field is flat. Simulation of the curvature of the field using CCD Inspector to analyze imaged stars. 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. 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. 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. Focuser 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 as they are too tall The CDK EFA is NOT required 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. Click here: Astrobin Users Gallery Sample Images (below) – Taken with the Rouz Astro “Fast” OAG imaging train on the CDK14 Feel free to contact us should you have any questions.
