There is subdued interest in my CDK250 astrographs at the moment - probably a post Covid effect as people are spending more on travel, rather than premium instruments.
However, I'm getting a bit of a procession of local astro people with equipment problems, and I thought that maybe I should let the IIS community to know about it.
I'm happy to track down and fix misalignment and collimating issues in catadioptric and refractive optical trains - not Newtonians though. Newtonians are more difficult and may also suffer from lack of rigidity, in which case there is no point in doing any benchtop alignment work on them.
A recent example is the C14 EdgeHD below, which needed the optics cleaned, the focuser reconstructed, the screws that attach the back end to the tube, tightened, and the secondary collimated. For the screws tightening I had to improvise a very long spanner, to reach to the bottom of the tube to stop the nuts rotating while tightening the screws. For the collimation I had to set up the OTA on my milling machine table and use an artificial star across the road, about 50 meters away.
I may also accept optical testing and aluminizing, depending on the specifics of each case.
Over the years, he's successfully helped me with several jobs, including collimating my Tak refractor, making many perfect adapters and re-machining focusers, etc., to better than original factory tolerances.
There's commercial quality, then premium quality, and somewhere way above that is Stefan quality!
I’ve only dealt with Stefan on two occasions for a small order of custom spacers for my coma corrector but they were precision made to spec , high quality finish and delivered in a timely manner.
A pleasure to deal with him
Stefan gets a from me. Fixed my RH200 that wasn’t put together correctly in the factory and own one of his CDK250 (SN002). Great to work with and excellent results.
Stefan gets a from me. Fixed my RH200 that wasn’t put together correctly in the factory and own one of his CDK250 (SN002). Great to work with and excellent results.
Astrophotographers please note that the largest tilt errors I'm finding in this type of optical trains is coming from the filter wheel assembly.
I think the reason is that the housing of these large FW's is machined out of solid plate and the remaining "skin" on both sides is only 3mm thick. So during the CNC machining residual stresses in the material are released and when the part comes off the machining fixture it changes shape.
No easy way to overcome this (machining) problem.
Very true, Stephan. One way to fix this during the machining process is to do all the roughing, then release the part from the fixture, even flip it to machine the underside face, re-clamp then run the finish passes. But like you say, this is not easy, and it adds time and cost.
Yes, that is what I do when turning the backplate for the CDK250.
Four setups, two for roughing and two for finishing. Also, the plate is held at 3 points so that it can move as the stresses are released during machining.
If the filter wheel cases are just 3mm thick they will warp or flex under the weight of a camera cantilevered off the back of them. I had good look at one at a club night and thought it really needed a couple of stiffening ribs across the front and back faces.
