Reply #18 on: December 22, 2013, 03:07:00 PM
Rubber support for tilted CCD:
 
I have read this topic with interest. I just discovered that my QHY8 from 2011 had a tilt of 0.5 mm!! On one side, I measure 6.0 mm between front and the CCD glass and the other side 6.5 mm. CCD inspector also indicates a linear tilt in pictures from my brand new APO astrograph.

Initially I was preparing to use some aluminum foil as indicated but I discovered that I could push the cold finger down. In the old design only the foam in the front is developing some light pressure on the CCD. I my case it was not enough to keep the CCD and finger in place. Also the foam under the cold finger is pushing the other way.  I newer designs this seem to be improved by three plastic spring loaded pins.  My QHY8 has the three screws to mount the CCD on the cold finger only. The cold finger is not screwed but only pushed against the peltier.

So assuming that the stacked peltier, cold finger and CCD are all machined well at not thecause of the tilt, I decided to improve the cold finger support and added some strips of foam rubber beside the CCD, so that the front is pushing the cold finger on the peltier. The peltier is then pushed against the back side. It works very well and I measure now symmetrical distances of about 6.4 or 6.5 mm. So the tilt should be gone or almost gone

The rubber strips are loose inserted. The pressure is enough to keep them in place. See attached picture

I should have noticed the tilt much earlier.  Too many of my pictures are not as they should be and I was blaming the optics.