Posts Made By: Chris Nisbet

Here is my 2 cents. I have a ST8-XME that experienced something similar. Bottom line, turned out to be frosting. Try this: take an initial pic as a reference then let the camera run for an hour or so before trying to take another pic. If that pattern has disappeared, more than likely frosting. Now how to correct. Bake or replace the desiccant and see if that helps. In my case, I had the camera in for repair and Bill (at SBIG) replaced some seal that he said was marginal that probably contributed to the frosting. Got the camera back, baked the desiccant and that pattern disappeared. Hopefully you can get by with replacing the desiccant.

Chris N
Cedar, MN

Now for the results. Collimated everything using Hotech and under the stars. I was a little disappointed that my focus shift didn't improve much upon initial testing. But now it was time to image. I picked targets on either side of the meridian and in different directions and did an imaging run. The morning arrived and I opened up the images with some (or a lot of) apprehension. I was pleasantly surprised. No, I was elated! No difference in image quality no matter where the scope was pointed (confirmed with CCD Inspector). I check the FM4 logs to see where the Optec ended up. To my surprise, the Optec did not have to move that much over the course of the night (at first I thought focus had failed and returned to an initial setting but it had not!). I still have focus shift (target moves in the FOV when focusing up to a point) but it would appear that the primary mirror does not shift around on the tube.

Last night I took 18 subs at 10 min each exposure and the Optec only moved 47 steps over the course of the night.

Below is a shot of CCD Inspector. My stars are noticeably "tighter" as was my guide stars.

This mod does not require any special tools just ordinary tools. A drill, a SHARP bit (buy a new one), a tap, nylon screws and a deep breath before starting. BTW, drilling through the rear of the cell took a little time but it was all aluminum. Did not have to center punch with a sharp bit. I would recommend someone hold a vacuum near when drilling to pick up the chips.

I have taken close to a 100 subs since this mod and all are consistent in quality. So far, so good. Time will tell.



Chris N
Cedar, MN