Fingerprints on a Schmidt plate / Replacing the collimation screws

When examining a decollimated customer C9.25, it was noticed that the Schmidt plate was full of fingerprints.

 

You can clearly see fingerprints directly on the secondary mirror mount and in the area up to the edge of the Schmidt plate; the entire Schmidt plate looked like this. I've never seen anything like this before.

We've previously advised against removing these to protect the coating and prevent further streaks from forming.

The dust is blown away with compressed air (it doesn't interfere with observation, but it can cause scratches during cleaning).

Then, we carefully clean the area with the fingerprints using our LensAid cleaning system (link). We didn't clean the other areas to minimize the impact on the optical coatings.

Here you can see the condition after cleaning.

The secondary mirror was significantly decollimated. What surprised me at first was that the telescope came from a very skilled astrophotographer. When I attempted to collimate it, the reason became clear: the screw heads (Phillips head) were overtightened and therefore no longer usable. It takes a lot of force to tighten the screws like that...

With a lot of sensitivity and patience, the M3 screws were replaced with corresponding Allen screws. After that, collimation was possible.