I just received a new-to-me second-hand and probably rather old C9.25 XLT (standard, non-Edge) I bought from a UK dealer with a good reputation for selling preowned scopes. The price was very reasonable and on the surface the scope is in a good, clean, but obviously used condition. No problem with that.
I noticed from the reflection that there was quite a bit of big dust particles on the secondary, and since it has Fastar secondary assembly, I figured it would be easy to remove the secondary and give it a good blow with a blow bulb. The "Fastar" text was obliquely upside down, but I didn't pay much attention to it first. Removed the secondary, blew the biggest dust bits away, and re-installed the secondary and tightened the locking ring. Dang! Only then I realized the whole secondary assembly was rotating freely. Not super-loosely, but without excessive force anyway. Quick internet search revealed that I'm not alone with this problem, and that it should be possible to tighten the assembly by pulling the corrector plate and tightening the assembly rings from both sides.
However, the assembly was not only rotating, but also wiggling sideways in any direction as well. Maybe appr. 1 mm or so. Another quick search, and I came across John Hayes' instructions on how to check the corrector plate centering by looking at the concentricity of reflections from a distance with the secondary removed. Dang again! The corrector plate itself seems to be decentered, because wiggling the secondary holder as much as it could move in its slightly larger hole was not sufficient to make the reflections concentric.
The third problem related to all this was that - probably due to lateral movement - there's a ring of glue (or something) residue visible around the secondary holding ring on the corrector glass. Not much, maybe extending appr. 2 mm from the side of the ring here and there, and perhaps invisible to the primary because of secondary baffle, but still a bit nasty.
Now, if this was a brand new scope, I would obviously return it. I may consider returning it even it's a second hand scope (I contacted the dealer and told about my findings - still waiting for a reply), but then again, I'm pretty sure that these are issues that come with aged SCTs, and I might as well bite the bullet and try and learn to deal with them. Especially since I immediately fell in love with the size and form factor of C9.25 - easily handled, reasonably light, yet not a small scope anymore
If I'll take that last route, I probably need some advice from you guys.
- How am I going to re-centralize both the corrector plate and the secondary holder ring based on concentricity of reflections, since I now have two degrees of freedom (decentered secondary ring & decentered corrector plate)
- Am I able to detach the whole secondary holder from the corrector plate to clean the glue (or whatever that gooey stuff is) - or should I even care, since it's such a narrow ring?
Thanks in advance!