Hi all,
Well, I think I found the source of the coma in my lens, and it is NOT repairable.
The primary mirror is not pinched - I was able to remove the back cover and rotate the mirror in it's mounting with my fingers. There is some eccentricity in the lens body, as the mirror would rotate a few degrees and then 'stick', and could be moved laterally a tiny amount when not in the 'stuck' position. I left it in the 'stuck' position because I didn't want the mirror moving around.
I was not able to remove the mirror because the alloy locking ring appeared to be glued in place. Nor do I have a suitable tool to rotate the ring, either.
Somewhere in it's life the lens has been dropped. I saw that the tripod foot is bent slightly. When looking at the lens yesterday I saw that the front of the body (just outside of the front glass) is deformed by a millimeter or so. There is no way I can straighten that deformation. (See attached image.)
So it looks like the lens is going to be either sold, or relegated to terrestrial imaging (and even then I have some doubts about the quality of the images I'll get from it.
)
I'm disappointed, obviously. So let's see what good I can get out of this situation...
Cheers,
V