A few months ago I bought a second hand 10" LX6 that was in very good
condition mechanically and optically except for the fact that it
looked as if about 40% of the AR coating on the corrector plate had
been "eaten off". (In other words the coating was nonexistent on about
40% of the front surface). I got the impression that the previous
owner started to clean the corrector with something that "ate" the
coating off and caught the mistake... This problem doesn't seem to
effect the optical performance other then light transmission.

Anyway, I carefully removed the corrector to clean some dust off the
secondary (noting the alignment marks, see #2 below) and I noted a
small 1/4" long radial crack in the corrector behind the bezel (out of
the optical path). Now that I've set the stage here's my questions.

#1. I was thinking about having the corrector recoated but was
wondering if I should in light of the crack I found? (I think it is
necessary to heat the corrector to coat it.) If I can, could I get a
recommendation for who I could send the plate to get it
"re-multi-coated"?

#2. When I removed the corrector, I noted one white mark on the OTA
behind the corrector and not one but THREE marks on the edge of the
corrector. One of them, the most prominent, also had a couple of
"4-3-71" (or maybe bad "91"s) pencil designations. The other two
markings were simple black marks, one was aligned with the "top" screw
hole for the bezel and the other was aligned with the white mark. The
prominent mark wasn't aligned with anything! I replaced the plate
after the dust removal EXACTLY as I found it. Do those marks seem OK
or does it sound like someone messed with the corrector plate? Any
thoughts?

#3. Anybody have any thoughts as to what may have "eaten" the coatings
off?

Thanx (Hope this wasn't too long!)
Frank Holub
West Bloomfield, MI
42d 34m 32.2s North
83d 24m 55.1s West

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