I have a lot of good camera and lense tools, so I grabbed the lense spanner and the lense and peered at it for a while, realizing that the lens retaining ring didn't have spanner grooves. Some research on the internet revealed that some people simply saw grooves into the front ring and remove it that way, but I didn't want to, as it's really easy to ruin something in the process, and the front of the barrel had been dented at some point in the past, so the threads were in poor shape. However, the same research revealed a downloadable copy of the repair manual for it. It turns out this is a popular lense, and has been offered in a variety of versions and configurations over the span of a few decades. The one I had didn't match the repair manual, but it was close enough for me to realize the tiny dimples at the front were actually tiny setscrews covered over with (essentially) black nail polish. With the setscrews removed, the front lense element assembly should simply unscrew.
I rounded up my Wiha precision screwdriver set and selected a bit that would just fit in the setscrew opening. A few turns abraded away the black nail polish, exposing the head of the setscrew. Some careful digging cleared out the slot, and I was able to back out the setscrew nicely. It's a really small screw, about the size of a grain of pepper. There was one each in front of and behind the line delineating the front lense assembly. So I removed both of them. Then I tried to unscrew the front of the lense. It didn't budge. So I found one of those grippy pads used to remove stubborn jar lids, and cranked away at it with that. Success! The front unscrewed smoothly. Now that I had access to the back of the lense, it was simple enough to carefully remove all the fungus without damaging the antireflection coatings (as far as I could tell, anyway). Then I screwed it back on. Replacing the tiny setscrews was tricky, as they wanted to lie in their openings sideways. I finally ended up lightly magnetizing the screwdriver and using it to place the screws in position. That worked a treat, I replaced the screws, and the lense works properly!
With it, and the last sunshine before this afternoon's thunderstorm, I got some good shots of the character matrix, in acceptable focus from edge to edge (I have to photograph it edge-on due to the construction of the tube). Originally posted at Dreamwidth.org comments