Well, I've added another Adaptall-2 prime to my lens collection. For a very low bid on an as-is Pentax ES body, I got the 54B f/5.6 300mm in the bargain. The seller didn't offer much in the way of condition description, but I figured the m42 Adaptall-2 adapter alone was worth most of what I was paying, even if the camera and lens weren't in usable condition.
The lens cleaned up well, but does seem to have a couple of small fungus spots on the inner surface of the rear element. Front glass was good. Internal dust was in the normal range.
Despite it being rather cloudy, I tried it out this morning, by putting a PK adapter on it and mounting it on my K10D. I bumped the iso up to 800, and still had to take a lot of the shots at very marginal speeds for hand holding, even shooting the the lens wide open.
Being able to take close-ups from long distance is an interesting capability, though most of these low-light shots would have benefited from a bit more depth of field. While it was cloudy, shots including sky had a bit of flare or in a few cases some purple fringing.
Here are three I liked from the first tests. The first and last are cross posted.