Thanks Steve and CGW.
Steve, point well taken. I often hesitate when using that phrase, but end up doing so for lack of a better way to express it. "I was happy to find a fairly nice ??? of this lens in the junk bin yesterday..." I know I could rewrite the sentence differently, but if I want to say it that way, what is a good word to insert there? "version" doesn't sound right...

Anyway, thank you very much CGW for the very informative link and resource materials. Exactly what I was looking for. I'm still not sure how far I'll need to go to get at the focusing mechanism but will give it a try.