Since I got my Pentax M42 Adapter in I've decided to use my Sears 80-200 F4 for the first time in a while.
This lens is interesting. It's not a great performer by any means, but the Bokeh transitions with this lens are simply sublime. When shooting portraits this lens has a bit of a glow to it, very cool effect although technically incredibly imperfect. When used for macro (a surprising 1:1.15 to 1.65 macro mind you) it actually does pretty damn well. Here are some quick and dirty macro shots done at 80mm, which is not the closest it can do it:
Very limited PP on this (except for the last one). Just minor highlight and exposure adjustments. These are shot wide open at F4, with a flash and smaller aperture you could probably get good results out of this lens.
My version is the (seemingly uncommon) m42 version, but I'd spring for the much less of a pain in the ass K version if you want it. I ended up getting mine for 5 dollars though so it's hard to complain.