Sigma 50mm Macro (manual focus)
I bought this lens new in 1993, to use on my Olympus at the time. Actually, it was obviously set up for Nikon, because the focusing went the other way round.
Optically not bad, but not anywhere near as sharp as the 55mm Micro-Nikkors we use at work. But mechanically! The aperture ring felt about as precise as a flea-market can opener. It rattled along from f-stop to f-stop. I shot a couple of hundred exposures with it - usually copy stand stuff out of books, or Kodalith slides. Eventually I began to notice very light slides, and first blamed myself for being too dumb to work out bellow extension factors. But what had happened was that the diaphragm had stuck in the full open position, and wouldn't budge.
Being out of warranty, I had nothing to lose. I own some pretty fair fine tools, but nothing short of an air compressor and jack hammer would open the back of the lens.
Basically a piece of junk, not worth the money. Interesting paperweight, 3 out of ten.