I recently bought 2 Nikkormats on Craigslist. They came with a 50 f/2, a 24 (a fairly old one) and a Vivitar 135 w/teleconverter. I tested the cameras through all the f/stops and shutter speeds with the same roll of film, going from top to bottom on the speeds, using the 24mm lens. Both cameras were virtually identical at all speeds, but I noticed something odd. The higher shutter speed exposures were all just a bit weak (film was HP5 box speed), but as the speed slowed down, the exposures were much heavier. Also, I noticed that in some later shots, just walking around using up the rest of the film, the depth of field was rather shallow. Some of you know where this is going, but in trying to figure out what happened, I pressed the DOF preview button and the stop down was rather slow. I put in my own newer 24, and it was instantaneous. I had never seen this happen before, but it explained everything. The slower speed shots used smaller apertures, and the diaphragm was still open too far when the shutter fired, also the issue with the DOF. Anyway, does anyone know what this might cost to fix, and is it worth it? It's an old version of the lens, and I already have a newer one.