have the 24mm 2.8 AI and love it on film but as mentioned, its a little soft on a FF digital. have used a few of the 50's and the only one I kept/bought was the 1.8d. if you can look past the non-ai buttery focus its a great lens that you can still get new for around $110
also look into the 85mm f2 Ai-s lens. great lens in a very small package.