i had a 100 f2, and now own a 85 1.8. the 100f2 was a terrific lens. The 100 has metal filter threads,while the 85's are plastic. they both focus very quickly, and are both very sharp. the 85 seems to have more CA than i remember the 100 having, while the 85 seems to have a bit better bokeh. they both are really great lenses, and i don't think you can go wrong with either. really the main differences are the focal length and speed, and even then there isn't much in it. The only reason i'm now running the 85 instead of the 100 is for that extra 1/3rd stop in speed. i already own 2.8 zooms, so i just wanted something more removed from them.