Jeremy,

I don't have experience with either the 75 mm or the 80 mm El Nikkor lens. For that reason I am not able to comment on any difference between them. My lenses in those focal lengths are Schneider(s) and Rodenstock(s). I do have a 150 mm El Nikkor that is extremely sharp. I prefer it over an older Schneider 135 Componon that I have.