El-Nikkors are cheap plentiful and they are great. 50mm f/2.8 kind are the better 6 element type. Many of them have haze issues (all of them I bought did) but they are relatively easy to disassemble and clean. f/4 kind are 4 element. Not bad but for the price difference, I'd get f/2.8.
For the same token 75mm kind are 4 element where as 80mm are 6 element.