I already have an 85mm prime and recently bought the 35mm. I never thought I would like a 35mm as much as I do. It has turned into my general take with me lens. I am considering the 50mm. But I keep asking myself the following question
"For what I shoot (street, landscape stuff), What would I be unable to do with both the 35 and 85mm?? If I were rich, the answer is clear -- I *need* every lens. However I am not rich and I do want to rebuild my prime kit with some discipline.
Maybe after I finish re-building my prime kit, I will go back and get the 50.
If I did not already have the 35 or the 85 the decision on the 50 would be a lot easier. So the posters who asked what do you already have bring up the key question. You really can't ignore your existing kit when making FL decisions.