Originally Posted by Markok765
Apart from the issue of engaging your subject etc, a long lens will affect perspective severely. It might be useful for picking off people from the distance like a sniper but it will result in severely compressed backgrounds. Might be good for candid portraiture but I don't regard that as street photography really. If I shoot portraits on the street I want them to be environmental portraits, people interacting with their surroundings, with each other and, on occasion, with the camera.
This shot I almost consider to be a portrait on the streets - 21mm - I was barely 4feet away: