I'll give a little tip that I sometimes use when I want to shoot candid portraits in the street / underground with a 50mm. Put the camera around your neck and up to your chest. Target your subject and try to frame and shoot, this way the person will not mind that you're shooting him. It will be a little hard to get a good picture the first times, but with a little practice you'll be able to take amazing candid portraits. Macclesfield Street (Chinatown), London