I'll give a little tip that I use sometimes 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, by this way the person will not mind you're shooting him. It will be a little hard to have a good picture the firsts times but with a little help you'll be able to take amazing candid portrait.
Macclesfield Street (Chinatown), London