Your choice of lens affects the way that you see the world. I would venture to say that your choice of lens is more important than the camera that you use. Vision is both a physical and a mental thing. The wrong choice of lens could be like wearing glasses with someone else’s prescription. What you envision in your mind and what you see in your viewfinder should be somewhat similar. Your choice of lens has an affect on that.
With that in mind, street photography lenses are typically wide angle. Street photography is about capturing humanity in its environment with or without people in it. An important aspect for me is the spirit of place. Street photography isn’t about portraiture. Street portraits and documentary photography are different genres altogether with different methods. If you frequently feel a need to crop your photos, you should get closer to your subject and fill your frame or use a slightly longer lens. Or both.
In general, 24mm-35mm lenses full frame equivalent are most common. It’s also best in my opinion to use a lens with a fixed focal length so that you’re not fussing with it while possibly missing photos. Restrictions can be very good for the creative process.
I’ve been shooting film again lately with lomo cameras which have very few controls! It’s a lot of fun and it will change the way that you see and take photos. It stretches your vision and the way you think when shooting!
It is also possible to shoot 50mm full frame equivalent as well. I am told that is what Cartier-Bresson commonly used. But if you have a close look at his work you will see that much of it encompasses a good amount of background. That is to say that he was standing a distance from his subject. That could be tricky in places like Chinatown in Manhattan!
To complicate matters, I recently discovered that Saul Leiter, possibly my favorite photographer, used a telephoto lens! When you look at his work you will see that he focuses on composition, colors, patterns and rarely do you see a persons face.
The problem with shooting street photography with a telephoto lens aside from doing it Leiter style, is that you can easily look like a paparazzi or a spy to others. I think about how I would feel if someone had a telephoto lens pointed at me! It’s easier to smile at people when they discover that you just took their photos when using wide angle lenses!