Originally posted by zswjy i always like take pics on street when i walk around city. i would like a lens with sharpness and quick focus. and i do not want the person i shoot will get notice, so the lens should work nice at long range.
There are many schools of thought on street photography without being noticed by your subjects. You can either use moderate telephoto and keep your distance, or wide angle up close but don't point the camera directly in your subject's face. And then some people have success with styles that do get noticed by subjects.
I've personally never tried the telephoto option. I've tried the the FA43 and even though it's a small lens people do notice the camera being pointed in their direction. A Tamron 10-24 zoom, despite being a larger lens, allows me to shoot hyperfocal (no need to focus) with the camera held inconspicuously low. It's my best street lens but I do intend to buy the DA21 eventually.
What lenses do you already own? If you have the 18-55 kit lens experiment with the wide end. Try Av or TAv mode at f8, zoom to around 21mm, manually focus on something around 9 feet away, and then everything from 4.5 - infinity should be in focus. See
Online Depth of Field Calculator for more info. Zoom out to 18mm and the focus is even more lenient than at 21mm. Similar things can be done in full M mode but I like the flexibility of letting the camera choose the proper exposure when I'm shooting from the hip. (apologies if that sounds condescending, I'm assuming you don't know what hyperfocal focusing is yet)