My “normal” lens for some time now has been 35mm, with the 28mm on the Ricoh GR coming a close second. With both of these focal lengths, you feel close to the action and the perspective is ideal for street photography. Neither of these lengths feel to me particularly wide angle, and I have been interested for a while in exploring something truly wide. I believe that Daido Moriyama for many years shot exclusively with the Ricoh GR21, a legendary street camera. So, on my recent trip to South East Asia, I bought a 21mm lens for the Leica M9; not a Leica 21mm unfortunately (prohibitively expensive!), but the Zeiss 21mm, f2.8 Biogon (see the excellent review at http://www.kenrockwell.com/zeiss/zm/21mm-f28.htm). The Biogon is a well-established favourite amongst landscape photographers, who appreciate its sharpness, but it also works very well for architectural shots and, when used properly, for street photography.
It is always good to move outside one’s comfort zone, and I certainly found using a 21mm a challenge. For one, on Leica M cameras, it requires the use of a 21mm viewfinder (I bought the excellent Zeiss one), which means that you have to get used to the counter-intuitive process of using two viewfinders: the usual one for focussing, and the 21mm one for framing. Secondly, the focal length does feel very different from even a 28mm, much wider and throwing the foreground into unique perspectives.
It is early days for me with this lens, but here are a few of my first images.