a very affordable lens ($US199) with high quality optical performance with reasonably fast AF and compact size makes for a great street photography or party lens (when used with an external bounce flash)
version II lens
announced Jan 2013
“redesigned with enhanced optical performance and included as part of Sigma’s new Global Vision category restructuring”
version I lens
great flare control, bokeh, sharpness
extremely sharp in the centre and reasonably sharp edges wide open but for best edge sharpness, use f/5.6-f/8
slightly high barrel distortion at 1.1% but this is correctable
Olympus cameras do not correct the higher levels of CA (1.5px), vignetting (1.5EV) and barrel distortion (3.3%) found on the Panasonic Lumix 20mm f/1.7 pancake lens
has faster, quieter AF and is cheaper
the main downsides are:
some barrel distortion
internal focusing elements move and rattle without power
takes 1-2secs to be activated once camera is turned on
why buy it when you have a kit lens covering this focal length?
wider aperture for lower light situations and improved ability to blur the background
nicer bokeh than most zoom lenses
sharper with less aberrations than consumer level zoom lenses
it is so cheap
specs
19mm focal length = 38mm in 35mm film terms = very nice for street photography
f/2.8-f/22 aperture = an almost an extra stop light and DOF performance compared to the kit lenses