The Sigma 50mm f/1.4 EX DG HSM Autofocus Lens is a bright, 50mm standard lens with a large f/1.4 maximum aperture. Upon Olympus and other Four Thirds system digital SLR cameras, it is an ideal portrait lens-in 35mm camera terms, this is like a 100mm lens with a 20° x 13° field of view. Its large aperture allows for sharply-defined, contrasty images against nicely blurred backgrounds, and because it is originally designed for 'full-frame' 35mm cameras it produces superior peripheral brightness at all apertures on the 4/3 system.
Sigma's DG lens design corrects for various aberrations, specially coated to get the best color balance while cutting down on ghosting caused by reflections from the digital image sensor. The lens provides the utmost correction against lateral chromatic aberration, a serious problem for digital SLR cameras.
This lens also incorporates HSM (Hyper Sonic Motor), which ensures a quiet and high-speed AF as well as full-time manual focus override.