Some Sigma lenses are designated “DG”. What does this mean?

The DG designation indicates that the lens has been optimised for use with digital SLR cameras. The DG lenses feature improved (more even) light distribution from image centre to edge, especially at maximum aperture, compared to conventional fast wide-angle lenses. This is important in digital photography, but is also useful in 35mm photography, especially when slide flm is used. The lens elements also utilise Sigma’s super multi layer coating which reduces flare and internal reflections from the highly sensitive surface of image sensors.