As the Sigma DP1 moves into users hands, it seems that it’s engineering compromise may be becoming clear- a tendency to produce green tinted vignetting, especially wide open and close focused. This image seems to show the problem pretty well. All four corners, but in this image, more at the lower two corners, there’s a shift toward green.
In the straight conversion from the camera it’s not very noticable, but this image processed through Sigma Photo Pro 3.1 on the Mac and then adusted in Aperture emphasizes the flaw. The bump in saturation and the contrast in the affect areas make it more obvious. As a few early adopters have shown, you can fix this in Photoshop pretty easily with the gradient tool. Carl Rytterfalk has posted a video on the basic method.
The suggestion on the DPReview message boards is that this is a result of the exit pupil of the lens being so close to the sensor. It might be why we have a lens with an f/4 aperture as well. I’m reminded of the Leica M8 release and the discovery of it’s infrared sensitivies. These issues must have been well known to the design teams, but these cameras have been so critical to the companies that they are released presumably pending further fixes.
On the other hand, I think of Olympus who designed the 4/3rds system for digital to avoid engineering compromises but ended up at a disadvantage to companies that made bigger compromises to incorporate larger sensors.