Sigma DP1 Optics

Fixed focal-length lens
Very good performance with the 28mm equivalent fixed lens. Digital zoom works reasonably well.

The Sigma DP1 has a fixed, 16.6mm f/4-11 wide-angle lens with an equivalent focal length of 28mm. Details are fairly sharp across the frame at full wide-angle, with low levels of coma distortion, negligible chromatic aberration and only slight blurring in the extreme corners. Digital zoom produces a soft image, with the usual losses in resolution associated with digital upsampling.

Macro
The DP1 doesn't really have a macro mode. It does have a "full"AF mode that focuses as close as 30cm (~1 foot), but with a 28mm eq. lens, that doesn't result in a capture area that we'd call macro. Here's a shot of our usual macro target to show you what we mean.

The DP1 captured a huge minimum area measuring measuring 12.0 x 8.0 inches (305 x 203 millimeters) at its closest focus distance. Resolution and detail were high, though with some softening in the corners from the lens. (Most lenses have some softening in the corners at macro distances; though again, we'd hardly call this macro.) Sorry, we didn't take a "macro" shot with the flash, so we can't tell you if it throttles down well at closest focus distance.

Distortion
Low barrel distortion from the DP1's fixed, wide-angle lens.

The Sigma DP1's 28mm equivalent lens produced less than 0.3 percent barrel distortion which is much lower than average, especially for a wide-angle lens. This is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide-angle) or inward (like a pincushion -- usually at telephoto). A very good performance here.

Chromatic aberration
Low and dull in all four corners.

Chromatic aberration in the corners with the Sigma DP1's lens is pretty low and dull, and hardly noticeable. C.A in the top corners was exacerbated a bit by additional lens softness. (This distortion is visible as a slight colored fringe around the objects at the edges of the field of view on the resolution target.)

Corner Sharpness
Slight to moderate softness in the corners when lens is wide-open.

We normally only show the softest corner and the center at each end of a zoom lens, but since the DP1's lens is fixed focal length, we decided to show all four corners. The Sigma DP1's lens produced slightly soft corners in a few shots, with the upper right corner being the softest, and the bottom left being the sharpest corner. The center was quite sharp. Keep in mind that these were shot with the lens wide open (at f/4.0), so corner sharpness will improve when stopping down.

Accuracy
Good accuracy from LCD viewfinder.

The Sigma DP1's LCD viewfinder proved fairly accurate, showing about 98% coverage. We did not test the DP1's optional optical viewfinder.