Sigma DP1 Merrill Optics

19mm fixed focal-length lens
Excellent far-field performance from the 19mm (28mm eq.) lens.

The Sigma DP1 Merrill is equipped with a 19mm f/2.8 fixed lens, with a 35mm equivalent focal length of approximately 28mm. Construction consists of 9 elements in 8 groups, with a 9-bladed diaphragm providing a minimum aperture of f/16.

Sharpness and contrast are excellent across the frame at f/8, coma distortion is very low in the corners, and flare is well-controlled. Chromatic aberration is visible towards the corners and edges of the frame along high-contrast edges such as the window frames, though it's pretty minor and can be easily corrected in software.

The Sigma DP1 does not offer digital zoom, which is just as well as you can usually get better results when enlarging using photo editing software, and the DP1's images respond to upsampling better than most cameras.

Overall, excellent optical performance in our Far-field test.

Macro
A larger-than-average macro area, with very good detail.

The Sigma DP1 Merrill captures a larger-than-average minimum macro area measuring 6.23 x 4.15 inches (158 x 105 millimeters). Detail is excellent, though, with just a touch of softness in extreme corners when stopped down to f/8. (Most lenses have some softening in the corners at macro distances, but the DP1's lens performs quite well in this regard.)

Geometric Distortion
Low barrel distortion.

The Sigma DP1 Merrill's lens produces about 0.3 percent barrel distortion; which is pretty low and not very noticeable in its images. 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).

Chromatic Aberration, Corner Sharpness & Vignetting
Moderate chromatic aberration. Very good corner sharpness.

Chromatic Aberration. Chromatic aberration is moderate in the corners with fairly bright green/purple fringing, and the camera does not appear to be suppressing it in firmware. Stopping down to f/5.6 reduces it a bit, but it's still visible. (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. The DP1 Merrill's lens produces pretty sharp corners wide open, with only minor blurring. The center is very sharp even wide open. Corner sharpness improves slightly when stopped down to f/5.6, though it's still not quite as sharp as the center.

Vignetting. A moderate amount of "vignetting" (corner shading) can be seen when wide open from the darker corner crop. A small amount of corner shading still occurs when stopped-down to f/5.6, but it's almost negligible and easily correctable.

Chromatic Aberration Suppression. As you can see from the crops comparing in-camera JPEGs (left) to converted RAW files (right), the Sigma DP1 Merrill appears to be applying at least some chromatic aberration suppression, as the magenta fringing is much less noticeable in JPEGs straight from the camera. Note that Sigma's Photo Pro bundled software does have a chromatic aberration correction tool with both automatic (lens profile driven) and manual options, so RAW files can be easily corrected.

Bottom line, a very good lens, though minimum macro area isn't great.

Coverage
Excellent accuracy from the LCD monitor.

The Sigma DP1 Merrill's LCD monitor showed essentially 100% frame coverage in our test, which is excellent.