Autofocus
The best shots from both the Sigma DP1 and the Canon G9 are sharp, but we found that the Canon G9 hit focus more often than the Sigma DP1. Both cameras have a grid of nine sensor sites laid out in a 3x3 grid centered on the field of view. The G9's sensors cover a bit more of the frame than the DP1's. Though some of Canon's focus mode nomenclature sounds like hype – AiAF implies “artificial intelligence,” for instance – the range of options and feedback are elements of a system that works. In AiAF, the Canon G9 highlights all of the focus areas that are sharp. Shifting the view and refocusing often yields different focus points, and is actually a pretty efficient way of getting focus on the right spot. The DP1 also lights up the focused area, but only one at a time.
In practice, we found that the DP1's focus areas are a bit misleading – they are smaller than the boxes, and we found that in some of our shots the DP1 focused on the background, rather than on the narrow stalk of a sunflower that passed through the focus area.
Focus took impractically long with both cameras. The Canon G9 reached focus in anywhere from half to a full second, which is trouble for moving subjects, and the Sigma DP1 consistently took nearly a second and a half to focus. The G9's performance is in line with other compacts, but the Sigma is truly slow.
Both cameras' displays lagged as the cameras were panned – it took a while for the viewfinder to catch up with camera movement. Given that problem, neither camera was able to track focus at all.
Manual Focus
Both cameras offer manual focus with magnified display. The Canon G9 shows a magnified central area, while the margins of the LCD show the edges of the image, allowing the user to frame the shot even while the magnification is on. With a 3-inch LCD, it's a useful option, providing the necessities. The Sigma DP1 uses its full 2.5-inch LCD for a magnified view, so the user has to switch back and forth between magnification and full-frame to focus and frame a shot. The G9 controls focus with buttons, and the DP1 input is a small wheel. We found the Canon control easier to use. Part of the problem is that the DP1's LCD is pretty dim, and hard to see outdoors.
