Whenever you turn the camera on or off, the camera vibrates the IR-cut filter to shake away any dust that may have settled on it. If that's not enough, the camera can find dust particles on the sensor, plot their locations, and store that data so the included Digital Photo Professional software can remove the dust spots in post-processing.
To process the data from the sensor, the camera uses a pair of Canon's Digic III processors, making it the first dual-processor camera we've ever seen. Instead of the 12-bit analogue-to-digital converters found in Canon's other cameras, the Mark III uses 14-bit converters, which theoretically allow for more tonal gradations than their 12-bit brethren. A dedicated AF processing unit drives the camera's 45-point autofocus system, which includes 19 cross-type points. For comparison, both the EOS 5D and 30D sport only one cross-type point, while Canon's 16.6-megapixel 1Ds Mark II has a mere seven cross-type points. Cross-type AF points provide a higher level of sensitivity than standard points. The points are both user-selectable and groupable, so you can fine-tune the AF system as you like it.
Exposure metering options are just as sophisticated as the AF system. The camera uses a 63-zone through-the-lens (TTL) metering system that offers full-frame evaluative metering, centre-weighted average, and partial and spot metering. According to Canon, the partial option uses the central 13.5 per cent of the frame to determine exposure, while the spot setting uses 3.5 per cent and can be set to the centre or linked to the AF sensor in use, or you can choose up to eight spot readings and let the camera average them. Canon calls this last option 'multispot metering'.
In our field tests, the 1D Mark III yielded remarkably accurate exposures and was rarely fooled by tricky scenes, but the 3D colour Matrix Metering found in Nikon's D2Xs -- with its 1,005-pixel sensor and onboard database of comparison image data -- barely edges out the 1D Mark III's system when it comes to very tricky situations. Ultimately, though, this may be a matter of preference on our part, since the Nikon tends to err on the side of caution in preserving highlight detail by slightly underexposing in some situations, while the Canon will serve up what is traditionally a proper exposure. Really, you can't call either approach 'wrong'. If you're really worried about highlights, though, you can activate the Mark III's Highlight Tone Priority custom function, which extends the upper portion of the dynamic range to help preserve highlight detail.
While most photographers will probably stick to a neutral colour mode, the 1D Mark III offers an entire Picture Style menu in which you can quickly adjust sharpness, contrast, saturation and colour tone to change the overall look of the images you capture. In addition to six presets, which can each be modified as you see fit, there are three user-defined settings so you can make up your own.
Among the presets is a monochrome setting, which includes filter effects that mimic traditional (yellow, orange, red and green) black-and-white filter sets. As well as the filters, there are also toning effects, such as sepia, blue, purple or green. The black-and-white filter effects are subtle, but do a decent job of approximating the effect of real filters. Best of all, you can access the Picture Style menu from a dedicated button next to the Func button, so if you want to create different styles for different situations, it's easy to switch between them quickly.
Including the one mentioned above, the Canon 1D Mark III has 57 custom functions. Just for reference, the Nikon D2Xs has 42. Both of them can be customised extensively, and it would make sense for any owner of either camera -- or almost any midlevel or higher digital SLR -- to read the manual to find out how to tweak the camera to suit their shooting style. Some functions lend themselves to once-only settings, such as the ISO speed range, which lets you set the highest and lowest available ISO from among the camera's range of L (aka ISO 50), all the way up to H (aka ISO 6,400). While the camera displays L and H for these two extremes, they show up as either 50 or 6,400 in your images' EXIF data.
Other custom functions, such as the number of bracketed shots (from two to seven), or linking spot metering to the selected AF point, lend themselves to more frequent changes. Thankfully, Canon groups the custom functions into four submenus to make it easier to find the one you want to change.
Canon officially joins the live-view SLR revolution with the 1D Mark III, which lets you frame images with the large 76mm LCD on the back of the camera instead of the optical viewfinder, should you choose to do so. Once the Live View mode is enabled in the setup menu, all you have to do is press the Set button to enter Live View mode. When you do, the camera locks the mirror up, thereby cutting off the optical viewfinder, and you're restricted to manual focus.