Following the current trend, the 1Ds Mark III includes a live view shooting mode, which lets you frame images with the big 76mm (3-inch) 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 are restricted to manual focus.
If you're worried about light leaking in through the viewfinder, you can block it with the built-in eyepiece shutter by flipping down the switch in the right side of the viewfinder. Conveniently, you can use the playback zoom controls to zoom in either 5x or 10x on your subject, to aid in manual focusing.
Canon doesn't set any strict limits on how long you can remain in live view mode, but it does mention that the sensor heats up in this mode and that you may encounter a thermometer icon on the LCD once the camera reaches a certain temperature. We never saw this icon when we used live view mode, but if you typically shoot in very warm environments -- studio hot lights, anyone? -- you may run into it. As you may guess, shooting at higher ISOs should make the sensor heat up faster than at lower ISOs. Canon also warns that increased temperatures can lead to increased image noise.
Canon has increased the number of cross-type autofocus points from 7 in the Mark II to 19 in the Mark III. Cross-type AF points typically provide a higher level of sensitivity compared to standard horizontal-only points. Those 19 cross sensors are joined by 26 "assist points" for a total of 45 AF points. Careful scrutiny of Canon's manual shows that the number of active cross-type points decreases drastically if you use a lens with a maximum aperture slower than f/2.8.
When you step down to a lens with a maximum aperture of f/4, only the centre point functions as a cross-type; the rest function as horizontal only. With a maximum aperture of f/5.6, all AF points become horizontal only and by the time you reach a maximum aperture of f/8 you're left with only the centre point active and it acts as a horizontal-only sensor.
This is essentially the same system that is employed in Canon's 1D Mark III, which still has an ongoing problem with continuous AF under certain conditions, including very hot and bright shooting conditions. We saw no such problems in our tests with the 1Ds Mark III, though we did most of our testing in winter. Still, there's no real reason to think that the 1Ds Mark III has any such problem in the first place.
To determine a proper exposure, the camera uses a 63-zone TTL (through the lens) metering system. The system offers full-frame evaluative metering, centre-weighted average, and partial and spot metering. According to Canon, the partial option uses the center 8.5 per cent of the frame to determine exposure, while the spot setting uses 2.4 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". All you have to do is press the FEL button to add another spot reading while you're in spot AF mode to begin with. The average of the total number of spots is used, and you can even apply exposure compensation. While it worked well, it took us a little time to figure out that you have to point the active spot at each part of the scene for which you want to add a reading and then recompose before capturing your image. Sure, that makes sense, but the manual probably could've communicated that a little more clearly.
In our tests, the 1Ds Mark III yielded remarkably accurate exposures and was rarely fooled by tricky scenes, but the 3D colour Matrix Metering found in Nikon's D3 -- with its 1,005-pixel sensor and onboard database of comparison image data -- barely edges out the 1Ds Mark III's evaluative mode 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 makes use of the camera's 14-bit digital conversion to extend the upper portion of the dynamic range to help preserve highlight detail.