Though it's not the first SLR to have a Live View mode, the Canon EOS 1D Mark III is the first professional camera to have a true, full-color live view. It's also the first SLR to allow both remote control and live view through a computer via USB, Ethernet, and WiFi (the latter two methods require a special adapter, the WFT-E2A). Note that many (it used to be all) Canon digicams and SLRs come with some form of remote control software that works via USB. Up to now, only the digicams offered live view through the computer.
See the illustration below (Courtesy of Canon USA) for the display and information available in Live View mode on the camera.
The computer screenshots below are cropped from my screen grabs, then resized and sharpened. To see the full-pixel versions, click on the images. They'll open in their own window, sized about 1,280 x 743.
When I connect the Canon 1D Mark III to the computer with a USB cable, the new EOS Utility launches. I click on "Camera settings/Remote shooting," and I'm taken to a window with just the right pane open (the one marked "EOS-1D Mark III" above. I have to click the Live View radio button down on the lower right to bring up the "Remote Live View Window at left. The image comes up horizontally oriented, as you see, though I have the camera mounted on a tripod in vertical format mode. No problem, I just press the left rotate button along the bottom, and get the following screen.
It's surprising how easy it is to focus on the Mark III in this mode, especially with a nice little lens like the Canon EF 50mm 1.8. I can physically turn the focus ring on the lens, or use the Focus controls on the screen at upper right. The three levels of movement in either direction make it easy to get fairly precise in your focusing.
It took a few presses of the level-two focus movement to get the photo almost in focus.
Press it one more time, and the focus pops. You can take a picture at any time, using the shutter button in the upper right of the screen (this didn't work on my PowerBook, for whatever reason), and the image begins to transfer. While it's transferring, you can still adjust any of the settings.
You can do a lot from these two windows, even adjust white balance via the eyedropper, and send the setting to the camera. Here, I have the Mode button pressed (double click to bring it up), and I'm switching to Manual mode. It took a long time to send this setting back to the camera (at least 30 seconds), but I attribute that to the beta status of the software.
Now in Manual mode, I'm able to change the shutter speed and aperture settings via the pop-up dialogs.
Thus... This, too, is a little slow in the beta software, though not as slow as the mode change.
The image doesn't change to reflect the new setting, however, until I press the Depth-of-field preview button in the Remote Live View window.
Not a big change, but you can see that the lamp and pens are slightly less blurry (especially if you look at the full size images by clicking on the one above).
If I really want to check fine focus, I can zoom in and pan around (the pan feature did not work in this beta version), and adjust focus either manually or again with the onscreen buttons.
Here it's a little sharper than above, about the sharpest I can get this image, which is a printed photograph hanging on the wall behind my desk. If I move this zoomed window to show the control cluster, I can take a picture, or else I can launch a new control cluster by pressing the little button in the lower left corner. I don't know what Display Mode is supposed to do at this point, because nothing happens when I press it. I would think it would return the view to the camera's LCD, or at least enable both, but neither happened.
So without going into everything, it's easy to see the potential of the Live View mode on the EOS 1D Mark III. I can see a lot of event portrait photographers taking great advantage of this mode, as well as creative types wanting to get remote shots from anywhere.