The first thing most people say when holding the 1Ds Mark III is that it's heavy, and they're right. At times though, that weight can help steady your shot and once you get used to shooting with a body that's nearly 1.5kg without a lens attached (but with the battery), the weight isn't as big of an issue, though your arm will feel more tired at the end of a long day of shooting than it would if you were using the 5D. Also, your back may feel it if you carry this camera and a few big pro lenses around for a while.
The 1Ds Mark III's viewfinder offers 100 per cent coverage, according to Canon, and in our tests, it seems like they're at least extremely close, making it a joy to frame images, since you're not guessing if what you see through the lens is all of what you'll get.
Compared with cameras with smaller sensors, the finder's 0.76x magnification won't look all that impressive, though it's plenty big and bright. If you don't enjoy the screen that comes with the camera, Canon also offers a choice of 15 optional focusing screens to which you can switch. We had no trouble focusing manually with the default screen.
Like the 1D Mark III, the hot shoe on the 1Ds Mark III has a raised hard plastic ridge around the hot shoe that mates with a rubber gasket around the connector on the 580 EX II Speedlight, to seal one of the few spots on the camera that aren't protected by rubber gaskets built into the body already. The shutter is said to last for up to 300,000 cycles, which is a notable increase over its predecessor and puts it even with the shutter in the Nikon D3.
The feature everyone will mention first about the 1Ds Mark III is its 21-megapixel Canon CMOS sensor. We wouldn't be surprised if that's followed by a small discussion of the camera's 14-bit per channel analogue to digital conversion, which theoretically allows for 16,384 levels of brightness compared to 4,096 levels with the 12-bit Mark II when shooting raw.
Nikon's D3 also offers 14-bit raw output, but also gives the option to roll that back to 12-bit if you're trying to keep file sizes down. You can't dial down to 12-bit on the Canon, so if you shoot raw, expect files in excess of 30MB each. Full size, finest quality JPEGs can approach 15MB.
Since the sensor's size is the same as a frame of 35mm film -- often referred to as full-frame -- you don't have to worry about any conversion factors to figure out the "equivalent" field of view that you'll get with any of Canon's EF lenses. However, you won't be able to use any of the company's EF-S lenses. While this bothers some folks, especially because Nikon lets you mount its digital-only DX lenses on its full-frame D3, Canon's EF-S lenses extend further into the body, so the large mirrors on its full-frame and 1.3x focal-length-multiplier 1D series cause a physical conflict. So, Canon's not likely to change this.
However, it's typically understood that anyone buying a full-frame Canon would know that you can't use EF-S lenses, since the company has been very upfront about this issue from the get-go. Also, we should note that the ability to use DX lenses on the D3 comes at the expense of precious pixels.
Outdoor photographers will appreciate the 1Ds Mark III's dust reduction system. It shakes the sensor whenever you turn the camera on or off to shake dust from the IR-cut filter in front of the sensor. That filter also has an antistatic coating to prevent dust from adhering in the first place. If you end up with any persistent marks on the sensor you can have the camera map the sensor and plot their locations, so you can remove them automatically with the included Digital Photo Professional software.