The Nikon D800 is viewed by many as the natural competitor for the Canon EOS 5D Mark III. Given its class-leading pixel count, it's not really a surprise that the Nikon D800 is capable of resolving more detail than the 5D Mark III.
What is a little surprising, however, is that the Nikon camera also produces raw and JPEG images that have a higher dynamic range when the lower sensitivity images are used.
We might have expected this to be the other way around, given that the pixels on the Canon EOS 5D Mark III's sensor have more space.
It is only when the sensitivity of raw files is pushed to ISO 800, or the JPEG sensitivity is ISO 3200 or higher, that the Canon EOS 5D Mark III's dynamic range is higher than the Nikon D800's.
Nevertheless, the Canon EOS 5D Mk III is extremely capable, and it resolves an impressively high level of detail in both raw and JPEG files, which only really starts to dip when the sensitivity is pushed to ISO 25,600.
Our tests also show that from around ISO 100 and above, the Canon EOS 5D Mark III has a slightly higher signal to noise ratio than the Nikon D800, so images have less noise.
However, as is usually the case, noise becomes quite noticeable when the upper sensitivity expansion settings (ISO 51,200 and ISO 102,400) are used, so these are best reserved for emergencies.
We also found that at the top settings, the camera can struggle to render tonal gradations in some red subjects, and small patches of uniform tone appear, giving parts of the image a posterised appearance.
Despite these issues, the Canon EOS 5D Mk III is capable of producing some very impressive results in low light.
When shooting some BMX riders in dim light, for example, the sensitivity was pushed to ISO 12,800 and the JPEG results look very good at A3 size.
Even at 100 per cent on the computer screen, images look respectable, with only a slight mottling of luminance noise and some softening of some fine details. Raw files, of course, can be processed to reveal a bit more detail provided you don't mind a bit of texture.
Canon produces one of the best white balance systems around, and the one in the Canon EOS 5D Mark III doesn't disappoint. When set to the automatic setting, images look natural and generally retain the atmosphere of the shooting conditions.
The Standard picture style is a great option for most situations, but others such as Neutral, Faithful, Monochrome, Portrait and Landscape are on hand, along with three custom options, if you want a different look.
One of the key selling features of the Canon EOS 5D Mark III is its impressive AF system, which is very similar to the Canon EOS-1DX's (except it doesn't detect colours or faces), and it has a dedicated menu section.
However, this means that existing Canon EOS 5D Mark II users have a steep learning curve when shooting sport and action scenes.
There are six AF Area Selection modes, including Spot AF (Manual Selection), Single-point AF (Manual Selection), AF Point Expansion (Manual Selection), AF Point Expansion (Manual Selection, Surrounding 8 Points), Zone AF (Manual selection of Zone) and 61-Point Automatic Selection AF.
On top of this, the the AI Servo (continuous AF) mode characteristics such as tracking sensitivity, acceleration/deceleration tracking and AF point switching can be adjusted.
Helpfully, there are a number of sport-orientated 'Case Studies' or setup arrangements that enable users to select the correct options for the subject.
According to Canon UK's David Parry, Canon is working on other non-sports case studies that should be available in the future.
We found that the AF system is fast and accurate. It did a good job of keeping up with skateboarders and BMX riders in subdued light in this test.
Wildlife photographers may find the Canon EOS 5D Mark III's Quiet Mode useful, because unlike other quiet modes, it doesn't rely on the mirror being held up after the shot has been taken. Instead the mirror moves more slowly, and a new mechanism dampens the movement to reduce the noise.
The end result isn't silent, but it's much quieter than in normal shooting mode, and it enables a maximum continuous shooting rate of 3fps.