This is our standard studio scene comparison shot taken from exactly the same tripod position. Lighting: daylight simulation, >98% CRI. Crops are 100%. Ambient temperature was approximately 22°C (~72°F).
Nikon D3 vs Canon EOS-1D Mark III
Since this review was first published we've been able to get an EOS-1D Mark III into the studio and have added some comparisons to various sections. The EOS-1D Mark III is perhaps the camera most likely to be seen as a competitor for the D3 by sports photographers (it too is built for speed).
The big difference is the sensor; where Nikon has taken the decision to produce a full frame sports camera the EOS-1D Mark III sticks to a 1.3x crop / APS-H. For telephoto shooters this gives the EOS the advantage of higher pixel density - cropping the D3's images to give the same field of view drops its usable resolution down to around 7.1MP (compared to Canon's 10MP). Of course what you gives with one hand you takes away with the other, and the D3 will give you considerably more latitude at the wide end of the focal length scale when shooting with the full 'FX' mode 12 megapixels.
Canon EOS-1D Mark III: Canon EF 50 mm F1.4 lens, Aperture Priority,
ISO 100, JPEG Large/Fine, Manual WB, Default Parameters (Standard PS), Self-Timer
Canon EOS-1D Mark III
4.4 MB JPEG (4256 x 2382)
3.1MB JPEG (3,888 x 2,592)
Again Nikon's default sharpening is lower, producing an image that looks softer; the EOS-1D's JPEGs have marginally better per pixel sharpness and detail and the D3's two million pixel advantage is barely visible (you can see it if you look closely at the third crop down). Putting aside depth of field and other optical differences it's fair to say there's not a lot between these cameras at base ISO (especially if you increase the sharpening on the D3 to match the EOS-1D), and certainly there's nothing here that would produce a visible difference at normal enlargement sizes.