The 5D2 would be the logical choice for me, but there are no wide-angle Canon zooms on a par with the Nikkor 14-24/2.8. I'll probaly eventually get a 5D2, or maybe I'll wait for its successor with improved video flexibility.
In the meantime, and on my next photographic trip to exotic locations, I'll probably carry the Nikon D700 with 12-24/2.8 lens and possibly a Nikkor 50mm prime; the Canon 50D with 17-55/2.8 IS, 24-105/F4 IS, 100-400/F5.6 IS, and leave the 5D at home.
You'll notice that all the Canon lenses mentioned have IS, which is an advantage when travelling with a lightweight and probably slightly inadequate tripod which one rarely uses.
What I want to determine is, if there is any disadvantage to taking a 50D instead of buying more lenses for the D700, or indeed taking along the 5D in place of the 50D.
In order to answer this question, I've resorted to examining DXOmark graphs, which is a lot less time-consuming than making my own tests and prints.
As always with the cropped format, shallow DoF is more difficult to achieve. The Canon EF-S 17-55/2.8 is roughly equivalent to the Nikkor 24-70/2.8, except it's slightly longer at 27-88mm FF equivalent, which is actually better for me.
What I'm more concerned about is the sharpness of a lens at its maximum aperture rather than its shallowness of DoF at that maximum aperture. The EF-S 17-55/2.8 really is surprisingly sharp at full aperture. I doubt that the Nikkor 24-70 is sharper. Once again we could do with some thorough and real MTF tests at various apertures and resolutions, but Photozone can give us a rough idea as to the comparative resolution of these two lenses.
Photozone advise against comparing results across different brands of cameras. I presume this is primarily because the pixel count of the different brands of cameras used may vary. In fact, most Canon lenses are tested with an 8mp cropped format (350D), and the Nikkor lenses are tested, I believe, with the 10mp D200.
However, a few Canon lenses have been retested by Photozone with the 15mp 50D. One such lens is the EF-S 10-22mm. One can compare results from a 350D with results from the 50D with this lens. The 50D results show approximately a 20% increase in resolution at 50% MTF.
If one applies this 20% figure to the EF-S 17-55/2.8 results with the 8mp 350D, one gets a centre resolution of 2490 LW/PH at 17mm and F2.8. (2075 x 20%).
If we look at the Nikkor 24-70 at F2.8 tested with the D200, we get an LW/PH figure of approximately 2210, significantly less than the Canon EF-S 17-55 with the 20% adjustment for the higher resolution of the 50D. But let's not quibble. A full frame sensor is less demanding of lens resolution, so let's call it a draw. I'm feeling magnanimous.
Let's now move to the noise and DR implications of using the 50D in place of the D700. Surely the D700 has lower noise and higher DR than the 50D. Could it be otherwise?
Well, maybe that's not such a big deal when you factor in DoF and shutter speed considerations, and especially when you factor in the IS advantage of the EF-S 17-55.
Typically at fairly close distances, there's a 2 stop difference between the cropped format and full frame with respect to DoF, and there's also a two stop advantage if the lens has IS or VR.
Comparing the 50D with 17-55 lens, with the D700 with 24-70 lens, the former has a 4 stop advantage with hand-held shots, at equal DoF. If DoF is not an issue and the fastest aperture is used with both cameras, the 50D has just a 2 stop advantage. It's sufficient to wipe out any noise and DR advantage of the D700.
Below is the DR comparison of the 3 cameras, 5D, 50D and D700, from DXOmark, at the pixel level rather than the reduced print size of 8x12".
The horizontal axis represents the real, tested ISO, and the blobs on the graph indicate that the 3 cameras' ISOs are all overstated (exaggerated).
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