Since I'm primarily a Nikon user, I chose to post this response to Drew's comparison under the Nikon section, but I'll link to it from the Canon section as well. While it's a reasonable initiative on Drew's part to do this comparison, with obvious interest from this forum's viewers, unfortunately, from my perspective, the current comparison is not a valid one. From what I know about the two new Nikon bodies, the D3 and the D300, which share many of the same components, including AF, there are several variables that have not been taken into account. And, with the amazing complexities of both these bodies, as well as the Canon's, I'm sure there are many more than I've considered or the few I've listed as follows:
First, the full frame vs 1.3 sensor dimension differences give a different subject size and perspective to the test as run. This provides a smaller target to the AF relative to the AF sensor size for the D3 compared to the 1D MkIII. This provides less scene information, particularly contrast differences of black/colored insignia on a white T-shirt, to the AF sensor, which skews the results in favor of the Canon.
Second, with the larger full frame sensor size of the D3, there's much more extraneous scene information in the frame. Since the D3/D300 AF interacts with the Matrix Metering system, the additional background could produce some detrimental effect on the D3 AF effectiveness. The metering mode is not specified in the write-up, but as a sports shooter, I have found much better results using spot metering than matrix metering, for both exposure and AF accuracy, particularly for distant subjects. Whether or not this holds true for the new bodies, I haven't had enough experience to definitively determine.
Third, with the entirely different AF engine in the Nikon bodies, instead of using the standard "single AF sensor", many sports shooters are finding much better results with the 9 or 21 point Dynamic AF, such as a poster in this thread at FredMiranda.com:
D3 set-up Sports - FM Forums
What affect the choice of Single AF point vs 9/21 point Dynamic AF has on a runner approaching the photographer directly head-on, I don't know. But if the insignia target on the white shirt is moving side to side as the runner switches feet, with the smaller target perspective of the D3, it could make a substantial difference.
While Drew's "Showdown" does show a difference in AF focus in this particular situation, I believe it's seriously flawed. My point in all this is not to suggest the Nikon system is better than the Canon, or visa versa. My purpose is to question the validity of this very limited comparison, because of the extreme complexities of the two new systems, and the difficulty in providing for all the variables to arrive at a thorough evaluation and a sound conclusion.
Linear Mode
