I spent the day today in Manhattan at the PhotoPlus Expo. Naturally a good bit of my time there was at the Sigma booth trying to shed some light on my Canon 1D and 120-300 f2.8 Sports lens issue. The first rep I spoke with (name withheld) blamed it all on Canon saying that I should already know about all the horrible focus issues the 1D series has been plagued with. Really? Aside from the well documented issue in bright sunlight with the early 1D Mk III bodies I am not aware of any "focus plagues", especially when it comes to the Mk IV. Aside from the fact that, as I mentioned before, my 1D Mk III and Mk IV focus perfectly on all my other lenses (including others from Sigma). The second rep I spoke with was more reasonable. After hearing my plight he invited me to personally bring my lens and all my camera bodies to their facility in Ronkonkoma, to see if the service department could figure it out. I may just have to make the drive and take them up on that in the near future.
Next I went to speak with the folks at Canon. A rep I have known there for many years (name also withheld) was able to help out a little. Though he of course can't comment directly on the Sigma lens, he did confirm for me that the focus systems in the 1D Mk III and Mk IV are completely different from the rest of their cameras, in that they have an additional processor devoted just to the focus. He also said that 3rd party lens makers don't always ensure full compatibility with high end "pro" camera bodies since they make up such a small segment of the market. He used the example that, even on their least expensive lenses Canon needs to make sure they all can close down to their minimum aperture (say f22) perfectly at 12 frames per second. Now that has nothing to do with the problem I am having with the Sigma, but does at least make some sense. It does seem plausible that Sigma either was not able, or didn't bother to, properly reverse engineer the different focus system in the 1D cameras. Maybe I am finally getting somewhere?