I can not make a firm comparison with Nikon, as I have shot the same subject from the same position, but in much worse light - very low light - with their 300mm f/2.8 only, on the D3. The Nikon missed a couple of shots (9 fps is much faster than 5 fps so I was able to get longer sequences) for exactly the same reason the Sony missed one - focusing shifting to a background object when the horse missed the active focus sensor, then recovering instantly for the next shot. I have also shot this view with the KM5D and 70-210mm f4 AF 'beercan' and even that was able to pick up focus pretty well (in sunny conditions, like this).
I'd say the A900 so far has proved as reliable as the D3 for focusing, and the 70-200mm SSM is about the same focus speed as the 70-200mm VR (the 80-200mm AF-S is a better lens by far, and also seems to focus faster, or more reliably). It is very slow when you switch on, and takes what sounds like a full second for the lens to set itself to infinity, but fine increments of focusing tracking moving subjects are very precise and fast. My experience with the D700 was not as good as with the D3, and I'd definitely rate the A900 as a better all-round performer than the D700 as far as focus, exposure and general file quality go.
Here is a contact sheet of the shots taken during this race - where one runner was 2 seconds ahead of the next clump (these are not professional jockeys, they are the town principals of all the Border town civic festivals - elected, need to have a good degree of horsemanship, but some have to learn during their year). With centre spot AF, I was firing a couple of shots at 5fps, then quickly aiming back to catch the next batch coming from behind a jump and firing three shots continuous - etc. Focus was picked up reliably all the time.
Go to this URL
http://www.pbase.com/davidkilpatrick/image/104213855 and click NEXT, you'll get a set of the shots, plus some more taken on Sunday of different subjects. The 2X converter's slightly softer image and noticeable CA can be seen, also the respectable but not brilliant performance of the 28mm f2, something from the 100mm macro, and a candid shot with the 70-300mm SSM G at 200mm which really shows the level of detail it can manage, plus the distortion:
I don't want to post strings of images here, it's probably better to visit the pBase pages and have a look. I will add some more later. Please remember - no capture sharpening, no output sharpening on most of my samples - where there is sharpening or NR, I'll give details.
David
