http://www.dpreview.com/previews/sony-alpha-slt-a99/4"Sony has featured focus tracking on its cameras for a couple of generations now, but its usefulness has always been undermined by the amount of time taken to engage it. Up until now, you had to press a button to enter focus tracking mode, then press it again to confirm the subject - not really practical with the sorts of moving subject you might with [sic] to track. The A99 makes a huge step forward in this respect, with the option to begin tracking simply by half-pressing the shutter button."
To focus track on flying birds, rodeo riders, and my hyperactive 2-year old niece, I set my Sony A900 focus mode to "C" (continuous focus). Half-pressing the shutter button instantaneously locks the A900 onto the moving biota. The A900 then automatically focus-tracks the object. The method of activating the A900 tracking (just half-pressing the shutter button) is the same as DPreview describes as the "huge step forward" for the A99, but there is nothing huge here. I have checked my Sony and Friedman manuals for the A900 and can find no method of focus tracking that DPreview describes. Do any of you Sony shooters have any explanation for DPreview's description?
DPreview continues:
In my personal experience, the A900 focus tracks very well, even under conditions, such as dim light and approaching objects, where Canon and Nikon owners complain of focus tracking problems. Has anyone here seen any actual comparisons of focus-tracking in Sony vs Canon and Nikon? DPreview cites none. Are their statements just prejudiced supposition?"Sony has traditionally struggled against Canon and Nikon when it comes to matching their sophisticated subject tracking AF systems. Decades of catering to the demands of professional sports photographers have helped the big two to refine their focus systems in a way it's hard for Sony to keep up with."
Below are some examples of focus tracking in my Sony A900. I could have never captured these if focus tracking in the A900 was as cumbersome as DPreview describes.
Subjects moving in dim light:
Subject moving toward the camera:
Subjects moving fast and accelerating:
Fast, erratic, multi-directional movement: