For this test I used the A55 for half of each period and used the A500 for the other half. I used the same Zeiss 135mm lens the whole game.
This was the first game I've shot with the A55 where I felt comfortable using the Electronic Viewfinder. In the past I've always struggled with the viewfinder and keeping the subject in the correct area.
A usable image is one that is in focus, doesn't cut out the players hands, doesn't have too many distractions from other players and doesn't look exactly like the frame before it or the one after.
My keep rate with the A500 was 30% while my keep rate with the A55 was 23% however I did end up with 2.59 as many keepers with the A55.
One reason I think the A55 had a lower rate of usable images was because so many of the images look the same but I only kept one. Once you get the subject framed and the focus square on the face you can easily blast off 5, 6 maybe even 10 frames. They look too similar to keep but you get to pick the best face out of the bunch.
You would think the A500 would work the same but you don't seem to get as many shots off that are in focus.
All the shots were done on continuous auto focus, with the motor drive in the highest setting. I set the ISO to 1600 for the most part and shot at 1/1250 second at F2.8. For some of the A55 shots I was using 1/1000 second but thought the images were a bit light.
I must have thousands of shots that look just like these two.