I've always used the "one shot" AF mode but when I was up at the Appleby horse fair last week trying out a my new 70-300 Is lens I got a dissapointingly high number of slightly soft shots. Testing in the garden on Sunday on a tripod shows that there is no problem with the lens. As I was shooting the majority of the time at 1/800 with IS on I don't think it can be camera shake. Therefore I've come to the conclusion that, with the lens mostly at 300mm and f7.1, with the shallow depth of field, in the time between achieving focus & IS lock, and actually releasing the shutter, the subject has moved out of the plane of focus.
As they always say, if all else fails read the instructions. In Al Servo AF the camera keeps adjusting the focus until the final moment when the shutter is released. So that might have been a better focusing mode. Then there is Al Focus AF which is "one shot" AF which switches to Al Servo when movement is detected.
What I don't understand is this - what are the advantages of the 3 modes? Is the one shot mode mearly to conserve battery power or is there some other reason for using it over the servo mode. Al Focus seems to offer the benefits of both the other modes so why would anyone use either of the other 2?
