I separate AF-ON from the shutter release. So it's a two-finger operation.
For the sake of discussion, let's say I'm in CL or CH mode, trying to catch a series on some playing field or other. Let's say there's plenty of light, and a fast (f/2.8 or better) lens. Let's say I'm shooting at 1/1000 second and f/2.8, and using Auto-ISO.
Why would I want to make exposures that weren't in focus? I'm confused by these modes.
As I understand it, the four modes are: (1) Release, which takes a picture any time you press the shutter release, regardless whether it's in focus; (2) Focus + Release, (the manual talks about dark or low-contrast subjects) which gives priority to focus for the first shot in a series, then to frame rate; (3) Release + focus, which starts like #1, though the frame rate will slow to try for improved focus if the subject is dark; and (4) Focus, where an exposure will be made only if the frame in focus.
I've read other places that AF "lock" (though focus never really locks on AF-C) is achieved faster in Focus + Release mode. Is this true? I could see starting a series early, to burn through a frame if it would mean faster focus for the rest.