How do you focus on a moving subject with a short DOF?
I do AI servo
focus back button (that * key) (do I hold this thing down so the camera continues to track or do I need to release and then press * each time subject relocates from frame)
and of course a fast shutter speed.

I am guessing it depends on the subjects movement too...maybe it's just skills on predicting where the subject will be and kind of focus there...but that's tough too b/c if there is nothing there (since the subject is not there) there is nothing to focus on and since DOF is so shallow one would need to get it just right...

Oh I don't have a specific picture in mind that I am taking--but just a thought...

Yeah I know of course one can do high DOF and catch the pic sharp, but yeah I want that smooth buttery background with some pumpin' action! oh yeah!

oh and hope everyone is having a happy Tuesday!!

Thanks again in advance!!

You need to hold it down while it tracks - that's the entire point of using the separate button for the focus.

And you take lots of shots.

That * button (at least on canon) is an exposure lock, not a focus lock. I usually use focus lock mode and just keep releasing, and repressing the shutter to re focus as things move. The reason I do that is because ai focus will sometimes grab the focus, and look good but before you get the shot is see's something else and refocuses to that. Sometime you just have to use ai id things are moving fast enough. And a second to taking lots of shots. Practice makes us all more perfect, but theres no replacement for the insurance that lots of shots gives us.

Gav

This is a great thread on the back button focus thingy!