focusing professors help

I will be using my 1dmk4 for some video action next week. I will be doing a photo shoot on a mountain for some skiiers. With that I'd like to get some vid. The manual is a bit confusing to me when it comes to moving subjects during vid filming. Can I use smilie quick mode once I have focus lock on a subject? Which approach should I use to maintain focus with a 70-200L from a good distance. Do I just need to have a large dof and wing it manual focus? Or is there a setting that will track a subject?

stop it down to about f/9 or so 720p60 at 1/120

The Autofocus in video mode is just shy of useless in that it is very slow and often picks the most contrasty part of the picture which may or may not be your subject.

The best option is to close the aperture to get a wider DOF and then use manual focus.

That's what I was afraid of. Too bad the camera doesn't have the ability to focus Al Swervo during vid. That lens and body combo can focus plenty fast in normal shooting conditions, why not video? Anyway, will plan accordingly, thanks

The mirror block sends light to a separate sensor for AF. When you hit the shutter the mirror block moves up and exposes the imaging sensor. When shooting video, the mirror is locked up obviously, so the dedicated AF sensor can't be used.


Sony's new a55 uses a Pellicle mirror system which sort of addresses this issue.