Manual focus in 30P mode?

[Greg Matty]

If my grad school plans fall through I will need a camera to replace the XL-1 I sold. I am leaning toward the DVX100 for its 30P mode and will of course wait until NAB to buy anything. As I understand it, you must use manual focus in this mode. Is this camera pretty easy to manual focus? With my XL-1 I usually used the push AF button and almost never used the focus ring.

Maybe someone can recommend a good book on the physics of focusing? I know that small apertures (f16, f22) yield a larger depth of field and I have set critcal focus as I think it is called but it would be nice to know not just what works, but why it works. Someone once told me that if you zoom in on a football player at the far end of the field and then set the focus, you could follow the player all around the field at various zooms and never lose focus. I have not tried this but it sounds too easy to be true.

Is there a physisist here who can clue me in?

Greg Matty

[Scott Davis]

Okay, this is not to be taken in a condescending way, but professional videographers NEVER use auto focus. Never, ever, ever. Cameras seek vertical lines and use those as reference for auto-focus. If something moves in your shot, you might reveal a new vertical line, and that might freak your AF out, and your focal point will change. It's just like an auto iris... you NEVER use auto iris. You should just go ahead and disable those features on your camera, then take those buttons right off!!!!!!

As far as zooming into a football player at the other end of the field, yes, everything from there to here will be in focus, but not while you are zoomed in... while you are widened out, everything will be in focus. The term is focusing to infinity. If you are all the way zoomed into the other goal line, focus, and then zoom into the 50 yd. line, I can guarantee to you that your subject will not be in focus.

The physics of the depth of field says that the further closed your iris is, the greater depth of field, and the converse. If you're shooting on video, video professionals (and I can't speak for all of us) try to emulate film as much as they can, so we want our iris as wide open as possible to DECREASE the depth of field- that's one of the inherent qualities of film that we go after, and will (hopefully) make our video closer looking to film. Engineers laugh that they use so much technology to make video look pristine, and videographers muck it up with Pro-Mist filters, Cine-gammas, "Film-Like" settings in a Sony camera, and shallow depths of field, much like editors will use Cinelook, Magic Bullet, or whatever else they can to give that film-feel (A.K.A video sex).

Good luck in grad school.

[Jeff Donald]

Auto Focus is a tool to be used judiciously, just like any other tool. I occasional use AF because it is the best tool for the job. But in order to make that determination you have to know the limits of your camera and it's AF. I also use AE from time to time (almost never the all auto Green Box mode). The trick to shoot a lot with your camera so you learn it's ins and outs.

Maximum DOF is achieved when you focus at the hyperfocal distance. Focusing on a distant object when zoomed in will not yield the hyperfocal distance and the subject may move out of focus.

The complete skinny on DOF is here and the discussion here