D.O.F./adjusting focus with lenses
 

This may be a simple question to answer but I have a question on composing two different types of shots.

1) If i have a close up of an actor with the background out of focus, how do I make sure the background stays out of focus when the actor moves but I want to keep the shot?

2) I have the actor in the foreground in focus and the actor in the background out of focus. If I want to rack focus between the two, is the best way to do this with manual focus?

Ive seen a thing called a Z finder, and things called follow focus, would these do what I'm asking?

Yep, you've got it!

Whats the best one to get?

What's your budget and needs?

The Zacuto products look like they're in my price range, I'm not really sure what the difference between them is though

I'm doing short narratives for school projects.

If the Zacuto products are in your price range, they are well regarded and well made.

what are the differences between the different types of z-finders?

You'll find as many answers and opinions as there are people. I'll jump off the conversation here as I don't own a z-finder and let someone with experience answer your question.

The Z-Finder (along with other brands/variations of viewers) and follow-focus both help with focus, but in different ways.

The finders attach to the camera's lcd screen and allow you to hold the camera to your eye. They generally enlarge the view of the lcd screen and block out light from the sides and back so it is easier to see the scene and adjust focus. Because you hold them to your eye, they also help to stabilize the camera because you have another point of contact with the camera and you aren't holding it out away from your eye to see the lcd. I consider a finder of some sort mandatory for handheld shooting, especially outside or where it is bright.

Follow-focus attaches to the lens, usually through some sort of rail or frame that attaches to the body of the camera and may allow the attachement of other devices (handles, monitors, matte boxes, etc). The follow-focus provides another way to manually turn the lens focus ring. Because of gearing, shape, position, etc they provide a much smoother way to adjust focus. They usually have a way to mark focus points on them so you can pre-determine point A and point B so you can easily rack focus between these points. Focus on larger cameras and productions is usually done by a person called the focus puller, and is separate from the person operating the camera. The follow-focus rigs can be operated by the camera operator with these little DSLR camera, but make sure you have a rig that allows you to use the camera in the way you intend to use it. For instance, if you are hand holding the camera, can you hold the finder to your eye and support the camera while still manipulating the follow-focus.

Good luck and have fun.

I recommend...
 

That you get your hands on a instructional DVD by Phillp Bloom called learn to use or shoot canon 7D, please correct me if I am wrong.
By your question I assume you might be using a dslr, and this DVD will explain all the essential tools that go hand in hand with workih with a dslr, with great examples. It should very well answer you two questions and possibly more.

M. T. Zaheer

Ah thanks for clearing that up. I thought the two were the same product. would it be best to get both?

EDIT: and yes I'm using a Canon EOS 7D, hence why I posted in here

also recommend doing searches--all of this has been covered over many threads here.

If you're on a student budget doing narrative films then I would skip the follow-focus. And you can get cheaper alternatives to the z-finder, such as the LCDVF.

If you want to hit you focus properly then you can use crayons or whiteboard marker or something else non-permanant to make little marks on your lens where you need the focus to be. Then mark out the spots of the floor where the actors have to stand. Blocking your scene like this makes it much easier to get your focus right, as well as giving everyone on set a better understanding of who is moving where and when. It won't be as easy as with a follow-focus but for a student film it's more important to learn about blocking the action and planning the scene in advance so everybody knows what to do, rather than focusing on and relying on one bit of gear to solve all your problems.