how to focus while dolly-in ?
 

I've seen lots of movies where they dolly-in to the character, and the focus is perfectly sharp. how do they focus? keep rotating the focus-ring while moving?

I would like to try it with my XL1s.

Watch the credits of a movie closely, and you will often see the credit "Focus puller".

This is the guy who stands next to the camera, and rotates the focus knob to keep the shot in focus as the camera or actor moves.

It helps if you have a focus puller adapter for your lens. This is a large knob that attaches at a right angle to the lens and gears into the knurls cut on the barrel. It also has a white pencil slate around the knob, so you can mark it with starting and stoping points in the movement.

It works best with a manual lens.

Basically, yes. There's someone called a focus puller whose job it is to keep the subject in focus at all times.

On some cameras, though, there's a "Push Auto" button which may accomplish the same thing, and stay focused while you zoom/pan/etc. In fact, the BBC has recommended you do that when moving a VX2000 around since they say the focus ring is annoyingly touchy. So as the dolly moved in, the cameraman would just hold the Push Auto button and not worry about the focus ring.

This is nearly impossible to do with the standard lens that comes
with the XL1S because it is server controlled and has no fixed
end and start points (ie, you can rotate it forever). If you put a
mark on the ring you'll see that setting the point at 12 o clock,
rotating it around a bit and then put it back at 12 o clock the
setting won't be the same. Therefor you can't do this very well.

You can however set sharpness at one point and learn by enough
trial and error how fast (and how hard) you need to rotate the
ring to have the focus shift correctly while moving. You'll probably
will need a bigger monitor then your viewfinder to correctly spot
the moving focus though.

Ofcourse you only have this problem when the distance from the
subject to the camera is varying. If you stay at the same distance
you won't need to adjust your focus at all.

If your subject does move then you'll only need to focus if you
are running with a very shallow depth of field (lowest f-stop
when zoomed in). If you have a large depth of field your subject
won't go out of focus unless it is moving at great distances.

This is sometimes called a "Hitchcock dolly" maneuver because Alfred Hitchcock popularized it in some of his films.

Basically, it's not an easy maneuver for anyone. It requires extreme precision with manual focus and camera movement.

Here's a thread that discusses it in more detail.

Ken, are you sure he is talking about that? That is when zooming
and dollying...

Ah, indeed, Nawaf only mentioned focus, not simultaneous zoom. Sorry.

Yeah, I think Nawaf was just referring to the process of following focus.

Because digital, DV in particular, is much more forgiving in terms of focus (because of its extensive depth of field), it can seem to some extravagant to have an individual who's job it is to keep the image focused. But while performing a shot as described on 35mm if the actor chooses to lean a certain way on a whim, the focus puller must take that into account or the shot will be soft. It's a very skilled and demanding position.

thanx everyone. yeah, you guys answered my question. I guess i need lots of practise with focus.

Couldn't you just stay completely zoomed out (widest angle of view), regardless of what type of lens (auto 16x, manual 16x) you use? Unless that gives you undesireable framing, of course. Otherwise, that's how I'd do it. You get pretty much infinite depth of field, with miniDV. Unless your subject's like two inches from the lens.

Josh,
actually, i'm using shallow DOF most of the time, to give it film look. so I'm zoomed-in most of the times, which needs lots of precise focusing.

But even then you have quite large depth of field, it might be
shallow enough to use it nicely for DOF effects, but if you practice
you should be able to keep your camera the same distance
from your character all the time and thus avoiding the need to
adjust the focus.

Nawaf, if you are using the stock 16xIS II lens with the XL1, you have your work cut out for you! It's much harder to follow focus with that lens. If you are shooting at telephoto a lot and interested in narrative-type filmmaking vs run-and-gun shooting, you might want to look at the manual lenses if you haven't already done so. Either the 16x or the older 14x give a much more tactile response to focusing. I like the 14x myself, and they can be found pretty cheap these days, even new.

I always wondered why people use the old manual focus lenses. now I know.

so, with the 16x AF lens I have, I won't be able to do very sallow DOF? for example: if I want to close-up on someone's mouth, and I want the ears to be out of focus. would I be able to do that ?

Off-hand I'd have to say that you won't be able to get -that- shallow of dof with the the 16x Auto (standard) lens.

You may be able to use the macro settings of either the 14x manual lens that Charles mentioned or the 16x manual servo lens to approximate that. (See this article for more information on these lenses.) But the lens would have to be extremely close to the subject.

BTW, there's certainly nothing "old" about manual lenses. Since the consumer camera market, and indeed much of the prosumer market, demands auto everything auto-focus lenses have become standard issue on these products. Manual lenses are generally found on professional cameras designed for more skilled operators.