im curious... how does a follow focus on a steadycam work ?
 

a question for the real cracks, i guess charles papert is one of them ;-)
i wonder how a real follow focus on a steadycam works, the real ones with 16/35mm cameras on top of it or even with the mini35 adapter and a camera on top of it, all the ones that dont have autofocus.
i understand how it works on a tripod i think, even when the subject changes position ect. but how on a steadycam ?
i guess i could focus on a subject lets say... exactly 3m away. then the floor is marked with crosses so i see when the actor moves on cross a1 i need to move to my cross called b1 for example so the actor is always 3m away and in focus.
but what when you would change the distance ? you cant turn the wheel while moving can you ? it must be something electronical involved i guess.
someone can explain it to me how it works ?

I guess some do it themselves other let the focuspuller do it..? But what do I know..
you can always keep the lens wide open so EVERYTHING is in focus..

Remote Focusing ? It's quite simple.

Depending on the rig and what the shot calls for, it's either operator controlled, or there is a focus puller with a remote, litterally running around behind the steadicam operator.

I know of a few operators who do multi-camera shoots like awards shows who pull their own focus via a gimbal-mounted controller, but the vast majority of operators require a camera assistant who use a radio controlled follow focus to do the trick (and they can control iris, zoom and camera start/stop also). Here's the most popular system for doing the trick. A complete system with three lens motors and cables will set you back (ready?) $20,000. For that money, you get a fabulously reliable, accurate and built-like-a-tank microwave system with a ton of torque to drive the stiffest lenses.

A more recent and also popular lower cost system is the Bartech.

As far as how the assistant knows how to calculate the distance on the fly, it's a learned skill. The best of them can assess the distance from lens plane to actor without any marks, down to a few inches of accuracy, while both are on the move. It's a skill that is right up there with operating the Steadicam. For some shots, it's even harder than operating.

(p.s. Alfred, opening the lens wide dimishes the depth of field, which makes the focus shallower...)

20,000! Just for the FF!! Sometimes I wonder how any money is made on films. But it is. And a lot of it!

In my experience pulling focus (just on a manual lens), I cannot fathom how someone can eyeball it and hit their mark. Seems like you would have to have years of experience to be able to do it at a level that would not hold up production--but where do you start? Almost a catch-22: Have to have experience to work. Have to have work for experience. See what I mean?

Jonathan:

Most AC's start by working as loaders or camera P.A.'s, then work their way up to second assistant and finally first assistant. However, I know a few who started as 1st's in the indie world and got lucky and managed to move laterally into union work.

Most of the good ones that I have worked with have had years of experience, as you said. For me, I wasn't particularly good at Steadicam for a solid 5 years after buying my rig.

Sorry, probably messed up with the vocabulary again.. What I meant was that, if I had the lens zoom all the way out, (wide) is that called "open"? That + the focus on infinit would have most things in focus, right?
I was not speaking about the lens iris.. but that's maybe the only way you refer to a lens as "open"? I get mixed up. (please correct me, I need to learn. =)

Thanks.

No problem, Alfred!

It is generally understood that setting a lens wide open will refer to the iris or aperture. The reverse is "close down" or "stop down". Pertaining to the zoom, you would use loosen/tighten, or obviously zoom in/zoom out.

Even with a wide lens in 35mm, not everything is in focus as with DV. There are few shots that require no focus pulling. 16mm is a bit more flexible, but it does restrict you when designing a move. I didn't own a follow focus for the first year or two after buying my rig and had to work around the restrictions, but I was only shooting 2/3" video and 16mm at the time. And no, I didn't start with the $20K Preston...I went through three used, lower-end follow focuses before I finally upgraded to the top-of-the-line.

This is one of those situations where good depth of field is nice. What I do when shooting with a steadycam (actually a Hollywood Lite Running Rig) with a DSR500 is rehearse the move and focus on the ending spot if the shot is going to hold there. Then I try to maintain a steady distance from the subject during the move. In almost all cases the moves are at a wide angle, so under most conditions there's plenty of depth of field and critical focus isn't too much of an issue. On a big 35mm shoot, that would be a different story and remote focusing would be used.