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 How Does The Focus Puller See The Viewfinder Image Remotely? 
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Joined: Wed Nov 11, 2009 10:45 am
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Location: Merritt Island, Florida, Estates Unitas
Post How Does The Focus Puller See The Viewfinder Image Remotely?
Naive question;

Wireless follow focus is big these days and its got me wondering something very basic. Why wireless if the focus puller is right next to the camera, or close enough to view a monitor plugged into the camera? Is there some gadget that wirelessly transmits the viewfinder image to a remote monitor? If the monitor has to be wired, why not the follow focus box?

I'm revealing how little i know about realtime production. Would appreciate a little education from anyone who has done this.


Mon Dec 15, 2014 4:17 pm
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Post Re: How Does The Focus Puller See The Viewfinder Image Remot
The crew will have practised the shot before and know the distances that the camera will be from the actor/s, the focus distances are marked on the ring on the follow focus, the focus puller just moves to these positions as the scene goes on. Often there will be marks or tape on the floor so people know where to stand, so that the distances are consistent.

If the camera is flying on a steadicam there will often be a large monitor that the focus puller can see, the wireless follow focus is used to reduce forces on the camera from wires.

Wireless monitors are also available:

http://www.abelcine.com/store/Wireless-Transmitters/

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Mon Dec 15, 2014 5:44 pm
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Post Re: How Does The Focus Puller See The Viewfinder Image Remot
Thanks!

We've been working on follow focus, but most of my experience with focus motors has been with timelapse. People are buying focus motors for regular video, so we're making a remote controller for that. The question of why the controller needed to be wireless came up and led to the question of how the camera assistant sees the viewfinder image if he's not looking at an on-camera monitor.

It looks like there are four distinct uses for focus motors and a different controller should be optimized for each;

Stopmotion/timelapse (with dragonframe controller, which we already make)

Scripted set (where actors stand on their marks and focus ring marks are set in advance)

Documentary (where an operator follows somebody and distance changes constantly)

Flying rig (where the focus puller needs to use a remote monitor to maintain focus in realtime)

Thanks for the link to the wireless HDMI transmitters. Those are really cool. We'll have to incorporate something like that when we get around to a flying rig version. The plan is to make controllers in the order listed (stopmotion, scripted, documentary, and flying if we sell enough of the others to not go bankrupt before we get to the flying rigs)

Any further comments on follow focus are welcome and appreciated.


Tue Dec 16, 2014 10:06 am
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Post Re: How Does The Focus Puller See The Viewfinder Image Remot
Hi A good summary. Though the lines between scripted and documentary are not always distinct since documentary can be scripted and drama can be unscripted... so perhaps "rehearsed" or "unrehearsed" might be more appropriate.

But in either case a measure of human skill and experience is required. A good focus puller will know the lenses well and have a feel for the depth of field, with some help from a calculator in critical situations. So even if it's not possible to make marks in advance, good focus can still be achieved, unless there is very shallow dof.

Technology like remote monitors can make things easier, but don't solve the whole problem. Good focus pullers often rely on simple judgment of distance, which can be easier if standing off the side of the set rather than at the camera, so wireless remotes are most helpful then.

To the category of "flying rig' you can add remote crane setups and dollies. It used to be necessary for the operator and focus puller to actually ride on the dolly or crane, which meant they were fairly heavy rigs. Now the fashion is for lighter setups enabled by remote focus and operator controls.

So there is more need for remote focus, but it needs to have low lag and be very reliable, and compete with an increasing number of other devices using available bandwidth. Xbees and bluetooth don't offer as good performance as more solid serial links. I've seen wireless remotes such as Wondlan from China for around the $500 mark. These use simple model aircraft servo motors and some reports indicate not always enough mechanical range to rotate the lens fully as well as some unevenness and noise. So professionals will avoid them and pay what they have to... for reference a low end pro system like redrock microremote is around $2500.

So looks like an area there is still some potential for a good low cost system?


Tue Dec 16, 2014 4:34 pm
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Post Re: How Does The Focus Puller See The Viewfinder Image Remot
geraldft wrote:
But in either case a measure of human skill and experience is required. A good focus puller will know the lenses well and have a feel for the depth of field, with some help from a calculator in critical situations. So even if it's not possible to make marks in advance, good focus can still be achieved, unless there is very shallow dof.


In my experience focus pullers/cameramen rehearse the scene and make marks where they should be at certain points and that requires the camera man, actors/subjects, and focus puller all to hit their marks at the correct time. Wireless would be great in tight situation where you can't physically touch the camera.

timt

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Tue Dec 16, 2014 5:28 pm
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Post Re: How Does The Focus Puller See The Viewfinder Image Remot
Gerald, Thanks for the input. Some of the original lookers used RC giant scale servos to pan/tilt. They were for spying on animals back when video was SD low def. They liked to jitter and twitch without any operator input, so I gave up on them. Don't think I'll use them again. Everything is stepper motors or DC gearmotors with encoders now. Both of those run real smooth.

If I use telescopic lenses, I can sometimes see the focus motor pushing the lens off center very slightly. It looks like there is some play in the mount, some bending in the rail system, some flex where the camera attaches to the rail system (probably the little bit of rubber between the top of the rail system and camera body). I guess the pro solution is to use the good lenses where only the focus ring moves so a brace can stabilize the front of the lens. (we have some of these braces for 15mm rail systems) I never paid much attention to how my lenses moved before. A lot of them have the entire front of the lens moving forward and backwards, creating issues if you want to brace the front of the lens.

We thought bluetooth was nice because an app could be used to alter microstepping, silencer modes, or even control the motor directly from a phone or tablet. What are the "good" radios?


Wed Dec 17, 2014 7:37 am
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Post Re: How Does The Focus Puller See The Viewfinder Image Remot
Hi James. Long lenses do pose a bit more a problem.. Unless they have internal focus the only answer is to make a support bracket that has some rollers to allow movement. The same applies to longer macro lenses, in fact even std lenses can shift when focus direction is changed. Another reason cine lenses cost more...

For wireless transmission it's also a case of what you pay for. The cheapest devices will have slower and less even transmission. Bluetooth is a network style system designed for two way communication rather than streaming. If you send a steady stream in one end, it won't arrive evenly at the other end.. so a motor signal will end up with jitter.

Most bluetooth is rated to work up to 10 meters. But even this is a bit marginal for film applications. When you press the camera roll button on that expensive stunt scene, you really want to know it will respond, and that the shot will be in focus...

So for more serious remote a more dedicated data streaming technology will be better. There is a lot of stuff available and it just depends on what you are prepared to pay.
I bought a set of 1watt Laird serial transceivers from Digikey for about $250 which are capable of sending 6 channels of motor data over 500 meters. They also use the 900mhz band which can more easily get past physical barriers. But they do use more power and the boxes are about the size of a 2.5" hard disk enclosure.

So likely Xbees might be the most practical device, they come in a range of varieties, some of which claim quite high data rates and decent distances.

But whatever transmitter you use, you need to work out how to deal with quickly setting the range and limits of the motors so they stop cleanly at infinity and minimum focus... that is a lot harder. Motors with encoder feedback are also desirable since they will more likely deal with the focus puller spinning the dial too fast.


Wed Dec 17, 2014 4:05 pm
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