2nd AC using a tape measure.

D

Droog

Well-known member
Ok, so I am a sound guy learning to shoot, so bear with me. I often see the 2nd AC measure from the subject to the lense. I realize this is for focus, but what exactly is he looking at? I assume that he is comparing the distance from lense to subject, to that of where focus ring is setting. Can you focus with out using a monitor/viewfinder?

Thanks!
 
35mm Cine lenses have VERY accurate markings on the focus scales. The cameras have a pin or hook at the film plane location so that a tape measure can be used to accurately measure the distance from the film plane to the desired focus point. The lens can then be set for that distance with confidence that focus will be correct, tho the camera operator may well confirm thru the viewfinder as well. (one of the jobs of the assistant is to verify the marks when preping the the equipment for the shoot- which is usually done at the rental house)

Video camera and lenses are not so calibrated (except for specially modified HD cameras like the Sony Cine Alta or the new generation of digital Cinema cameras like the Arri, Genesis, Viper etc.

In video one needs to focus with the viewfinder or a monitor, tho in some cases you can mark the lens barrel or follow-focus drive and focus to those markings- but the marks will almost certainly be determined by using the viewfinder or a monitor.

Bill Turner
Schneider Optics
Century Division
 
For professional shoots the lenses are marked in real distances. A plain ground glass viewfinder or low res video tap/monitor leaves a margin for error, especially if the the image is dark. Many consumer/prosumer video cameras have less than full resolution in the viewfinder.

Note that the AC may also measure multiple points, especially if an actor is close up. The DP can then calculate depth of field and adjust accordingly.
 
Scottdvx100 said:
For professional shoots the lenses are marked in real distances. A plain ground glass viewfinder or low res video tap/monitor leaves a margin for error, especially if the the image is dark. Many consumer/prosumer video cameras have less than full resolution in the viewfinder.

Note that the AC may also measure multiple points, especially if an actor is close up. The DP can then calculate depth of field and adjust accordingly.
Click to expand...

When you say "calculate DOF and adjust accordingly" are you saying that the DP will know his DOF by the measurments and then adjust if he wants a different Depth? In order to maintain the same frame yet change the DOF wouldn't the camera need to be moved and the length of the lense changed? Like move the camera back from the subject and then go more tele-photo to get less DOP?

Thanks alot, learning is fun!
 
Bill__Turner said:
35mm Cine lenses have VERY accurate markings on the focus scales. The cameras have a pin or hook at the film plane location so that a tape measure can be used to accurately measure the distance from the film plane to the desired focus point. The lens can then be set for that distance with confidence that focus will be correct, tho the camera operator may well confirm thru the viewfinder as well. (one of the jobs of the assistant is to verify the marks when preping the the equipment for the shoot- which is usually done at the rental house)

Video camera and lenses are not so calibrated (except for specially modified HD cameras like the Sony Cine Alta or the new generation of digital Cinema cameras like the Arri, Genesis, Viper etc.

In video one needs to focus with the viewfinder or a monitor, tho in some cases you can mark the lens barrel or follow-focus drive and focus to those markings- but the marks will almost certainly be determined by using the viewfinder or a monitor.

Bill Turner
Schneider Optics
Century Division
Click to expand...


We were shooting on a Varicam. I know the guy has experiance with film, but is it possible that his measurements may have been superflous? I can definately see the use in measuring with film, but if the lenses on the HD may or may not be all that accurate, maybe the monitor would be a better reference. What if the viewfinder,monitor, and directors monitor all show focus, but his measurement indicates that its incorrect? Then what?
 
You can use a focus chart showing distance vs the "MF" numbers. There's one floating around here, somewhere.

Dan
 
Someone correct me if I am wrong please.

Aren't some Cameras and Lenses not WYSWYG? I am not talking Non-Reflex here but even the Reflex ones? Or am I tripping?

I know today they have Video Assist and Video Village where everything is in Glorious Color, Letterboxed to 2:35:1 and in perfect Fpcus even during the Rack but I thought older cameras did not have this luxury?
 
Normally it is the 1st AC who measures. Sometimes the 2nd will just take one end of the tape measure to the subject.

He is measuring the distance from the film plain (marked on the side of a camera with a '0' with a line through it, and there is oftentimes a tape hook) to the subject he wants in focus.

If your camera & lenses are all in good shape, and not out of calibration the "witness marks" with the focus scale on the lens are accurate. This is why at camera prep one measures to a focus chart & then checks focus by eye to make sure the lens is working properly. This is done at several distances and on every lens.

The depth of field will just determine how much leeway in front and behind the distance the lens if set to. The higher the F-stop the more DOF you have, the wider the lens, the more DOF you have. The inverse is true as well.

If the actor walks towards camera, the 1st will measure several distances that the performer will travel & have the 2nd AC make marks on the floor, while the 1st will mark the follow focus.

A video assist is not by any means WYSIWYG (not that you said it was). It is for framing only. The quality of video assists has been going up in recent years.

In film cameras, with a reflex viewing system, an optical viewfinder is the only way to judge focus with any degree of accuracy other than tape measuring. The ground-glasse’s frame line marks are also extremely accurate. You can also see the DOF effects in a scene, but it won't be able to tell things like split focuses, etc.

A non-reflex cameras has a problem called parallax, but even then some of the viewfinders are parallax corrected.

If the camera uses a prism system, you just can’t see if the shutter is actually spinning

The above all assumes properly setup gear.

Kevin Zanit
 
Regarding Depth of Field - the DP or his asst may consult a chart/dial to see if they can hold both actors in focus. Depending on what the DP and director want they can increase the light and get an f-stop that gives the depth of field they need (and set the actual focus point between the two actors) or they do a rack depending on the action.

Good reflex cameras show what you see is what you get but they require marked ground glass. The old Mitchel cameras used a rack over system. You had a viewfinder on the side that would provide an approximate view and could rack it over to look through the actual lens.
Most of these have been converted to full reflex.

No assistant I've worked has ever used video asst to focus. The quality even of today's video taps is awful. Panasonic does have a electronic measuring device and I've seen assistants use electronic handheld measuring devices. Unfortunately even in many feature films there still a closeup shot or two where the actors eyes are soft.
 
First off, thanks guys, for sharing your knowledge.
Second, I was wrong about it being the 2nd AC it was the 1st.

I have some more questions, if you all don't mind.

When you say video assist, this is when shooting film, correct? A video conversion of whats going to tape? I can see how that may be less than exact.

What is meant by reflex? I would assume it is similiar to SLR, in the photo world, but I still have an unclear understaning of what is happening.

Thanks again, I know is may be a bit mundane for some of you, but I really appreciate it, I love this stuff. Recomend me a good book and I'll leave you alone :laugh:
 
Yes, video asst is for shooting film. The image coming through the viewfinder is also captured by a small video camera on the film camera. This allows other people besides the operator (director, script supv, etc) to see what the camera is recording. It's also used to record and playback to check different takes. Since it low quality video of the full ground glass area (not just the area being filmed) the end result is poor for anything more than check basics.

SLR means Single Lens Reflex. The camera person sees the exact same image that will be recorded. Simpler, cheaper cameras have viewfinders so you're looking through a separate optical path which won't match exactly. This is expecially true if you can change the lenses on the camera. A reflex camera also allows you to see the depth of field with the iris set.

Reflex works in still cameras by using a mirror to bounce the image to the ground glass in your viewfinder. At the moment the picture is taken the mirror moves out of the way and the shutter opens to expose the film or digital array. During that moment the photographer sees black.

Film camera work fairly similar. There's a mirror reflecting the iamge to the viewfinder. If the camera is filming then the mirror spins so the viewfinder shows the image while the shutter is closed between frames and is advancing the film. The mirror is usually a butterfly type mirror. It looks like bow tie made of mirror and spinning in the center. The image area is one side of the tie so that it psins once for every two frames. The other option is a beamsplitter or prism that reflects some of the image and provides it to the viewfinder at the same time as it's being filmed. This is the way the Bolex reflex cameras worked. Downside is darker viewfinder and darker camera image that had to be compensated for.
 
I see, so what you are seeing in a film viewfinder is actually image from the lense, but between frames, every 2 frames. So does that make viewing wile rolling kind of wierd, because you would effectively be viewing at 12 FPS right?

The prism/beamsplitting technique seams like a bad idea, wouldn't you want 100% of your beam to hit the film? Guess thats why cheaper cameras do this.

Thanks again.
 
Sorry to confuse. With the mirrors (one on each side) it actually showing 24fps per second (since there are 2 mirrors it alternates). Think of a propellor in slow motion.
You see a slight flicker and the image darkens a bit when you're shooting.
 
Scott your almost there. Projectors have shutters like a bowtie or propeller, but film cameras are mostly half a circle (180 degree) The newer film cameras are adjustable to a smaller or larger percentage of the shutter (circle). So in effect you never see what you are recording, you can see in the viewder when the claw is pulling down on the film sprocket to the next fram. But is as close as you can get. The only time it ever really causes problems is if you see the muzzle flash of a gun in the viewfinde, you may have missed it on film, or camera flashes.
 
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