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Shooting CRT Screen or LCD in 16mm


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#1 Al Santana

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Posted 27 November 2007 - 02:39 AM

Greetings, I've got a shoot coming up where the director wants to shoot video images off of a CRT and an LCD screen with 16mm film. I'm concerned about exposure readings, and shutter stutter issues. I'm using an Arri sr2. There isn't much time for testing and therefore am in need of any insights as to how approach this. Is it best to read incident light generated from the screen and as the image brightness fluctuates decide on an average exposure? Also, what would be the best shutter angle to use to eliminate scan lines?
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#2 Jonathan Bowerbank

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Posted 27 November 2007 - 03:01 AM

An incident reading won't do you any good, you'll need a spot meter to meter it correctly. Speaking of which, does anyone know the best method for this? Would it make sense to put up an image of a middle-grey card on the monitor and take a reading of that?

I know shooting a CRT television a shutter angle of 144 is the basic. But is it a CRT computer monitor or a CRT television? Because with the CRT computer monitor you'll have to find out at what Mhz the signal is being sent to it, which you can find out in your display settings.

I don't think LCD screens have sync problems, you should be able to shoot it fine without any worries.

Someone please correct me if I'm wrong :)
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#3 David Mullen ASC

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Posted 27 November 2007 - 03:19 AM

An LCD should be fine.

The Arri-SR2 doesn't have an adjustable shutter angle as far as I know, so you're sort of screwed trying to sync to any CRT that isn't a special one running at 23.976 fps, and then you'd have to run the camera at 23.976 fps, and the material being played back would have to be converted to 23.976 fps, etc.

Unless you can run the camera at 29.97 fps for shooting an NTSC monitor.

Then in both cases, a 180 degree shutter will be fine.

Computer CRT monitors run at all sorts of rates so syncing is very difficult unless you set it to run at a specific rate that the SR2 can handle, and if you want sync-sound in the shot, then hopefully you can get it to run at 24 fps.
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#4 Michael Nash

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Posted 27 November 2007 - 05:55 PM

For exposure you can take a spot reading of any given subject on the screen you like (like an image of a gray card) and make an estimation. Some spot meters can be tricked by the "flicker" of CRT display, sometimes not. Just be aware.

For monitors that appear within a scene (not a full-frame of the monitor image), the easiest "cheat" is to rough-in the balance between the screen and the surrounding area by looking at the camera's video tap, or using a digital still or video camera. If the exposure balance is acceptable on the limited dynamic range of a video tap/camera, it won't look any worse on film. Don't try to estimate screen brightness by eye though; luminous subjects are very deceiving and chances are good that you'll have to turn the brightness of the CRT down significantly to make it look right on film.
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#5 John Sprung

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Posted 27 November 2007 - 07:02 PM

Computer CRT monitors run at all sorts of rates so syncing is very difficult unless you set it to run at a specific rate that the SR2 can handle, ....

If you have a 180 degree shutter and a CRT running at an unknown rate, one thing you could do is take the mag off the camera, and look thru the finder while you vary the frame rate. When you get a stationary roll bar, you have a ratio of small integers between the camera and CRT rates. If you can finnesse the frame rate to noodge the roll bar out of the finder, you'll be able to get the same full frame image on film. Just remember that what you see in the finder is exactly what you *don't* get on the film, so you want to see the bar in the finder for the actual takes. This being a computer, I'm guessing that you don't need to worry about realistic motion at 24 fps for this shot.




-- J.S.
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#6 Al Santana

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Posted 02 December 2007 - 11:31 PM

If you have a 180 degree shutter and a CRT running at an unknown rate, one thing you could do is take the mag off the camera, and look thru the finder while you vary the frame rate. When you get a stationary roll bar, you have a ratio of small integers between the camera and CRT rates. If you can finnesse the frame rate to noodge the roll bar out of the finder, you'll be able to get the same full frame image on film. Just remember that what you see in the finder is exactly what you *don't* get on the film, so you want to see the bar in the finder for the actual takes. This being a computer, I'm guessing that you don't need to worry about realistic motion at 24 fps for this shot.




-- J.S.



Thank you all for you insightful suggestions. They've all given me food for thought. I've decided to take the easy route and will shoot off of an LCD screen, spot reading the various parts of the screen and guestimating an average. My next question has to do with color temperature. Is there a Kodak color neg stock that would work best for this situation? I have done something similar many years ago using 7247 without any filtration and the result was a somewhat greenish cast. It actually worked well for the story at that time, but for this I'm looking for a more or less realistic rendition.
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#7 Chris Keth

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Posted 03 December 2007 - 01:29 AM

LCDs are usually very high in color temperature, often being 5500K or 6500K. On some, including apple displays, you can set the white point to nearly anything, including 3200K. You might see if that is an option on your monitor.
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#8 Michael Nash

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Posted 03 December 2007 - 01:36 AM

You can also preview the color temperature of the screen with a video camera or digital still camera.
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#9 John Sprung

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Posted 03 December 2007 - 04:07 PM

I have done something similar many years ago using 7247 without any filtration and the result was a somewhat greenish cast.

That sounds like the LCD display may have had a flourescent backlight. Like Michael says, test it with a digital still camera or video camera. That'll tell you a lot about both CT and exposure.





-- J.S.
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