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Filming Computer monitors on 35mm


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#1 Phil Thompson

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Posted 21 November 2011 - 11:52 AM

I need some help.

Im soon to shoot a spaceship cockpit sequence. The plan was to have PC monitors displaying animations and the like. CAn these be shot as normal at 25fps? Im not very sure on the refresh of screens but suffice to say, I don't want horrible scan lines.

Any ideas?

p
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#2 Phil Rhodes

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Posted 21 November 2011 - 02:32 PM

If they're TFTs, you won't usually get scanlines, but you might get a slight pulsating shift in colour.

Most computer displays now refresh at 60Hz by default, but there are, unfortunately, several layers of interpretation between the file on your hard disk and the light coming out of the display. It is often possible to alter the settings of the graphics card to a more appropriate rate that's a clean multiple of your taking rate (such as 50Hz in your situation), and that's certainly worth investigating. However, you may still have problems as some displays do not respect the timing of the input signal and may resample it back up to 60Hz. Sometimes, the backlights themselves (which are invariably small cold-cathode tubes) may introduce flicker that is nothing to do with the display device itself. Finally, few if any programs actually take any notice of the output rate of the graphics card, and use their own timing. The importance of this will vary depending on what's in the animation and if you need it to look completely smooth and faultless, but you may find you get some frames doubled and some skipped entirely, depending on the relationship between the frame rate of the animation, the output rate of the graphics card, and other factors.

You can solve this problem (and create a system that can potentially be genlocked to the camera) by using a "real" video output card such as one of the Blackmagic Decklink range and using either SDI displays, or DVI/HDMI displays that do respect the input frame rate.

Yes it's complicated, sorry.

Minor self-plug - if you need any help with this please feel free to get in contact as I have done a bit of it.

P
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#3 John Sprung

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Posted 21 November 2011 - 02:37 PM

A quick pre-production test you can try: Given that you're shooting with a 180 degree mirror shutter, just take an empty camera body and lens, and see if you get flicker in the finder.



-- J.S.
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#4 Vincent Sweeney

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Posted 21 November 2011 - 05:25 PM

I've done some LCD shoots lately and we never had an issue, although that was an LCD TV. Much difference?
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