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Shooting a DLP projector which probaly displays images at 59.94 hertz a video shot at 25fps with a 35mm film camera set at 24fps


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#1 Mr. Macgregor

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Posted 20 May 2007 - 01:09 PM

Sooo. I am shooting film at 24 fps. In the back i have a rear projector displaying images shot in HD at 25fps ( i might easily resampled them to 24 fps anyway) but usually DLP even in PAL countries run at 59.94 fps.

How can i achieve a flicker free image? i am lost.
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#2 Tony Brown

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Posted 23 May 2007 - 05:06 PM

Test.

Any sync sound? If not shoot the sequence using a phase sensor
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#3 Mr. Macgregor

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Posted 23 May 2007 - 06:22 PM

No sound.
What is a phase sensor?
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#4 John Sprung

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Posted 04 June 2007 - 03:33 PM

Sooo. I am shooting film at 24 fps. In the back i have a rear projector displaying images shot in HD at 25fps ( i might easily resampled them to 24 fps anyway) but usually DLP even in PAL countries run at 59.94 fps.

How can i achieve a flicker free image? i am lost.

Definitely test. If you'll be shooting with a 180 degree shutter, then just running a mirror shutter camera empty and looking in the finder (provided it's a 180 degree mirror) will tell you a lot.

The bad news is that DLP's are not all the same, and the results for one make and model aren't valid for another. This is because the pixels on the chip are either on or off, so to make a gray scale, they have to do something called duty cycle modulation. Basically that just means that they turn them on and off very rapidly, and by varying the number of clock periods on vs. off they get all the different brightnesses they need. But that's done off the actual display chip, and each display or projector make and model may do it differently. The good news is that most of them have very high clock rates, and their algorithms tend to spread the on's and off's around quite evenly. What may be a bigger problem is that single chip DLP's -- the ones with a color filter wheel -- can only put up one color at a time.

Bottom line, test with the actual projector and the actual playback material.



-- J.S.
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