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shutter in video


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#1 Gabriel Rochette

Gabriel Rochette
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  • Qu├ębec, Canada

Posted 06 April 2008 - 07:28 PM

OK !
I'm just more friendly with motion picture cameras.... and i'm scrtach my head for this !!!

My film camera work with a rotering shutter who expose and mask the film on and on.......
But what kind of system (shutter) work in digital cam ?????

I can down my shutter speed to 1/4 sec. for 30 frames /sec.
I'ts a weird mathematic.....

If you have answer !!!!
Tanks
Gabriel Rochette
Canada
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#2 Michael Nash

Michael Nash
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Posted 06 April 2008 - 08:44 PM

Shutterspeed works the same way for video cameras as it does for film cameras, only there's no physical shutter that masks the sensors. Instead, the sensors are "scanned" for different amounts of time.

For shutterspeeds that are longer than the duration of 1 frame (longer than 1/30th second at 30fps), the camera takes the information and buffers it in memory before laying it down on tape. In order to keep up with the tape that's constantly moving at 30fps, the camera simply lays each captured frame repeatedly onto tape until the next 1/4 second, when it has another frame to lay down. What you see on tape from a 1/4 second shutter is motion sampled at 7.5 fps, and then "step printed" onto tape to create 30fps.
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