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#1 Michael Ryan

Michael Ryan
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Posted 02 November 2007 - 07:47 PM

Hello All,

I'm trying to get my mind around this, and I just want to know if this is correct.

If you film a person walking across your front lawn at 24 fps and you project that image at 24 fps the movement will look real (the person will be seen to walk as they do in real life).

Now, is this correct: If I shoot the same person walking across the front lawn at 64 frames per second and project it at 64 fps will they also appear to be walking normally?

I have been told that as long as the shooting fps and the projecting fps are the same the movement will look natural. However, what I want to know is there must be a low end fps where this rule is not true. For example if I shot at 8 fps and project at 8 fps the movement is going to look like a hand cranked silent film?

How low can you go before the movement will not look natural? 16fps? 12fps?

Thanks,

Mike
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#2 David Mullen ASC

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Posted 02 November 2007 - 07:55 PM

Shooting and projecting at the same speed means that time will be represented normally -- i.e. if it takes him 20 seconds to cross the lawn in real life, it will take him him 20 seconds of screen time to cross the lawn.

This is true whether you shoot and project at 1 fps or 1000 fps (assuming you could even project at 1000 fps).

The difference is that lower frame rates will sample that motion in fewer "bits" or slices of time than higher frame rates. At a high frame rate, the motion will be very smooth because persistence of vision will make it seem like fluid continuous motion. At a very low frame rate, the motion will be very "steppy", staccatto, jumpy, because you have so few frames representing the motion and you become aware of the fact that they are made up of individual frames. 16 to 30 fps are somewhere in the middle -- they are sort of the minimal rates that still looks fluid, but still somewhat strobey if the motion gets too fast. Obviously 16 fps will be steppier, strobier than 30 fps. There isn't really a sharp dividing line of acceptability because it depends on how fast that motion is.
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