When you use a motion picture camera, if you say for the sake of argument, shoot at f 5.6 at 24 fps, then you shoot again at f5.6, except this time at 48 fps, besides the footage obviously being slower, would it be darker or lighter (when compared to 24 fps). Can changing the frame rate in film affect light the same way if you change the shutter speed on a conventional still camera?
Filming at 48 fps
- Thread starter rc444
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Hans Moleman
Carbonite Member
it'd be darker, because with twice as many frames passing in the same amount of time, half of the amount of light would reach them, the same as bumping up the shutter speed.
Andrew Brinkhaus
Veteran
If you shot something at 24fps @ an f5.6, and then again at 48fps also @ f5.6 like you said, the resulting shot would be 1 stop underexposed. You would need to shoot at an f4 in order to maintain your exposure match. Like Hans said, you are halfing the amount of light each frame receives, which means you will need to double the amount of light allowed into the camera by opening 1 stop. This is called compensation. Anytime you are overcranking (slow motion) or undercranking (fast motion) you will be compensating with an aperture adjustment.
The reason, in this situation you compensate by 1 stop is because of the chosen frame rate. Here, we are moving from 24, to 48 frames per second, exactly double the amount of frames. So, we also want to double the amount of light allowed in. If you were shooting 60fps, we would compensate by opening up 1 1/4 stops, 90fps, 1 2/3 stops, etc.
What you are thinking of, with the frame rates being effected by blur and smearing, does not apply. On a still or motion picture camera, slowing, or "dragging" the shutter to increase the time a certain frame is exposed will also increase motion blur, and soften the image. This happens when the shutter is larger than 180 degrees. A faster shutter speed, like 90 degrees or 45 degrees, will obviously decrease motion blur, and make the frame sharper and more crisp with fast moving objects. (Saving Private Ryan, Bourne Supremacy, etc) Increasing or decreasing the frame rate will not affect the amount of motion blur or ghosting in an image, it will only become overexposed, or underexposed, depending on your situation.
Hope that helps. Happy shooting!
The reason, in this situation you compensate by 1 stop is because of the chosen frame rate. Here, we are moving from 24, to 48 frames per second, exactly double the amount of frames. So, we also want to double the amount of light allowed in. If you were shooting 60fps, we would compensate by opening up 1 1/4 stops, 90fps, 1 2/3 stops, etc.
What you are thinking of, with the frame rates being effected by blur and smearing, does not apply. On a still or motion picture camera, slowing, or "dragging" the shutter to increase the time a certain frame is exposed will also increase motion blur, and soften the image. This happens when the shutter is larger than 180 degrees. A faster shutter speed, like 90 degrees or 45 degrees, will obviously decrease motion blur, and make the frame sharper and more crisp with fast moving objects. (Saving Private Ryan, Bourne Supremacy, etc) Increasing or decreasing the frame rate will not affect the amount of motion blur or ghosting in an image, it will only become overexposed, or underexposed, depending on your situation.
Hope that helps. Happy shooting!
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