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Re: 48 or 60 fps for only a slight slow-mo effect

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Rick Wise
Re: 48 or 60 fps for only a slight slow-mo effect
on Oct 18, 2015 at 6:07:35 pm

As always, Todd's advice and observations are terrific! I do have a tiny quibble with one issue: shutter speed. I suspect one does NOT need to increase the shutter speed when shooting at a higher frame rate. When we shoot at, say, 48 fps instead of 24, the amount of time each frame is exposed is 1/2 of the 24-rate. That means the image will be far more crisp. To increase the shutter speed from 48 to 96 again crisps the image even further. But too much crispness can be a problem, creating a staccato effect. While it is possible the filmmaker wants such an effect, for "normal" viewing I suspect 1/96th will be excessive. It also cuts in half the amount of light reaching the film/sensor, which is the equivalent of one f/stop. Since you have already lost one f/stop of effective sensitivity by speeding up the camera from 24 fps to 48 fps, you have by doubling the shutter speed now lost the equivalent of two f/stops of sensitivity. Could be that's no problem, if there's plenty of light and your ISO is high enough. Or the two-stop loss could in some situations make the shot impossible.

Here too, tests would be good. I have not tried shooting at 48 fps and a shutter speed of 1/48th and then again at 1/96th. Just operating from logic.... I could be wrong.

Rick Wise
MFA/BFA Lighting and Camera Instructor Academy of Art University
San Francisco Bay Area

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