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Tip #565: Frame Rate Does Not Create Motion Blur

Motion blur is based on shutter speed, not frame rate.

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A frequent email from filmmakers asks about how to change their project’s frame rate to make it more “cinematic.” Specifically, they are looking to convert to 24 fps. The problem is that changing the frame rate will only make a video look worse.

Motion blur, which is a slight blurring of the edges of a moving object, is caused by something moving while the shutter is open. If the shutter speed is slow, meaning the shutter is open for a longer time, the motion blur is exaggerated. If the shutter speed is fast, the motion blur is minimized.

Changing the frame rate after an image is recorded won’t affect motion blur. Motion blur is determined at the moment the original image is recorded.

Changing the frame rate after a clip is recorded can only be done by removing or adding frames. For example, changing the frame rate from 30 fps to 24 fps means that every fifth frame of the original media will be removed. There’s no other way to do this, you can’t “reallocate” frames to match a different frame rate; you can only drop or add them.

In the case of dropping frames, this means that the video will have a slight “stutter” every five frames, which will mess with any kind of smooth camera move.

The moral of this story is: shoot the frame rate you need to deliver and don’t change frame rates after the fact.

EXTRA CREDIT

The web supports any frame rate you can upload, unlike broadcast or cable. There’s no benefit to converting frame rates.


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3 Comments
  1. Christopher Meurer
    Christopher Meurer says:

    This is one of the trickiest parts of teaching the digital only generation. It seems irrelevant to them to tell them how film cameras work yet if we don’t this is the result we see, lots of confusion on things like this (and lighting especially) I think it’s fantastic how enthusiastic young filmmakers are and they help force us experienced ones to continually find ways to tap into the creative approaches that come from not knowing everything. But on the occasion when I teach filmmaking it’s definitely interesting to see how few students are willing to learn the concepts of yore realizing that they do apply to the filmmaking of today even if actual film is not in the mix.

    Reply

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