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I found a few interesting effects, which was labelled under the rolling shutter effect, however I was told that this was NOT an example of rolling shutter effect, what would you call this effect?

The question is 3 fold: I heard they used this effect in movies, which ones, an example clip would be nice, what do they officially call it, and why does this happen?

These are the examples I am referring to:
REALLY interesting effects:
For example, the water looks like its static. [PetaPixel][1] explains it; "by pressing a water tube against a speaker, bibio was able to control the vibration frequency of the water flowing through the tube. He then adjusted the pulses of the water to match up with the frame rate of his Canon 5D Mark II."



Another example was the static helicopter:

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Do you just seek for the word for it or an explanation why this happens? –  Professor Sparkles Jul 19 at 16:30
    
Ideally what I am looking for is the explanation, examples of usage in movies, and what is the official word used to describe it. (Especially since its used in movies, they must have a term for it) –  eLouai Jul 19 at 17:59
    
I think the second video is mistitled. Shutter speed is the time the shutter stays open for every image. Here, what matters is the framerate, that is, the number of images in one second, which has to be equal to the frequency of the cyclic movement you are filming. In the first video, the person applies to the water some sort of movement based on the frequency of the sound in the speaker, and this frequency is set to be the same as the camera framerate (usually 24, 25 or 30 i/s) In order for this to work nicely, I guess the shutter speed has to be very short, or there will be blur motion. –  Niavlys Jul 19 at 18:14

2 Answers 2

up vote 5 down vote accepted

This is called stroboscopic effect. It refers to when the sample rate is synchronized or very slightly out of sync resulting in a much slower representation of the motion that results from taking a picture that is at the same point or slightly advanced point in a subsequent cycle of a higher frequency cyclic motion.

You can actually do the same exact thing in real life for your own eyes by using a strobe light, which is the more common demonstration, though frame rate can be used too if you can adjust it closely enough.

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From old western films, this became known as the 'wagon wheel' effect, where the spokes of a forward-moving wagon's wheels often appeared to move backward. When that happens it's technically equivalent to 'aliasing' since the sampling frequency (frame rate) is insufficient to resolve the frequency of interest -- it violates the Nyqvist limitation. –  Jim Mack Jul 21 at 15:08

I'm unsure if there is a specific "official" word for this effect. I guess I would call it frequency synchronisation.

This effect appears whenever the framerate (e.g. frequency your camera takes a picture) of you camera matches the frequency of another recurring action. It doesn't have to be the exact same frequency but a multiple of it. So if the rotor of the helicopter is turning at 50 rotations per seconds, filming this with 25 fps would theoretically be enough for the effect to appear (not accounting for motion blur and other artifacts when dealing with fast moving objects). So the camera always captures a frame when the moving object completed a full movement giving the illusion that it doesn't move because we only capture it every time its at a specific position. Being slightly over or under the frequency of the object will make it look like its moving in slow motion forwards or backwards because we only increment in the position by tiny amounts.

The movement has to be an exact recurring loop, otherwise this can not work.

In movies you can see this in tire movement but usually its not a desired effect, I haven't seen a movie where is effect was deliberately used.

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