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A while ago I found this post on reddit which showed a ruler vibrating differently depending on the light: https://www.reddit.com/r/blackmagicfuckery/comments/ccymjq/ruler_flicked_in_different_lighting/

I started reading the comment section and everybody talked about the shutter speed of the camera. I understood how it worked, but I would like to know if there is some more deep physics (i.e. optics of the camera or refraction) involved on it.

Is there anyway of calculating the wave it creates or it's just a camera thing with no physics involved?

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  • $\begingroup$ Possibly stroboscopic effect $\endgroup$
    – Superfast Jellyfish
    Commented Feb 24, 2020 at 12:16
  • $\begingroup$ I've read that stroboscopic effect is almost always for rotating objects, does it apply for any motion which is periodical? $\endgroup$
    – bacjist
    Commented Feb 24, 2020 at 12:22

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I think this is due to the effect called rolling shutter effect. What this means is that in a single frame each slice (of the frame) don’t come from the same instant of time.

enter image description here

SmarterEveryDay has a video on this effect. A gif taken from that video depicting the effect which is closer to the ruler case is: enter image description here The frames on the left are like the actual motion of the strings but the image on the right is the formation of a single frame that is formed by combining the slices of different instances of the actual motion.

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  • $\begingroup$ It looks like, thank you. Do you know if there is a way of explaining it by using frequency, waves or light refelction? $\endgroup$
    – bacjist
    Commented Feb 24, 2020 at 18:05

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