ELI5- why do screens/lights flicker in videos taken by phone or even yt vids, but not in movies and professional productions?
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Shutter speed of the camera vs refresh speed of the screen. Your camera doesn’t take an image instantly. Instead it goes down row by row kinda like a printer. Your monitor does the same thing. When these two speeds line up poorly they cause the flickering. You don’t see this in movies cause they can do tricks like CGIing in the screens later, rotate the camera so the camera is going left to right instead of top to bottom, or you can get cameras that can sync with screen refresh rates to eliminate the flicker.
Lights and screens blink 50 times in one second in places like Europe, or 60 times in a second in places like the US, because of how electricity is sent through your country (this is called the *refresh rate*). You can’t see this with the naked eye, but your camera can.
Phones normally take one frame 60 (or 30) times in a second (because they’re made in places where that’s the normal refresh rate of electricity – this is called the *shutter speed*), while professional cameras can come in more shapes, sizes and (most importantly) *things you can change manually.*
If you are in Europe and filming with a smartphone made in California, the speed at which your phone camera and the lights or screen that you’re filming refresh will not match, resulting in that flickering effect. Most of the time you can’t change this on your phone without getting some app to do it manually. This mismatch only gets worse with slow-motion video (regardless where you live).
Movie cameras can adjust pretty much everything about how they’re filmed manually, meaning they can correct for this kind of problem by changing the shutter speed to sync with the refresh rate it’s filming.
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