Why do those moving black bars appear when trying to take a photo of an older tv or computer screen? And not on modern ones?
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crt television work by rapidly drawing the image line by line from top to bottom, of course it’s fast enough that you never notice with the naked eye
however cameras aren’t eyes, and they will only photograph what happen when the shutter was opened, so it will only show some lines rather than all
if you want to take a good picture you need to make sure the exposure time is at least 1/60 (for NTSC television)
modern screens can hold the image on the screen so it’s no longer a problem, however some projectors still have a similar problem where photos turn out rainbow because the colors are displayed sequentially
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