We're All Living in the Past: Galactic Rolling Shutters and Why Cameras Never Capture the Present

Vsauce is one of my favorite YouTube channels. Their quirky, engaging videos make understanding some tricky scientific ideas straightforward and fun. If you've ever wondered about rolling shutter or love learning about all the funky properties of light (which is the main ingredient of photography, after all), this is the video for you. 

Rolling shutter is a phenomenon caused by the fact that most cameras do not read all the data from the sensor at the same time (a camera that does do that has a "global shutter"). Instead, they read the data in lines that advance across the frame (think of an inkjet printer). When an object in the frame moves relatively quickly compared to how fast the readout proceeds across the frame, it appears in multiple places during the same exposure and thus, the rolling shutter effect kicks in. Airplane propellers are one especially notorious offender:

The rolling shutter effect is a relatively simple phenomenon to explain; on the other hand, nothing about light is simple to explain, which is what makes it one of the coolest things in the universe. One peculiar property is that as fast as light is, it still only moves at a finite speed. This has all sorts of consequences, from the rolling shutter effect on the scale of galaxies to the fact that everything our eyes or cameras see is actually something that happened in the past. Check out the video for a more in-depth explanation of these fascinating properties.

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Bavarian DNA's picture

Man you are in the past :), i doubt the majority will be interested in this kind of info. But me, i dig this kind of articles and information, i remember when i studied Modern Physics, my mind was spinning 360 degree.

IMO, we are who we call ourselves humans living a 5D if you include the physical to it :) and we are all living an imag.

Anyways, this is one of the reasons i follow you, this is awesome and refreshing to me, Keep it up bro

Alex Cooke's picture

Modern Physics was one of my favorite classes. :) I always love seeing how photography concepts apply to the universe at large or vice verse. Thank you so much for the kind words; I totally appreciate that! I'll keep the geekery coming!!!

Spy Black's picture

Nice video. As far as rolling shutters on cameras are concerned, of course the effect is greatest in video. In old school film camera mechanical focal plane shutters, the effect is most noticeable when shooting stuff like race cars and whatnot. However in digital cameras, if I'm not mistaken, we have a double whammy in having a rolling electronic shutter AND a focal plane mechanical shutter. Whether or not their motion action is sync'd isn't clear to me.

Which begs the question however; why, as we approach 2016, are we still dealing with rolling shutters? It's not like it's some kind of monumental technological feat to implement global shutters in cameras, but yet you can only find them in upper end (re: expensive/overpriced) dedicated video camera models. Why is that I wonder? ;-)