Why no 'rolling shutter' effect on still images?

Started Oct 5, 2009 | Discussions thread
tko Forum Pro • Posts: 12,484
Re: focal plane shutter

The normal sequence is shutter opens, image recorded, shutter closes, image read out one line at a time. Once the shutter is closed, the image no longer changes.

In a movie mode, shutter opens, image is being recording, image is read out while image is still being recorded. So, as the image is being read out it's still being changed because the sensor has light on it and there is no electrical way to turn off the light gathering process.

Let's say you can read out the image in 1/200th of a second. With a 1/10th second exposure the read time is only 10% of the exposure time. But with a 1/200th exposure the read time is equal to the exposure time, not good.

Anyone who knows more can correct me, that's what I'm thinking.

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