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Perhaps I'm just not understanding the exact mechanism of how light interacts with our eyes and is interpreted as an image, but for cameras light goes through the lens and hits the image sensor/film and the longer the shutter is open, the more light goes in. If too much lights hits the sensor/film, the resulting image is overexposed and all white.

My question is, why doesn't this happen with our eyes? Is there a physical mechanism inside our eyes that closes a "shutter" to prevent the retina from getting too much light for a single exposure? Or is this a case of our brains being smart about interpreting the signals? (Sorry if this is the wrong community for this, not sure if this made more sense here, photography, or biology).

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    $\begingroup$ Actually, they do get overexposed sometimes. Have you ever seen a bright cloud that has just hidden the solar disk? The "silver lining" of this cloud is so bright compared to the surrounding sky that you need to squint to see details there. Otherwise it's just white (or yellow/orange, depending on elevation of the Sun). $\endgroup$
    – Ruslan
    Commented Aug 11, 2022 at 22:24

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The sensitive cells in our eyes respond to flux (photons/second) while photographic sensors respond to fluence (photons). It's easy enough to make a sensor that responds to flux: measure the current generated by a photovoltaic. But if you block the current, so that charge builds up in the sensor, you can then measure fluence by measuring the charge built up. If you let the charge build up too long, the sensor will saturate.

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  • $\begingroup$ I see, so the different here is that camera sensors capture a snapshot of an amount photons within some timeframe (shutter speed), whereas eyes are continuously measuring flux? Is it truly continuous or are there discrete periods that the brain processes? $\endgroup$
    – ROODAY
    Commented Aug 13, 2022 at 18:18
  • $\begingroup$ @RODAY It's not exactly continuous. The photosensitive cells generate impulses at a rate that depends on the flux. But there is no fixed exposure time. $\endgroup$
    – John Doty
    Commented Aug 13, 2022 at 20:08

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