Like, for instance, I’ve seen photos of the night sky with crazy details of the stars and they say that this picture was taken with “12 hours exposure”. What does that mean exactly and what does it do?
In: Technology
The length of the exposure is how long the sensor/film on a camera is exposed to light for.
To record a photo, a camera sensor wants to ‘see’ a certain amount of light – too little light and there is nothing recorded, to much light and it overloads the sensor.
On a bright sunny day there is a lot of light, so to collect the right amount of light can take a tiny fraction of a second.
At night however there is very little light, so the camera will take a lot longer to collect enough light to record a clear picture.
As an analogy, try filling up a glass of water from a tap. The glass will hold a certain amount of water – to little and you have nothing to drink, but too much and your glad over fills and water spills everywhere. A bright sunny day is like turning the tap on full, where it will fill the glass very quickly. A photo at night would be only letting a trickle of water out of the tap, so it will take a lot longer to fill the glass up. In the middle you could turn the tap on a reasonable amount, which fills the glass up reasonably quickly, but not as quick as turning the tap on full – like taking a photo on a full day compared to a really bright one.
So when someone says they used a 12 minute exposure, that means the lighting was very dim, so they needed to set the camera up and let it take 12 minutes to record the photo (which means you need a tripod to hold the camera steady, as if it moves at all during those 12 minutes the photo will be all blurry).
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