How does photography work? How do you take a moment in front of you and put it on paper and keep it forever?
In: Technology
All you need is light (which is bouncing off everything all the time), something that’s sensitive to light (such as photographic film or a digital sensor), and a way of controlling how much light falls on the sensitive thing and for how long.
A camera in it’s simplest form, is an empty box with a hole at one end and a light sensitive thing at the other end. You open the hole cover (the shutter) for a brief moment and that lets the right amount of light into the box and onto the sensor. The first cameras just had the hole covered by fabric and the photographer would uncover the hole, time how long it was open, and cover it back up again. It’s exactly the same principle in modern cameras except you’re pressing a button instead of lifting up a curtain.
Lenses help to focus the light into one place on the sensor to get a sharper image, but they’re not vital to actually capturing an image, that’s why you can make homemade “pinhole” cameras.
Your eye, though much more sophisticated than a camera, works in basically the same way. Light enters it through a hole (your pupil) that is controlled as to how open it is by a shutter (your Iris), and falls on light sensitive tissue (your retina) at the back of your eyeball. A camera is really just a man-made replica of an eye.
The word “camera” comes from “[Camera Obscura](https://en.wikipedia.org/wiki/Camera_obscura)” which is basically a hole in a box. Light comes through the hole and projects what is outside the hole on to the inside of the box opposite the hole.
Now if you have a light-sensitive medium inside the box, i.e. film, the image outside the box is transferred through the hole (or lens) on to this medium. You then take the film to a dark room, and pass light through it on to light sensitive paper, and the photo develops.
Your eyes actually never see any “THING” that exists anywhere. All they detect is the light bouncing off those things. A camera simply captures the light bouncing off the things its pointed at in a very small span of time (the time it takes for the shutter to open and close again, roughly 1/60 of a second).
During the time the shutter is open, light enters the camera lens, and is refracted and focused onto some type of light detection device. In older film-based cameras this was literally a thin strip of plastic coated with tiny silver crystals in a gelatin. The crystals chemically react to light that hit them differently depending on the frequency and intensity of the light, (color and brightness). The result is a semi-transparent square in the same configuration of whatever light hit it at that time. Then, in the dark room, the strip of film has other light passed through it onto another larger piece of paper (like an overhead projector in school). The light that passes through the film reacts to chemicals on the paper to reproduce the image, but with the correct colors, and a larger size so you can view it nicely. (there are more details, but this is ELI5)
With digital cameras, the process is the same, but instead of light hitting a photo-reactive film behind the camera lens, it hits a device called an image sensor (https://puu.sh/F7PUY/63f7b62ee1.png).
This sensor is an array of photosites (one site for each pixel in the resulting image) which reacts to light photons by generating a tiny electrical charge. The brighter the ligh, the more photons are collected and a higher charge is generated. Different photosites will register different electrical charges and, once the shutter exposure period is over, each individual pixel photosite’s charge is then measured and turned into a digital value by a simple computer inside the camera’s electronics.
Then later those values are reassembled and converted into color pixels to display on whatever you’re viewing the image on (your computer screen, or phone screen, for example).
Light is everywhere, moving in all directions. Lenses allow us to use that direction information to take all light coming from the same place and send it to the same (different) place. This creates a projected image behind the lens. A sensor right where this image is measures how much of each color of light is at each point in the image, and saves that data. A picture can then be recreated from this data.
Do you remember when the eclipse was approaching and cheap people were making [eclipse viewers](https://en.wikipedia.org/wiki/Camera_obscura) with a box and a piece of foil with a hole poked through it? Those worked by projecting the sun on the inside of the box, allowing a safe view of the crescent sun.
They work because when light passes through a small enough hole, all the light moving in any direction can only go to one spot on the back of the box, so it creates a clear image. Cameras use the same principle (the earliest cameras used a pinhole), modern cameras use a lens that lets more light through but projects in the same way.
To capture the image the camera either it uses chemicals (silver salts) that change color in response to light, or it uses tiny solar cells each covered by a color filter that blocks out almost all light that isn’t Red, Green, or Blue. Then the voltage generated is measured which indicates the how much light entered or how bright that color was.
We use other chemicals to stop the silver from reacting to light (this needs to be done in the dark), or software to reassemble the data captured into an image that can be viewed on an electronic device or printed.
sun or lamp emits light. light hits a, say, cat. cat reflects light a tiny bit (each type of material & color reflects light differently btw), and the light hits everything around the cat, including your eye. multiple rays of light from the cat goes through your eye & lenses inside it, hits nerves, your brain gets information, draws a picture, yay.
the same way, rays of light are reflected from the cat, hit lenses in a camera, go trough them, and hit a piece of special material. the material is a kind of chemical. you can think of it as if it was ‘ink’ that ‘dries’ forever the moment it’s hut by light. so now the picture is onto that piece of stuff.
digital cameras also have lenses etc, but when the light finally hits the end target – the matrix – and hardware+software writes how much each portion of the matrix was activated (how much light it got)
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in order to get an idea about lenses, you can take a magnifying glass and try to get an image of a lamp onto your wall. be careful: getting an image of the Sun can start a fire.
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