Imagine the sun up in the sky. It's really just a rather large flaming sphere of gas. As you can imagine, it puts out quite a bit of light which you can imagine as a rain of tiny particles flying straight from the sun  outwards. Quite a few of these particles travel through space towards us and strike parts of the earth near us.

Imagine one of these particles as a pinball and you’ll see that it will bounce off things it hits changing it’s direction. So a rain of these particles will bounce off any object, flying off in various directions. For various reasons, these particles generally can’t ‘hit’ each other so we won’t worry about that for now.

Now some of these particles bouncing off of say a shiny new red porsche boxster (ooo…) will fly in your direction and perhaps they’ll hit your eyes traveling in through your pupil. When the particles hit the red boxster there color is moved in the direction of the surface they hit, so they’re quite a bit more red now rather than the white/gold of the sun. They then strike the rear of your eyeball, stimulating nerves there which tell your brain that a particle has struck there with a certain color.

Your brain eventually reassembles the messages from all the nerves at the backs of your eyes and is able to reveal to you the scene which you are ‘seeing’.

Now you might wonder how there are darker and lighter reds rather than just red, purple, blue, etc. if your nerves only pick up information on A) whether a particle struck or not, and B) what color it was. Go back to the particle striking the boxster and realize that if you put your hand ON the boxster it probably feels a bit warm ‘from the sun’. So the boxster’s paint job is absorbing some of the light particles rather than letting them ‘bounce’ off. These absorbed light particles are warming the boxster rather than entering your eye, so the way your eye tells light from dark is the NUMBER of light particles that strike.

So what happens if there are too many light particles for your eye to count very well, or so few that it’s hard to count them and get meaningful information from them? Well that is what the pupil is really for. I’m sure you recall that in bright light your pupil gets much smaller, and in the dark it gets much larges. Your pupil is the opening through which light travels so it automatically adjusts in size to allow more or less light particles through depending which it would rather have. Of course there is a limit, looking into the sun is a very bad idea, and no one can be expected to see in near total darkness without special equipment.

How a camera ‘sees’

So in some ways a camera ‘sees’ the way that a human does. Light particles fly into the lens, through the body of the camera, then hit the film which lies against the back of the camera. The film ‘counts’ how many particles strike it in some spot, and what color they are. <To be completed>