This is going to be covered in a bunch of different articles, but first I want to present this in a basic, all encompassing article.
A camera can actually be a really simple gadget.
A) You need something to catch the light, this can be film or a digital sensor.
B) You need something to block the light, ideally a way to block the light until you are ready to expose the thing used in step A, and then it can be opened and closed for a period of time to properly expose the thing in Step A to the light coming through the thing in Step B.
Ok, see? Simple. Maybe more detail is needed.
The simplest camera that creates an image we might be familiar with is known as a pinhole camera. It consists of a box that holds a piece of film, and a pin hole with a cover opposite the film. No lens, no variable aperture, no electronics, nothing but a box, film, and a hole with a cover. You then point the hole in the box at your subject, remove the pin hole cover, count to <an appropriate number depending on the light available> and then replace the pin hole cover. You then develop the film and see what you got.
All the other doodads like electronics, lenses, the ability to focus, apertures, exposure meters, mode dials, screens on the back of the camera, film advance gearing, and so on, all exist to enhance your options and capabilities when capturing the image. But in the end you need to expose the film/sensor to light sufficient to imprint an image. Everything else is just giving you creative options for accomplishing that very simple task.
You have 3 tools to control exposure on pretty much every camera.
- Sensitivity of your film/sensor (ISO / ASA)
- The shutter speed
- The Aperture
All 3 of these variables work together to determine whether the light coming from your subject will properly register in your camera. Its a triangle of sorts. Low ISO (less sensitive) + super fast shutter + Tiny aperture opening (big F numbers) = dark image unless you flood it with light, I mean give your model a tan in 1/1000th of a second kind of light. So you play a game, if it is perfectly exposed at say ISO 200, a shutter speed of 1/200th and an Aperture of F5.6 then going to a shutter speed of 1/100th (half the original value) of a second would drive a need to change ISO to 400 (double the original) or going to F4 (1 stop bigger opening in the aperture). Simple right?
So, let the detailed stuff begin.