Camera Exposure 101
Camera's control how much light gets in by adjusting one of three things.
How LONG the camera lets light in for.
How MUCH the camera lets light in at a time.
How SENSITIVE the camera is to light.
Shutter Speed, measured in seconds, is how long we let light into. One second? One Thousandth of a second? Less time, less light, and (all else equal) the darker the image. I know "speed" is a weird way to talk about "time" but, let it go. Just don't worry about it. If it really bothers you, then be like Canon and call it "time value" if you want.
Aperture, measured with in "f-stops" (whatever that means), is an adjustable hole in the camera. This hole can get bigger or smaller. Basically, it lets the lens get bigger - and let in more light, or smaller, and let in less light. These numbers often have a decimal in them. Like "5 point 6" or "2 point 8", or just "8".
ISO, measured in... nothing, it's just ISO. ISO stands for "International STandards Organization", the people who decided what numbers to use so that all camera and film manufacturers would agree. Thank's ISO! It referrs to how sensitive the camera is to light.
Getting The Exposure Correct
Let's say you're at a soda machine. You want to fill up your cup with the perfect amount of soda, right to the rim. Too much and it overflows and your hands get all sticky. Too little and your left thirsty and dissapointed.
The shutter speed would be how long you hold the cup against the lever, how much time we let the soda out of the machine.
The aperture would be the nozzle. Think about the difference between getting a soda vs. the little water lever. The water trickles out, or comes rushing out.
The ISO would be the size of the cup. How much soda do we need anyway? How much before we are overflowing? Overflowwing for a small dixie cup isn't overflowing for a KFC chicken bucket!
How these different settings work with each other and how they affect your image - we'll come back to that. Let's learn how to mess with these settings on our fancy cameras!