A is for Aperture
Cameras let light in through an opening in the lens called an aperture. It does not matter exactly how it works, suffice it to say that the bigger the aperture the more light that is let in and the smaller the aperture the less light coming in.
The amount of light determines the exposure of the digital image. If there is too much light then the image will tend to be washed out and bright. If there is too little light the image will be dark.
On automatic settings, the camera will determine the aperture size and therefore the amount of light coming in. However, you have the ability to control the aperture on other settings and this can be used to good creative effect.
Unfortunately, in order to confuse us, the powers that be have decided that apertures sizes are round the wrorg way. So a small aperture (less light) has a large number and vice versa. As long as you remember this you will be ok.
The other thing to remember is that the larger (smaller number) the aperture the less things will be in focus in front of and behind your subject. This can also be used to creative effect but if you want as much in focus as possible, use a small (large number) aperture.
Eric Hartwell runs the photography resource site http://www.theshutter.co.uk and the associated discussion forums as well as the regular weblog at http://thephotographysite.blogspot.com
