R32 - Camera Work - Understanding Exposure

Could be understand through using the example of filling up a cup with water. The cup represents your image and the water represents light. There are different ways of filling the cup up. You could turn the tap all the way so that it gushes into the cup or you can barely crack the tap so the water dribbles in and it takes a much longer time to fill up.

This describes the relationship between aperture and shutter speed. If you open your aperture all the way wide, light streams into your camera and fills up your image quickly giving you a short shutter. Changing your aperture smaller and it takes a while for that light to fill up the image resulting in a long shutter speed.

However, over filling your cup or over exposing your image means there is too much light let in for too long. On the other hand, you can also under fill your cup, which means that little light is let in to your image leaving it under exposed.