Using your camera
There is no way to get away from it. The aperture – shutter speed relationship is at the base of everything in photography. Some people want to bury their head in the sand because they feel it is too difficult to understand but if you truly want to start taking control of your camera you need to understand it. If you still have the feeling of, “I hope that turned out” or “I don’t know why that picture didn’t ‘work out'” the you need to look more closely at the relationship between aperture and shutter speed.
I have my camera set to aperture priority mode (A or Av on most cameras) 95% of the time. This means that I select the aperture and the camera selects the shutter speed it thinks will result in a correctly exposed image. Is the camera right all of the time? No. But 99% of the time it does a great job.
The aperture is the size of the opening in the lens that allows light to hit your camera’s sensor (or film). You decide if you want this opening to be large (which allows a lot of light in) or small (which allows less light in). So with a large aperture (remember more light) you get a faster shutter speed and with a small aperture (remember less light) you get slower shutter speeds. When looking at your camera’s LCD panel, the aperture is the number with the F and the shutter speed is the other number.
On this example the aperture is f3.5 and the shutter speed is 1/640th of a second.
A great place to experiment with this is on this website. Remember to click the choice of aperture priority mode.