2 2.8 4 5.6 8 11 16 22 32
Of course, you can choose an f/stop between these numbers, but these are standard increments that will help you keep track of the changes you're making to exposure.
Taking control of your aperture has two significant benefits:
- It helps you set the shutter speed you want and maintain the exposure you need. If you need a fast shutter speed, open up your aperture to the largest possible on your lens (smallest f/stop number). If you want a slow shutter speed, stop down your aperture so that it's smaller (larger f/stop number). Many lenses will let you shoot at f/32, but be careful about going smaller than f/16--in some cameras and lenses you begin to lose some sharpness at smaller apertures than f/16.
- It helps you control your depth of field. We use the term "depth of field" to describe the amount of your scene that you have in focus. In other words, depth of field is the distance in front of and behind your subject that appears to be in focus. The larger your aperture (smaller f/stop), the narrower your depth of field will be--that is, it will make the area in front of and behind your subject look more blurry. The smaller your aperture (larger f/stop) the wider your depth of field will be--it will make the area in front of and behind your subject look more sharp. In the above photograph, I shot the butterfly at f/5, a fairly wide aperture, especially in macro photography. The result was a relatively fast shutter speed (1/250 sec) and a narrow depth of field--notice that only the butterfly's head and the front of its wings are in focus.