Exposure explained

Aperture values and shutter speeds can be confusing. Here’s some information and examples that should help you understand.

Learning objectives

  • Interpret shutter speeds and aperture values and their relationship to exposure
  • Identify the effect an aperture value and shutter speed has on image quality
  • Evaluate the application of depth of field

Aperture values are really fractions.

The numbers get bigger, but the picture gets darker. This is the tricky part that you may not know about shutter speed and aperture values: They’re fractions. Here’s an example:

f22 is really f 1/22 when you think about it.
f22 is really f 1/22

That’s why when the number gets bigger, the aperture gets smaller, taking in less light. The same is true for shutter speed. If you ever get confused, just remember you’d rather have half a pizza (f 2) rather than a twenty-second of a pizza (f 22). You get more light the smaller the fraction.

Reading aperture symbols

Cameras can provide a wide range of aperture values, and the widest value is the one that’s advertised on the front of the lens. In the case of a zoom lens, there may be a variable aperture, as demonstrated in the example below. When the lens is zoomed to the widest field of view, the aperture uses the larger aperture, and when the lens is zoomed out to the most telescopic field of view, it will use the slightly smaller aperture.

Image of an camera lens, focused on the text surrounding the lens glass.
This zoom lens will use f3.5 at 18mm, and f5.6 at 55mm.

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