Why is an understanding of the aperture so important? The reason is immediately obvious when the exposure wrong. A scene that is overexposed (aperture is bigger than it should be) or underexposed (aperture is smaller than it should be) looks terrible. So the goal is to get the exposure right.

In the f-stop simulator to the right, you can see the how adjusting the f-stop changes the image. Notice that at f8 the image begins to lose detail in the bright areas. And at f4 it's a bit dark.

(Of course, in a brighter room, f8 might be the better setting. The correct f-stop depends on the lighting of the situation)

Modern cameras have automatic f-stop settings, but professionals often override those controls for good reasons (discussed later in this lesson). So it's important to have an eye for good exposure.