Pentax ZX-5N - Manual (Page 90)

Effect of Aperture
The aperture increases or reduces the amount of re­
flected light from an object which passes through the
lens, controlling how much light strikes the film. If the
aperture is opened up to increase the amount of light,
objects in front of and behind an in-focus subject will
not be in focus. That is, the range of focus (depth of
field) becomes small. If the aperture is closed down to
reduce the amount of light, the depth of field increases.
For instance, if you shoot a person against a landscape
with the aperture open, the landscape in front of and be­
hind the person will be blurred, making the person ap­
pear to rise out of the landscape. By contrast, closing
down the aperture increases the in-focus range.
Open aperture