Question

aperture is controlled by what in the camera?

Answer 1

Haha, immediately I thought of "Aperture Laboratories." (Sorry, huge Portal fan here. :P)

Anyways, the aperture is an opening within the lens whose size is controlled by a series of overlapping blades. Its sole purpose is to control the amount of light that reaches the film or digital sensor during the exposure time. Anything else, such as depth of field, is a spin off of its function.

The size of this opening is controlled by settings on the camera shutter speed/aperture dial or on the lens. Many cameras do not have the ability to "stop down" the aperture before the moment of exposure, so it is not something most people can observe. At the moment of exposure, the blades move to create an opening within the lens just before the shutter opens to control the duration that this occurs. Together, they control the exposure.

Hope that helps a bit. :)