shutter controls the amount of light that hits the film. Cinematographers
are limited in the choice of shutter speeds, but they can
control exposure time by using a variable shutter, which controls
not the time the shutter is open but the size of the opening.
Museum of the Moving Image. [www.ammi.org]
Choose "Shutters, Sprockets, and Tubes consists of
six animated interactive tutorials that explain the science
and technology behind movies and television."