Lens: Special glass that has been ground to exacting shapes so that it focuses light accurately on the film. Each lens has a maximum aperture. Lenses are made from multiple pieces of glass with exposed surfaces on the front of the camera and in the film chamber.
Aperture: The hole through which the light passes, formed by an adjustable diaphragm mounted between the lens elements. The diaphragm has settings called f-numbers. Each numerically smaller number lets in twice as much light, e.g., f /8 lets in twice as much as f /11. If the shutter is in the lens you can generally only see the diaphragm with the shutter open.
Shutter. While the diaphragm controls the amount of light that passes through the lens, the shutter controls the duration that the light is allowed to enter. Shutters can be between the lens elements (between-the-lens type) with leaves that open and close, or at the back of the camera (focal-plane type) which has a curtain with slits that pass horizontally or vertically across the film. Since, in a basic camera, the shutter the the main mechanical device, it is the element most likely to have a mechanical failure.

08/03/2006 1:59