An SLR (Single-Lens Reflex) camera is a multi-component hardware/software system that is used to take photographs on standard film. A real modern SLR contains microprocessors to control the film advance, exposure, focusing and flash illumination.

For more information, check out the following:

• Any of the major camera manufacturer's sites ( Canon, Nikon, etc.) contain descriptions of current models of their SLRs
• A requirements document written by a CS 3302 team in 1999.

Film

The Film subsystem is responsible for

• monitoring whether a film cartridge is in the camera, and if so the light-sensitivity ("speed") of the film;
• remembering the frame number of the next exposure;
• advancing the film to the first frame when the film cartridge is first loaded;
• rewinding the film into the cartridge when it runs out or when the photographer manually rewinds it;
• advancing the film to the next frame position.

The exposure subsystem is responsible for making and correctly exposing a frame:

• taking a lightmeter reading;
• activating the pop-up flash, if necessary;
• stopping down the lens in preparation for the photograph;
• opening the shutter;
• readying for next exposure.

The Lens subsystem simulates the real lens. It is responsible for

• Controlling the amount of light entering the camera during an exposure;
• Focusing or indicating the failure to focus.

The Flash subsystem controls the operation of a flash ("strobe") gun. It is responsible for the following:

• Indicating whether the flash is charged;
• Firing the the flash;
• Monitoring the incoming light during a flash exposure;
• Shutting itself off when sufficient light has been reflected.

The Controls subsystem is the camera’s user interface. It provides the following photographer inputs

• Open and close camera back;
• Half- and fully depress shutter release;
• Rewind film;
• Exposure mode selection (manual, aperture-priority, manual-priority, program).

• Frame counter;
• Set or recommended lens aperture and shutter speeds.