Six essential parts of a box camera include:
1.lightproof box, 2.film advance or film holder, 3.lens assembly, 4.diaphram - which regulates how much light enters, 5.the shutter, and 6.the viewer so you can see what photo is being taken.
Here is the most basic definition of a camera. A camera is defined as a light-tight box equipped with a lens, a shutter, a diaphram, and a method of supporting the film. When a camera takes a picture, the shutter opens for a brief moment (fraction of a second) and allows light to pass into the camera. While the shutter is open, light rays that are reflected from the object are gathered by the lens. The lens enables this concentrated light to be projected as an image onto the film. The film then retains the image.
Now I'd like to take a few parts of a basic box camera and describe its function a little more in detail:
The Lens A lens bends light rays that pass through it so that these light rays from a particular object can meet at the same point behind the lens. The point at which these light rays meet is called the focal point. The distance from the lens at which point the light rays meet is called the focal length. The focal length of the lens will control the size of the image cast on the film. The greater the focal length, the larger the photographic image. The focal length of a lens is nonadjustable.
The Diaphram The size of the opening through which light passes throught the lens and into the light-tight box is called the diaphram. The larger the diaphram, the more light will enter, and the faster a photo can be taken. The diaphram and the focal length of the lens critically depend on eachother to take a good picture. This relationship is expressed through an f number (for example: f/2, f/5.6, or f/32). The number to the right of the slanting line is the lens aperture. This number is generated through a ratio of focal length and diameter of the diaphram opening. Incidently, the larger the f number the smaller the light opening.
The Shutter The length of time that light passes throught the lens is controlled by the shutter. The shutter speed on a camera can be adjusted. There are settings such as 1, 25, 50, 100, and 200. The numbers simply indicate the fraction of a second that the lens is open (for instance 200 speed = 1/200s). Different cameras can have more shutter speed as well as different types of shutters.