Most often, when asked about how a camera works, people will refer to the classic pinhole camera. The light waves of the object to be photographed passes through a small hole in a sealed box, forming an inverted image at the back wall of the box where a photographic film is to be placed. There is not much more to it than that. A discussion of a more common camera, the SLR (Single-lense Reflex) camera, should prove more interesting.
Like other cameras, SLR cameras have a body that houses the film, a lens to focus the image, a shutter to control the exposure times, and a diaphragm to control the amount of light. There is an obvious resemblence between the camera and the eye. The aperture opening, controlled by the diaphragm, can be compared to the pupil of the eye. The diaphragm itself can be compared to the iris of the eye. The lens of the camera, obviously, can be compared to the lens of the eyes. What is the film then? Why, the retina, of course!
However, the resemblence stops here. Unlike the retina, once the film is exposed to light, the image stays there. A chemical, silver-halide, on the film will undergo a reaction when exposed to light, forming what is called a latent image. When processed with a chemical agent, known as a developer, silver is formed according to the tones of the latent image. More silver is formed in areas that have been exposed to more light, so, the dark areas on developed negatives will be bright on the picture. As you can see, the amount of light explosed to the film is crucial for a picture to come out correctly. On SLR cameras, light can be controlled by setting the shutter speed and F-stop (controls the disphargm, hence the aperture opening). A faster shutter speed will allow less light to enter, likewise, a higher F-stop will produce a smaller aperture opening, also allowing less light to enter. In most SLR cameras, there should be a meter indicating if the current setting allows proper amount of light to enter. There can actually be several acceptable combination settings for the same image, however, the resulting pictures will look slightly different. The reason for this difference lies on the aperture opening. A large opening will produce a picture focused only on objects a certain distance away, everything else will be blurry. A small aperture opening will produce a picture with everything focused, providing better depth of field.