Basics

• The basic principle of photography was developed long before photography was possible. In the 11th century, the concept of the pinhole camera was discovered. The concept is that if a tiny hole is pricked into a box or the side of a dark room, a well-lit image from outside will project through the hole. Reversed left to right and upside down, the image will be projected on the opposite side of the box or room. This was called a camera obscura and people could get inside the room and draw the image that was projected. It was another eight centuries, however, before this principle was expanded with the development of glass lenses along with light-sensitive materials and the chemicals to develop these images.
  
  

Film and Digital

• Once light-sensitive chemicals were "painted" onto glass and exposed through the camera lens, the camera could create a permanent image called a photograph. The plate was then developed in chemicals that brought out the latent image in negative form. By projecting this image onto light-sensitive paper, a positive image was created. Later, the image was changed to digital information with the charge-coupled device (CCD) and the need for light-sensitive material was negated.
  
  

How It Works

• Essentially, the principle has remained the same. The lens, substituting for the pinhole, focuses the image coming into the camera, either manually or with autofocus. The image is composed by the photographer who looks through a viewfinder. In single-lens reflex-style cameras, the image travels through the lens, hits a 45-degree mirror and is projected through a focusing screen into a pentaprism. The pentaprism corrects the image from left to right and right-side up. When the photographer trips the shutter button, the mirror flips up. In a film camera, a shutter curtain then opens for the desired amount of time, exposes the film and closes again. The mirror flips back into place and the next shot is ready. In a digital camera, the same process takes place except that when the mirror flips up, the CCD is activated for the desired exposure.