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How Does a Camera Work?

By: J.A.J Aaronson - Updated: 26 Nov 2010 | comments*Discuss
Camera Photograph Photography Film Lens

When looking at the most important inventions in history the camera must surely rank highly. It has transformed the way that we look at the world and, in many ways, has transformed peoples’ view of art and its place in society.

Furthermore, without the camera, the immediate impact of news stories and important events in the last 100 years would have been radically different.

Simple Technology

As with many such inventions, however, the technology which makes the capturing of the photographic image is remarkably simple. The modern-day camera has evolved from the ‘camera obscura’, or ‘dark chamber’, but the principles of today’s SLR models is much the same.

This article focuses on the technology involved in SLRs, as they also form the basis for today’s digital models. Furthermore, a manual SLR requires no extra power source, and can therefore be used as an excellent illustration of the fundamental principles involved.

The Three Elements

Essentially, a camera comprises three parts: the optical element; the chemical element; and the mechanical element. The optical element is the lens. This is generally a piece of convex glass or plastic, although the shape may be different on some ‘special effect’ lenses such as fish-eyes.

Light travels at different speeds in different substances and, for this reason, it slows down when it hits the lens. As a result of this change in speed the light bends when it enters the lens, and then again when it leaves it. This means that the available light, which diverges away from the light source, converges again in the lens in order to be redirected towards a set point at which an image can be formed. This point is the chemical element: the film surface.

When you focus a camera, you alter the distance between the light source and the chemical element. When the source of light is closer to the lens, the light exiting the lens converges at a point which is farther away than that at which they would converge if the source was at a greater distance from the lens. This ‘focal distance’ determines whether the image that is produced is in focus or not.


Once the light has exited the lens, it is projected onto the film surface. This is made up of minute light-sensitive elements, each of which undergoes a chemical reaction when it is exposed to light. When the roll is developed it is exposed again, but this time to a series of chemicals. The reaction that occurs this time depends on the type of film; in black and white film the developing chemicals make the exposed light-sensitive elements darker, and vice versa.

Colour film, on the other hand, is made up of particles which react differently to red, green and blue light, each of which are on an individual layer of film.

These layers are dyed by the developing chemicals and, when they are placed on top of each other, a full-colour negative image is formed. When the image is printed, regardless of whether it is black and white or colour, the negative is reversed in order to create a true printed image.

The mechanical side of the camera is also dependant on elements such as the shutter and the aperture that is created by it. These are covered in more detail in an article elsewhere on this site.

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