The camera

The diagram at the top of the page shows a drawing of a camera that uses film. Most modern cameras use a CCD as the detector of light but the rest of the camera is similar to the one shown in the diagram. It is very much better for taking pictures than a pinhole camera because it takes in much more light through the lens than could pass through a pinhole and so the exposure times can be much shorter. Also the amount of light getting into the camera can be controlled, as can the focusing.

The essential parts of the camera are:
(a) a lens - this focuses the light onto the film;
(b) the film - the image is produced here;
(c) the diaphragm - this controls the amount of light that enters the camera;
(d) the shutter - this controls the length of time that light falls on the film.

The diaphragm opens and closes; in dull conditions it is open to allow as much light as possible to enter the camera, and in bright conditions it is nearly closed. Both the diaphragm and lens are fixed to rings so that they can be adjusted. On a good camera the diaphragm will be marked with numbers from 2.8 to 22. A setting of 2.8 means a large aperture (dull conditions) and one of 22 means a small aperture (light conditions).

There is also a shutter speed control which allows the shutter to be open for a range of times between 1 second and 0.001 seconds. If the object that you are photographing is moving fast you will need a fast shutter speed (0.001 s) or else the image will be blurred. A shutter speed of say 1/250 s means that light will only be falling on the film for 1/250 s.

The next diagram shows a simple cross section of a camera and also a simple ray diagram.

For objects close to the camera, the lens should be further from the film. Many simple cameras are made without focusing adjustments and cannot be used for taking pictures of objects closer than about 1.5 m.

A single lens reflex (SLR) camera is one where the viewfinder looks through the main lens of the camera.

A video camera behaves much more like your eyes. It automatically adjusts to the light level and there is no film on which to permanently store the image – the picture being formed on a small screen in the camera and finally on video tape or disc.

Digital cameras store the image as a set of numbers which can be fed into your computer so that you can edit your pictures via your keyboard and monitor screen.

The photograph is of the window in Lacock Abbey, Wiltshire, England where William Fox-Talbot took one of the first photographs on paper in 1835.

The negative of his photograph is the earliest surviving example of a photographic negative.

Early work on photography was also done by Joseph Nicéphore Niepce (1765- 1833) and Louis Jacques Mandé Daguerre (1789 -1851).