The lens of a camera is placed in front of the small aperture or opening that lets light into the dark chamber, known as the camera obscura.

The more perfected the lens, the sharper and more accurate will be the photograph produced; the wider the lens, the greater the amount of light that will enter the camera. In this way, to photograph an object in poor light the ideal lens should be as wide as possible; to photograph an object in brilliant sunshine only a very small lens aperture is needed.

That is why the camera is fitted with a mechanism to adjust the aperture of the lens. The mechanism consists of a diaphragm that works just like the iris of a human eye: when the light is bright the hole in the diaphragm is small and when the light is poor the hole is made large.

There is an adjustment scale on cameras that gives various degrees of apertures. This is known as the f scale. On the f scale the lower the number the wider the aperture. Therefore an aperture of f 2.8 is usually the widest the iris of a camera will open. An aperture of f 16 of f 22 is the smallest iris opening.

In any reasonably well developed camera the aperture must be set and the time of the exposure fixed before a photograph is taken. These two operations depend on the amount of light around the object to be photographed.

Another factor to be regulated before taking a photograph is the distance between the camera and the subject. In a good camera the lens can be turned and set to various distances. These are shown on the edge of the lens in figures that represent distances in meters from close range up to ‘infinity’ for very distant objects.