Photographic Equipment Part V

For SLR and view cameras, extra lenses are major accessories. They can be used to give images of different sizes and to take pictures far away or very close-up.

Every lens has a certain focal length. Lenses come in normal, short, and long focal lengths. A normal lens shows about what your eyes sees when looking at the scene. In 35mm cameras, this is a lens with about a 50mm focal length. A 50mm lens provides about a 45-degree angle of view.

Lenses with very short focal lengths are called wide-angle lenses. They take in a very large area of the scene. But they produce a small image of any given object in the scene. One of the most interesting wide-angle lenses is the fish-eye lens. An 8,, fish-eye has a 180-degree angle of view. There are even special lenses that take in everything around the photographer. That is, they produce a 360-degree angle of view.
Telephoto lenses-lenses with long focal lengths-"see" less of the scene from a given spot. But they enlarge part of the scene on the film. A lens with a long focal length makes a larger image.

Simple lenses can be added to the front of the normal lens to allow close focusing. These are called close-up lenses. With them, you can photograph flowers and other small objects.
Lenses with a focal length that can be changed to make a larger or smaller image are called zoom lenses.

There are three main types of photographic film for general use. Each produces a different kind of photograph. Black-and-white negative film is used to make black-and-white photographs, or prints. And color reversal film is used to make color slides, or tranaparencies.

All films has a plastic base thinly coated with crystals of a silver-bromide compound. The crystals are mixed in a transparent gelatin. This mixture is called an emulsion. In black-and-white film, there is usually only a single layer of emulsion. In color film, there are three layers of emulsion. Each layer is very sensitive to blue, green or red-the three primary colors.

When choosing a film of any one of these types, there are three factors to be considered-film speed, graininess, and contrast.

Films vary in their sensitivity to light. This sensitivity is commonly known as film speed. Graininess is the degree of visibility of the silver crystals, or grains, in the photographic image. Graininess is especially noticeable when a photograph is enlarged. Contrast is the degree of difference between the light and dark areas of the subject. Generally, the faster the film, the grainier the photograph will be and the less contrast it will have. Photographs with too high contrast lack fine detail.