Updated: Sep 26, 2017
The range of film types available often seems bewildering. When faced with a choice between different films, each with its won peculiarities, there is a great tendency to simply stick to one well-tried type and not experiment.
This can be a big mistake. Although it is a good idea to get used to one film type before you branch out, so that any variations in results are definitely due to yourself and not the film, after a while, it is worth looking at the choice available.
The choice breaks down into three categories—colour negatives, colour transparency, and black and white. Everybody is familiar with the appearance of negatives—with the light parts of the image appearing dark and vice versa. While black and white negatives appear with black images on a clear background, colour negatives usually have an overall orange colour, with the images in colours different from the originals—a red object appears greenish for example. The print that is produced from negatives is sometimes called a positive copy.
Transparencies or Slides are also positives, but are produced directly from the original material by a process of reversal. The film is first processed to give a negative, then immediately reversed in its tones to give a positive. The continental name for slides is diapositives.
Though colour films occupy most of the market, black and white film still has many enthusiasts, most of whom process it themselves. Almost black and white films give negatives, from which prints can be made, black and white printing, like processing, is easy and can be done at home.
For some people, the reduction of all colours of the spectrum to shades of grey is too much of a sacrifice to make, but the rewards of working in black and white are considerable. It is easier to process and print your own pictures in monochrome than it is in colour, and costs are far lower than for colour prints or transparencies. On the other hand, it is far less easy to find laboratories which will process and print black and white film, if you cannot do it yourself and the cost may be as high as for colour.
The range of black and white films is formidable, and even for films that are in day to day use, speeds range from 25 ASA to 400. Specialist black and white films abound, with the slowest of these being only a fraction of 1 ASA used for scientific photography. At the other end of the scale, black and white films are often rated at 2000 ASA or more.
Reference: Photography Techniques