Sensitivity of Photographic Film
Photographic film is the medium used most often today in photography. However, because digital photography has become more and more affordable and accessible, it is not as widely used for still and motion picture photography as it once was. Nonetheless, film still has a use in specific photographic applications and is used by professionals and even amateurs alike. An important feature of photographic film is the sensitivity, or its response to light.
When a photographic image is taken using a camera, light enters the camera and is projected onto the film. The film is then exposed to the light, which is recorded into the emulsion. The emulsion contains a variety of light-sensitive chemicals, which when combined with light and heat, cause a reaction that produces a photographic image. The sensitivity of the film determines how well and how quickly the reaction to light occurs. Depending on the sensitivity of the film, images can be produced in a variety of light conditions, low-light or within a flash.
Sensitivity is typically measured in terms of speed. This is because faster films require less light to produce an image than slower films, so faster films can produce an image quicker than slower films. The speed of a film is typically measured in degrees on the American Standard (ASA) or the International Standard (ISO). The higher the speed, the faster the film and the more sensitive it is to light. For instance, a film with an ISO speed of 100 is twice as fast as a film with an ISO speed of 50.
In addition to speed, film sensitivity can be determined by its grain size. Grain size is the measure of the size of individual particles of the silver halide emulsions, which dictate the film’s sensitivity. Generally speaking, finer grain film is better in terms of clarity and sharpness than coarser grain film. As the grain size decreases, the image produced by the film becomes sharper and clearer, though the film also becomes less light sensitive.
The sensitivity of a film is also influenced by its type, or the chemicals it contains. Films are typically described as being either color or black and white, slide or print, and negative or positive. The differences between these types of films usually relate to the chemicals used in them and how sensitive the film is to light. For example, some black and white films are more sensitive to light than color films, because of the different chemicals used in their construction.
In conclusion, understanding the sensitivity of photographic film is important for selecting the appropriate film for any particular situation. Each type of film has its own unique characteristics, so it is necessary to know its speed, grain size, and type in order to determine its sensitivity relative to the light it will be exposed to. By understanding these factors, photographers can more easily be assured of getting the best possible results for their work.
