Development
The developer selectively reduces silver halide crystals in the emulsion to metallic silver, but only those having latent image centres created by action of light. The light sensitive layer or emulsion consists of silver halide crystals in a gelatin base. Two photons of light must be absorbed by one silver halide crystal to form a stable two atom silver metal crystal. The developer used generally will only reduce silver halide crystals that have an existing silver crystal. Faster exposure or lower light level films usually have larger grains because those images capture less light. Fine grain films, like Kodachrome, require more light to increase the chance that the halide crystal will absorb at least two quanta of light. The metallic silver image has dark (black) appearance. Once the desired level of reduction is achieved the development process is halted by washing in a dilute acid and then the undeveloped silver halide is removed by dissolving it in a thiosulfate solution, a process called fixing. Most commercial film developers use a dual solution or "push" (pushes the films speed) development (compensating developer, like Diafine) procedure where the reducing agent e.g. hydroquinone solution soaks into and swells the gelatin then the film is introduced into the alkaline solution which activates (lowers reduction potential) of the developer. The areas with the most light exposure use up the tiny amount of developer in the gelatin and stop making silver crystal before the film at that point is totally opaque. The areas that received the least light continue to develop because they haven't used up their developer. There is less contrast, but time is not critical and films from several customers and different exposures will develop satisfactorily.
The time over which development takes place, and the type of developer, affect the relationship between the density of silver in the developed image and the quantity of light. This study is called sensitometry and was pioneered by F Hurter & V C Driffield in the late 19th century.
Read more about this topic: Photographic Developer
Famous quotes containing the word development:
“If you complain of people being shot down in the streets, of the absence of communication or social responsibility, of the rise of everyday violence which people have become accustomed to, and the dehumanization of feelings, then the ultimate development on an organized social level is the concentration camp.... The concentration camp is the final expression of human separateness and its ultimate consequence. It is organized abandonment.”
—Arthur Miller (b. 1915)
“Sleep hath its own world,
And a wide realm of wild reality.
And dreams in their development have breath,
And tears, and tortures, and the touch of joy.”
—George Gordon Noel Byron (1788–1824)
“Understanding child development takes the emphasis away from the child’s character—looking at the child as good or bad. The emphasis is put on behavior as communication. Discipline is thus seen as problem-solving. The child is helped to learn a more acceptable manner of communication.”
—Ellen Galinsky (20th century)