Film speed or sensitivity

The sensitivity of the film to light is prescribed by the manufacturer. It is obviously of importance in assessing the camera exposure and also needs to be known to the film processer, because it affects the processing time. Generally, film sensitivity depends on the size of the silver halide grains in the emulsion. Larger grains lead to higher sensitivity, which means that less camera exposure is necessary. An indication of sensitivity or speed is given on every film carton in the form of an ASA or DIN figure or both. The figure is simply a guide to a relative position on a scale. It does not carry any such description as ‘speed’ or ‘sensitivity’. The usuarinscription is recommended meter settings, meaning that any meter used to assess the camera exposure should be set to that figure. This is because the sensitivity of an emulsion cannot be stated in isolation. It depends on other factors, the most important of which is the processing. The ASA scale of film speeds is arithmetic. A doubling of the film-speed figure indicates a doubling of film speed or sensitivity. The DIN scale is logarithmic. A doubling of the film speed is indicated by an increase of 3 in the DIN figure. Use of the DIN scale is confined largely to Continental Europe. Most of the rest of the world uses the ASA scale.

Film Developers

The image on a film is formed by the action of light on materials coated on the film surface. That is not enough in itself to form a usable image, so the effect has to be amplified. There is a parallel with the electrical signals picked up by a radio receiver or from a tape or disc player. They are much too weak to provide sufficient power to drive a loudspeaker, so they have to be amplified. The electrical signals are amplified by electronic means. The effect of light on films is amplified chemically. The image is formed by a plastic strip coated with a light-sensitive material called the emulsion. It is actually a suspension of tiny grains of a silver compound in gelatin. The emulsion is microscopically thin but the silver halides within it are too small to be seen even by the ordinary microscope. Consequently they are suspended at various depths within the emulsion and can overlap. It is the silver halide grains that are light-sensitive and the gelatin is simply a binder. Light reflected from the subject is picked up by the camera lens and projected to form an image on the film. The image consists of various densities of light representing the darker and lighter parts of the subject. The silver halides are affected by the light according to its intensity. The whole of a grain or only part of it may be sufficiently affected to contribute to the image. Grains at various depths within the emulsion are affected according to how far the light penetrates. The stronger the light, the deeper it penetrates into the emulsion.

Photographers Satisfaction

The Photographers process their own films mainly for personal satisfaction. There is a sense of achievement in carrying an operation through from beginning to end. In many cases, a skilled processor or printer could perform the tasks more efficiently and provide a better end product but he cannot give the photographer that pride in something that is all his own work. Many are interested only in operating the camera and refuse to be involved in any way with the tiresome processing stages. The Specialization makes sense in the business world. Taking photographs, processing the film and selling the product are skills that do not necessarily have anything in common. It is reasonable to expect that the different skills required for each task might best be performed by different people. Many photographic businesses work in that way. On the other hand, photography is a business that can be carried out on any scale, large or small and it can certainly be a single-handed operation. Film processing is a simple enough procedure. For very many years now, it has been a purely mechanical process depending only on time and temperature. A certain amount of care is needed and cleanliness in working conditions is imperative but virtually no skill is required, even in color film processing. Experience can lead to the application of special procedures to overcome faults in camera operation or to obtain a particular kind of result, but the actual process of putting the film through the various chemical solutions is routine. All normal photographic films have to be developed in total darkness.

Darkroom

Darkroom technique can perform all the steps from buying a roll of film to producing and mounting a finished print, making a proof sheet to judge negative quality and process all prints, film processing to make printable negatives from exposed film, enlarging and related techniques for accurate control over the final print, chemical mixing for economy and consistent results, darkroom safety to protect oneself and one’s equipment and Print mounting and finishing to present an exhibit or enter a photographic contest. The Film processing tanks and the different chemicals steps to bring out and stabilize the latent image made by light striking the film during exposure in the camera. The photographic paper and how light transmitted by the exposed and developed film forms a latent image on the paper which is then brought out and stabilized by chemicals. The enlargers machines for projecting light through negatives onto photographic paper, allowing control of image size and cropping to improve composition. To make a proof sheet and let each student makes one. Have some negatives on hand, with a good proof sheet for quality comparison. Also, have all the necessary chemicals prepared. If you’ve processed your own film, you have already prepared the stop bath and fixer. Mix the developer according to the instructions. Be sure to label jars as DEKTOL Developer, Stop Bath and Fixer. Make up a working solution by diluting your prepared developer with water as recommended on the package.