Developing Digital Photography Films

As consequence of the exposure, silver atoms appear in the emulsion with an electric charge. This effect provides the exposure level. This image we call a latent image. During developing a reduction of the silver compounds occurs and black metallic silver deposits are formed. The developer is an agent which decomposes the sliver halides, as light does. The commercial developers are designed for the action to start around the silver atoms already present in the emulsion. The decomposition of the silver salts evolves from a few atoms to millions of them, given place to visible densities and provide the exposure level. In the zones were the exposure level is inferior to minimum, no halide reduction occurs (the negative remains transparent); were the exposure level has been sufficient, a variable density is appreciated. Above a maximum, the density is the same for any exposure level.

Types of Developing

The way the developer acts has consequences on the characteristics of the negative, referring to sensitivity, contrast and grain.

•  Grain: The grain, or minimal description unit of light, has a variable size according to the emulsion.. Likewise, the size of the grain depends on the type of developer: the more intense and energetic the developing, the more visible the grain in the print, specially in the medium densities. A control (minimization) of grain becomes necessary when we need maximum sharpness and detail, or for very large prints or murals. In this case, a fine grain developer is used, which developer superficially to reduce the size of the grain visible on the print. At the same time, this causes a slight loss in sensitivity and a reduction of contrast .

•  Contrast: The variety of tones, the energy of the image and the description of light in a black and white photograph require the formation of different densities. Such as the density that is achieved through the formation of greater quantities of silver, the size of the grain increases in consequence. This, on one hand, diminishes the sharpness and fine detail, but on the other hand increases the difference of density in the border of the different zones. The definition sensation of a black and white image depends not only on the size of the grain but also in the detail of the description of original brightness and there differentiation as different densities (local contrast). A high definition developer acts in these two ways: maintains the grain at an acceptable level but develops more thoroughly, expanding the tonal range in comparison to a fine grain developer.

•  Sensitivity: a black and white negative can be developed in a wide range of intensities since it is an emulsion that is not fully developed. The sensitivity that appears in the wrapping of the film corresponds to a recommended intensity (standard developing). An increment in the time, temperature or concentration of the developer regarding the standard produces an increment in the obtained densities. If the nominal sensitivity of a negative is not enough to photograph a determined scene, we can assign a greater sensitivity and then give it a more intense developer (forcing). It is also applicable to underexposure errors in an entire roll (wrong sensitivity on the photometer, errors with the flash or filters, etc.). Overdeveloping implies an increment in the density which will be proportionally greater for the lights than for the shadows Forcing is associated with an increase in grain and in characteristic contrast. This last one implies a drastic reduction of the exposure latitude .

On another hand, as long as we want to increase the contrast of the developed negative we have to think about overdeveloping. Forcing has to be decided when loading the camera. If we have decided to overdevelop to increase the contrast, then we will have to increase the sensitivity on the photometers selector to avoid overexposing the lights

Normally we force to obtain better sensitivity from a slow emulsion or to compensate an accidental underexposure and, occasionally, to obtain more grain or more contrast in all a roll. The problems that come from a large increase in sensitivity (more than double) as an increase in veiling level and a very high characteristic contrast, with minimal exposure latitude. For intense forcing there are "specialist" developers ( high energy developers).

On the opposite sense, a diminishing in time, temperature or concentration of developer regarding the standard produces a diminishing in the obtained densities, which is equal to a reduction of sensitivity . If because of errors in the measurement or exposure and an entire roll has been overexposed, we can always underdevelop the emulsion to avoid destruction of the lights. Underdeveloping causes, in regard to the standard, a diminishing of the density that will be proportionally greater for the lights than for the shadows , and also finer grain . The characteristic contrast is greatly reduced, which implies a noticeable increase in the exposure latitude .

As long as we want to reduce the contrast of a developed negative, or we have to photograph enormously contrasted scene, we will have to think in underdeveloping regarding the standard, this has to be decided when loading the camera. If we have decided to underdevelop, then we will have to reduce the sensitivity in the photometers selector (overexposing in regard to the nominal sensitivity) to compensate.