Density and image effect of black-and-white darkroom technology

Whether the development is correct directly affects the density of film and photographic paper. Neither overexposure nor underexposure can obtain the "ideal density", which can only make it lose the level of light or dark.

In order to obtain the image effect with rich layers, normal contrast and bright tone, we can only rely on the negative with correct exposure, development and density. Tolerance refers to the ability of photosensitive materials to correctly record the brightness range of a scene in proportion. The difference between the largest part and the darkest part of the scene surface can be expressed by the proportion between light and dark.

The ability of photographic film to correctly express the difference between light and shade of the photographed scene is the tolerance of photographic materials, which is commonly called exposure latitude.

The tolerance of black and white film is1; 128 or so, the tolerance of color negative film is about 1:32-64, the tolerance of color reversal film is only about 1: 16-32, and the tolerance of photographic paper is about 1:30.

In photographic exposure, using a photographic film with large tolerance to shoot scenes with small brightness difference has little effect on film density even if the exposure is a little more or less.

From a practical point of view, the greater the tolerance of photosensitive film, the better the exposure control.