Digital Camera Photography Exposure Latitude

We have seen in 4.1.4 that the visible brightness interval is simultaneously much larger than the interval that the emulsion can register. For the eye, the “black” is the tonal darkness, or a brightness level so low regarding the general level that it remains indistinguishable; in the same way, “white” is a blinding light, or of such a strong intensity regarding the rest of the environment that we can't distinguish the details. On the other hand, for film, black is an exposure level below the minimum (transparency), and white, the overexposure limit. The difference between the eye and the film is huge, and implies that we have to be conscious of the latitude no matter how low the contrast of the scene is.

The exposure latitude depends directly on the characteristic contrast: The greater the characteristic contrast, the narrower the exposure latitude will be. The brightness differences of the scene (and therefore of exposure levels of the different zones of the negative) give way to greater differences in density, the

greater the characteristic contrast of the emulsion is (4.3.1.1). This implies that the extremes of the density range (maximum and minimum densities), in a high characteristic contrast film, are given for exposure levels that are very close to each other. On the other hand, with a low characteristic contrast emulsion, the change of the transparency to maximum density is produced for a much higher exposure level interval . Since the characteristic contrast depends on the sensitivity: The exposure latitude is greater, the higher the emulsion's sensitivity is. A black and white negative's latitude, with a characteristic contrast equal to 1 (normal) can be set around five exposure values. It's an approximate value, that not only marks the limit of what the emulsion is capable of registering, also the maximum interval of negative densities that we can print on paper. If the characteristic contrast of the emulsion is different than 1, the maximum density interval (32:1) on the developed negative is given for a different exposure level interval, and the increase or decrease of the latitude can be considered inversely proportional to the variation. For example, if the emulsion's contrast, taking the developing in account, is 1.2 (increase of 20 out of 100), the latitude is reduced in the same amount (from 5 to 4 exposure values); If the contrast is 0.8 (reduction of 20 out of 100) the latitude increases 6 exposure levels (12.3.5). Since the characteristic contrast depends on the kind of emulsion and developing (it can normally vary between 0.6 and 1.2), in the laboratory we can notably alter the latitude of any material (11.3).