Callier coefficient

The ratio of specular density to diffuse density is termed the Callier coefficient, or Callier Q factor, and can be expressed as:

specular density diffuse density

This ratio, which is never less than 1.0, varies with grain size, the form of the developed silver and the amount of the deposit. As far as the grain is concerned, the finer it is, the lower the resultant scattering and the nearer to unity is the Callier coefficient.

The factors above which influence the value of Q vary quite markedly with the degree and type of development used. Consequently, the Callier coefficient varies with density and contrast in a complicated way, even when a combination of only one film and one developer is investigated. An example of such behaviour is illustrated in Figure 15.2, where the value of y for each curve indicates the degree of development received by the film. At low degrees of development, with this particular combination of film and developer, the value of Q is approximately

Negative Integrating sphere

Negative Integrating sphere

(1) Direct (specular) density

(3) Doubly-diffuse density

Figure 15.1 Optical systems for measuring different types of density

(3) Doubly-diffuse density

Figure 15.1 Optical systems for measuring different types of density constant at densities above about 0.3; for more complete development, however, there is no single value of Q that can be adopted; consequently no simple correction for specularity can be applied to densitometer readings.

Digital Cameras For Beginners

Digital Cameras For Beginners

Although we usually tend to think of the digital camera as the best thing since sliced bread, there are both pros and cons with its use. Nothing is available on the market that does not have both a good and a bad side, but the key is to weigh the good against the bad in order to come up with the best of both worlds.

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