Exposue in Photography and its Application to Photogrammetry 
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definition.. Generally speaking the same problem arises when the regions of interest in the image are located in the lower density part 
of the curve for an image made with an important illuminance contrast over the field of view. The basic rule for compensating this 
effect is to consider that shadow regions should be located at 0.3 above fog density and the resulting apparent speed of the film is 
roughly half the ISO speed. 
The above consideration shows that exposure and development conditions are significantly linked to the conditions in which the film 
will be used. For those who are interested in practical details, we should mention the works of Ansel Adams who defined in the 
forties a practical method, called the Zone System, which enables precise determination of exposure and development related to the 
subject illuminance and the final support or use of the image. 
The "Zone System" divides the light of a scene into eleven zones, from pure black to pure white. Each zone is numbered Roman 
numerically from 0 to X. Zone V is what exposure meters read, or 18% reflectance. Sometimes when you meter a certain portion of a 
scene you may not want it to fall on zone V in the final print, so using the Zone System you can change the exposure to give that 
certain subject a different [McMullan 2000]. 
zone 0 zone V zone X 
Figure 3: The Tonal Scale used in the Zone System. Pure black is 0 and Pure White is X. 
Zone V is what light meters are calibrated to set film exposure to. 
Most film will only record details in the ranges from Zone III to Zone VIII. 
The following images show examples of underexposed , correctly and overexposed photographs respectively (figure 4). At left side 
the underexposure put the high light in zone VIII, middle : correct, the instrument (dark) is in zone IV), at the right side over 
exposed : instrument in zone VI, back and floor in zone X. 
Photograph of the instrument used for the photogrammetric restitution projected by Ing. E. Santoni (Calci 1896, Firenze 
1970) and built in 1926 as an unique copy, by the Italian Geographic Military Institute workshop. 
It is an “optical - mechanical” instrument with stereoscopical vision visible in Firenze. 
Figure 4: Examples of underexposed, correctly exposed and overexposed images 
1.3 Properties of image and structure 
Below some definitions are quoted and their influence on exposure is explained. 
1.3.1 Graininess and Granularity 
"RMS granularity represents 1000 times the standard deviation of density produced by the granular structure of photographic images. 
It is determined by scanning a 0.1 density sample with a microdensitometer having a 48 pm circular measuring aperture. The RMS 
value correlates with the subjective appearance of graininess when viewing the sample with 12x magnification" [Albertz-Kreiling, 
1980]. "Since granularity increases with density, the detectability of small low-contrast details is impaired for objects recorded on the 
shoulder of the D-log H curve" [ASP, 1980] Graininess is related with the film speed and become higher when the film speed 
increases. 
1.3.2 Resolving power 
"Resolving power values result from the study of tri-bar resolution chart images on the test film under a microscope. The value 
quoted is the reciprocal of the center-to-center distance (in millimeters) of the lines that are just distinguishable in the image. This 
value depends upon the test-object contrast. Usually resolving power values are reported for a test-object of 1000:1 (density 
difference 3.0). For aerial films 1.6:1 contrast (density difference 0.2) is more representative" [Albertz-Kreiling, 1980]. 
The resolving power of a photographic system is bound by each element of the system and the optical frequency response is better 
suited to describe the ability of the optical system to reproduce object details.