1 The Director of Photography – an overview

80 Practical Cinematography
Figure 7.4 D–log E curve
showing the effect of changing
the speed of the emulsion
Figure 7.5 Contrast ratios
for various delivery systems
Density
High Speed Film
Medium Speed Film
Low Speed Film
Exposure
For Television
Black Contrast Ratio � 0
�1 Stop Contrast Ratio � 2 : 1
�2 Stops Contrast Ratio � 4 : 1
�3 Stops Contrast Ratio � 8 : 1
�4 Stops Contrast Ratio � 16 : 1
�5 Stops Contrast Ratio � 32 : 1
For the Cinema Screen
�6 Stops Contrast Ratio � 64 : 1
�7 Stops Contrast Ratio � 128 : 1
Modern Extended Latitude Negative
�8 Stops Contrast Ratio � 256 : 1
�9 Stops Contrast Ratio � 512 : 1
�10 Stops Contrast Ratio � 1024 : 1
�11 Stops Contrast Ratio � 2048 : 1
confused. As we have seen, gamma is a measurement of the rate of
change of the exposure–density relationship. Contrast refers to the
brightness range and the gradation between the highlights and the
shadows; it is therefore expressed as a ratio. For instance, a television
picture, even on a perfectly set-up screen, will only be able to show a
brightness range equivalent to five stops of exposure; it will therefore
have a contrast range of 32 : 1, as shown in Figure 7.5. The contrast
range that can be shown on a first-class cinema screen is the equivalent
of seven stops of exposure. Recently, developments in the construction
of camera negative emulsions have made it possible to
manufacture a negative able to record the equivalent of 10 stops of
brightness; this gives the film a contrast ratio of an incredible 1024 : 1.
The value of this range to the working cinematographer is discussed in
Chapter 11.
Despite the definitions above, we still think of a ‘contrasty’ film as
one having severe blacks and whites with little information in the midtones.
This kind of image would probably be described in sensitometric
terms as having a high gamma, i.e. one having a steep straight-line
section, as shown in Figure 7.6. It would, in all probability, have a low