The requirement 0 in analog photography: Practical Consideration Reversal Film

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Let’s start with the simplest for a change, the slide. There isn’t much to consider, as the slide represents the final product. Emulsion and development are matched in such a way that the required contrast enhancement is obtained. Figure 31 shows the color density curves of a typical reversal film. It slopes quite steeply from a high maximum density at low exposure to a low density at high exposure. This initially strange behavior is explained when we realize that the reversal film is not copied and a dark subject spot must directly leave a heavy blackening on the film. Apart from that, the diagram shows a homogeneous picture of the three individual curves. Typical reversal films have maximum densities of 3.0-3.5 and gamma values between 1.9 and 2.0. With a dynamic range of 2.4 log₁₀ units, you can image a subject contrast of 8 exposure stops. However, we can only expect a completely correct reproduction of the tonal values on the linear part of the curve. Under this condition, the dynamic range drops to a good 5 exposure levels.

Assuming a dynamic range of 3.3 log₁₀ units, we can calculate the exposure range in exposure levels if we take into account that one exposure level means doubling or halving the amount of light and the logarithm of 2 = 0.3 (or 10^0.3=2). The result is therefore 3.3/0.3 = 11 exposure levels.

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