Film speed (S) is defined as the reciprocal of the radiation dose required to produce a density of 1.0 above base and ______ densities.

Film speed (S) is defined as the reciprocal of the radiation dose required to produce a density of 1.0 above base and ______ densities.

• A. secondary
• B. primary
• C. fog
• D. mid

Answer: (C)

Film speed shows how sensitive a film-screen system is to exposure. It is defined as the reciprocal of the exposure needed to produce a net optical density of 1.0 above the base plus fog. Fog represents the baseline density inherent in the film from base plus processing, so the criterion uses density 1.0 above that baseline to measure speed. That’s why the missing term is fog. Higher speed means less exposure is needed, since speed is inversely related to the required dose.

Film speed shows how sensitive a film-screen system is to exposure. It is defined as the reciprocal of the exposure needed to produce a net optical density of 1.0 above the base plus fog. Fog represents the baseline density inherent in the film from base plus processing, so the criterion uses density 1.0 above that baseline to measure speed. That’s why the missing term is fog. Higher speed means less exposure is needed, since speed is inversely related to the required dose.