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Part III: Tools and Techniques: Producti... > Chapter 14: Lighting and Exposure: B... - Pg. 321

Lighting and exposure: Beyond the Basics Now that you are familiar with the fundamental concepts and techniques of exposure and lighting, which are applied everyday on every movie set, we can turn our attention to slightly more intricate issues related to image control. We need to look a little closer at how the film stock or the CCD chip itself actually responds to the various light values in a scene, beyond just its general sensitivity (i.e., exposure index [EI]). Two additional con- cepts are essential to a more advanced understanding of lighting and exposure for both film and DV: contrast range and exposure range. 14 Chapter Contrast range and exposure range Contrast range (also called luminance range) is the difference between the brightest and the darkest significant areas of your scene. Remember, "bright" and "dark" consist of a combination of incident light intensity and reflectance values. Contrast range can be expressed either in terms of a ratio or in terms of the f-stops difference between the two luminance extremes. For example, it is not unusual to discover, through multiple light meter readings, that a scene's lightest area is 16 times brighter than its darkest area. We can express this as a contrast ratio of 16:1 or as a contrast range of four f-stops. Why? Remember that each stop is a halving or doubling of brightness, so four stops from dark- est to brightest is 2 × 2 × 2 × 2 = 16. It should be noted that four stops is a relatively narrow contrast range. In a complexly lit scene, it's not usual to have a contrast range of 256:1, or eight stops or even more (Figure 14-1). One central question concerns how much of this contrast range our film stock or DV sensor can faithfully reproduce. Broadly defined, exposure range (sometimes called dynamic range for DV) is the range of luminance values your specific imaging device (film stock or video sensor) can render with detail before falling off into complete overexposure (blown out or clipped whites) or complete underexposure (crushed blacks), where no image detail is visible. Exposure Figure 14-1 In this scene from Godard's Masculin Feminin (1966), we have an example of a wide contrast range (left), where the street outside the café is extremely bright compared to the darker areas inside. In the kitchen (right), there is very little variation between the tonalities, producing a narrow contrast range for this scene. 303