9 Exposure determination

9.1 Introduction

Following considerations of subject composition, perspective and sharpness, the optimum (‘significant’) moment is chosen (or possibly remotely triggered by an event) at which to make an exposure on the film or photosensor in the photoplane of a camera by opening a shutter for a suitable time to allow an optical image of appropriate intensity to reach the sensor. This electromechanical process of camera exposure and its analogue for electronic systems is controlled by the combination of lens aperture (N) and shutter speed (t). More generally, the photographic result of exposure (H)isthe product of image illuminance (Ei) and exposure duration:

H = Eit (9.1)

Note that the properties of various types of ...

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