#29. Midtone Exposure, Photosensitivity, and Exposure Meters
True or False?
The direct connection between the midtone exposure and the photosensitivity allows photographers to use any type or speed of emulsion in their (emulsion) cameras.
The point of the explanation in Photographic Myth Buster #28 was to demonstrate that it is precisely the photosensitivity of the chosen (solid-state or emulsion) photosensitive array–and not the exposure meter–that points to the midtone exposure that photographers are so used to using.
Since the photosensitive range of the array extends an equal measure above and below the midtone (midpoint) and since the photosensitivity (film speed) of an array points to the midtone exposure of the array (and not to the speed point exposure of the array), it is the choice of photosensitivity that offers the photographer significant exposure latitude above and below the midtone for whichever array is being used.
It does help the photographer to know the actual width of the photosensitive exposure range of the photosensitive array that he or she is using, but with the photosensitivity pointing to the midtone, even a novice photographer is exposing within a range of usable exposures.
In the same sense, it doesn’t matter which type of array or which value of photosensitivity a photographer uses in a camera because the photosensitivity (film speed), the common (midtone) Exposure Equation, and any exposure meter points to a midtone exposure surrounded by usable exposure latitude.
Copyright 2008 Michael G. Prais, Ph.D.
For a readable but in-depth analysis of this concept along with many other concepts associated with photographic exposure, take a look at the book Photographic Exposure Calculations and Camera Operation. This book provides insight into the equations that govern exposure, exposure meters, photosensitive arrays (both solid-state and emulsion) and the Zone System as well as concepts associated with resolution, dynamic range and depth of field.
The book is available through Amazon.com where you can Search Inside!™.
Check http://michaelprais.me under Photography for the table of contents, an extensive list of the topics and subtopics covered, the preface describing the purpose of the book, and a diagram central to the concepts in the book.
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