Page 174 - Friedman Archives

174 The “Recording” (Camera icon) Menu Settings

5.21.1 CENTER-WEIGHTED AND MULTI-SEGMENT METERING
Since the advent of the “18% grey” principle (in the 1960’s!), reflectance
meters have been incorporated into cameras. A depiction of the most
popular implementation appears in Figure 5-33a (left), where the camera
would weigh the reflected light coming from the center of the viewfinder
more than it would the edges. This “Center-weighted” metering pattern (a
Nikon invention) makes the reasonable assumption that your subject (the
important thing worth metering) is more likely to occur in the center than
the edges. (Clearly, nobody at Nikon had ever heard of the rule of thirds!
) Center weighted metering was in use in all cameras throughout the
1970’s and 1980’s.
Starting in the 1980’s, there were many attempts to improve upon the
accuracy of the built-in exposure meter for scenes that are not “average”,
such as subjects that are backlit. Usually these entail dividing the picture
into smaller areas and analyzing each of these areas in terms of absolute
light measurement (with an emphasis on what’s behind the focus point) and
comparing the values against each other and against a tiny in-camera
database of “standard compositions” with rules like “When the metering
pattern looks like this pattern, overexpose by ½ a stop; and when the
pattern looks like this other pattern, then underexpose by 0.75 stops.”

Figure 5-33: The older Center-weighted metering pattern (left) and the modern
Multi-Segment metering pattern (right). (Well, truth be told the A77 II uses about
1200 zones, not the 40 honeycomb pattern pictured on the right. But you get the
idea.) With the advent of full-time live view it’s hard to find a reason to use
center-weighted anymore.

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