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Subject: Re: ACR Calibration

The only metering technique that I find to work well with real-world images,
as opposed to theoretical images referred to via numbers alone, is to
meter the brightest diffuse highlight in which I want detail, then make
whatever adjustment is needed to render as a diffuse highlight. IOW: an
unscientific variation on the Zone System


This matter was discussed extensively in a previous thread:

Bill Janes, "Exposure to the right and tone placement" #90, 12 Nov 2005 11:44 am

Two resident experts, Bruce Fraser and Jeff Schewe, recommended just your approach. To make full use of the dynamic range of the sensor, it makes sense to place the non-specular highlights as far right in the histogram as possible and the highlight reading allows this.

Most cameras are calibrated for 12% reflectance and you could use a Kodak gray card and give 0.5 EV more exposure and reach the same result with the Color Checker calibration. In the field however, it is difficult to select the proper 12% gray from which to meter.

A reading from a mid gray would give a result similar to an incident light reading. Ansel Adams himself discouraged the use of incident meters since they do not take the dynamic range of the subject into account. When they became available, he used a 1 degree spot meter and took readings from the highlights and shadows.

I agree with Rags that the basics of exposure have not changed that much over the years.


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