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Exposure Metering and Gray Cards

jcgoodsonjcgoodson Member
edited January 2011 in general photography
Neil,

I stumbled upon your site about a month ago. Your blog posts and your book dealing with on-camera flash have been very helpful for this amateur photographer.

I would like to ask a question regarding exposure metering techniques. I have successfully used your "histogram" metering technique to obtain proper exposure for the brightest relevant tone, e.g., by setting the exposure 1.7-2.0 EVs above what the camera's built-in meter says is correct for a white shirt. This seems to be a reliable metering technique when there is something with a near-white tone nearby. However, as you imply in your book, if there is nothing nearby with a near-white tone, then using the histogram to determine exposure is a little more subjective, requiring one to guess the tone of a subject's skin, for example.

In such situations, I wonder if a gray card could be used to determine exposure by filling the camera's frame with a gray card and zeroing the camera's built-in meter. My reasoning is that, as you note in your book, the camera's built-in meter "see's gray," and hence showing the camera a gray card and zeroing the meter should work. I've performed a small experiment that suggests this method is valid, but I am wary that my inexperience is causing me to miss something fundamental. My experiment consisted of two steps. In both steps, I fixed my camera's aperture and ISO and adjusted only the shutter speed to change exposure. First, I filled my camera's frame with a white cloth and set the exposure 2.0 EVs above the zero-point on my camera's built-in meter. Second, I filled the frame with the gray card and noted the shutter speed that zeroed the built-in meter. In both steps, I arrived at the same shutter speed, suggesting to me that either method is valid for obtaining correct exposure. I realize it is not always feasible to whip out a gray card for metering, but perhaps using something nearby with tonality similar to that of a gray card would result in good exposure when near-white objects are nowhere to be found?

Thanks in advance for any feedback or suggestions regarding whether or not my "gray card" method is correct, or if it could be tweaked to yield something more useful.

Justin

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