This is discussed in the latest issue of Shutterbug. There is no international
standard but there *is* an ANSI standard. And it's 13%.
The writer in Shutterbug contacted Kodak to ask why there gray cards are 18%even
though the ANSI standard (to which cameras and handheld light meters are
calibrated) is 13%. It turns out that it's been going on so long that no one at
Kodak remembers! (Or has been with the company that long.) The people at Kodak
speculated that, because Ansel Adams lobbied hard for 18% when the standard was
originally being decided upon, Kodak used 18% to please Ansel... Even though
ANSI eventually settled on 13%.
Tom Rittenhouse <[EMAIL PROTECTED]> wrote:
>A couple of weeks ago there was some discussion here about
>how the camera manufactures are calibrating their meter to
>13% rather than 18%. Someone commented that Kodak is now
>suggesting that you open up a 1/3 to 1/2 when using a gray
>card to set exposure.
>
>WHAT!!!!
>
>18% gray was chosen because the real world approximates
>that. If you average the exposure for all outdoor scenes it
>comes out to 18% reflectivity. So if the meters are
>calibrated to 13% you will always get the wrong exposure.
>
>I do believe that maybe the meters really are calibrated to
>13% that would explain why I get the best exposure when down
>rating the exposure index of the film 1/3 to 1/2 stop. That
>would compensate for the difference and give correctly
>exposed film. An interesting aside is get the proper
>response from my film scanner when I use ASA 320 instead of
>400, or 80 instead of 100, with the films I use. Which
>further leads me to suspect that the meters in my cameras
>are off about 1/3 stop.
>
>Does anyone have anything info to contradict the above?
>
>BTW, 12.5% would indicate that he manufactures are using ND
>filters to calibrate their meters from a reference standard
>light source.
>
>--Tom
>
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