My Nikon D70 and D200 comply closely to the ISO standard. Here is an experiment with the D70. I took a Kodak 18% gray card and Q14 target and placed them on a background. Since the ISO standard for light meters pegged to 12% reflectance, rather then 18%, I took an exposure reading from the gray card and gave 1/2 stop more exposure than indicated. The gray was rendered at about 118 in aRGB and the steps in the Q14 target were more or less as they should be. I used the default ACR tone curve
FYI
I have been given a gray card shot RAW from a Nikon D200 and after gamma 2.2 conversion yields a gray level of
86. With +0.5EV exposure correction the gray level raises up to
103.
The D200 seems to have ~3 stops of overexposure safety margin before starting to blow the metered area:
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D200 gray card linear histogram[/span]