On 6 Dec 1998 16:52:40 GMT, hybwolf@aol.com (Hybwolf) wrote:

>How come I am getting a shutter speed of 1/640 with a gray card reading and
>1/120 with a reading from green grass? I thought grass was a good estimate for
>18% reflectance. I didn't expect the readings to be identical,but thats a big
>difference.
>I used a 50mm lens and camera was in spot metering mode. There was overcast
>conditions when I took the reading. I placed the card on the grass in a way
>that there where no shadows ,hot spots, or shiny areas on the card. I focused
>on the grass and left it there during my readings.The camera was in aperture
>priority with f/2.8 set. What would cause such a big difference?

First, a correct orientation of the grey card would be with it aimed
directly back toward the camera. If pointed up, it would expect it
may be lighter in tone than middle grey... Second, average green grass
is about 2/3-1 stop darker than middle grey, in my experience. The
two together may account for the 2+ stop difference you found - and
meter color response error could add-to/subtract-from the measured
difference.