The obvious has just occurred to me. (I think).
to answer your straight question:
Of course it will render a Kodak 18% grey card as K50%. It would render a 70% grey card as K50%. And it would render a 20% grey card as K50%. Regardless of orientation of the card.Why does a digital camera record a Kodak Gray Card (Zone V) as 50% gray?
There is a light meter in the camera and, as we all know, camera light meters give enough exposure to render what ever they are looking at as a mid grey. If that always turns out to be K50% then that is correct. The camera does not know what reflectance or colour your grey card is.
And by the way, an 18% reflectance card is only approx 2.5 stops less than 100% reflectance and therefore on a 10 stop scale it is between zone VII and VIII. Only on a 5 stop scale is it the midpoint.
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