“Set your camera to any of the auto or semi-auto modes. Photograph a dark tone (such as a black jacket), a mid-tone (the inside of a cereal packet traditionally makes a useful ‘grey card’) and a light tone (such as a sheet of white paper), making sure that the tone fills the viewfinder frame (it’s not necessary to focus). Add the shots to your learning log with quick sketches of the histograms and your observations.”
White Card
Grey Card
Black Dress
The auto metering on even today camera is confused by the 3 images and try to make them all grey.
by switching to manual mode and using the histogram we can get the true shades:
White Card
Grey Card
Black Dress
What we have to remember is no matter how complex the metering in our modern camera it just sees the scene as 18% grey and adjusts for that. In most situations it gives a good result but extremes like above illustrate the problems.