I have been going on about this exercise in various forums and now have to write about it. I am going to give it my best shot but I am still not sure of the correct interpretation of the notes.
This exercise gives us a practical and empirical way to discover the dynamic range of our own cameras.
In order to do this we need a subject that itself covers the entire range of light from bright white to dark shadow. It is suggested that we place a piece of white card into the image to get the bright end of the scale but since I was shooting a white building it that was not required. Having shot the photograph, exposure reading were required from a few areas, in particular the lightest and darkest areas with a few in between.
My image is below:
The image has the exposure readings from my notes appended and it can be seen that from the brightest area, the white columns to the darkest area, a black window in hard shadow, there is a difference of 8 stops. Whilst the measurements I took may seem a bit random and it might have been easier sticking to one aperture and showing the change in speed it doesn’t invalidate the readings. I used a simple on-line calculator to input the various exposure settings and get the stop differences (rounded to the nearest whole number).
So from this example it would seem that the dynamic range of my camera is 8 stops… a little low for a high end SLR (Canon 5DII) so I must examine why. My thoughts are that although the building is a bright white it isn’t pure white and the stone is matt which will reduce its light reflecting quality; this would probably be worth 1 stop of light value. In addition, there weren’t any truly black areas as even a black window in shadow is going to receive reflected light from the surrounds and the shiny ground and this would be worth 1 more stop of light. In the dark areas I had no difficult in raising the brightness to examine the detail which makes me think that I wasn’t completely at the limits of the available dynamic range.