Itís a simple case of misinterpreting the data. The exposure range is smaller than the scene luminance range do to the effects of flare. We know that flare affects the shadows to a greater proportion than the highlights. Flare reduces the exposure range between the metered exposure and the shadow exposure. It shifts the shadow exposure toward the metered exposure.
But when testing for negative contrast, it is common to use the speed point as the base point to calculate the film gradient. In the example below, the film is processed to a CI 0.60 which is slightly higher than the standard model, but fits the ideal Zone System model (CI 0.595).
Zone NDR example.jpg
The difference between the two values for the negative density range of 1.06 and 1.27 is the difference in the range from the shadow to the highlight exposure. One uses a seven stop scene luminance range and the other a 7 1/3 stop scene luminance range to begin with, but factors in a 1 1/3 stop flare factor making for an exposure range of 1.80. (To simplify the comparison, you can also think of it as a 7 stop scene luminance range with one stop flare.)
The difference in ranges come from measuring different points on the same curve. But conceptually, one is recognizing the difference between the scene luminance range and the camera exposure range and one is not.
Last edited by Stephen Benskin; 01-21-2012 at 11:07 AM. Click to view previous post history.