Quote Originally Posted by AndreasT View Post
I have been trying to make a mental picture about the Delta-X Criterion. Where I agree is that when pushing to expand contrast keeping the speed near the normal EI one moves up on the curve which results in a steeper gradient (one could shorten the development as a result) and one gets away from the toe.
What bothers me is when pulling. Looking at curves left of the 0.1 speed point the curve has largely the same shape as right of the speed point. So shortining the exposure would work out mathematically.
But in my point of view in the shadows we have dark places next to light places, in the dark places we have even more dark places which I feel may have too thin a density.
Andreas, you are drawing conclusions based only on assumptions. Jones' tests proved that quality isn't defined by a set minimum shadow gradient, but that the minimum shadow gradient is linked to the average gradient. It's a question of perception. While the shadows might be flatter, their appearance is related to the average gradient. Of course, personal taste will play a factor.

Don't forget that with extended development while the shadow gradient is increased, so is the overall gradient and with the Delta-X Criterion, the relationship remains the same. Also, the fractional gradient speed point defines the minimum useful gradient, not where to place the exposure.

The Delta-X Criterion will produce identical film speeds for a delta D = 0.80 as will the ISO method even though the speed point is approximately a stop below the ISO's 0.10 fixed density.