Tim - Perhaps I misunderstand, but you may be confusing apples and oranges.



With Photoshop, one can divide up the brightness range (from 0 to 100%) by many small increments. For example, by dividing 0 to 100 by 100, one can make a stepwedge with 100 steps. A well-profiled printer can print out that stepwedge, and faithfully represent each shade. Given an 8-bit image, 256 shades of grey can be deliniated. Each step is not, however, twice the brightness of the previous step.



With film or paper, once can also make a stepwedge with many steps. Again, each step will not represent twice the exposure of the previous step. For example, if you went into the darkroom and made a test strip where you gave each step a 1/2 second exposure from a weak light source, at a very small f-stop, at a great distance, you could easily make a step wedge with many steps. In fact, since paper and film are analog, you could theoretically make more steps than any instrument could detect.