Quote Originally Posted by Donald Miller
Interesting dialogue on this subject. I also do not understand why one would measure the step wedge density in UV mode. The only time that this would appear to be a valid consideration would be when the step wedge exposure on film would be facilitated by UV light.

The step wedge density would seem to be valid when measured by the densitometer channel most closely approximating the spectral qualities of the light that would be exposing the step wedge onto film.

What am I missing here?
The purpose of the H&D curve you get by exposing the step wedge on film is to see how the image will print on paper. The film should be exposed by the light you expect to use when exposing actual photographs. The step tablet as developed on film is what the paper will see and so should be read by blue light for graded paper. VC paper can be a problem as it is sensitive to blue through yellow but gives different contrasts with blue than with yellow. I have not found a really good way to measure the printable density range of stained negatives so as to get a good working print on VC without test strips.