U of S | Mailing List Archive | alt-photo-process-l | RE: pt/pd stops

RE: pt/pd stops

Bob wrote:

The acutance of my T-max and Tri-X images is much higher than with non pyro developers. But many things might account for our different findings. For pt/pd I dev to a D range of 2.7 to 2.9 and the same negs print very nicely at contrast 1 or maybe 1/2 in the extreme case. Of course, if you don't use vc papers, this is a moot point.
How are you measuring the negative DR? Do you know how much of the total actinic density is due to the stain and how much is due to the silver image? The latter is not so easy to determine without preparing three identical negatives, bleaching the silver image away in one, and bleaching the stain image away in another. If you have a six-channel densitometer (Status A or M plus I), you can get some idea by comparing the DR in the yellow channel with the DR in the blue channel. Or, you can measure the DR in the blue channel, bleach the stain, then measure DR again in the blue channel. Either gives at best a useful approximation because most non-UV densitometers have lamps that are not rich in UV, so they cannot accurately determine the actinic density of the stain.

Best regards,