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

RE: pt/pd stops

	I just measure the blue density (blocking of blue light).  I know
that it is only an estimate of the density to UV but it is sufficient for my
PD/PT printing.

-----Original Message-----
From: etienne garbaux [mailto:photographeur@nerdshack.com] 
Sent: Tuesday, April 14, 2009 9:48 PM
To: alt-photo-process-l@usask.ca
Subject: 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,


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