Sandy King (sanking@hubcap.clemson.edu)
Sun, 24 Jan 1999 10:26:14 -0400
My measurements are certainly accurate within reasonable tolerances and the
Densitometer is calibrated to a step tablet of known values. As is
customary when measuring negatives stained in Pyro I use the blue channel
of the Densitometer to measure the stain + silver, the B&W to measure just
the silver.
>From a previous response to Liam, which I just posted to the list, you will
understand that although both our experiments involved re-development in
Pyro we were in fact using two very different kinds of negatives. He used
conventional negatives, bleached them, then re-developed in Pyro. As Liam
notes, this process has the potential to use all of the developable silver
plus stain, thereby giving the possibility of increasing contrast over the
original. I believe that the reversal negatives which I used, because they
were already bleached and re-developed before to create reversal
processing, have more limited amounts of re-developable silver. I don't
understand the theory of this but my tests indicate it is so. So, it is not
really fair to compare the results because we are really talking apples and
oranges.
Sandy King
>I'm following with great interest this thread about Pyro and density
>measurements. How accurate are the readings? Is your densitometer
>calibrated? How sure are you about your measurements? I've had three
>different readings in three different densitometers, all calibrated as per
>manufacturer. With Pyro I just run tests based on trial and error.
>Sometimes measurements can be misleading. Films and developers can be
>changed by the manufacturers, by storage and a myriad of reasons.
>shutters can be more unreliable than the whole processing chain involved
>for making a print. I've spent high bucks on gizmos for film , paper and
>development apparatus. The only one that paid for itself was a shutter
>tester.
>Jacques
This archive was generated by hypermail 2.0b3 on Sat Nov 06 1999 - 10:06:44