From: Sandy King (sanking@CLEMSON.EDU)
Date: 08/19/03-11:17:50 AM Z
Arie,
I don't know any way to filter a Visual reading densitometer to read
UV stain. If the sensor cell has sufficient sensitivity to UV light
you might be able to filter the light with an actinic color filter to
approximate a UV reading (brownish/orange for example) but I think it
would be pretty complicated to calibrate the reading.
Even a reading from a color densitometer in blue channel can be
tricky to apply to a UV sensitive process. In addition to the fact
that the amount of stain is dependant on film type, it is also
dependant on the staining developer being used. For example, there is
much more actinic filtration with the brown stain of pyrocatechin
developers such as Pyrocat-HD and Diaxactol than with the typical
greenish stain of pyrogallol developers like PMK, ABC Pyro and Rollo
Pyro.
The best way to evaluate printing density of a stained negative with
a UV process is by the step tablet method described by Clay. A
densitometer that reads UV light will also give a very accurate
indicator of the actual printing density of a UV sensitive process
but such densitometers, although not rare, are much less common than
those with Visual and RGB color reading capability.
Sandy
>Arie:
>
>Phillipe's guidelines sound about right. But if you want some more
>accurate information for your particular situation, the simplest and
>most foolproof test, IMO, is to contact print the film you are using
>with a Stouffer's step wedge using the BTZS procedure. Briefly, that
>is a known quantity of light for 0.4 seconds (under the reciprocity
>wire). This exposure can be done for you by anyone with an enlarger
>with a light integrator/timer affair. Or you can have it done for
>you by The View Camera Store in Phoenix. Anyway, take this exposed
>film test and develop it normally in your staining developer.
>Measure the all-channel white light densities of each step with your
>transmission densitometer. Now contact print this new, stained wedge
>with the whatever process you are using for a 'standard' time that
>will leave at least 3 or 4 of the steps completely black, and a few
>completely white. Measure the reflection densities of your print
>test. If you now plot the reflective densities of the print (Y-axis)
>versus the transmission densities of your stained test
>wedge(X-axis),you will have your very own film/paper curve that will
>tell you exactly what the target density range of your negative
>should be, without having to resort to UV densitometers or anything
>like that.
>
>I like this approach because everything is tuned to your own
>variables, from negative development to the light used for your
>printing, and makes no assumptions about light source wavelength,
>print process UV sensitivity or anything else.
>
>As Phillipe pointed out, each film is likely to have a different
>amount of staining for a given silver density, so you would want to
>be careful about extrapolating your results to other films without
>an independent test. This is much less hassle than you would think.
>
>Clay
>
>
>On Tuesday, August 19, 2003, at 05:47 AM, Monnoyer Philippe wrote:
>
>>Hello Arie,
>>
>>I don't have my charts at hand, but I can tell you that a density
>>of around 2.4 measured in blue (do you have a color head with your
>>densitometer ?) on a pyro neg (FP4+) is as dense as a 3.2 non pyro
>>step. In other words, a 2.4 (blue density) pyro neg will print as a
>>3.2 (normal white light) unstained neg (for FP4+). The stain is
>>very dependant on the film you use. For example, AGFA films hardly
>>stain, ilford FP4+ and PANF are staining strongly.
>>I have more detailed info. Yo can contact me offlist later.
>>
>>Philippe
>>
>>-----Original Message-----
>>From: Arie [mailto:ariek@pacbell.net]
>>Sent: Tuesday, August 19, 2003 05:07
>>To: alt-photo-process-l@skyway.usask.ca
>>Subject: densitometer and pyro
>>
>>
>>Hi
>>I was wondering if someone could give me some hints. I have a B&W
>>densitometer but I process my negs in PMK. Is there a way I could trick the
>>densitometer into giving me at least a ball park reading? such as a filter.
>>If so which one, or can I use a rosco lighting gel? The other option that I
>>figure is, has anyone calculated a factor that I can multiply my readings
>>by? By the way the densitometer is a Tobias TBX
>>Thanks
>>Arie
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