From: Sandy King (sanking@clemson.edu)
Date: 10/13/02-08:34:08 AM Z
Hi Shannon,
As you can see, the film and paper tests are two different beasts.
First, about the film, as I understand your story. For the film tests
five sheets of TRI-X film were given the same exposure by View Camera
Store. They returned the film to you and you developed the sheets and
returned them to VCS. VCS read the densities of the five different
step wedges and plotted the densities. They then ran curves from the
data with the Plotter program and printed out the results. What you
appear to have received from VCS is a package of printout for TRI-X
which will show the following.
1) a family of curves for the different times of development,
2) a SBR chart which shows the time of development needed for a
subject brightness range from perhaps a high of 10 or 11 to a low of
5. This is for use with the incident metering system.
3) a chart showing CI, also called G or average gradient, for the
different times of development.
4) A chart showing time of development needed for different N
development, typically from N-3 to N+1
5) A special printout of a curve for each of the five times of
development.On the right hand side of the chart, on the Y axis, you
will see the figures for base + fog (b+f), IDmin (ideal minimum
density), DR (density range) and IDmax (ideal maximum density). At
bottom of the chart, on the X axis). The information on the bottom of
the chart relates to effective film speed. Notice the point on the
curve that corresponds to IDmin. That point shifts to the left with
the increase in speed which is typical of longer development times.
6) When the negative curves were produced by the Plotter program it
was assumed that your printing process has either an exposure scale
of 1.24 (silver=Ilford) printing) or 1.38 (AZO printing).In other
words, you have two separate print outs of the TRI-X tests, one for
silver printing with conventional materials, the other for printing
with AZO.
From the paper curves the only thing of real importance at this point
is the ES, or the Exposure Scale, which you will see in log values at
the bottom of paper chart. Basically, when you develop your film you
need to develop long enough to get a negative DR that matches the ES
of the paper, assuming you want a print with a full range of tones.
So, assuming that you want to make a silver (=Ilford) print of a
scene with normal subject brightness range of 7, find the time of
development from the TRI-X tests that were plotted to give a DR of
1.24 that shows a SBR of 7. You do the same thing for scenes of
higher or lower SBR. For example, a very flat scene would probably
have a SBR of 5-6.
You do the same for the set of TRI-X curves that were plotted for AZO
(ES=1.38). If you compare the curves for silver and AZO you will see
that for the same SBR you will need to develop the TRI-X longer for
AZO than for silver (Ilford).
To repeat, in determining time of development, assuming you want a
print with a full range of tones, you need to match the DR of the
negative to the ES of the paper.
If you have available a copy of Davis' book spend a few hours
reviewing what he writes about sensitometry. Your curves will have a
lot more meaning to you if you understand some of the basic terms.
Sandy King
>Hi, thanks for writing back.
>
>Yes, it is the view camera store service. I sent four kinds of
>paper--Ilford, Azo, cyanotype on Crane's and cyanotype on Arches. Also,
>they exposed five sheets of tri x for me and I developed it for different
>times as per their instructions, in tubes, in D76 1:1. I got back a huge
>package of printouts the other day, but I'm having trouble interpreting
>them. There was one bundle that seemed to be just about the film itself.
>There are five curves on this chart, and each one has an ISO and a
>development time and an SBR. On this chart it says, "paper ES = 1.24."
>This is about what Ilford is. So I assume that these curves apply if you
>are shooting for Ilford paper. But, weirdly, the page of film curves for
>Ilford paper is actually a little different. So I don't know what that
>other page refers to.
>
>For Azo, there is another family of curves geared to the azo paper's ES of
>1.38. These curves are labelled with times in minutes and SBRs, but the
>ISO is left blank for each curve. Same for the cyanotype print outs. So
>I called Fred Newman and asked him what speed to shoot for the azo paper,
>and he said that all the papers worked out to have about the same ISOs. I
>guess that's why he didn't put the ISOs on the other curves. He says to
>shoot for all papers at ISOs between about 250 and 320, for SBRs of 4.4 to
>7.4, in the case of Azo paper. (To find out what the curves are for
>higher SBRs, it seems I am going to have to do another film test at a
>dilution of 1:2 for D76 instead of 1:1 as I did for this test.) Does this
>sound right to you? I was sort of surprised that there was that much
>uniformity for four different papers.
>
>--shannon
>
>
>> Shannon,
>>
>> I will be happy to try to answer any questions you have about the film
>> tests. From what you write I understand that may have had film tested
>> by the View Camera Store. If so, I am familiar with the method of
>> testing since it is the one described by Phil Davis in Beyond the Zone
>> System and it is a good system for calibrating film speed and contrast
>> to your printing process.
>>
>> Sandy King
>>
>>
>>
>>
>>>I have a question about paper and film testing that I'd like to discuss
>>> with somebody knowledgeable about these matters, off the list, because
>>> it involves the services of a business that does this. I had a paper
>>> and film test done and I'm not sure how to interpret the results that I
>>> got back. The company sent me five sheets of film that had been
>>> exposed with a stouffer step tablet, and I processed them at different
>>> times, and sent them back with paper samples that had also had a
>>> stouffer step tablet printed on them. The idea was to figure out what
>>> the right film speeds and development times were for different papers
>>> and subject brightness ranges. I think Sandy was discussing his own
>>> tests of this sort this past summer.
>>>
>>>--shannon
>>
>>
>> --
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