Zone System Testing When Using Pyro : LUSENET : Large format photography : One Thread

When you're using PMK pyro and doing zone system tests, it's my understanding that the densitometer readings are taken with the blue filter in place (i.e. you need a color densitometer). Fortunately, I have a color densitometer. However, I'm not clear on exactly what the blue filter accomplishes. Is it supposed to "read through" the pyro stain, so that in theory at least the numbers you get with pyro would approximate the numbers you would get with a normal developer? I ask the question in part because as I've started doing the tests, I've gotten very high base plus fog numbers with devleopment times of 8 minutes or more, much higher than the numbers I got with times of 4 minutes and 5 1/2 minutes (I use Phil Davis' testing system, not "traditional" zone system methods). This despite taking the readings with the blue filter in place on my Macbeth color densitometer. I realize that base plus fog increases to some extent as development times increase but the difference here is much greater than anything I've seen using developers other than pyro. Since there is no exposure given to the base plus fog area of the film, I can only assume that the increase is caused by the increased staining as the development times increase but I thought the blue filter was supposed to more or less allow the staining to be ignored. If it does, then why is the base plus fog increasing so much?

As an aside, the color wheel on my densitometer has two sides with identical colors on each side. The only difference is that on one side the letter "A" is next to the three colors. The instructions don't say anything about what the letter "A" stands for or what the difference is between the two sides of the color wheel. Does anyone happen to know?

-- Brian Ellis (, April 29, 2001



I know nothing about PYRO development. wish I did. But i do know about densitometers. Most color densitiometers have two status channels. Status channel M is for color negatives, and status channel A is for transparencies.


-- Kevin Kolosky (, April 29, 2001.

Brian, The reason you use blue with pyro readings is because the stain will block the blue light. Since the stain makes up part of the image, using the blue filter will allow you to read both the stain and silver combo on the neg.

Although I've never had that much base fog. Is your developer fresh? I've always gotten a clear base on all negs, even on N+ situation (FP4, TMAX, HP5). One thing that you will notice is the reduced speed that you;ll get from PMK.

-- Dave Anton (, April 29, 2001.

Maybe your increased fog density is caused by aerial oxidation of the pyro due to the longer development time. You could try a test changing to fresh developer at 1/2 the time and seeing if the fog is reduced.

-- Chuck (, April 29, 2001.

The blue filter does measure the stain as well as silver density. You then ideally correct the reading you get using a table, such as that provided in Dick Arentz's Platinum Book, and I think in various articles that have come out on the subject.

The amt of base plus fog you get with Pyro is very dependent on the film. It does increase with longer dev times, and is particularly notorious for doing so with HP5+. This can become a prob with processes/light sources which are blocked by the pyro stain, such as UV/Platinum. The main issue I think is that you just get very long printing times, which is one reason why a lot of people using pyro for Pt/Pd go with Tri-X or FP4+ over HP5+. Are you using HP5+ by any chance?

Hope this helps.


-- Nathan Congdon (, April 29, 2001.

Thanks to all who responded. I should have mentioned that the film is indeed HP5+.

-- Brian Ellis (, April 29, 2001.

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