personal film speed with tri-x and pyro w/ no color densitometer : LUSENET : Large format photography : One Thread

I'm about to run my first film test using Tri-x and pyro developer. I understand that I need a color densitometer to read the pyro stained neg. How can I read/measure the test negs to detrmine zone 1 density w/o a densitometer?

Help with all phases of the testing procedure will be greatly appreciated...Thanks!

-- Craig Uecker (, January 10, 2001


Only the density to blue-green light is important for B&W printing. You don't need a colour densitometer.
A normal densitometer can be used with, say, a 50 cyan filter under it, or you can do a visual comparison with a known density wedge, again viewing through a cyan filter.

-- Pete Andrews (, January 11, 2001.

Hi Craig:

Maybe I'm off base here, but it is my understanding that you have to test all the way through the print phase in order to establish a personal EI for a film/developer combo. There are additional variables intoduced in the printing of a negative. (enlarger bulb, paper, paper developer, lens contrast, etc.) A densitometer will quantify Zone I, but it won't really tell you how it looks in the final output (print).

Steve Simmons "Using the View Camera: A Creative Guide....." outlines the procedure in detail. You need a B&W darkroom. I guess if you don't have a darkroom, a densitometer reading is the next best substitute. I never went through this elaborate testing. Using the mfrs. EI and recommended time/temp in processing has almost always yielded an acceptable image. Good luck with your efforts. You should get great results because of your dilligence.

-- Joseph Wasko (, January 11, 2001.

In his "Te Book of Pyro" Gordon Hutchins provides a section on EI tests. I have found these to be excellent starting points for the establishment of a personal EI, but as others have said you must test to determine the normal processing time to print in your enlarger, in your darkroom, with your developer on your paper.

Good luck.


-- Michael J. Kravit (, January 11, 2001.

For my particular set of equipment and processes, when I use Tri-x and pyro, I found that I needed to cut the time recommended in the Hutchings book by about 25%. Try it and see.

-- Mark DeMulder (, January 11, 2001.

I am not sure that Pete Andrews is correct in saying that a black and white densitometer can be used to read pyro negatives if a cyan filter is used. Hutchings says: "Densitometers designed for black and white materials usually do not respond accurately to the greenish negative color even if an auxiliary blue filter is added." Of course Hutchings isn't Ansel and is therefore fallible :). But of course one would need a color densitometer to determine if the result is the same.

Just comparing pyro negatives with regular negatives of known density is probably not too accurate because of the color difference and the ease with which the eye can be tricked in such a situation.

You might try the following. Get a calibrated step wedge from Stouffer - about $15.00 if I recall. Then contact print the step wedge alongside the pyro test negatives. The exposure is not critical. You then seek the pyro contact which most matches the .1 density step on the step wedge contact print.

I haven't tried it because I have a color densitometer!

-- Alan Shapiro (, January 11, 2001.

Depends on the design of the densitometer. If it's a visual comparison type, there should be no problem. If it's an older selenium cell or PM type, again there should be no problem.
The big bugbear is Infrared. Many cheaper modern instruments don't filter Infrared efficiently, and use a sensor which has extended red sensitivity.
A fairly simple test for this problem is to put a piece of heat-absorbing glass from a slide projector under the densitometer. This glass has a light cyan tint, usually with a density that should measure around 0.25 to 0.3. If the reading is much higher, then your densitometer has an Infrared problem. Such an instrument won't even read neutral density gels correctly either, and you shouldn't use it for reading Pyro negs or chromogenic B&W film.
In fact, I'd go so far as to say you shouldn't use it, full stop.

-- Pete Andrews (, January 12, 2001.

Sorry, another afterthought. The step wedge printing method outlined above has a flaw. You're looking for a certain density in the negative above base+fog, not an absolute density value.
Your negative almost certainly won't have the same Dmin as the step wedge, and this will make a comparison between the absolute density of the wedge, and the relative density of the negative pretty difficult. The way round this is to sandwich the density tablet with the base+fog region of the negative to print it. Using a hard paper grade will make the comparison easier.

-- Pete Andrews (, January 12, 2001.

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