I want to read pyro negatives with my B+W densitometer. I hear I am supposed to use the blue channel of a color densitometer for this, but I am not about to buy one of those. Can I use a blue gel filter sandwiched with the negative to simulate the blue channel?

-- William Marderness (wmarderness@hotmail.com), April 05, 2000

Answers

William,

Probably not. Use of the blue filter or blue channel assumes a balanced color response from the receptor cell, and there's no reason to assume this is true of a b&w densitometer. The simplest way to check is probably to print a picture and step-tablet together, using the picture to see what makes a good print, and the step tablet to tell what range of values is being printed.---Carl

-- Carl Weese (cweese@earthlink.net), April 06, 2000.

I agree with Carl. I found that the actual printing contrast is between the ordinary density reading and the blue-channel reading, a little less than halfway. Best to just make some test prints.

-- John Hicks (jbh@magicnet.net), April 06, 2000.

Even filtered, a densitometer may give misleading results. A densitometer for photographic purposes usually gives a diffuse density reading, because a lot of the density in the "toe" of a normally developed film is due to scattering by the film grain. The stain or dye generated in pyro doesn't contribute much to this scattering effect, and so the printing density may be significantly different from the densitometer reading.

-- Pete Andrews (p.l.andrews@bham.ac.uk), April 07, 2000.

There is one idea I have not tried, but which might work. There is a method for measuring density which involved making prints of test negatives and matchin gray areas. Since it works with actual prints, it should work with pyro or other staining developers. The method was described in a recent issue of one of the photo magazines. I do not have the reference in front of me, but there is a link to it in my website www.vsta.com/~alrob.

Al Robinson

-- Al Robinson (alrob@vsta.com), November 22, 2000.