Finding semi accurate Dichro enlarger filtering

[Bruce Osgood]

Finding semi accurate Dichro enlarger filtering

I set out yesterday with an Ilford EM 10 meter, Stoffer 21 ½-step 4X5 Step Tablet and Chromega Dichro head to establish filter values of this enlargers filtering system.

My premise was I could project the Stoffer negative with NO filtration at f-16 (mid point of my Componon S 150mm lens) onto the base board from an 11X14 elevation and with the EM 10, measure the light for each step. Then remove the Stoffer and duplicate each EM 10 measure by dialing in filtration until the measured amount was met. This would give me 21 half steps of filtration that would equal the Stoffer densities.

The exercise was a failure and I don’t know why.

What I did learn was the EM 10 could not read beyond Stoffer step 8 at f-16 at “High” brightness. I could open the lens two stops and continue but that seemed like introducing a variable that I would not like to include in my printing routine. Secondly, for the values I got from steps 1-8, when transferred into Chromega filters the Yellow (45) matched the Stoffer 1 while Stoffer 2,3, were matched at Magenta 45, 80 and Stoffer 4 was met M-24 by opening to f-11.

Can someone tell me why the premise is flawed? Or am I mixing apples with oranges again?

[Nick Zentena]

I'm not sure what you're looking for.

Anchell's book on variable contrast printing includes a section on figuring out contrast grades. Basically you print the tablet and count the number of non pure black or pure white steps. The numbers compared tot he chart give you contrast grades. At least that's what I remember.

[Donald Miller]

Bruce,

It would seem to me that you are mixing reflective and tranmissive density readings.

What may work best is to expose the Stouffer tablet to each of the contrast grades that you choose and then having the resulting prints read on a transmission densitometer you will have a clear picture of the exposure scale of the paper at that contrast grade.

I would be happy to read the densities for you if that would help you. PM me if I can help.

[Bruce Osgood]

I'm not sure what you're looking for.

Yea, I know, sometimes I wonder that myself. What I thought I could accomplish was to establish filter grades for my particular enlargers' filter glass and not accept what the papers' manufacturer says is a grade 2, but actually prove my grade 2.

Bruce,

It would seem to me that you are mixing reflective and tranmissive density readings.

What may work best is to expose the Stouffer tablet to each of the contrast grades that you choose and then having the resulting prints read on a transmission densitometer you will have a clear picture of the exposure scale of the paper at that contrast grade.

I would be happy to read the densities for you if that would help you.

This is an offer I can not refuse...
I'll PM you for further instructions, Thanks very much

[Bob F.]

Paul Butzi has a method here (http://www.butzi.net/articles/vcce.htm) for finding the contrast grades with a step wedge and EM10 that may be useful. I've not tried it.

Cheers, Bob.