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?