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luxikon
10-Oct-2012, 05:12
I exposed a Fomapan 100 together with the Stouffer TP 4x5 transmission step wedge and developed.
To determine the gamma of my negative I measured the densities of the steps with a densitometer.
Now I wonder how I can translate the 31 steps of the wedge into re. log E values.
Who helps?

Klaus

Drew Wiley
10-Oct-2012, 08:12
You need to get this read on a transmission densitometer. Maybe someone in your area
or a local lab has one. But used units can often be purchased reasonably.

Stephen Benskin
10-Oct-2012, 17:45
Finding log-H
log((1 / antilog Step tablet density) * Illuminance) = log of transmitted light or log-H

Finding Transmitted Light
Take the speed you have assigned to the film and plug it into:
0.80 / film speed = transmitted light necessary to create the 0.10 over Fb+f density
example 0.80 / 125 = 0.0064 mcs

Finding the Incident Light
Incident light = transmitted light / transmittance
Find the step tablet density that created a film density of 0.10 over film base plus fog
Take that step tablet density along with the transmitted light value and plug it into the equation:

Incident light = transmitted light / transmittance
example: 0.0064 / (1/10^2.75) = 3.6 mcs (lxs)

Use the incident light value with the first equation to find the transmitted light or log-H for each step of the tablet.