# Thread: Plotting Film Speed test

1. ## Plotting Film Speed test

After running a film speed and zone test how do I plot the results. I have acess to a densitometer. Do you have to convert your expousures to LOG? Any suggestions about a good but simple book on Doing your own d/ logE Curves? I am new to large format photography. Shooting with a Burke & James press camera. Thanks> kenn

2. ## Plotting Film Speed test

Kenn,

Use regular graph paper. Scale the vertical axis in units of 0.10 density and the horizontal axis in full Zone units of exposure (i.e., 0, I, II, III, etc.). On the graph, the vertical distance of 0.30 density units should equal the same physical horizontal distance of one Zone. In other words, scale the graph physically so that one stop (zone) of exposure equals 0.30 density units, two stops equals 0.60 density, etc., and a line at a 45-degree angle originating at (Zone 0, 0.0 density) would go through the intersection points (Zone I, 0.30), (Zone II, 0.60), etc. Hope that is clear.

3. ## Plotting Film Speed test

Kenn,

Oops. I forgot to answer another part of your question.

Plot your density values from the densitometer against the respective zone exposures you gave the film. I have an old X-rite (301?) densitometer that I can set to automatically subtract the film-base + fog density values so I end up plotting zone exposure against NET density (although you could also plot exposure against the full density of the image + fbf as many people do).

As an example, a typical Zone I exposure might have a gross densitometer reading of 0.31. If the filmbase-fog density is 0.21, the NET density is 0.10 for zone I and is plotted at the point (Zone I exposure, 0.10 net density). Net densities for the next few zones might work out to be: (Zone II exposure, 0.21 net density); (Zone III exposure, 0.35 net density); (Zone IV exposure, 0.50 net density); (Zone V exposure, 0.70 net density); (Zone VI exposure, 0.90 net density) and so on where the beginning of the graphed line in the shadow zones has a very flat slope with a steeper slope for the middle values and a flattening again in the high values.

If you were plotting the full density values instead of net densities, the graphline would go through the following points instead: (Zone 0, 0.21); (Zone I, 0.31); (Zone II, 0.42); (Zone III, 0.56); (Zone IV, 0.71); (Zone V, 0.91); (Zone VI, 1.01); and so on. However, I think it much simpler to just plot the net density values, especially if you are trying to figure out other measures such as contrast index.

4. ## Plotting Film Speed test

Get "Beyond the Zone System" by Phil Davis. It will answer many of your questions in this regard.

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