Film sensitometry for the zone system in an app?

[Evan_Mathis]

Howdy all, I'm new. But I've been shooting film for a very long time. Over the last few months I've been trying to get my process a lot tighter, and to figure out how I can have a better system to log / catalog the various processes / film / developer combinations and what the tangible effects are. As a started playing with it, I shared some screen shots with other film nerds and folks began to ask if I' consider actually making my tool into an app. So, I built a macOS tool to organize densitometry data and make comparisons easier and more consistent and now I'm sharing it with some other folks that might find it useful

The app is called ZoneLab and is currently in public beta.

It’s designed around traditional zone / step-wedge testing: recording density values, calculating effective ISO, gamma / CI, tonal range, and exposure latitude, and allowing direct comparison of multiple tests on the same graph. This has been especially useful when evaluating development time, dilution, or film batch differences.

There’s also a simplified ISO-only mode for quicker EI checks.
Tests can be entered manually or via a USB densitometer (Printalyzer is currently supported), and all data is stored locally. CSV import/export is included for long-term record keeping or independent analysis.
I'm looking to add additional densitmeter integrations and curious what folks are using if they have USB / Serial connection capabilities.

Hopefully this is an easy entry point for folks getting into the Zone System and / or sensitometry, and was designed to reduce friction in the measurement and evaluation side of the workflow. If you’re already doing your own testing and care about repeatability, it may be of interest.

You can get the app free here: https://zonelab.app

I'm curious if this is useful for this community? I'm happy to answer any questions.

 

[koraks]

I'm not a Mac user and I do very little with sensitometry, but the screenshot looks really nice! Also, I'd like to thank you for highlighting this to the community and taking the time to register an account to do so. Welcome aboard!

 

[Sirius Glass]

Welcome to Photrio!

 

[Evan_Mathis]

Thanks! i was looking for places where folks might find a use for what i've built, looks like i found it!
for those curious to see the methods and math (and madness) behind the app, it's all here: https://zonelab.app/guide.html

 

[spookyphoto]

How are you digitally calculating C.I. ?

 

[Evan_Mathis]

I've got all of my methodology documented in the user guide, but this is the math that i'm using based on the densitometer inputs.
Now I could be totally off base, and this is why I'm willing to put myself out here to find out the holes in my theory, but
my CI formula is based on Kodak's official sensitometry workbook plus the foundations of the Zone System (1 stop = 0.30 log H). The 2.10 divisor is derived from 7 zones × 0.30 log H per zone.

CI = (Density at Zone IX - Density at Zone II) / (Log Exposure Range)

Where:
- Log Exposure Range = 7 zones × 0.30 log H = 2.10 log H
- Each zone = 1 stop = 0.30 log H units

Simplified formula:
CI = (D_IX - D_II) / 2.10

Curious to hear if what I'm thinking here is correct.

 

[spookyphoto]

Evan - What I did was to first input all 21 film densities along with the exposure values at each step. Then I run a numerical data smoother (3RSSH) over the data to remove any flyers. Then I run a spline function over the data and interpolate the curve in .01 log H increments. I now have both density and Log H values in .01 log H increments plus the 1st derivitive at each point. From here I can do almost anything.

Dmin
Dmax
log H at .1 above Dmin
Gamma
Fractional gradient point (Jone's point)
Delta X
Vertex ratio
C.I.
Av. Gradient
Etc.
The values that need to actually be calculated from the data are C.I., fractional point, vertex ratio, and delta X which we need to locate the fractional gradient point

I'l write more in a while

 

[Evan_Mathis]

That's definitely more thorough than what my app does!

But, the goal of my app is to give a more advanced film users a way to log, chart and compare their different processes and what effects changes to those processes have on their film characteristics using a 10 exposure step of films they use. I do plan on adding a print / paper component that can go deeper by using a calibrated step wedge, but for now I want this to be a bit simpler using the Zone system* for folks to be able to understand what the effects of different combos of film, developer and dev process have... not necessarily to be a definitive scientific record, and I've had to adjust some of my language away from things like effective ISO to EI to make sure I'm not giving people the wrong impression.

*(I know even trying to suggest that Zone System is some sort of standard will make some people upset, but it's universal enough that it has good math backing it up and is simple enough for non-scientific folks to understand)