This is super interesting to me, and thank you all for for the info, and it seems like I'm tapped in to the actual source here.... (I wish I had found this thread like 6 months ago)
I was working on my own way to log / graph / compare my film processes and it started pretty simply.
I had shared what I was working on with a couple of my nerdier photo friends, and a they had asked if it was possible to actually develop this into an app that they could use, and I've been working on it for the last few months.
So the app is called
ZoneLab, (currently in beta and available to test for free, but MacOS only for now) and in my initial digging for resources I hadn't seen the "Way Beyond Monochrome" methodology until yesterday. When I finally saw it and poked around the spreadsheet and the chapter on film testing, I realized I was close but missing some crucial nuances.
Full disclosure, I'm basing the EI on the Zone V grey card exposure, which i realize isn't the scientific way of doing it (based on the toe), and I'm also only using 11 steps (mostly because I primarily shoot medium format and i can get b+f then zones I-X on a single roll for testing).
While I've been getting some good results, after seeing this thread yesterday, I've made some changes.
How ZoneLab used to work (prior to me reading this thread)
I was calculating EI using a fixed number: 0.3 density units per stop of exposure. So if someone's Zone V grey card came out at 0.80D instead of the expected 0.72D, I'd calculate:
Density difference: 0.80 - 0.72 = 0.08D
Stops = 0.08 / 0.3 = 0.267 stops
Effective ISO = Metered ISO × 2^0.267
The problem that I saw after seeing this thread was t hat 0.3 factor only holds true for "normal" contrast films. It kind of ignores that a high-contrast combination like TMax in Rodinal behaves differently than, say, HP5 in dilute D-76.
How it works now:
Now I calculate the actual gradient for each film/developer combination by measuring the slope over the working range (Zones II-VIII), just like the spreadsheet does:
Gradient = (Density at Zone VIII - Density at Zone II) / 1.8 log H
Then I use that gradient to adjust the density-per-stop factor:
Density per stop = 0.3 × (actual gradient / 0.57)
Where 0.57 is your "normal" gradient target. So for that same Zone V reading with a high-contrast film showing gradient of 0.68:
Adjusted density per stop = 0.3 × (0.68 / 0.57) = 0.358D
Stops = 0.08 / 0.358 = 0.224 stops
Effective ISO = Metered ISO × 2^0.224
The difference might seem small (EI 117 vs 120 in this example), but it should be accurate to that specific film's actual behavior rather than assuming everyone's film responds identically.
Would love to hear some thoughts especially if I've misunderstood anything from the spreadsheet or the book.
My goal is to make this methodology accessible to photographers who want to have a better understanding of how their particular film / development processes affect their film characteristics, but don't want to be data scientists as a side job.
I just updated all of my current math and methods on the user guide portion of the web site:
https://www.zonelab.app/guide.html#understanding-results
and I've added "Way Beyond Monochrome" as a source (just below the "understanding results" section) to give credit where credit is due. If you have a specific link to your book that you'd prefer I use, please let me know.
