Yes I did see the big long discussion and I'll have to go back and have another look at it. However I recall concluding from that discussion that I needed a flashmeter reading of about f/16 at the film-plane to make a test and that doesn't match BTZS recommendations.

My "sensitometer" is a flash bounced off the ceiling, exposing some film through a Stouffer wedge. I can put the flashmeter where the film will go and therefore measure the net flux though it will be in f-number units instead of lux-s. The aim of course is to adjust the flash power so that I get an exposure through my step wedge where I KNOW the H value for each step.

For example, say the formula I posted above was correct (it or my interpretation of it is quite possibly not):
Ef/Es = 0.18 / N^2
For example with an f/1 lens, that gives Ef/Es = -2.47 stops. Or at f/8, Ef/Es = -8.47 stops, etc.

Now I can hypothetically say that if I metered at an 18%-grey subject (filling entire field of view) and metered again at the film plane with an ideal f/1 lens, the reading at the film plane will be 2.5 stops lower. With my objective's aperture matching the Es reading, I can expect Zone V on a normally-developed film. Therefore I know that the flashmeter reading at the film will be 2.5 stops lower than f/1 to achieve Zone V when there is no step-wedge present.

Now the step-wedge (Stouffer 21-step, 0 to 10 stops): I want the densest step (D=3.01; 10 stops) to be 5 stops below Zone V and the thinnest to be 5 stops above it, so I need an additional 5 stops of exposure. Therefore, if my flashmeter reads f/2+0.5 at the film-plane, I suspect that I should get an appropriate exposure spanning the useful part of the film's HD curve.

In comparison, the BTZS book (4ed, page 71) says to expose for 0.4s in EV4 light metered at the film-under-test. It doesn't say what the expected wedge densities are or whether there's a correction factor in there for enlarger warmup/cooldown and/or spectral issues. Assuming perfect reciprocity though, I think that's equivalent to a flash meter reading of f/2+0.67, which means my guess is remarkably close to the exposure that Davis recommends for film-testing.

As a backup, I have purchased a roll of Delta 100 for the explicit purpose of having a fairly-widely-agreed-to-really-be-ISO100 physical reference with good QC.


PS I'm not seeing a formula in your post, just a list of variables... and u should cancel out entirely unless you want to include bellows factor for being focused at u. Which I don't.