Film test results

[Bill Burk]

Expose sheets of film for testing with a sensitometer and process each sheet for a different amount of time. Interpret the results in a similar manner as you would interpret the results of Zone System tests.

Compared to exposing film tests with a camera, using a sensitometer eliminates many possible causes of the unexpected results that we have discussed on this thread (lighting, shutter speeds, f/stop, bellows, lens, flare, meter, test card reflectance and spectral reflectivity), and gets you closer to revealing the characteristics of the film.

[Stephen Benskin]

How many people actually ask themselves what the testing conditions they read about mean and if they are even accurate? The exposure meter places everything at Zone V. Great, but what is Zone V? It can't be a point of density. Films have different shaped curves, and exposure meters are intended to work for negative and positive films. It must be an exposure. Exposure meters are designed to calculate an exposure of 8 / ISO = camera exposure in lux seconds. As the film speed is part of the exposure equation, there must be a relationship between the speed point (point where the film speed is determined) and the metered exposure point, generally referred to as H_g. For reversal film the speed equation is 10 / H_m.

Reversal film speed was once 8 / H_m. That is a change of 1/3 stop. This means that while the method of determining reversal film speeds remained the same, reversal film today is receiving 1/3 stop less light than in the past because the speed equation changed the ratio with the metered exposure point.

Black and white negative ISO film speed is calculated using 0.8 / H_m. That’s 10x or 1.0 logs smaller than the metered exposure of 8 / H_g. In comparison, Zone System testing has the speed point 4 stops below Zone V or 1.20 logs. That’s a difference of 0.20 log-H units.

What this means is that a film, developed to a given point, will produce a different film speed using the Zone System testing method than with the ISO testing method. Ever notice how ZS speeds are almost universally around ½ to 1 stop slower than ISO speeds? Without factoring in the 0.20 log-H difference, a direct comparison between the two speed methods isn’t realistic.

Not only should this bring into question the idea of the accuracy or importance of a "tested" personal film speed; but do to the known difference in exposure between the two methods, Zone System EI’s can pretty much be estimated without testing when developing in a general purpose developer.

Below is the graphed concept for a 125 speed film.

[ic-racer]

One could argue that in the world of B&W large format photography, safety factors in film speed ratings have little adverse consequence and great potential benefit. Especially when one can own perhaps a hundred shutters.

[Stephen Benskin]

One could argue that in the world of B&W large format photography, safety factors in film speed ratings have little adverse consequence and great potential benefit. Especially when one can own perhaps a hundred shutters.
[/ATTACH]

One could argue very successfully because it's true. My concern isn't about the need for greater precision. It's about obtaining a greater understanding of the material and avoiding a false sense of accuracy. What's the point of testing using incorrect theory and wrong scales. In addition Zone System testing yields little information for the effort compared to sensitometric testing.

[ic-racer]

Yes, very good points.

[Bill Burk]

How about presenting a scenario, at a level of detail comparable to the ZS process already described.

Your challenge got me thinking... this really CAN be simplified.

I took your suggestion of a mid-tone test, though I argue it's no good for speed tests. It's great for contrast tests.
With fresh film, I calibrate my sensitometer to the test results anyway.

So I am happy to take the speed as a KNOWN.

For fresh film in standard developer...

1) Make a two-sample "test strip" (take two shots of anything gray - one at meter recommended setting, and one as if bracketing, two stops over).
2) Develop the film for a length of time you wish to test.
3) Measure the density difference between the two resulting negatives, precision 0.1 is good enough, for example one Pentax Spotmeter V needle interval.
-Rule of thumb: A good target is a needle drop of one stop from one negative to the next for a two stop exposure difference. (I'd estimate that as 0.50 CI).

http://beefalobill.com/images/CallingYourShot-Trust.pdf

[Leigh]

Your challenge got me thinking... this really CAN be simplified.
I took your suggestion of a mid-tone test, though I argue it's no good for speed tests. It's great for contrast tests.

Very good, Bill. Looks like a straight-forward process that removes some media variability (i.e. toe shape).

Thank you very much.

- Leigh

[Bill Burk]

Thanks,

I want to add, since it was pointed out in another thread and it relates to ic-racer's chart in post #63.

I don't know if I can fit it into the poem without overcomplicating...

The speed on the box is what you get, for sure. But you choose your relationship with film speed for the quality you want.

In fact I use 2/3 stop less than box speed in many cases as that is MY preferred relationship with film speed.

I test and confirm the rated speed but I use a lower rating in practice.

[Stephen Benskin]

This is an example the ideal Zone System testing scenario using a three quadrant reproduction diagram. It's simply a more analytical and visual way to illustrate the process.

The quadrant in the lower right is the camera image. The subject has an illuminance range of 2.10 logs or 7 stops (Zone I to Zone XIII). The quadrant in the lower left is the film curve. Zone I exposure is placed at 0.10 over fb+f. Zone VIII falls at a density of 1.35 for a density range of 1.25. Exactly how it is described in The Negative.

The quadrant in the upper left is the paper curve. Here a problem arises. The negative density range (NDR) is too large to fit the paper’s log exposure range (LER). The paper has an LER of 1.05 which corresponds to a grade two paper. So instead of Zone I falling at 90% of D-max, it falls in the shoulder of the paper curve. The negative is too contrasty for a grade 2 paper. (Bill and Dale - no helping).

[Leigh]

The subject has an illuminance range of 2.10 logs or 7 stops (Zone I to Zone XIII).

Nice presentation, but a fundamental error.

A subject with a tonality range from ZI to ZIII is eight stops, not seven.
You count the number of zones, not the number of intervals between zones.

I would not expect to capture an eight-stop range on regular film with normal development
printed on #2 paper. That's exactly what your graph shows.

- Leigh