Something that I have been planning to do for a long time, is to do some proper testing of the films that I most often use. And now recently I got gifted even more Neopan 400, which means I have over 60 rolls in the freezer, all that are slightly expired. The results that I have been getting from them are great, box speed, no problem. For most of my photography it doesn’t matter if I’m half a stop underexposed or whatever, but sometimes I really want to nail the exposure and make sure that my development regime puts my highlights exactly where I want for easier darkroom printing.
This is where zone system film testing comes in. There are some variations on how to do this, but the one that I like and feels logical to me is the method described by John Finch in these videos here:
Film speed test
Developing time test
The short version of how this works and what we are actually testing
The zone system splits the grayscale from maximum black to maximum white into 10 pieces. Zone 0 is as black as it can get and X is as white as it can get. You could see the exposure as setting the black point, and where do you want to put your black point? Well, just above where you are getting some detail. That would be zone I. So you take a light meter reading (which gives you Zone V) and take test exposures, 4 stops below at various EI (ISO) settings. Then you develop the film, and go into the darkroom, take a note of the time needed to get maximum black on your paper (to account for fog plus base), and then do a test of this frame where you should have zone I with that paper exposure time. If it is slightly lighter than maximum paper black, you have found your EI (Exposure Index). Then you do the same for zone IX, but white point is set by development time. Take the EI that you found, take a light meter reading, and give it 4 stops more light. Same test again in the darkroom, but this time you want your test strip to be just slightly darker than paper white.
Usually you will have to cut back on your development times a bit to achieve this. As a rule of thumb, you will probably get 1/3-2/3 of a stop of less speed on your film and the development time is around 15% too long. Rerolled aerial films will give 2-3 stops less speed and development time is halved.
As the Wikipedia article for the zone system states:
"The ISO standard for black-and-white negative film, ISO 6:1993, specifies development criteria that may differ from those used in practical photography (previous standards, such as ANSI PH2.5-1979, also specified chemistry and development technique). Consequently, the Zone System practitioner often must determine the speed for a particular combination of film, developer, and enlarger type; the speed determination is commonly based on Zone I. Although the method for determining speed for the Zone System is conceptually similar to the ISO method for determining speed, the Zone System speed is an effective speed rather than an ISO speed.”
Does any of this matter if I scan my film and never do darkroom prints?
Short answer, not really. Pushing film is pretty much the same as grabbing the white point in your scanning software and dragging it to the left. There is not that much difference between doing it chemically or in the software. If your highlights are clipping in your scanning software, you should reduce the development time, but this is unlikely. Being able to use the entire range of tones that you could get, without massive contrast adjustments might give you better image quality, depending on the scanner. Eventually you’ll probably start seeing artefacts, if you take software editing too far (remember to do contrast adjustments with 16bit files or in the scanning software before it has saved the image).
Having a good exposure is more important, or at least knowing where the best results lie. You cannot scan anything that isn’t on the negative, and if you know that you will need a EI 320 exposure to get anything in zone I, having that information will give you more control in your work flow. If you then decide that you like “deep blacks” or whatever the current term is for underexposed negatives, then you know that you can go up to EI 800, sacrifice Zone I and II and still have 8 zones left of range to work with.
My personal results
These are my personal results for my personal films and my personal cameras and my personal development method. Don’t let them be anything else than guidelines for you. As previously mentioned, don’t think too much about the EI/ISO ratings here, usually you get 2/3 of a stop less than the ISO rating by testing this through this method.
I have these here just as a backup in case my notebook gets destroyed or something.
Ilford HP5 (fresh)
EI 320
XTOL 1+1, 20c, 9min 45sek
Neopan 400 (bulk rolls, expired ~10 years ago, freezer stored)
EI 250
XTOL 1+1, 20c, 9min
Tri-X (bulk rolls, expired ~30 years ago, unknown storage)
EI 100
XTOL 1+1, 20c, 9min
NOT CONFIRMED RESULTS, GUESSTIMATES ON FAILED TESTS