Schwarzschild effect compensation of different photographic films (ADOX, AGFA, FOMA, ILFORD, FUJI, KODAK) - V3.2
Download High Resolution Pictures in PNG-Format:
Or you can dowload it here in the PDF-Format.
Here is the most recent version of my Schwarzschild compensation factor sheet. For your information: None of these Factors are tested or in any case "right" since your choice of development (developer, duration temperature) has a crucial influence on the brightness and contrast of your photo.
The information of ILFORD and KODAK TriX films has been aquired by using vector graphic analysis of the graphs included in the film data sheets. The other graphs have been calculated by using the increment values supplied by the manufacturer (eg. for AGFA APX +1 f-stop for 1 to 10 seconds, +2 f-stops for 10 to 100 seconds, +3 f-stops for 100 to 1000 seconds) and a linearization method based on the logarithmic dependency of the correction factor.
V3.1a: Same data as V3.1, but time-vs-time plot, not time-vs-f-stop plot..
V3.1: New calculation based on data from V3.0, new readout procedure from vector graphic plot from PDFs. Miscalculation with all Fomapan films.
V3.0: Only f-stops, but more films added. Crappy data aquisition for ILFORD and KODAK Tri-X.
V2.0: Logarithmic "time-vs-time" graph and "f-stops to add" graph for B&W films of ILFORD, KODAK and FUJI. Crappy data aquisition for ILFORD and KODAK Tri-X.
V1.0: "Time-vs-time" graphs (linear and logarithmic) and "f-stops to add" graph, but only for ILFORD Films
For explanation: I used b&w films during the night and I was annoyed not to find a single comprehensive list of Schwarzschild factors for B&W films in the internet. So I made one. The first question I asked myself was, if I should use a standardized exposure and development method and check the density. But that would have been way out of proportion due to the fact, that I would have needed at least 3 to 5 different films from different production batches to guarantee a high precision and a minimized deviation of the measurement.
So I came to the conclusion, that the only reasonable solution (by means of money and time) would be a comprehensive list based on the Schwarzschild factors provided by the films manufacturers. There I face d another problem: Some manufacturers provide diagrams (only KODAK Tri-X 400 and ILFORD), the others only provide incremental values for magnitudes of exposure times in the log10 scale. This is just a very mean generalization. An exposure of 1.5 seconds demands a much lower (depending of the film) correction factor than an exposure of 9 seconds. Still, film charts say “use +1 stop for exposure of 1 to 10 seconds”.
Extracting the information of provided diagrams was quite easy: Since both data sheets are PDFs and the containing diagrams are vector file format, I could import the diagram into a vector program, extract the values and extrapolate it.
To get graphs based on the incremental values I had to go a little bit deeper: Almost nothing in nature is linear, most is logarithmic – as it is with the Schwarzschild effect. I used the incremental values uniformly distributed on a log10 scale to approximate a linear regression. (Basically the Schwarzschild effect is a probability issue which occurs, if not enough photons reach the film within a specific time frame to form a so called “latent picture” – which then demands a prolonged exposure to guarantee a standardized film density).
There are other factors which should be taken into account like film thickness, silver-grain size, type and distribution and (most important) development method, but that would have been far too extensive.
So I ended up with this graph. It is, as I’ve written before, only based on the information provided by the manufacturers and no experimental work was done. I’m a chemist at the end of my PhD and my main work is based on R&D of optical chemo- and biosensors. That’s why I used an, you could say, scientific approach to this problem rather than an “photographers” approach. I’m using analogue photography in my spare time, and I’m not as experienced as a professional photographer. So if there are questions or remarks about that – please do not hesitate to write me.