Quote Originally Posted by Stephen Benskin View Post
This is why Zone System testing consistently produces EIs 1/2 to 1 stop slower than the ISO speed. While the 1.20 log-H method will produce quality negatives and will create perfectly acceptable EIs, it shouldn't be regarded as a reliable way to determine film speed. Of course, if the additional exposure from the lower EI matches your style, why not save the time and just use the ISO speed and make the 2/3 stop adjustment. Afterall, what's the point of doing the test if it's not going to produce a reliable number.
So the bottom line of the endless Zonistas testing [This is not an attack on Stephen, I am just using his data to make a point] is a difference of less than a stop based on poor assumptions and uncalibrated equipment, sloppy testing and developing that the Zonistas are basing their work on. << Duh>> with the present dynamic range of both black & white and color C41 film of 12 to 14 f/stops depending on the choice of film, developer, developer dilution, and whom you choose to believe, less than one stop change will not produce any signifacant advantage or disadvantage. That being the case, why was time, money, film and chemicals to do all this testing when one will end up with essentally the same results using the box speed? Testing was useful when cameras and light meters were not that accurate, the results from the variation developers' result was wider ranging for all the dilution recommendation at that time1 and the film quality and dynamic sensitivity range was narrower.






1Since then Kodak and others recommend a narrower range of dilution, staying closer to 1:1 and 2:1 than the 4:1 then.