Nope, they distinguish between condenser and diffusion, and recommend a lower CI for condenser. I was referring to CI, and forgot the values differ a little.miha wrote:As you are very well aware of, Contrast Index (CI) is not gamma.Ornello wrote:No, it isn't. Kodak recommends CI of 0.42 for condenser or 0.55 for diffusion. I think those values are too high by one-half to one grade.
Kodak recommends CI of 0.56 in every tech sheet for their various B&W films.
http://www.kodak.com/global/en/professi ... /f4043.pdf
These starting-point recommendations are intended to produce negatives with a contrast appropriate for printing with a diffusion enlarger. To print negatives with a condenser enlarger, you may need to adjust the contrast by reducing your development time; see “Adjusting Film Contrast.” Tank development times shorter than 5 minutes may produce unsatisfactory uniformity."
"Note: These tables apply to negatives you will print with a diffusion enlarger. If you use a condenser enlarger, shift your selection one column to the left.."
http://www.kodak.com/global/plugins/acr ... /z-133.pdf
"0.58 is the contrast-index aim for printing negatives with a diffusion enlarger; use 0.43 if you will print negatives with a condenser enlarger."
I suggest those aim-point values be lower yet, based on the need for optimum results for 35mm film. If you reduce development even more and print on grade 3, you get better results. How do I know this? I experimented and compared the results.
There has been considerable erosion of once-commonplace photographic knowledge. When I refer to a book or manufacturer web site, it is not because I just learned this yesterday, or that I have not tested it myself. It simply is a means of making available to many that knowledge which has been available in the past but has forgotten or ignored.
These values of CI that Kodak has recommended for diffusion and condenser are of quite long standing. They are not news. It is unfortunate that many people have in fact never heard of them. That is why I presented them in this thread. Some would argue that the values are wrong or irrelevant. To this I would simply reply that the values are averages, and that as such, slight deviations from them are perfectly permissible. But if someone claims that a CI of 0,75 is the best for 35mm film with a condenser enlarger (and I am sure someone out there will make such a claim), I would have to say that this represents enough of a deviation to be an 'error', not an aesthetic choice.
'Aberrant' practices have become much more popular than before, due to the fact that many more students take classes in photography than in past, and this has created an atmosphere of confusion, as one student tells another this or that 'tip'. It is possible to develop one's film any number of ways, and print it any number of ways, and get some kind of results that may please someone. What standards serve to do it provide a reference point, so that the aberrant does not become the norm.
It is possible to establish, through trial and error, the validity of these recommended CI values. Since most of us have better things to do with our time, the amount of testing we perform has to be relevant. Since the time when I was much more involved in B&W photography, new emulsions and developers have made their appearance, and others available for a number of years never found their way into my work, simply because I was not motivated to experiment. I was also using Kodachrome almost exclusively for the last 10 years or so, and avoiding B&W.
Thus, recently, I have begun a series of tests on these new or unfamiliar B&W products, to bring myself up to date with them.