Recent content by dpgoldenberg

In addition to the various complications mentioned above, there is a fundamental reason that these calculators are unlikely to be reliable. In order for a solution to have a predictable and stable pH, that is for it to be an effective pH buffer, it must contain both a weak acid and its...

I'll just add my personal/professional perspective. I have worked and taught for many years in biochemistry labs, where the range of chemical hazards is on roughly the same scale as in a darkroom. (Some things we use are more hazardous, like concentrated acids and bases and some more...

Here are curves measured for Ilford Delta 400 developed in Pyrocat-HD, comparing the overall density and that for the blue channel only (using a X-rite 810 densitometer). The data show that both densities increase with exposure, but the difference between them also increases markedly. So...

Bernard, Actually, this is the part of the conventional wisdom that I don't think is right: Moire patterns are generated by overlapping two regular patterns, so that they show up in digital images of regular patters of the proper frequency. Noise, by definition, has no defined frequency...

Some of this has been mentioned in earlier posts, but let me give my perspective, starting from the beginning. With B&W negative film, the "cardinal sin" is underexposure. Where there is insufficient exposure to create silver density after development, there is nothing that can be done to...

Rafal, Here is another function that does include a shoulder: f(x) = a1*log(1+exp(a2*x+a3))/(a4+log(1+exp(a2*x+a3))) This is based on my original function for the toe and linear regions, but then modifies the result of that function by a rectangular hyperbolic function to form the shoulder...

Rafal, I'm glad to hear that my suggestions were helpful and that you were able to implement them in R. You might want to try fitting your data to the function I suggested in the earlier thread: D(x) = a1*ln(1+exp(a2*x + a3)) where D is density, x is exposure (on a logarithmic scale) and...

Bill, My words may not have been as clear as I intended, but I think that the equations are correct. The equations define the distances between the points in two dimensions, not just the distance along the horizontal axis. (That's where Pythagoras comes in.) The first two equations define...

Rafal, I am the fool who started the first of the APUG threads you listed, in which I suggested a simple mathematical function for fitting densitometric data. Suffice it to say that my methods were not instantly adopted by thousands of photographers, leading to the fame and fortune that I...

For a concise introduction to the zone system, I would suggest taking a look at: http://www.normankoren.com/zonesystem.html Norman Koren's web page is primarily devoted to digital photography, and has not been updated much in quite a while. But, there is a lot of good information there on...

On a historical note, there is a direct connection between the work at Weston and the Zone System. A couple of months ago, I posted a link to a set of articles by John Davenport, published in 1940, which Ansel Adams acknowledged (somewhat belatedly) as the basis for the ZS. Davenport, in turn...

Oops! This is not quite right. Gamma is the slope of the linear region the exposure is plotted on a log base 10 scale. So, gamma=1 does have special significance: A ten-fold increase in exposure results in a 10-fold reduction in the fraction of light that passes through the negative. But, I...

I think that this probably represents a misconception. There is nothing magical about a gamma of 1. Gamma is the slope of the linear region of the characteristic curve when the exposure is plotted on a log base 2 scale versus density, which is a log base 10 scale of the fraction of light...

Mark, I have used FX-37 with TMY-2, and did my own tests. Since they are personal tests, I can't really say anything about absolute speed. But, my impression was that FX-37 didn't do any speed magic on TMY-2. I wound up using an EI of 320. On the other hand, FX-37 did seem to boost the...

Hi, In Ansel Adam's 1981 edition of The Negative, there is a rather cryptic acknowledgement to articles by John L. Davenport in U.S. Camera, as forming the basis for the Zone System. I was curious about these articles for some time and was able to track them down, with no small help from a...