Quote:
Originally Posted by Photo Engineer  Patrick;
I was merely commenting that Kodak used the same method. And, as such the data is pretty much as you have shown, but they only do it for one contrast value.
PE |
If I seemed a little prickly, it's because I was having trouble getting my graph through to the screen. NOBODY had seen my data at that point, unless they remembered it from a paper in Photo Techniques a few years ago. IIRC, it was titled "Photographers Can Ride on Logs."
The graph actually is an analog of the charging of a capacitor through a fixed resistor to a fixed potential which makes it also a pretty good analog of the developing process as far as the shape of the curve goes. The charging potential is the analogy of Gmax. Gmax doesn't come with the film instructions these days, but the means of calculating it from 2 properly chosen experiments has been around a long time. I found it in Principles of Optics by Hardy & Perrin. The method of doing it by successive approximation from found data where you can't choose the developing times you'd like to have is mine, or at least I like to think so.
The solid black circles show the raw data I used to define the general equation. The two at 65 F defined the slope and Gmax, and the third at 70 F defined that line. The line showing Gmax - G at constant 5 minute development time allowed me to interpolate to make lines for other temperatures. The hollow circles show where other Kodak data fall that were not used in generating the graph. There was no least-squares curve fitting used.
The time constant of the development can be influenced considerably by agitation.