   |
I've just obtained a Stouffer 21-step tablet, and am all anxious to perform some film analysis of HP5+ in XTOL and D76 (and Pyrocat-HD, although I'm not sure how much help analysis will be for stained negatives). First, let me say that I don't plan on purchasing the plotting software; I'm quite at home with Excel, and if need be, pencil and graph paper. I should also mention that I've performed calibrations in the past using Adam's technique for exposing a negative to determine 0.1 over fb+f. I'm interested, however, in performing more detailed analysis of the papers, films and developers that I use.
I've been reading the 4th edition of Phil's book, and I'm a bit confused as to how I go about determining my film speed using the step wedge and my enlarger.
Phil states that for 100 ISO film, setup your enlarger so you get a meter reading off a white card of EV 4.0. Elsewhere on this site, I read that for 400 speed film, you want to geta reading of EV 2.0. My meter won't even read EV 2.0...so what am I supposed to do for this film?
Now, here's where I'm *really* confused. When I originally calibrated my system, I metered the surface in front of the camera, and closed down 4 stops. I then exposed 4 areas on one sheet of film, one at the original reading, and three each with 1/3 stop more exposure. In other words, I exposed the film for Zone I at 400, 320, 250, and 200. Develop them, and pick the one that's 0.1 over fb+f, and that's your film speed. Then move on to determine the correct development time for zone VII with a density around 1.25 - 1.35.
However, by exposing under the enlarger, and metering off the white card, do you really know what your original assumed speed is? You're metering off a white card, which is reflecting the light that will instead be falling directly on the negative when you make the exposure. Use the wrong color board, and your initial exposure of EV 4.0 will be the wrong exposure.
So you adjust the exposure to get about 2 clear patches on the developed negative. Then what?
Where I get really stuck is how you determine your film speed from this information. Using the 'old' way, you at least know what your assumed film speed is. Here you don't. Or do you? Or do you have to developer 3-5 sheets of film to create a family of curves?
I've been through the book a few times, and just don't get it. I'm missing something pretty fundamental here, and I can't figure out what it is.
Therefore, I'm asking for some direction.
Many thanks!
-klm.
|
|
|
|
|
|
|
