   |
Rich --
First, remember that the purpose of all this is to produce a negative that will match the paper; that is, the negative Density Range (DR) should be approximately the same as the paper's Exposure Scale (ES). In these illustrations we're using an ES of 1.0 (second paragraph, page 47) so that's our target DR.
Second, we pick a range of development times for the test, planning to include times that will provide very low contrast (to tame contrasty subjects) as well as times that will produce very high contrast (for dealing with flat subjects). These times are arbitrary but I generally try to use about 8 minutes for "normal" development and adjust the developer dilution to make that possible. Then I like to complete the time sequence geometrically (since development action is approximately geometric) so that the curves' slopes (gradients) will increase in more or less uniform increments. In these illustrations I've used times of 3:00, 4:30, 6:30, 10:00, and 15:00 minutes, as shown in fig. 4-17. I can't tell you right offhand why I picked those numbers; my usual sequence follows the familiar "f-stop" sequence: 4, 5.6, 8, 11, and 16 minutes. That's easy to remember and, if the developer is adjusted to provide "normal" contrast at 8 minutes, this range covers most of the useful range of the film/dev combination.
Having established the film curve family, we determine IDmin, which in these illustrations I've set at the traditional "0.1-over-B+F." Then we add the paper ES (1.0) to each IDmin point to find the value of each IDmax point, and connect the points with (in this illustration) a straight line. Then the horizontal distance between each pair of IDmin/IDmax points displays the subject range in log terms (1.12 through 3.31 here) and dividing each of those values by 0.3 (approximately equal to one stop) we find the subject luminance range (SBR, white numbers in black rectangles -- 3.7 through 11) in stops for each curve.
Since you didn't mention a problem with the method of determining the EFS values from the speed points, I assume that's described well enough in the book. I hope this will clarify the illustrations for you but if you have more questions, I'll be happy to try to answer them.
Unfortunately, (perhaps for you but not for me!) my wife and I are leaving on vacation tomorrow morning and will be gone for about two weeks. If all goes as planned I'll be back here on Feb. 10th, and I'll be glad to pick up this correspondence, if necessary, then.
Actually, I know there are quite a few BTZSers who could answer questions of this sort and at least some of them are probably lurking around this forum. Step up to the plate and help out, guys!
|
|
|
|
|
|
|
