[pure-silver] Re: ZONE VI VC HEAD, was No More Below the Lens Polymax Filter Kits?

  • From: Jean-David Beyer <jeandavid8@xxxxxxxxxxx>
  • To: pure-silver@xxxxxxxxxxxxx
  • Date: Mon, 09 Feb 2009 09:17:54 -0500

mail1 wrote:

Jean-David Beyer wrote in part.

I do not remember how to convert density range to Exposure Scale (which is
what I suppose you mean by ES). I thought they were identical, but your
results are so different from mine that i doubt they are experimental
error, so I hope we are talking about different things.


To clarify my understanding of this matter.

It starts by measuring the subject luminance range, then the determination
of the negative exposure, and then developing the negative to produce an
image. The negative density range can be measured either by an on easel
photometer, or a densitometer, or by eye, to determine the print exposure
scale and a paper grade that matches the negative.
OK so far. I skipped all that by using a calibrated step wedge with nominal steps of 0.15. The steps are actually very close to this.
Density Range of the paper is the IDmax minus IDmin of the paper. 

OK this far.


The IDmin
is usually defined as 0.04 over B+F (paper white) and IDmax is usually
defined as 90% of the maximum obtainable density of the paper.
That may be true, but not what I do. I define my Dmin as the whiteness of the developed, stopped, fixed, washed paper. I define my Dmax as the maximum black I can get from the paper at the point where I can see no darker steps from the wedge; I.e., one more than the step that I can (barely) see is lighter than the darkest. I get this darkest step with reasonable exposure in the enlarger; i.e., 22 seconds at f/8 at a height where I get an 11x14 print from a 4x5 negative (in this case, the step wedge). Not a several minute exposure with the room lights on, or something like that.
Since my negatives sometimes have such a range, it seems reasonable not to tighten up the range by losing 0.04 at the top for specular highlights or losing maximum black by losing 10% of the shadows. I develop my negatives so that the subject where I want Zone V density on the negative comes out at a net negative density of about 0.9, and then take what I get at the extremes. I use the additional negative exposure because otherwise I do not get maximum black from the paper, since the negatives never get negative density (or course), and if I put Zone I at 0.1 net density (as Ansel Adams did), and develop to normal contrast, the Zone V then produces too much density on the print. With my exposures, Zone I usually comes out at around 0.3 net density. I think I get different results from Adams is because nowdays, maximum density you can practically get from most papers is around 2.2 whereas when Adams did most of his work, it was much closer to 2.0 (or a little under) so there was little point in exposing negatives more. Also, in his time, many more films had shoulders and he did not wish to lose highlight detail by exposing up there.
So my density ranges represent an actual count of the steps I get with each color of illumination (i.e., each contrast grade), with exposure set so I match the 18% grey card with the 0.9 net density step from the wedge. The exposure time is always the same, and the aperture is adjusted to match the grey card. With my conditions, this amounts to only a total range of one f/ stop. If I had a finer step wedge, I could measure the highlight densities more accurately, but I doubt it would make much difference in the shadows because it is quite difficult to tell the difference between the last non-max black and the max black by my calibrated eyeball. ;-) 


The IDmin is
usual 0.09 and is represented as a horizontal line starting from the density
scale on the left side of the graph. This line intersects the toe of paper
curve where a perpendicular line is drop to the log exposure scale on the
bottom of the graph.  This establishes the toe side of the paper (ES)
exposure scale. The IDmax varies with the maximum density of the paper and
is another horizontal line that crosses the paper curve where a
perpendicular is dropped to determine the shoulder side of the exposure
scale. This difference between the two points paper is the paper exposure
scale. IT is also equal to the ISO Range. (ES1.0 = ISO Range 100). The ES is
also a relative log exposure which is a measure of Logarithmic value. It is
usually represented on a scale of 0.10 units of density with 0.30 units
equal to approximately 2 steps of a 21 step table. A grade 2 paper, ES 1.00
divided by .15 units equals 6.6 steps of the step table. If you used an
incident light meter modified to measure a projected image by the enlarger
you would measure approximately 3.3 EV values between the high lights and
the shadows of the projected image.
I have a MacBeth TD-901 transmission densitometer, and a Beseler color enlarging meter. I do not know how accurate the enlarging meter is. It is good at reproducing illumination, but it is not especially good at actually measuring it. I.e., it is really a null meter, and wereas the dial of the meter is calibrated in seconds, these are not well calibrated.
Jonathan Ayers [mail1@xxxxxxxxxxxxxxxxx]> 


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