When talking with other photographers about digital negatives in general, and scaling an image more specifically, there seems to be a misunderstanding about the difference between density range and the contrast index curve. Both are inexorably linked, and would be dependent variables of processing, yet not the same constructs. I have written on this subject twice now, although for a different reason. Those posts had to do with the differences in procedure between the two processes.
The above chart shows three contrast index curves. Each represents a difference in contrast, yet not a change in density range. If one were printing on silver gelatin papers, what would be seen in the finished print, using the same print paper, would be the contrast differences of the finished image. Silver gelatin print papers have a tonal range somewhere in the vicinity of 50, where black and white negative film has a potential tonal range five times that. Finding the right tonal range on the negative to match that of the printing paper is the key to a fully scaled print.
The tonal range of a hand coated silver print far exceeds that of silver gelatin paper, and therefore requires a negative commensurately scaled for such an extended tonal range. As has been demonstrated, the density range of a negative can be scaled without altering the original shape of the contrast index curve, as shown above. The contrast index curve (above) is scaled proportionately in each CI curve. That is all densities along that curve are increased proportionally with the increase of the density range.
The other method being used for digital negatives (Dan Burkholder) alters the middle of the curve proportionately to the other tonal values; See below
As can be seen in the graph, the method above increases the density range of the negative, yet not proportionally. To arrive at the needed density for Zone VII & VIII, the spectral density is employed. This method works just fine. The difference between this method and my own is the appearance of the image when printed. There will be far less area of the image with Zone II and Zone III, simply because of the inflation in density of those tonal ranges in proportion to the original contrast index curve, which is a much flatter line, although moved upward in density, proportionally. The final print of the above method will be very similar to the outcome of my practice of pushing the CI curve to the shoulder, away from the toe, eliminating the lower densities; Zone II & III, from the increased densities of the lower tonal range due to the movement of all densities upward.
The first curve represents the method I employ to digitally increase the density range of a digital negative. The second curve represents the Burkholder method of this procedure. The second curve will show an emphasis in the texture and detail of the middle tones, and a bit less highlights, than my method, which is more proportionally related to the original curve. What I take away from this is the need to follow Burkholder's increase in the middle tones, more proportionally than the increase in overall densities; respectively. The middle tone range of my prints are a bit thinner than they should be in my view, to keep the print image brighter. The heuristic value of these two methods is simply that it offers two different procedures for photographers. A choice in practice that fits their photographic vision of how they want their prints to look like.
The basic difference between 'density range' and 'contrast index curve' is simply this; the density range is a measurable difference between dMax black (Zone I) and pure white (Zone VIII). Those two points identify the full range of tonalities of a print, black to white. The contrast index curve is the 'shape' or identity of the printable range. It is what is in between the black and the white ends of the tonal scale. That shape can be altered without altering the black and white points. Subtle, yet pertinent. It is possible to have a short tonal range from black to white, or 'contrasty' and a long tonal range between the black and the white points. This was far trickier to accomplish traditionally using chemical development & careful placement of light values on a desired Zone before shooting. Digitally, this becomes a fairly easy task, by adding or decreasing densities in a chosen tonal range of the digital negative, as per Burkholder's or my method for scaling a digiral negative.
I should add here that PJ uses Burkholder's method with good success. I of course employ mine, and that keeps us both quite happy with our print results. One of the next print tests will be variation in UV intensity and image outcome. I'll raise the printer 4", which is 50% increase in source to print height as it is now. Roughly speaking, that should decrease light intensity in half. Theoretically, this will increase print time, which reciprocally increase print contrast. That is derived from past experience using the sun, either in north light with low intensity of around 15-20 lumens, to printing facing full sun, when there is no practical means of actually measuring the intensity in lumens, beyond it being amazingly bright. All other variables will remain constant. Stay tuned.
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