[Alt-photo] Christopher James - terminology question
john.isner at gmail.com
Fri Oct 27 19:12:15 UTC 2017
Good explanation, thanks! I need a new pair of reading glasses so I don't
misread "steps" as "stops."
I have been following Peter Mrhar's book on digital negatives. The book is
not specific to any specific alternative process. In his method, you
develop a correction curve from a step wedge, then apply the correction
curve to the digital image from which the negative is made. But before
making the negative, you use a second curve that enables you to "soft
proof" the image on your computer display, and to make adjustments (under
the curve) to "modify the image to suit the process." It is here that I
encountered my problems with contrast / tonal range, particularly in
low-key images. Attempting to bring out detail in dark areas of the image
by "dodging" in Photoshop resulted in a posterized appearance (see below).
I now understand that this is because there are not enough tones between
the shadow and the detail to make a smooth transition. Hence my desire to
reduce contrast in the shadows. I hope I can do this without giving up the
deep blues of the shadows themselves (what Mrhar calls "maximum black").
On Thu, Oct 26, 2017 at 7:55 AM, bobkiss caribsurf.com <
bobkiss at caribsurf.com> wrote:
> Awwwwwwwwwwrighty then. The problem is that contrast and tonal range can
> refer to many different things. E.g., are we discussing "input" or
> "output" to put it in your terms.
> I looked on P 185 of my 3rd edition but didn't find that exact quote.
> ***DISCLAIMER: The following is a very distilled summary but, I think, is
> I believe he is suggesting that you would get 2 or 3 more steps (usually
> 1/2 stops of exposure), not stops, in the image of a step tablet printed on
> cyanotype. He is saying that instead of, let's say, 9 steps between the
> darkest shadow, Dmax, and lightest highlight (just below paper white), you
> might now get 11 or 12 steps using a dilute vinegar or citric acid bath.
> These are TONES in the print (output). But, because it takes a wider range
> of exposure (input) to create these extra tonal steps which STILL only go
> from the same Dmax to the same lightest highlight, by definition, the print
> from the same negative would appear a little "flatter", i.e., it would
> render the original scene as captured on the negative having the same fixed
> density range, a bit "flatter", lower in contrast.
> So you might want to review:
> 1) Scene Brightness Range (SBR); The range of brightness usually measured
> in stops between the objects in your scene that you want to render as your
> lightest highlight and your darkest shadow. You can "Zone Out" and define
> these more rigorously as which ones have either the lightest and darkest
> distinguishable tone or which have just discernible texture.
> 2) Density range of the negative. This is determined by the SBR, the
> characteristics of the film, flare and other characteristics of the camera
> lens and the type, time, temp and agitation of the dev.
> ***Nota bene: This density range of the negative (output of camera/neg
> process) becomes the input of the printing process in that the neg density
> range translates into the (input) brightness(intensity) range of the
> light/energy exposing the coated paper.
> 3) Then, assuming one process (let's stick with cyanotype) the
> brightness/intensity range of light/energy (input) coming from the negative
> translates (after processing) into print density (tonal) range on the print
> which can be influenced by many things, including but not limited to, paper
> type, coating soln formulation & ratio and any additives, processing, water
> pH, use of special baths (dilute acetic or citric acid, strong peroxide,
> 4) From the "ol Silver Gelatin" perspective, Ansel Adams warned that,
> using pull processing to extend the SBR (input) that the film could handle
> to give the right density range in the neg that would translate into the
> right exposure range for the paper (scale index) would often result in the
> reduction of both overall and "local" (or midtone separation) contrast.
> I hope this helps...
> ----- Original Message -----
> From: "alt-photo-process-list at lists.altphotolist.org" <
> alt-photo-process-list at lists.altphotolist.org>
> To: "alt-photo-process-list at lists.altphotolist.org" <
> Alt-photo-process-list at lists.altphotolist.org>
> Sent: Thursday, October 26, 2017 9:16:40 AM
> Subject: [Alt-photo] Christopher James - terminology question
> I am new to alternative process, having come from a digital photography
> background (no darkroom experience). This is my second post to the mailing
> I'm struggling to understand two terms that Christopher James repeatedly
> mentions in his book, but never explicitly defines: contrast and tonal
> range. For example, on page 185 in the cyanotype chapter, he says that
> using a particular developer chemistry will give "a significant increase in
> the range of values (2 to 4 stops) but a decrease in contrast."
> My understanding of contrast and tonal range is based on the histogram in
> digital photography: An image with a large tonal range has a wide
> histogram, that is, large "distance" between the darkest and lightest tone,
> while a high contrast image has relatively few midtones. To my mind, the
> alt process equivalent of the histogram is a printed sample of a step wedge
> with 256 brightness levels from black to white. When James says a
> "decrease in contrast," I interpret this to mean that the tones bunch up at
> the dark and the light ends of the step wedge, with very few tones in
> between. That makes sense to me. However when he says "a significant
> increase in range of values (2 to 4 stops) I'm confused. Since you can't
> get any whiter than paper white, an "increase in range of values" could
> only mean one thing: the darkest tone gets darker! I suspect this is NOT
> what he means.
> Can someone help me understand this?
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