[Alt-photo] Christopher James - terminology question

bobkiss caribsurf.com bobkiss at caribsurf.com
Thu Oct 26 14:55:21 UTC 2017


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 correct.

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, etc).  

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...

           CHEERS!
                BOB

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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
list.

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?
Thanks,
John
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