[Alt-photo] Christopher James - terminology question

John Isner john.isner at gmail.com
Fri Oct 27 18:08:02 UTC 2017


I think I understand now.  In quoting James, I misread "steps" as "stops."
More steps means more intermediate tones visible between any given pair of
tones in a step wedge, while fewer steps means more abrupt change in
tonality, hence higher contrast.

In my initial experiments with cyanotype, I got high contrast in the
shadows and moderate contrast in the midtones and highlights.  By altering
the process (e.g., developing in acid + water instead of just plain water,
or adding a few drops of distilled water to the sensitizer), I was able to
lower contrast in the midtones and highlights, but the shadows remained
stubbornly high contrast.  Furthermore, the transition from shadows to
midtones occurs fairly abruptly.

Is it possible to lower contrast in the shadows without increasing contrast
in the midtones and highlights?  In other words, is it possible to lower
contrast across the entire spectrum?  Or is contrast a zero-sum game, as it
is with a Curves adjustment in Photoshop (Curves let you push contrast
around but not eliminate it).




On Thu, Oct 26, 2017 at 7:28 AM, David Hatton <davidhatton at totalise.co.uk>
wrote:

> A long tonal range ie more tones visible is low contrast whereas a short
> tonal range  ie less tones visible is high contrast
> David
>
>
> On Thu, Oct 26, 2017 at 2:16 PM, John Isner via Alt-photo-process-list <
> alt-photo-process-list at lists.altphotolist.org> wrote:
>
>> 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
>> _______________________________________________
>> Alt-photo-process-list | altphotolist.org
>>
>
>


More information about the Alt-photo-process-list mailing list