Digital BW, The Print

>
>  > >Martin wrote-


>I was talking about the higher density end of the curve, specifically the
>shoulder. At what is normally considered maximum densities of 1.2 to 2.0 for
>Zone X, I don't see any significant non-linear behavior with modern films
>from Zone II to IX.

For photographers not used to "reading" characteristic curves (not 
meaning Martin here, of course), the graphs provided by the 
manufacturers can be confusing. The "original" Zone System defined 
the lightest shade of gray as Zone VIII, later iterations as Zone IX 
(due to the greater precision of spotmeters). Zone I is taken as the 
darkest possible gray above black (the printable threshold of the 
toe). The X axis on the graphs is in log exposure units, which means 
nothing to most photographers. Or my students, I'm afraid. They think 
a logarithm is a polka for lumberjacks. But each .3 units represents 
one stop, so the "printable" exposure range for normal development is 
roughly 3 log units (ten stops/zones). More for "contractions", less 
for "expansions". Virtually all films show non-linearity over that 
range with normal development (Zone VIII or XI densities around 1.3).

The differing non-linearities are mostly what gives each film (Tech 
Pan, TMY, Plus-X, Fuji 400 for example) the tonal flavor that some 
love and some hate. However, as few photographers have densitometers, 
most evaluate film characteristics by printing negatives on paper. 
Not very helpful, as they are "overlaying" the film's non-linear 
shoulder with the paper's non-linear toe. Welcome to art as crap 
shoot. Multigrade's toe (i.e. highlights), for example, is designed 
around Ilford's film shoulder curves, and is one of the reasons T-MAX 
developed T-MAX 400 is so tough to print on it.

It is very illustrative to shoot "Zone Rulers" (that is, exposing a 
uniform surface at each Zone in sequence to create your own 
stepwedge) for several films and contacting (or scanning) them 
together.

>  Push them far enough and they will break down but I
>think you will have lost any useable detail before you get that far.

No, detail (tonal separation) continues (increasing with TMY and 
TXPro 120, decreasing with most other films) for several stops above 
Zone X.

>  They
>all have a toe of course and I was not suggesting they didn't. Overall, if a
>film was significantly non-linear I suspect we wouldn't use it much.

I think most of us do, most of the time. We associate the highlight 
and shadow compression of a silver print as "photographic", and we 
filter, dodge and burn to enhance that. Not so, platinum printing, 
which is much more linear. Probably why Jon Cone compares Piezo's 
shadow separation to platinum. And why he tried to increase the Dmax 
of the "Selenium" inkset (which is what selenium toner does on a 
silver print).

>Different films do have different characteristics but this is due to more
>than just the different density vs. exposure relationship.

Yes, color sensitivity affects skin tones, green vegetation, and blue 
sky rendition. That can be more important to some photographers. And 
grain structure, acutance, halation, response to a favored developer, 
and so on.

>
>  > Certainly true for condenser enlarger printing of small format negs.
>>  Large format, not so clear.
>
>I have not found extra image density to be of any help with 4x5 in a cold
>light enlarger either.

Bruce Barnbaum's revisionist Zone System thinking includes placing 
shadows on Zone IV or higher, to avoid the toe and increase low value 
separation, so his negs get dense. Of course, he's a roots and rocks 
guy.

Enlargers differ. I use an Ilford tungsten bulb VC head for MF 
and4x5, a classic single contrast fluorescent cold light for 5x7 and 
8x10, a Focomat with a colorhead for 35mm BW. My school has Beseler 
condenser and color heads, Cachet/Seagull and Aristo VC diffusion 
heads. Each has a distinct tonality, but all the diffusion heads 
require more highlight density (or film contrast) to match the 
condenser units on graded paper. On VC paper, all but the very blue 
standard cold light unit need more contrast to match. Classic cold 
light starts at around grade 4 on VC, and needs significant yellow 
filtration to print grade 2. So if you print cold light on VC papers, 
I'd agree.


>  >
>  >
>>  I always calibrated my Zone System times for grade 2 paper by contact
>>  or diffusion head enlarger. That produces a fairly robust negative,
>>  and vibrant prints. But as I get more involve with digital, I expect
>>  to re-calibrate to grade 3 in order to have slightly thinner, more
>>  scannable negatives.
>
Just recalibrate to your digital output.

Actually, what seems to work well with the 2450 I use for MF/4x5 is 
calibrating the scan. I drilled two holes in the film holder between 
the two openings. One has a ND filter, usually 2.5. I set my black 
and white points there and go. I see this as equivalent to using a 
standard developing time, and allows the scanner/software to map each 
negative over the same range.

Regards,

Bruce
-- 
Bruce C. Kinch
Associate Professor of Photography
The Art Institute of Boston at Lesley University