Contrast, Tonality and the zone system.

Grandpa Ron

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The more I read on Black and White film developing the more confused I get. Some may be the differences in the semantic being used to describe the same thing. I am working with 4x5 negatives so I have a decent size area to examine.

If I understand things correctly, based on the Zone system, film has a latitude of 11 f stops; if you want to include all white and all black. (#5 middle gray +/- 5 stops). Typically you adjust the film exposure so the object of interest will be middle gray and the rest of the objects will fall according to their brightness or luminosity. That all make sense.

Now come the two terms that confuse me,
1. Contrast - If I print the same negative on #2 paper and on #3 paper I can see the difference in contrast. So the question is; am I loosing some of the films latitude or can I still get all the zone shades from white to black?

2. Tonality - This is another term that I do not quite understand. I read that some films/developers/ processing methods etc. will provide better tonality. Does this mean that some combinations will give all the zone shades while other will not?

The third option of course is that the Zone system has nothing to do with contrast of tonality and I am mixing apples with oranges.
 
If I understand things correctly, based on the Zone system, film has a latitude of 11 f stops ...
11 stops? Not really. Terminology is crucially important to navigate the interlinked set of concepts that make up the Zone System.

Given a normal sort of 4x5 film and a very small exposure nothing happens. But if the exposure is doubled in steps eventually the film reacts enough to form, after normal development, a optical density barely discernable above the film's base+fog density . If the exposure doubling now continues film density increases with each step. Modern large format films can accept at least 15 or more doublings, stops in other words, and still register a density change. This is often called the dynamic range of a film and it implies that very large brightness ranges can be recorded.

Using modern variable contrast papers it is possible to pick a single contrast grade so that any connected row of 11 (say) density steps can be represented by a gray scale running from black to white. And yes , there will be a middle gray somewhere between the extremes. But the same thing can be done with 8 density steps or 6. Just change the paper grade.

In the real world the maximum distance from black to white isn't 11 stops. Out there you'll find black things in the shade and white things in full sunlight that are way more than 11 stops apart. It is up to the photographer to decide which things to render in which tones by a process of visualisation. It is the Zone System that turns that visualisation into a matching picture.
 
The more I read on Black and White film developing the more confused I get. Some may be the differences in the semantic being used to describe the same thing. I am working with 4x5 negatives so I have a decent size area to examine.

If I understand things correctly, based on the Zone system, film has a latitude of 11 f stops; if you want to include all white and all black. (#5 middle gray +/- 5 stops). Typically you adjust the film exposure so the object of interest will be middle gray and the rest of the objects will fall according to their brightness or luminosity. That all make sense.

Now come the two terms that confuse me,
1. Contrast - If I print the same negative on #2 paper and on #3 paper I can see the difference in contrast. So the question is; am I loosing some of the films latitude or can I still get all the zone shades from white to black?
Your instinct is right there. Same negative printed on a higher contrast paper and you push both ends (black/white) and lose detail the lower contrast paper would keep.
2. Tonality - This is another term that I do not quite understand. I read that some films/developers/ processing methods etc. will provide better tonality. Does this mean that some combinations will give all the zone shades while other will not?
This is a fair definition of tonality: The tonality of a photograph is its visual appearance in terms of the distribution of tones and levels of gradation between them. - Amar Guillen

The distribution of tones and levels of gradation between them in a film can be affected by processing.
The third option of course is that the Zone system has nothing to do with contrast of tonality and I am mixing apples with oranges.

The Zone System has a lot to do with contrast and tonality.

Take concerns about personal artistic expression and set them aside for a moment.

A given film has an ideal X exposure and X development such that a negative will make the best print on a #2 paper. More or less than ideal exposure and more or less than ideal development and you get a negative that makes a poorer print on #2 paper and to improve it you may use a #1 or #3 paper. Those improved prints on #1 and #3 paper aren't equivalent to and are not as good as the best print on #2 paper. In other words there is a target for exposure and development for any given film that produces an ideal result.

One component is missing in the equation above of X exposure + X development + #2 paper and that's the lighting contrast/dynamic range of the scene being photographed. There is also an X scene lighting contrast/DR range and for that best print on #2 paper that scene lighting/DR also has to be in place. For reference that would be a front-lit sunny day blue sky scene like the one here.

sun-front.jpg


Put all the components together: we'll call it normal scene contrast/DR + X exposure + X development + #2 paper = you win!

The one place where that equation easily gets screwed up is the scene contrast/DR. Up until now we've had no need to mention the Zone System. It doesn't apply to the ideal target. That's worth repeating. The Zone System doesn't apply to the ideal target. If the scene contrast/DR is altered from normal (I'm sitting here right now with light rain falling that I can see through the window) fix it and you're good to go. This is why the Zone System doesn't apply in the studio -- you can always fix the lighting and here's the most important thing I will say: Fixing the lighting is the better and ideal solution. In other words the Zone System is a compromise solution to a problem when you can't do it right. Zone System believers tend to lose track of that and often fail to pass it on.

So what makes the Zone System work. In a sentence the Zone System is founded on the scientific fact that film's density response to development is disproportional. Take that away and there is no Zone System. I found this old Hurter Driffield film characteristic curve on the net. It's old but this hasn't changed. What they call the knee region we now call the toe. It's a graph of increasing film density over exposure for X development. More exposure produces more density in the film. Between the toe and shoulder we see gamma = slope. What we want to observe here is that the straight line indicates a proportional relationship between exposure and film density. The toe and shoulder are threshold limits. Eventually more exposure won't get you more density and the inverse of that at the toe.

4-Figure3-1.png


Let's for instance assume that the curve in the graph above is our ideal target response for a given film. Now for the Zone System key: Imagine you can put a thumbtack into the curve at the toe/knee and hold it in place. Next we'll change the development time but keep the same exposure. With more development the shoulder will happen sooner and the gamma/slope of the straight line will steepen while the toe stays anchored in place. This is the fact that film's density response to development is disproportional. More or less development has nominal effect on the toe region compared with the shoulder and straight line. So it's kind of like you can thumbtack down the toe and with more or less development swing the shoulder up or down with a corresponding change in the gamma/slope of the straight line. Gamma is a measurement of the contrast in the film negative. It measures the steepness of the straight line section of the curve. As the line steepens the contrast goes up.

Back to our ideal target conditions. You head out to take a photo and with your trusty spot meter you check the DR range of the scene and discover it exceeds normal scene contrast. If you apply ideal exposure and ideal development to the film you'll end up with highlights in the puffy white clouds that will burn out on your #2 paper. FIX THE LIGHTING. You can't. Ok, then you can compromise and use the Zone System. You know that you can decrease development (N- in Zone System lingo -- N is normal) and that will leave the shadows much the same in the film but pull down the highlights. Too bad it will also reduce gamma as the straight line becomes less steep. That's the Zone System compromise. If you could fix the lighting you wouldn't have to reduce development and you could keep normal contrast in the straight line section of the film. You're N- negative should now print with those cloud highlights retained on a #2 paper but you may not like the tonality of the midtones as much with the film's straight line section flattened.

Now put your art hat back on (Adams was always an artist first) and change the language to describe what's happening. You measure the scene DR and discover it doesn't match your pre-visualization of the final print and so you alter either development and/or exposure or both to come up with the best compromise result given that you can't fix the lighting.
 
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Thanks for the information guys, it is a lot to absorb. I definitely will re-read Ansel's book on the negative.

Initially, I find two things very interesting. The impact of the film curves non-linearity on the zone system and the "artistic" interpretation of the tonal values. It seems that understanding these two areas is part of what separate a lucky snapshot from a well planed fine art photograph.

Thanks again,
 
Adam's book on the Negative is a great read (sadly I lent mine to someone that never returned it).
The Print is OK ... a companion.

Yes, it can make a difference.
I remember in our Darkroom course we had to find a subject specific favourable to have adjustments of neg and print based on the Zone System ... we had to take different exposures and mark our holders with what we calculated at the time of shooting with N +/- ... it was really interesting to see the various results.
 

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