"Long" Tonal Scale Film

Kirk Keyes , May 07, 2004; 05:20 p.m.

Greetings all,(This is kind of long, so please bear with me.)

I have been going through my recently arrived copy of Anchell and Troop's "Film Developing Cookbook", and I'm finding a term that they are using. I've run across it in the past and I've found it confusing at best and annoying at worst. The term is "tonal scale".

They start the book out they briefly discuss Contrast and Gradation, covering concepts such as macro- local and micro-contrast. I'm with them there - all is good.

But when they start talking about films, they start tossing in the term "tonal scale". Here's a couple of examples:

"FP4+ reponds well to a wide range of developers and techniques. It produces a full tonal scale, fine grain, and high sharpness [...]."

And when talking about Pan F+, "[It] is not as fingrained as APX25, but due to it's lower contrast and longer scale, is much easier to handle in a broad range of developers. Its tonal scale is longer than the old Pan F."

I also hear "Tonal Scale" tossed around by the Azo fan(atic)s, such as "Azo has a long tonal scale which makes it easier to print."

I see this phrase making more sense when applied to slide films, such as "a film has a long tonal scale" - which means that it is low in contrast. What they actually mean is that the film has a wider exposure scale, meaning it will capture more stops in exposure before a tone is rendered pure black or white. You usually can't change contrast in silde films by adjusting development times without messing up color balance - the contrast is intrinsic to the film and the standardized E-6 processing.

Sometimes it seems like people are meaning that a film with a longer tonal scale gives distinct steps in the range of tones, i.e. the black flows smoothly in to the darker grays, the darker grays translate into lighter grays, which then smoothly moves into white.

At other times, people use "long tonal scale" to mean that a films response to light extends very linearly past the exposure for say Zone X - like Tech Pan (when developed in POTA or Technidol) which can record exposure many stops above Zone X, even if it is not normally put onto the print.

Looking a grey scale - there are an infinite number of grey values on the scale. When there are a lot of tones for describing the scale (properly exposed and processed with sufficient contrast to be printed on a non-high contrast paper), the tonal scale is reproduced smoothly. When a film is underexposed or over development is given, fewer greys recorded in the negative, and then the representation of the scale on the print is less smoothly reproduced, i.e. it looks more coarse or rough.

Anchell and Troop even kind of point to this in the Pan F+ quote above "lower contrast and longer scale". I think the two are really interconnected - low contrast = long tonal scale, high contrast = short tonal scale. So what they really mean "exposure scale", and not tonal scale, right?

I believe that every consumer film made (i.e. not litho films or special low contrast films) can be exposed and developed to a sufficient Contrast Index so that it will reproduce the exact same "tonal scale" as any other film, when we are talking about normal, everyday scenes. Of course there may be differences in local and micro-contrast, but the overall, macro-contrast will be the same. All it takes is proper exposure and a development time that is suitable for your working conditions (enlarger light source, paper...). Film reproduction graphs show this as well. Just match the exposure to the film, match the film to the developer, match the neagative to the paper, and everyone can have a "long tonal range" film.

I'm curious to see what other's take on this? Are there really "long tonal scale films"? Or are there just films that are simply developed to higher or lower contrasts?

Kirk

PS - Sorry for this being so long, but I wanted to try and fully explain my point of view.

Responses

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Rowland Mowrey , May 07, 2004; 06:07 p.m.

Kirk;

The tonal scale of a film is merely the shape of the curve of the response of film to light as a function of exposure density. It is an H&D curve or a plot of Density vs Log exposure.

Contrast is the slope of the curve, and the tone scale is the 'length' of the straight line portion of that curve.

A film with a long straight line portion produces a long or complete, or good tone scale. A large range of differences from light to dark as it were.

Negative films usually have a tone scale with a slope of 0.6 or a rise of 0.6 density units for each one unit of exposure. The d-min (light portion) is usually about 0.1, and the dark portion is usually about 3.0. Reversal films usually have a slope of about 1.7.

Negative paper has a slope of about 2.5 for normal contrast. Since slopes of materials during printing are multiplicative, the slope of the final print is 0.6 x 2.5 = 1.5 which is nominal for a reflection print pleasing to the eye. (notice that it is similar to the slope of a transparency material. Reversal paper has a slope of about 1.0 or slightly less, and the print is about 1.7. That is why reversal prints are slightly more contrasty.

Negative prints are made on the straight line portion of the negative film and therefore have a full tonal range with no compression due to toe or shoulder except that of the negative paper.

Reversal prints are made on the full curve and therefore have compression built in due to the toe and shoulder of the film and paper both and therefore do not look as good. For this reason, making reversal prints of transparencies for magazines or for normal display viewing involve highlight masking and color masking to fix up these problems. If you don't you have prints with severe compression of the scale and a 'dupey' look.

If a negative film has a short straight line portion it is manifested in several ways. It has a short tone scale, it has less overexposure latitude, and it allows the tone compression of the shoulder to show up in the final print giving reduced detail in highlights. This usually arises when a film has low d-max, less than 3.0, or high contrast.

Does this help?

Regards.

Ron Mowrey

james p. , May 07, 2004; 06:38 p.m.

Lots of good info in this thread. Thanks people!

Conrad Hoffman , May 07, 2004; 07:22 p.m.

Sez Ron. I have no problem with that description, but I don't think there has ever been any agreement on what the term means. In fact, I'd put it more in the category of marketing blather than scientific terminology. I love Anchell & Troop, and have learned a huge amount from the book, but at the same time, it contains many general statements that may be true under specific circumstances, but cannot be considered universal truths. The deeper I get into this stuff, the more I want to see graphs and deal only with carefully defined terms. Those are the only things that can be repeated by multiple workers and inspire some degree of confidence.

Bruce Watson , May 07, 2004; 07:38 p.m.

Conrad,

The university near me has a copy of the Grant Haist two volume tome Modern Photographic Processing which has many graphs and diagrams, and which explains in detail what tests he performed, how he performed them, what data he generated, and how he interprets the data.

Having read (well, studied might be a better word - it's such a huge work) Haist, and Anchell and Troop, it looks to me as if the Anchell and Troop book pulls largely from Haist's work. You can see this in their footnotes.

What I'm saying is, the gory details that Anchell and Troop left out, are in the Haist books. Henry's book is also interesting, even if I can never remember the name of it. Sigh...

Stephen Benskin , May 07, 2004; 07:46 p.m.

Yup, I'm with Conrad. Kirk, don't forget the more modern term for tonal scale - "tonal range." Just as meaningless, but less dated.

Jorge Gasteazoro , May 07, 2004; 07:59 p.m.

Henry's book is also interesting, even if I can never remember the name of it. Sigh...

Controls in B&W photography....

A paper like Azo has a long tonal scale because the paper's exposure scale can accomodate a negative with a greater density range than normal. Azo can easily print a negative with a density rangeof 1.6 to 1.8, compared to a "normal" enlarging paper this is a great range.

When talking about negatives it is a little bit more confusing, you are correct in thinking that a negative which has the ability to easily change contrast index with development can have both "long" and "short" tonal scales, but then there are films which have inherent "short" tonal range (high contrast) and others that have a long tonal scale (low contrast). Examples are Tech pan and HP5+.

Without getting in long and technical discussions of the films, developers and characteristics, IMO interchanging the terms long tonal scale for low contrast and the opposite, amounts to the same thing.

Patrick Gainer , May 07, 2004; 08:09 p.m.

You think this is bad? Listen to a wine connoiseur. They have the excuse that much of the sensation of a wine would be hard to put in a graph. We use terms that are difficult to graph, like local contrast, and that are sometimes imaginary. That makes me a heretic, but at least I won't go to hell for it...Will I? Please tell me I won't.

Stephen Benskin , May 07, 2004; 08:31 p.m.

Local contrast is a term with two definitions. One type of local contrast is the difference between two points on the curve. The other use is a small area of the scene rendered either on the negative or print, or even the original subject. I still think tonal range wins out for the term that has the most possible non-specific meanings.

Rowland Mowrey , May 07, 2004; 09:07 p.m.

Sez Ron, and sez Grant Haist, a very good friend of mine!

I helped him edit his book and we worked together at EK for many years. We also used to work together in my darkroom developing color film and prints, as Grant didn't have a home darkroom.

Please look in the credits section of the book for my name. I believe Grant placed it there. IDK for sure, but then I really didn't care. The friendship of such a great person and great photographer was enough for me!

In any event, it is not hype, it is part of the science necessary to develop a good photographic product. I have coated my own Gold 400 and Ektacolor paper and had fun using them even if they were experimental.

So, I say yes. I'm giving you straight information.

You may believe it or not, as you wish. I was an engineer at EK for 32 years, 15 of them developing products that you have probably used. I hope you still enjoy using them.

Regards.

Ron Mowrey

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