Long, short, and normal toe paper curves

[jisner]

I have been searching for formal (mathematical) definitions of these terms, but I can't find them in BTZS Plotter's help files or in Phil Davis book "Beyond the Zone System." Perhaps these terms are defined elsewhere. Does anyone have a reference?

 

[Mr Bill]

Hi, I don't think there IS a formal definition to distinguish between these with respect to photo papers.

There is an ISO standard that specifies, I think, a method of defining both a "speed" and loosely, a contrast rating (more properly a usable exposure range), but I don't believe it says much about the toe. I can probably find the number of the ISO standard if you want.

If you wanted to see some comparative curves, albeit for obsolete b&w papers, there are about a dozen or so sets in an old Kodak publication, G-1, from about the 1980s. If you were to look at those you'd probably see that the length of the toe changes along with the paper's contrast grade. Meaning that it's not as simple as it might seem to give hard definitions for each toe type.

 

[RalphLambrecht]

I have been searching for formal (mathematical) definitions of these terms, but I can't find them in BTZS Plotter's help files or in Phil Davis book "Beyond the Zone System." Perhaps these terms are defined elsewhere. Does anyone have a reference?

There is no mathematical definition. It simply means how long it takes for the film or the paper to get into the straight line section of their H-D curves.

 

[jisner]

There is no mathematical definition. It simply means how long it takes for the film or the paper to get into the straight line section of their H-D curves.

BTZS Plotter gives the toe classification along with other paper curve characteristics, so I was just wondering how Plotter defines it. Maybe there's no formal (e.g. ISO standard) definition, but just something Phil Davis came up with becase he found it useful. I could come up with my own definition, but I'd rather use his if I can find it.

 

[Mr Bill]

I could come up with my own definition, but I'd rather use his if I can find it.

Here's something I posted a couple years back, including some curves. If you don't have your own paper data perhaps you can use some of this.

It's a set of curves from long-gone Kodak Medalist paper, showing all the paper grades. So you can see that if you ignore the paper's contrast grade there is quite a variety in the toe of the curves. I would question if it's proper to label these as, for example, normal toe, long toe, extra-long toe, etc. Because they would have been used largely to compensate for variations in film contrast.

Anyway the link is below.

https://www.photrio.com/forum/threads/kodak-medalist-characteristic-curve.171661/#post-2233707

Ps, I have an early copy of Davis' book, before personal computers were a common thing. So no information about his software. But he does have a diagram from an ANSI paper standard showing the key parameters they used. It looks about the same as the later (I think) ISO standard.

 

[DREW WILEY]

Let me start with film first, because it's not only analogous, but determines everything afterwards. And with today's VC papers, the cumulative question can develop a lot of layers fast. In other words, to make sense of it all, you need to think
of any specific film regimen as if a marriage to a specific paper, or even specific style of exposing a VC paper per se. It's
all relative. Old school terminology of paper "grades" gave a clue, but only with respect to a certain product line within a certain manufacturing brand. There never were absolute values.

H&D graphs are plotted visually for a reason. Sure, there are all sorts of match shortcuts people use to determine film speed, average contrast gamma, and so forth. But one really has to take in the entire cumulative curve, of better still, learn how to plot these for themselves, before the picture really hits home. Neither the Zon System nor any neo tweak thereof is a real substitute. You see, it's not just about whether a curve is long, short, or somewhere in between, but about the actual shape of that curve in relation to your own printing needs, and how that shape can potentially be altered or fine-tuned through selective exposure and development.

Still referring to film, even the definition of what constitutes the "straight line" portion of the curve can vary, and sadly, often according to over-optimistic marketing parameters. So you need to be aware of the character of the toe itself, and what shadow information within that to include or exclude from your film using the appropriate amount of exposure; and likewise, where the shoulder will appear, and how to control that if it's encountered.

Sounds complicated? No, it's not. Just learn the basics and practice. Exposure experiments combined with simple test strips from your favorite papers will tell you a hundred times more of practical value than all the math combined. But that does have it's place. I own two densitometers myself, and frequently use them. But they aren't essential. What is crucial is understanding how you want to distributes the tones in any given scene to please your own aesthetic taste. That applies, like I already hinted, to thinking of the film and paper in a combined sense, cause that's what you have when printing.

So did I answer your question? No. But if you have specific papers in mind, and specific films and developers too, perhaps I can. Otherwise, there are just too many variables to give a generic answer.

Sometimes there was a deliberate attempt to match film toe and straight line characteristics to a specific paper, like FP4 to MGIV. Or if you today compare MGWT to Bergger Neutral Tone VC, you'll discover that the toe of the latter drops off more steeply than MGWT, producing bolder but less detailed shadows unless one properly exposes the film for the differential - and Ilford/Harman happens to make both,even though they're marketed under different companies.

 

[MurrayMinchin]

My guess is there are too many variables once you chuck in the quality of the negative, print developer choice/time/agitation/temperature, light source, and processing gymnastics like the Sterry Method, etc. Papers are so malleable that each grade of paper could probably be made to have a long, or short toe.

The manufacturers would have standardized it to some degree to make sure there is consistency between grades within paper types, but once it's the hands of the consumer anything can happen.