Pivot point

Hello,

This is rather a theoretical question, but I'm struggeling with it.
Given 5 identical exposed films and a developer of your choice.

The films are than developed N-2, N-1, N, N+1, N+2.
Since the slope of the straight part of the characteritic curve will change, a common point on all 5 slopes can be determined - kinda pivot point. Can this pivotpoint be used a characteristic parameter for the film/developer combo ?

just wondering ...

M.

I actually don't think that there would necessarily be one single point common to all curves. But of course I could be wrong.

I think that if there was to be a common, or pivot point, in all five exposures it would be whichever part of the subject you "placed" to determine your exposure, and the rest of the subjects values would be determined by how the film was developed. If you based it on a part of the subject being on zone III, or zone V, then that part of the image would result in the same-ish print value for all five in a contact print or proof print at a standard exposure and development. I say same-ish because the local contrast within the placed area of the subject will be totally different in each print...which makes it debatable whether it could be called a pivot point? Fun question!

Murray

Just read your question again...were you asking if there would be crossing of the characteristic curves if they were plotted on the same graph? No, there wouldn't be...they would be close at the base but then fan out, seperating more with increased exposure. In my earlier reply I was coming at it from a print value angle and had automatically assumed I would have given exposure compensation for the + and - developments.

Murray

You will only have one neg that will be worth anything, and that will be the one with the matching exposure. I think you will not find the common point you are looking for. You will be able to verify for yourself why the others won't work. Different developing times require exposure shifts. The toes may be close but with increased development you will bring up the bottom also, but not as much as the shoulder.

MurrayMinchin said:

Jthey would be close at the base but then fan out, seperating more with increased exposure.

Click to expand...

That's exactly what I was thinking. And even in the case that they may eventually cross each other, there is no reason why it should happen in the same point for ALL pair of curves.

If you use a shadow point, say Zone I, and equalize for the base fog, then yes.

If you think in terms of of Zone V or VI, then, absolutely there is a pivot, or fulcrum.

.

df, did you read Murray's considerations?

I agree that you can create a pivot point if you bias the curves and play with rescaling to force them to pass over a common point. And then? If you only want, you can rescale so well that you may even superimpose the curves altogether.

Which kind of information you think you can derive from such a point you artificially created?

"Which kind of information you think you can derive from such a point you artificially created?" Marco Gilardetti

Since I make pictures with a camera, in the real world, and print them to suit my taste, I gain everything. There is no artificial point: it is real, and unlike lab based evaluation, not arbitrary.

An evaluation of the negative can be made at any density point. It is conventional today to read bf+x to determine Zone I, but there ARE other ways.

For one who is most concerned with mid tones, and with local contrast, bi-directional control is much more effective. As a portraitist, especially one who photographs people of differing complexions, daily, together, it is very efficient to use incident readings and allow one's subjects to fall naturally rather than to abide by the limitations of conventional conceptions of the tone cycle.

Problems which stress conventional System thought and practice are handled gracefully, and simply.

This is treated far better than I have done in The New Zone System Manual,
by Zakia, White, and Lorenz.

Below: A conceptualization of how exposure and development can pivot at a given zone to provide a practical alternative to System convention.


.

I'll second Don's comments on bi-directional control and the book recommendation. Was going to recommend the New Zone System Manual myself this morning because it speaks directly to this topic. (But I had to get out for errands.) It's a very good book and worth looking for used. It's complete without being overly technical, and the concepts are very clearly represented and expressed in words and heavy use of graphics. It will make your zone system thinking more flexible. I recently used the illustrations in it in a class for two 11 year olds to explain the concept of tone placement, without getting bogged down in technicalities.

Lee

Hey, that's pretty slick!

So, by disregarding zone I and reducing exposure by 2 stops for +2 development for a zone V placement, it does create a "pivot point" at zone V. I have to go away now and visualize what effect this would have, and when it might come in handy...

Murray

I also agree with dons comments. The graphs show the result of exposure and development COMBINATIONS. This thread though specifically states a condition of constant exposure and various developments. That would make the graph look completely different.

vet173 said:

I also agree with dons comments. The graphs show the result of exposure and development COMBINATIONS. This thread though specifically states a condition of constant exposure and various developments. That would make the graph look completely different.

Click to expand...

Right. But by sliding the curves side to side ( exposure ) does provide an alternate pivot point... well, it was a leap of reason. And lots of coffee !

.

df cardwell said:

Right. But by sliding the curves side to side ( exposure ) does provide an alternate pivot point
.

Click to expand...

I totally agree

df cardwell said:

Right. But by sliding the curves side to side ( exposure ) does provide an alternate pivot point...

Click to expand...

Which is exatcly what I said: biasing and traslating, not mathematically in this case but by changing exposure. That was not the question.

The curves will not intersect by changing developement time, thus the so-called "pivot point" DOES NOT EXIST unless you change other parameters. I will be glad to learn something if someone can prove this sentence to be wrong.

Marco Gilardetti said:

Which is exatcly what I said: biasing and traslating, not mathematically in this case but by changing exposure. That was not the question.

The curves will not intersect by changing developement time, thus the so-called "pivot point" DOES NOT EXIST unless you change other parameters. I will be glad to learn something if someone can prove this sentence to be wrong.

Click to expand...

Because Photography has to do with making pictures, and is not a pure science, everything about it is a systematic application of data and imagination. A craft, if you will.

Over the years there have been several systems for describing the mathematics of density and exposure. Some, like the system en vogue, derive from a more theoretical performance in the laboratory. Others, describe qualities of negative considered useful to image making but less useful to research applications.

As a forum of photographers, I felt it appropriate to respond as I did to Mr Leest's question. Expressed as a Zone System inquiry, I felt it appropriate to respond within the context of Zone System. This was not, I felt, a sensitometry issue.

Mr. White, Mr. Zakia, and Mr. Lorenz were quite significant in the photographic community before it existed in the virtual domain of the internet. Because much of the current discussion of 'serious' photography' here is heavily biased toward a particular interpretation of photographic practise, it may be assumed there is one way and one way only to work with curves. There is not. Alter the premise, and the identical logic presents a different picture.

If one assumes that curves must be drawn relative to Zone I, they obviously cannot intersect. Change the premise, and they must always interesect at V or VI, or wherever the photographer chooses.

This is all a bit like bicycles. All one sees in races today are fine instruments for going fast in races, and the assumption is that carbon fiber, titanium, and aero wheels are essential to being able to ride a bicycle efficiently. Many new to the sport are shocked to learn that there are 50 year old bicycles that can go quite fast, comfortably, when the premise is changed from a Team Time Trial in the Tour de France to an amateur's tour from Paris to Brest and back, or across the Pyrenees.

Today's time trial bicycles are brutally fast and aerodynamic, a great deal like Phil Davis' BTZS. Minor White's approach to photography is more like an Alex Singer rando bike. And in White' world, curves intersect whenever they need to, to make a good picture.

If I missed the point of your question, I apologize. It is cold and snowy today, and I would dearly love to go ride my bike !


d

Yes, there are lots of ways to skin that cat, but in the end, it all comes down to how it applies to your need at hand.

If you want to interpret the data within classic sensitometric/densitometric methods, I don't think it can be done.

If you want to take the characteristic curve generated by multiple identical exposures of a negative processed at differing compaction and expansion times out of formal sensitometeric interpretation, sliding the curves up and down, left and right (but NEVER rotating them), forcing all curves to intersect on a particular Zone, then you CAN make the curves cross each other, slight as it may be, without changing exposure, and you can get some useful information from that exercise.

You are essentially changing the dynamic range and gamma of the filmstock with compaction and contraction, but the amount of slewing around the fulcrum is going to depend heavily on how radically you alter your processing from "normal" (actual gamma), where you put your aim point on the curve (usually within the straighline portion) AND where the majority of the information falls on the straight line portion of the negative (apparent contrast) within the dynamic range of the emulsion.

Come to think of it, I don't know if that description is actually valid, because I am attempting to describe an event using descriptors that depend on a rigid implementation of a process that we just threw out the window, if you see what I mean!

Precision densitometry and sensitometry required to make this a science, lends itself more to machine-based processing than tank/tray processing (yes, there are many out there who are remarkably consistent, no doubt) because of generally uniform, batch to batch results.

When you mix a certain developer in 50 gallon batches and have a 150 gallon tank from which you replenish a 500 gallon, well-seasoned developer, and run and plot control strips 4 times a day, you tend to fairly consistent results that can be tweaked fairly tightly to a certain process gamma.

However, even this process has "wobble" and acceptable limits of variation, so you can imagine how relatively useless it probably would be to try to run this sort of system daily in your darkroom for quality control if you operate on well seasoned intuition!

That's not to say that this sort of information cannot be useful to home lab users; it can be, but I would imagine it would be only in a very general, comparative sort of way; a jumping-off point from which to fine tune your experience base.

Shoot two identical negs, soup them in a known developer and an unknown developer, measure identical patches and compare densities; "oh, it's a stop more dense, I gotta remember to back off a stop when I want to develop this stock in this developer"'; that sort of thing.

To be stupidly obvious, I think art photographers have a very sophisticated internal database, for lack of a better term, that is called "experience" and from which flows intuition. I also think it follows the same rules of classical sensitometry, but not it a manner that sensitometric language would approve!

If you were a photolab that needed to nail this process down for repeatability, you would invest heavily in testing and documenting this process to ensure repeatability.

As a art photographer, you may do the same, but have much more room to experiment a fine tune on a case by case basis.

I'll shut up now...

DF, there is no need to write in defence of the Zone System. I, personally, as some other Europeans (not many to tell the truth), am known as an Anti-Christ of the Zone System, but as an aid tool I have no problems to acknowledge its simplicity and usefulness. And it was perfectly fine to treat the matter as zonal, as the question itself was put in Zone terms, however always keeping in mind that the Zone System is a mere formal aid, and that it doesn't change the physics of things a bit.

I beg your pardon if I gave you the impression of turning the topic into a personal thing. This thread is and should be nothing but an academic conversation among fellows, but I know myself and know that I tend to overreact when a picky and confusing question has been debated and there is a general consensus, but then perhaps someone kicks in messing things up again from the start.

By reading the question, I assumed that "...identical..." meant "kept all things equal", which implies "at constant exposure". If you look at the graphic you posted and what's written in it, I guess you understand that you didn't exactly enlightened a matter which was already confusing for the poster (and at least under some aspects even for those who answered, me of course included). The fact that you didn't expand the concept but rather closed with a "read this and that and you'll know better" made the rest.

But now that I've re-read the question again, honestly I'm not even sure anymore if the word "identical" was referred to the exposition, or instead to the brand of films (that is: take five Ilford FP4 films and not two Ilfords and three Agfas) or to the days of the week or to whatever else, so you may have gotten the question better than I did in first place (very likely, since I speak English as a foreign language) and I beg your pardon again if that was the case.

Making a long story short, I stand on my position that - keeping all things equal but development time - there is no crossing or "pivot" point simply because the curves do not intersect. By changing parameters, by biasing, or by shifting the graphics, I agree with you that a common point can be created, and that all considerations coming from it can be useful or at least educative.

Good Morning Marco

First, your English is wonderful.

Now, in this forum, I usually assume the atmosphere over coffee, or wine, with friends, rather than an academic, nor thoroughly rational, approach. There is a variety of backgrounds and experience, and a generally common purpose, and interpreting a question is necessary. Our inevitable errors must be accepted, and taken in friendship. Insight is welcome. But I worry that a too literal reading can be more misleading than an educated guess.

I will usually rely on my experience as a teacher in my interpretation of questions of this nature. Intuition is merely reaching a conclusion through reading the data as a whole, and can help interpret otherwise puzzling datums.

As for the Zone System, I've come to believe that today it is universally misunderstood.

Adams rooted the Zone System, as did Minor White, in the act of Visualising how the picture will look. All subsequent creative and technical choices, therefore, pertain only to that Visualisation. It was not envisioned, practised, nor taught by Adams as the "Verification of Densitometry by an Expensive Camera".

I believe, and I am certain Adams and White would agree, that Baudelaire had it right:

" Art is Technique, charged by emotion";
and
" Of it's own, Technique is impotent to create anything ".

White expanded much of what Adams originally proposed, and Adams was supportive of White's doing so. White taught there was nothing sacred about 10 zones, that 8 or 12 zones might be more correct for an individual's vision. Over, and over, they stressed individual's Seeing, Vision, and a clear reason for making the picture rather than a literal, technical, and 'correct' practise according to some arbitrary and inviolate standard. They both used music as an analogy for their photographic principles. I 'correct 10 zone scale' is to me boring as all music played in C Major. I prefer minor keys, and often various modes, and my own photographic palette reflect that.

Are you a Zone System Anti-Christ ? Good. I think the the tendency today is to practise the Zone System as though a Torquemada will hunt us down for violating good doctrine. Perhaps an occasional photographic Savaronola would be a good thing. But I prefer a quiet life.

To be honest, I don't care too much about physics. Gravity is fine, but I'm more interested in what I can do with it. Barbaric, I know.

I look forward to a bike ride with you... as long as I know where you're heading, I'll probably catch up !

Will you be seeing any of the Olympics ?


don

df cardwell said:

Will you be seeing any of the Olympics ?

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Yes, probably tuesday! I went to photograph the torch at the stadium this morning, and I have planned to repeat the photographs overnight...

It's so cool being in the middle of the action!