No Shoulder on most Ilford curves?

Hello,

 

I'mm starting to use Pan F and Delta, and looked up their

characteristics curves. Surprisingly, neither of them show a

shoulder. So I checked other common Ilford films, HP and FP, and

only FP shows a shoulder. I also checked Kodak's curves fo VP and

they also show no shoulder. Do they just not print that part of the

curve, or what's the deal? Also, where can I find a comparison of

full curves between slow, medium, fast and new technology(delta or

tmax) films?

Not wanting to appear stupid or something, but does this really matter? I mean, what are your references? Are you going to shoot and then process your films to exact standards? Personally photography's about "bend the rules", not sticking to them. Unless of course you're doing scientific, aerial or other types of technical photography?

Gabriel,

 

Over the years, Ilford has published film curves for their films in several of their developers. For some reason, sometimes they do not show the graph plot out to the shoulder. I can assure you that all Ilford films do shoulder-eventually. Pan F+ shoulders faster than their medium and high speed films. In general, the higher speed films have longer curves and shoulder later. In many developers, FP4+ and HP5+ have very long essentially straight curves. Unless you are either seriously over exposing or photographing a scene with a very long brightness range, the shoulder may be meaningless anyway.

 

Some developers, such as Diafine, with force the early shouldering of the Ilford films, and some films, such as Agfa APX 100, have a natural tendency to have a gentle early shouldering in many developers.

Rogan:

 

Checked your web site and you are a way better photographer than I. Beyond that your verticals are vertical. Which to me is one of the things that separate real professionals from amateurs that charge.

 

I get fairly good results in my B&W dark room. However, I have seen B&W prints in museums (some taken over 100 years ago with wet plates) that you can almost believe you could step into.

 

It seems to me that that last 5% of quality in a B&W print produces an impact way disproportionate to the actual measurable difference in tonal range, contrast, gradation or resolution.

 

I have a densometer, I have never used and a step wedge if I can find it. If I have to study film curves, take densometric readings and print a step wedge at the beginning of every dark room secession to get that type of quality then I guess I will. I may have to wait till I retire to get enough time though.

 

However, I am hoping I won't have to.

 

I guess it is safe to say that those photographers 100 years ago got those results without any of those things. I just wish I knew how they did.

It's the same answer you get to the question, "How do I get to Carnegie Hall?" The answer: "Practice, Practice, Practice."

I had a friend of mine who by the time I met him had been a professional photographer for over 40 years. He was a master of Gamma and film curves, he just didn't know it.

 

Maybe that is exactly why those of us who don't do it everyday all day long need to study.

Gabriel, guys;

 

It is a law of nature. All films have a shoulder and a d-max. The development process runs out of silver sometime or another. It just may not be shown on the plot. If it above about 3.5 it is difficult for instrumentation to measure, and so is simply not shown by most mfgrs.

 

Well, as a matter of fact, all films have a toe and a d-min as well.

 

Nature does not have a toe, shoulder or dmax (unless you consider the blackness of space and the white of a nuclear explosion being limiting factors ;-)). In fact, nature is linear with a slope of 1.0 by definition. A reversal film or print has a slope of about 1.7 to 1.5 so that the eye integrates it as an overall 1.0 by the fact of having a toe and shoulder with lower contrast. The overall effective contrast of a slide or print is interpreted by the eye as being about 1.0.

 

Ain't science wonderful. There is a lot of it involved in making film and paper work right whether it is color or B&W.

 

Ron Mowrey

Ron,

I understand what you mean, and you are right in a certain sense, but the human eye is part of nature and it does not have a gamma of 1. However, if the reproduction of a scene has a gamma of 1 and the same brightness range as the scene, the eye will see it as it would see the original scene. Our camera's eye should not match the performance of the human eye.

 

We don't usually want the utmost in realism except perhaps when photographing a crime scene or copying a work of art. The pictures we enjoy most are abstractions to a certain degree, or should I say an uncertain degree.

Neal, you're comments are appreciated.

 

I was going to leave this thread. However, would like to add this. I haven't been in a real darkroom in almost 10 years - something that's sorely missed. Beside printing and getting familiar with my work, this was always my "quiet time".

 

In the intervening time I've been working with PhotoShop. This may come as something of a contradiction given some of my "anti-digital" posts elsewhere on this site.

 

The point I'm trying to make is that yes, through PhotoShop I've "learnt" about the value of "curves" albeit in a slightly different context to Gabriel's intial post.

 

Through this experience, and only just recently, I've now come to appreciate my own work in ways that were never apparent before.

 

Neal, like you, I've been striving for that "jump in transparency" in my prints where the shadows are alive with detail and the highlights - eluding to Rowland's "atomic blast" - still hold.

 

All this stuff was in there as it could be seen in the negs. Do you think I could get this right in the prints? Rarely if ever. That is, until passing this lot through PhotoShop and this is where its happened.

 

Take a look at my recent post on digital sepia toning to get an idea of how I work this lot - using quadtones.

 

For the most part, the results look good on screen, have looked good on the printed page. Still "struggling" to get a decent print though - most of the issues appearing to be ink/paper combinations.

 

Coming back to Gabriel's post and noting comments of the other contributors here, yes it helps to understand the materials you are working with. However, between the ideal and real there's usually a huge gulf which can only be bridged by experimentation and accummulated experience. There's a world of difference between Ansel Adam's Rising Moon over wherever and scrabbling around in the gloom of some boogey bar photographing a musician who's bopping around to his own groove.

Patrick;

 

I never said that the human eye had a gamma of 1. It sees nature which by definition has a gamma of one. That is the density to 'exposure' ratio or slope of a natural scene and has no toe or shoulder. The dmin is total brightness and the dmax is total darkness. That is related to my bad joke above, but it has an element of truth as well. There is no cutoff limit in nature, and it is linear. They eye, being chemical in the nature of its imaging process has a toe and shoulder, although I don't, offhand, have the range or the contrast.

 

Chemical and physical 'processes' such as film and digital photography have a toe and shoulder in the D Log E and V log E curves as a consequence of physical and chemical laws or limits. The lower contrast toe and shoulder render the overall impression of a scene, interpreted by the eye and compared to the original, as being low in contrast unless something is done to compensate for these 'artifacts'.

 

Therefore, to make the scene appear more natural in integration by the eye, due to the toe and shoulder, the mid scale contrast has to be higher.

 

There are numerous textbook treatments of this, so I'm not stating anything new here. If you wish to get into it and the very complex mathematics, I can post the references, but many of them are out of print and at least one is a proprietary SPSE text for members only IIRC.

 

It also relates to the method in which a 'compensating' developer affects the film and print tone scales, as the final print curve is the integral of the sum of two curves, the film and the paper. (That is a very simplistic answer to a complex problem and does not really do it justice)

 

Ron Mowrey

Ron,

 

Have it your way for your own use, but it is not proper to speak of the "gamma" of nature in a photograpbic forum. Gamma was defined a long time ago as the slope of the linear portion of a graph of photographic density vs Log of illumination in meter-candle-seconds that caused the density through development. Without that curve there is no gamma. We now use the toe and sometimes the shoulder of films, and so refer more often to "contrast index" than to "gamma".

 

Without reference to some sensor responding to the illumination provided by Nature, there is no point in talking about gamma.

 

Nature does have limits. If you want dark, stand in the hills of West Virginia on a cloudless night. You can still see the outline of trees against the stars, so if you really want dark, go down into one of our coal mines.

 

Photographic emulsions are a part of nature that humans discovered. They certainly have limits. In some sense, their limits are not as great as those of our eyes, but our eyes can adapt in 15 minutes to darkness that would take hours of exposure to record on film.

 

I don't know exactly what we are arguing about, but if you really want to find something of mine to contradict, go to www.APUG.ORG.

Patrick;

 

I'm just explaining something in laymans terms. Of course nature has no 'gamma' but it does have a 1:1 relationship WRT to density vs light intensity. The average user here can 'understand' gamma in that context.

 

Dark is the absense of any light whatsoever, and actually space does not quailfy due to the sun and stars. The coal mine might. The absolute in brightness has been defined but I don't remember off hand what it is.

 

See DeMarsh et al. Bartleson et al. and others for references.

 

I'm trying to explain that a natural scene, by definition has no toe and shoulder. They are artifacts introduced by the physical and chemical processes of the eye and photography.

 

They are 'defects' in the original scene that during reproduction are multiplied over and over during the replication process unless some method is taken to remove the 'errors'. Like making a tape of a tape of a tape, etc. The 'gamma' of a photograph, or 'contrast' of a photograph is carefully adjusted so that the integration of that scene when percieved by a viewer is a close reproduction of the original. To do that, the contrast of the photographic materials must be carefully adjusted to give the viewer that 'feeling' of the original scene. This requires careful attention to the toe, shoulder, and mid scale contrast of the final photographic print. Usually, mid scale contrast of a print must be ~1.5 and mid scale contrast of a slide must be ~1.7. Those are unarguable facts.

 

Neg-pos systems are made to minimize defects, but pos-pos systems are not by their very nature.

 

I'm trying to introduce some tiny bit of quantitative science into discussions that are otherwise qualitative in nature. I'm not arguing per-se, unless the individual reader takes it that way or is wrong, neither of which I am imputing to any of your responses, BTW.

 

Regards.

 

Ron Mowrey

Perhaps we are on the same page after all.

 

So, let me take a little different approach to explaining what I think you are saying in other words. When I teach something (how could I not, with 6 kids to bring up?) I find that the more different ways I can explain something, the more likely it is to be understood.

 

In an absolute sense, there are reflection densities in Nature, and there are various degrees of illumination falling on them. We can design instruments that measure both incident and reflected light. Using such instruments and the method of just noticeable difference we can establish response curves for human eyes. It is less difficult to establish response curves for photographic materials. In either case, we can find a mathematical equation that represents the response curve, though it may be a piecewise conglomeration of several equations.

 

In early days, the linear part of the response curve was thought to be the part that should be used for most realistic representation of the original scene. The slope of that curve was labelled, for no good or bad reason, with the third letter of the Greek alphabet.

 

Subsequent research found that the human visualization of a print, even one that had the same measured brightnesses as the original, was not the same as the visualization of the original. Well, the eye is after all a scanning device, with rapidly variable aperture over some range, and less rapid change of sensitivity over a much wider range. It might be that the best simulator of the eye would be a (bad word coming) digital system, but its output would probably not be a good photograph.

 

There was a time when some designers of "hi-fi" audio systems thought that the best system would send out what an average listener would hear upon listening to the original music.

 

Now I really have lost track of the discussion. See you later.

Patrick;

 

You have stated it well up to where you left off.

 

The name of that curve is a cubic spline BTW. That is the curve that nature imposes on the photographic response to it by virtue of the chemical reactions in development. They cause a toe and shoulder to form. The toe is formed due to uneven sensitization and development, and the shoulder is formed due to exhaustion of the silver halide resource in the film itself. The more blended emulsion and silver present, the longer the straight line portion of the spline, and the shorter the shoulder.

 

Printing on this straight line is best so that the toe and shoulder of both film and paper are not multiplied by each other. You see, the reproduction process is the multiplication of the derivatives of the two splines (in simplistic terms). So, a straight line film of 0.5 and a paper of 2.0 would produce a final print of 1.0 which is what you 'think' you saw in nature, but due to the toe and shoulder of the print material, you actually see about 0.8 or maybe less.

 

Therefore, films are built at about 0.6 and papers are built at about 2.5 for a final contrast of about 1.5 for a percieved tone scale with an approximate curve of 1.0 to the eye integrating toe, mid scale, and shoulder.

 

Ron Mowrey