Understanding EI???

[Stephen Benskin]

Originally Posted by Stephen Benskin View Post
The first thing one needs to understand is that the ISO speed is the actual speed of the film.

Imagine that!

That is to say it is not arbitrary, purposefully overrated by manufacturers, a guesstimate, not the "real" speed that has to be personalized, or a value arrive at by scientific means and does not have to do with reality.

 

[2F/2F]

Originally Posted by Stephen Benskin View Post
The first thing one needs to understand is that the ISO speed is the actual speed of the film.



That is to say it is not arbitrary, purposefully overrated by manufacturers, a guesstimate, not the "real" speed that has to be personalized, or a value arrive at by scientific means and does not have to do with reality.

Yes, yes. I agree with all of it...hope you didn't think otherwise.

 

[RalphLambrecht]

Originally Posted by Stephen Benskin View Post
The first thing one needs to understand is that the ISO speed is the actual speed of the film.



That is to say it is not arbitrary, purposefully overrated by manufacturers, a guesstimate, not the "real" speed that has to be personalized, or a value arrive at by scientific means and does not have to do with reality.

Stephen

I cannot entirely agree. I agree, the ISO speed is not arbitrary, it is not purposely overrated by manufacturers and it is not a guesstimate, but it has to be personalized, because the ISO speed is determined by methods and standards, which may differ from what the photographer wants to achieve.

This is the reason to conduct personal film testing and the need for EI vs ISO. And, since these personal test consistently return a speed that is lower than ISO, the ISO standard seems to differ from what photographers want to achieve, and therefore, it differs with customer 'reality', which is an unavoidable fact. How can ISO know what developer I'm using?

This is not a criticism towards the ISO speed, method or the people who put it together. The ISO speed is a valuable comparative measure, but it is not the all-encompassing answer of the actual film speed. For that, the photographer needs to do his or her own testing. This is, to answer the original question, the reason for an EI.

 

[Chuck_P]

The following said with all due respect, but...........

Ralph is not talking film speed when he says to rate the film 2/3 stop higher. He is talking about exposure.

Of course! Rating the film differently than the ISO figure is all about tweaking one's exposure, no one said differently, I don't think so anyway. Why you insist on informing all of us that when we rate our film a different speed, then we are somehow misunderstanding the whole concept of film speed or confusing film speed with EI or whatever-----is mind boggling to me. The ZS, flawed as it may be, in it's bubble gum sensitometry, is a very practical method of applied photographic technique. That, with all due respect, is something I can take to the field and use.

I'm sorry, but you’ve totally misinterpreted what I was saying. I never said anything about densities below fb+f. The 0.29 log units was log-H units (not density units) below the exposure required to make 0.10 density above film base plus fog.

My apologies.

As far as I know, no one has ever said that 0.10 is the minimum useful density in any scientific paper. It's only in popular texts.

Pardon my "simpleton" point of view, but I invite you to come to my darkroom and put a negative density of less than .09 onto my paper and we will see just how useful and practical it is. If I can't put it on my paper, it don't mean "jack" (intentional poor grammer).

But there's a noticeable and quite useful difference at 0.1, the commonly accepted practical threshhold of a film's sensitivity to light, and the commonly accepted and very practical determination of a working man's film speed. Perhaps that won't be found in any scientific paper either or the Delta-X equation but it does quite well to define one's personal film speed, or very own EI, or "working" film speed, or whatever may be the term that is acceptable in the scientific papers.

I do not necessarily doubt all that you say and the apparent mental acumen with which you say it. But to all the "newbs", just remember to "expose for the shadows and develop for the highlights", that will never change with the 'negative' film that is in your cameras.

 

[Stephen Benskin]

Stephen

I cannot entirely agree. I agree, the ISO speed is not arbitrary, it is not purposely overrated by manufacturers and it is not a guesstimate, but it has to be personalized, because the ISO speed is determined by methods and standards, which may differ from what the photographer wants to achieve.

This is the reason to conduct personal film testing and the need for EI vs ISO. And, since these personal test consistently return a speed that is lower than ISO, the ISO standard seems to differ from what photographers want to achieve, and therefore, it differs with customer 'reality', which is an unavoidable fact. How can ISO know what developer I'm using?

This is not a criticism towards the ISO speed, method or the people who put it together. The ISO speed is a valuable comparative measure, but it is not the all-encompassing answer of the actual film speed. For that, the photographer needs to do his or her own testing.

Ralph,

This might just be about semantics, but I think it's an important distinction in order to really grasp certain concepts. There is film speed and there is personal taste in exposure or personal experience with exposure (EI), but it shouldn't be considered film speed.

Again, I've stated why the personal testing isn't so much about gaining a personal EI that is really different from the ISO. If you really evaluate the structure behind the "personal film test", it really doesn't reflect anything. It introduces multiple experimental errors and there are many factors no body considers. It also isn't an apples to apples comparison with the ISO test, so it can't comment on anyway with the the ISO speed, which for me has to be considered the actual film speed. Anything and everything else is choice. I think it's important to have a believable standard. The ISO speed may not work for a particular individual, but that doesn't invalidate the method.

The almost universally obtained lower results from the personal testing is really the result of using two different methods that don't relate. It's really like one person using the standard prior to 1960 and another using the post 1960 standard. The results will have a constant 1 stop difference in speed between the two.

People who use the ZS testing method will obtain results that are consistent with the type of results obtain prior to 1960. Remember the ZS testing procedures haven't changed since the forties while the ISO speed standard has. Zone System speeds agreed more readily with the speeds obtained from the pre 1960 film speed standard. The results obtained with film shot prior to 1960 were excellent as are the results for the people who obtain similar EIs doing ZS testing today.

But, let's remember the reasoning for the speed adjustment in the 1960 standard. Many people were already automatically rating their films a stop faster. There was a two stop safety factor which was no longer necessary because of the improvement in exposure meters and lenses (lens coating included). Smaller cameras meant the additional exposure will have a noticeable affect on sharpness and grain because of the higher degree of enlargement as well as longer printing times. Now, because of the discrepancy between the two testing systems (because the ZS testing was never updated, and because of many other problems with it) people are obtaining EI speed values 1/2 to 1 stop slower than the ISO speeds. So, how does the concept of the pre and post 1960 speed example compare with the ISO and personal ZS speeds? It is the same concept. There isn't any difference. Speeds were once a stop slower and people complained. Now, they are a stop faster and people want to change back. Or do they? I don't think people really are aware this is the difference. Most incorrectly think they are obtaining more accurate speeds for their personal working conditions than the ISO speeds. Don't agree with my premise? Break down the Zone System testing method and compare it to the ISO method (you will also have to overlay the standard exposure model onto the ISO method). I think this could be educational for a lot of people. Personally, I do sensitometric testing with a calibrated sensitometer and obtain speeds relative to today's ISO speeds.

I have to disagree with the idea that "the ISO standard seems to differ from what photographers want to achieve, and therefore, it differs with customer 'reality', which is an unavoidable fact." It is way too speculative, vague, and subjective to be supportive. Jones found that any additional exposure above the first excellent print didn't show any appreciable increase in perceived quality. And the ISO standard is already one stop over the first excellent print. Even if you want to justify the use because of increased shadow contrast (which is valid), some could argue that the perceived increase in "quality" in a such a small area of the tonal range doesn't justify the loss of sharpness, increase in grain, or increase in printing times. Also, many factors can negate the "advantage" such as a higher flare factor or various paper curves. Saying that the customer wants a higher safety factor is something that can be supported.

I also think people are thinking they are getting the "real" speed of their film using the ZS testing method so therefore they think it is superior, but in actuality, they are just unaware of anything else. I mean, how diligent are most people with their testing? For example, I know most don't take into consideration latent image keeping. It's also almost impossible to do accurate real world confirmations on the results. One would have to be able to measure flare for that. What about those who test using a meter with a high red sensitivity under open shade (blue light) using a lens without 1/3 stop increments, obtains their personal EI then goes out and shoots a scene using an orange filter with a lens they didn't do the test with? How many do that unaware of all the influences to the exposure results (notice not film speed) yet are confident in their EI over the ISO because they determined it themselves so that it reflects their personal working methods? So how good are personal speeds when the assumed testing method could be over a stop off and/or imposes so many variables that it probably doesn't reflect actual shooting situations?

Basically, since you really don't see an appreciable increase in quality with the increase in exposure, the photographer not knowing this assumes the additional exposure is better because it reflects his approach and because some popular book told him so. They are happy with the results they get. They have less loss because of accidental underexposure, and they never do a head to head analysis because, let's face it, most of us aren't scientists and just want to get to the business of shooting. Thus, they conclude their system is superior to the ISO standard - a subjective conclusion.

What about different developers? The current ISO standard doesn't use a standard developer anymore. The T-Max films kind of initiated that change. The reason why they only had EIs when they first came out was because they did poorly in the ISO developer. Kodak ran their tests according to the ISO standard except for the developer used but since you can use the ISO prefix only when the standard has been explicitly followed, Kodak had to use EI. In order to reflect a better real world usage, manufacturers can use any developer they wish in their ISO testing but they must note it. Chances are Ilford films are tested in ID-11 and Kodak films are tested in D-76, T-Max, and/or Xtol. Anyway, most general purpose developers will produce speeds around the ISO speed. Specialty developers should be tested for, but again, how accurate can you guarantee the testing to be?

Now, take into consideration how film speeds don't really change much with the Delta-X Criterion / fractional gradient method and the need for testing for your personal EI really comes into question. This might sound cryptic to some, but it really is an important consideration.

 

[Steve Smith]

There is film speed and there is personal taste in exposure or personal experience with exposure (EI), but it shouldn't be considered film speed.

There is also compensation for metering technique and/or errors in shutter speed (although this may come under the personal experience heading).



Steve.

 

[Stephen Benskin]

CPorter,

So, your argument is about how far we should dumb theory down? If you want to argue about what works, why not just go with Sunny 16 and call it a night? I'm talking about the CONCEPT of film speed and you are countering with what works in a practical manor. Heck, a disposable camera works. (We could actually have a good theoretical discussion as to why a disposable camera works in most situations.) If you only like posts containing practical shooting suggestions then don't read the posts containing theory. It's that simple.

I think we should also remember an earlier post where the poster said basically, sometimes it takes awhile for new stuff to sink in and start to make sense. I used to stare at the equations for hours, days, weeks, and months input different values. I remember calling up Dick Dickerson at Kodak and asking about some concept. He gave some answer in a nonchalant manor. The answer made no sense to me and I got the impression that he kind of blew me off. Well, months later, I realized he gave me a very straight and concise answer to my question, but I just wasn't ready to understand it.

One of the things I like to do is to review old texts that I've read years ago. It's amazing how differently you interpret them and how many new concepts you stumble across that you simple missed the previous times through because you weren't ready for them. Recently, I went back through my photography books looking for references to the Delta-X Criterion. I was amazed at how many of them talked about it in one way or another. Many would only have the phrase like "they found a correlation between the fractional gradient method and the fixed density method." First time through that meant very little, but now I know it was referring to the Delta-X Criterion. I just find those little discoveries exciting and it's a great yardstick to measure the growth in knowledge especially when I frequently get the impression I've forgotten more about photography than I'm retaining.

 

[Stephen Benskin]

There is also compensation for metering technique and/or errors in shutter speed (although this may come under the personal experience heading).

Steve.

Definitely metering technique, but I often wonder how much modern shutters really have to do with any variation or how much testing people actually do to compensate for variations in shutter speeds. If you think about it, you would have to test each shutter speed in order to determine the variation from setting to setting. How many people do that, therefore, how many people actually incorporate shutter variation into their personal testing? How many people do a test for each of their lenses too?

I know much of my actual film speed and personal choice discussion is coming across as kind of ridged, but that is not what I'm going for. Many people get confused by the concepts of exposure, ISO speed, personal speed, etc especially when they are starting out. One of the things I am attempting to do is trying to work through ideas to find a way to straighten that out. I'm thinking that maybe if we use the ISO film speed as a solid base to work from, the other concepts which are variations to the ISO speed would be more clear and therefore more flexible and freeing. It's a work in progress.

 

[Steve Smith]

Definitely metering technique, but I often wonder how much modern shutters really have to do with any variation

Not all of us always use modern shutters though.

If you think about it, you would have to test each shutter speed in order to determine the variation from setting to setting. How many people do that, therefore, how many people actually incorporate shutter variation into their personal testing?

I have a shutter speed tester but have not tested every shutter at every speed. As most people don't have shutter speed testers, I would say that the answer to your question is - not many.


Steve.

 

[Chuck_P]

CPorter,

So, your argument is about how far we should dumb theory down? If you want to argue about what works, why not just go with Sunny 16 and call it a night? I'm talking about the CONCEPT of film speed and you are countering with what works in a practical manor. Heck, a disposable camera works. (We could actually have a good theoretical discussion as to why a disposable camera works in most situations.) If you only like posts containing practical shooting suggestions then don't read the posts containing theory. It's that simple.

Your wrong and if you actually knew anything about me, you would not suggest such thing about "dumbing theory down."

The original post did not ask for theory, it wanted to know why people rate film different than box speed, what is the reason for doing so, etc... You offered the theory and all its nuances and in so doing proceded to tell (ok, imply) that we all have it misunderstood, we are confusing EI with film speed, with all due respect, it's insulting. That is not a helpful response. The answers I, Ralph and others provided were something of concrete value to the OP where an action could be taken and definite response observed. Whereas yours was offered up in mixing bowl convoluted by theory, and intellectual fantasy. Note that I did not say it was all wrong, but I am saying that it is of little to no value in terms of the OP putting film in his camera and proceeding to expose and develop it.

My post sounds like I'm being a smart ass, but only a little annoyed really, perhaps some of my own doing. I'm off to work and I'm probably overdrawn.

 

[Photo Engineer]

This kind of sounds a lot like the concept behind the inertia speed method which was unanimously rejected by the Ninth International Congress of Photography in 1935 because the inertia speeds varied as much as 500 percent with increasing gamma. It also didn’t work because like Berg said, it was “a purely academic linking of the speed with an almost entirely arbitrary property of the characteristic curve.” It also goes against findings with psychophysics and perception. I've probably just misread your post.

It is not an inertial speed.

If one assumes that the gamma is 0.65, the optimum for negative films, then the method works, as you are not forcing overdevelopment and high gamma.

PE

 

[Thomas Bertilsson]

I use the EI exposure index of film to adjust contrast.

Flat scenes with no deep shadows I underexpose, scenes of extreme contrast I overexpose. Then I adjust agitation and subsequently development time to compensate for the exposure to bring the midtones and highlights to where they belong.

You can argue what ISO is all day long, but if you want perfect contrast negatives every time that print on your paper of choice, you can't religiously subscribe to it as it has very little practical meaning for a photographer. Tri-X, for example, is used and exposed by photographers from EI 50 to EI 3200 in ways that work for various photographers.
Forget what the box says, expose lots of film and learn how it reacts to various exposures and development regimes, and soon you'll see that you simply must learn to adapt to the lighting of what's in front of you when you do the shooting. That is if you want perfect negatives every time that print with ease.
This is one reason why it's so much easier to use a single emulsion if you can. It takes a lot of time to learn what exposure index you must use in various situations. There are so many variables.

Anyway, that's how I interpret my EI, and how I use "film speed" to get the results I want.

- Thomas

 

[sharris]

fyi...be sure to check our www.scribd.com for books that may be out of print or other older reference manuals. A ton of info there. Cheers. (click the 'explore' function as I recall)

 

[Stephen Benskin]

Your wrong and if you actually knew anything about me, you would not suggest such thing about "dumbing theory down."

The original post did not ask for theory, it wanted to know why people rate film different than box speed, what is the reason for doing so, etc... You offered the theory and all its nuances and in so doing proceded to tell (ok, imply) that we all have it misunderstood, we are confusing EI with film speed, with all due respect, it's insulting. That is not a helpful response. The answers I, Ralph and others provided were something of concrete value to the OP where an action could be taken and definite response observed. Whereas yours was offered up in mixing bowl convoluted by theory, and intellectual fantasy. Note that I did not say it was all wrong, but I am saying that it is of little to no value in terms of the OP putting film in his camera and proceeding to expose and develop it.

My post sounds like I'm being a smart ass, but only a little annoyed really, perhaps some of my own doing. I'm off to work and I'm probably overdrawn.

One of the problems with posting is that there are people with different levels of knowledge on the forums. My original post was to correct characterizing ISO film speed as "arbitrary" which I thought was misleading the OP. Then Ralph made a comment, and since Ralph is very advanced in his knowledge I addressed him but I tried to maintain my original concept and directed some of the conclusions toward people who weren't just at Ralph's level. It's a difficult balancing act to do, but I also tend to reference sources so they know it's not just my opinion and so people can look into it further if they wish. Maybe it would be more productive if you addressed specific points that you disagree with so that there can be a discussion of the issues instead of a generalized attack about documented concepts being fantasy?

Ralph was the first to put up a graph of the ISO standard. Do you think a newbe would understand that? Do you think they would understand why the contrast parameters were chosen? He posted it for more advanced people. But even for those, many (not all) have the common misconception that the ISO standard doesn't reflect accurate film speed for normal processing because the contrast parameters equal an average gradient of 0.62 or they assume that 0.10 is the target density for exposure just because it is the speed point. So, I then presented a graph showing the underlying theory for the ISO standard because simply presenting the ISO standard's graph doesn't explain enough about film speed. Why shouldn't there be information presented for people on all levels?

I'm sorry if you found it insulting, but there are many people who believe the Zone System testing gives them the "real" or "actual" film speed results and that the ISO is somehow false. Thus the EI / film speed distinction. Also, most photographers believe that film speed is based on density instead of contrast and have never heard of the Delta-X Criterion. While this doesn't hurt your shooting, Ansel did much of his best work before developing the Zone System, I think understanding theory helps. Like the theory of gravity, you can tell someone that when you drop something it falls, or you can explain what gravity is and they can fly to the moon.

 

[RalphLambrecht]

I always learn something in these exchanges. APUG is a great place!

 

[Sirius Glass]

Your wrong and if you actually knew anything about me, you would not suggest such thing about "dumbing theory down."

The original post did not ask for theory, it wanted to know why people rate film different than box speed, what is the reason for doing so, etc... You offered the theory and all its nuances and in so doing proceded to tell (ok, imply) that we all have it misunderstood, we are confusing EI with film speed, with all due respect, it's insulting. That is not a helpful response. The answers I, Ralph and others provided were something of concrete value to the OP where an action could be taken and definite response observed. Whereas yours was offered up in mixing bowl convoluted by theory, and intellectual fantasy. Note that I did not say it was all wrong, but I am saying that it is of little to no value in terms of the OP putting film in his camera and proceeding to expose and develop it.

My post sounds like I'm being a smart ass, but only a little annoyed really, perhaps some of my own doing. I'm off to work and I'm probably overdrawn.

I do not know what your background or experience is.

Yes, the OP did not ask for theory, but In My Not So Humble Opinion, IMNSHO, I found what Steve said and took the time to carefully write enlightening. I frankly is tired of people complaining about ISO when the meter the sky and can't get the shadows, I frankly is tired of people complaining about ISO when they call correcting for aperture or shutter variabilities and inaccuracies as the Zone System, and I frankly is tired of people complaining about ISO when they are N-1, N-2, N+1, N+2 processing and are unaware of the results in contrast and accuity. That is not to say that there are many here that really know what they are doing and why. Steve's post combined with Ralph's and PE's comments are were not only refreshing but also articulated with a scientific approach what I had learned from experience.

Steve

 

[Photo Engineer]

Thanks Steve.

I have some additional thoughts. These come from the standpoint of one who designed films and papers and who had to carry out ISO measurements constantly for both materials as well as grade papers.

It is impossible for a researcher or manufacturer to test all new products in all developers under all conditions. All they can do is their best. And, they apply some sound scientific methodology along the line. In the final analysis though, one must work backwards from the print to the original and also one must use only one process. At Kodak, we used D-76 for most all release tests and used a constant exposure of something like 1/100 seconds to light at 5200 K for film. I may not have this correct, but you can see the conditions if you look up Kodak specification sheets.

Most all papers were tested in Dektol 1:2 or 1:3 with a 10" exposure for enlarging papers and another set exposure for Azo and other contact papers.

As I stated before, and can be seen above, the aim contrast of an in-camera consumer negative film (color or B&W) is about 0.65. A grade 2.0 paper (VC or graded) has a contrast of about 2.5. I have posted both scales here. There are about 3 or 4 useful ways of getting at the ISO speed of either (film or paper scales respectively), but common to both is the need to use the straightest part of the curve. Bumps and bows and soft toes and shoulders don't count. They distort the results. Push and pull don't count, as they distort contrast.

Yes, you can get some better result under some conditions by push pull or over or under exposures along with push or pull, but the film was not designed for that, nor was the guideline ISO determined under any of those conditions. So, it is no wonder that many people wish to test their own conditions. They may under expose, over develop and use a low contrast grade paper as an example. This combination might give results very close to an over expose, under develop and high contrast paper, or to "normal" processing. Or, it might give a desired or "custom" effect.

The point is that a film, developed to a gamma of 0.65 in any developer, as measured by the longest straight line portion of the curve, is being treated as it should be and the ISO should be as stated on the box and should give optimum results under the widest range of conditions.

Now, others may speak theoretically, but I've done the experiments not only in processing, but in emulsion coating to see how these things come about and what changes. I don't discourage anyone from experimenting, but I do encourage them to look at the Kodak and Ilford curves that are published and try to hit the sweet spot suggested in the instruction sheets. I guarantee that the stated conditions have been tested by the respective company R&D teams.

PE

 

[Sirius Glass]

There are about 3 or 4 useful ways of getting at the ISO speed of either (film or paper scales respectively), but common to both is the need to use the straightest part of the curve. Bumps and bows and soft toes and shoulders don't count. They distort the results. Push and pull don't count, as they distort contrast.

Yes, you can get some better result under some conditions by push pull or over or under exposures along with push or pull, but the film was not designed for that, nor was the guideline ISO determined under any of those conditions.

Emphasis Added.

Steve

 

[Chuck_P]

I always learn something in these exchanges. APUG is a great place!

Indeed, APUG is a great place, I was elated several years ago when I happened upon it, and I've learned some good stuff.

But, being human, I have also been most annoyed at times too in these forums. As a good friend of mine likes to say, "this too shall pass".

 

[Stephen Benskin]

I've attached a graph by Jack Dunn from his book Exposure Manual which shows the distribution of exposure on a film curve. Please note how step 1 falls about one stop lower than step 4 which is 0.10 density point. Notice how there is tonal separation in the curve between the two which means there is usable density. You might also notice how there is some separation below step 1 but according the the fractional gradient method, exposure in that section wouldn't produce quality results. Also telling is how step 4 is labeled "film speed computation point" because 0.10 isn't necessarily where the shadow exposure is supposed to fall.

One other interesting thing I'd like to point out while the graph is here is the difference between step 4, speed point, and step 5, the meter exposure point. The difference is 10x or 1.0 log units. Imagine the difference between Zone System testing with this relationship. With the ZS, you stop down four stops, which is 1.2 log units. Notice where that would place the exposure. That's why people tend to find a difference in results between personal ZS testing and ISO speed on such a consistent basis.

 

[Photo Engineer]

Steven;

In your graph, by my criteria, point (4) should not be part of a good imaging area as it is on the part of the curve that is beginning to toe out. This slightly compresses data and will lose some amount of shadow detail in the print. And, that is part of my point in using as much of the straight line portion as possible. It is also why I and others suggest that by your criteria we are over exposing by about 1/3 stop.

PE

 

[2F/2F]

This slightly compresses data and will lose some amount of shadow detail in the print.

...and this means what, exactly? Your implication is that this is a bad thing. That this is a "bad thing", however, is a "bad thing" to assume. It is a strictly technical argument. Part of the aesthetic characteristics that make each film unique have to do with how it compresses or doesn't compress tones. That is what gives a film the most important part of its character, or "look". If we truly wanted to expose everything on to a straight line, then digital would be the best option. If we truly want all of our films to look similar to one another, then we will consistently place all tones onto the straight line portion of our films' curves. I purposefully expose onto toe or shoulder areas, depending on what I want the picture to look like. I am glad that films compress in the way that they do. It is the main thing that makes them look so much better than digital, IMO, and that differentiates them from other films.

 

[Chuck_P]

I'm sorry if you found it insulting, but there are many people who believe the Zone System testing gives them the "real" or "actual" film speed results and that the ISO is somehow false

The following spoken without ill meaning or otherwise sarcastic enuendos, .

Well, those folks just don't understand the ZS, let them go on their way. ISO is not re-defined in the ZS, only discarded when the proper testing indicates it should be. Hell, my ZS test with TMX and D-76 1:1, gives me the box speed, but not with HC-110.

Also, most photographers believe that film speed is based on density instead of contrast and have never heard of the Delta-X Criterion.

Well, in the ZS, personal EI IS based on neg density of .1 at Zone I. Period. It's not gamma, it's not mean gradient, and it's not contrast index-----it was never meant to be. Simply put, EI in the ZS is not originally intended to be based on any contrast measurement at all. One can determine their EI from from any quantitative measurement of contrast (Ralph L. comes to mind if I remember), but at that point, it becomes a specific user defined application of determining EI, IMO. It is not the original intended method of determining EI wihich is the fixed density point method of 0.1 at ZI. Which is better or more right, I personally don't care and I think it is literally a waste of time to argue it; their different, we all do what we feel works best.

I understand PE has noted that speed should be determined from a straight section of the curve such as using gamma, but I fail to see why that it should. The toe of the curve is vitally important in the ZS, whereas methods that devise a straightline from the curve, ignore the "toe", hence CI, mean G, and gamma.

I personally find it more intuitive to consider the toe of the curve in deciding on a particular film for a particular subject (in my case D-76 1:1 or HC-110). TMX is upswept, i.e., a softer toe with HC-110 and very linear with D-76 1:1, and a particular subject will dictate which of those "toe" responses I prefer.

Chuck

 

[Photo Engineer]

...and this means what, exactly? Your implication is that this is a bad thing. That this is a "bad thing", however, is a "bad thing" to assume. It is a strictly technical argument. Part of the aesthetic characteristics that make each film unique have to do with how it compresses or doesn't compress tones. That is what gives a film the most important part of its character, or "look". If we truly wanted to expose everything on to a straight line, then digital would be the best option. If we truly want all of our films to look similar to one another, then we will consistently place all tones onto the straight line portion of our films' curves. I purposefully expose onto toe or shoulder areas, depending on what I want the picture to look like. I am glad that films compress in the way that they do. It is the main thing that makes them look so much better than digital, IMO, and that differentiates them from other films.

The starting point should be the straight line. I said above that benefit can be derived from placing the image on the curve either by exposure or process by means of determining your own "personal" EI.

That is what it is all about.

But, if you place the image partly on the toe with no experimentation, then you will never know, will you? That is why we make over and under exposures. Isn't it?

I said as much before.

PE

 

[Stephen Benskin]

ISO is not re-defined in the ZS, only discarded when the proper testing indicates it should be. Hell, my ZS test with TMX and D-76 1:1, gives me the box speed, but not with HC-110.

Who said ISO is not redefined in the ZS and if it isn't redefined like you say, how would you define proper testing in order to discard ISO? What would then be proper testing? As opposed to what type of improper testing? And what's wrong with comparing the two speed methods? And personal results are anecdotal and open to experimental error.

Well, in the ZS, personal EI IS based on neg density of .1 at Zone I. Period. It's not gamma, it's not mean gradient, and it's not contrast index-----it was never meant to be. Simply put, EI in the ZS is not originally intended to be based on any contrast measurement at all.

Then why does Adams have you do contrast testing and then suggest to double check the speed afterward? Actually, the three methods you mentioned concern overall contrast. Fractional Gradient Method is about the quality being connected to the contrast of the shadows or separation of the shadows if you will. For instance, if the curve flattens out at 0.10, there will be no shadow separation and the shadows will be blocked up even though the density was at 0.10. And if there is separation in the curve below 0.10, it will have shadow separation in the print. It's that simple. The ISO method does incorporate the 0.3x the average gradient concept into its structure. And just because someone says it's supposed to be a certain way doesn't make it correct.

But what this comes down to is that the Zone System is simple sensitometry and more specifically a simplified version of tone reproduction theory. It is not the be all and end all of photography. It's not the authoritative standard. The world of photography is a much bigger place and there are people who design the standards and invented such things as sensitometry and tone reproduction theory which Adams only used and interpreted. If one goes to the source material, they will understand things better and not be limited to understanding only one system like the Zone System, which is in fact just someone else's interpretation of the source material. Ansel Adams, The Negative, p 84, "The Zone System is a practical expression of sensitometry, the science that relates exposure and density in photography. If the Zone System is understood, the underlying sensitometric principles should not be difficult to grasp and can provide much information useful to the photographer." All I'm doing in my posts is pointing out the underlying sensitometric principles.