Box ISO rate and Real ISO

[Stephen Benskin]

What makes people confident that their testing method is yielding reliable results?

 

[yulia_s_rey]

What makes people confident that their testing method is yielding reliable results?

I guess it's rather subjective to a point. For my serious work and non-experimentation, I mainly do reversal and follow the box speed at first. If I personally don't find the rated speed to my liking, I assign it my own EI. But, I always make it a point to follow the manufacturer's specs for processing to the letter, this way I don't introduce any other variables that may cause inconsistencies.

 

[Bill Burk]

Sorry to bring up a new argument in the conclusion... But the first debate I won in high school was because I had a suprise argument.

The Delta-X Criterion, which I use for my own speed determination (so I subscribe to it but I want to explain something)... is based on the agreement that 0.3 Gradient is the appropriate speed point... Based on the study of The First Excellent Print.

Zone System speeds are NOT based on the study of the The First Excellent Print. So there is no reason except coincidence that the speeds even closely relate.

The First Excellent Print is based on people who viewed prints and pointed to the ones they liked. Built into this study is a Standard Observer's Opinion that "some" of the shadow detail is not important.

The biggest difference between this and the Zone System is... You will never hear anyone who uses the Zone System saying that shadows are not important.

 

[Xmas]

Sorry to bring up a new argument in the conclusion... But the first debate I won in high school was because I had a suprise argument.

The Delta-X Criterion, which I use for my own speed determination (so I subscribe to it but I want to explain something)... is based on the agreement that 0.3 Gradient is the appropriate speed point... Based on the study of The First Excellent Print.

Zone System speeds are NOT based on the study of the The First Excellent Print. So there is no reason except coincidence that the speeds even closely relate.

The First Excellent Print is based on people who viewed prints and pointed to the ones they liked. Built into this study is a Standard Observer's Opinion that "some" of the shadow detail is not important.

The biggest difference between this and the Zone System is... You will never hear anyone who uses the Zone System saying that shadows are not important.

Sorry shadows are not important if you are shooting slides.

If you are shooting negatives if you get zone 1 below the halide fog it is not present so no detail.

If zone1 is into the toe it will be more difficult to print unless you like dark prints with compressed shadows.

Some people do like that and it can add emphasis.

Until 1960 the box speed had a safety factor of 2.5 stops, post 1960 this was reduced to 1.5.

HP3 boxes changed from 200 ASA to 400.

Some manufacturers don't put the ISO speed on the box, eg Forma and I'm picking Forma as a good example.

Forma as well provide a data sheet for each film type with the 'ISO' speed for developers you might use like eg DK76 as little graphs of fog, contrast and speed and temperature.

If you look at the graphs it tells you a lot even if you are never to use Forma.

Id already discovered that the Formapan 100 was nearly as fast as the 400 before I looked at the graphs. I should have looked at the graphs first.

 

[Doremus Scudder]

... It's a very common misunderstanding. Film speed isn't determined by density because negative density by it self isn't relative to print quality. Film speed is determined by gradient. The fixed density of the ISO standard is a short cut to determining the fractional gradient point. As per Nelson, the fixed density method is only accurate when the contrast falls within the ISO contrast parameters. Otherwise you need to plug ΔD and Δlog-H into the Delta-X equation because with increased and decreased negative development, the fixed density method is less accurate. You're probably conflating it with how an increase in film density usually is accompanied by a higher gradient. This isn't always the case and definitely not to the same degree in different film types. This is all explained in Simple Methods of Determining the Fractional Gradient Speeds of Photographic Materials by C.N. Nelson and J.L. Simonds. If the OP really wants to understand what the REAL ISO is about, this is the paper.

As for a personal EI, whatever makes you happy.

The statement that very manufacturer deciding for themselves what the contrast for the standard should be is patiently wrong. The contrast parameters are clearly defined in the standard. Any variation and the ISO prefix cannot be used.

Stephen,

Obviously I'm working from an over-simplified model and using the terminology imprecisely...

But, for the sake of clarification, when I develop, say N-2 in order to accommodate a rather high subject brightness range, am I not changing the gradient and therefore the effective speed of the film? Or would you say that this is outside the parameters of ISO testing standards and simply does not apply?

If the latter, then what would you call the E.I. I need to use for N-2, simply E.I.? Is that not somehow "film speed" as well? "Effective speed" maybe?

In any case, I feel we need some more easily-accessible and usable terminology to deal with changes in film response with different development schemes. Maybe you have some suggestions in this department that could be simply understood and utilized by non-specialists while avoiding conflation, ambiguity and confusion at the same time; something in Feynman vein.

I never meant to imply that manufacturers can decide for themselves what the contrast standard for ISO determination is. However, it does seem that they can choose a developer, so there is no fixed standard in that department. Plus, there is a growing practice, especially for films designed to be used in low-light situations to have a number on the box, i.e., "box speed," that is not the true ISO speed (Ilford Delta 3200, et al.). This just adds to the confusion IMO.

And, although I'll more than grant you the point that ISO is a strict and reliable value arrived at by rigorous methods, I still find a bit of a disconnect about how it is practically applied. Certainly, you would not advocate my using the film ISO as my basis for metering for an N-2 negative... or when using a developer that is known to not deliver full ISO speed. Or would you?

I've spent a lot of time testing to arrive at development schemes that allow me to accommodate scenes with varying subject brightness ranges. While not completely quantified and constantly being refined, I feel I am much better off giving a tested and field-proven amount of increased exposure and reduced development for high SBRs and the converse for low SBRs. I have made Zone Rulers a lá Zakia and White for all my development schemes and am fairly confident using them. Should I really be questioning whether my testing method "is yielding reliable results"? Are the Zone System and BTZS tests unreliable?

All the above in the spirit of refining my knowledge and technique with thanks in advance for taking the time to answer.

Best,

Doremus

 

[markbarendt]

Sorry shadows are not important if you are shooting slides.

Well, I wouldn't put it that absolutely. I don't think that Dunn & Wakefield or others say that shadows aren't important.

What I might suggest is that with slides, that there are physical limits to what can be in the final artifact and that "we" need to decide what is most important.

The testing Dunn & Wakefield used does show that most people find mid-tones and highlights more important but we do well to remember that we don't have to conform.

 

[Xmas]

Well, I wouldn't put it that absolutely. I don't think that Dunn & Wakefield or others say that shadows aren't important.

What I might suggest is that with slides, that there are physical limits to what can be in the final artifact and that "we" need to decide what is most important.

The testing Dunn & Wakefield used does show that most people find mid-tones and highlights more important but we do well to remember that we don't have to conform.

Well ok I'll give you subjective but I've never had a bride who liked her wedding dress other then right on the edge of burnt out on the projector screen.

They never liked the 1/2 stop bracket if it was darker.

Kchrome 25 was nice film.

The grooms never minded or never said.

 

[Xmas]

Stephen,

Obviously I'm working from an over-simplified model and using the terminology imprecisely...

But, for the sake of clarification, when I develop, say N-2 in order to accommodate a rather high subject brightness range, am I not changing the gradient and therefore the effective speed of the film? Or would you say that this is outside the parameters of ISO testing standards and simply does not apply?

If the latter, then what would you call the E.I. I need to use for N-2, simply E.I.? Is that not somehow "film speed" as well? "Effective speed" maybe?

...

And, although I'll more than grant you the point that ISO is a strict and reliable value arrived at by rigorous methods, I still find a bit of a disconnect about how it is practically applied. Certainly, you would not advocate my using the film ISO as my basis for metering for an N-2 negative... or when using a developer that is known to not deliver full ISO speed. Or would you?

...
Doremus

Well if you just increase the development time you might increase the 'ISO' speed for your developer if the fog level increases less than the image level, otherwise the speed might be static or reduce.

All you can be sure is your mid tones separate.

The shadows and the highlights may be in toes and shoulders respectively.

You need to pick soft working developers with log fog levels to allow a wider range of 'capture' and control if your sceanes are high contrast.

For a while Ansell used D25 and a post alkaline bath or water bath. The D25 held the highlights the post bath the shadows if you were lucky.

 

[markbarendt]

Well ok I'll give you subjective but I've never had a bride who liked her wedding dress other then right on the edge of burnt out on the projector screen.

They never liked the 1/2 stop bracket if it was darker.

Kchrome 25 was nice film.

The grooms never minded or never said.

And this is essentially what Dunn & Wakefield found as the norm, you are not wrong there.

Yep, IMO most grooms just seem to follow the bride's lead on the photos.

 

[Stephen Benskin]

This is the first part from one of the two key papers used in the decision to change the standard in 1960 and is where the Delta-X Criterion originates. C.N. Nelson and J.L. Simonds, Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials, Journal of the Optical Society of America, V 46, N 5, May 1956.

part 1
View attachment Approx Fractional Gradient Speeds.pdf

 

[Stephen Benskin]

And the other, C.N. Nelson, Safety Factors in Camera Exposure, Photographic Science and Engineering, v 4, n 1, Jan-Feb 1960.

View attachment Safety Factors pt 1.pdf

View attachment Safety Factors pt 2.pdf

 

[Stephen Benskin]

Sorry shadows are not important if you are shooting slides.

If you are shooting negatives if you get zone 1 below the halide fog it is not present so no detail.

If zone1 is into the toe it will be more difficult to print unless you like dark prints with compressed shadows.

Until 1960 the box speed had a safety factor of 2.5 stops, post 1960 this was reduced to 1.5.

Bill kind of misrepresented the first excellent print test. I'll go into more details later.

Xmas, the safety factor pre 1960 standards was 2.5 times, not stops. Afterward it was 1.2 times. You can read about it in Safety Factors in Camera Exposure that I've uploaded.

 

[Xmas]

Bill kind of misrepresented the first excellent print test. I'll go into more details later.

Xmas, the safety factor pre 1960 standards was 2.5 times, not stops. Afterward it was 1.2 times. You can read about it in Safety Factors in Camera Exposure that I've uploaded.

Hi Stephen

Thanks, so in round terms there is not a safety factor in the ISO any more, or maybe 1/3 of a stop, given the ISO quantization.

Noel

 

[Stephen Benskin]

Hi Stephen

Thanks, so in round terms there is not a safety factor in the ISO any more, or maybe 1/3 of a stop, given the ISO quantization.

Noel

Pretty much. The third of a stop basically comes from factoring flare into the exposure. It's easy to think that the 1/3 stop comes from the speed equation being 0.80 / Hm instead of 1 / Hm, but it doesn't. This is in Safety Factors also.

 

[c6h6o3]

Just for giggles can we have some context for that rating.

Developer?
In comparison to manufacture's specs are you using minus development, stand...?
Are you "zoning"? If so details?
Subject matter?
Spot meter or incident?
Are you using old Petzvals or newish multicoated lenses?
Is part of that rating a safety factor?

My intent here is not to put you on the spot c6h6o3, but to help marciofs understand how you made your choice and at least some of considerations that go into the decision.

Developer: Harvey's 777 OR ABC Pyro OR Pyrocat HD 1.5:1:175.
I use the Zone System. I rate sheet film at 200, but place the shadows on Zone IV. So by Adams' philosophy I'm rating at 100. I meter for roll film at 100 and take incident readings. Therefore the answer is 'both'.
Subject matter is anything that strikes my fancy: portraits, landscapes, abstracts.
For sheet film I use a Nikkor 210mm large format lens, or an uncoated 12" f6.3 Dagor from 1911, or a 19" APO Red Dot Artar. My rollfilm camera is a Hasselblad. (250mm Sonnar, 150mm Sonnar, 80mm Planar, 50mm Distagon). So again the answer is 'yes to both'.
I don't know what you mean by 'safety factor'.

My point, both here and in the post you responded to, is that your film rating is an independent variable. "Expose for the shadows". Once you do that it's development that determines everything else about your negative. The old saw is "Develop for the highlights". But I develop for highlights, overall contrast, microcontrast in the midtones, all kinds of things depending upon what kind of negative I'm after.

So I reiterate: The correct film speed is whatever gives you sufficient shadow detail in your prints.

 

[Stephen Benskin]

My point, both here and in the post you responded to, is that your film rating is an independent variable. "Expose for the shadows". Once you do that it's development that determines everything else about your negative. The old saw is "Develop for the highlights". But I develop for highlights, overall contrast, microcontrast in the midtones, all kinds of things depending upon what kind of negative I'm after.

So I reiterate: The correct film speed is whatever gives you sufficient shadow detail in your prints.

You're talking about exposure and EI, not film speed. Conflating them can create a lot of confusion and misunderstanding.

 

[Photo Engineer]

Pretty much. The third of a stop is basically comes from factoring flare into the exposure. It's easy to think that the 1/3 stop comes from the speed equation being 0.80 / Hm instead of 1 / Hm, but it doesn't. This is in Safety Factors also.

And this is why I use 320 for a 400 film when doing critical work.

PE

 

[Stephen Benskin]

Sorry to bring up a new argument in the conclusion... But the first debate I won in high school was because I had a suprise argument.

The Delta-X Criterion, which I use for my own speed determination (so I subscribe to it but I want to explain something)... is based on the agreement that 0.3 Gradient is the appropriate speed point... Based on the study of The First Excellent Print.

Zone System speeds are NOT based on the study of the The First Excellent Print. So there is no reason except coincidence that the speeds even closely relate.

The First Excellent Print is based on people who viewed prints and pointed to the ones they liked. Built into this study is a Standard Observer's Opinion that "some" of the shadow detail is not important.

The biggest difference between this and the Zone System is... You will never hear anyone who uses the Zone System saying that shadows are not important.

Bill, you're under selling the importance of the first excellent print test. The speed method resulted from the first excellent print test was the first to link exposure criteria to perceived print quality. W.F. Berg explains it very nicely in his book Exposure Theory and Practice, "In his book the whole of the exposure problem is treated from the point of view of obtaining a satisfactory picture; it has been stressed over and over again that the quality of the picture is the factor which decides what exposure should be given. This consideration outweighs all others when it comes to choosing the speed criterion, since on its choice, together with the conditions of the subject, will depend the camera exposure to be given.

Thus all those speed criteria must be rejected which are based merely on a property of the negative material alone; unless and until it can be shown that this property is intimately liked with the quality of the print. Nevertheless, speed criteria are in practice invariably determined from the behaviors of the negative material alone. Where progress has been made in recent years in fixing a sensible criterion, it has been in the direction of linking print quality with the characteristics of the negative material...

We consider as our next speed criterion that introduced by Jones and adopted both the American Standards Association and the British Standards Institution. With this criterion, we complete the circle which started from a purely academic linking of the speed with an almost entirely arbitrary property of the characteristic curve, then led us to the purely practical concept of speed, to end up with what appears to be the most successful attempt so far of connecting print quality with a characteristic of the negative material.

Realizing that speed must be based on print quality, Jones decided to make a large number of exposures on a large variety of subjects on many negative materials and to submit the prints to a number of observers who were asked to judge the print quality. These prints were made on a grade of paper best suited to the negative in hand, i.e. on hard paper for underexposed negatives of low contrast, and on medium or even soft paper for the more correctly exposed negatives…

The final step was to link this criterion with a property of the characteristic curve. The point was to find that characteristic of the negative material which best tied up with the exposure necessary to yield the first excellent print."

Not sure where you found that the study concluding some of the shadow detail wasn't important. Jones' conclusion kind of contradicts that.

No one said the Zone System speeds were based on the fractional gradient. There's no indication Adams was aware of it or would understand it if he was. What he was trying to do is to come up with a testing method that can be done by the photographer that will approximate the ASA film speed. Which he did. My argument has always been about understanding the test. I don't care if the Zone System produces an almost universal 1/2 to 1 stop slower results than the ISO speed. Just don't call it "true" or "correct" speed. Personally, I believe the reason there is so much emphasis on determining a personal EI with the Zone System is because you can't test for the aim contrast without it. Otherwise, I can't see the purpose of doing such an imprecise test.

Finally, I'll just touch on this point for now, the speed point isn't necessarily where the shadow exposure is intended to fall. The fractional gradient point is approximately one stop below the ISO speed point, yet the pre 1960 speeds were twice as high as today. The reason why the density of 0.10 over Fb+f was chosen for the speed point in the current ISO standard was not because it represents the minimum useful exposure, but because it is easy to find.

 

[Stephen Benskin]

And, although I'll more than grant you the point that ISO is a strict and reliable value arrived at by rigorous methods, I still find a bit of a disconnect about how it is practically applied.

Could you elaborate on the disconnect that you've found? Meanwhile I'll work on addressing your questions. I can tell you that most of the answers can be found in the Simple Methods paper.

 

[Stephen Benskin]

Last page (part 2) of Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials.

View attachment Simple Methods last page.pdf

 

[Bill Burk]

I love the "First Excellent Print" study and I did not mean it any ill will when I accused it of saying some shadow is unimportant - that's just my take. I figure since it puts you down on the toe a bit where there's little separation - and when you print, the paper curve is also in its shoulder where there is little separation - you get double compression. But it looks good to viewers. And what looks good is EXTREMELY important, it's a great baseline for the ISO standard.

Zone System, on the other hand, stresses an educational approach to illustrate the principle "expose for the shadows and develop for the highlights." This is a fundamental principle, but it leaves Zone System on the rejected side of the standards because its aims are arbitrary, based on a point where you can see separation of tone in the shadows on the print.

They are two different ways of deciding the minimum exposure.

The "First Excellent Print" method: Minimum is the least where the whole print looks excellent.
The "Zone System" method: Minimum is the least where you can see detail in the shadow.

I amuse myself exploring these two different definitions of quality, and I am not surprised they result in different speed ratings for the same emulsion.

 

[Bill Burk]

Last page (part 2) of Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials.

View attachment 87257

Looks like I am wrong to associate Print Judgment Speed with 0.3G speed. This compares them as three different criteria.

 

[Stephen Benskin]

I love the "First Excellent Print" study and I did not mean it any ill will when I accused it of saying some shadow is unimportant - that's just my take. I figure since it puts you down on the toe a bit where there's little separation - and when you print, the paper curve is also in its shoulder where there is little separation - you get double compression. But it looks good to viewers. And what looks good is EXTREMELY important, it's a great baseline for the ISO standard.

Zone System, on the other hand, stresses an educational approach to illustrate the principle "expose for the shadows and develop for the highlights." This is a fundamental principle, but it leaves Zone System on the rejected side of the standards because its aims are arbitrary, based on a point where you can see separation of tone in the shadows on the print.

They are two different ways of deciding the minimum exposure.

The "First Excellent Print" method: Minimum is the least where the whole print looks excellent.
The "Zone System" method: Minimum is the least where you can see detail in the shadow.

I amuse myself exploring these two different definitions of quality, and I am not surprised they result in different speed ratings for the same emulsion.

Bill, I'm afraid you may have succumbed to the dark side.

 

[Stephen Benskin]

Looks like I am wrong to associate Print Judgment Speed with 0.3G speed. This compares them as three different criteria.

Basically, the print judgment speed is the most accurate method of determining film speed. It is based directly on the finished prints; however, it is incredibly laborious and therefore impractical to do on a regular basis. The next best method is to find a mechanical approach that will yield speeds similar to the print judgment speeds in the majority of cases. The fractional gradient method is that method. Fixed density methods were evaluated but weren't as consistently accurate. The fractional gradient method was determined by finding the spread between the proposed method and the speeds resulting from the print judgement speeds. Just like the spread example with testing alternative methods to the fractional gradient method. Of the three methods shown, the fixed density 0.10 method had the highest degree of spread and therefore the least consistently accurate to the print judgment speeds.

 

[Bill Burk]

Interesting that W speed, Delta X speed and 0.3 gradient all are reasonable. But heck no to 0.1 speed. And I know you've said that the standards get away with using 0.1 - only because they specify conditions that make them fit 0.3 gradient.

But this is another fun thought for the conclusion...

Maybe we should be designing "print judgment" tests, since they're the best. And we have all this determination to pick a personal speed...