ISO film speed point relative to in-camera exposure

[Anon Ymous]

Teenagers. Always trying to get a date!

I didn't know these are called dates, couldn't figure out what the joke is. I learned something today.

 

[Tim Stapp]

Tim, he posted a picture of dates!!!

Sorry, just remembering my youth (faded memory, at that).

 

[Stephen Benskin]

Stephen,I'm glad to see that our results match so closely.

Me too. What's surprising is they are based on different assumptions.

What I also find interesting is how focused so many are on film speed, but practically ignore contrast. Even books. Yours is one of the few (perhaps only) that includes a development model.

 

[ic-racer]

Fellow members and subscribers, I doubt if there is another member here that has had to do this on a real basis for film or paper. I have had to do both. No single method is best, but the one that approaches best is one that works making good negatives (or slides) and prints. It does it over and over. Mees and Haist show it. I have done it and it really works.

You can use the zone system (a dumbed down system of 21 step sensitometry) and other methods, but use is what works. First acceptable print works. Whatever you use though, remember that what works for you is OK. It is just that it may not work for the rest of us due to your conditions.

PE

Exactly. This brings up what I have taught in the past that the experienced photographer just might be better at determining his or her best acceptable print than the much touted "Panel of Observers" from the original 0.3G literature. Historically the development of modern speed standards satisfy goals for the commodification of film products and image making. It [ISO standardization] is for snapshooters and commercial film production and distribution. I am not involved with that, but I appreciate having the number on the film box! Like buying a thermometer with the numbers already on it. I'm still free to use the thermometer however I want.

 

[MattKing]

Like buying a thermometer with the numbers already on it. I'm still free to use the thermometer however I want.

I hope you don't think the same about the speedometer in your car!
I do agree though that "first (not best) acceptable print" may very well vary from photographer to photographer, and with the context of any particular subject.
The number on the box really helps though, particularly if you use a lab.

 

[Stephen Benskin]

No two people see the color green the same way, but statistically, the vast majority see it similarly enough for the word to have meaning. We all have different concepts of quality depending on our experience with the subject and what is possible for the time. A well typed paper in the 1970s would probably appear sloppy compared to today's computer print outs. A good color image that had blown out skies and heavy shadows is less acceptable today because of high dynamic range imaging. Special effects in movies are another good example as is movie editing.

For the first excellent print test, the judges were given instructions to pick the print that best represented what the original scene might have looked like if they where standing at the scene's location. Did the instructions influence their interpretations? Does this suggests any image where the photographer wants to interpret a scene differently would begin to fall outside the judged parameters. So the test results may not apply universally, nor can they. The test; however, establishes an understood frame of reference which the majority of people can relate to. As with most phenomena, everything else falls somewhere else on the bell curve.

Here is why the test yielded a lasting concept of film speed. The two film curves below are from a long and short toed film. The fixed densities of 0.10 and 0.20 are shown. As is the fractional gradient point, 03G. Notice the differences in log-H between the fixed density points and the fractional gradient point in the two examples? This isn't intuitive and could only be found through psychophysics.

 

[removed account4]

I didn't know these are called dates, couldn't figure out what the joke is. I learned something today.

I thought they were dates they kind of look like that
LOL i wasn't trying to be funny ( sorry )
I LOVE those things and wish I could eat them everyday ! If they
aren't dates, my-bad, I guess I like them so much and crave them often enough
that when I see something that looks like them, its like the Pavlov and his Dogs

 

[Photo Engineer]

No two people see the color green the same way, but statistically, the vast majority see it similarly enough for the word to have meaning. We all have different concepts of quality depending on our experience with the subject and what is possible for the time. A well typed paper in the 1970s would probably appear sloppy compared to today's computer print outs. A good color image that had blown out skies and heavy shadows is less acceptable today because of high dynamic range imaging. Special effects in movies are another good example as is movie editing.

For the first excellent print test, the judges were given instructions to pick the print that best represented what the original scene might have looked like if they where standing at the scene's location. Did the instructions influence their interpretations? Does this suggests any image where the photographer wants to interpret a scene differently would begin to fall outside the judged parameters. So the test results may not apply universally, nor can they. The test; however, establishes an understood frame of reference which the majority of people can relate to. As with most phenomena, everything else falls somewhere else on the bell curve.

Here is why the test yielded a lasting concept of film speed. The two film curves below are from a long and short toed film. The fixed densities of 0.10 and 0.20 are shown. As is the fractional gradient point, 03G. Notice the differences in log-H between the fixed density points and the fractional gradient point in the two examples? This isn't intuitive and could only be found through psychophysics.

View attachment 215104

Stephen, the curve with the sharper toe is much slower. This is why we tried to maximize the toe and also get the highest toe speed. The actual speed of an emulsion is the inflection point of the curve over fog. Anything else is meaningless due to variations in toe and contrast. One works with this value to optimize the curve that "follows".

PE

 

[Stephen Benskin]

Stephen, the curve with the sharper toe is much slower. This is why we tried to maximize the toe and also get the highest toe speed. The actual speed of an emulsion is the inflection point of the curve over fog. Anything else is meaningless due to variations in toe and contrast. One works with this value to optimize the curve that "follows".

PE

.3G is the fractional gradient speed point which falls at a point 0.3 times the overall film gradient. It tends to fall further to the left in relation to the 0.10 fixed density with long toed films and when the film is developed to a lower overall gradient, Because of the changing relationship between the two points, the ISO standard needed to have stricter contrast conditions than the fractional gradient ASA standard pre-1960 which only suggested the film be processed over a minimum gradient. Please see all the references and examples that I've presented that support this.

BTW, the two examples from Jones also contain inertia speed points.

 

[Bill Burk]

Haa, the photo was of dates.

 

[Anon Ymous]

You are really close to having the ISO parameters. But, since your developer is the variable you want to test, I'd do a control test with D-76 and try to hit the ISO parameters with that (a more standard developer). Later, when you hit the ISO parameters with your home-made developer, you can compare the x-axis differences between the standard developer and your developer.

From that you can determine whether your developer gives more or less speed. Chances are the speed difference will be negligible.

Late response, but what the hell... Yes, I've done such a test in the past with homebrew D76d and 400TX IIRC. I had followed Kodak's recommendation and indeed, the characteristic curve had two points where it met the ISO criteria, for whatever speed it was. It has been a while, but I used the same homebrew Xtol with some outdated (7-8 years) Agfa APX100. I followed Kodak's recommended time from an old Xtol datasheet. The film had quite a lot of fog (fb+f = 0,8!) as you can see at the following figure, but the curve meets the ISO criteria for a speed of 64 as it seems:

In this curve, normal exposure of the test target (gray card) would be at 1,5. Shots at -5, -3, -1, +1. +3 and +5 stops were used. The film was shot at EI100 and most shots show obvious signs of underexposure. Textures at the shadows are mostly gone. Bracketed shots that were given more generous exposure came out ok and fine grained actually.

 

[Anon Ymous]

Interestingly enough, here are the developer formulas per the old ASA standard. This is out of Practical Photographic Chemistry by O’Hara & Osterburg.

View attachment 214844

Of course, I said f’ it and just base my dry plate speed estimate on developing in HC-110 dil B for 5 minutes.

Nice find, thanks for posting it. No problem in using HC110 for a speed estimate though. IIRC the ISO standard doesn't require a specific developer for testing anyway. Any developer is ok and you actually get slightly different speed when using different developers.

... All the calculations in the world won't help you if you don't understand this fundamental fact first, or really, how to interpret film curves with respect to toe, straight line, and shoulder. I personally consider the specific characteristics of the toe to line transition far more important than any ISO conventionality. And even this kind thing is affected by developer variables...

Yes, that's true. I've tried the same film in different developers and it behaved differently, even plotted curves to make it clearer. One had a fairly normal toe, with a smooth transition to the straight line, the other had a pronounced toe that turned to a very steep straight line, followed by strong shoulder. Dmax was about the same and needless to say, the latter was pretty bad. Sometimes I really wonder how some people can claim that film X, developed in Y can give them a usable EI of Z.

But all these said and done, you can disregard the whole ISO standard and use whatever contrast - EI makes you happy. I'm more of a low contrast guy. Some of the best negatives I've ever made were pull processed and both printed and scanned beautifully. I had to use a lower EI, but IMHO it was worth it.

 

[removed account4]

Haa, the photo was of dates.

whew ! i was starting to think they were a large box of pencil erasers and the yoke was on me
john

 

[Photo Engineer]

.3G is the fractional gradient speed point which falls at a point 0.3 times the overall film gradient. It tends to fall further to the left in relation to the 0.10 fixed density with long toed films and when the film is developed to a lower overall gradient, Because of the changing relationship between the two points, the ISO standard needed to have stricter contrast conditions than the fractional gradient ASA standard pre-1960 which only suggested the film be processed over a minimum gradient. Please see all the references and examples that I've presented that support this.

BTW, the two examples from Jones also contain inertia speed points.

Stephen, the inflection point is the actual speed point and cannot be changed. All of the rest is manipulation of toe and mid scale gradient. The inflection point is the actual minimum sensitivity to light detected by the fastest grains.

PE

 

[Stephen Benskin]

[ QUOTE="Photo Engineer, post: 2145496, member: 6399"]Stephen, the inflection point is the actual speed point and cannot be changed. All of the rest is manipulation of toe and mid scale gradient. The inflection point is the actual minimum sensitivity to light detected by the fastest grains.

PE[/QUOTE]
Ron,
We are probably using the term "speed point" differently. I would be happy to hear more If you wish to clarify what you mean.

I found this reference to inflection point in The Theory of the Photographic Process, 1st ed. It appears to refer to where the toe becomes the straight-line section.

 

[Photo Engineer]

Advanced measuring methods can detect the actual inflection point, or deviation from the straight line fog level. These methods were not published by Mees, but were used to even look at the latent image itself, that is, the silver metal specks that formed from exposure, not fog. It was found that this point, for a given emulsion, was invariant. You can't get something for nothing. All you can do is develop such as to attain that point and achieve enough density to get a reasonable curve. This, in practice, is what is done. A new emulsion is stressed to find speed, toe contrast and mid scale contrast in a series of coatings made with the raw emulsion and then with a series of levels of chemical sensitization. The emulsion is then assigned a "fixed" speed that generally cannot be surpassed when the inflection point is considered.

Once this is determined, then work is carried out on the toe and mid scale. I did considerable work on that part, trying to fine tune the chemistry that gave the best curve shape with the desired speed. In actual fact, a 400 film may contain a 900, a 600 and a 400 emulsion, and then it is dyed back to a mid scale speed point of 400 to give some leeway in manufacturing. They dying process controls speed and moves sharpness around a bit as the turbidity varies.

This is just an example. We were never able to sharpen the toe as much as we wished. If we did, then there would have been another speed jump in products with no change in grain or sharpness.

PE

 

[Stephen Benskin]

Sounds like a case of design mode vs usage mode

 

[DREW WILEY]

Where was Super-XX sheet film actually coated? It had the steepest toe of any general-purpose Kodak film I'm aware of. Now I'm fiddling with certain developer tweaks with an added toe-cutter, allowing a steeper landing even at low gamma.

 

[Photo Engineer]

Drew: There is a film here that purport to show Super XX being coated. It was made in Rochester and probably other locations.

Stephen: They end up being one and the same.

PE

 

[Stephen Benskin]

Drew: There is a film here that purport to show Super XX being coated. It was made in Rochester and probably other locations.

Stephen: They end up being one and the same.

PE

Sorry, I still think you are applying the term "film speed" differently. It appears that you are using it as a indication of a film's sensitivity. But the idea of photographic film speed also incorporates intended usage and desired exposure placement which is not part of a film's physicality or part of your description. Before the ISO standard, there were multiple methodologies existing at the same time and were often included the purchase of the same emulsion. ASA and DIN are the last examples of this. Since each one differed on it's method, the results also differed which they couldn't if speed is inherent and unchanging as per your description. This is why I think we are referring to two separate definitions. Here is a list of some obsolete film speed methods. Many of which were in contemporaneous usage.

Some might find this interesting. A few of the speeds are determined using the inertia method (ί), but produce a different speed value. The reason for this is each method uses a different value in the numerator. These are good examples on how the determination of the film speed point isn't necessarily in direct correlation to the film speed value or E.I. Today's ISO method using the fixed density point of 0.10 over Fb+f as part of the Delta-X Criterion method to determine the fractional gradient speed point is the current example. Even when the ASA standard used the fractional gradient method, the resulting EI wasn't just the reciprocal of the exposure value.

 

[Bill Burk]

One thing I like about characteristic curves is that they don’t change when you talk about them.

You can call the speed point anything you want, the curve is the same.

 

[Bill Burk]

I think you might be confusing inflection with inertia.

H&D “inertia” is a projection of the straight line portion. It’s not what PE is talking about. He’s talking about identifying the place where you are first able to detect a density change above base plus fog.

There’s certainly nothing useful ‘to the left‘ of that point.

 

[Stephen Benskin]

One thing I like about characteristic curves is that they don’t change when you talk about them.

You can call the speed point anything you want, the curve is the same.

Film curve changes with choice of developer and development.

 

[Stephen Benskin]

I think you might be confusing inflection with inertia.

H&D “inertia” is a projection of the straight line portion. It’s not what PE is talking about. He’s talking about identifying the place where you are first able to detect a density change above base plus fog.

There’s certainly nothing useful ‘to the left‘ of that point.

I used the speed methods to illustrate that Ron and I are talking about two different things. I then saw an opportunity to illustrate how the speed point isn't necessarily where the photographic exposure should fall. A concept the vast majority of photographers are unfamiliar with.

 

[Stephen Benskin]

From Tutorial: A Review of Speed Methods by H.N. Todd & R.D. Zakia: