I think the posts which discuss fine detail may have been off-topic (#30-35), but posts about ISO and exposure seem to fit...?
... but then, this is Photrio where off-topic posts are not unheard of ... ;-)
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I think the posts which discuss fine detail may have been off-topic (#30-35), but posts about ISO and exposure seem to fit...?Maybe someone could move the last few posts to a new thread.
Which company uses ISO standards? I don't know any!
Foma's box speed definitely is too high with any standard developing process.
The Ilford film data sheets state: “It should be noted that the recommended exposure index(EI) is based on a practical evaluation of film speed and is not based on foot speed, as is the ISO standard.”
Kodak uses a Contrast Index CI, that has nothing to do with the definitions in the ISO standard. CI can only be evaluated in a graphical manner with a special ruler and cannot be converted into Ilford's G or into gamma.
The only way to deal with this is to carry out your own film tests and use your own personal EI.
The density curve used in ISO (see #29 above) has nothing in common with a typical curve of modern b&w films. This ISO standard is completely outdated and is obviously ignored by today's suppliers.
So, I would call into question the claim that no company uses ISO standards. They all do.
Foma webpage shows boxes using ISO, so...
It does, however the curves on the charts they provide seem strange in some cases. It’s not entirely clear. I looked at them because at least anecdotally I’ve seen a lot of assertions these films (in particular the 200 film) are underexposed at the speeds indicated on the boxes. I don’t know for sure.
Which company uses ISO standards? I don't know any!
Foma's box speed definitely is too high with any standard developing process.
The Ilford film data sheets state: “It should be noted that the recommended exposure index(EI) is based on a practical evaluation of film speed and is not based on foot speed, as is the ISO standard.”
Kodak uses a Contrast Index CI, that has nothing to do with the definitions in the ISO standard. CI can only be evaluated in a graphical manner with a special ruler and cannot be converted into Ilford's G or into gamma.
The only way to deal with this is to carry out your own film tests and use your own personal EI.
The density curve used in ISO (see #29 above) has nothing in common with a typical curve of modern b&w films. This ISO standard is completely outdated and is obviously ignored by today's suppliers.
Slightly off-topic, but let me answer in more detail:
Does it make sense to discuss a proposed (but never implemented) change to the speed criterion published by C.N.Nelson in 1959, based on a standard from 1954 or even earlier? Back then, unlike today, films had an extremely S-shaped densitometric curve.
Other reasons why I think ISO 6 is outdated and no longer useful:
Modern films have a more or less straight line that starts at zone II (maybe II-III) and goes beyond zone X. Applying the ISO process to such films results in a high contrast gamma of about 0.7. ISO film speed is thus based on N+1 development (in the zone system). For this you would need multigrade paper with grade 0.5, but normal contrast should fit on grade 2!
ISO places the speed point in the flat foot of the curve in zone I with a density of 0.1 over base+fog. This was a compromise that still exists today in ISO 6. The base of the density curve below D=0.2 is of no interest for practical photography, as details are no longer resolved. Many large-format photographers tend to place the shadows in zone III with a density of at least 0.35. The film density in zone I is ultimately irrelevant.
Personally, I see the ISO number on the film box as nothing more than a primitive classification into low, medium or high speed. Which EI we set on the light meter is left to our experience with a certain combination of film+developer+enlarger+paper.
I’ll leave it to Stephen Benskin to address your points because I’m tired(it’s also probably best not to have multiple people going into detail on this to avoid muddying the waters).
I’ll leave it to Stephen Benskin to address your points because I’m tired(it’s also probably best not to have multiple people going into detail on this to avoid muddying the waters).
However one thing you wrote which I agree with is “Which EI we set on the light meter is left to our experience…”. In my opinion that is the sensible way to depart from ISO speeds if required. If one finds he is consistently struggling with insufficient shadow information, use a lower EI (or vice versa although that is probably rare). On the other hand the kind of “personal EI” “test” people are encouraged to do at the outset is superfluous, and also isn’t really testing for anything. If you want a Zone System EI, downrate the film by 2/3 stop and you’re done.
I looked at a box of HP5 today, and the speed was given as ISO 400, not EI. When T-Max films were first introduced, they were rated as EI, because they did not reach full speed in the ISO developer (which was required at that time). Later, the ISO standard was changed to allow for other developers.EI and ISO are different things. Anyone claiming an ISO speed should be using the relevant formal standard to compute that speed.
EI is the pragmatic speed that considers the individual's manner of metering, preferred development discipline, measurement equipment, and so on.
So, I would call into question the claim that no company uses ISO standards. They all do. That just doesn't map directly to EI.
Maybe. This assumes you have accurate thermometer, meter, and shutter. This assumes that you're either using distilled water to mix the developer or your tap water isn't a factor in developer activity (and I have seen it be exactly so). This assumes you have a fairly proper ZS way of metering the shadows. And so forth.
The whole idea of "personal ASA" as originally proposed by Adams was at a time when these things could not reliably be counted upon and the idea was to map your world onto an effective "ASA" that would give desired results.
These days, thermometer and meter variability are less of an issue. The water issue can be made moot by using distilled. But - having tested a lot of shutters over the years - I can say with some conviction that shutter variability, especially with older leaf shutters, is still very much an important variable.
I just want to first make a few factional corrections before moving forward.Does it make sense to discuss a proposed (but never implemented) change to the speed criterion published by C.N.Nelson in 1959, based on a standard from 1954 or even earlier? Back then, unlike today, films had an extremely S-shaped densitometric curve.
As for being outdated, the standards are reviewed every 5 years. While the ASA standard was later adopted as an ISO standard in 1974, and then revised in 1993, the changes were primarily methodological and didn’t change the core theory. It has not been revised since.Other reasons why I think ISO 6 is outdated and no longer useful:
Modern films have a more or less straight line that starts at zone II (maybe II-III) and goes beyond zone X. Applying the ISO process to such films results in a high contrast gamma of about 0.7. ISO film speed is thus based on N+1 push development. For this you would need multigrade paper with grade 0.5, but normal contrast should fit on grade 2!
ISO places the speed point in the flat toe of the curve in zone I with a density of 0.1 over base+fog. This was a compromise that still exists today in ISO 6. The base of the density curve below D=0.2 is of no interest for practical photography, as details are no longer resolved. Many large-format photographers tend to place the shadows in zone III with a density of at least 0.35. The film density in zone I is ultimately irrelevant.
Which EI we set on the light meter is left to our experience with a certain combination of film+developer+enlarger+paper.
What if the intention wasn't a realistic reproduction of how something looks but an interpretation that departs from a realistic impression of the subject or for lack of a better term, an artistic interpretation?
So the intention was a simple realistic interpretation of the subject. What was the manner in which those negatives were actually printed for a psychophysical evaluation of the print for film speed. Sorry if I have missed it stated somewhere. For me, an enlarged proof print at a standard 5x7 or 8x10 enlarger height with the exposure time based on the minimum time to print the paper's D-max through the fb+f density of the negative is an excellent way to evaluate the negative.
It's fine as long as it works for you; however, that method is more about exposure than speed, and it's a somewhat arbitrary method at that (see what Jones says about density).
All I can say is if you look at the methodology and criteria for the typical personal EI test, the test is not doing what you’re describing.
If the purpose of a personal EI test was to find an adjustment to the ISO speed to account for any of the variables you listed, the test would have the same speed determination criteria. But we know right off the bat a typical personal EI test targets a fixed density of 0.1 (net) 4 stops below the metered exposure while in the ISO criteria that density is 3 1/3 stops below the metered exposure. Not a good start if a speed test is ostensibly supposed to adjust the box speed for personal metering/processing conditions, and could do a pretty good job explaining why (barring extreme processing) personal/ZS EI tests typically find something roughly 2/3 stop slower than the ISO speed.
Even if the test methodology is altered to ISO targets/criteria in an attempt to find an EI that corrects for personal conditions, I’m not sure how that works:
Unless a shutter gives the same exposure error at all settings, wouldn’t you potentially need many EIs?
How specifically is the personal EI test accounting for metering and meter variability?
How specifically is the personal EI test accounting for an inaccurate thermometer?
What about other things such as flare, which could creep into a methodology?
As an aside, the water variable puzzles me. It would be a very long shot (or horrendously bad water) if somehow that played a role, and if something like that was going on I doubt it would be a consistent effect either.
So the intention was a simple realistic interpretation of the subject. What was the manner in which those negatives were actually printed for a psychophysical evaluation of the print for film speed.
The speed of T-Max films is now listed as ISO, not EI. In any case, a little more exposure than the absolute minimum is not in any way deleterious. It's best to err on the side of generous exposure, especially in rapidly changing situations.This is the only part of the post I can agree with. You find what works for you and has the results you like. Here's the thing. It doesn't go against the ISO speed standard. There's no contradiction if a person is willing to understand the theory. Sure the standards need to be tweaked from time to time, but for the most part, any blame directed toward the speed standard is generally misplaced. You don't need to understand theory to photograph, as the next section from a Kodak data sheet demonstrates, but theory helps it all make sense so we can stop misplacing blame.
This is from the exposure section in Kodak's technical data sheet for TMX.
View attachment 383365
As Kodak's statement suggests, the ISO standard is a guide. ISO 6 is not intended to be universally applicable. It is designed to accurately work under certain conditions. The further from those conditions, the less accurate the results. There are a number of caveats involved including both physical and psychophysical. In the forward to ISO 6, "the ISO speeds will provide correct exposures for average scenes with the exposure meters conforming to ISO 2720 or ISO 2721 when the film is processed as specified in this international standard." As a scene moves further from the average scene or if the film is processed differently, the agreement is reduced.
Jones says in The Psychophysical Evaluation of the Quality of Photographic Reproductions, PSA Journal, Vol 17, Dec 1951. "In this discussion, the term photographic quality will be used in referring to the degree of perfection with which the photographic picture reproduces in the mind of the observer the subjective impression which he received when looking at the original." What if the intention wasn't a realistic reproduction of how something looks but an interpretation that departs from a realistic impression of the subject or for lack of a better term, an artistic interpretation? A situation where the emotional element supersedes a strictly technically reproduction. How would this affect Jones' print judgement speeds and consequently sensitometric speeds? Or looking at it from a different perspective, how would film speeds based on Jones' print judgement speeds be applicable to the artistic work of photographers like Bill Brant, Brett Weston, or Michael Kenna?
The fractional gradient speed point has excellent correlation with psychophysical testing and is used to accurately compare the limiting gradient across films of various characteristics. It means the same for all film types. This is the basis for black and white film speeds. The old ASA standard had an ASA speed and an ASA film exposure index. The ASA standard was the fractional gradient speed while the exposure index takes into consideration the meter's characteristics, a scene's luminance range and distribution, flare, and other factors including any safety factors. In other words the factional gradient speed is the film speed and the EI is how the film is to be applied. While the current ISO speed standard doesn't make a distinction between the two, the ISO speed is still determined in relation to the fractional gradient speed and can be considered an EI. A user’s choice of EI can then be further based on an individual's situation which may include many additional variables including taste, but the actual speed of the film is defined. It's common for people to conflate speed with exposure.
Apart from all that, what makes more sense, people who use EIs other than the ISO value have a better understanding or more ridged testing procedures than the people that researched and developed the methodology or that they have found a value which works for them?
The speed of T-Max films is now listed as ISO, not EI. In any case, a little more exposure than the absolute minimum is not in any way deleterious. It's best to err on the side of generous exposure, especially in rapidly changing situations.
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