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Speed difference between Acros II, TMX, and Delta 100 at same CI?

Today there are all kinds of diffusion light sources, variable speed papers are standard, and back when I used graded papers, I never did standardize on Gr 2, nor did many others, and grades varied somewhat brand go brand anyway. Degree of enlargement had a lot to do with it to. As long as we all know what each of us personally needs, we're on target. Otherwise, generic contrast prescriptions are only of so-so value at best.
 
ic-racer said:
I have seen negative or derogatory comments about forum participants’ personal film speeds and/or contrast index (including my own) in just about every thread on the subject.
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I’ve spoken derogatory comments to myself on the topics.

How do I get two wildly different CI (0.45 v 0.55 and speed (250 v 320 by Delta-X) for the same film (ok different batch) developed in the same tank for the same time?

A couple significant factors people are not checking is the hold time on their sensitometry exposures and “how promptly” they process the photographs they have taken.
 
miha said:
If they are all developed to the same contrast index, is there any real speed difference between them?

Thanks.
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To get ISO =100 for Acros II it was developed in Fuji Microfine, not the formerly used developer for ISO measurements. The contrast index is given in the data sheet (average gradient).
I guess the use of a different developer means that the Fuji result is not much help for comparison purposes.
 
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John Wiegerink said:
I would never say someone's own personal film speed is wrong as long as it was within the ballpark of normal. My saying that I get an EI of 320 for Acros is not normal as Drew pointed out. Different strokes for different folks!
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My point is that when I developed the films so that they printed alike (i.e., they had the same contrast), Acros was noticeably slower than the others. It is also finer-grained (very close to Pan-F+). I see no reason for anyone to use Pan-F+. It is inferior in every way to Acros.
 

Every measurement has noise. Every instrument has limits. Every model is an approximation. Every inference is probabilistic, not absolute. Sometimes small errors and variances cancel each other. Sometimes they compliment each other. ISO speed is the mean of multiple samples.

From ISO 6, 6.2 - ISO speed of a product. "The ISO speed of a product (as distinguished from that of a specific sample) shall be based on the arithmetic mean of the values of log10 Hm, determined from various batches of the product when selected, stored and tested as specified above."

It goes on to state, "Since ISO speed is dependent on the exposing and processing conditions, these should be indicated when quoting ISO speed values." The same principle should apply to any stated exposure index: the EI is inseparable from the method used to derive it. Without the accompanying information—testing procedure, development conditions, and evaluation criteria—the number itself has little relevance. It becomes an isolated result that cannot be compared, reproduced, or interpreted with any confidence.”
 
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I agree. I do not know how Acros can be rated as ISO 100, when everyone who uses it gets a much lower number.
 
You could say that about pretty much any “technical” thread though.

I actually think there is some potential value to threads about film speed because they are opportunities for people to (maybe) come away with a better understanding of the ISO speed determination, what it means / what is is based on, how it relates to the typical non-printing-based EI methods etc. exposure theory, and in particular ISO speed, is not generally well understood and over time a lot of misinformation has become gospel. A basic understanding of exposure / tone reproduction theory and the lineage of ISO speeds can actually simplify things.



gbroadbridge said:
This is such a pointless discussion.
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Acros is a fine film rated at 50 or 100, and it can even go up to 400 in some limited circumstances. That works better on dull days and low contrast lenses.

Augustus Caesar said:
I see no reason for anyone to use Pan-F+. It is inferior in every way to Acros.
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Completely different films in their character. I'm glad both exist and wouldn't ever consider one as a substitute for the other. Acros is better for general purposes but not for everything. I found Pan F+ to excel for graphical detail shots on subjects with a lot of texture. Ex:

 
Pan F has an exaggerated S-curve with limited contrast range; but under the right conditions that can provide some lovely results. And with the right developer it can exhibit a special "wire sharpness" edge effect which is somewhat unique. Very different indeed from Acros.
 

Well, I think Acros is better across the board than Pan-F +. Faster (1 stop) easier to process, longer tonal scale, sharpness as good as Pan-F+ and grain is basically the same.
 
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