"True film speed" vs just developing the film more?

[Pere Casals]

The storm is clearing and I'm about to go out and shoot, Pere. I wish you well and recognize that numerous people like things like apps for simplifying exposure issues, and that to some degree your formula will probably work, but only in a generic sense. There's no point discussing this further unless you are willing to study it in more depth than you already have. There are all kinds of relevant factor you seem unaware of.

Drew, ISO speed is calculated from this graph:



When we have the "m" exposure, in lux·second, we multiply that by 10, and that value is aimed by meters if using the rated ISO speed, with 1/6 stop margin depending on meter manufacturer.

You may now that 3.3 stops is x10...

So, Drew, where is the toe personality in the calculation?. -3.3 is 0.1D over BF with Normal. Always. This is factual... Any deviation is from inaccuracies in the manufacturing/metering/exposure/processing.

[Drew Wiley]

I don't mean to be rude, Pere, but I'm done unless you're willing to at least think over what I've already repeatedly stated. Everything that you contend is written in stone, simply isn't. You're in the realm of hypothetical generalities and elementary stereotypes rather than real-world specifics. Not all curves are the same, just as not all films are the same. And effective speed is highly dependent upon the specific character of the toe or bottom of the curve itself. What you just gave was a textbook-style diagram showing a very long toe and conspicuous slow drift up onto the shoulder. Now go look up a family of curves for something like Kodak Super-XX, and for sake of learning, note just how different those are from your textbook curve; or in case of a current film, either version of TMax. The curve you posted is almost like old Plus-X, with a very long toe, the very opposite kind of film in terms of shadow rendering ability.

[Pere Casals]

Everything that you contend is written in stone, simply isn't.

You are right, simply not written in stone: It's written in the ISO 6:1993, harder than in any stone.

[Tin Can]

"This standard was last reviewed and confirmed in 2015. Therefore this version remains current."

You are right, simply not written in stone: It's written in the ISO 2240:2003 , harder than in any stone.

[Pere Casals]

I corrected ISO 2240:2003 by ISO 6:1993 https://www.iso.org/standard/3580.html
(This standard was last reviewed and confirmed in 2018. Therefore this version remains current.)

ISO 2240:2003 is for color slides...

[Tin Can]

Yes, I saw that

I like how you backup your facts with links

[Drew Wiley]

(Still waiting for the storm to clear). To hell with Kindergarten level links, Randy. Please tell me something I haven't already known for the past fifty years! Get a good sensitometry textbook and read it while you're snowed in. It's all about interpreting the curves, not just posting a generic blackboard sample curve from Film 101! That whole speed point convention is for sake of generically pigeonholing film speeds that take off like a commercial airliner at a modest angle of entry (long toe) before they achieve cruising altitude (the straight line section of the curve). It at least gives you something. But some films take off more like an F15. Yet with special developers, I can make even those predictably behave like a hoverboard just above the ground. So the name of the game is APPLIED sensitometry. Otherwise, you're just a film carton labeler. What both of you call "facts" simply betrays your very superficial grasp of the entire subject. I'm not interested in disputing some alleged industry convention; I had to deal with those for decades - but that's all it is, a convenience protocol which might or MIGHT NOT help you make more accurate exposures. Did every single pressure gauge where you once worked, Randy, imply the same thing? - as if every pipe and device to which they were connected was intended to have the same amount of pressure? Do I want the same air pressure cleaning off a delicate negative as I use for a nail gun? Same goes for toe placement on film. It's all relative to the specific application. Box speed ratings don't change the need to think things out first, and no palm app or internal camera chip is a substitute for using one's own brain. Gadzooks.

[Pere Casals]

So the name of the game is APPLIED sensitometry.

Drew, this is applied sensitometry...

This is important because if we are able to agree on what film does with a Normal development and ISO speed then we may debate about what film does in non standard conditions. If not we are enterely lost and then we have no way to communicate and share our experiences with advanced processings.

[Bill Burk]

Drew wants you to look in the region of the characteristic curve to the left of m

If you've got the rattler's head a knuckle above the ground, he can stick his tongue straight down or across to the left. This can mean the two films have different real speeds. It's not much, just as far as the snake can spit his tongue, but Drew wants you to recognize there is potential for two films to have the same ASA speed and at the same time have two different "True film speeds".

My thought is that ASA speed's not a measure of a film's true speed. It's a standard that defines what a manufacturer can claim. It does give a basis for comparison, for that I am grateful.

I also think you will find frustration trying to get 0.1 density on your film. My shadows tend towards 0.25 to 0.4 because of flare. I could “feed back” the higher than necessary densities and choose to increase my EI, but I like the longer printing times

[Drew Wiley]

Well, right down there in the rattler's den is where shadow gradation begins with certain films, at least in the kinds of mtn and desert conditions I often encounter. But let me try a little different approach with Pere and Randy : What specific step tablet do each of your use for your own densitometer plots? For purposes of future discussion it will help to know if it's on a clear or yellowish base. But for the present, please note that in either case, some kind of commercially available film was involved, yet there's not only an extremely long 21-step range, but that each of these steps are evenly spaced over the entire range, indicating the whole thing, almost right down to the fbf, was exposed onto the straight line section of the film curve. Now using whatever exposure model you wish, and any film you think is appropriate, try to contact print a replica of that step tablet with exactly the same density and step distribution. Once you've figured that out, then do the same thing using each of typically preferred black and white contrast filters. Remember, all these curves have to precisely match (no post-exp PS tweaking); and in this case, there shouldn't be an evident "curve" at all except maybe at the very bottom. But what you'll soon discover, if you don't suffer an outright TKO during the first round, is that not only does the overall gamma shift with significantly different colored filters, but the curve shape itself, and hence your hypothetical speed point. This is a completely different issue than mere filter factors. Then this gets exaggerated as reciprocity failure comes into play. For this reason I suspect your "True Film Speed" model of exposure, seemingly brought into discussion for sake of simplifying exposure and development issues in large format photography, is actually less predictable than ordinary ole Zone System lingo, which at least allows one to add discrete steps below the generic Zone 2 boundary if necessary. Your model might work fine for moderate exposure scenes, but sure as heck not when your hand is right next to that rattler's hole. ... The other day I was at the camera store and they have access to every bells n' whistles current Nikon, Canon, and Fuji camera you can think of, plus a lot of automated used film cameras. But even though they sell TMax film too, not one of them working there has had any luck predictably using TMax themselves. That's because they're all addicted to fancy TTL algorithms and don't know how to use a basic light meter. Those chipped algorithms might be great for sports or other sudden action photography, but they were never meant to peek down the snake burrow where a lot of the action begins in terms of full rich print gradation.