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

[Drew Wiley]

Re-read what I posted, Pere. I was referring to cross-usage of meters between black and white photography and COLOR PHOTOGRAPHY, not just filter factors and peak meter sensitivity. If one does both, basing settings on the mid-point marking just makes sense. It makes sense for monochrome photography alone too. How else do we compare things in a quick easy manner? It was therefore convenient for AA and other to teach exposure methodology relative to 18% gray reflectance equalling Zone V, just like the center mark on every meter does, whether the film involved is color or black and white.

[Pere Casals]

Drew, IMHO what's the most important from ZS is visualization of the print from the zones in the scene. Many times we may not "see" how the image will be in fact, because on paper we may have a reduced dynamic range compared to the scene. If we select something in the scene then we have a visual reference...

In the other side the "true speed" says what density we'll have in the negative if we do a ISO normal development. We know that spots metered at -3.3 will have 0.1D density, while those metered at -/+0 will have 0.72D, both over base+fog.

...so I feel basics are quite easy.

[Drew Wiley]

The only problem with your "basics" is that it's based on an erroneous generalization, and only works, at that barely, if the target from which -3.3 is subtracted (in other words, Zone V) is a floating rather than fixed point of 18% gray. You're welcome to build an exposure model like that, but it wouldn't correspond to either the Zone System or typical meter usage. It's also easy to disprove using a densitometer with various real film options rather than a hypothetical stereotype. Just another straightjacket set of artificial rules that deserve to get broken.

[Bill Burk]

The ASA parameters define speed concretely at the 0.1 speed point. The distance to metered point and density there is not so spelled out. But by calculation confirmed with some tests, 10x is a reasonable approximation (Pere calls it 3.3 stops / I call it three and a third and we mean the same thing), and Pere gave density expectations that help confirm the contrast is reasonable.

But the density at the meter point is a confirming value, not a target.

[Drew Wiley]

Once again, that kind of model assumes that all planes take off the runway at around the same angle of trajectory, which they obviously don't. And yes, I realize that due to this, the lower part of the curve gets mathematically extrapolated a bit to make the formula fit. But that's right where we should be most concerned about the actual characteristics of the curve and not just the ASA convention, which blatantly differs from product to product anyway. Color films have less an issue in this respect because the toe and shoulder of the film are basically worthless; so the ASA ratings seem to be spot on relative to 18% gray. I would therefore contend that with black and white films, the ASA rating is as much a marketing tool as predictive of anything "concrete". Private label film can be even worse - the relabeled product rated at even high speed than the brand name master roll it was cut from. I've seen that several times. And I've sure as heck done enough densitometer plots of my own to know that minus 3-1/3 is far more hypothetical than real.

[Bill Burk]

I'm comfortable locking down where you meet ASA parameters at the 0.1 speed point.

At that point you're holding the rattler down on the ground by his head. He's not going to hurt you.

I'm not worried about the noise he makes at the other end.

Once you've got that, you can compare different developers and films. If the toe is specially long you can tell from the curve if there's another stop you can get out of it.

I know there's something magical about placing exposures as low as you can, so that you can have more of the negative density scale available in the mid to upper scale. I'm not so talented that I can use that to pictorial advantage. I prefer to put my pictures all on the straight line, so a film with a sharp toe fits my needs just fine. Generous exposure fits my needs just fine. But there are people who can feel it, sense it and use toe exposures to the advantage of the mid to upper tones. You can call it "micro tonality" but basically the idea is that the film has wavy curves and if you know where it is, and can put a bit of an upsweep in a person's face, it can put detail where it's most needed. Most people don't care about detail in the shadows. But they like detail in faces.

[Pere Casals]

Once again, that kind of model assumes that all planes take off the runway at around the same angle of trajectory, which they obviously don't.

Drew, single problem is inaccuracy in our side.

If you shot a Nikon F5 this is exact, because meter is a true scientific instrument, you meter TTL so glass transmission and flare is accounted. Then shutter is electronically re-adjusted automatically to be really exact, from long exposures to 1/8000.

We can meter/expose very accurately with a view camera, but it is not as easy. We may require a metering probe and a shutter tester.

With the Normal ISO processing it is true that a film may a have perticular curve, but we know that the calibration made by a good manufaturer is good.

Drew, just make a test, take fresh TMX and FP4+ rolls and an F5, use the F5 spot meter and shot an scene. You will find that -3.3 zones nail the 0.1D range and the -/+0 zones nail 0.72D, both over fog + base.

Me, I've tested it, and I found that it's like manufacturers and ISO norm say it has to be. If we vary processing, then we may calibrate the non ISO process or we may simply make some bracketings to see, both ways are good !!!

But let me reiterate that sensitometry is science, and ISO is industrial norms, so IMHO there is no discussion about that, it's about reading what says the norm.

[Drew Wiley]

TTL doesn't solve this kind of thing at all. It introduces other variables. For instance, incorrect filter factor readings. TTL meters certainly aren't "color blind". I've found Nikon TTL metering to be less dependable than handheld spot metering. Under certain circumstances one might use a Sinar film plane meter probe; but that's inconvenient in the field. Flare is pretty much a non-issue for me because I mostly use modern multicoated lenses and an efficient shade system. I have lab meters that can measure that kind of thing far more accurately in a controlled environment than any ordinary light meter. I've made HUNDREDS of tests, Pere, densitometer read and often plotted too; and I'm referring to actual sheet film tests, not just roll film. Most of these were done using an expensive thermoregulator that kept dev temp inside 0.1 deg F. I had a good reason to plot film with this level of accuracy due to using films like FP4 and TMX in relation to predictable advanced color printing applications (masks, separation negs etc). This would have been ridiculous overkill for general black and white photography. And your contention that -3.3 consistently lands 0.10 above fbf is nonsense. There's no point trying to explain this to you anymore because you simply aren't grasping the basic issue. FILMS DIFFER IN TOE PERSONALITY. Therefore, no "one shoe fits all" ASA convention is anything more than that - a nominal marketing label that is, at best, only a starting point for personal testing. It doesn't really tell you how those lower values are going to reproduce. Only the actual curve will, relative to your specific exposure and development regimen. What you are doing, Pere, is preaching a religion that requires blind faith in some rote formula you can simply plug into a computer program, and Voila, exposure is solved. The real world of film and light does not work like that. Films differ.

[Pere Casals]

And your contention that -3.3 consistently lands 0.10 above fbf is nonsense. There's no sense trying to explain this anymore because simply aren't getting the basic issue. FILMS DIFFER IN TOE PERSONALITY.

Drew, please read https://en.wikipedia.org/wiki/Film_speed Determining film speed chapter and please tell me how it is possible that a -3.3 exposure is not aiming 0.1D (over F+B), without mattering the kind of toe we have.

With any kind of toe film speed is calculated to give the same 0.1 at -3.3 with normal development, toe personality does not matter for that, at all.

[Drew Wiley]

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.