Potential Density in B&W films

[Crysist]

These are a few open questions and thoughts I have about film, this can apply to color film, but part of what I speculate only seems possible in B&W.

The main question I have is what range of densities are contained in the latent image versus what densities result from the developed image? While on a far smaller scale, I'm just thinking the densities of the latent image in a similar way: concentrations of silver, but instead it's silver formed from photons reducing the AgX. The latent image is described similar to an invisible imprint that gets magnified millions of times through the development process.

I have two follow-ups to this. Let's say that the range of densities the latent image can represent, the point at which you can distinguish image above base fog, the classical "toe" of an HD curve of a developed negative, to the densest it can be, is far greater than those of the developed image. Is this a fair assumption to consider? I suppose this is limited by the amount of AgX in the emulsion and aspects of the developer. Peak density means all the AgX in that area has been converted to silver. If the latent image just hosts small "sensitivity specks", and from how they are described, they take up small centers of larger crystals. Isn't there a point which there are enough specks on a crystal to develop the entire thing to metallic silver, while still being able to have carried even more sensitivity specks? Is there more hilight detail in the latent image than can possibly be developed?

Let me consider the other cases. If it isn't a limitation of the amount of silver, what's the reason for it? Doesn't that mean normal films should be able to be printed out with a regular exposure that would reach max density? If there is no gap between how much silver is formed in the latent image, that all the AgX is used up in the latent image, then you should be able to throw fixer on it and get a visible image. Or is there another factor at play causing there to be a far earlier limit to the density in the latent image? Is it instead some saturation of crystals with metallic silver that prohibits more from forming on the same crystal?

If the former is true, that there is just a limitation by AgX, does physical development help? From what I understand, physical development involves introducing new metal to form the final image, instead of developing the existing AgX. I mean it's still chemical, but it makes sense that the focus is not on the reaction reducing ionic silver instead of just precipitating it in the right places. I presume this can also oversaturate all the same, that there might be so much silver added such that the latent image no longer has an effect on where silver is formed. I'm probably just unclear on how things work in this case. My main interest with physical development is if you could use it to just get a higher max density, or if there's some way that it can be used to retrieve more highlight detail that would be limited by traditional chemical development.

In summary, this is merely asking specifics about the chemistry, I've read through the relevant sections of a couple books and articles and these are some questions I'm left with. And some pretty big assumptions which I hope some other members of the forum can clear up! Thanks!!

PS: Is daguerreotype development, with mercury vapors depositing on an exposed plate, a form of physical development?

 

[RalphLambrecht]

These are a few open questions and thoughts I have about film, this can apply to color film, but part of what I speculate only seems possible in B&W.

The main question I have is what range of densities are contained in the latent image versus what densities result from the developed image? While on a far smaller scale, I'm just thinking the densities of the latent image in a similar way: concentrations of silver, but instead it's silver formed from photons reducing the AgX. The latent image is described similar to an invisible imprint that gets magnified millions of times through the development process.

I have two follow-ups to this. Let's say that the range of densities the latent image can represent, the point at which you can distinguish image above base fog, the classical "toe" of an HD curve of a developed negative, to the densest it can be, is far greater than those of the developed image. Is this a fair assumption to consider? I suppose this is limited by the amount of AgX in the emulsion and aspects of the developer. Peak density means all the AgX in that area has been converted to silver. If the latent image just hosts small "sensitivity specks", and from how they are described, they take up small centers of larger crystals. Isn't there a point which there are enough specks on a crystal to develop the entire thing to metallic silver, while still being able to have carried even more sensitivity specks? Is there more hilight detail in the latent image than can possibly be developed?

Let me consider the other cases. If it isn't a limitation of the amount of silver, what's the reason for it? Doesn't that mean normal films should be able to be printed out with a regular exposure that would reach max density? If there is no gap between how much silver is formed in the latent image, that all the AgX is used up in the latent image, then you should be able to throw fixer on it and get a visible image. Or is there another factor at play causing there to be a far earlier limit to the density in the latent image? Is it instead some saturation of crystals with metallic silver that prohibits more from forming on the same crystal?

If the former is true, that there is just a limitation by AgX, does physical development help? From what I understand, physical development involves introducing new metal to form the final image, instead of developing the existing AgX. I mean it's still chemical, but it makes sense that the focus is not on the reaction reducing ionic silver instead of just precipitating it in the right places. I presume this can also oversaturate all the same, that there might be so much silver added such that the latent image no longer has an effect on where silver is formed. I'm probably just unclear on how things work in this case. My main interest with physical development is if you could use it to just get a higher max density, or if there's some way that it can be used to retrieve more highlight detail that would be limited by traditional chemical development.

In summary, this is merely asking specifics about the chemistry, I've read through the relevant sections of a couple books and articles and these are some questions I'm left with. And some pretty big assumptions which I hope some other members of the forum can clear up! Thanks!!

PS: Is daguerreotype development, with mercury vapors depositing on an exposed plate, a form of physical development?

I'm afraid your questions can only be answered by what I call ' pretty hefty photographic literature written by experts such as Mees or Haist (pretty dry but in-depth knowledge of the funamental photographic processes). I, for one, wouldn't even know how to measure latent image densities.

 

[Mr Bill]

The main question I have is what range of densities are contained in the latent image versus what densities result from the developed image?

Hi, I don't think it's really relevant to talk about "density" of a latent image. Measuring optical density is something typically done on a much larger scale. A typical densitometer uses a measuring aperture of about 3 mm diameter, with typical accessory apertures of perhaps 2 or even 1 mm diameter.

My understanding of a latent image is that it must be at least several ATOMS in size, depending on what type of sensitization is used. Such a latent image is allegedly both stable and developable. There is also a so-called sub-latent image which can also be stable yet not able to be developed. Either of these, I think, is too small to be seen under a light microscope, much less measure optical density.

Regarding maximum density of a b&w film, both Kodak T-max 100 and 400 are able to reach densities of 4.00 when developed in D-76 developer (for an extended time). This is coincidentally, and historically the highest reading common densitometers (various Macbeth units, as well as X-rite 810, I believe). I'm getting the T-max data from a set of characteristic curves once published in a not-well-known Kodak technical publication (Kodak Tech-Bits). To put a density of 4.00 into perspective, it let's through only about 0.01% of the light. So it would be very difficult to deal with this in a common enlarger.

[Update...] I had previously posted about this here:

Where would film technology be now?

I don't think Moore's Law even applies to computers any more. In the beginning, processor and memory capabilities increased at a neck-break pace. But for many years it has just been creeping up in small steps each year. Reportedly it's still going, though barely. At some point the original...

www.photrio.com

And... the missing T-max graphs can be seen here. https://media.invisioncic.com/l3234...orig.jpg.b3ee32ce67bdb914b7d8279716377649.jpg

 

[Yezishu]

A small part of the issue is whether film can record highlights far beyond its designed range—I believe it can. To do this, you can press a negative against the film and expose it to strong sunlight or ultraviolet light for tens of minutes. The large amount of silver will cause the film to turn dark or even black directly, and it can then be fixed without development.
If you have sufficiently precise measuring instruments (as in this paper), it might be possible to record both ordinary latent images and those silver image from strong exposure at the same time.

Nail, N. R., F. Moser, and F. Urbach. "An incremental photometer and optical measurements in the photographic latent-image range." Journal of the Optical Society of America 46.3 (1956): 218-222.

 

[koraks]

what range of densities are contained in the latent image versus what densities result from the developed image?

This ranges from infinitesimally small to virtually undetectable.

Let's say that the range of densities the latent image can represent, the point at which you can distinguish image above base fog, the classical "toe" of an HD curve of a developed negative, to the densest it can be, is far greater than those of the developed image. Is this a fair assumption to consider?

I'd warn against a couple of possible sources of confusion:
1: Don't confuse the range of illuminant flux (e.g. as a result of scene brightness range) with metal-layer density on the film.
2: Don't confuse how film negatives are developed with paper development; the former does not go to completion.
Having covered that, the density range of the latent image is evidently and without any doubt millions of times smaller than that of the developed negative. So your question as such does not make sense, and I suspect it's because of the confusion in (1).

Going out on a limb, I can see how your question might actually be about the latent image recording a larger illumination range than the developed negative does. The underlying question would be: does the process of development somehow 'shoulder off' while this shouldering off does not occur during the exposure stage? Ultimately, it'll happen at both stages, without a doubt. In the latent image/exposure stage, self-masking at some point becomes a noticeable effect. During development, all manner of processes of inhibition take place that reduce the rate of development in places of already high density. So I think the quick & easy answer to your (corrected) question would be "yes, to an extent".

Doesn't that mean normal films should be able to be printed out with a regular exposure that would reach max density?

To an extent, but as said, self-masking will take place. There may also be other inhibition effects (e.g of chemical or physical nature) that may limit the density buildup.

If the former is true, that there is just a limitation by AgX, does physical development help?

I honestly think that before going to this, you'd have to go into the depths a little more of your preceding assumptions. At this point you've built a conceptual card house that's so narrow and shaky that it's hard to make sense of it anymore.

I've read through the relevant sections of a couple books and articles and these are some questions I'm left with.

Could you try to formulate your questions a bit more specifically in relation to the texts you've read? I feel that the standard works that are often referred to such as those by Mees & James and Glafkidès cover your needs more than adequately and you could answer all of your question on the basis of those works.

 

[Rudeofus]

I have two follow-ups to this. Let's say that the range of densities the latent image can represent, the point at which you can distinguish image above base fog, the classical "toe" of an HD curve of a developed negative, to the densest it can be, is far greater than those of the developed image. Is this a fair assumption to consider? I suppose this is limited by the amount of AgX in the emulsion and aspects of the developer. Peak density means all the AgX in that area has been converted to silver. If the latent image just hosts small "sensitivity specks", and from how they are described, they take up small centers of larger crystals. Isn't there a point which there are enough specks on a crystal to develop the entire thing to metallic silver, while still being able to have carried even more sensitivity specks? Is there more hilight detail in the latent image than can possibly be developed?

It's not entirely sure, that there is a need for higher density ranges on film:

1. Film is a low contrast medium, which means you'd need a contrast range beyond 5 or 6 to get a contrast range of 4 on your film. Note, that these are density units, not photographic stops!
2. Film is typically enlarged through a lens, and every lens has some degree of flare. A density range of 4 will not make it onto your paper.
3. Photographic printing paper increases contrast. You can already print a D range from 0 to 2 only with dodging and burning.

These reasons may explain the fact, that modern film rarely reaches D=3 in theory and even less in practical shots.

Let me consider the other cases. If it isn't a limitation of the amount of silver, what's the reason for it? Doesn't that mean normal films should be able to be printed out with a regular exposure that would reach max density? If there is no gap between how much silver is formed in the latent image, that all the AgX is used up in the latent image, then you should be able to throw fixer on it and get a visible image.

There are some photographic techniques, where the latent image is used as actual image. These techniques require hours of exposure in broad daylight.

If you accept 3-4 silver atoms as stable, developable latent image speck, and compare this to a 1µm³ Silver Bromide crystal, then this crystal has a weight of 10-18m³ * 6473 kg/m³ ~ 6.5 10-15 kg. These 6.5 10-15 kg Silver Bromide correspond to 6.5 10-15 kg / 0.178 kg/mol = 36.5 10-15 mol, which corresponds to 36.5 10-15 mol * 6.022 1023 1/mol ~ 21.9 109 formulaic units, containing the same number of silver ions.

These numbers will vary with crystal size, bromide vs. iodide and so on, but a ball park number of 4*109 atoms won't be far off, which means, that photographic development raises density by roughly 9 units. What you call a gap between latent image density range vs. developed image density range is actually a huge canyon. You will also notice, that a sun print typically does not reach density levels of developed images, since these cubical crystals have a lot less density that the equivalent mass of filament silver.

If the former is true, that there is just a limitation by AgX, does physical development help? From what I understand, physical development involves introducing new metal to form the final image, instead of developing the existing AgX. I mean it's still chemical, but it makes sense that the focus is not on the reaction reducing ionic silver instead of just precipitating it in the right places. I presume this can also oversaturate all the same, that there might be so much silver added such that the latent image no longer has an effect on where silver is formed.

Image wise, there is little difference between the physical development process as described by you and the regular photographic development process, where the silver ions are taken from the emulsion. Even if you supply the silver through the photographic solution, there's a chance, that filaments will develop, giving you the exact same result.

Photographic development has been thoroughly researched, and I would not expect a silver bullet here for much improved development. There are some approaches, which were discovered in the eighties and never commercialized in B&W (like HQMS, DIR couplers, ...), but even these give you no more than incremental improvements. "Reaching higher Dmax" was never really seen as something to aim for, and my previous paragraphs may provide ample reasons for this.

I'm probably just unclear on how things work in this case. My main interest with physical development is if you could use it to just get a higher max density, or if there's some way that it can be used to retrieve more highlight detail that would be limited by traditional chemical development.

What you really want is "filaments in the weakly exposed regions and spherical silver in the highlights", and modern film plus modern developers are as close to this as it gets. "Straight H&D curve with tiny toe region and slightly concave upper region" is how you would recognize this. The strongest determining factor to achieve optimal results (quantum efficiency aka "optimum of speed, grain and sharpness") are "how long does it take to develop?", and even there the benefits of slower development level off after about 10-15 minutes. This was known and published in the early 60ies, and I haven't seen anything contradicting this since then.

PS: Is daguerreotype development, with mercury vapors depositing on an exposed plate, a form of physical development?

To some extent it is, but it's not something you want to do at home. It's also not really development, since the mercury is already present in metallic form. It's also very unlikely to yield the insanely high image amplification you get with chemical development.

 

[Bill Burk]

Hi, I don't think it's really relevant to talk about "density" of a latent image. Measuring optical density is something typically done on a much larger scale. A typical densitometer uses a measuring aperture of about 3 mm diameter, with typical accessory apertures of perhaps 2 or even 1 mm diameter.

My understanding of a latent image is that it must be at least several ATOMS in size, depending on what type of sensitization is used. Such a latent image is allegedly both stable and developable. There is also a so-called sub-latent image which can also be stable yet not able to be developed. Either of these, I think, is too small to be seen under a light microscope, much less measure optical density.

Regarding maximum density of a b&w film, both Kodak T-max 100 and 400 are able to reach densities of 4.00 when developed in D-76 developer (for an extended time). This is coincidentally, and historically the highest reading common densitometers (various Macbeth units, as well as X-rite 810, I believe). I'm getting the T-max data from a set of characteristic curves once published in a not-well-known Kodak technical publication (Kodak Tech-Bits). To put a density of 4.00 into perspective, it let's through only about 0.01% of the light. So it would be very difficult to deal with this in a common enlarger.

[Update...] I had previously posted about this here:

Where would film technology be now?

I don't think Moore's Law even applies to computers any more. In the beginning, processor and memory capabilities increased at a neck-break pace. But for many years it has just been creeping up in small steps each year. Reportedly it's still going, though barely. At some point the original...

www.photrio.com

And... the missing T-max graphs can be seen here. https://media.invisioncic.com/l3234...orig.jpg.b3ee32ce67bdb914b7d8279716377649.jpg

Nice graph.

4.00 is indeed as dense as could be practically desired.

But in the graphic arts, I often exposed and processed Kodak imagesetter film which reached densities beyond 4.00, maybe 4.20 but we used 4.00 as the minimum and tried to keep at or above it. I think 4.05 was a typical reading.

When we switched to cheaper 3M film we had to settle for about 3.60

 

[reddesert]

Let me consider the other cases. If it isn't a limitation of the amount of silver, what's the reason for it? Doesn't that mean normal films should be able to be printed out with a regular exposure that would reach max density? If there is no gap between how much silver is formed in the latent image, that all the AgX is used up in the latent image, then you should be able to throw fixer on it and get a visible image. Or is there another factor at play causing there to be a far earlier limit to the density in the latent image? Is it instead some saturation of crystals with metallic silver that prohibits more from forming on the same crystal?

I am not really sure what you are trying to ask, but let me suggest a home experiment.

Take a piece of unexposed undeveloped 35mm B&W film, like the film leader, and take it out in full light, like room light, or even direct sunlight. Now try shining a light through it, such as a flashlight. You should be able to see the light through the leader. I didn't actually try it this moment with B&W film, but it's certainly true that an undeveloped C-41 leader doesn't block much light, and I'm pretty sure that's also true of B&W leader.

Now, this leader has been blasted with light. Its latent image is as overexposed as you can get, unless you leave the film out in the sun for hours. If you develop the B&W leader, it will be opaque to a flashlight, and almost opaque to the sun (I don't recommend using developed B&W film as a solar filter like in the bad old days. Undeveloped B&W film is of course totally unsuitable.)

So what that tells you is that physical development or printing-out of the leader hasn't gotten you very far. What makes the film high-density is the chemical conversion of the silver nitrates to clumps of metallic silver. It's not the raw mass of the element silver in the film. The chemical form it's in and the geometry of the clumps make a huge difference.

 

[Crysist]

Wow, thank you all for your great feedback!

I'm afraid your questions can only be answered by what I call ' pretty hefty photographic literature written by experts such as Mees or Haist (pretty dry but in-depth knowledge of the funamental photographic processes). I, for one, wouldn't even know how to measure latent image densities.

Me neither, haha! I've read parts of Mees' for those fundamental details, it's an stellar reference. But I don't know if this was explicitly dealt with.

Hi, I don't think it's really relevant to talk about "density" of a latent image. Measuring optical density is something typically done on a much larger scale. A typical densitometer uses a measuring aperture of about 3 mm diameter, with typical accessory apertures of perhaps 2 or even 1 mm diameter.

My understanding of a latent image is that it must be at least several ATOMS in size, depending on what type of sensitization is used. Such a latent image is allegedly both stable and developable. There is also a so-called sub-latent image which can also be stable yet not able to be developed. Either of these, I think, is too small to be seen under a light microscope, much less measure optical density.

This ranges from infinitesimally small to virtually undetectable.

I'd warn against a couple of possible sources of confusion:
1: Don't confuse the range of illuminant flux (e.g. as a result of scene brightness range) with metal-layer density on the film.
2: Don't confuse how film negatives are developed with paper development; the former does not go to completion.
Having covered that, the density range of the latent image is evidently and without any doubt millions of times smaller than that of the developed negative. So your question as such does not make sense, and I suspect it's because of the confusion in (1).

There's one thing I misjudged when writing that I should have clarified better. Please excuse me for using "density" to refer to the latent image. What I intend when I write that is "concentrations of stable centers of silver reductions in the AgX crystals due to photons". In short, where photons have struck the emulsion and the emulsion has recorded a lot or a little.

I was comparing that reduction of silver to the silver formed by development, so I had called it "density" presuming it would be understood merely as a word for "concentration". I didn't mean it would be visible or that you'd be able to to measure it as it's on the order of very few atoms. Apologies for the confusion.

And I'm not sure I am confusing paper development with film development? Could you expand on that, I actually thought the opposite, that paper development doesn't go to completion and works just like film. In either case, I wasn't trying to reference it at all here besides the one reference to "developing out".

Regarding maximum density of a b&w film, both Kodak T-max 100 and 400 are able to reach densities of 4.00 when developed in D-76 developer (for an extended time). This is coincidentally, and historically the highest reading common densitometers (various Macbeth units, as well as X-rite 810, I believe). I'm getting the T-max data from a set of characteristic curves once published in a not-well-known Kodak technical publication (Kodak Tech-Bits). To put a density of 4.00 into perspective, it let's through only about 0.01% of the light. So it would be very difficult to deal with this in a common enlarger.

[Update...] I had previously posted about this here:

Where would film technology be now?

I don't think Moore's Law even applies to computers any more. In the beginning, processor and memory capabilities increased at a neck-break pace. But for many years it has just been creeping up in small steps each year. Reportedly it's still going, though barely. At some point the original...

www.photrio.com

And... the missing T-max graphs can be seen here. https://media.invisioncic.com/l3234...orig.jpg.b3ee32ce67bdb914b7d8279716377649.jpg

Ah, that's a very interesting graph! I feel many film datasheets can abridge data too much, this is really neat!

My interest with expanded densities is actually not for printmaking, I mean perhaps I am slightly intrigued if that also has use, but it's for slide projection/viewing instead.

A small part of the issue is whether film can record highlights far beyond its designed range—I believe it can. To do this, you can press a negative against the film and expose it to strong sunlight or ultraviolet light for tens of minutes. The large amount of silver will cause the film to turn dark or even black directly, and it can then be fixed without development.
If you have sufficiently precise measuring instruments (as in this paper), it might be possible to record both ordinary latent images and those silver image from strong exposure at the same time.

Nail, N. R., F. Moser, and F. Urbach. "An incremental photometer and optical measurements in the photographic latent-image range." Journal of the Optical Society of America 46.3 (1956): 218-222.

I see! That was what I was implying. If you could reach those heights from exposure, it seems like the range could be far larger. Especially an ordinary latent image and an exposure that strong simultaneously!

Going out on a limb, I can see how your question might actually be about the latent image recording a larger illumination range than the developed negative does. The underlying question would be: does the process of development somehow 'shoulder off' while this shouldering off does not occur during the exposure stage? Ultimately, it'll happen at both stages, without a doubt. In the latent image/exposure stage, self-masking at some point becomes a noticeable effect. During development, all manner of processes of inhibition take place that reduce the rate of development in places of already high density. So I think the quick & easy answer to your (corrected) question would be "yes, to an extent".

I believe you have picked the correct limb! Again, my apologies for not getting my idea across as clearly!

And the sources of "inhibition" you refer to was what I was getting at when I wondered if there was a separate "saturation" effect that causes an earlier shoulder.

To an extent, but as said, self-masking will take place. There may also be other inhibition effects (e.g of chemical or physical nature) that may limit the density buildup.

And, likely, with a different gamma? It seems you're more familiar with self-masking, what effect does it usually cause in practice?

I honestly think that before going to this, you'd have to go into the depths a little more of your preceding assumptions. At this point you've built a conceptual card house that's so narrow and shaky that it's hard to make sense of it anymore.

I'm feeling a hard to suppress urge to apologize again lol. When writing the post, I knew that if I kept building assumption off assumption, it would be like repeatedly cutting a slice of cake, cutting that slice smaller, then cutting that slice smaller, etc. So that's why I tried to explore the opposite cases.

Could you try to formulate your questions a bit more specifically in relation to the texts you've read? I feel that the standard works that are often referred to such as those by Mees & James and Glafkidès cover your needs more than adequately and you could answer all of your question on the basis of those works.

I can point only broadly. Most of the finer details I've gathered are from Mees' "The Theory of the Photographic Process". Part of what I refer to is the section about "the nature of the latent image" for talking about silver, how it exists in the latent image and what I'm extrapolating about what is possible with it. Then "The relation between exposure given to a light-sensitive layer and the density obtained after development", but that section is far more dedicated to quantifying the relationship and not specifically about measuring how the latent image may differ in where the shoulder would be. So it doesn't seem to answer all my questions.

 

[Crysist]

It's not entirely sure, that there is a need for higher density ranges on film:

1. Film is a low contrast medium, which means you'd need a contrast range beyond 5 or 6 to get a contrast range of 4 on your film. Note, that these are density units, not photographic stops!
2. Film is typically enlarged through a lens, and every lens has some degree of flare. A density range of 4 will not make it onto your paper.
3. Photographic printing paper increases contrast. You can already print a D range from 0 to 2 only with dodging and burning.

These reasons may explain the fact, that modern film rarely reaches D=3 in theory and even less in practical shots.

The reason I think about higher densities is for two reasons. One, just to proportionally expand the highlights. If the highlights didn't shoulder off where an exposure produces an image that develops to a density of 4, then naturally you'd get higher densities. Two, is it mainly relates to projection. I am thinking back to the "Kodak Vision Premier" line of color print films, which boasted a comparatively insane DMax of 5.5 and above for "extremely rich blacks"!! At that stage, you approach contrast ratio of 1000000:1 instead of 1000:1 for D=3!! This would be, of course, in conjunction with a reversal process.

There are some photographic techniques, where the latent image is used as actual image. These techniques require hours of exposure in broad daylight.

If you accept 3-4 silver atoms as stable, developable latent image speck, and compare this to a 1µm³ Silver Bromide crystal, then this crystal has a weight of 10-18m³ * 6473 kg/m³ ~ 6.5 10-15 kg. These 6.5 10-15 kg Silver Bromide correspond to 6.5 10-15 kg / 0.178 kg/mol = 36.5 10-15 mol, which corresponds to 36.5 10-15 mol * 6.022 1023 1/mol ~ 21.9 109 formulaic units, containing the same number of silver ions.

These numbers will vary with crystal size, bromide vs. iodide and so on, but a ball park number of 4*109 atoms won't be far off, which means, that photographic development raises density by roughly 9 units. What you call a gap between latent image density range vs. developed image density range is actually a huge canyon. You will also notice, that a sun print typically does not reach density levels of developed images, since these cubical crystals have a lot less density that the equivalent mass of filament silver.

Right. I have heard of development called a process of "intensifying" by "a billion times".

But this is the exact kind of math that makes me think something is being lost. Development expands the latent image speck to take up more and more elemental silver from the Silver Halide crystal. It seems like development can easily run out of Silver Halide to convert. On the other hand, at what point will an exposure run out of Silver Halide to reduce?

Also, does developed silver form in filaments? I saw one photo from a blog once that showed off photomicrographs to show how grains didn't merely have an "on/off state".

Image wise, there is little difference between the physical development process as described by you and the regular photographic development process, where the silver ions are taken from the emulsion. Even if you supply the silver through the photographic solution, there's a chance, that filaments will develop, giving you the exact same result.

But it wouldn't run out of silver, though. That's the difference I was curious about taking advantage of.

"Reaching higher Dmax" was never really seen as something to aim for, and my previous paragraphs may provide ample reasons for this.

Certainly, in some circumstances, but my previous paragraphs give some possible reasons for it. And regardless, I am interested in it! It sounds cool!

What you really want is "filaments in the weakly exposed regions and spherical silver in the highlights", and modern film plus modern developers are as close to this as it gets. "Straight H&D curve with tiny toe region and slightly concave upper region" is how you would recognize this. The strongest determining factor to achieve optimal results (quantum efficiency aka "optimum of speed, grain and sharpness") are "how long does it take to develop?", and even there the benefits of slower development level off after about 10-15 minutes. This was known and published in the early 60ies, and I haven't seen anything contradicting this since then.

Well, different developers still can give very different results. People choose different ones for different purposes. "modern film plus modern developers" will, as you describe, give you a specific result in terms of the characteristic curve. I'm asking what differences could be made, not whether they are worth making from one standpoint. Lastly, this is all theoretical but if there is somethings that can affect these limits more beyond traditional modern development practices, it'd be fun to learn about!

To some extent it is, but it's not something you want to do at home. It's also not really development, since the mercury is already present in metallic form. It's also very unlikely to yield the insanely high image amplification you get with chemical development.

Ah! I spoke about a lot of hypothetical stuff, but I am not interested in playing with mercury anytime soon! Don't worry about that!

As an aside, have people exposed daguerreotype plates but developed them in modern developers instead of mercury vapor amalgamation?? I wonder what those look like! The fact that they're formed on uniform plates instead of grains (okay the silver halide layer is formed on top of the plate and may not be as uniform) makes me curious!

Nice graph.

4.00 is indeed as dense as could be practically desired.

But in the graphic arts, I often exposed and processed Kodak imagesetter film which reached densities beyond 4.00, maybe 4.20 but we used 4.00 as the minimum and tried to keep at or above it. I think 4.05 was a typical reading.

When we switched to cheaper 3M film we had to settle for about 3.60

I, too, like the graphs! I didn't know they went that high. But for large densities I'm mainly interested in how it improves slide reproduction.

And also, I just figured, might it increase the fidelity of the tonality if it's not in such a small density range? Like if you fit a scene in a density range of 1 versus a range of 4, and then print them so they have the same contrast, will you notice any difference in quality of the tonal reproduction? Would things look muddy if you try to reproduce or print from a smaller range? Do tonal differences begin to disappear at certain, low contrasts? It seems like it, after all this is closely tied to whether film can record fine details, if that goes in low contrast, can't anything else? Or does that apply only to scene/exposure contrast and not the contrast in the developed image?

I am not really sure what you are trying to ask, but let me suggest a home experiment.

Take a piece of unexposed undeveloped 35mm B&W film, like the film leader, and take it out in full light, like room light, or even direct sunlight. Now try shining a light through it, such as a flashlight. You should be able to see the light through the leader. I didn't actually try it this moment with B&W film, but it's certainly true that an undeveloped C-41 leader doesn't block much light, and I'm pretty sure that's also true of B&W leader.

Now, this leader has been blasted with light. Its latent image is as overexposed as you can get, unless you leave the film out in the sun for hours. If you develop the B&W leader, it will be opaque to a flashlight, and almost opaque to the sun (I don't recommend using developed B&W film as a solar filter like in the bad old days. Undeveloped B&W film is of course totally unsuitable.)

So what that tells you is that physical development or printing-out of the leader hasn't gotten you very far. What makes the film high-density is the chemical conversion of the silver nitrates to clumps of metallic silver. It's not the raw mass of the element silver in the film. The chemical form it's in and the geometry of the clumps make a huge difference.

Oh yeah, I've "performed" this a number of times! Not intentionally, but I've held onto developed leaders! I've also taken the developed leader and put it in front of a bright light and observe how well it blocks it. I still recall there being a slight difference, that I couldn't see through it when undeveloped, but barely saw through when developed. I'll need to pay attention next time I develop some B&W. I tried doing an impromptu density "measurement" by comparing what exposure is needed to make a light appear similarly exposed through the leader as without any obstruction. I don't know how accurate that kind of measurement is though. I forgot what I calculated with my method, somewhere around 3 for some Ilford Delta or Pan F, I believe?

I worry the latter part misses what I was suggesting. The limit of how much silver can be formed is what I'm trying to assess compared to how much more might be represented in the undeveloped image. And I'm not sure that experiment is relevant to physical development if one isn't used, right?

I appreciate all your input!!

 

[koraks]

And I'm not sure I am confusing paper development with film development? Could you expand on that, I actually thought the opposite, that paper development doesn't go to completion and works just like film. In either case, I wasn't trying to reference it at all here besides the one reference to "developing out".

My remark was triggered by this:

Isn't there a point which there are enough specks on a crystal to develop the entire thing to metallic silver, while still being able to have carried even more sensitivity specks?

The implicit assumption in that statement appeared to be a binary model of silver halide development: a grain develops, or it doesn't. In reality, development progresses from activated centers, producing particles (typically filaments) of metallic silver. The size of these particles scales with the degree of development (as controlled by concentration, temperature, duration, agitation etc.) When taken to excess, development will of course proceed to include non-exposed halides as well: i.e. it fogs. At least in paper, there's a more or less stable plateau between these two parts of the process which is exploited; it's the stage at which development has acted on all exposed silver halide and progresses no more (or only marginally). At some point, fog does start to build. In film development, this plateau is (1) present to a much lesser extent as fogging tends to happen even during normal development and (2) it's not used as a natural end to development since gamma and thus final density range are controlled by limiting the degree of development.

Your question whether there's an exposure level that 'shoulders off' under normal conditions of film development can be answered with a 'yes', and in fact even more so: there comes a point where density drops as exposure increases. This is exploited in direct positive materials, it's the basis of solarization (not to be confused with Sabattier effect) and it's also visible in HD curves if they extend sufficiently (which in datasheets they commonly don't).

 

[Yezishu]

I see! That was what I was implying. If you could reach those heights from exposure, it seems like the range could be far larger. Especially an ordinary latent image and an exposure that strong simultaneously!

The question is: when do we actually need to record such a large dynamic range that ordinary images end up as just a thin layer of gray? In practical, the maximum dynamic range of display media like photo paper, slides, or LCD screens is limited. Even if we had a perfect display medium, the dynamic range of our eye still has its limits. Otherwise, we will use photometers like Moser’s when scanning photographs.

 

[Rudeofus]

The reason I think about higher densities is for two reasons. One, just to proportionally expand the highlights. If the highlights didn't shoulder off where an exposure produces an image that develops to a density of 4, then naturally you'd get higher densities. Two, is it mainly relates to projection. I am thinking back to the "Kodak Vision Premier" line of color print films, which boasted a comparatively insane DMax of 5.5 and above for "extremely rich blacks"!! At that stage, you approach contrast ratio of 1000000:1 instead of 1000:1 for D=3!! This would be, of course, in conjunction with a reversal process.

It's a big difference, if you aim for Dmax = 5.5 in a high contrast medium like print film or slide film with gammas around 2, or whether you try to get that density range on negative film with target gamma of 0.7. Think about the input contrast range, and how you would get this kind of dynamic range through a lens! What you could get would be a negative with D between 3 and 5.5, which would be exceedingly painful to print.

One more thought about high densities: if you look at a developed emulsion with D=2: this would look like a random pattern with 1% of the area translucent and the remaining 99% opaque. The imagine an area with D=0.3 with 50% translucent and 50% opaque. Compare the potential resolution of these two. With D=2 you'd lose a factor 10 in linear resolution, and with D=4 you'd lose a factor 100. Even fine grained ISO 100 film would look awful. BTW this is not just a silly theory: I have some 6x7 negatives developed in some experimental soup, and these negs have Dmin around 2. These negs appear grainy as hell and even 18x24cm enlargements are unusable. I'd hate to imagine the same material (Tri-X) at D=4.

Also, does developed silver form in filaments? I saw one photo from a blog once that showed off photomicrographs to show how grains didn't merely have an "on/off state".

As silver halide start development, initially the latent image specks develop spherically. These tiny specks are hard to develop, so they develop slow enough such that silver can deposit uniformly. As the speck increases in size, development picks up speed and at some point filaments start to appear. When that happens depends on development speed. These spheres have lower covering powder than filaments, i.e. the former need more silver to achieve a certain density than the latter. Strongly exposed specks will develop filaments earlier than weakly exposed ones, so at a gamma of 0.7 you can expect the darker parts of your film to be filaments. If the weaker exposed parts remain spherical, they will have extra low density, i.e. you'll get speed loss.

Well, different developers still can give very different results. People choose different ones for different purposes. "modern film plus modern developers" will, as you describe, give you a specific result in terms of the characteristic curve. I'm asking what differences could be made, not whether they are worth making from one standpoint. Lastly, this is all theoretical but if there is somethings that can affect these limits more beyond traditional modern development practices, it'd be fun to learn about!

The easiest way to explore higher densities is starting with a developer you know and add KSCN in 1 g/l increments. As you add more, you will get higher contrast but also base fog. As mentioned before, I doubt you can get a dynamic range of 1:10000 through your lens, but you at least have a way to look at a very dense negative and then decide what to do with this type of image.

 

[Crysist]

My remark was triggered by this:

The implicit assumption in that statement appeared to be a binary model of silver halide development: a grain develops, or it doesn't. In reality, development progresses from activated centers, producing particles (typically filaments) of metallic silver. The size of these particles scales with the degree of development (as controlled by concentration, temperature, duration, agitation etc.) When taken to excess, development will of course proceed to include non-exposed halides as well: i.e. it fogs. At least in paper, there's a more or less stable plateau between these two parts of the process which is exploited; it's the stage at which development has acted on all exposed silver halide and progresses no more (or only marginally). At some point, fog does start to build. In film development, this plateau is (1) present to a much lesser extent as fogging tends to happen even during normal development and (2) it's not used as a natural end to development since gamma and thus final density range are controlled by limiting the degree of development.

Your question whether there's an exposure level that 'shoulders off' under normal conditions of film development can be answered with a 'yes', and in fact even more so: there comes a point where density drops as exposure increases. This is exploited in direct positive materials, it's the basis of solarization (not to be confused with Sabattier effect) and it's also visible in HD curves if they extend sufficiently (which in datasheets they commonly don't).

Ah, okay, I see. I was talking about something else: is there a threshold where more "photon hits" can be recorded, yet development at that point would cause Dmax to be reached? I didn't mean to suggest any on/off behavior myself.

I'm going to markup the HD plot @Mr Bill shared, as an example:

The exposure I marked in red aligns with a point where the density doesn't go any higher with more exposure. Gamma is 0. However, consider the latent image in that case of increasing exposure after the red line, where the blue arrow begins and points towards. What is the state of the reduction of silver in that case? Does it stay linear? Does it begin to level off due to the "masking effects" you referred to before?

Also, is solarization a result of the action of the developer? Or does that reversal effect actually exist in the latent image? Do the stable silver reductions become unstable in that case?

I've been using "sensitivity speck" and "silver reduction" kind of interchangeably and I'm not sure which one is better.

The question is: when do we actually need to record such a large dynamic range that ordinary images end up as just a thin layer of gray? In practical, the maximum dynamic range of display media like photo paper, slides, or LCD screens is limited. Even if we had a perfect display medium, the dynamic range of our eye still has its limits. Otherwise, we will use photometers like Moser’s when scanning photographs.

Aren't the photometers you're saying we'd use actually drum scanners with their ultra sensitive photomultiplier tubes?

Yes, the practicality is more limited, but sometimes less-practical things have fun use-cases. In this case, it's merely headroom, and I wanted to know what's possible.

It's a big difference, if you aim for Dmax = 5.5 in a high contrast medium like print film or slide film with gammas around 2, or whether you try to get that density range on negative film with target gamma of 0.7. Think about the input contrast range, and how you would get this kind of dynamic range through a lens! What you could get would be a negative with D between 3 and 5.5, which would be exceedingly painful to print.

I am only suggesting trying to hit a higher Dmax, not raise Dmin either in tandem or in isolation. If a B&W slide has a range from Dmin=0.1 to Dmax=3.5, is there a way to instead produce Dmin=0.1 to Dmax=5.5 instead?

One more thought about high densities: if you look at a developed emulsion with D=2: this would look like a random pattern with 1% of the area translucent and the remaining 99% opaque. The imagine an area with D=0.3 with 50% translucent and 50% opaque. Compare the potential resolution of these two. With D=2 you'd lose a factor 10 in linear resolution, and with D=4 you'd lose a factor 100. Even fine grained ISO 100 film would look awful. BTW this is not just a silly theory: I have some 6x7 negatives developed in some experimental soup, and these negs have Dmin around 2. These negs appear grainy as hell and even 18x24cm enlargements are unusable. I'd hate to imagine the same material (Tri-X) at D=4.

I wouldn't want that, I'm not suggesting raising Dmin at all.

As silver halide start development, initially the latent image specks develop spherically. These tiny specks are hard to develop, so they develop slow enough such that silver can deposit uniformly. As the speck increases in size, development picks up speed and at some point filaments start to appear. When that happens depends on development speed. These spheres have lower covering powder than filaments, i.e. the former need more silver to achieve a certain density than the latter. Strongly exposed specks will develop filaments earlier than weakly exposed ones, so at a gamma of 0.7 you can expect the darker parts of your film to be filaments. If the weaker exposed parts remain spherical, they will have extra low density, i.e. you'll get speed loss.

So filaments are associated with development towards higher densities, right? The base fog area might be composed of few spherical grains, but as the density gets higher, more silver filament has been formed at that point?

Do they form in filaments because it's akin to growing crystals?

The easiest way to explore higher densities is starting with a developer you know and add KSCN in 1 g/l increments. As you add more, you will get higher contrast but also base fog. As mentioned before, I doubt you can get a dynamic range of 1:10000 through your lens, but you at least have a way to look at a very dense negative and then decide what to do with this type of image.

Slide film arguably doesn't produce the scene as it came through your lens, though! And would that addition also raise the base fog that profoundly? Like a flat addition of density across the whole range??

Is there no way to merely cause a multiplicative effect? Where Dmin might raise slightly but Dmax is drastically affected?

 

[Bill Burk]

It turns around and goes the other way after a while, then it turns around again, and this cycle repeats.

This is a graph showing theoretical solarization curve from Todd-Zakia, Photographic Sensitometry.

 

[Crysist]

It turns around and goes the other way after a while, then it turns around again, and this cycle repeats.

This is a graph showing theoretical solarization curve from Todd-Zakia, Photographic Sensitometry.

I've been trying to keep the two very separate. I know about the solarization effect producing these densities per exposure in the developed image. But does that change with developer? What is the underlying state of the latent image?

 

[Bill Burk]

The regions of reversal and re-reversal happen to the latent image. If you use such a bright flash that puts the portrait exposure in region of reversal (5 in the Todd-Zakia graph) and develop normally, the result will be a positive image.

 

[koraks]

I know about the solarization effect producing these densities per exposure in the developed image.

You're confusing Sabattier effect with solarization. I also indicated this back in #11.

 

[Bill Burk]

You're confusing Sabattier effect with solarization. I also indicated this back in #11.

Although I think Crysist might be inquiring about the physical atomic/electronic state of the latent image.

In the case of the Sabattier effect, you’re interrupting development and adding a fog exposure then developing further. The silvery shimmering effect comes about because some of the developed silver blocks the new fogging exposure so the result is uneven.

Also a reversal process, where you develop, bleach, fog and redevelop. Works with the remaining silver halogen after the original exposed and developed latent image is revealed.

In the case of true solarization you and I are talking about, the reversal and re-reversal occurs in the latent image. I think electrons are knocked out and regained

 

[Lachlan Young]

I am only suggesting trying to hit a higher Dmax, not raise Dmin either in tandem or in isolation. If a B&W slide has a range from Dmin=0.1 to Dmax=3.5, is there a way to instead produce Dmin=0.1 to Dmax=5.5 instead?

Yes there is, but it's visually pointless. The viewer cannot usefully see more than the Dmax 3.5 transparency delivers.

And that is the central fault with your reasoning - you have not considered that all the hypotheses you've been throwing around have been very thoroughly tested over the last century or so by the major research labs and that the products they produced had a tight feedback loop to visual double-blind reference tests. You might not like the outcomes, but they have a far more solid basis in science than those who have acquired a densitometer and ***********

Moderator's note: edited for civility.

 

[Crysist]

The regions of reversal and re-reversal happen to the latent image. If you use such a bright flash that puts the portrait exposure in region of reversal (5 in the Todd-Zakia graph) and develop normally, the result will be a positive image.

You're confusing Sabattier effect with solarization. I also indicated this back in #11.

I possibly am. I just can't seem to make heads or tails of whether the effect is on the latent image or only the developed image.

Although I think Crysist might be inquiring about the physical atomic/electronic state of the latent image.

That's what I've been trying to convey. I think I might be tripping over my words a lot in this thread

In the case of the Sabattier effect, you’re interrupting development and adding a fog exposure then developing further. The silvery shimmering effect comes about because some of the developed silver blocks the new fogging exposure so the result is uneven.

Also a reversal process, where you develop, bleach, fog and redevelop. Works with the remaining silver halogen after the original exposed and developed latent image is revealed.

In the case of true solarization you and I are talking about, the reversal and re-reversal occurs in the latent image. I think electrons are knocked out and regained

Right, I've definitely been referring to solarization. Where higher exposures can produce lower density than lower exposures. Like the effect on nuclear test films where the fireball may look dark for a moment at the brightest point.

I wasn't familiar with the Sabattier effect so I'm not referencing anything it's doing with my question.

Yes there is, but it's visually pointless. The viewer cannot usefully see more than the Dmax 3.5 transparency delivers.

And that is the central fault with your reasoning - you have not considered that all the hypotheses you've been throwing around have been very thoroughly tested over the last century or so by the major research labs and that the products they produced had a tight feedback loop to visual double-blind reference tests. You might not like the outcomes, but they have a far more solid basis in science than those who have acquired a densitometer and ***********

Moderator's note: edited for civility.

um okay. is this meant to be more productive than sharing any of it. I'm not trying to be combative in any sort of way in this thread, I just like density in neg/pos films and wanted to know about how their latent images relate to it in more depth. Whether it had looser constraints, etc.

Anyway, densities above 3.5 did seem important for Kodak when creating the Premier line of print stocks. And whether you can see it depends on the light shone through it.

 

[Lachlan Young]

Anyway, densities above 3.5 did seem important for Kodak when creating the Premier line of print stocks. And whether you can see it depends on the light shone through it.

Because it's a neg/pos system with more latitude.