Film development speed.....

CMoore · Feb 15, 2019

I have read and heard conflicting opinions.
Assuming we use some kind of Zone System analogy.....Zone-0 through Zone-9
Not sure if i can really explain my question in text, but here it goes.
Generally speaking, with black and white film...something like FP4 or HP5...do the lower zones (initially) develop at the same time as the higher zones. ....... developing at the same time, until the lower zones are "fully" developed, and the higher zones keep going to their fullest.?
Or...Do the lower zones keep developing also, but just at a slower rate.?
Thank You

Photo Engineer · Feb 15, 2019

The emulsion grains develop at different speeds. Fine grains develop more rapidly than coarse grains and the coarse grains are fastest in speed. It is complicated if the film has one emulsion or a blend of several.

PE

CMoore · Feb 15, 2019

Photo Engineer said:
The emulsion grains develop at different speeds. Fine grains develop more rapidly than coarse grains and the coarse grains are fastest in speed. It is complicated if the film has one emulsion or a blend of several.

PE

Great...Thank You

And....... Ian C sent me an excellent reference that explains it quite well.
Thank You also Ian.

Black & White Photography
3rd Edition, Revised
Henry Horenstein
Page 153

Exposure and Development

Although this chapter is about film development, don’t underestimate the importance of film exposure in producing a good negative. Both exposure and developing time are critical in determining the overall density of your negative. The density of the shadow areas of your negative is primarily determined by film exposure, and the density of the highlight areas is determined primarily by development. Thus, this commonly stated rule of thumb:

Expose for the shadows; develop for the highlights.

Here’s how it works. In your subject, the shadows are the darkest areas. This means they reflect the least amount of light back to the camera. If you give film too little exposure, the developed shadows will not render with enough density to render good, textured detail. Changing development cannot change subject detail were there are none on the film; It can only modify the contrast of existing detail. So, to produce a negative with good shadow density, you must give the film adequate exposure.

Film develops in proportion to exposure, which means that the development time does not have a significant impact on the shadow areas. Shadow areas are the areas that received the least exposure; they do not take much time to form on the negative. For instance, if the normal developing time for a roll of film is 10 minutes, then the shadow density fully forms in about half that time—possibly 5 minutes. The remaining 5 minutes mostly affect the highlight areas.

The highlight areas are the lightest areas of your subject, which are the areas that reflect the most light back to the film. This means that they have far more exposed silver particles needing development than shadow areas. Thus, the longer you develop your film, the greater the highlight densely in the developed negative. If you develop your film for 15 minutes rather than 10, the highlights get significantly denser, but the shadows do not. As the difference between the shadow and highlight density becomes greater, so does the negative contrast, meaning that increasing film development time increases negative contrast.

The opposite happens when you reduce the negative time from 10 minutes to, say, 8 minutes. The highlight areas render with less density and the shadow density stays about the same. This minimizes the differences between the shadows and highlights, resulting in less negative contrast.

Photo Engineer · Feb 15, 2019

The above is grossly oversimplified and verges on being a bit incorrect. You see, developer exhaustion contributes to this as you vary process time and look at low and high densities. The fine grains develop very rapidly but are less exposed and so they come up first in the Dmax area or area of highest exposure. But then Iodide content is highest in the high speed emulsions and this influences development time as well by crossing grain types and within grain types.

Different developers act differently as shown by Haist and others. You can get filaments, tablets and mixtures of other types of silver and this type of developed silver causes variations in both density and image tone.

As I said, a very complex subject. I could probably teach a course on this. The real expert on a lot of this passed away recently. He helped teach me when I took EK courses.

PE

CMoore · Feb 15, 2019

I understand what you are saying.
I did not mean to do disservice to the author.
Other text made it clear this was not a definitive statement, it was designed as a beginning introduction for students who are just starting their education as Photographers.
Again, as a painter, i understand your points about the different behaviors of different chemicals. Temperature, age. dilution, etc etc.
I appreciate your expertise.

Photo Engineer · Feb 15, 2019

Thanks. I understand. If you want more information please contact me directly here.

PE

John51 · Feb 16, 2019

CMoore said:
Generally speaking, with black and white film...something like FP4 or HP5...do the lower zones (initially) develop at the same time as the higher zones. ....... developing at the same time, until the lower zones are "fully" developed, and the higher zones keep going to their fullest.?
Or...Do the lower zones keep developing also, but just at a slower rate.?
Thank You

My understanding is that the lowest zones develop to completion while the higher zones can go too far if overdeveloped.

Shadow detail has very little light hitting the film so there isn't much to develop. Once what little there is has been developed, a stronger developer and/or longer times will make very little difference as there is nothing left to develop.

Rudeofus · Feb 16, 2019

Weakly exposed grains hold tiny silver clusters of just a few atoms, whereas strongly exposed grains hold multiple larger silver clusters. Larger silver clusters have greater surface (i.e. can interact with more developer molecules at a given time), and require less energetic developer to grow (i.e. are more likely to react). There may not be much to develop in weakly exposed areas, but whatever is there takes a lot longer to develop than grains from strongly exposed areas.

An ideal developer would develop weakly exposed areas to completion, while at the same time developing only a tiny fraction of unexposed areas.

ic-racer · Feb 16, 2019

CMoore said:
...do the lower zones (initially) develop at the same time as the higher zones. .......

If the high and low zones developed at the same rate the film curve family would look like this.

Photo Engineer · Feb 16, 2019

This incorrect graph is indeed incorrect.

PE

ic-racer · Feb 16, 2019

I suspect everyone knows what a correct film curve family looks like. But, just in case...

Photo Engineer · Feb 16, 2019

Notice that the inflection point of each film remains constant. This is the true speed and cannot be exceeded. The only thing you can do is change contrast.

PE

MattKing · Feb 17, 2019

ic-racer said:
I suspect everyone knows what a correct film curve family looks like. But, just in case...

This would make excellent wallpaper - for the darkroom!

Rudeofus · Feb 17, 2019

Photo Engineer said:
Notice that the inflection point of each film remains constant. This is the true speed and cannot be exceeded. The only thing you can do is change contrast.

In practical printing there is a minimum viable contrast needed to get a usable image, and this starting point of minimal viable contrast moves to the left as you push develop. This inflection point may be a theoretical limit, but the practical limit is quite a bit further to the right with normal development.

ic-racer · Feb 17, 2019

Jones published that the minimum contrast for an excellent print was a dependent on the overall contrast. So, yes the separation of values in the toe is greater with extended development, the overall contrast is greater, so the ratio of overall contrasts to minimum useful gradient moves back to the right. The nice thing about photography, is that when processing one's own film and paper, one can decide for themselves what an excellent print looks like.

Photo Engineer · Feb 17, 2019

Rudeofus said:
In practical printing there is a minimum viable contrast needed to get a usable image, and this starting point of minimal viable contrast moves to the left as you push develop. This inflection point may be a theoretical limit, but the practical limit is quite a bit further to the right with normal development.

If the toe is made sharper without a big change in contrast or better still, none, then the effective speed is dramatically increased.

PE

Photo Engineer · Feb 17, 2019

ic-racer said:
Jones published that the minimum contrast for an excellent print was a dependent on the overall contrast. So, yes the separation of values in the toe is greater with extended development, the overall contrast is greater, so the ratio of overall contrasts to minimum useful gradient moves back to the right. The nice thing about photography, is that when processing one's own film and paper, one can decide for themselves what an excellent print looks like.

Graphs showing "first acceptable print" and other descriptors are published here and can be found in Haist and in Mees. Mees' data goes back nearly 80 years.

PE

Trask · Feb 17, 2019

ic-racer said:
So, yes the separation of values in the toe is greater with extended development, the overall contrast is greater, so the ratio of overall contrasts to minimum useful gradient moves back to the right.

Does this analysis thereby argue that, all things being equal, it is preferable to have an extended development regime, perhaps by using a more dilute developer? Perhaps with increasing agitation to increase development in the highlights further up the curve?

removed account4 · Feb 17, 2019

CMoore said:
Great...Thank You

And....... Ian C sent me an excellent reference that explains it quite well.
Thank You also Ian.

Black & White Photography
3rd Edition, Revised
Henry Horenstein
Page 153

Exposure and Development

Although this chapter is about film development, don’t underestimate the importance of film exposure in producing a good negative. Both exposure and developing time are critical in determining the overall density of your negative. The density of the shadow areas of your negative is primarily determined by film exposure, and the density of the highlight areas is determined primarily by development. Thus, this commonly stated rule of thumb:

Expose for the shadows; develop for the highlights.

Here’s how it works. In your subject, the shadows are the darkest areas. This means they reflect the least amount of light back to the camera. If you give film too little exposure, the developed shadows will not render with enough density to render good, textured detail. Changing development cannot change subject detail were there are none on the film; It can only modify the contrast of existing detail. So, to produce a negative with good shadow density, you must give the film adequate exposure.

Film develops in proportion to exposure, which means that the development time does not have a significant impact on the shadow areas. Shadow areas are the areas that received the least exposure; they do not take much time to form on the negative. For instance, if the normal developing time for a roll of film is 10 minutes, then the shadow density fully forms in about half that time—possibly 5 minutes. The remaining 5 minutes mostly affect the highlight areas.

The highlight areas are the lightest areas of your subject, which are the areas that reflect the most light back to the film. This means that they have far more exposed silver particles needing development than shadow areas. Thus, the longer you develop your film, the greater the highlight densely in the developed negative. If you develop your film for 15 minutes rather than 10, the highlights get significantly denser, but the shadows do not. As the difference between the shadow and highlight density becomes greater, so does the negative contrast, meaning that increasing film development time increases negative contrast.

The opposite happens when you reduce the negative time from 10 minutes to, say, 8 minutes. The highlight areas render with less density and the shadow density stays about the same. This minimizes the differences between the shadows and highlights, resulting in less negative contrast.

Henry Horenstein is a great teacher and his book is an invaluable resource !
He has an appendix in the back of the back of the book that SHOWS common development &c errors and explains why they happen and how to make photographs so they don't happen. Often times his book is THE reference book that teachers have their students buy in Photo 1 classes. He studied under Harry Calahan and has been a teacher at RISD for years. https://horenstein.com

Rudeofus · Feb 17, 2019

Photo Engineer said:
If the toe is made sharper without a big change in contrast or better still, none, then the effective speed is dramatically increased.

ic-racer has posted a table of H&D curves for modern films with modern developers, and not a single combination offers what I would consider a sharp toe. If this is the best which film industry could come up with, then I would expect even rounder toes with Tri-X, HP5+ or Fomapan 400. We shall not be surprised that Tri-X and HP5+ are all time favorites with folks who like push development.

Don't get me wrong: of course you won't turn Tri-X into an ISO 3200 emulsion with forced development, but my impression is that at least a stop of extra usable shadow detail is possible.

Photo Engineer · Feb 17, 2019

But that is part of the problem. One must design a different developer (none known presently), or change the emulsions toe. The latter has been and is being done by means of a tighter size frequency distribution of the grains making them form a sharper curve, and adding addenda to sharpen the toe.

PE

Rudeofus · Feb 17, 2019

Photo Engineer said:
But that is part of the problem. One must design a different developer (none known presently), or change the emulsions toe. The latter has been and is being done by means of a tighter size frequency distribution of the grains making them form a sharper curve, and adding addenda to sharpen the toe.

In the toe region we're talking about a few photons hitting the grain - or not. The toe region shown is not the region, where every grain will get the same 2, 3 or 4 photons, it's the area where only few grains will be rendered developable at all. This region is governed by Poisson distribution, and contrast is low. If you increase toe contrast through emulsion changes (as suggested by you here), you increase "amplifier gain" and will get higher grain, and I am not even sure you can bring up the low contrast all the way.

What we are seeing in ic-racer's charts is state of the art, and in a time in which we already cheer when yesteryear's emulsions are brought back into the market, I would not expect much sharper toes in the foreseeable future.

Photo Engineer · Feb 17, 2019

Rudi, this is a very fine point of film design and the result can be had with no substantial gain in grain. If it were not possible, then we would have awful grain today, but many modern films take advantage of this design feature and are used today. I have seen films with very high speeds and no significant sacrifice in grain or sharpness.

PE

Rudeofus · Feb 17, 2019

Photo Engineer said:
Rudi, this is a very fine point of film design and the result can be had with no substantial gain in grain. If it were not possible, then we would have awful grain today, but many modern films take advantage of this design feature and are used today. I have seen films with very high speeds and no significant sacrifice in grain or sharpness.

Yes to all that, but evidently they got there with round toes. There is a good chance, though, that these toes we see today are already very sharp compared to yesteryear's film toes ....

Photo Engineer · Feb 17, 2019

Try comparing today's curves with those of yesteryear.

PE

Film development speed.....

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