Scientific reason why some developers causes decrease film speed

[Fatih]

Hi all,
I have had the source which explains this scientifically but for some reason, I cannot find it anymore.
What is the scientific or chemical reason why some developers causes effective film speed reduction, effective film speed increase or full film speed. For some reason, the shadows don’t develop fully, and why would that happen?

Is it just because short development times causes speed reduction and long development times causes speed increase as shadows don’t have enough time to fully develop and the opposite for the latter one?

I can also understand some ultra fine grain developers causes effective film speed loss, ie loss of details as they eat away little remaining silvers in the shadow areas but like Rodinal which is said to cause film speed reduction but a course grain developer, why does it cause effective film speed loss.

Cheers,
Fatih

[Robert Bowring]

Developers do not increase or decrease film speeds.

[Peter De Smidt]

Sure they do. When developed to the same contrast, Microdol-X and Xtol, for example, give different film speeds, i.e. Zone 1 at least .1 above film base plus fog.

[paulbarden]

Developers do not increase or decrease film speeds.

Look up FX-37. It was formulated specifically to achieve an increase in film speed, and it does so, by at least 1/2 stop with most films.

[Bruce Watson]

What is the scientific or chemical reason why some developers causes effective film speed reduction, effective film speed increase or full film speed. For some reason, the shadows don’t develop fully, and why would that happen?

It would take a book to explain it. Fortunately, that book has been written. It's called The Film Developing Cookbook by Anchell and Troop.

[Bernice Loui]

The entire process of B&W image making cannot be separated. Yes, developers (reduction process) do bend effective film speed. But it interacts with the print making process. Negatives used for traditional B&W prints (silver gelatin) might not do well for alternative printing process like carbon printing.

Essentially, film _ film processing _ print making are all interactive and should NEVER be separated from the goal of the print image.

Recommended to read pages 21 to 40 in this book
http://www.processreversal.org/publi...developing.pdf

which explains the development process, how film reacts to the development process and how each component of the developer alters the development process (in the next chapter in this book).

There have been renewed interest in developer agents like Pyrogallic acid and others like XTOL and ... they ALL remain part of the print making process which MUST work together as a complete system from film exposure in camera to the finished print.

Key is figuring out what photographic materials work for your print making goals, learn and know them well, then apply what has been learned and practiced to fit your expressive print making needs. Experiment and tinker yes, but at some point this needs to stop once sufficient mastery of these materials and process has been achieved which brings forth the goal and objectives of expressive image making.


Bernice

[SergeyT]

Developers do not increase or decrease film speeds.

+1
It is a property of the emulsion

[reddesert]

Let's set aside the question of whether film speed (as in ISO) can actually be changed, and talk about shadow detail instead. Ask the question of why some developers might result in more or less shadow detail with normal development.

It's not just longer developing times - generally you can develop longer than a recommended time but you'll mostly increase contrast without improving the shadows much.

The action of film development is to convert exposed, latent silver halide crystals into metallic silver. During this process, adjacent halides become clumped and developed together. That is, the individual halide crystals are much smaller than what we see as "grains" in the developed film. I believe that a large part of the activity of developers is how they extend development from one latent crystal through its neighbors.

Some developers have a more aggressive solvent effect on the crystals, here I quote from "The Darkroom Cookbook" by Steve Anchell: "All films have a grain structure predetermined by the manufacturing process. ... Fine-grain developers tend to inhibit acutance (sharpness). This is because they effectively etch each grain particle into individual 'islands.' These islands do not connect with one another, as do less fine grains that are clumped together. The result is that visible lines in the image that should appear continuous are broken into small segments as they jump from grain to grain."

Here he's talking about the effect on acutance, not speed/shadow detail, but you can begin to see how the solvent action on particles will trade off between acutance, shadow detail, and the appearance of graininess. A developer like Rodinal preserves acutance by enhancing edge effects, I believe.

[Drew Wiley]

Changing the characteristic curve of any particular film often DOES in effect change its real-world film speed. Launching off the toe quicker, for example, means that you need less exposure to get the same shadow gradation or printable threshold density, and therefore obtain a faster film speed. "Expose for the shadows, develop for the highlights." The devil is in the details, and that's why there are all kinds of books and websites dedicated to that. There's no simple generic equation. Lots of variables involved. So it's NOT JUST a property of the emulsion. How a cake tastes is not due just to what ingredients come the cake mix box and gets poured in a pan, but about how you specifically bake and frost it too.

Anyone who has densitometer plotted a substantial "family of curves" for a particular film knows how the effective threshold take-off of that film can in numerous instances be affected by not only the degree of development, but by the type of developer too. Likewise, controlling things at the top end via staining developers, for example, inherently alters what is needed further down or not.

[Michael R]

Fatih,

Unfortunately there is no single answer. The type of film emulsion is a very important variable, of course. When it comes to how a developer behaves with a specific film, there are a variety of mechanisms at work which can effect the shape of the film’s characteristic curve and therefore potentially effect “emulsion speed” (choose a definition first) to some degree.

However when it comes to properly formulated general purpose developers, differences in emulsion speed are small. In many cases they are negligible. The things you typically read about differences in speed like half a stop (or more) are almost always highly exaggerated, especially when speed is said to be increased. There are a few special cases where you lose maybe up to half a stop, but beyond that it is largely a non-issue.