Compansating speed loss by dev time?

I read that some developers reach to 1-2f speed loss (e.g. sease no.3).
Does that mean I have to expose the film by the half of the box speed (e.g. box speed is ISO 100 -> expose for ISO 50).
But what about streching the dev time instead. When the development takes longer the density should become stronger (until some point).
I mean I could expose with box speed (for instance Stouffer's wedge) and measure the dev time untile I get the desired gamma.

olk said:

Does that mean I have to expose the film by the half of the box speed (e.g. box speed is ISO 100 -> expose for ISO 50).

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Yes.
Although a 2-stop speed loss in a developer is kind of rare. Up to 1 stop is more likely in some developers.

olk said:

But what about streching the dev time instead.

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Longer development generally doesn't recoup shadow detail that wasn't recorded in the first place. In this particular case of developer activity, you may regain a little, but you'd have to experiment how much exactly. And you'd have to live with the much higher contrast in the negatives, which may become problematic especially in high-contrast scenes.

olk said:

I mean I could expose with box speed (for instance Stouffer's wedge) and measure the dev time untile I get the desired gamma.

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I think you're confusing gamma with shadow detail. The notion of developers with speed loss is that they record less shadow detail at a normal gamma. Developing longer to recoup some of that shadow detail loss would result in a higher gamma. So unless your desired gamma is very high, aiming for the desired gamma isn't going to help you in terms of shadow detail.

It's also worth adding that increasing development may well negate the desired effects of using an Ultra Fine Grain developer, and also lose sharpness.

Ian

If shot at box speed, shadow detail was actually recorded, but in the case of developers that cause a speed loss, that information was lost to solvency.

Extending development time will only increase contrast.

To reduce or eliminate speed loss, try diluting the developer and extending dev time.

Use XTOL and the speed will be greater than box speed. That way you can quit worrying about loss of film speed.

Developers either lose speed by not having any (or very little) solvency and therefore not being able to expose latent image centers that are not on the surface of the grain, or by being very solvent and dissolving latent image centers on the outside of the grain. There is a happy medium in there where you get to develop some of the non surface image centers and substantially all of the surface image centers. That’s roughly box speed. Clever developers that get the balance just right can beat box speed by a little bit.

But, you can see how in the case of a very solvent developer, developing longer will just dissolve more and more and won’t improve speed—it could make it worse. In a non-solvent developer, going past the correct dev time will not do much good—there is nothing more that will be accessible to develop.

In both cases there is a limit to where you can push the film through development without making things worse and/or raising fog substantially.

Sease #3 loses speed, because the developer inhibits itself. This leads to serious underdevelopment and results in loss of a few stops of speed. Because of this mechanism I do not expect much improvement from longer development.

PS: don't try to trade speed for grain. An ISO 400 film developed in Sease #3 will be still coarser grained than a similar ISO 100 film in a speed preserving developer, and it will be easier to print from a normally developed negative. Sease #3 was popular 100 years ago, when no such thing existed as fine grained film. It quickly lost appeal, after finer grained film hit the markets.

I did leave out that whole category of issues with developer formulas that don’t work well: not enough dev agent, byproducts that inhibit development too much, too much restrainer, etc.

olk said:

I read that some developers reach to 1-2f speed loss (e.g. sease no.3).

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If you have experience using a Stouffer scale exposure to check contrast when you develop, you could simply do two tests to find the speed gain/loss of an experimental developer. Compare two curves to see how much they shift left or right from each other (e.g., Make the same Stouffer scale exposure on two pieces of the same film, develop one in D-76 and one in Sease #3). Share the 42 densitometer readings here and we could interpret together how Sease #3 affects film speed.