Understanding development curves?

[OMU]

Hi

I need a little help understanding development curves. I’m looking at a curve from Foma and fomapan 100.

http://www.fomafoto.no/div/teknisk/film/F_pan_100_en.pdf

The data sheet has a curve that shows development times, ISO values and some other information: D min/S/Ḡ

I'm shure anyone can help

 

[sandermarijn]

The graphs show that the film captures more info (higher ISO or sensitivity, S) with increasing development time, at the expense of an increase in averaged contrast (gamma, G).

For the top graph (Sensitivity) use the vertical scale on the left, for the Gamma graph use the scale to the right.

Base fog (D min) is apparently independent of development time (or almost).

 

[AgX]

These curves show that:

-) with prolonged development time speed rises, up to a certain point

-) with prolonged development time the gradation (the overall contrast) rises

-) from some point in developing time D-min rises, which means more of actually unexposed film will be slightly developed


They are aimed at finding an optimum development time for a special use aside from that given for the speed established by standardized procedure.

 

[OMU]

Hi agian and thanks.

Then I understand S and Dmin.
S = sensitivity.
Dmin = minimum denseti

But what about G?

G = Overall contrast. (E.i. 0,6)
That must be a different number than what I get when I messer my negatives with a densitometer?

OM

 

[AgX]

Well, I was technically not correct when I said "gradation (overall contrast)". I just wanted to keep things simple...

Gradation is the Steepness of the linear part of the Characteristic Curve (D/logE).

Contrast what you measure with your densitometer is log Dhigh/log Dlow.

So, of course you get different numbers. But, the greater the Gradation you yield in your processing, the higher the the contrast will be when you you take measurents between the same two areas within your negative.

 

[OMU]

Thanks a lot, I know the mathematical term steepness.
Now the graphs make sens.
Thanks again

 

[ic-racer]

The minimal useful gradient (as in the "0.3 x G" speed determination) is likely the same for all those differnet development times. They have not zeroed the curves to the film base, either. So if you are using the 0.1 ISO speed determination, you have to subtract the film base density to make a comment about speed.

Best and easiest to think of film speed and development as independent.