Reciprocity - how far?

[xkaes]

Darn!!! This entire discussion has convinced me to give up on trying some pinhole shots by moonlight.

[Vaughn]

I have used Kodak Copy Film (4125) in-camera for landscapes. Its reciprocity curve shows less than a stop loss at 100 seconds...extending the curve looks to be about a full stop loss at around 10 to 15 minutes. My last exposure with it was 20 seconds with no adjustment for RF. Like Doremus mentioned...it is a great way to help expand contrast.

https://www.largeformatphotography.i...9&d=1536954345

[Kiwi7475]

Grant Haist in his book (vol 1) explains that

“during the early stages of growth the latent image consists of a few silver atoms. Thermal energy may eject an electron from one of these silver atoms or an electron from a silver atom may be removed by a bromide atom liberated during exposure. A bromide ion may be formed by the union of the bromide atom and the electron thus negating the effect of the photons of the exposed light. The electron may be captured in some other way as well. The silver ion formed by the loss of the electron may wander away from the latent image site. Unless the latent image is built up faster than the silver ions are lost, it will be destroyed and the effect of the exposing light will be lost.
With low intensity exposures the efficiency of latent image formation is lowered. Because of the slow release of electrons by the relatively scarce incident photons of light the latent image can build up only very slowly. During this initial stage of formation the latent image is relatively unstable and may be dissipated by thermal disintegration or chemically induced action.
(….)
With low intensity exposure there are simply not enough electrons available to form stable latent image specks or to form stable and developable latent images. The size of the silver halide plays a part because finely divided silver halide crystals with their limited cross-section area to intercept the exposing light would capture only a few photons. “

And to my previous question on the diversity of observed reciprocities failures across different film he answers

“Emulsion makers control reciprocity failure during emulsion making or by after treatments such as baking or treatment with hydrogen”.

[Bruce Watson]

Grant Haist in his book (vol 1) explains that

“during the early stages of growth the latent image consists of a few silver atoms. Thermal energy may eject an electron from one of these silver atoms or an electron from a silver atom may be removed by a bromide atom liberated during exposure. A bromide ion may be formed by the union of the bromide atom and the electron thus negating the effect of the photons of the exposed light. The electron may be captured in some other way as well. The silver ion formed by the loss of the electron may wander away from the latent image site. Unless the latent image is built up faster than the silver ions are lost, it will be destroyed and the effect of the exposing light will be lost.
With low intensity exposures the efficiency of latent image formation is lowered. Because of the slow release of electrons by the relatively scarce incident photons of light the latent image can build up only very slowly. During this initial stage of formation the latent image is relatively unstable and may be dissipated by thermal disintegration or chemically induced action.
(….)
With low intensity exposure there are simply not enough electrons available to form stable latent image specks or to form stable and developable latent images. The size of the silver halide plays a part because finely divided silver halide crystals with their limited cross-section area to intercept the exposing light would capture only a few photons. “

And to my previous question on the diversity of observed reciprocities failures across different film he answers

“Emulsion makers control reciprocity failure during emulsion making or by after treatments such as baking or treatment with hydrogen”.

Nice find. I knew Haist must have studied it and written about it. Thanks for sharing it.