Quote Originally Posted by doughowk
Great explanation, Donald, for the increasing contrast that occurs with low-light/night photography. Andrew Sanderson in Night Photography says that the zone system becomes useless because can't properly read the light levels (lights become spectral while shadows become too dark to read) and contrast increases as exposures lengthen. How then are we to determine when to decrease development time & by how much?
In night photography, I would not apply the normal exposure and reduced development at all. For limited spectral light sources, I would first begin by using a catechol based developer such as Pyrocat (see Ansel Adams example in The Negative). Next I would tend to think in terms of expanding contrast at the development stage to afford all of the low value tonal separation that I could obtain. I would probably also downrate the film EI to move the exposure up onto the straightline portion of the H and D curve. I would plan on handling the excessive film contrast at the printing stage by preflashing the paper. Preflashing the paper compresses highvalues downward while maintaining low value tonal separation.

Insofar as night exposure calculations, one almost needs to test the film under actual conditions if the meter does not read the low light levels.