N+ and N-

[Ian-Barber]

When talking about N+ and N- how much longer does one need to keep the film in the developer for an increase or decrease of 1 stop

 

[Stephen Batey]

I gave my answer in another thread, but for anyone who comes directly here and misses it the summary is

As a starting point: to reduce contrast by one stop, try 85% of the developing time; to increase by one stop, add 20%.

 

[Alan9940]

Ian,

If you're really critical about your work, please keep in mind that film speed changes as you extend or reduce development time.

 

[Ian-Barber]

film speed changes as you extend or reduce development time.

Can it change by a significant amount

 

[Alan9940]

Can it change by a significant amount

Depends of what you'd call significant... Depending on the film and developer used, I've seen a stop or more loss of film speed for N- (essentially a pull development technique.) N+ development doesn't seem as sensitive in that I've seen, maybe, a 1/3 to 2/3 stop increase in film speed; not enough to worry about. To my mind, that's the beauty of MPD...no minus development where you'll have to worry about how much film speed you're actually losing, and no plus development because if the scene has a flatter overall SBR (subject brightness range) you'll be exposing as far up the straight line on the curve as possible. Think of it as ETTR (exposing to the right) with a digital camera. In the darkroom, you'd just increase the paper grade or on the desktop you'd just apply whatever technique you use to increase contrast to compensate for the flatter negative.