N+1 Explanation

Discussion in 'Black and White' started by jonpaul_hills, Oct 9, 2011.

  1. Hi everybody, I need something explained to me. I'm just learning about expansion and contraction of black and white film during processing for value control, and I am a little confused. I understand that N+1 is an expansion, and N-1 is a contraction, but I don't understand how long the +1 is. If you had a developing time of 10 minutes, is N+1 11 minutes? And N-1 9 minutes? I don't understand if the +1 and -1 are a set amount of time, or if it is a percentage of the original time. If anybody can help me understand, I would appreciate it.
    Thanks everybody.
  2. The times are based on the characteristics of the film and developer combination. The idea is that a +1 development will move a zone V exposure to Zone vi and a -1, will move zone v to zone iv. Each film and developer combination/dilution will have different characteristics and thus different times.
  3. Ansel Adams's book The Negative explains the process of determining these values very well.
  4. JohnPaul, If you use Tri-X and Adams' developer solutions (D-76 is still available--or Ilford ID-11), you should approximate his results. When you use other (usually more modern) films and developers, you need to calibrate the process. There is a good explanation of zone system calibration in the book: Way Beyond Monochrome.
  5. The best resource I know of is the DVD sold by Calument called, Black & White Photography. It has 3 videos by Fred Picker. The one on the negative is great. $40.00. It has a clear presentation of the film speed test, proper proof sheet, print speed test and talks about expansion and contraction. You will need to do those tests to properly use n + 1 and n-1 refinements. Basically, for scenes that lack contract you want to expand the negative to get good blacks and highlights. For scenes where the range of tones is too high to print all values from black to white with detail, you will want to compress the negative so that all of the values will fit the tonal scale of the photo paper you are using.

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