<p>When Adams and Fred Archer devised the Zone System back in the 1940’s , they made the Zone I the anchor; 0.1 above film-base plus fog. The other Zone densities “fall” based upon the amount of development the film receives. In the early versions of the Basic Photo Series there was a very good graph that plotted Zones and density based upon development. He showed how increased development would raise Zones IV through VII and how decreased development would compact Zone IV through VII. He based the development on Zone V being 0.9 density units for Normal development. For N+1, Zone IV would have a density of 0.9. For N-1, Zone VI would have a density of 0.9. NOTE: In the early series there were 9 Zones; later the Zone System was revised for 10 Zones.<br>
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In later versions of the Basic Photo Series the density value for Zone V was reduced, I suppose it had to do with the changes in film and paper and the amount of silver in the emulsions. Adams also suggested using either Zone V or Zone VIII for Zone testing and gave densities for the two Zones as a guide for Normal development. He also gave density suggestions for condenser or diffusion printing.<br>
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When I performed my Zone standardization, after finding the ISO for Zone I, I exposed my negatives for Zone V and Zone VIII; developed them together, fix, dry, and read the densities. I found the developing time that placed both Zone V and Zone VIII in the range Adams suggested for my diffusion enlarger. I then did the same for N+1. Exposed negatives for Zone IV and Zone VII, developed them together until the Zone IV exposed negative had the same density as my Normal Zone V, and the Zone VII exposed negative had the same density as my Normal Zone VIII. To find N-1 development I exposed negatives for Zone VI and Zone IX. Reduced the development until Zone VI = Zone V, and Zone IX = Zone VIII.</p>
