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Zone System - part 3/3
Slow, medium or fast?
If using a slow ISO 50 film the additional films should be exposed at ISOs 64, 40, 32 and 25. For medium speed ISO 125 films try extra ones at 160, 100, 80 and 64. Finally for fast ISO 400 films make extra tests at 500, 320, 250 and 200.
Canyon de Chelly
Art Print
Adams, Ansel
30 in. x 24 in.
Buy at AllPosters.com
Framed
Probably once you have established that your equipment or processing procedure has variables in a certain direction you should be able to estimate which ISO to aim for immediately and only have to perhaps expose one additional film in that speed group.
9. Process and dry the test film as normal. If you have several films of the same type process them together to eliminate any further variables.
10. Then examine the negatives against a well lit white surface... but not directly against a light source.
Visual Inspection
The first exposed frame should be the Zone V mid-tone and the next a Zone 0 clear negative having the same density as the film's edge rebate. Note that the slight difference in film's FB+f levels is caused by different base thickness, anti-halation coatings, age, heat, X-rays and so on.
The third frame on the negative test strip is the important one. This represents a Zone I negative where exposure is first visibly recorded on the film. This third frame should have a perceptible tone just denser than Zone 0, the FB+f frame. Confusion happens here because it may appear on all of the under-rated test films... what you have to decide on is which film has the "just perceptible" difference in tone between Zone 0 and Zone I. That film then becomes the film on which you should base all your speed ratings in future... the film's ISO becoming your EI (exposure index) because you have altered the information that programs your exposure meter.
Having arrived at your EI for that particular film type you should always use it... until you change your camera system! Then the test has to be done all over again to sort out the potentially new variables. Remember that a film's ISO rating is calculated by the manufacturer under perfect lab conditions... the films are not exposed in cameras and they are processed in non-commercially available chemicals. Your own equipment and testing procedure is necessary to set a "norm".
From now on by using your EI instead of the manufacturer's ISO rating your negatives should have a fuller range of tones (at least in the shadow areas) for printing. Tones in the negative's highlight areas depend more on the film's development.
Remember that old adage concerning black-and-white photography... Expose for the shadows, develop for the highlights. Your EI will prove this because you can only produce good shadow tones in the print by exposing for them on the negative. If further proof of this is needed, grossly over or under-developed films will not show any substantial difference in the Zone I and Zone II shadow density tones on the test frames.
...page 1 / page 2...
...and click to read part 4 of the Zone System
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