Zone System - A Photography term, used to describe a method of exposing film in such a way as to get the desired expsure that catches all details that the photographer wants.

Quick description: An image (or view) is broken up into lighting zones, which span from black to white. The photographer will set the exposure to ensure that both dark gray and near-white are both captured on the film. If the exposure is not set properly, (under) then dark-gray would show up as black, or (over) then near-white would show up as white. All detail in these areas will be lost, and can not be reproduced on the final print.

Overexposing or underexposing can be used to increase or decrease the number of 'zones' available, and essentially decreases or increases the contrast of the image.

Printing can be adjusted to get the desired effect from properly exposed film by varying exposure time and paper type (high-contrast or low-contrast).

Ansel Adams is one of the best examples of a photographer who used the zone-system to set his exposures. He used his creativity and imagination to create an image in his mind. He would then use the 'zone system' method to achieve that image on film and print. He as a Genius in this respect!

The other factor involved in the zone system is development: by over- or under-developing the film, the contrast is changed, which again influences the final gamut of the image.

Notice, though, that this is practical only with large format, where film comes in sheets that you can individually develop. A spot meter is also handy.

Ansel Adams actually invented the Zone System: he always stressed the importance of previsualization for the photographer.
The Zone System (and Adams' photography) is about absolute image control. You are master of what ends up on paper.

It also worth observing that the Zone System in all its might only really works for Black and White, where you can pretty much play around with development times and fluids.
In color, you have much less freedom with the negative: you can still modify things when printing, though.

Taken from The Maine Photographic WorkBook:

The Zone System
A short list of the zones with some physical equivilants for each.
(IMR = Indicated Meter Reading)

The pure white of the paper base.
Snow, clouds, specular highlights, any whites without detail.
(4 stops more than the IMR)

The last zone with remnants of texture.
Direct sunlight on white clothing will render some detail.
(3 stops more than the IMR)

Bright textured detail.
Average snow, light sand, white clothing, deatail on the clapboard of a white house.
(2 stops more than the IMR)

Caucasian skin in open sunlight. Skin in portraits made entirely in the shade or overcast light.
(1 stop more than the IMR)

This is middle gray - 18% reflectance.
Average weathered wood, green grass, gray stone orpavement. Panchromatic rendering of the clearnorth sky.

Medium dark tone, average dark foliage, open shadows. Recommended value for portraits in open sunlight. Brown hair], new blue jeans.
(1 stop less than the IMR)

Darkest shadow area with full detail. Dark clothes, black hair, shadows under cars, etc.
(2 stops less than the IMR)

The first discernable tone above total black, and is the darkest part of a picture where a sense of space is required.
(3 stops less than the IMR)

The blackest black a print can be made to yield.
Doorways, or the enterance into a tunnel; windows opening into unlit rooms.
(4 stops less than the IMR)

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