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Jose Edwards
Jose Edwards

The Practical Zone System: For Film And Digital...

The Practical Zone System: for Film and Digital Photography, 4th edition is an updated version of what has become the classic book on the technique developed by Ansel Adams in the 1940's. The zone system was designed to provide photographers with a precise and intuitive way to control the dynamic range of their negatives to produce printable results regardless of the contrast of the subjects they are shooting. What Chris Johnson has done in this edition is completely update his approach to teaching the zone system with film/developer testing data, illustrations and examples.

The Practical Zone System: For Film and Digital...


Incident meters were great for film photography but are inadequate for assessing adequate digital exposure as they cannot assess sensor saturation. They are also impractical in many situations as they require the meter to be close to the subject and facing the camera, they cannot meter for subjects which are themselves luminous, they are pretty hopeless in backlit situations and cannot be used with flash/fill flash.

Zone values III, V, and VII are the deciding zones. Zone V is middle grey and is used as an average reading for all light meters. If the subject you metered is brightest white or darkest black, it will appear middle grey on the film. We need to correct for this.

Before I get into the details, I just quickly want to touch on the fact that it's impossible to discuss zone focusing without also talking about reciprocity, or through how reciprocity is commonly explained "the exposure triangle". The exposure triangle is the diagrammatical way the reciprocal relationship of the three main settings of a camera: aperture, shutter and film speed work. This tutorial does assume prior knowledge of what these settings do, and why one might change them. That said, when I taught myself how to zone focus, it became the trigger for the all of the pieces of the exposure triangle puzzle falling into place. As such, even if you don't know what the exposure triangle is, I would still encourage you to read on!

Looking at the picture below you'll notice that if you line up all those markings you'll find the lens is set to 3m and f/8. This combination of settings is pretty much the base line for zone-focusing. Everything from 1.5m to infinity, good middle ground aperture for the balance between sharpness and light gathering. This is the "f/8 and be there" setting. Set your camera to this with a 400 ISO film, and in many daytime circumstances, you can snap away without any thought to setting focus.

In short, and in practical terms, this means that when you are zone focusing, you are not shooting with a zone of perfect focus, you are shooting with a zone of what's commonly defined as acceptable focus. Those markings on the lens simply show the limits of what the science says on average is right.

The invention is particularly advantageous for use with practical storage media in which the position or location and the differentiable characteristics of the symbols are subject to statistical variations, i.e., they are not uniform. For optical-storage media, nonuniformity of differentiable-locational characteristics of the symbols can be caused by optical and locational variations or distortions in the optical-storage medium itself, or by inconsistencies in the application of the symbols to the medium. Examples of optical variations or distortions in an optical storage medium such as motion picture film stock include over- or under-developing, and surface defects such as scratches or smudges. Examples of locational variations in motion picture film include stretching in one or more dimensions, and variations in the location of symbols with respect to the film. Examples of inconsistencies in application of symbols to the media include variations in the position of the symbols with respect to the boundaries of an underlying medium, and variations in the density and/or shape of the symbols themselves.

Although the invention in its broadest aspects contemplates the use of any means for oversampling the symbols, the invention is particularly advantageous for use with practical sensing arrangements such as optical sensing arrangements in which the optical characteristics and/or location characteristics of the symbols, referred to herein as optical-locational characteristics, are distorted by the sensing arrangement. Such distortion can be caused by optical and locational variations or distortions in the optical sensing arrangement itself, or by variations in the relative location and/or motion of the optical-storage medium with respect to the optical sensing arrangement. Examples of optical and locational variations in a sensing arrangement for motion picture film include lenses which are out of focus or which have optical aberrations, and lateral and/or azimuthal misalignment of optical sensing elements. Examples of variations in relative location and/or motion of a medium such as motion picture film with respect to a sensing arrangement include horizontal motion or weaving within an optical plane, horizontal motion and twisting of the film out of an optical plane, rotational or azimuthal motion, short-term fluctuations in film speed sometimes called jitter or flutter, and longer-term fluctuations in film speed.

Although there may be a slight skewing of the lines of fixels on the film relative to the CCD array as a result of film motion, such skewing need not be compensated by skewing the CCD array position. This is because the digital information is recovered from the film by deriving a two-dimensional image representation, as described further below. In a practical embodiment of the present invention, there is tolerance of substantial azimuth errors up to about 15 degrees. In principle, very substantial azimuth alignment errors may be tolerated if the recovery system has sufficient processing power.

In the preferred embodiment, the edge detector confines its search to a rectangular region within the image representation referred to herein as a "search zone." A distinct search zone of 50-by-120 samples is defined for each of the four field edges such that the zone abuts the boundary of the image representation adjacent to its respective field edge. The "exterior border" of each search zone abuts a boundary of the image representation. The "interior border" of each search zone is on the opposite side of the zone from its exterior border. The longer dimension of each search zone is parallel to its exterior and interior borders, and parallel to its respective field edge. FIG. 10 illustrates the field edge search zones. Under ideal conditions, the field 210 is substantially centered in the image representation 200 which is stored in the RAM 52, and each field edge is approximately centered between the exterior and interior borders of its respective search zone. Under practical conditions, film weave and jitter cause the field to move around in the image representation; however, each search zone is large enough to insure that its respective field edge falls between its exterior and interior boundaries under nearly all conditions.

Although calculations for the zone system were originally based on black and white sheet film, the Zone System is also applicable to roll film, both black and white and color, negative and reversal, and even to digital photography. 041b061a72




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