The zone system was invented by Ansel Adams, one of
the most famous photographers ever. He was a master of technique,
and had an eye for light that few are blessed with. His photographs
were the result of a happy combination of comprehensive technique
and the knack of taking a picture when the light was at its best. A
distinguishing feature of his black and white photographs is how
light and dark areas play off each other in an instantly appealing
manner.
Yet Adams did not approve of what he saw as the 'abuse' of his zone
system. As an old man, he thought far too many people had
misunderstood the method and burdened it with too much mystery. Why
had it turned out like that? Most likely it was poor communication
that was to blame: Ansel Adams was a much better photographer than
he was a teacher. His first books on the zone system are very hard
to follow. The final editions of 'The Negative' and 'The Print' are
much better.
The zone system is simple
The zone system is very simple and its principles are logical and
easy to understand. Its scientific basis had been known long before
Ansel Adams and Fred Archer hit upon the method in the 1940s. The
pioneers were Ferdinand Hurter and Vero Driffield who, at the end of
the nineteenth century, studied the way in which light sensitive
photographic materials reacted during exposure and development. They
succeeded in describing the properties of light sensitive materials
in a graph that showed what was termed the H&D curve, a curve
still in use today in sensitometry.
Art or science?
Some of the difficulties in understanding the zone system probably
had to do with the conflict between art and science. Is photography
an art or a science? Is it in fact both? If you decide photography
is an art, it becomes difficult for some to treat it as a science,
and thus it inevitably becomes much harder to grasp what is going
on. If, on the other hand, you accept that photography is both art
and science, and understand its principles on a scientific and
logical basis, it becomes much easier. To my mind this approach does
not necessarily intrude upon the artistic side of photography. On
the contrary, a better understanding of techniques can greatly
improve personal creativity. When you really understand what is
happening, you can exploit to the full all the means photography
provides to express your artistic vision.
Visualization, exposure and development
In brief, the zone system is made up of three basic components, all
of which were very important to Ansel Adams: visualization, exposure
control, and contrast control.
Visualization is not really a question of technique. It is a method
used to picture the finished photograph before it is taken, and is
useful for everybody, regardless of whether they are using the zone
system or not.
Exposure control is key, partly because it is important to learn how
your own photographic equipment works, and partly because you want
to choose a shutter speed and aperture that will provide a negative
with as much detail as possible. It is with exposure that you control
the reproduction of shadows.
Contrast is controlled by development and the contrast grade of the
paper used for printing. It is the contrast control that determines
how white the picture's light areas will become in the finished
photograph. You should learn to use a suitable development time that
will give you the contrast you are looking for.
Difficult terms
Visualization, exposure, and contrast control are terms that are
simple to understand. What can be confusing are the words Ansel
Adams used to describe exposure and contrast control: Zone V or Zone
III exposure, N-2 or N+1 development. However, we will save these
for later and concentrate first on a few basic requirements.
Brightness levels
It is a common mistake to think that you only take one exposure each
time you press the shutter button. You take an exposure with a
specific aperture and at a specific speed. However, another thing
that affects the exposure is the reflected light from the object you
are photographing, and this can vary greatly for the same object.
The darkest details reflect less light than illuminated white
details. Normally you have a number of different exposures every time
you take a photograph. The object has many different levels of
brightness, sometimes ranging from black in the shade to white in
the sun. The range of exposure values is a result of variations in
both the incident light (sun and shade) and the ways the object's
various surfaces reflect light.
Measuring the range of the contrast in a picture is easy. It is best
to measure the contrast according to the number of exposure stops
from the darkest part of the picture to the lightest. One exposure
stop is the equivalent of a halving or doubling of brightness. From
1/125 to 1/250 seconds is one exposure stop. From f5.6 to f8 is also
one exposure stop. By first pointing the light meter at the darkest
part of the picture and then the lightest, you can calculate the
number of exposure stops between them. Normally there are seven
stops between shaded black and illuminated white, but it varies
depending on how harsh the incident light is. Direct sunlight on a
clear day will give a very wide range of contrast, while a gray,
hazy day will give a low contrast with few exposure stops between
black and white. Normally, the contrast range varies between five
and nine stops.
Nine stop contrast range, plus all black and all white
Seven stop contrast range, plus all black and all white
Five stop contrast range, plus all black and all white
Film's exposure latitude
Photographic film reacts to exposure. When film is developed, the
blackness increases to a large extent in proportion to the exposure.
A strong exposure (a white surface in sunlight) means that
development heavily darkens the negative. A weak exposure (a black
surface in shade) results in little darkening of the developed
negative.
However, film has its limitations. Very weak exposures will not give
any darkening at all, while very strong exposures do not give any
more darkening than slightly weaker exposures would. The exposure
must not be too weak or too strong. You are interested in the range
of exposures that lie between the two extremes of underexposure and
overexposure. This is called the the film's exposure latitude. A
negative black and white film has a wide exposure latitude of up to
fifteen stops. This is much more than the brightness range of almost
all objects you might want to photograph.
A negative black and white film with an exposure latitude of
fifteen stops.
Ideal exposure
When a film is going to be exposed in a camera, you have to make sure
that all the object's individual exposure values fall within the
film's exposure latitude. If you use too short an exposure (too small
an aperture or too fast a shutter speed) the darkest areas of the
object will end up outside the film's exposure latitude, and the
photograph will be underexposed. If you expose for too long (too
large an aperture or too long a shutter speed) you risk overexposing
the lightest parts of the object, giving flat, bright areas devoid
of contrast.
At a level of two stops underexposure, you will lose the two
darkest stops of the object.
The best results are achieved if you use as short an exposure as
possible without losing any of the shaded details. The way to do
this is to measure the darkest element in the object and then pick a
shutter speed and aperture as close to the threshold value for
underexposure as possible.
The ideal exposure is to place all the tones of the object except
all black, just within the films threshold to the left.
The reasons for choosing short exposures are the numerous advantages
you gain. You have the smallest possible aperture, something that is
generally desirable. You also have a fast shutter speed, which again
works to our advantage. You end up with negatives that are not overly
dark, thus shortening the exposure times when printing the
photographs. Last but not least, the negatives will have a fine
grain (the lighter parts of the negatives being more fine grained
than the darker), which is almost always preferable.
Photographic paper's dynamic range
The point of taking a photograph is to produce a finished picture on
photographic paper. It is the blackening of the paper that forms the
image. In principle, a wide dynamic range produces the best results.
The paper is said to have a wide dynamic range if it turns fully
black in the darkest areas of the image and is wholly white in the
lightest areas, which means that there is the widest scope for
reproducing the image's details. One of Adams' strengths was that he
knew which material to use, and he always used the best photographic
papers.
A very good paper will have a dynamic range corresponding to more
than six exposure stops.
A paper's dynamic range can be measured with a densitometer, and it
can be described in terms of stops of exposure. A very good paper
will have a dynamic range of about six exposure stops. If you
compare this with the object to be photographed, which normally will
have a range of seven stops, you will see that the paper can
therefore reproduce the object's detail with little or no
compromise. If you choose a paper with a range of four stops, the
range of detail will have to be compressed to make it fit the
paper's capabilities. For some photographs this is not much of a
problem, indeed they can even benefit, but if you are looking for a
picture with a full gray scale running from black to white, paper
with a narrow dynamic range will not give particularly good-looking
results.
I want to stress that the point of using the zone system is not
always to produce this kind of photograph. Your aim should be to
learn how to take the kind of picture you want, regardless of
whether you want every last tonal detail, or whether you want your
picture to be soft and gray.
Exposure controls shadows
This is an old adage that most people have heard more than once.
What does it mean? Simply put, because it is normal to use the
shortest exposure possible that will still preserve those details
that are in shadow, you should get as close to the threshold value
for underexposure as you can. If you were to go too far, the detail
in the darkest shadows will be lost, and you will end up with an
underexposure. In deciding the exposure, you also decide how much of
the detail in the shadows will be kept. Exposure controls shadows!
Development controls highlights
This is another adage that still holds good. The longer the
development time the higher the contrast, and the greater the
difference between black and white. If you print the photograph so
that the shadows come out right, the highlights will vary with
different development times. A longer time produces lighter
highlights and shorter time produces darker highlights. Development
controls the highlights!
Two controls
What you have here are two controls, one for the darkest areas and
one for the lightest. Once you have accepted this way of thinking,
things become much easier. An object is made up of different tones
ranging from black to white. To produce pictures with a full tonal
scale you need to know how to control all the tones. To do that, all
you need to do is to adjust the darkest and the lightest parts of
the image. All other tones land between these two extremes, and will
automatically fall into the right places. You control the darkest
tones by learning how your camera and film react to exposure (by
calibrating your equipment) and by then choosing an exposure that
will ensure that the darkest tones will appear on the negative (by
exposing in the correct zone). After this, you control contrast by
picking a development time that ensures that the lightest areas of
the picture will be reproduced on the photographic paper. The two
controls are exposure and development. It is that simple.
Top left: With correct exposure and correct development, the image
will get a full tonal range from dark tones to bright highlights.
Top right: With two stops underexposure the result is an image with
lost shadow detail. With a longer exposure and/or larger aperture
opening, the shadows would have been correctly exposed.
Bottom left: Less development gives lower over-all contrast and in
this case to gray high-lights. With 20% more development this image
would have been better.
Bottom right: To much development gives to high contrast. The
high-lights are too white without any detail. 30% less development
would have been better.
Recommended Books and Supporting Reading Material
<- The Zone System - Part Two (Next)
