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High
Resolution and High
Definition
In a
nutshell:
Image sharpness
is by no means a requirement for excellent photographs. It is one of many
aesthetic choices that a photographer can make.
When sharpness,
fine detail, and a full contrast range are the aesthetic goal, the photographer
has three tools available that offer a surprising amount of control. Of course, the photographer
must use his or her camera correctly, so that camera shake and lens
flare do not intrude. Then it is
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film choice,
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developer choice, and
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processing
technique
that largely
dictate image sharpness.
Sharpness, and
the illusion of sharpness, result from the resolving power of your negative
material and the rest of your optical system, and your processing methodology. The two key
concepts are
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image resolution, and
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image definition.
“Image resolution”
This term describes image sharpness achieved by
maximizing the ability of the film to record image detail.
Image detail can be lost in two ways.
-
First, all optical
systems are by their nature limited in the detail they can
resolve. These limitations are dictated by the laws of physics, which dictate
that light is not only focused by lenses, but also refracted (scattered) by
the same lenses.
-
Second, films have granular properties which limit
the detail they can record.
High-resolution films have inconspicuous or invisible
grain, when correctly processed. They achieve high
resolution by minimizing the detail lost due to grain. They cannot compensate
for resolution losses elsewhere in the optical system.
Grain is a function of the film's
physical characteristics, and of the developer and processing technique used.
Grain size, film
speed, and film contrast are related. A high-resolution film will necessarily
have
Conversely, a high speed film will necessarily have
These relationships are dictated by
the laws of physics which describe how light reflects from sub-microscopic
particles of differing sizes.
Maximum
resolution, reasonably high speed, and a full range of pictorial contrast can
only be achieved with high-resolution films through the use of specialized
developers.
“Image
definition” This
term applies to an image in which the
edges of fine detail are sharply distinct. Such an image is said to
have prominent microstructure and exhibit
"high acutance." It may or may not have prominent
grain. Microstructure is influenced more by choice of
developer and development technique than it is by choice of
film. Any black and white film can be developed for acutance, but not all
developers are suitable. Coarse-grained
films developed for high acutance give the illusion of sharpness, even though
close examination reveals that detail is indistinct. The visual effect
can be quite stunning. Fine-grained
films developed for high acutance often give the appearance of striking clarity.
High definition
(in other words, "high acutance") images are obtained with a special
development technique. This technique was first promoted by the very inventive
German photographer and photochemist Willi Beutler (1903-1978) in the middle of
the 20th century. It is essentially an agitation technique which includes
periods of time in which image density is allowed to build up at the edges of
grain aggregations, such that the image has sharply defined edges at the
microscopic level.
Beutler called
this "compensating" development. It is most effective when practiced
as an agitation regime, for example, you might agitate for five seconds, then
allow the film to sit for three minutes. Exact timing depends on the specific
film and developer being used, but the compensation principle applies: the edges
of the image's granular microstructures become sharply defined.
Maximum
definition can be carried too far, creating bizarre images (which may, of
course, be exactly what a creative photographer has in mind). When practiced
carefully, with appropriate films and developers, the Beutler "compensating
agitation" technique creates images of extraordinary brilliance and
clarity.
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