Technology of grain in film photography
Historically, film technology has been
locked into a rigid relationship among film speed (sensitivity),
sharpness, and grain structure. Alter one and you surely change the
other two in the opposite direction. Demands for ever faster films led
to the introduction of high-speed films, especially of the color print
Indeed, we do get to use higher speed
film. Emulsion speeds of ISO 200, 400, 1000, and even 3200 are
available. There is a price to be paid for all this speed. Initially,
high-speed film was very grainy, with huge, rough-edged crystals. These
films were not particularly sharp. We had speed, but it wasn't useful
for anything except small snapshot-size prints. If you produced
anything over a 5 x 7-inch enlargement, the quality just wasn't there.
Critical photographers were not content to settle for mushy,
ill-defined, low-light images and they voiced their disapproval with
their wallets. High-speed-film sales didn't go anywhere.
Then, several major producers of
photographic film around the world launched a major research effort to
change the traditional film-quality triangle relationships. They asked
one question: Could one design a film that was faster (more sensitive)
while at the same time limit or eliminate the adverse effects that such
speed increases had on image sharpness and the appearance of grain? The
first positive answer to this question came in 1983 when Eastman Kodak
announced a new method of making silver halide crystals. Until this
time, crystals were formed in a more or less pebble shape and were
randomly distributed within the film emulsion layer. To change this,
Kodak researchers did two things. First, they computer-designed the
now-famous pioneering T-Grain (tabular), a crystal whose thinner,
flatter shape presented more surface area and thus was able to capture
more light for the same amount of silver than conventional grains. To
increase their efficiency, T-Grains were also designed to align their
surface parallel to the emulsion surface automatically.
What Kodak accomplished in one decisive stroke was to make a grain structure that improved on previous crystals in a number of highly significant ways. First, the new structure was more regularly shaped with fewer large crystals that had heretofore been the cause of visible and objectionable grain patterns, specifically in high-speed film. Also, the new design was able to limit the number of very small grains that had downgraded sharpness. An additional benefit of T-Grain research is that it allows for a measurably thinner emulsion layer, which in turn reduces light scatter Film Resolution.
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