Buried throughout the gelatin are microscopic crystals that are there to make a record of where
the light strikes the film. They are the chemical equivalent of the photodiodes in a digital
camera’s image sensor. The crystals are made by combining silver-nitrate with differ-
ent mixtures of halide salts, including chloride, bromide, and iodide. Their
crystalline structure allows film manufacturers to grow them smaller or
larger. The greater surface areas of larger crystals make the film
more sensitive to light but result in lower resolution and contribute
to noticeable grain, the speckled equivalent of noisein digital
photographs. Smaller crystals, while not able to gather in as
much light, can delineate smaller features in a photograph.
The result is a trade-off between film that can take photos
in dimmer light, with faster shutter speeds and using larger
apertures, or film that captures more and smaller details with
less grain but requires more light.2
The sensitivity of the crystals, which ordinarily are mediocre
receptors of light, increases when certain chemicals are fused
into the crystalline structure. These organic molecules, called
spectral sensitizers, increase silver halide’s sensitivity to light
generally. In color film, different combinations or sensitizers
make crystals embedded in separate layers in the emulsion
respond to specific colors.3
How Film Photography Captures
an Image
Digital and film cameras are 90% the same. Optics, exposure, timing, and the skill it takes to use either of the cameras are not much different
from one another. Where the difference is greatest is in the topic of this chapter—how light streaming through the lens is trapped and pre-
served, how film and electronics both take a slice out of time and space to make them into something immutable. We’re going to step into our
Way Back Machine for a short hop to a few years ago, when digital photography was esoteric and imperfect. When all professional photo-
graphy was still an analog process—a process that was itself so esoteric as to make it a snap to learn how to use those new digital computers.
Although we usually think of light as something to help us avoid walking into walls, it’s also packed with energy—a fact you can
demonstrate to yourself by lying in the sun too long. That energy is essential to photography. In film photography, the energy in light
ignites chemical reactions when color or black-and-white film is exposed to the light when a camera’s shutter is tripped. The light,
focused by the lens, shoots through layers of a gelatin emulsion about a thousandth of an inch thick that rests on a base made of
celluloidorpolyester, both transparent plastics. The base, four to seven times thicker than the gelatin, exists primarily to support
and protect the fragile emulsion layers.1
(^100) PART 2 HOW DIGITAL CAMERAS CAPTURE IMAGES