The film experiences a loss of film speed in these
cases, which in turn causes underexposure. Reci-
procity law failure is typically encountered with
exposures greater than 2 seconds, but varies from
film to film.
Exposure and Its Effects on Film
Exposure is directly responsible for the amount of
detail captured on film, ultimately determining the
quality of the image on film. A film that is able to
maintain a great amount of detail, despite some
over- or underexposure, is thought to have wide
exposure latitude. Black and white films are con-
sidered to have good exposure latitude, due to the
fact that they are forgiving in the amount of expo-
sure they need to produce a quality image. Color
slide films are considered to have very narrow
exposure latitude, meaning the exposure needs to
be very exact to render detail.
The greater the amount of exposure, the greater
the recorded density will be on negative film.
Increased density on a negative corresponds to
the highlights of a scene in a final print. Conver-
sely, shadow areas correspond to areas of less
exposure on a negative. For this reason, shadow
detail tends to be the first thing lost when the image
is underexposed. Because the amount of light in the
shadows of a scene is so low, they are not given the
amount of time needed to record on film in under-
exposure. The highlights in an underexposed image
never achieve the proper amount of density to
allow them to appear as light as they were in the
original scene. Instead of appearing white, the
highlights may instead appear grey. The result of
an underexposed image is one with lowered con-
trast and little to no shadow detail. The result on
positive (slide) film is identical, though it happens
even more quickly given slide film’s narrow expo-
sure latitude.
Overexposure on film will cause details in the
highlight region of a scene to disappear. Film is
not able to handle an infinite amount of expo-
sure. Once maximum density is reached, film cha-
racteristically begins to level off. If even more
exposure is given, the already overexposed light-
sensitive particles in film will begin to grow lar-
ger, causing an obliteration of highlight detail.
This phenomenon is known as a ‘‘blocking up’’
of the highlight detail.
Film’s response to both exposure and develop-
ment can be graphed in the form of a characteristic
curve. A characteristic curve plots exposure versus
density in a chart that can be compared in terms of
that film’s contrast and exposure latitude.
CHRISTYESissonFurther Reading
Adams, Ansel.The Negative (Book 2). Boston and New
York: Little Brown & Co, 1995.
Adams, Ansel.The Camera (Book 1). Boston and New
York: Little Brown & Co, 1995.
Langford, Michael.Basic Photography. New York: Focal
Press, 2000.
London, Barbara and John Upton.Photography. 7th ed.
Upper Saddle River, New Jersey: Prentice Hall, 1998.
Meehan, Joseph.The Photographer’s Guide to Using Filters.
Amphoto, 1999.
Schaefer, John.An Ansel Adams Guide: Basic Techniques of
Photography, Book 1. Boston and New York: Little
Brown & Co, 1992.
Stroebel, Leslie D., ed.Basic Photographic Materials and
Processes. New York: Focal Press, 2000.EXPOSURE