515
Texts and Controversies: An Anthology, 1816–1871], Paris:
Macula, 1989.EXPOSURE
In photography, common understanding of the term
“exposure” suggests simply exposing a fi lm, plate or
paper to light. More scientifi cally, it can be defi ned as
the effect produced on a sensitised material by light,
which is proportional to the product of intensity and
time. Correct exposure depends on four variable fac-
tors; the quantity of light, the nature of the subject, the
aperture of the lens, and the sensitivity or ‘speed’ of the
negative material.
Long exposure times severely limited the scope of the
photographic pioneers. The fi rst process used success-
fully to produce a permanent image, the heliographicprocess of Joseph Nicéphore Niépce, required an ex-
posure time of several hours and was therefore of very
limited potential. The fi rst practicable processes, the
daguerreotype process of L.J.M. Daguerre and W.H.F.
Talbot’s photogenic drawing, both announced in 1839,
required shorter exposures but still long enough to
severely limit the photographer’s subject. The earliest
daguerreotypes requiring minimum exposures of fi ve
minutes and often up to thirty, depict almost exclu-
sively, static landscapes, architectural views and still
life subjects. The subject matter of Talbot’s surviving
photogenic drawings is even more limited. Most are
shadowgraphs, as Talbot described them or what we
would call photograms today. Surviving camera pic-
tures are rarer and again show static subjects. Exposure
times were probably a little longer than contemporary
daguerreotypes. In The Pencil of Nature (1845–46),EXPOSURE
Bell, William Abraham. Canyon of
Kanab Wash, Looking South.
The Metropolitan Museum of Art,
Gilman Collection, Purchase, The
Horace W. Goldsmith Foundation Gift
[2005 2005.100.585 (10)] Image ©
The Metropolitan Museum of Art.Hannavy_RT72353_C005.indd 515 7/5/2007 11:18:37 AM