Slow films generally exhibit narrower
exposure latitude than do medium or high speed emulsions.
Black-and-white and color negative
material offer significantly more latitude than do transparency films.
Negative materials show much more
overexposure latitude than on the underexposure side. For some negative
films, this can amount to two or three times as much overexposure
Transparency films are much more tolerant
of underexposure than of overexposure. They exhibit at least twice as
much latitude on the underexposure side. Even so, transparency films
have the least exposure latitude of any film type.
Exposure latitude is greatest when film
is used to photograph subjects under low-contrast lighting. It follows
that as subject contrast increases, exposure latitude decreases.
Exposure latitude is controversial
a. There is no objectively correct exposure.
b. What appears to be a well-exposed frame to one observer is over- or
underexposed to another.
c. Published exposure latitude figures are judgments and represent
consensus at best.
Exposure latitude is up to 50 percent
greater when shooting under even, diffused light (as on an overcast
day) than under bright, direct sunlight or non-diffused electronic
A majority of experienced photographers
indicate the best starting point for exposure is to rate the film at
its manufacturer's recommended ISO. Numerous published tests confirm
this judgment. The ratings were arrived at by taking an average of ISOs
used by the panel of expert photographers working with the author on
the preparation of this volume. While many felt the rated ISO was
optimum, especially in low-contrast light, numerous films were rated at
ISOs other than their designated speed.
It is of interest to note that almost all
panel members used personal EIs (Exposure Indices) different from
manufacturer recommendations when using slide film and were more likely
to accept nominal speed ratings for print film. This is probably due to
the wide exposure latitude inherent in print film as compared to slide
In practice, applying corrections to
established ISO numbers sets a personal exposure index most suitable
for your own equipment, applications, and taste. Even though stated
ISOs are used by many photographers, they should not represent an