Minolta XG-1 - Exposure Control Fundamentals

20
EXPOSURE- CONTROL FUNDAMENTALS
The two camera exposure-control settings
are lens
opening (aperture) and shutter speed.
The size of the aperture determines the amount
of volume of light reaching the film from a
given
subject and lighting. The shutter speed
determines the length of time this light acts
upon the film . Apertures are expressed in
f-numbers, wh ich are larger for small openings
and vice versa (e.g.,
filS represents a small
opening, f/2 a large one). Shutter speeds are
expressed in seconds
or fractions thereof, which
are generally the reciprocals of the numbers
shown on shutter-speed scales (e.g. SO = 1 ISO
sec., and 2 = 112 sec.). At usual apertures, each
f-number setting (e.g., f/S) lets in twice as much
light as the next numerically larger one (fIll)
and half as much as the next smaller (f/5.S)'
Simi larly, each ~hutter speed (e.g., 1 ISO sec .)
allows light to strike the film twice as long as
the next higher ,speed (1/125) and half as long
as the next lower one (1/30). The interval
between two standard f·numbers (say, f/4 and
f/5.S) or shutter speeds (say, 1/15 and 1/30) is
one "stop." Total exposure on the film is
determined by the combination of aperture and
speed.
Other things being equal, using the next
smaller f-number (i.e., giving one stop more
exposure) will balance using the next higher
shutter speed (i.e., giving one stop less expo-
sure), and so on '. A great range of combinations
(e.g., f/5.S at 1/30, fl4 at 1/S0, f/2.S at 1/125,
f/2 at 1/250, etc.) will thus yield the same total
exposure. The specific combination you choose
under given lighting conditions will depend
upon the degree to which you want the greater
depth of field (see p. 3S) of smaller apertu res
and the greater movement-blur preventing abili-
ty of faster speeds (p. 2S).