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The
F3
has
two
separate
settings for time
exposures
.
On
"B,"
the
shutter
remains
open
for as
long
as
the
shutter
release
button
is
depressed.
On
"T,"
the
shutter stays
open
until
the
dial is
rotated
to
another
setting, making
it
ideal
for
really
long
time
exposures.
Being a
mechanical
setting, "T" will not
cause
battery
drain
regardless
of how
long
the
shutter
remains
open.
"X"
provides
a
shutter
speed
setting of 1/80
sec.
It
is
used
18 to
provide
proper
synchronization with
electronic
flash
units
other
than
the
Nikon SB-12.
The
amount
of light
reaching
the
film
plane
is
determined
by
a
combination
of
the
shutter
speed
and
the
lens
aperture.
Since
the
two
are
interrelated,
different combi-
nations will
give
the
same
degree
of
exposure.
A
one-step
change
in
shutter
speed,
or
.a one-stop
change
in
aper-
ture
setting, will
either
halve
or
double
the
degree
of ex-
posure.
For
example,
a shutter
speed
of
11125
sec. lets
in twice
as
much
light
as
a setting of 1/250
sec.,
and
only
half
as
much
light at 1/60 sec. For
an
aperture
setting of
fill
, twice as
much
light
as
flI6
and
half at
much
as fl8,
is let in. Thus,
if
the
correct
exposure
for a
particular
picture-taking
situation is 1/125 at
fill,
then
1/60
at
fl16
or
1/250 at fl8 will
give
the
same
exposure.
The following
table
illustrates
the
interrelation
between
shutter
speed
and
aperture
.
The
best
combination
will
depend
on
the
results you
want. Use fast shutter
speeds
to freeze motion; use slow
speeds
to
produce
a
deliberate
blur.
(See
the
example
pictures
on
the
opposite
page.).
Also, small
apertures
give
greater
depth
of field, while
large
apertures
restrict
sharp
focus to
the
main subject. (See
page
26.)
A
good
rule
to follow in
preventing
camera
shake
is to
select
a minimum shutter
speed
which is
the
reciprocal
of
the
focal
length
of
the
lens in use. For
example,
when
using a normal
50mm
lens, select a
speed
no
slower
than
1/60 sec. (the closest
number
to 1/50). For a 500mm
super-telephoto, use
no
less
than
1/500
sec.,
and
so forth.