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Glossary-continued
Flexible Program
Flexible
Program
function
temporarily
shifts
an
automatically
selected
shutter
speed
l
aperture
combination
whi
le
maintai
n
ing
correct
exposure
.
That
is
,
the
desired
shutter
speed
or
aperture
can
be
selected
in
Auto-Multi
Program.
f-number
The
f-
number
represe
nt
s
th
e
aperture
va
l
ue
and
is
calculated
from
lens
'
focal
length
divided
by
the
effective
aperture
open
in
g.
The
standard
numbers
for
calibration
are
1,
1.4
, 2, 2.8, 4, 5.6, 8,
11
,
16
,
22
,
32
,
etc.
The
smallest
f-
number
is
called
maximum
aperture
and
the
largest
f-number
is
called
minimum
aperture.
Lenses
with
large
maximum
apertures
(
smaller
f-
numbers)
are
'
fast
'
lenses
that
allow
photographers
to
use
faster
shutter
speeds
in
dim
light.
Lenses
with
smaller
maximum
apertures
(larger
f-
numbers)
allow
the
use
of
lower
shutter
speeds
for
available
light
but
are
also
lighter
and
smaller
than
faster
lenses.
With
some
zoom
lenses
,
aperture
varies
depending
on
the
foca
l
length
setting
.
Focal length
The
distance
from
the
principal
point
to
the
focal
point.
In
35mm-format
cameras
,
lenses
with
a
focal
length
of
approx
.
50mm
are
called
normal
or
standard
lenses.
Lenses
with
a
focal
length
l
ess
than
approx
.
35mm
are
called
wideangle
lenses
,
and
l
enses
with
a
focal
length
more
than
approx.
85mm
are
called
telephoto
lenses.
L
enses
which
allow
the
user
to
continuously
vary
the
focal
length
without
changing
focus
are
called
zoom
lenses.
122
Focus Tracking
Enables
the
camera
to
ana
l
yse
the
speed
of
a
moving
subject
according
to
the
focus
data
detected
,
and
to
obtain
correct
focus
by
anticipat
ing
the
subject's
position-at
the
exac
t
moment
of
exposure
.
Lock-OnTM
Autofocus
keeps
focus
firmly
on
a
main
subject
during
Focus
Tracking
even
if
some
other
object
momentarily
blocks
it
in
the
viewfinder
.
Front-Curtain Sync
The
flash
fires
an
insta
nt
after
the
front
curtain
of
a
focal
plane
shutter
has
completed
its
travel
across
the
film
pl
ane
.
This
is
the
way
the
N751N7500
operates
w
it
h
the
flash
sync
mode
at
Normal
Sync
.
(See
"
Rear-Curtain
Sync"
.)
Guide number
The
guide
number
indicates
th
e
power
of
a
flash
in
relation
to
ISO
film
speed
.
The
guide
number
of
the
built-in
Speedlight
of
the
N751N7500
is
12139
(ISO
100
, m/
ft
.).
Guide
numbers
are
quoted
in
either
meters
or
feet.
Guide
numbers
are
used
to
calculate
the
fl
stop
for
correct
exposure
as
follows:
guide
number
fl
stop
=
-------
flash-to-subject
distance
Using
a
se
l
ected
aperture
,
we
can
calculate
the
required
flash-to-subject
distance
with
the
formula
:
guide
number
flash-to
-
subject
distance
=
-=----,-,-----
fl
stop
Useful
for
determining
the
maximum
flash-to
-
subject
distance
for
flash
photography
.