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LENS APERTURE
Nikkormat
10 11
~
56
.4
L 0 , '.
~{r""\:j
.
.
The
lens aperture controls the amount
of
light
and at the
same
time
the
depth of field
(see
P. 1B)
.
The F·numbers
-
the focal length of
the lens divided by the diameter of
the effective aperture
of
lens
-
for ex
-
ample
,
1.4, 2, 2 .B
,
4
,
5.6,
B,
II, 16,
22
....
are
engraved
on the
aperture
ring
of
each
lens
,
and
can be
set
by turning the ring to the
index
dot
.
Each
number
will permit the passage
of half the light of the number preced
-
ing it
.
Thus
,
F
1
8
will allow half the
light
allowed
by
F/5
.6
.
COMBINATION OF SHUTTER SPEED AND APERTURE
The
amount
of light admitted through the lens to fall on the film is
adjusted
by
the exposure which is
determined by the combination
of the shutter speed
and
aperture
of the lens
.
Therefore,
a
number of different
combinations
are possible
for the
same
exposure
;
for example
,
1/250
sec. with
F/
1.4
will
give
the same
exposure
as 1 /60
sec.
with
F/2
.B or l
i
B
sec
,
with
F/8
.
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