Canon FTb - Aperture Control

Pre
set
Aperture
Ring
cable
release.
r
lt is
possible
to
perform
a
long-time
exposure
measure-
ment
by
attach
ing
the
optional
Canon
Booster,
the auxilia-
ry
meter
for measuring
subjects
under
dim
light.
I
The
'
'
60
' '
index
is
used
for synchron
izing
an
electronic
flash
unit
such
as
Canon
Speedlite.
lt is
equivalent
to
a
very
short
exposure
time
during the
flash
of
the
flash
unit.
Aperture
f ncoming
light and
depth-of
-f
ield
are
adjusted
by
turning
the
preset
aperture
ring
to
the
desired
f/stop.
r
As
the
f/stop
number
gets
larger,
the
amount
of
light
reaching
the
f
ilm
plane
becomes
correspondingly
less.
For
each
f/stop
up, the
light
is
reduced
one-half
.
Accordingly,
when
the aperture
is
increased
by
one
f/stop,
the
exposure
is
doubled,
and
when
it is
increased
by
two
f/stops
the
exposure
is
quadrupled.
r
Certain
lenses,
however,
have
no
relation
to the
bright-
ness
halved
between
the
maximum
and
the
next
f/stops
on
the
preset
aperture
ring.
I
The
ratio
between
the aperture
and
the
amount
of
ex.
posure,
using
f
/2
as
the
basis,
is
as
follows
:
f/stop
:
t.2
t.4
1.8
2
2.8
3.5
4 5.6
8 tl
16
22
Exposure
Ratio
:
3
2
1.25
1
L/2
r/3
L/4
L/8
r/16
L/32
L/64
L/r28
15
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