EasyManua.ls Logo

Minolta XE - Automatic Exposure Control Systems; a. Light Measuring System; b. Control System; B. Logarithmic Compression and Addition

Minolta XE
167 pages
To Next Page IconTo Next Page
To Next Page IconTo Next Page
To Previous Page IconTo Previous Page
To Previous Page IconTo Previous Page
Loading...
17
in
which
the
rotary
angle
per
step
is
logarithmically
compressed
at
a
certain
constant
(graduations
at
equal
intervals).
and
the
exposure
correcting
figure,
will
add
these
figures
to
the
aperture
which
is
logarithmically
compressed
as
well
as
the
ASA
number,
figure,
via
the
metal-covered
resistor,
and
at
the
same
time,
will
convert
the
sum
into
an
electric
volume
(voltage).
The
electric
value
(voltage)
will
be
added
to
another
electric
volume
(voltage)
in
which
the
brightness
of
the
object
is
logarithmically
compressed
by
the
photoelectric
converting
part
(C
part
of
the
circuit)
made
up
of
2
CdS
and
several
resistors.
The
sum
will
be
equivalent
to
the
exposure
time,
and
will
be
charged
to
(memorized
by)
the
condenser
(C,
of
the
E
part
of
the
circuit).
On
the
other
hand,
the
exposure
time
will
be
indicated
in
the
finder
by
the
meter
via
the
indication
circuit.
b.
Control
System
Next,
when
released,
the
light
measuring
output
point
and
the
condenser
(C,)
will
be
sapa-
rated
from
each
other
by
the
memory
switch
(D
part
of
the
circuit
diagram),
and
the
mea-
sured
light
quantity
(voltage
corresponding
to
the
exposure
time)
immediately
before
the
release
will
be
memorized.
Light
to
the
CdS
will
be
converted
by
the
automatic
diaphragm
and
the
mirror
operation.
Even
when
the
light
measuring
output
voltage
may
change
because
of
the
blocking
of
light,
the
charged
voltage
of
the
memory
condenser
(Ci)
won't
be
affected
and
the
memory
will
be
accurately
kept.
When
the
operation
of
the
camera
advances
further,
the
first
curtain
will
begin
to
run,
the
relative
trigger
switch
will
work,
and
the
memorized
quantity
(loga-
rithmically
compressed
quantity)
will
be
converted
into
a
logarithmically
extended
current.
Then
the
current
will
be
charged
to
the
condenser
(C,).
When
the
voltage
reaches
a
certain
level,
the
first
switching
circuit
(F
of
the
circuit
diagram)
and
the
delay
circuit
(I
of
the
current
diagram)
will
work
one
after
another.
After
a
certain
length
of
time,
the
second
switching
circuit
(J
of
the
circuit
diagram)
will
work,
the
current
of
the
magnet
(K
of
the
circuit
diagram)
will
be
cut
off,
and
the
second
curtain
will
run.
Thus
the
exposure
will
be
completed.
@
Manual
Time
In
the
case
of
the
manual
time,
the
memory
will
be
switched
from
the
logarithmic
extension
circuit
(F
of
the
circuit
diagram)
to
the
manual
resistor
(G
of
the
circuit
diagram)
in
order
to
form
the
CR
time
set
circuit.
Then
the
exposure
will
be
controlled
in
the
same
way
as
the
automatic
control
system.
Note:
Exposure
correction
means
an
increase
or
decrease
of
a
certain
figure
(up
to
2Ev)
to
or
from
the
standard
exposure
in
the
case
of
automatic
photography.
For
example,
a
i
el
exposure
correction
means
to
add
lEv
to
the
standard
exposure.
B.
Logarithmic
Compression
and
Addition
®@
Logarithmic
Compression
Logarithmic
compression
is
necessary
to
determine
the
adequate
exposure.
Variations
are
usually
given
in
the
manner
of
geometric
progression
to
those
in
the
ASA
number,
the
aperture
figure,
the
exposure
time,
etc.
(For
example,
2Ev,
4Ev-
+
+
are
given
to
lEv,
2Ev-:
-
-,
respectively;
25, 50,
100,
200-
-
+
for
the
film
sensitivity
figure;
and
1
sec.,
1/2
sec.,
1/4
sec+
+ +
for the
exposure
time.)
Since
the
power
source
needs
a
high
voltage
to
convert
such
figures
that
will
change
in
the
manner
of
geometric
progression,
no
camera
can
practically
afford
to
have
so
high
a
voltage.
Then
it
becomes
necessary
to
convert
variations
in
the
Ev
figure
to
those given
in
the
manner
of
arithmetical
progression
(for
example,
lEv,
2Ev,
3Ev-
- -
to
1,
2,3-
+
-).
This
sort
of
conversion
means
logarithmic
compression.
(Example)
If
the
exposure
time
of
1~1/1000
sec.
is
converted
into
a
voltage
at
the
rate
of
0.1V
per
second
without
giving
logarithmic
compression,
1/1000
sec.
will
be:0.1V
x
2!=102.4V.
If,
however,
1/1000
sec.
is
logarithmically
compressed,
the
obtained
figure
will
be:0.1V
xX
10=—1V,
or
less
than
1/100
of
the
102.4V.
This
smal]
figure
is
quite
practical
for
cameras.
An
explanation
will
be
given
about
how
the
following
factors
can
be
logarithmically
compr-
essed:

Related product manuals