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Minolta XE - Logarithmic Compression and Addition; Addition; C. Memory; D. Logarithmic Extension

Minolta XE
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a.
Film
Sensitivity,
Exposure
Correction
and
Aperture
Figures
As
mentioned
before,
the
ASA
number
changes
in
the
way
of
25,
50,
100,
200-
-
-
When
the
set
dial
is
graduated
at
equal
intervals
(rotary
angle
per
step),
the
rotary
angle
of
the
dial
will
respond
to
the
shift
of
the
brush
of
the
metal-covered
resistor
with
a
linear
property
(A
and
B
of
the
circuit
diagram),
and
these
figures
will
be
converted
to
resistance
values
(voltages)
which
change
in
the
manner
of
arithmetical
progression.
Similar
methods
are
used
for the
exposure
correction
figure
and
the
aperture
figure.
b.
Brightness
of
Object
As
apparent
from
the
circuit
diagram
shown
later,
in
the
photoelectric
conversion
circuit
(C
of
the
circuit
diagram)
comprising
2
CdS
and
several
resistors,
the
brightness
of
the
object
will
be
electrically
converted
and
logarithmically
compressed
thanks
to
the
special
property
of
these
CdS
and
the
special
construction
of
the
circuits.
No
diode
or
transistor
is
used
for
logarithmic
compression.
c.
Exposure
Time
The
exposure
time
will
be
memorized
as
the
logarithmically
compressed
output
of
the
light
measuring
circuit
by
adding
the
before-mentioned
factors
in
the
manner
of
logarithmic
compression.
@
Addition
As
stated
previously,
all
factors
in
determining
the
adequate
exposure
are
added
in
the
manner
of
logarithmic
compression.
First,
the
ASA
number
and
the
exposure
correction
figure
will
be
mechanically
obtained.
Then
they
will
be
added
to
the
aperture
figure
and
the
total
will
be
electrically
converted
simultaneously
via
the
metal-covered
resistor
(A
and
B
of
the
circuit
diagram).
Further,
the
addition
of
the
total
to
the
brightness
of
the
object
will
be
electrically
made
in
a
circuit
with
IC-B
as
the
nucleus. This
sort
of
mechanical
adding
system
is
called
the
adding
system,
while
that
of
electrical
adding
system
is
called
the
addition
circuit.
C.
Memory
Since
light
is
measured
after
its
passage
through
the
take
lens,
its
reflection
on
the
mirror,
and
its
passage
through
the
focus
plate,
light
to
the
CdS
is
changed
or
blocked
by
the
automatic
diaphragm
and
the
mirror
operation,
Therefore,
it
is
necessary
to
withhold
the
light
value
measured
immediately
before
the
release
operation
in
connection
with
the
operation
itself.
The
memory
means
to
withhold
the
measured
value.
In
the
case
of
XE,
the
condenser
C,
(E
of
the
circuit
diagram)
will
be
charged.
The
memory
switch
(D
of
the
circuit
diagram)
will
open
along
with
the
release
operation,
and
the
charged
voltage
will
be
withheld
(memorized).
This
sort
of
circuit
is
called
the
memory
circuit.
D.
Logarithmic
Extension
As
mentioned
before,
the
electric
volume
(voltage)
corresponding
to
the
exposure
time
is
memorized
in
the
form
of
a
logarithmically
compressed
figure.
Therefore,
the
volume
must
be
converted
into
an
adequate
exposure
time
(1,
1/2,
1/4
sec.
or
else).
This
sort
of
conv-
ersion
is
called
logarithmic
extension
(or
simply
extension).
In
the
case
of
XE,
the
memo-
rized
voltage
will
be
converted
into
a
current
in
the
manner
of
logarithmic
extension
by
utilizing
the
special
property
of
the
transistor
(F
of
the
circuit
diagram).
The
condenser
Cz
constituting
the
time
set
circuit
will
be
charged
with
the
logarithmically
extended
current,
and
the
control
of
the
magnet
will
convert
the
current
into
the
required
exposure
time
via
the
subsequent
switching
circuits.

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