Minolta XG7 - Page 23

17
2. Control system
The
control
system
of
XG
is
more
complicated
than
that
of
XE
because
XG
employs
a
system
that
the
desired
exposure
is
achieved
when
the
shutter
is
released.
When
release
switch
(S;)
is
operated,
the
release
circuit
operates
to
check
to
see
that
the
shutter
sec.
time
is
within
the
interlocking
range.
At
the
same
time,
the
power
source
voltage
is
checked
by
the
voltage
detecting
circuit.
And
only
when
the
conditions
are
satisfactory,
the
release
magnet
is
operated
to
start
the
mirror
system.
On
operation
of
the
release
magnet,
the
memory
circuit
operates
to
store
the
voltage
corresponding
to
the
exposure
time
at
that
point
into
condenser
(C,)
for
memory.
Even
when
the
light
to
CdS
is
changed
and
shut
off
due
to
auto
exposure
control
or
mirror
operation,
the
charge
voltage
already
stored
in
the
condenser
will
not
be
affec-
ted
at
all.
As
the
operation
is
further
performed,
the
first
curtain
starts
running
and
the
trigger
switch
operates
in
connection
with
the
first
curtain,
then
the
control
cir-
cuit
operates
to
change
the
stored
voltage
into
logarithmically
expanded
current.
Condenser
(C,)
is
charged
with
the
current,
and
when
the
charge
voltage
reaches
a
certain
level,
the
current
of
shutter
control
magnet
is
cut
off
by
the
function
of
the
control
circuit,
then
the
second
curtain
runs
to
complete
the
exposure.
When
the
exposure
is
completed,
the
mirror
system
is
reset
and
the
winding
stop
is
released.
The circuit reset switch (S,) being interlocked with the winding stop turns off to
reset the release circuit.
The indication LED turns off with S; turned on. When the release button is kept
depressed, LED turns on again with reset switch (S,) OFF.
@ Manual sec. time
When the speed dial is set to 1~1/1000sec., the mode selector operates and the
standard resistor is set instead of CdS, then the film sensitivity and override resist-
ance are changed over to manual resistor. Also, the diaphragm resistor is released
from the circuit and the power supply to the indication circuit is cut off, hence the
indication LED does not light up.
When metering switch (S; or Si) is turned on, the calculation is performed by the
standard resistor and manual resistor, then voltage corresponding to the set sec. time
is charged into condenser (C,). Next, when release switch (S;) is turned on, the
power source voltage is checked by the voltage detecting circuit, then the release
magnet is operated. The operations, after that, are the same as for the control system
in auto mode.
When XG is used with manual sec. time, shutter sec. time is memorized, So, the shutter
is controlled at the initially set speed even when the set speed is changed during
shutter operation.
® Bulb mode
When the speed dial is set to "B", the mode selector operates to turn off the power
source holding circuit, and power supply to the indication circuit is also cut off, then
the indication LED does not light up. Next, when release switch (S;) is turned on, t
the power source voltage is checked by the voltage detecting circuit, and then the
release magnet is operated. As the operation continues, the trigger switch operates,
but the bulb is given priority by (S;) over control circuit, therefore, the shutter
contro] magnet keeps operating while the release button is depressed, then the second
curtain is stopped. When the release button is returned to the original position,
release switch (S;) is turned off and the power source holding circuit is also off,
therefore, the shutter control magnet turns off thus completing the exposure.