ring then comes against the minimum-
aperture lever, Fig. 1. As the tab pushes
the minimum-aperture lever from left to
right, it programs the metering system for
the smallest f/s to p of the particular lens.
Only the MD series of lenses has the
minimum-aperture tab on the diaphragm-
setting ring.
Although the earlier MC
lenses will couple to the diaphragm-
metering ring, they d o n 't have the tab
w hich positions the minimum-aperture
lever. So, if you install an MC lens on the
XD-11, the LED display w o n 't indicate an
automatically programmed f/s to p . You'll
only be able to turn on one LED — the
overrange LED.
You'll also get no diaphragm readout if
you forget to set the smallest f/s to p on
the MD lens. The calibration for the
smallest f/s to p has a green color code.
Since an optical system reflects the
selected calibration into the finder, you
can quickly set the diaphragm fo r the " S "
mode. Simply rotate the diaphragm-
setting ring until the green number ap
pears in the finder, Fig. 4.
Now turn the speed knob to select the
shutter speed you want. As long as the
LED display indicates an f/s to p in the
usable diaphragm range, the camera
delivers the s h u tte r speed yo u 'v e
selected. It then limits how far the
diaphragm can close according to your
selected shutter speed and to the light
conditions.
Since the XD-11 already has shutter-
speed control circuitry, it can go an extra
step to make sure you d o n 't get an incor
rect exposure. Perhaps the camera can't
program the right f/s to p for the particular
combination of light level and shutter
speed. A glance at the LED readout tells
you to select a different shutter speed.
But, if you fail to make the necessary cor
rection, the camera's "co m p u te r" takes
over — it automatically changes the shut
ter speed for you.
The camera lets you know when you're
going to get a shutter speed that's dif
ferent from the one you've selected — it
turns on one of the range-limits LEDS as
you start depressing the release button. If
the overrange LED turns on, you’ll get an
exposure time that's faster than the speed-
knob setting. If the underrange LED turns
on, you'll get an exposure time that's
slower than the speed-knob setting.
To program the diaphragm opening,
the XD-11 controls the movement of the
diaphragm-closing lever, Fig. 5. The
diaphragm-closing lever moves from right
to left before the mirror swings to the tak
ing position. If the diaphragm-closing
lever moves its full distance, it allows the
diaphragm to stop down to the smallest
f/s to p . However, by limiting the move
ment of the diaphragm-closing lever, the
XD-11 selects other aperture sizes.
A combination magnet (permanent
magnet plus electromagnet) limits the
movement of the diaphragm-closing
lever. As the diaphragm-closing lever
starts to move, the permanent magnet
holds its armature. Then, when the
diaphragm reaches the proper opening
size, the circuit discharges a capacitor
through the coil that's wound around the
permanent-magnet core. The spurt of
current momentarily disables the perma
nent magnet.
Now the armature of the combination
magnet jumps away from the core. And
the pawl-shaped end of the armature
engages the ratchet teeth of a gear which
rotates as the diaphragm-closing lever
moves. Stopping the rotation of the gear
also stops the m ovem ent o f the
diaphragm-closing lever.
In turn, the diaphragm-closing lever
stops the spring-loaded diaphragm from
closing any further. A t the other settings
of the mode selector, the capacitor never
discharges through the coil of the com
bination magnet. As a result, the
diaphragm-closing lever always moves its
full distance. And the diaphragm stops
down to the f/s to p you've selected on the
diaphragm-setting ring.
The third setting of the mode selector
— the " M " setting, Fig. 2 — provides
manually calibrated shutter speeds. W ith
the mode selector at " M , " the shutter
always delivers the selected shutter
speed. The LED display now serves as a
cross-coupled meter; it tells you what
shutter speed will provide proper ex
posure according to the light conditions
and to the diaphragm setting. Also, as
you turn the mode selector from the " A "
position to the " M " position, the
viewfinder mask uncovers the shutter-
speed calibration in the finder, Fig. 4.
Although the speeds are manually
selected at the " M " mode, they're still
electronically controlled. Consequently,
all three functions depend on battery
power. In fact, even the shutter release
requires battery power. A second com
bination magnet in the XD-11 releases the
mirror when you push the release button
far enough to close the release switch.
The XD-11 uses tw o S-76 silver-oxide
batteries housed at the bottom of the
camera. W hat if the batteries die? You'll
then find that the shutter w o n 't release.
But the XD-11 does provide tw o
mechanical settings — " B " and " 0 , " Fig.
2. A t the " B " setting, the shutter delivers
a mechanically controlled bulb action. A
mechanical system then releases the mir
ror. A t the " 0 " setting, the shutter
mechanically delivers the fastest full-
aperture shutter speed — 1/100 second.
So, if the batteries die, you can turn the
speed knob to " 0 " and continue using
the camera w ith electronic flash.
The electronically controlled " X " set
ting also provides the flash speed of
1/100 second. However, the " X " setting
does depend on battery power — both
fo r the electromagnetic release and for
Figure 5
Figure 6 Front-plate/m irror-cage/shutter assembly
