Minolta XG7 - Page 22

16
Each mode of XG is described in accordance with the block diagram.
|Manual resistor] {Override| [Film sensitivity]
i= it I
Indication Calculation Photoelectric | Brightness of scene |
circuit circuit converter
| LED in finder | STY
Release A.M
circuit
} s
Voltage detecting |_| {
=
Logarithmic
Mode
selector
circuit
Exclusive
strobo
ee expansion
B.C circuit
Control
circuit B.X
Self-indication
circuit
Control
} magnet
|_| Indication LEI)
Reset
switch
®@ Automatic exposure control system
1. Metering system
In the auto exposure control system of XG, the film sensitivity, aperture, and exposure
correction value are preset. The exposure time is automatically determined according
to these values and the brightness of the scene to achieve the appropriate exposure.
When metering switch (S, or Sy) is turned on, the film sensitivity and exposure
correction values are mechanically added, and the values are converted into resistances,
making the rotating angle constant per step, and the aperture value is also converted
into a resistance value (logarithmic operation). These electrical amounts (resistances)
and the brightness of the scene are treated by the photoelectric converter consisting
two CdS and resistors, and the resultant electrical amount (resistance) is put into
the calculation circuit. (The converted value (brightness of scene) is subjected to
logarithmic compression during calculation.)
The result of calculation is an electrical amount (voltage) corresponding to the expo-
sure time, which is charged into condenser (C,). Then, the exposure time is indicated
in the finder by LED through the indication circuit.
The calculation in the above is as follows:
TV : Shutter speed
BV : Brightness of scene
TV- (BV-—AV,)+SV-P AV._: Max. aperture value
SV : Film sensitivity
P : Number of steps for set aperture