Canon A-1 Repair Manual page 58

4) Ultra smooth double sided flush surface plate
The aperture control system of the A-l is operat-
ed in the following manner. The brush, that is
driven by the lens aperture signal lever, slides
over the segmented aperture value electrode plate
pattern at a high speed . The number of pulses of
the ON / OFF signals that
a~e
generated at this
time are counted and the f-numbers are digitally
detected.
As the number of pulses are counted by ON/OFF
signals mistaken counts due to - chattering must be
completely eliminated.
So a new technique was incorporated.
In the A-I, a segmented aperture value electrode
plate pattern is formed on a
23~m
(microns)
copper foil plated "TETORON" reinforced epoxy
board . This board is then heated and pressed.
Thus, we succeeded in bri nging the degree of
smoothness of the board to within
5~m
(microns).
With the incorporation of this new technique, macro
chattering no longer aris es and micro-level
chattering is eliminated
~y
newly designed circuitry.
This smoothing process is called the flush
process. Aperture control accuracy is improved
by making the pitch smaller (0.22 mm) of the
segmented aperture value electrode plate with the
employment of high-le vel fine pattern techniques .
The segmented aperture value electrode plate
(positioned on the outer side of the AE unit),
used for this aperture detection, is called the
SAVE (segmented aperture value electrode) plate.
69