Canon Canovision8 E50E Service Manual page 42

2. New Technologies
2-1 Automatic backlight correction
Conceptual scheme of automatic
backlight correction
Characteristic of compressing circuit
,Non-compressed
is) 50 100 150 200 Input (%)
Fig. 1-3 Fig. i-4
Fig. 1-5 presents the block diagram of auto backlight correcting circuit, Under a backlight con-
dition with bright background, a luminancé signal attained through spot metering on the iris is
compressed to suppress closure of the iris, Thus, the backlight correction is accomplished by,
keeping the iris slightly wider that in the center-emphasis averaging photometry (conventional
approach). Since this automatic backlight correcting mechanism carries out backlight correction
using a luminance signal obtained from spot exposure metering, closure of the iris is slightly
suppressed also when the subject is illuminated with a spot of light (resulting in slightly exces-
sive exposure). .
Block diagram ct sutomatic backlight correcting circus
t
LENS IRIS _—— a Be oo |
C ut | ve i
cco + S/H
n
ep
MAGE
opp 18 METER
162203 | enous al
ty
I
1
t
ALC
GATE
1 pe comorenss
Comores ator
I
rt
py
=== mr | GATE 2
Wide blanking pulse
i
Wide blanking pulse
Fig. I-5