How Automatic Flash Control Works - Canon SPPEDLITE 577G Instructions Manual

HOW AUTOMATIC FLASH
CONTROL WORKS
The 577G's sensor acts something
like the camera's photocell; it
measures the intensity of light from
the flash which is reflected back from
the subject. When it decides that the
subject has received enough light, it
automatically cuts off flash emission.
In order to do this properly, the
sensor must, like a camera's photo¬
cell, be as close to the film as possi¬
ble and facing the subject. Since the
577G's sensor is separate in the
camera's accessory shoe, it is always
in the best position to measure the
light correctly even while the flash
unit itself can be aimed in many dif¬
ferent directions for the best lighting
effect.
Flash Mode Camera
Shutter Speed
Setting
Aperture Settir>g
-
1
Full Autoflash
A-1,AE-1 PROGRAM.
AE-1, NewF-1 (Shutter-
Priority AE Mode)
Automatically switches
to X-sync unless on
"B"
Automatic (When
using FD lens set on
"A" mark)
Automatic
Shutter Setting
Autoflash
AL-1,AV-1, NewF-1
(Aperture-Priority AE
or Manual Mode)
Automatically switches
to X-sync unless on
"B"
Manual
Normal
Autoflash
F-1 or other
cameras
.
Manual
(to X-sync)
Manual
To make its decision on when the
subject has received enough light,
the sensor must know three things:
1) the film speed, 2) the aperture and
3) the shutter speed. You must
always set the ASA film speed on the
flash by hand, but depending on the
camera you use, the flash may set
the aperture, the shutter speed or
both automatically. The table on the
left shows the various ways that the
aperture and shutter speed may be
set with various cameras.
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