How automatic flash control works – Canon 577 G User Manual

Page 13

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HOW AUTOMATIC FLASH

CONTROL WORKS

The 577G’s sensor acts something

the

camera’s

photocell;

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 Setting

Full Autoflash

A-1.AE-1 PROGRAM,

AE-1, New F-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, New F-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.