Canon 577 G - Manual (Page 27)

MANUAL FLASH
PHOTOGRAPHY
Setting the flash mode switch on the
back of the 577G to MANU puts the
unit on manual operation. While on
automatic the 577G’s sensor auto­
matically cuts off the flash duration
at the correct point, on manual the
flash operates at maximum dura­
tion for every firing. The shutter
speed should be set as usual (p. 12),
but the correct aperture can no
longer be found with the unit’s cal­
culator dial. Instead, it must be cal­
culated using a guide number for­
mula, which follows:
f/stop =
Guide Number
Shooting distance
Since the guide number changes
with film speed, the 577G is provided
with a sticker which gives the guide
numbers in meters for various ASA
film speeds. Guide numbers are also
given for when a Tele Adapter 577G
or Wide Adapter 577G-24 or 577G-
20 is attached. The sticker should be
attached to a convenient place on
the flash unit, such as on the under­
side of theflashhead.
Since these guide numbers are ex­
pressed in meters, the shooting dis­
tance in the guide number formula
should also be in meters. When the
flash is used normally, pointed
straight at the subject and neither
tilted or swung nor held away from
the camera, the shooting distance
may be read directly from the lens’
distance scale after focusing. If the
flash is held away from the camera,
the shooting distance means the dis­
tance from flash to subject, which
should be measured with a tape
measure if necessary. (Remember
that for holding the flash away from
the camera a synchro cord is
necessary.)
The 577G’s pilot lamp lights up once
the flash has reached sufficient
charge, which does not mean that it
is fully charged yet. While compen­
sation for this is automatic when the
flash is on automatic operation, it is
not when the flash is on manual.
Therefore, it is necessary to wait for
about 15 seconds after the pilot
lamp lights (i.e., until the flash re­
aches maximum charge), before you
press the shutter button. If you are
not using new or fully charged bat­
teries, it will be necessary to wait
longer. If it is absolutely necessary to
fire the flash immediately after the
pilot lamp glows, open the lens
around one f/stop to make up for the
fact that the flash is not yet fully
charged.
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