Canon 155 A - Manual (Page 33)

there may be a very rare occurrence
where the pilot lamp will light up while
the shutter is in operation if the flash is
charged. If this should happen, the frame
will be improperly exposed.
Precautions in Automatic Flash Photography
In some cases AE flash photography may
not be suited to your subject. If, for instance,
your main subject is small while the back­
ground is dark or distant or if the background
is whitish or bright with strong reflections,
AE flash exposure may be affected by the
background, causing under- or overexposure.
This can be avoided by switching to manual
flash control.
If using a self-timer, do not press the shutter
release until the pilot lamp glows.
When the shooting distance is less than one
meter, the difference between the optictil
axes of the lens and the flash may result