Canon Speedlite 420EX Instruction Manual page 35

: TTL Autoflash and Aperture-Priority AE
When you want to control the depth of field or when you want both the
subject and background exposed correctly, use aperture-priority AE. You
set the aperture, and the camera sets the shutter speed automatically to
expose the background correctly. The TTL autoflash exposure is based on
the aperture you set.
A
v
In low-light conditions, a slow sync speed is set automatically. A tripod is
recommended for slow sync speeds.
If the camera's fastest sync speed blinks, the background will be overexposed. If
the sync speed blinks, the background will be underexposed. Change the
aperture setting until the sync speed stops blinking.
Flash in Other Picture-Taking Modes
1
Set the camera to <
priority AE).
2 Set the desired aperture.
• Turn the camera's electronic dial to
set the aperture.
3 Take the picture.
• Focus the subject, check that the
< > icon is lit in the viewfinder, then
take the picture.
> (aperture-
35