Canon Speedlite 420EX - Manual (Page 20)

You can also use E-TTL autoflash with the camera set to <Av> (aperture-
priority AE), <Tv> (shutter speed-priority AE), or <M> (manual).
Shutter Speed and Aperture Settings According to Mode
Flash in Other Picture-Taking Modes
Mode Shutter Speed Flash Aperture
P (Program AE) Automatically set (1/60 sec. - 1/x sec.) Automatically set
Av (Aperture-priority AE) Automatically set (30 sec. - 1/x sec.) Manually set
Tv (Shutter speed-priority AE) Manually set (30 sec. - 1/x sec.) Automatically set
M (Manual) Manually set (buLb, 30 sec. - 1/x sec.) Manually set
Manually set: Set by you.
Automatically set: Set by the camera.
1/x sec.: Camera’s fastest sync speed, (-»page 52)
When you press the shutter button completely, a preflash is fired immediately
before the main flash is fired for the picture taken. The preflash is used to obtain
subject brightness information to determine the optimum output of the main flash.
The background exposure is set according to the shutter speed and aperture
combination.
- While the 420EX's main switch is on, the E-TTL indicator lights automatically when
you press the camera's shutter button halfway.
Q If flash is used in the <DEP> (depth-of-field AE) mode, it will be the same as
using flash in the <P> (Program AE) mode.
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