If the 420EX receiver unit is not used for about 10 minutes, the SE mode will take effect (indicated by a blinking channel No.) automatically to turn off the power . Pressing the sender unit's test firing button within 30 minutes after the SE mode starts will turn the receiver unit back on.
With the 420EX attached to a camera body equipped with a depth of field preview button, you can fire a modeling flash to check the shadow effects on the flash or the lighting balance in the wireless flash system before you take the picture. Set the wireless selector to the <SLAVE> setting
The batteries are installed in the wrong orientation Install the batteries in the correct orientation The Speedlite's batteries are exhausted If the flash recycling time takes 30 sec. or longer, replace the batteries. Install the Speedlite's batteries even when you use an external power source
If the lens focal length is 105mm or longer, the 105 autozoom position indicator lights When the wireless selector is set to <SLAVE> the flash coverage is set automatically to 24mm
