2nd curtain sync

[amcorona]

I was looking at this site to find out more about the EX flashes.

http://web.canon.jp/Imaging/flashwork/

On the second curtain sync page, it states the flash will fire while the curtain is closing.
http://web.canon.jp/Imaging/flashwork/functions/curtain/index.html

When I try the same, my 420EX actually fires twice. Once when the shutter is depressed and once again before is closes. Is that normal?

[tiha]

Yes - the first flash is actually a preflash used for determining flash exposure and second one (fired when shutter begins to close) is the "real" flash. If exposure is short enough they look like single flash.

[scottbergerphoto]

Yes - the first flash is actually a preflash used for determining flash exposure and second one (fired when shutter begins to close) is the "real" flash. If exposure is short enough they look like single flash.

Xactly! The preflash is more noticeable in 2nd curtain sync, especially when the exposure is longer because the actual flash isn't going off until the end of the exposure. The pre flash always goes off just before the shutter opens.