2nd Curtain Sync question

[alloy]

I was playing around with the 2nd curtain sync feature at different shutter speed when i realised that the flash emits 2 burst when the shutter speed gets rather low (2 sec), cannot see the difference at higher speed of 1/60 and above . It emits 1 flash in sync with the 1st shutter curtain then another at the 2nd curtain. I thought the flash is suppose to go off only at the 2nd curtain? I have read the manual already but no mention of 2 flash outputs at all.
Wont 2 outputs end up with the subject being "captured" twice or does it?

Thank u for ur advises

 

[StreetShooter]

Actually there are always 2 flashes - the pre-flash (used by the E-TTL system to calculate the actual exposure) followed by the actual flash, during the exposure.

In first curtain sync, the actual flash always immediately follows the pre-flash, so you never notice that there are 2 flashes, because the interval is too short for the human eye to notice (but if you use an external flash on the G2/G3/G5, you will be able to notice a double flash).

In second curtain sync, the pre-flash will fire as usual, but the actual flash will fire only when the shutter is about to close. If the shutter speed is fast, the interval is too short for you to notice. If the shutter speed is slow (as you have noticed), you will see the preflash fire first, followed by the actual flash when the shutter finally closes. Try this at 1s or 2s shutter speed. Or you can set it at 4s shutter speed and switch off the flash before the second flash fires. When you look at the picture, it will be very underexposed because the pre-flash does not illuminate the exposure. Not sure if this will damage anything, though, so try it only at your own risk.

 

[alloy]

Oh yah hor!! :bsmilie: Haiz why didnt i think of that. I was jus reading about halfway through ur reply when it suddenly all makes sense to me. If im not mistaken u meant that for 2nd curtain sync, the 1st flash that was emitted is being used to calculate the output amount and the 2nd flash thats being emitted is the actual flash that captures the image. Actually this also applies to the usual 1st curtain sync jus that for 2nd curtain sync the pre flash and the actual flash gets separated in accordance to the duration of the shutter speed. So when the shutter speed is real slow the two flash outputs can be seen separated for the duration of the shutter speed period as we will be able to see it. If shutter speed is high, even though the same thing is happening we wont be able to see it as the duration is too short for us to notice it jus the usual preflash from the 1st curtain sync.

Thank u streetshooter. U have been really helpful and detailed in ur explanation.