Rear-curtain flash - why does it flash before as well?

[sOnIc]

Hello .. say you're in a dark night-club environment and want to do a 1 second blur/trail with a flash-lit portrait at the end - with the D3200 I'm getting a flash before the 1 second exposure; and also a flash at the end as well. Example being a portrait of a DJ; you turn/zoom the camera during the 1 second exposure to get an arty light trail, but the rear-curtain flash captures a perfect portrait on top at the end. This is using full manual mode with the flash opened up and Rear-flash selected. Why the first flash?

 

[nickt]

I think that is your ttl preflash determining how much power is needed. Normally you don't notice it with front curtain, but now there is a delay before the main flash. If it distracts and makes people turn their heads you can set the flash to manual in the menu and it will stop, but no idea how much power to set. Wayne can probably help you with that or just experiment.

 

[WayneF]

Yes, the first flash is the TTL preflash, used to meter the scene for the flash. It occurs just before the shutter opens, so it does not affect the scene lighting. You are only aware of it because of the one second delay until the rear curtain sync. You can suppress the first flash by selecting manual flash mode (no TTL preflash).

 

[sOnIc]

Ok thank you both for that : ) I'll try without. I'm also very concious of the auto-focus assist light these days so I'm going to try running without that for a while, tricky in low light conditions obviously .. I'm concerned about annoying people, "Really enjoyed the fire show, except that idiot and his flashing lights all the way through it!".