D3 rear flash question

[Hamish Gill]

I seem to still have an issue with the d3...
Set to rear flash it fires the flash as the shutter opens and closes ... Am I being stupid?
It does this with both sb600 and sb900!

 

[Pete Askew]

Isn't the first just the pre-flash used to calculate power etc. You just don't notice it with front curtain 'cos the 'gap' between is too short.

 

[Hamish Gill]

... hmmm ill experiment ... not from what i have seen before ... but i may be being silly!