I'm not sure you're right...

For effective second curtain synch, the flash needs to
fire =immediately= before the shutter closes.  A
non-dedicated flash gets a signal at some point when
the flash is fully open, but does not know exactly
when the flash opened, or when it will close.  For
second-curtain synch, the flash either needs to know
when the flash opened and the shutter speed, or needs
to get a signal a millisecond or so before the curtain
starts to close.  Those are easily encoded so that
only a dedicated flash "knows", it would seem.

Rick

--- Godfrey DiGiorgi <[EMAIL PROTECTED]> wrote:

> I've never understood why second curtain sync should
> require a  
> dedicated flash unit. HSS I can understand ... it's
> a very careful  
> dance of strobing the flash to precisely match the
> shutter ... but  
> second curtain sync should simply trigger the flash
> some milliseconds  
> prior to the second curtain closing to accommodate a
> reasonably long  
> electronic flash duration. That's what the Sony R1
> and Panasonic L1  
> do ... any flash unit can do second curtain sync
> with them, dedicated  
> or not.
> 
> Godfrey
> 
> On Oct 13, 2007, at 11:17 AM, mike wilson wrote:
> 
> > But digital flash control offers so many other
> things, such as  
> > second curtain sync and, er, .......
> 
> 
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