Nicolas Calimet wrote:
> 
> Warp wrote:
> >
> > Christoph Hormann <Chr### [at] schunteretctu-bsde> wrote:
> > : Quite right about the motion blur, but when combining flash with long exposure
> > : times in photography, you can achieve an effect similar to the one you
> > : criticise.  Of course that's a rare occasion, and would require the main light
> > : source being near the camera, but i wanted to mention it.
> >
> >   Should I mention this? If yes, could you write a more specific description
> > of the phenomenon?
> 
>         If the shutter of the camera is open for a relatively long time (say
> for instance one second) and that a bright light flashes the scene for a
> short interval (i.e about 1/1000 of a second), this will "fix" the moving
> objects due to their higher brightness at that time. In photography it is
> more common to flash the scene just before closing the shutter to give a
> "fixed" object with a dimmed trace behind (for better composition) or to
> flash several times to give different snapshots of a moving object on a
> single photo (as when studying human walk). There may have others examples
> of using this effect, called "slow synchronization" from my french vocabu-
> lary ;-)

Right, and there are two ways to obtain this effect, depending on if you
fire the flash just after opening the shutter (front curtain sync), or
just before closing (rear curtain). An example can be found at:

http://www.minolta.com/camera/dynax7_img/synchro.gif

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