filmscanners: Shutter sync speeds - WAS : Pixels per inch vs DPI

["Austin Franklin" <darkroom@ix.netcom.com>]

> > That is certainly not the case with vertical shutters, which
> all but one of
> > my 35mm cameras have (Contaxes and Nikons), the exception being
> my Leica M.
> >
> It _is_ related to the synch speed,

I'm not convinced this is true with all FP cameras.  It may very well be,
and it does make sense.  That's why I asked if anyone could provide a
reference for this.

> because electronic flash is
> so fast that
> it needs the entire image area exposed when the flash goes off.

That is a given.

> If the camera
> speed is set above the synch speed, then the "moving slit" effect
> means that
> only that portion of the film exposed by the "slit" at the moment
> of flash
> will get the benefits of the flash.

I have no problem with that.

> The maximum synch speed is set at a value at which the leading
> shutter blind
> has completed it's run across the film before the following blind starts
> moving.

I agree with that, but that doesn't mean that possibly some speed(s) above
the max sync speed don't also have the film gate fully exposed for some
time...that's the part I'm not convinced is a given.  It certainly makes
sense though.  I certainly agree that all speeds at the sync speed and below
do have the film gate fully exposed.

> Cameras with an inter-lens shutter do not suffer with this
> problem, as
> the shutter opens and shuts with a single action, avoiding the
> "moving slit"
> effect.

Of course (I intentionally shoot leaf shutters at times for this reason,
that's how one does daylight fill flash effectively).