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Re: filmscanners: Pixels per inch vs DPI

"B.Rumary" wrote:

> Austin Franklin wrote:
> > > As many people probably realize, in a typical rear curtain/focal plane
> > > film cameras (as most 35mm SLRs are), any shutter speed beyond the
> > > maximum flash synch shutter speed exposes the film via a moving slit
> > > opening between the shutter curtains.
> >
> > I know what you say CAN be certainly true for the highest speeds of some
> > cameras, but I did not know it was specifically related to the synch
> > speed...I believe it's more related to shutter design than specifically tied
> > to sync speed.  Would you mind citing a source for that information?
> >
> > 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, because electronic flash is so fast that
> it needs the entire image area exposed when the flash goes off. 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. The "flash-lighted" area will then be
> correctly exposed, while the non-lit area will be heavily under-exposed.
> Note this only applies to electronic flash guns, which give very short
> duration flashes - typically 1/30,000 sec. The old fashioned flash bulbs
> "burn" much more slowly and give light for long enough for the "slit" to do
> it's full run across the film.

I think you will find that very few, if any, flashes are of such a short 
duration.  It has been my experience
that the difference between, a 250th, 125th and 60th of a second exposure and 
almost any brand electronic
flash will yield very different film exposures, no matter what type of shutter 
you are using.

Harvey Ferdschneiderpartne
partner, SKID photography, NYC


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