That makes sense, thanks Chuck.
On Wed, Jun 18, 2008 at 4:52 AM, Chuck Norcutt <
chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
> It's necessary for the scanner to focus on the film and, more
> specifically, focus on the emulsion side of the film. The scanner could
> have a fixed focus position if all film was perfectly flat or all slide
> mounts were exactly the same thickness but that's not true. The scanner
> lens does have some depth of field but it is very shallow. If the film
> is curved the center and edges will be at different distances and the
> scanner may have to focus to find the best compromise.
>
> Most flatbed scanners typically have much greater depth of field,
> perhaps 10mm or more. You can see this if you scan a three-dimensional
> object. I don't think focusing is necessary on a flatbed.
>
> Chuck Norcutt
>
> Komtanoo Pinpimai wrote:
> > I'm always curious what autofocus in scanner is actually mean because
> when
> > we take a photo,
> > we already have made focus on the camera lens, why do we need to do it
> > another time when scanning.
> >
> > I bought Minolta Dual IV film scanner years ago. On the spec, it's
> supposed
> > to support autofocus,
> > but when I enable it and scan with its software, it usually stopped
> scanning
> > and freezes the process, the same happened with vuescan.
> > I guess it's probably hardware or driver issue, I didn't bother returning
> it
> > but turned the autoscan off, since then.
> > The output of scanning is pretty okay, no weird blurring, or sign of
> > out-of-focus which makes me more curious of how
> > autofocus in scanning is supposed to improve my images.
> >
> > It also sounds like autofocus in film scanner makes more sense than
> flatbed
> > because we can place a film any where on flatbed scanner. It shouldn't
> know
> > how to autofocus.
> > So, another of my guess is scanning film on flatbed scanner cannot do
> > autofocus, am I right ?
> >
> >
> >
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