RE: filmscanners: Scanwit: Seeing through mount?

["Frank Nichols" <frank@theNichols.net>]

Mark,

The ascii art reflects the mount and film correctly as I saw it under the
scope. But I still think I am seeing image in the ccc area. However, you may
be correct, and I agree turning it around will prove the point. I didn't
crop anything off of the right side, but vuescan may have...

I have already shut everything down here tonight - it is 2:00 AM here, so I
will turn it around and rescan tomorrow.

Thanks for the info -

/fn

> -----Original Message-----
> From: owner-filmscanners@halftone.co.uk
> [mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Mark T.
> Sent: Friday, July 13, 2001 11:47 PM
> To: filmscanners@halftone.co.uk
> Subject: RE: filmscanners: Scanwit: Seeing through mount?
>
>
> At 09:36 PM 13/07/01 -0600, Frank wrote:
> > >..you are just seeing a shadow effect where the slide
> > > mount is blocking only some of the light path along the edge.
> >
> >Yup, I took a couple and looked at them under a microscope at
> low power and
> >what you describe is definitely what is happening - one side has
> a slightly
> >smaller aperture. However, this still says the Scanwit is able to "see
> >though" that one smaller side's edge.
>
> I would rephrase that - I think you are still only seeing through
> the film.
> My guess is the wider aperture is on the side of the ccd?  So at the edge
> the ccd sees the film very darkly illuminated from the light
> leaking around
> the inner edge of the mount.  Ie (forgive ASCII art - done in arial,
> probably won't line up very well in other fonts..  :)
>
> | | | |              light source
> | | | |
> | | | | =====   slide mount (smaller aperture)
> | | | \ \ \          leaking light!
> =========  film
>
>             ===   slide mount (wider aperture)
> ++++++++    ccd sensor
> aa  bbb ccc
>
> (I've left out lenses and other unnecessary items!)
>
> So at aa you see your normal image, at bbb you see a weakly
> illuminated bit
> of image,  and at ccc it should be black (probably cropped out of your
> sample).  To check this theory, just turn the slide around - I reckon the
> edges will be black.
>
> >And what the result seems to be is that area has higher contrast with no
> >more noise than the film area next to
> >it.
>
> But do you *want* higher contrast?  I played with your image, and by
> selectively fiddling with the different areas, couldn't see any real
> advantage to the darker area - in fact if anything, the reverse.
> Is this a
> Provia slide by the way?  If it is, then it looks like your
> scanner is like
> mine - I find the noise is just far enough below the max density of most
> slides to not be a problem, but some Provia's, Velvias and
> K-Chromes start
> to push the envelope..
>
> >I think the bottom line is that my next scanner will definitely have a
> >manual exposure mode!
>
> Agreed.  But for the market the Scanwit is aimed at, I can
> understand their
> thinking...
>
> MarkT.
>