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P3D Re: RE: Scanning


  • From: "Greg Wageman" <gjw@xxxxxxxxxx>
  • Subject: P3D Re: RE: Scanning
  • Date: Thu, 30 Sep 1999 15:16:52 -0600


From: Green, Dennis (D.H.) <dgreen16@xxxxxxxxxxx>


>I, too, am interested in scanning stereo slides, and I would like to
>understand better what is involved.  When I picture scanning a slide in
an
>HP scanner, I envision inserting the slide in its mount from one end,
>selecting the image in some kind of preview window and scanning it.
For the
>opposite chip I would rotate the slide to the other end, select the
image
>again (which would be upside-down compared to the first chip) and
scanning,
>then rotating the chip 180 degrees so that both were right-side-up.  I
>assume that the "windows" of the slide are square to the top and bottom
>edges, so a rotation error is something I wouldn't expect.  Am I making
a
>bad assumption?


The procedure you describe is sensible.  However, what you overlook is
the fact that slide scanners are made to accept 2x2 mounts (50.8 mm
height).  The 41 mm height of a Realist mount leaves considerable play
in such scanners, making rotational errors quite frequent.

To scan Realist slides in my Nikon Coolscan II, I made a simple jig out
of 2mm thick sheet styrene from a model shop.  I used a 2x2 slide as a
template to measure width, and a Realist mount as a template to cut out
the interior.  This leaves a rectangular frame that a Realist mount will
pop into, which has the exterior dimension of a 2x2 slide.

My first (and only, so far) attempt produced a jig with a six degree
rotation error.  That sounds like a lot, but it isn't obvious to the
naked eye when looking at the jig.  However, you certainly wouldn't want
a 12 degree rotation error in your stereo scans!  The good news is that
this rotation is fixed, so once you determine the amount by
trial-and-error, you just counter-rotate the scanned image to remove it.

>Also, what other problems would occur?


Image loss and fuzzy mount edges are the biggest problems I run into.
Image loss because the apertures of most slide mounts aren't
rectilinear, but are filleted in the corners.  Unless you can live with
the resulting round black corners in your scans, you have to crop.
Paper mounts often produce intolerable black fuzz, again requiring
cropping.  Really, the "right" way to do it would be to remove the slide
from its mount, scan, and re-mount, but I'm too lazy to do that.

>I've seen a lot of stereo photos on the web.  What successful practices
are
>used by those who post those photos?


My gallery at Vrex's 3D Expo was scanned from separate 2x2's, so that
probably doesn't help you, but I have images on disk scanned using the
jig described above which are equally good, IMO.

     -Greg W. (gjw@xxxxxxxxxx)