[photo-3d] Re: Spicer mounting problems

[Ralph Johnston/Linda Sherman <copley@xxxxxxxxxxxxxxx>]

My thinking now is that the Brackett Fader projector needs adjusting.  Bob
Brackett offered to adjust the spring tension after this Sunday's Stereo New
England meeting.  The slide is held against two wide upper rails by two
narrower springs at the bottom of the slide.  If these are not matched one end
of the slide may bow more than the other end.  I get up to 1" vertical
error in
the window outlines out of 20" so this is pretty bad.  It may also depend on
how tight the tape is across the bottom.  Maybe it isn't as tight on one
end as
on the other.  If that is the problem, then adjusting the spring tension won't
help.

I measured 10 mounts folded but not taped and could not see any difference end
to end.  But after mounting, taping, and projecting I could.  That is why I
had
to add the scotch tape on the right image.

More later on this subject.  I would like to keep using the Spicers if at all
possible.

Regards -Ralph




>
> Message: 8
>    Date: Tue, 12 Sep 2000 21:58:59 -0500
>    From: Paul Talbot <list_post@xxxxxxxxx>
> Subject: Re: Spicer mounting problems
>
> Ralph Johnston/Linda Sherman wrote:
> > 
> > I mounted a few recent rolls of RBT 8-perf slides in Spicer wide 8perf
> > mounts.
> > They look great in a viewer, but when projected in a Brackett fader
> projector,
> > had vertical alignment problems.  About 1/4 of the slides had an inch of
> > vertical error on the screen.  (The image was about 20 x 30") [snip]
> > Then I measured the slide  with a
> > digital caliper and found that it was tapered!  One end was 40.0mm while
> the
> > other end was 39.9mm.  Or one end was 40.0 and the other 40.1mm.
>
> Ralph, the observed error appears to be due to something other than the
> mounts.
>
> First let me point out that manufacturing tolerances are going to be
> some non-zero value for any mount.  If you've ever had some of those
> RBT mounts that don't securely hold the pin bars in place, you know
> that even the most expensive mount on the market is not made to zero
> tolerance.  (I submitted an RBT-mounted slide to a competition and by
> the time it arrived one chip was not even completely visible inside the
> aperture window anymore, due to the pin bar shifting inside the mount.)
> I previously mentioned that our new mounts were spec'd to .003" precision
> (about .076 mm).  So 0.1mm manufacturing deviation is plausible for any
> cardboard mount.  Deviations for plastic or aluminum could conceivably be
> a bit less, but that comes at a significant cost!
>
> Second, there seems to be a problem with the math of the above analysis.
> Spicer extra-wide mounts are full height (23 mm).  If the image was
> projected to a height of twenty inches, the magnification factor was
> about 22x.  Mutliplying the magnification factor by the measured size
> differential of 0.1mm yields a possible on-screen effect from the
> manufacturing tolerance of only 2.2mm.  That is less than 9% of the
> on-screen error that you observed!  There clearly must be some other
> factor at work here to result in eleven times as much deviation as can
> be attibutable to manufacturing variations in the mounts.
>
> Perhaps you could investigate further and let us know what else is going
> on to cause the observed error.
>
> Paul Talbot
>
>
> _______________________________________________________


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