P3D Re: Zoom lenses on Ektagraphics (hijacked from Sell 3D)

["Greg Wageman" <gjw@xxxxxxxxxx>]

From: Greg Dinkins <dinkins@xxxxxxxx>


>I have little experience with 2x2 projection, (like 6 times), but I'm
>chipping into the discussion because all those experiences were in
different
>places and the zoom offered a nice accommodation for different screen
sizes,
>different throw, etc. in 4 of those cases. I had no problem setting the
two
>4-6 inch zoom lenses to match on 4 and 5 foot screens, viewed from
about 10
>feet away. Two times we were using a Wess alignment slide and that made
>setup easier.  As far as the two polarizers' orientation, the zoom
>magnification was set once as we set up for projection of the widest
image,
>then the polarizers were simply taped to the front of the lenses.
Focusing
>during projection did not affect orientation of the polarizers.
>
>Greg, I wonder if you've personally had problems matching zoom sizes?
Or are
>you relying on good advice from AV professionals whose philosophy is to
>eliminate variables in projection?


I'm simply speaking as a potential audience member who knows how painful
a bad stereoscopic presentation can be, as well as how excellent a good
one can be (Bob Bloomberg's at the Exploratorium, the many fine examples
at NSA '97, etc.), as well as a 2x2x2 user.

If the proper care is taken (several posts have mentioned the use of an
alignment slide which I would deem essential), it can no doubt be made
to work, but this is not something that I would want to have to do every
time I wanted to project some slides at home (i.e. set up projectors,
set up screen, match zoom settings, affix polarizers, re-affix
polarizers to fix ghosting, round up [or wake up] audience...).  If I
were setting up a multi-projector show like some of the ones I alluded
to above, I wouldn't want the extra task of aligning umpteen zooms,
certainly not with external polarizers added to the equation.  Being
forced to use internal (i.e. behind-the-slide) polarization may make
some slides (but certainly not all, or even most) unprojectable.

Fixed-focal-length, flat-field lenses are readily available in a
selection of focal lengths for all Ektagraphic/Carousel projectors and
they are not very expensive (B&H lists 85mm/2.8 for $55, 100mm/2.8 for
$48, 180mm/3.5 for $100; compare with 75-120mm/3.5 for $72 or
100mm-200mm/3.5 for $176).  As pointed out, they are usually faster than
zooms, which is particularly valuable in stereo projection with its
inherent loss of illumination due to the polarizing filters.

But as you say, zooms have their advantages where you can't control the
projector-to-screen distance as you might otherwise like.

     -Greg W. (gjw@xxxxxxxxxx)




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