Date: Tue, 12 Oct 1999
IMAX 3D Imaging Theaters
Thomas M. Miovas, Jr.
Sometimes knowing something about physics and paleontology can
make one's movie entertainment even more enjoyable. A friend and
myself recently attended the new IMAX 3D theater in Dallas where
we watched "T-Rex: Back to the Cretaceous." I had wanted to see
this for quite some time, but as the theater just opened, the
crowds were packing in. I didn't think much of the story, but I
was curious about seeing a 3D movie on a screen that is seven
stories tall and wide screen at that.
We were given special glasses to see the effects, and they
weren't the usual red and blue lenses one might have used at
previous 3D movies. The lenses were polarized -- one in the
horizontal plane and one in the vertical plane (meaning light
vibrating up and down could be filtered from light vibrating
left to right). Two images are projected onto the screen, each
one being filtered by one of the lenses and the other by the
other. When the two images are processed by the optical
pathways, a spectacular three dimensional image is produced.
Some of the imagery is so realistic, one believes the objects to
be right in front one's face, even if one is sitting 30 feet or
so away from the screen.
The warm-up cartoon had some characters running around with
buckets of paint that get spilled; the contents then float
around as if in zero-g. I actually reached my hand out and it
seemed to disappear behind the blobs of paint! Of course, the
paint blobs had no reaction to meeting my hand -- we are a bit
away from the holideck of Star Trek -- but it was
extraordinarily realistic. When the movie started, I was
impressed by the illusion that one would be able to walk right
into the set. When the paleontologists were chipping away at
their rocks in extreme close-up view, one swore the chips were
bouncing off the audiences' heads! And the dinosaurs! Someone
went through a great deal of trouble to make them very
realistic, including pulsating blood vessels under their skin.
The T-Rex seemed to chomp away one aisle in front of me, making
me glad I was out of reach ;) Oh, and if you see this movie, the
small dinosaur eating the T-Rex eggs is the real life-size of
the veloceraptor, about four feet tall at the head -- "Jurassic
Park" made them about three times normal height to make them
more scary.
There are some drawbacks to this system. One nuisance is that
one has to keep one's head horizontal, or the two images begin
to separate. Another one is that objects moving in relation to
the background tend to fuzz out and get jerky; but one gets this
in regular movies, too, because the number of frames per second
just isn't high enough to capture a solid looking moving image.
The only exception to the fuzzy motion were the computer
generated dinosaurs, making them more realistic than the human
actors at times. Overall, it was worth the higher-than-usual
price of admission.
It was easy to confirm that the glasses were polarized, as I
borrowed my friend's set and put one lens in front of the other
and rotated them. Sure enough, the lenses got lighter and
darker. But I don't know how one image was vertically polarized
while the other was horizontally polarized. As I understand it,
all reflected light is circularly polarized (meaning it tends to
vibrate in every plane perpendicular to the direction of
travel). That's how polarized sun glasses filter out glare, they
only let light vibrating in one plane come through the lens,
removing a large percentage of reflected light. Since the two
images were reflected off the screen, as far as I know, each of
the two images had to be circularly polarized, but it didn't
seem to act that way. Maybe the screen was made of a special
thread (IMAX screens are not solid, as are regular movie
screens, but are made of a mesh, like woven cloth); or maybe it
works because the threads are woven horizontal and vertical. I'm
not sure exactly how it works, but I know it works very well.
