You have two eyes.
This gives you a chance to experience
depth perception
as you triangulate the position of objects
lets you know how far away they are. But
there's a lot of 3d vision that can be
experienced with just
one eye. For example close one eye
and look at your finger right in front
of your face, then
at something that's far away and then
look at your finger again,
and then and that i think that's far away.
And you'll notice
that your finger passes in and out of
focus. Here's another trick.
Close one eye and hold your finger in front of your face again then move your head from
side to side.
You'll notice that the objects that are
closer seem to move more than the
objects that are far away.
That's called parallax. You often witness
parallax when driving around.
The distant objects seem to move a lot
less
than the close ones. This is also how the
distance to stars are measured.
As the earth goes around the Sun the
further away stars
move less. Also sometimes an object seems
closer simply because it's larger
this is called foreshortening. All of the
affects you've seen have been done with
a single eye,
the lens of our camera
But what about 2 eyes? For 3d to be convincing
each eye must see a slightly different
image both in angle
and in parallax. This was achieved more
than a hundred years ago
with photographs taken with two very
close cameras.
It's called a stereogram.  Here is one a
man-eating tiger
doesn't it feel like the Tigers really
there? Now
I can't really show you 3d in this video
but I can explain how it's achieved.
The real trick is in getting each eye to
see something different
on the same screen. These two images are
then blended in the brain
as a single solid 3d object. Try this out.
Hold up both arms in front of your face
and look past them.
This will make a third 3d floating thumb
appear between them.
It looks real and solid doesn't it?
That is a stereogram. Your eyes are like two
cameras assembling a 3d image.
But how do you convince each eye that's
seeing something different than the
other?
The old way was to look through two
separate tubes
at a pair of slightly different
images. Another way is to filter out
which type of light
is getting each eye. Sometimes this is
accomplished by projecting red light
for the right eye and green and blue light
for the left eye.
Later these images are assembled
in the brain. Another method is to
project two images
of individually polarized light. One is
polarized horizontally for one eye
and the other image is polarized
vertically for the other eye. Another problem
is
that you can't turn your head very much
when you're watching the movie. Well that is
unless you have
circularly polarizing sunglasses which do
allow for some head rotation. Ah.
You might wonder why it is so easy to
fool the brain into assembling images.
But that's what the brain does all the
time. It assembles two different images
into one blended reality. Here's an
experiment you can try.
Go to a dim room and bring a
flashlight with you. Then cover 1 eye
and shine the light in the other eye.
The pupil contracts
even though it has not seen any extra
light. The eyes are not individuals
but are permanently linked in the back
of the mind.  The are exciting new
developments in 3d viewing
without glasses. The way it's being done
is there are bars
in the TV that are letting each eye see a
different thing.
So you don't need the glasses anymore. This
technology is new and its not quite ready
yet.
But who knows what the future will hold?
