but these are really amazing it's i'm
gonna do something that i've never done
before in a 60 symbols video i'm going
to invite you brady to come to the
toilet with me let's do it
so we're going to talk about 3d movies
and how do 3d movies and 3d glasses work
what's the technology behind these
things i want to see hugo which is a
wonderful wonderful film before
christmas with my daughters so how does
it work well it's based around what i
guess your first question got to ask is
well why do we have depth perception how
do we how do in the real world do we get
some sense of
brady so far away from me i can sort of
see that he's a solid object rather than
a plane um
where do we get that from the key thing
is we've got obviously got two eyes and
they're separated by certain distance so
both of these eyes see a slightly
different scene and your brain is
unbelievably clever at taking those
different scenes and bringing them
together and giving you that depth
perception so the question then is how
do you get something that's flat on a
screen in a cinema or on a television
and give you that depth perception well
again what you need to do is to have
those
you're
playing different scenes to different
eyes that's the key thing but what you
do is you have um two cameras when
you're filming um the the movie one
camera is filming what goes to the left
eye one karma is filming what goes to
the right eye and you bring those
together and you have a slight offset
which is why um when you take your
glasses off everything looks quite
blurred um on the screen so the
challenge at the cinema is well how do
you take something on a flat screen and
how do you deliver those two separate um
scenes each to one eye how do you how do
you get the the how do you trick the
brain into thinking that scene has got
real depth and the way you do that well
it used to be you may remember some of
the slightly older viewers might
remember that you used to have red and
blue glasses you'd have these tinted
things and you threw in the 80s i think
it goes all the way back to maybe the
the 40s
could be wrong there but i think that
that sort of red and blue approach has
been around a long time and what are
they doing there well what they do is
they basically have red and blue filters
they take the
the the film that one camera is shot and
they take the film that the other camera
is shot one of which has a blue tint the
other which is a red tint and then they
use blue and red um filters to separate
those out so the one that's got the red
tint will come to the the the red eye as
it were and the one that's got the blue
tint we'll call it the blue eye yeah
we've moved on the problem with red and
blue obviously is that you're playing
with the colors you're losing color
definition they look washed out the
depth perception isn't as good actually
with the with the colors and um it's
very problematic
in terms of getting a nice high
definition
movie
so what do we do now well actually what
we do is we play with something called
the polarization of light you've come
across polarization you've come across
polaroid before and polaroid is
basically a thin film i've got some of
it here and in that thin film are lots
and lots of polymer molecules long chain
molecules that are stretched in a
particular direction
and so i'm sure you've seen this before
we take a piece of
polymer unfortunately it's a bit i've
just broken it we'll do it this way um
you're going to take a piece of of
polaroid film if you match them up like
that you can roughly see through it i
guess and then when you turn it together
turn it turn it round through 90 degrees
it blocks the light
why does it do that
okay so we've got to go back i'm afraid
to undergraduate physics a level physics
high school physics
this is going to be tricky to explain at
um at
a non-scientific level but light's a
wave let's start with that
other times it behaves like particles
but for the purposes of this we're going
to take that light as a wave
so light is a wave what is it a wave off
well it's what it is is electromagnetic
wave it's an electric field and a
magnetic field we're going to
concentrate here only in the electric
field because that's all really that
matters
so this thing light's propagating like
that
in that direction now it's got we call
it an electric field vector
and what that basically is is tells us
which direction the electric field's
pointing
so in this case it's propagating that
when the electric field is pointing that
way if we turn it around like that it's
propagating that when the electric field
is pointing that way turn around like
that the electric field is pointing that
way of course this is going back and
forth
gazillions of times a second to use the
technical term that's all you really
need to know you've got this this
characteristic of the wave which tells
you basically in which plane it's
vibrating so what the polaroid does is
when you've got
you've got the lights you've got all the
the light that's in this room and that
light is is basically unpolarized right
that means that that it's it's you've
got some light waves which
are like that some which are like that
so much i like that so much like that
all wide range of different
polarizations so all the lightness room
wasn't um
uh or random but it was actually going
in one direction then what you'd have is
if you align your polaroid in the
direction of the the east of the
electric field
um then what you find is that the light
can get through very simply however if
you rotate it round just like i did with
the polaroid before them
it doesn't get through
and that's
a very very
useful property of light and of certain
materials like polaroid so when i went
to see hugo what what happens is that
you use these glasses so in one side
the simplest version of these
is that on one side we have a polaroid
basically which is aligned like this
and on the other side we have a
polarized or polaroid film which is
aligned like this so what happens is
that you take those two um
different versions of the movie which
are filmed in different cameras and you
polarize you put a polarizer in for each
one of those cameras as it were and that
means that the light coming from the
screen
associated with the left i say is
polarized this way and the light coming
from the screen associated with the
right eye is polarized this way and then
you put these on and now bingo you've
got a way of differentiating
distinguishing between what should be
going to the left eye and what should be
going to the right eye it's very clever
yeah you're watching two movies and once
with slightly different scenes and then
you are using the polarization of the
light coming from the screen to to trick
your brain into thinking well okay what
i'm seeing here is is real life and
therefore it must have a depth
i told a little fib it isn't really
linear polarization here what we
actually have with these glasses and
many of these glasses is something
called circular polarization there
instead of this electric field being in
the plane like this it rotates around so
it's rotating like this
or in the other direction it can be
rotating like this and we call that left
and right circularly polarized light
because if you look if you imagine my
fingers going like this it's traveling
forward but if you just look in this
plane what you see is a circle that
circles either going like that or it's
going like that so the tip
we described in terms of a vector an
electric field vector which rotates
around that would have looked so good if
we were filming in 3d oh it would have
looked really good yes but it's the same
it's the same principle so you can have
left and right circularly polarized like
you might argue but what does this now
look like so so what that well you you
getting tricky brady because what you
have to do to convert circuit what you
do is you take that circularly polarized
light and you convert it to linear
polarized light and then you use the
same approach where does the conversion
happen the conversion happens here
you've basically got within the glasses
you've got um you've got the polarizer
but you've also got something that
converts that circularly polarized light
to linearly polarized light so why are
you adding that complexity then what
because for various reasons i'm not
going to go into here
um
unless we want to make an hour-long
video
uh there's various advantages to having
circularly polarized light in terms of
the ability to move your head around to
keep the the depth um while you have
your head at different angles which you
don't get from linear polarization but
these are really amazing it's i'm going
to do something that i've never done
before in a 60 symbols video i'm going
to invite you brady to come to the
toilet with me
i've told you about circular
polarization now one of the remarkable
things with murders
is that a mirror will convert
right circularly polarized light so
light that's going say this direction
into the other direction
so when it when that
light which is polarizing a particular
um
handedness as we call it right or left
hits the mirror it gets converted from
right-handed to left-handed now that's
really amazing because
now when we look at these and i invite
you to do this at home it's really quite
quite neat and i'll certainly be
bringing these home and doing it with
i'm showing it to my daughters this
evening
you put it in front of the mirror
and what you can see is that as you go
from this eye to this eye
that it appears black so looking down
through it you can see so in this case
now the one on the left is black and one
on the one right you can see through if
we now move over to this one one on the
right
is black and the other one you can see
through what the hell is going on there
so the light is coming from all the
lights in here it's bouncing off my face
and it's striking the mirror and then
it's coming back and hitting me so
what's happening here is that the light
comes down strikes my face
bounces off my face goes through this
thing right now initially all that light
is randomly polarized it's right and
left circularly polarized however
remember this thing acts as a filter so
it makes sure that only light with a
particular polarization state can get
through this is where it gets really
clever so it comes through goes through
here
that light has got a particular
polarization state which this one is let
true let's say right-handed strikes the
mirror the murder changes its
polarization state so it comes back and
oh dear i can't get through because i've
now got the opposite polarization state
which is really quite clever so it's a
really nice example of him
well you can look it in two ways
classical physics quantum physics but
quantum physics at the movies basically
it's a really really um clever example
of polarization i think and i'm blown
away by this type of technology it's
it's really quite neat
we could perhaps go into 3d television
but that's a different type of
technology which maybe we'll leave to
another day