American Cinematographer - July 1983 - 24

his

right eye will (mostly) see the im¬
reflected from the right projector
and his left eye will (mostly) see the
image reflected from the left projector.
In this method the disadvantages are
the great effort in designing and build¬
ing the screen and determining from
what angles the two views should be
projected, as well as the fact that a
good 3-D effect can only be seen from
limited "viewing zones'' in the the¬
age

ater. These limitations make such a

C. Polarized 3-D: This is

a

method

for

achieving full color stereoscopic
motion pictures and is the method of
presentation of by far the majority of
all 3-D motion pictures made to date.
It is similar to the anaglyphic system
except that the coding filters in pro¬
jection and the decoding filters in the
glasses are polarizers. The principle
of polarized light is explained in the
Fifth Edition of the American Cin¬

ematographer Manual on page 403,
and is illustrated here in FIGURES 2
and 3.

Light waves can be thought of
vibrating in two dimensions, both
at right angles to the direction of
travel of the wave. When a polarizing
filter is interposed, it acts as a sort of
optical "Venetian blind'' to pass only
those parts of the wave which are
lined up with its particular orientation.
The light passed is said to be polar¬
ized-that is, it has a particular orien¬
as

tation.

When, as in FIGURE 3,

polarized light enters another polariz¬
ing filter of the same orientation, noth¬
ing happens - the light passes
through unchanged. If, however, po¬
larized light enters a polarizing filter
with its orientation rotated

90°, the
light is blocked, and nothing emerges

from the other side.

projection and in the glasses, are
neutral (gray), color values are not af¬
fected, so full color motion pictures
are possible. This is the main advan¬
tage of polarized 3-D. The main dis¬
advantages are that this method
requires a silver screen and presently
always requires a special projection
setup.
D.

Lenticular 3-D: This is

a

tech¬

nique which, though used mostly for
still photographs, has been applied
with some success to motion pic¬
tures, principally in the U.S.S.R. In
lenticular 3-D, it is the screen which
decodes the views. No

needed.

glasses are

FIGURE 4 shows

section of the

screen

to be

a

cross

composed

of many lens-like ridges or wedges.
When projected upon, these ridges

reflect what
the

comes from the right to
right, and what comes from the

left to the left. Therefore, for a person

sitting near the middle of the theater,

system impractical for multiple-the¬
ater presentations, even though it is a
full color, glasses-free 3-D system.
I will now say a few words about
holography because every article on
3-D says a few words about hologra¬
phy. Holography violates our two
rules-needing two views (right- and
left-eye) and some way to code and
decode them for viewing-yet, it is
still a true 3-D imaging system. In
fact, it is probably the most realistic
and true-to-life of them all (stereoscopically speaking). The process
of holography is much different from
conventional photography and in¬
volves the use of lenses, mirrors and
a laser as the only light source. The
resultant hologram is unlike a photo¬
graph in that there is no image of the
subject on the film; the physics in¬
volved is much subtler than

photography. A holographic
image is more like an image seen in a
mirror, rather than an image formed
by a lens. A mirror image is seen in
true stereo relief and, depending on
the size of the mirror, you can look
around the sides and/or

top and bot¬
image. However this kind
of image cannot be projected onto a
screen or enlarged in a practical way
for mass audience viewing. The same
is true of a hologram. The size of a
holographic image is limited by the
physical size of the photographic film
tom of the

itself; in order to produce a three foot
square

holographic image, one would
three foot square of film. The

projection, each view is pro¬
jected through a polarizing filter, and

need

the two filters are oriented 90° to each

atrical motion

other. A silver screen is used to retain

obvious.

In

the

polarization of each image. Here's
happens when both images, re¬

what

flected from

the screen,

hit the

glasses of the spectator: the polariz¬
ing filter in front of the right eye blocks
the image whose polarization is op¬
posite and passes the image whose
polarization is the same. Hopefully, if
everything has been set up correctly,
this will be the right-eye image. The
same thing happens with the left eye.
Since the polarizing filters, both in
22

conven¬

tional

a

basic limitations for wide-release the¬

I

pictures

are

hope this article has clarified

quite
some

of the basics for those readers who
may have been
In essence, 3-D

confused about 3-D.

imaging systems are
nothing more than common sense
employment of certain principles; and
when these

principles are known, any

investigation into the workings of
whatever stereo cinematography sys¬
tem will prove

fruitful. As with under¬
standing most things, there is no
substitute for plain common sense. ■
AMERICAN

CINEMATOGRAPHER, JULY, 1983
American Cinematographer - July 1983

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