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Re: [Phys-l] A geek's observations on "Avatar"

Fun movie, but I definitely had the impression that I had seen this western before.

Depending on the theatre it may or may not be stealing the glasses; some theatre's sell the glasses to the audience. I so Beowulf and paid $2.00, for my glasses and saved them.


Joel Rauber, Ph.D 
Professor and Head of Physics
Department of Physics
South Dakota State University
Brookings, SD 57007
605.688.5428 (w)
605.688.5878 (fax)

-----Original Message-----
From: [mailto:phys-l-] On Behalf Of LaMontagne, Bob
Sent: Sunday, January 03, 2010 1:53 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] A geek's observations on "Avatar"

I'm afraid that collecting "extra" glasses after the show is stealing.
My daughter works part time for IMAX and the glasses are an incredible
expense for them. They have to be collected by staff after each show
(although some people hide them and sneak off with them), sterilize
them, and then hand dry them so there will be no streaks or spots. They
are of no use as polarizing sun glasses. As you noted, the polarization
is not in the vertical plane so they will not serve to reduce glare the
way that traditional polarized sunglasses do.

They movie was technically astounding. I definitely intend to see it
again. However, I was aghast at the racism in the film. The only blacks
portrayed were at the very beginning when the transport ship was being
boarded on earth to go to the planet. Once the "evil" deeds were
started, not a black or Hispanic face was to be seen - just evil white
European types - and of course the usual military and corporate
villains. There was one Hispanic female who, of course, went rogue and
defied the Anglo defilers. The plot was ripped whole cloth from
"Dancing with Wolves".

Despite this, I would highly recommend the movie - great fun and the
best 3-D so far. Definitely see it at an IMAX theater if possible.

Bob at PC
From: [phys-l-] On Behalf Of Leigh Palmer
Sent: Sunday, January 03, 2010 1:47 PM
Subject: [Phys-l] A geek's observations on "Avatar"

I haven't contributed anything to this group in a long time, but thanks
to an improvement in my physical health I feel inspired to do so again.
This won't be deep physics, but it is interesting, especially for
teachers going back into classrooms tomorrow.

I, my wife, two of our sons, and a family of four friends saw the
remarkable film "Avatar" in RealD 3D. A member of our AAPT section had
kindly posted a technical writeup* which sons David, Aaron and I had
read in advance. The experience was well worth the time and money
spent, especially since Aaron treated us all!

My principal interest was in seeing the finished product. It was not
quite perfect, I'm afraid, but it was much, much better than any
previous 3D movies I had seen. The rendition is effectively at 24
frames per second, regular movie frame rate. As a consequence the
motion is not smooth, something that showed up dramatically in the 20th
Century Fox logo before the start of the film itself. As the CGI image
rotates, some small objects at the bottom of the screen are supposed to
appear to be moving rapidly from right to left. They don't; they jump
across instead in ten or fifteen discreet steps each. Once I had
recognized this "shortcoming" I continued to watch for it in the movie,
but I really didn't see another instance where it was noticeably
annoying. As I understand it, the problem could have been addressed by
the in-betweening process of computing intermediate images up to the 72
frames per second rate at which the images are projected to each eye,
in the same manner that

modern TV displays produce 120 Hz and 240 Hz frame rates to smooth

The other thing that really interested me is the glasses. They are
circular polarizers that alternately transmit and block light reflected
from the screen. I stood outside the theater after the show and
collected half a dozen pair because I knew they would be fun to play
with. The family's nine and eleven year old girls were fascinated by
the tricks I could do with the lenses. Of course I have played with
circular polarizers a lot previously, so I already knew exactly what to
expect, and I was able to put on a good series of demonstrations,
including using them as simple plane polarizers, showing that light
reflected from a kitchen floor is strongly plane polarized, for
example. I also showed how a single lens could suppress reflections
from a shiny coin, and that the antireflective capability cold be
destroyed by simply adding a second filter in series. It was a
remarkable instance of a teachable moment, even though my only handy
students were 10- and 13-year-old girls. I ha

ven't yet removed any of the lenses from the frames, but doing so will
make them easier to use in demonstrations.

It is interesting to note that the package in which the glasses were
handed out says:

These glasses do not screen ultraviolet
light. Wearing them as sunglasses will not
protect your eyes. Use only in the theater.
Keep out of reach of children under 3."

This is a CYA disclaimer, of course, but it is interesting to note that
the glasses can be used to function like Polaroid sunglasses - to
reduce glare from water or pavement, rather than to screen out
ultraviolet radiation. However this can only be done by modifying their
use; they won't work as provided in the theater. For the pairs I
examined the lenses work as plane polarized light blockers if one looks
through them backwards. However the plane polarized light they transmit
is horizontally polarized, and that's the component that must be
blocked to reduce glare. Thus to use them as ordinary polarized
sunglasses you must remove the lenses, reverse them front-to-back, and
also rotate them 90 degrees about the line of sight. That would
scarcely be worth the effort, by the way.

If you take a child to the movie a child-sized pair of glasses will be
offered. Before accepting them be sure your child cannot use the full
sized glasses. The whole screen cannot be viewed within the width of
the child sized lens from a reasonable distance. We were sitting three
rows above the middle aisle, and I sent the 13-year-old back to trade
glasses before the film started. I should have sent the ten year old
back too, as it turned out.

If you are a geek you must see this film, and you should read the short
pdf* first. Don't forget to collect some extra glasses after the film
is over. The two lenses are different, and you need at least two of
each kind to explore their fascinating properties. If you don't know
how the circularly polarizing lenses work and you want to know, I can
give you little help. A brief Googling yielded one good result, but I
could read only the cached version. You can reach it via Googling
"circular polarizer 45" (without the quotes, of course) and clicking on
the cached version of
izer/Products/circularPolarizers.htm> which shows up on the second page
of results. Briefly, a circular polarizer consists of a linear
polarizer laminated to a quarter wave retardation plate at 45 degrees
to its fast axis. Scarcely a good description. (The textbooks I have
don't include good descriptions either.)


*See <>. This writeup is by Matt
Cowan, q.g.
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