Re: [Phys-l] Physics problem of 3D presentation

["John Clement" <clement@hal-pc.org>]

There is a defunct monitor that uses linear polarization, but their system
caused way too much ghosting.  The popular LG 3D TVs all use circular
polarization as does the RealD theater system.  The advantage here is that a
slight tilt of the head does not cause ghosting.  Basically the TV has
strips of what they call retarders across the screen or more properly a
quarter wave retardation plates.  I am puzzled by the reflection info.  So I
just tested a pair of glasses and the results are that R with R or L with L
shows no preferential axis.  But L with R shows strong reduction in light
intensity, but there is also an axis effect.  So apparently it may not be
exactly a quarter wave plate.  I suspect this is to make the glasses work
optimally with the particular presentation system.  The RealD and LG glasses
have similar characteristics but the RealD glasses have more ghosting on an
LG monitor.  So they have done some other things besides circular
polarization.  The old 3D system used linear polarization, but it suffered
from ghosting when you tilted your head.  Many writers seem to think they
used red/blue glasses in theaters, and this is a gross misconception.
Perhaps the third run theaters used it with B&W 3D movies.  Certainly prior
to Land's invention of cheap polarizers they used R/B glasses.

Nothing beats the old Realist camera slides viewed through good doublet
lenses in a bright lighted viewer.  But that is a very personal experience
and not shared, nor a video.  Indeed the high Dmax of Kodachrome (difference
between light and dark) is not reproduced by current digital cameras or TVs.
Kodachrome is nearly impossible to scan well in anything other than a
professional quality scanner, and then the dynamic range has to be
compressed. Every medium has its advantages and disadvantages, so in a sense
McLuhan was right about the message being the medium.  Kodachrome also lasts
for close to a century with good color.

Closed captioning can be fairly large text.  I am talking about very small
text not the usual captioning which is designed to be seen easily.  The text
I see in this message is readable with both eyes, or either eye through the
3d glasses, but it is funny looking at a distance.  The seraphs on the lower
case l have the top missing in the right eye, and the bottom missing in the
left eye.  But If I move close to the screen both eyes see the l clearly
because the large angles subtended prevent proper polarization.  At the
proper viewing distance of about 1 m this text is readable, but it vibrates
and parts pop in and out.  I estimate it is 6 or 8 pixels high.

It just occurred to me that you may have been using active glasses which do
have linear polarization.  LCD monitors produce polarized light and the
active glasses go black if you tilt your head 90 degrees.  I have a pair of
active glasses which worked well with an old fashioned monitor, but ate
batteries by the gross.  But when my son gave me a newer LCD monitor the
glass showed only a black screen because the polarization of the screen and
glasses did not match.  I gave up on them because they would only work at 90
deg which is NG for 3d viewing.

I love 3D, but unless they solve some of the technical problems at a
reasonable cost, it might die.  However the gamers may be sufficiently
addicted to it to keep it going, and then it allows 2 gamers to use the same
screen but see different things (with R only or L only glasses).  And with
circular polarization cheating is not feasible.

So the 3D systems might be helpful when you try to explain things like
polarization.  Circular polarization may seem like an arcane subject, but in
the FPR monitors it is vital technology.

John M. Clement
Houston, TX

> On 2011, Dec 05, , at 10:50, John Clement wrote:
>
> > 3D is going through a cycle of popularity, and it is not 
> clear that it will
> > last, but this time there seems to be a lot of technical 
> innovation which
> > has resulted in acceptable presentation to groups.  But 
> each method has
> > problems.  So far the best method for home presentation 
> seems to be using
> > circular polarization to separate right and left images, 
> but it has problems
> > as all the methods do.  So can anyone come up with some 
> ideas for fixing
> > some of the problems.  Here is a list of current methods:
>
>
> My last trip to Costco included a demo 3-D.  I viewed thru 
> the glasses grazing reflection from a nearby slickly covered 
> box.  Rotating the glasses caused partial extinction 
> (oxymoron, I know) of the reflection.   So I concluded linear 
> polarizers. ***  this is how my projector works.  I't been > 
> twenty years since I set up and maintained the optics lab. at 
> UCSC, so I may be all wet.
>
> bc
>
> *** IFIRC, both lenses oriented the same, so I'm likely 
> confused -- I could google instead of posting.
>
>
> The FPR method is currently cheapest, and is fairly satisfactory
> except when you want to mix 2D and 3D.  It makes 2D small 
> fonts hard to
> read.  
>
>
> There goes closed captioning.
>
>
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