Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site ecsvax.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!ucbvax!decvax!mcnc!ecsvax!dgary
From: dgary@ecsvax.UUCP (D Gary Grady)
Newsgroups: net.graphics
Subject: Re: Stereo Picture TV
Message-ID: <1597@ecsvax.UUCP>
Date: Tue, 9-Jul-85 12:35:22 EDT
Article-I.D.: ecsvax.1597
Posted: Tue Jul  9 12:35:22 1985
Date-Received: Thu, 11-Jul-85 20:30:09 EDT
References: <8794@ucbvax.ARPA>, <5760@utzoo.UUCP>
Organization: Duke U Comp Ctr
Lines: 48

> There is also a persistent technical problem, in that the 3D image one
> gets from orthodox techniques (like polarization) has some tendency to
> produce mild eyestrain.  The difficulty is that it requires viewers to
> vary the convergence of their eyes (which is a function of how near the
> objects appear to be) independently of the focus of the eyes (which is
> a function of how far away the light-emitting screen is).  Most people
> are not used to this, and I am told that it gets uncomfortable after a
> while.  (Either I don't have a problem with it, or I've never watched
> 3D material for long enough to run into trouble.)
> -- 
> 				Henry Spencer @ U of Toronto Zoology

The focus/convergence problem is often cited as a cause of eyestrain
and sounds quite plausible, but Lipton and others claim that experiment
has shown it to be false.  A well-shot and well-projected 3-D film has
no such problems (see the article on the unreleased Owensby feature
"Rotweiler" in The American Cinematographer about 1982).  Indeed, I have
never experienced eyestrain clearly attributable to that from watching
3-D films or from using a Viewmaster.

A much more serious problem is camera convergence.  This is a
surprisingly difficult and counterintuitive problem (how to set the
distance between the two taking lenses and whether and how much to toe
them inward).  Most eyestrain in 3-D projection probably comes from
dirty glasses, out-of-sync flicker (much rarer with modern one-projector
systems), and poor convergence.  As Henry notes in another paragraph of
his posting, there is a "frame" problem in 3-D.  If you have a closeup
of a person, you have a problem with the edge of the screen (at a
perceived distance of several meters) cutting off something much closer,
which gives your brain all sorts of trouble.  One way around that is to
use a huge screen, possibly curved, so that there is no perceived frame.
That runs into some technical problems as well (using lenses that wide
is liable to put each lens in the other's field).

I haven't had a chance to see it yet, but I'm told ultra-widescreen 3-D
has been used with considerable success at Disney's Epcot Center.  I
suspect we'll see touring ultra-widescreen 3-D before too long.  Already
we've had Imax tours and 3-D seems to be the next step.  Wouldn't you
pay to see a top-quality, eye-filling 3-D tour of the Amazon complete
with snakes jumping into your face?  Well, suppose I promise to leave
out the snakes?  How about a trip aboard the Space Shuttle?  How about
... [here the author was found gazing off into space and thinking about
a Certain Actress] ...
-- 
D Gary Grady
Duke U Comp Center, Durham, NC  27706
(919) 684-3695
USENET:  {seismo,decvax,ihnp4,akgua,etc.}!mcnc!ecsvax!dgary