P3D Re: Review - Into the Deep

[Andrew Woods <andrew@xxxxxxxxxxxxxxxxxxxxx>]

boris@xxxxxxxxxxxx (Boris Starosta) wrote:
> The show did have one technical error, however - what I thought was a
> pretty severe vertical misalignment.  It was hard to judge on the big,
> featureless screen, but I would guess that the left image was being
> projected some one to two feet higher than the right image.  I spoke with
> the projectionist afterwards, who revealed that the vertical alignment
> adjustment mechanism on the projector was inoperable, and that they could
> do nothing about it until a technician came down from Canada to fix it.
> 
> I would like to hear from more experienced members of this group, whether
> this magnitude of misalignment could have contributed to some of the
> eye-discomfort that I felt in some of the scenes.  I was seated six rows
> back (30-40ft?) More on that below.

In my opinion vertical misalignment is the biggest problem with most
3D movies.  Large amounts of vertical parallax will definitely give
people eye strain - It's just a question of how much and over how long.

There was a 3D movie festival here in Perth 2 years ago.  Vertical parallax
was a big problem.  I wrote reviews of the movies and a discussion of 
alignment issues which is available from: 
   http://info.curtin.edu.au/~iwoodsa

IMAX projectors are fitted with an alignment adjuster which can be
dynamically controlled by a computer.  It is probably this system which
was malfunctioning in the Arizona system.  The system allows alignment
errors (which may occur during filming, printing, etc) to be trimmed out
at the projector end during the screening.

With regards to seating position, I usually prefer to be seated 
about 4 or 5 rows from the top and in the centre of the row.  This
I estimate is approximately perpendicular to the centre of the screen.
Sitting further back in a 3D theatre has it's advantages.  With the
screen at a greater optical distance away, the eyes have to focus
at a distance closer to infinity which in turn reduces another
problem called focus/fixation mismatch or accommodation/vergence mismatch.
(See http://info.curtin.edu.au/~iwoodsa/spie93pa.html  for more information)
A greater viewing distance also allows the eye to more easily cope
with alignment errors, because the visual angle is less.

Mark Chapman wrote:
> Imax places infinity at the screen instead 
> of the window at the screen.  The can do this because of the 200 db of image 
> isolation.

When I attended the IMAX 3D theatre in Sydney back in December, infinity
was actually set in front of the screen.  It should be set at the 
screen if not slightly behind.  I was going to try to say something
to the projectionist or write them a letter but I'm getting tired of
getting indifferent responses when I try to tell theatres about their
bad 3D projection.

Cheers,
Andrew Woods.     



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