P3D Re: IMAX 3D projection

[boris@xxxxxxxxxxxx (Boris Starosta)]

Paul Talbot's last posting points out a need for me to clarify my statements.

First of all, "Into the Deep" is the first and only 3D Imax film I've seen,
so my comments apply to it exclusively.  This film consists almost entirely
of close ups - objects within four or five feet of the camera - I thought
that was great!  You remember my theorizing last year on what stereo is
good for...

When I say they were pushing even my preference for close-ups, by showing a
few scenes with very small creatures only 10 inches from my eyes, that was
not based on Paul's previous comments.  That is my estimate of the actual
perceived image distance, based on where I was sitting in the Theater (6
rows back, rather close to screen, certainly closer than I wanted to be -
but I had no choice).  It is understood that a person at the rear of the
theater would have perceived the same image maybe 20 - 30 inches from their
eyes.

Now, to elaborate on my comments regarding "mounting to the screen."
Assuming you sit 50 ft. from the screen, and the perceived stereo image
does not "pierce" this screen, AND the image is orthoscopic - then you are
looking as if through a window six stories tall, 80 ft. wide, and fifty
feet away... at subject matter that cannot have very much depth, because it
is so far away to begin with.  In essence, mounting to this screen would
mean limiting your disparity to 2.5 inches max "on-screen," which is not
much on a screen 80 feet wide.  So the stereo effect, and perceived depth,
would be miniscule at best.

That's why Imax wouldn't bother with anything other than infinity at the
screen.  With the scale of things, they cannot possibly ensure that
infinite homologous points are separated exactly 2.5 inches (for
example)... Heck, their tolerances are probably such that they are happy to
have "infinite" points fall within five inches of each other, one way or
the other.  However, as I indicated in my post form a few days ago, that
doesn't mean you can't have a stereo window preceding the close-up images.
It just means that such a stereo window will not be superimposed physically
on the screen.  I actually would have preferred a nearby "floating" stereo
window...  Most of the time, the sheer size of the Imax screen made me
oblivious of "window violations," but not all of them time.

My biggest problem was with only very few scenes of extreme close ups.
Others have now confirmed my suspicion that my discomfort was likely
aggravated by a serious vertical misalignment on screen.  So maybe the
extreme close ups would have been quite tolerable in a well functioning
theater...



>Boris Starosta wrote:
>
>> if you are going to shoot and present orthoscopy, there's not much
>> sense in "mounting to the screen," because there's not much depth from
>> fifty feet to infinity.
...
>> (Conversely, a high disparity close up, mounted to
>> the screen non-orthoscopically, would give you strongly wall-eyed
>> homologous points on screen as you go back in depth
...
>> You know I don't like to shoot things more than ten feet out - and
>> apparently the Imax people feel similarly

To which Paul Talbot asked:

>Forgive me Boris, but I'm completely dense about the technical
>side.  Of course binocular disparity falls off rapidly, but could
>you go over what you mean by the part before ", because?"  In
>particular, why does the assertion necessarily follow from the
>stated reason.
...
>I never meant to suggest that close-ups should be forced back to,
>or behind, screen level, and apologize if my writing caused such an
>interpretation.  I like off-screen effects and through the window
>effects, but as a "spice" rather than as a steady diet (borrowing
>a DrT analogy from a different discussion).
...
>Was the "within 10 inches" based on the film you saw?  I must
>have missed that.  Or was it based on my "in the lap" comments?



Respectfully submitted,



Boris Starosta

usa 804 979 3930

boris@xxxxxxxxxxxx
http://www.starosta.com
http://www.starosta.com/3dshowcase



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