P3D Re: IMAX 3D projection

[boris@xxxxxxxxxxxx (Boris Starosta)]

>Tony Alderson  <aifxtony@xxxxxxxxxxxxx> wrote:
>> Andrew Woods wrote:
>> >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.  <
>>
>> Wow! Really? I guess it ISN'T "obviously impractical to adjust the
>> alignment shot-to-shot during projection of the movie."
>>
>> I have considered the possibility, but decided the engineering wouldn't be
>> worth the trouble.  I stand corrected on that, anyway. How much time lag is
>> there for the corrections? Can the system keep up with quick cuts? I think
>> I'll have to dig out my stuff on IMAX and recheck things.

I think, given the history of this thread, that two different alignments
are being discussed here.  One is the "on the fly" vertical alignment that
apparently is done using computers (this was mentioned to me by the
projectionist also), the other is "on the fly" disparity adjustment, to
correct for extreme close up shots.

Two more comments from me on this.  Correcting for extreme close ups seems
to me easiest at the camera.  But I am unfamiliar with the technological
constraints that the camera designers face for this format.  Perhaps having
shift lenses is just one too many variables to add.  I did get the
impression, that the camera has no adjustments of any kind for stereo base,
vertical alignment, toe in etc.

That's just a hunch of mine.  It would be easier for the cameraman that way too.

On the vertical alignment question and projector adjustability:  That film
was obviously shot and projected running horizontally - so I do not see
where vertical misalignment can even enter into the system!?  Horizontal
alignment (disparity) seems more of a troublesome variable for this system.

>> Boris Starosta (digest 2758) Reviewed: Into the Deep
>> >I did not perceive any flicker at first, though later I saw a little
>> >"jumpiness" in bright objects moving rapidly across screen.<
>>
>> I suspect this was strobing from the frame rate, not stereo ghosting.  You
>> can see this artifact in horizontally (rapidly) moving objects in most

I thought that in regular cinema, motion blur hides strobing effects like
this.  I am a skeptic here, and propose that either the shutter glasses or
the horizontally running film format (or both) have something to do with
it.

>Andrew Woods.     http://info.curtin.edu.au/~iwoodsa
>

... and separately, from Paul Talbot:

>But one of the great thrills of stereo is the realism, and I felt
>that having infinity at the screen destroyed almost all sense of
>realism in the film.  It has been mentioned on the list that "stereo"
>is derived from a word meaning "solid."  Objects floating in space
...
>images in the lap of the audience instead of on the screen will
>probably keep me from going back for very much more.
>

With the tremendous image pair isolation apparently achieved by the system
(i.e. perfect lack of crosstalk), projecting a "virtual" window close to
the viewer should be no problem.  It should be easy to do - maybe someone
there will try it.

Paul, 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 - my intuition is that
having people cross their eyes to accomodate disparity is a safer bet than
having them pull their eyes beyond parallel).

You know I don't like to shoot things more than ten feet out - and
apparently the Imax people feel similarly - so they have no choice but to
mount their image in front of the screen.  But putting things within ten
inches was pushing even my preference for close ups.



Boris Starosta

usa 804 979 3930

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



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