Re:Widescreen 3d

[hticheno@xxxxxxxxx (harold lee tichenor)]

In PHOTO-3D digest 1178 Stephen Kearney asked:
>
>Is it possible to take and view stereo images that approximate the eyes'
>field of view and perspective? How could it be done?

A possible and definitely informed source of information on this subject is
the IMAX corporation in Toronto.  In addition to their standard
ultrawidescreen presentations, they have also produced in 3d.  Whether they
would share information I cannot say.  One shouldn't be intimidated by the
fact that their screens are up to eight storeys tall; that size is dictated
more by the size of the audience than it is by the fundamental technical
problem at hand.  A smaller audience allows a smaller screen placed closer.
It is the angle of vision that is important.  The quickest way to accomplish
your goal is to sit closer to the screen :-)  To do this however you should
establish a smaller circle of confusion when determining the depth of field
of the original photograph because of the effective increase in projected
image size.  

I believe the workable field of view differs for each person.  Whether that
person tends to wear glasses regularly also influences the individual's
field of view.  Actually, I think field of view is not the best term, since
the eye and brain view images in a fashion somewhat differently from the
still camera. In fact the eye is constantly scanning the field in front of
it and the centre of the retina (but for the blind spot just off centre) is
used to clearly "focus" on the subject in the centre of the field at any
given moment.  The remainder of the retina surrounding that area is used to
perceive periferally and objects in that area are "viewed" with less detail.
Periferal vision's principal purpose appears to be to perceive motion that
may be of interest to the viewer, who then responds by moving the eye to
bring its central area to focus on the object that moved. 

Therefore if the eyes are not allowed to move in viewing, the field of view
that would be sufficient for "fixed viewing" would be considerably less than
that needed to allow natural "scanning".  The old three-panel Cinerama,
today's Omnimax and other ultrawidescreen formats offer up to 180 degrees of
image in the horizontal plane and over 90 degrees in the vertical.  However
during production one is careful to keep the principal subject matter within
the central third of the frame (except for certain dramatic effects) and use
the outer areas for recording the dramatic equivalent of periferal matter.

A more useful and specific answer to your question would be to suggest that
an aspect ratio of about 3:1 could be obtained by using anamorphic optics on
the camera and projector in order to squeeze the "image" onto the film and
expand it onto the screen.  (This is the traditional 35 mm motion picture
Cinemascope technique and such add-on lenses were built for 16mm and I
believe 8mm cameras).  In viewers the problem is certainly different because
producing a screen size large enough to give a field at a 180 degree angle
of view, but still far enough from the eye to be focussed upon, might become
a bit cumbersome.  Perhaps using anamorphics in the viewer's optics is the
answer.

Harold Tichenor


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