P3D Re: Divergent Infinity

[aifxtony@xxxxxxxxxxxxx (Tony Alderson)]

Thanks to those who responded. Abram Klooswyk's reply was especially
useful.  I also liked the bit from Gabriel about starfields.  (I'll search
for this)

At SCSC, we can't keep our hands off the controls.  I try to follow the
"normal infinity rule", but the judges sometimes request either
superimposing the window or ghosts, depending on whims of the moment (as
far as I can tell ;-)  )  We only vary adjustments for Realist format
slides;  2x2x2 slides have the window converged on the screen, and we let
'em run.  Apparently we vary Realist slides because we can, not because we
need to...  We use a TDC 716 for the Realist format (opened to 7 perf) and
twin Carosels for the separated pairs.

In case anyone is interested, our screen is 96" wide.  The 2x2x2 slides
almost fill the screen, but the Realist format slides (5 perf) were closer
to 50 inches wide.  (We cater to all tastes in California! :-)  )   The
front row (where the judges sat) was 10 feet from the screen.  Yes, I
brought a tape to the meeting and measured the distance.  I don't have my
trig calculator handy, but if I had over 2 degrees divergence at the back
of the audience (about 25 feet from the screen) the front row had to be
more.

We had a variety of slides with different depth gradients, so I can't
generalize that.  But I meant the perceived far point of the image, with
the window at the screen.  (See above for our inconsistent adjustment
tradition....)

I think I'll have to shoot some test slides and project them in a
controlled situation to examine this matter.  This seems quite relevant to
my experience and observations with 3D movies, where the large screen sizes
make some divergence almost unavoidable.   (IMAX excepted!)

I'll return to this subject when I have something useful to add.

Abram, could you direct me to a reference on this issue of "photographic
and viewing convergence" so I don't have to derive the math? I have
Ferwerda's book at home, but I don't recall this topic. You could send this
to me off-line, or   post on tech-3d.  And doesn't this shoot the maofd
thesis to pieces?  Of course, the depth-range equation works, but isn't
this interpretation missing what's really happening in the perception of
stereo projection?  Probably a topic for tech-3d, we'll just confuse and
annoy everyone here!

Thanks for the help,

Tony Alderson



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