T3D Re: stereo math

[aifxtony@xxxxxxxxxxxxx (Tony Alderson)]

Just subscribed to T3D, and will jump right in.

>Tom Deering wrote (digest 353):
>I visualize 1.2mm of onfilm deviation as being related to the amount of
>convergence the eyes can comfortably do. Would it be just as correct to
>measure it as an angle?<

It is actually more correct to measure stereo viewing as angles--that's
what's really happening.  Thinking this way helps explain a lot of things
about stereo projection, such as the stretch observed as one moves away
from the screen.

>And is that why the 1.2 mm is actually f/30?<

Not sure what you mean here.  The ISO standard specifies lenses of 35mm
focal length, and 35/30=1.166666...

The standard of 1.2mm is really a shortcut; linear math and measures are
easier than angular. At least I can't do trig in my head.  Not only that,
but we should keep in mind that the 1.2 mm standard is, to some extent, an
arbitrary figure that Rochwhite settled on so he could stop chasing his
theoretical tail and actually build a stereo camera.

The Realist system was worked out so average humans could take reasonably
good stereo without a lot of agony and risk.  We've seen on P3D that even
experienced stereographers don't like to wring their hands endlessly;  if
you adhere to the standard, you'll get acceptable stereos for the most
common viewing conditions.  There are numerous compromises, but at least we
don't have to think about it.  However, we get into a little confusion when
we start shoehorning other formats into the Realist system.

>And is any of this related to the reason why perfectly mounted slides
>don't look right when projected?<

Probably you're seeing a mismatch of viewing angles (vs. taking lens).
This changes the perceived perspective of the scene.  In any large
audience, most people won't be even close to the ortho seat.  Try moving
around the theater next time you project your slides, and see if you can
find a position where things "look right."  Then seek out the math, if
you're still interested.

More later

Tony Alderson
aifxtony@xxxxxxxxxxxxx



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