Re: "Converging" fields of view

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Mon, 17 Jun 1996 16:29:42 -0500
>From: P3D  <Gregg_Podnar@xxxxxxxxxxxxxxxxx>
>Subject: "Converging" fields of view

>Neil Harrington wrote:

>>How is the adjustment done that "sets the stereo window"?  If you have some
>>method _other_ than converging the fields of view, I'd sure like to know
>>what it is.  Seriously.

>If you define the "field of view" as the pyramid within which points will be
>imaged on the film, then you may think of these pyramids as converging.  This
>contains little information about the geometry of the cameras and is why we
>avoid the use of the term.

I think that's a good point. In principle one could have a 2-lens camera
the axes of which *diverge* by 30 degrees, but if they have a wide field
of view and all but the (more or less) overlapping parts of the field of view
are masked off, we could say that the camera has "converging fields of view",
but that would leave out some important parts of the geometric description. :-)

The word "convergence" has many definitions and interpretations - by the
broadest definitions, any 2-camera system where the two views are not
*totally* different would have convergence - the term doesn't really mean
anything significant. A narrower definition which has sometimes been used
in the field of 3D implies a toe-in of the lenses (the axes of the two lenses
intersect at some finite distance). In this sense, saying that "the two
fields of view converge", while technically true by the broader definition,
can be misleading to people who work in 3D, because they see the word
"convergence" and jump to the narrower interpretation of toed-in lenses.
It certainly misled *me* - I own a Toshiba 3D camcorder, and when I read
about how to adjust the "convergence", I automatically assumed that it meant
toe-in of the lenses - it never occurred to me that it might refer to a
lateral adjustment of the sensor. I like the previous poster's use of the
term "coincidence" in that context.

The (main) purpose of language is to convey information as clearly as
possible. There are usually several different ways to express a given
concept. If one of these ways confuses people and causes them to get the
wrong idea, then it's time to decide whether to use an alternate expression
or to launch an educational campaign to convince people to accept the "true
interpretation" of the expression. If the expression in question is really
pretty vague and doesn't convey much information, and alternative expressions
are much more precise and already widely accepted, then it will probably be
more useful to go to an alternate expression.

John R


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