Converging fields of view

[P3D Neil Harrington <nharrington@xxxxxxxxxxxxx>]

Larry Berlin writes:

>It is true that the fields overlap but it is NOT true that they converge.
>The fields spread out fan like and OVERLAP as they proceed in a generally
>parallel arrangement. The center of each field is OFFSET from the other and
>these centers are supposed to be parallel for the least amount of
>distortion. 

Not so, Larry.

Several here have observed that the LEFT frame includes more of the RIGHT
side of the subject, and vice versa.  As I have mentioned, this is true, but
only beyond the window.  Put a subject close in front of the camera and you
can easily see that at closer distances the reverse is true: the left frame
will contain more of the left side of the subject, and the right the right.
Move the subject as close to the lenses as is necessary to convince yourself
of this.    ;-) 

So the field of view as experienced (so to speak) by each side of the camera
starts out entirely on its own side and ends up more on the other side.
There is no way this can happen without convergence and crossing over.  The
point at which crossover occurs establishes the window distance.

>It is the viewer's eyes that converge on one pair of details or
>another within the overlapping areas of these fields of view. If there were
>no offset and overlapping areas you would not have stereo information. 

Yup.  No argument there.  



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