T3D Re: viewing disparity

[jacob@xxxxxxxxxxxxxx (Gabriel Jacob)]

John Slivon writes:
>>I have recently learned how to view stereo pairs uusing the crossed
>>eyes method. I have noticed that when viewed cross-eyed, the stereo
>>image appears to be about 60% of the size of either image of the
>>pair. When I view images using the parallel method, the stereo
>>image appears to be the same size as either image of the pair.

As Jim C. wrote, this is perfectly normal. Welcome to the freeviewers
club! :-)

Yes definitley, crossviewing will yield a sense of a smaller image.
And likewise parallel viewing will yield a larger image. Not only that
but varying the separation between images will have an effect on the
apparent size (of course this is a function of the convergance angle).

For example, if you have a left and right image stereopair not mounted,
put them side by side and freeview them crosseyed. They will look
slightly smaller. Now separate the images and continue to freeview
them. You'll notice the fused image get progessively smaller. 

Bringing them back closer together will make them progressively larger
till they are side by side. Overlapping them, and assuming you could
still freeview them, you'd reach a unity factor. Meaning that at this
point the "fused" image would neither be larger or smaller at the
particular fixed viewing distance (eyes to image). 

Now separating them further so that your now parallel freeviewing, the
image will get progressively smaller (instead of larger as in the case
of crossviewing).

Jim Crowell writes:
>It's called "vergence micropsia". The convergence angle of your eyes
>has an effect on how big things look (which makes sense; if your
>eyes are converged, then you must be looking up close & whatever
>you're looking at must be small).  However, this effect is basically
>unnoticeable unless your eyes  are converged pretty close in.

It's interesting that they have a word for this but have they
figured why and how the convergence angle determines the apparent
image size. I remember reading some speculation on P3D that it might
be simply the optical paths. Simple experiments have led me to
speculate that rather it's a psychological effect.

Gabriel



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End of TECH-3D Digest 364
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