P3D DVG effect explained (I think)

[boris@xxxxxxxxxxxx (Boris Starosta)]

>From: Peter Abrahams <telscope@xxxxxxxxxx>
>
>As a nearsighted person, for years I've made 'pinholes' by squeezing two
>thumbs & forefingers together, to sharpen a distant view when I didn't have
>my glasses.  Every once in a while, a post to a vision newsgroup asks about
>pinhole spectacles.  These aren't exactly what DVG uses, but close.  They
>sharpen the view considerably, at the expense of field of view; in the same
>way that stopping down a lens increases depth of field.  I've never heard

That explains Dunkley's description of increased sharpness.  He does
recommend that you stay several feet away from the brightly lit photograph,
which would comparatively enhance the impression of increased resolution.
Also, the smaller the pinhole, the more it acts as a lens itself - this is
important, as my explanation of the DVG effect will show.

>To sum up, I'm going to keep these pinhole viewers, but not because they
>added much depth to flat images.  I can believe that others saw a
>significant effect, but I did not.

I've done some more thinking about how this might be working, and have
concluded that the depth effect is apparently and functionally similar to
how Chromadepth glasses work.

Here's how I think it works:  You are instructed to hold the pinholes
somewhat aside the center of vision from each eye.  This causes the rays
from the photo, which form the image that you examine, to pass through the
_edge_ of your eye's lens.  That is, the pinholes optically mask away most
of the lens of each eye, leaving you essentially (optically) with two
prisms in your eyes, which naturally cause a certain amount of chromatic
aberration.  This chromatic aberration, in opposite directions for each
eye, creates the illusion of stereo disparity, i.e. different depths for
different colors.

Notice that the instructions for maximizing the DVG effect say that as you
pull the pinholes apart, the depth effect will increase.  This is because
the lenses of your eyes will function more and more like prisms as the
pinholes are pulled apart.  The effect is really very dramatic, and
surprised this skeptic when it was first observed.

Chromatec glasses appear to function the same way, the chromatic aberration
which gives rise to depth effects being caused by a grating.

Thank you, Ken Dunkley, for bringing this interesting optical effect to our
attention.  I still don't have your URL handy, so you may want to repost
it.

Respectfully submitted,



Boris Starosta

usa 804 979 3930

boris@xxxxxxxxxxxx
http://www.starosta.com
http://www.starosta.com/3dshowcase

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