P3D Re: The Dunkley Effect

[boris@xxxxxxxxxxxx (Boris Starosta)]

>From: Bruce Springsteen <bsspringsteen@xxxxxxxxx>
...
>I have seen the Dunkley Effect (strong depth perception in "flat"
>photographs through partial blocking of the field of view) courtesy of

I have also observed the Dunkley Effect, though not with the Dunkley
apparatus (which I've no doubt improves the effect - but would you lend me
yours?).  There is in fact a perception of depth, though I disagree that
the depth is always perceived correctly.  In other words, that objects
always appear at their "correct" depths.  Possibly, to the inexperienced
observer, simply the perception of depth where none is expected can be
impressive and overwhelming;  thus the need to make a more careful
observation is forgotten.

My more careful observation of the Effect leads me to believe it is similar
to that given by the use of ChromaDepth glasses.  To give it more credit,
the Dunkley effect looks a lot better on ordinary photographs than the
"Chromadepth" effect.

The ChromaDepth process appears to use diffraction gratings to separate the
different colors of light in the image and displace them different amounts,
just like a prism would separate a shaft of sunlight into a full color
spectrum, or shift any pure colors by a different amount.  The disparate
shifting of different colors in a picture creates a stereoscopic effect,
just as if the colors actually existed at different depths.

I propose that the Dunkley Effect is functionally the same thing.  Instead
of using a grating (or prism) in front of the eye, it is the lens of the
eye itself that is utilized to shift the colors.  This is revealed by the
instructions for observing the Dunkley Effect, and by the perception of the
Effect itself.

The Dunkley Effect requires the use of a pinhole for each eye; the smaller,
the better.  It requires the pinholes to be positioned off-center
(off-axis) over each pupil, AND in opposing directions (i.e. to the left of
center of the left pupil, and to the right of center of the right pupil).

The use of pinholes like this will have two effects.  First, the relative
darkness of the image will cause the pupils to dilate, exposing the
periphery of each eye's lens to the optical path.  The instructions for
viewing the effect are to slowly separate the pinholes more and more.  This
produces the second effect of using the pinholes: that the rays which form
the image are passed through only a peripheral section of the eye's lens.
This is where the eye's lens will be acting much like a prism,
differentially refracting the different colors in the picture.

The "prismatic" or "Chromadepth" explanation is supported by the
observation of images.  The perception of depth is strongest for those
images displaying brightly colored objects, and weaker for pale colors or
grayscale images.  Careful observation will reveal that redder objects
always appear closer than bluer objects, as would be expected - in color
landscapes, this conveniently places the blue sky further away than most
other objects in the picture.

Finally, photographs do appear sharper and more detailed when looking
through the pinholes.  I suspect this may be because the pinholes will tend
to "hide" lens imperfections that would otherwise degrade the quality of
the image at the retina.  That's just a pure guess, I don't know enough
about the eyes to really be sure that use of pinholes will improve
resolution or acuity.  This increased apparent sharpness may also
contribute to the perception of depth.

So the Dunkley Effect is a neat illusion, worthy of study.  But it is not
magic.  It does not create two views of a scene, where there is only one.

Boris



Boris Starosta            boris@xxxxxxxxxxxx
                          http://www.starosta.com
usa 804 979 3930          http://www.starosta.com/3dshowcase



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