P3D Re The Dunkley Effect

[Peter Homer <P.J.Homer@xxxxxxxxxxxxx>]

Boris Starosta wrote

>
>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.

Diffraction would displace in the opposite direction to refraction however
with blue the least red the most. Refraction would seem to work the correct
way round  with the blue of the horizon of a scene  looking towards the
blue sky being displaced the most . Refraction certainly works as I have
noticed odd effects with a Holmes viewer with strong reds coming forward
and even with a mono slide viewer with single large lens. This seems to
have been exploited in earlier viewers even pre-Wheastone with large lenses
accomodating both eyes and even with two lenses which were used with single
coloured prints.
 I wonder if the Chromadepth glasses are actual diffraction gratings or an
array of microprisms unfortuneately I dont have a pair to examine under a
microscope although I have something similar which came with a video but
this displaces the image off screen top and bottom and at different depths
but within it it
 remains flat.

>
>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).

I wonder if diffraction can produce the right displacement could
diffraction at the edges of the pinholes be responsible at least in part
for the effect.


>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.

Pinholes I believe remove lens imperfections by using the inner part of the
lens only and imperfections tend to occur at the edges . If the pinholes
are positioned off-centre  they will be positioned towards the edges where
the imperfections are.  If the images are viewed closer than the "minimum
distance of distinct vision" of about 25cm could the pinholes help by
improving the depth of field . I recently bought a simple stereoscope (but
have not assembled it yet) which uses pinholes instead of lenses to allow
the focus to be close enough  it otherwise is conventional using two
monchrome views some of them in fact are copies of some of Wheatstones
original drawings.     P.J.Homer



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