Re: an optical illusion?

["N. Pete Lohstreter" <petel@TENET.EDU>]

The binocular effect is expected.  Judging depth or distance requires
the two different points of view.  As to the effect that glasses are
required, I'm not sure that that is the case.  I pasted up a red/blue
message on a black background with a paint program and found the effect
present with or without my glasses.  The effect did seem to diminish
some due to the fuzzy edge left on the letters when I removed my specs.
When I adjusted the viewing distance to sharpen things up, the effect
came back as before.

I suspect that the illusion is not caused by one eye viewing the red
differently than the blue, but, rather both eyes working together must
slightly modify the viewing angle as you adjust your gaze from one color
to the other.  The color that is in your peripheral vision is slightly
out of focus and your brain interprets that as being at a different
distance.

Rick Tarara wrote:
> The red/blue contrast does suggest chromatic aberration but for me it is
> definitely related to wearing my glasses.  However, I tried 3 pairs--one old
> (and expensive)blended bifocals, my current pair, and a pair of single
> prescription reading glasses and I see the effect with all--maybe my eyes
> aren't very aberrant but the glasses are.  The question still remains why
> the brain would trigger one eye to preferentially view the blue and the
> other the red (I'm assuming this is the case since covering one eye makes
> the illusion disappear.)  I suppose this could be related to however those
> 3-D pictures that you have to stare at cross-eyed work, but then I don't
> understand that either.
>
> Rick
>
> ----- Original Message -----
> From: "N. Pete Lohstreter" <petel@TENET.EDU>
> To: <PHYS-L@lists.nau.edu>
> Sent: Sunday, July 02, 2000 7:53 PM
> Subject: Re: an optical illusion?
>
> > I was under the impression that the effect has to do with the differing
> > index of refraction of waves of differing wavelength by the eye.  The
> > blue is focused closer to the lens and requires a slight focus change to
> > see it clearly.  The brain interprets this as a change in distance to
> > the object being viewed.  I supposed this is the same as chromatic
> > aberration mentioned in another reply.
> >
> > Rick Tarara wrote:
> > > Help me out in understanding this one:
> > >
> > > Riding home from a wedding today I was looking at the list of songs on
> the
> > > Santana 'Supernatural' CD.  The titles are written in many different
> colors.
> > > What struck me was that they appeared VERY 3-D, with reddish letters
> > > standing out and blue being pushed into the background--except that one
> > > title (The Calling--if you have the CD) had the red letters on dark
> > > background stand out while the red letters on blue background were
> pushed
> > > back.
> > >
> > > OK, my 'experimental observations'.  The number one feature was that I
> only
> > > observe the 3D behavior when looking through my glasses (blended
> bifocals)
> > > but I can hold the case away and look with the distance part or closer
> and
> > > use the reading part and maintain the 3-D look.  The phenomenon does
> require
> > > both eyes (not surprising) but does not require the plastic case of the
> CD.
> > > It seems to require pretty good illumination, but both sunlight and
> > > fluorescent light work.
> > >
> > > Anybody want to explain?  My main concern is whether the phenomenon
> somehow
> > > is related to a 'fault' in my glasses.  Can anyone with this CD and
> glasses
> > > see the same behavior.
> > >
> > > Rick
> > >
> > > **************************************************
> > > Richard W. Tarara
> > > Associate Professor of Physics
> > > Department of Chemistry & Physics
> > > Saint Mary's College
> > > Notre Dame, IN 46556
> > > 219-284-4664
> > > rtarara@saintmarys.edu
> > >
> > > Free Physics Instructional Software
> > > www.saintmarys.edu/~rtarara
> > >
> > > Win9.x, WinNT/2000,  Win3.x, Dos, Mac, and PowerMac
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> > > ****************************************************
> >
> > --
> > Pete Lohstreter                   "Reality is merely an illusion,
> > The Hockaday School               albeit a very persistent one."
> > Dallas, TX 75229                                    A. Einstein
> > petel@tenet.edu
> > plohstreter@mail.hockaday.org
> > http://www.hockaday.org

--
Pete Lohstreter                   "Reality is merely an illusion,
The Hockaday School               albeit a very persistent one."
Dallas, TX 75229                                    A. Einstein
petel@tenet.edu
plohstreter@mail.hockaday.org
http://www.hockaday.org