Re: Lunar Illusion
- From: "Jeff R" <contact.me@xxxxxxx>
- Date: Sun, 26 Jun 2005 20:13:55 +1000
Uh huh.
I like the idea a stereograph may reveal different images which suggest the
moon is *closer* and hence *larger*, but I still see the need for a standard
in sizing. So - the moon is larger... larger than what? What is the basis
of comparison? Is the stereograph producing a representation which is
"larger" than a single "2D" image? Even though the image scale is identical?
That would be a relatively simple test to take - I'd do it right now if it
wasn't cloudy!
As to the post-exposure-image processing (anything past the cornea), I'll
leave that to neurologists (or priests).
--
Jeff R.
"imipak" <imipak@xxxxxxxxx> wrote in message
news:1119776206.742556.56270@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> My reasoning is a little convoluted, so bear with me. :)
>
> The problem I want to tackle is exactly where in the sequence of events
> the illusion actually occurs.
>
> There are several elements in any optical illusion - the light has to
> enter the eyes, which are of different sizes and different offsets.
> That is why we have stereoscopic vision. :)
>
> Once the light has entered the eye, it gets processed by the retina.
> The retina has a mix of rods and cones for processing greyscales and
> colour. They are not of uniform density and do not have uniform
> responses - in time, frequency or magnitude - but I don't know of any
> optical illusion that works at this level. Certainly the moon illusion
> won't.
>
> The optic nerve then carries the data to the brain, which then does all
> kinds of image processing, not to mention relating images to memories.
> There is some leakage between the senses in all people - some more than
> others - but it is the image processing and the memory relationships
> that are the cause of many optical illusions.
>
> Ok, so how would we narrow down the possibilities? The obvious first
> step is to capture what the eyes would see, then replay that data to
> the eyes at a later date.
>
> If the illusion is in part a property of stereoscopic vision (ie: the
> eyes are seeing slightly different images, and the brain interprets
> that as the moon being slightly larger), then replaying those different
> images to each eye will always reproduce the illusion, even if the
> images show the moon to be the normal size.
>
> If the illusion is entirely a property of stereoscopic vision (ie: no
> interpretation is required), then a composite stereoscopic photograph
> will show a moon that is larger than it "should be" for the camera
> settings.
>
> If the photographs cannot produce the illusion, then it is really not
> about what you are seeing at all, it is about what your brain is
> perceiving. A "real researcher" would then carry out all kinds of tests
> to see exactly what was involved in the illusion occuring, but as an
> armchair "illusionologist" I will content myself with knowing if it is
> a mechanical (ie: to do with the eyes) or neurological (ie: to do with
> the brain) illusion.
>
> The idea is to isolate one characteristic at a time, and see if that
> characteristic can reproduce the whole of the effect. If it can, then
> that is the likely cause of the illusion. If it cannot at all, then it
> is unimportant.
>
> It is very hard to test the retina or the brain, but it is extremely
> easy to test the mechanics of a stereoscopic optical system, and it is
> also easy to test to see if the illusion can be produced by a
> reproduction of what each eye would have seen.
>
> To go much further, you'd need to muck about with white light
> holography (yes, this does exist, but it is somewhat rare), optic nerve
> induction, and all kinds of other esoteric tricks. None of which are
> even remotely within the reach of any but the most dedicated of
> researcher. As such, it's best to ignore those tests we can't do, and
> concentrate on the ones that are entirely practical.
>
> Jeff R wrote:
> > "imipak" <imipak@xxxxxxxxx> wrote in message
> > news:1119662924.626668.201770@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > > The illusion of the moon being larger, when close to the horizon, is
> > > well-known and well-documented. Explanations are varied and range from
> > > a page or so of text to entire books. Ptolemy's explanation of the
> > > illusion was that there is a frame of reference near the ground and
not
> > > in the sky. This explanation is generally held to be the most likely.
> > >
> > > The illusion does NOT occur if you close one eye, and also does NOT
> > > occur when using a conventional modern camera.
> > >
> > > This, however, does NOT answer the question of whether the effect
> > > exists when using a stereoscopic camera. These have existed since
> > > Victorian times, so somebody has presumably taken a picture of this
> > > kind. Does anyone know whether the illusion shows up in this case?
> >
> >
> > Not sure I understand your reasoning here.
> > (I've taken lots of stereo pairs, so I understand *them* !)
> >
> > The effect is a naked-eye effect.
> >
> > If reproduced photographically, then the "size" of the moon is dependant
on
> > focal length, enlargement etc etc; i.e. it is dependant on the
reproduced
> > image size.
> >
> > Are you suggesting that a stereograph will reproduce the image scale of
the
> > moon larger than a simple single photo? ...or that the combination of
the
> > two images will tend to "enlarge" them?
> >
> > Sorry.
> > I'm not making myself clear.
> >
> > My question:
> > How could a stereograph perpetuate this illusion?
> >
> > --
> > Jeff R.
>
.
- References:
- Lunar Illusion
- From: imipak
- Re: Lunar Illusion
- From: Jeff R
- Re: Lunar Illusion
- From: imipak
- Lunar Illusion
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