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Author Topic: Why does a french horn bell reflect a left-right flopped image?  (Read 3675 times)

David Falterman

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David Falterman  asked the Naked Scientists:
   
Dr Chris,

I am an avid French horn player, and have noticed that if I look directly across the bell of my horn, the image is the exact thing other people see if they look at me, instead of a mirror image. Why does it do that even though it is a mirror?

David from the U.S.

What do you think?


 

Offline Vern

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The only thing I can think of is maybe the image you see is doubly reflected so that you see your image as if it were reflected from two mirrors.
 

Offline Soul Surfer

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Your image in the french horn is very distorted. You are in effect looking at a concave cylindrical mirror image from beyond the focus and this produces a laterally inverted, laterally inverted image, which has the effrect of making the image look as you say.
 

Offline yor_on

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Soul Surfer?
A laterally inverted image is the one you get from a ordinary mirror as I understands it?
And the reflection you study when stretching out your right hand will, if imagining that a real person stood there instead, be that persons left hand.

Reading you again you could mean that this image being is reflected two times inside that horn.
Which makes me wonder where that first image being reflected a second time will be, and why it seems not to be noticed by David Falterman, or is it noticeable DF?

It reminds me of that French(?) art form where they made paintings on vases and such, that you only would see correctly when observing them 'indirectly' from an mirror.
 

Offline yor_on

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It wasn't a French invention at all.
It was Chinese and it's called Anamorphosis from http://en.wikipedia.org/wiki/Anamorphosis

"There are two main types of anamorphosis: Perspective (oblique) and Mirror (catoptric).
Examples of perspectival anamorphosis date to the early Renaissance (15th Century).
Whereas examples of mirror anamorphosis (or catoptric anamorphosis) occurred at the time of the baroque (17th century).

With mirror anamorphosis, a conical or cylindrical mirror is placed on the drawing or painting to transform a flat distorted image into a three dimensional picture that can be viewed from many angles. The deformed image is painted on a plane surface surrounding the mirror. By looking uniquely into the mirror, the image appears undeformed. Current in the 1600s and 1700s, this process of anamorphosis made it possible to diffuse caricatures, erotic and scatologic scenes and scenes of sorcery for a confidential public.

These "anamorphoscopes" were invented in China and brought to Italy in the 16th century, about the time Renaissance artists like Leonardo da Vinci were mastering 3-D and discovering slant anamorphosis"

So it was probably me seeing anamorphosis vases from the baroque that made me draw that erroneous conclusion.
Sorry about that.
http://www.anamorphosis.com/links.html

And a coffee to go http://www.alibaba.com/product/6821811-11699470-11048318/Anamorphic_Cup.html
« Last Edit: 24/02/2009 15:57:59 by yor_on »
 

Offline Soul Surfer

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when a concave spherical mirror reflects an image from beyond twice the focal length the image is inverted (just like the inverted image you get from a convex lens)  when a concave cylindrical lens does this the image is only laterally inverted about the axis of the cylinder so as you say the image has been laterally inverted twice and is therefore back to normal.
 

Offline yor_on

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Didn't know that.
Cool.
 

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