653b0d0c   
   XPost: sci.physics, sci.optics   
   From: boyd@apt0.sao.arizona.edu   
      
   RichD wrote:   
   > This may be a dumb question, I never studied acoustics....   
   >   
   > If you look into the wrong end of a telescope,   
   > everything looks reduced, 'anti-magnified'.   
   > Is there anything analogous acoustically?   
   >   
   > In both cases, the phenomena is described   
   > by wave equations -   
   >   
   > --   
   > Rich   
      
      
   It should be simple  to demonstrate a Galilean telescope (one positive   
   and  one negative lens)  which will magnify or minify an acoustic image   
     using an ultrasonic imaging  device and some  common optical lenses.   
   They would only  need to be made of a material with a different velocity   
   of propagation of sound  than a liquid they are submerged in.  The   
   velocity of propagation of sound is somewhat  analogous to the velocity   
   of propagation of electromagnetic energy to demonstrate refraction at   
   material boundaries.   
      
   "Magnify" doesn't have the same meaning in imaging and  non-imaging   
   situations.   
      
   An acoustic "telescope" doesn't have to be refractive.  A two mirror   
   Cassegrain reflecting telescope  can  focus sound as well as   
   electromagnetic energy.   I've experienced that working on microwave   
   antennas.   
      
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