From: wolftracks-nospam@sbcglobal.net   
      
   On 3/24/2013 8:09 PM, W. eWatson wrote:   
   > I've searched the web for caustics and optics, but mostly see pictures   
   > of them. They seem to have some positive use. In some fashion they seem   
   > to magnify. They seem to be somehow related to critical curves, whatever   
   > they are. Both seem to be helpful in gravitational lensing or in other   
   > areas of optics. How?   
      
   Well, this pretty well nails it for me, since my original interest is   
   how it is used in gravitational lensing.   
      
   "Caustic and critical lines have important properties regarding the   
   number and parity of the images. For instance, if we consider a source   
   far away from the line of sight to the lensing distribution, there will   
   be just one image of the source if the lens are non-singular.  However,   
   if were to displace the background source towards the center of the   
   lensing distribution, additional images will appear in pairs whenever   
   the source crosses a caustic.   
      
   This goes on for a 1/2 page.  It's from the book Grav Lensing and   
   Microlensing by Silvia Mollerach"   
      
   Look at it on Amazon. You can Look at pages or search for words. This   
   material is on page 43f.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)