From: wolftracks-nospam@sbcglobal.net   
      
   On 3/25/2013 9:13 AM, Phil Hobbs wrote:   
   > On 03/24/2013 11:09 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?   
   >   
   > Caustics are curves defined by the crossing of rays.  Back in the 1970s,   
   > there was a fad for making cheesy sculptures by stretching string on   
   > patterns of nails, so that curves and patterns emerged.  Those curves   
   > defined by straight strings crossing are effectively caustics.  (A   
   > particularly cheesy example is here: http://tinyurl.com/bppp2r4 .)   
   >   
   > They aren't much use in imaging applications, since you have to have   
   > gross amounts of aberration before you get any.   
   >   
   > I think some folks use them as a shorthand method for non-imaging   
   > concentrator design, but otherwise they're things to avoid.   
   >   
   > Cheers   
   >   
   > Phil Hobbs   
   >   
   Thanks. In my reading of gravitational lensing they both are mentioned   
   fairly often. They seem to have some value there. I've only recently   
   become interested in GL through a book that is quite good, and is not   
   mathematical. I'm not a physicist.   
      
   Caustics are mentioned here.   
      
      
      
      
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