From: into@oblivion.nothing.com   
      
   Phil Hobbs  wrote in   
   news:5150EAD0.4030600@electrooptical.net:   
      
   > On 3/25/2013 7:04 PM, Skywise wrote:   
      
   >> Would not even the focal point from a lens system be considered   
   >> a caustic? To qualify, isn't it a special case?   
   >   
   > Sort of.  In a stigmatic optical system, the rays all cross at one   
   > point, so the caustic curve consists of just that one point.  I think   
   > the distinction is useful enough that I'd say no--a caustic has to be   
   > larger than the diffraction limited spot, at a minimum.   
      
   Not being an optics pro I'm not 100% sure what "stigmatic" means   
   in this context, but I get the gist. I agree it's not what is   
   generally meant by a caustic. However, in the context of CGI, it   
   is technically a caustic as those settings are what control the   
   rendering of the image, even if it's just a picture of a lens   
   focusing a light source to a spot.   
      
      
      
   >> I am familiar with the concept of caustics from the other kind   
   >> of ray-tracing - CGI. In that field, any form of light pattern   
   >> rendered onto another object/surface after a refracting or   
   >> reflecting surface is termed a caustic. It may be that it's   
   >> not considered such in the 'real world' of optical design, but   
   >> I've not encountered any different usage.   
   >   
   > "Any form of light pattern" is pretty general.  Would that include the   
   > face of the guy you shave with?  ;)   
      
   Yeah, I'm being too generalized. For example, a glass object   
   sitting on a table, and light is refracted through it. The light   
   pattern on the table is the caustic.   
      
   Your whimsical example I don't think would be considered a   
   caustic even in CGI. Diffuse reflections would be called   
   radiosity, and that can be modeled as well. The mirror would   
   certainly reflect those radiosity rays, however.   
      
   Rendering these effects realistically is CPU intensive, both   
   caustics and radiosity. But, they go a LOOOOONG way towards   
   making a scene look realistic. The subconscious eye-brain expects   
   to see these things and when they are absent, the image will   
   look 'wrong' even if you can't say why. (I like trying to find   
   CGI errors in movies and other imagery)   
      
   I don't do a lot of rendering, but when I work on something, my   
   goal is photorealism. The most recent example of my work which I   
   did about a year ago is here:   
      
   http://www.luxrender.net/forum/gallery2.php?g2_itemId=22240   
      
   Dang, I need to get back to doing this. Too many hobbies, not   
   enough CPU time.   
      
   Brian   
   --   
   http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism   
   Sed quis custodiet ipsos Custodes?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)