Hi folks.

Perhaps we're not agreeing because implicitly we're using different definitions for the words we're throwing around?

In Becco_UK's beautiful ruby a couple posts above, I agree that there is something red shining in the shadow, and that Poser doesn't model that. I disagree that the term for that is a "caustic".  I can only go by the dictionary on these issues. The American Heritage Dictionary gives me this for "caustic":

• The enveloping surface formed by light rays reflecting or refracting from a curved surface, especially one with spherical aberration.
• Since the definition of caustic encompasses both reflecting and refracting light, the key is the word "curved". I totally agree that there are reflections in a gem seen through the gem's surface and also that those reflections can hit the table beneath it and light up the table. I disagree that those are called "caustics" - they are called reflections and refractions.

The notion of a caustic in optics is related to the other meanings of caustic, having to do with burning or stinging. For example, when you use a magnifying lens to focus the sun's rays into such a small area that you can cause paper to burn, that particular hot refraction is a caustic.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)