I am on the road and don't have Poser with me to verify, but I'm pretty sure the lens obstructs Posers notion of "depth". Depth does not transcend refraction - the depth registered would always be of the lens itself, rather than what you're seeing through the lens.

Now if there was a Refract_Depth node, a node that returns the depth of what is encountered by refraction rays, then it would be possible. In fact, other important effects would be possible in general. For example, many attenuated refraction effects, such as obsidian, could be done if we had a Refract_Depth node.

When light passes through an attenuating medium (such as colored glass), the amount of coloring varies with how much volume was traversed. The formula is simple, but the information needed to pass to the formula is just not available in the current material nodes.

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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)