@ bagginsbill,

Quote - I'm confused by the occasional phrase of the form "If one could implement a realistic refraction in Poser".

I did not mean to suggest that refraction is not possible in Poser. I was referring to the specific difficulties of implementing it in the case at hand. As you yourself pointed out, the problem is to combine refraction with transparency and this can be "damn tricky to tune".

Whilst I applaud your efforts to implement refraction in this situation, I can't help thinking that a more usable solution in every day situations, for node novices like me, might revolve around shaping the iris.

Would you agree that a real iris is convex, and that refraction serves to make it look even more convex than it really is?

Do you think that a concave iris is preferable to a convex one, or vice versa?