(click image for larger view)

@ odf,

Quote - A convex shape is definitely not going to produce the correct image.

I find I must disagree with that statement.

I will grant that refraction must play an important part in the appearance of a real eye. As air has a very low refractive index (1.0003), and I have been told by an optician that the refractive index of an eye is higher. This would serve to make the iris look more convex that it actually is.

A real iris is convex (see insert in diagram above), so I assume that refraction makes it look more convex. With that in mind I am mystified as to how making a poser iris concave would make it look more real. If one could implement a realistic refraction in Poser, the same as a in real eye, the the iris would need a real convex curve, the same as a real eye.

Without refraction the iris would need to be more convex  to compensate for the lack or refraction. At least this is how the logic appears to me, and looking at Poser images seems to reinforce this. **I can't imagine any way that a concave iris could look convincingly real, as it seems diametrically opposed to the real situation.

Links:
Ray Optics, Light Refraction.
Wikipedia; Refraction.

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