Issue with the modeling of the eyes

[blindsaypatten]

There seems to be an issue with the way the eyes are modeled causing unrealistic shading of the eyeball. I can only guess that the problem is that the glossy transparent outer shell is two dimensional rather than being a solid. If you make the eyeball itself glossy it looks like this:

But if you make the surrounding shell glossy using Fresnel as the mix factor the result is this:

The reason for the "shadow" is that the light from the lamp is mostly getting reflected instead of refracting onto the eyeball, it's just unlit rather than being a real shadow. I don't know what the effect of a two-dimensional surface instead of a solid/liquid layer is but that's all that comes to mind for the difference. Although the specular reflection are correct in the second image the shadow-like effect is clearly incorrect. Using a specular map to make the white part glossy but the iris non-glossy and using a glossy cornea instead of the outer shell would, I think, more accurately model real eyes, although I won't be surprised if the edges around the cornea are tricky.

Please correct me if I've got this wrong, or if not post your thoughts on the best "fix" for this.

[blindsaypatten]

Reducing the size of the outer transparent layer to the size of the cornea, and adding a specular map for the eyeball produces good results.

Object view

Render

Surface cornea (left) versus solid cornea (right)

Far eye is surface

Far eye is solid

[jujube]

I'm not totally sure what you mean about the cornea not being a solid... do you mean that it's not a closed mesh? All objects in blender are composed of a series of infinitely thin faces rather than truly being made of solid matter. Based on the object view it looks like what you've actually done is made the transparent layer smaller, not made it less like a surface/more like a solid. *this was part me being nitpicky, part me being stupid and confused*

[blindsaypatten]

I'm not totally sure what you mean about the cornea not being a solid... do you mean that it's not a closed mesh? All objects in blender are composed of a series of infinitely thin faces rather than truly being made of solid matter. Based on the object view it looks like what you've actually done is made the transparent layer smaller, not made it less like a surface/more like a solid. *this was part me being nitpicky, part me being stupid and confused*

I meant that it is not a closed mesh. I'm fairly sure that one can model a glass with an inner and outer surface and that it will look different from a glass with only one surface, perhaps I should try it. I don't know if one has to do more than produce a closed mesh.

[jujube]

It could also be due to a lack of polygons. A side view cycles I render I did, with subdivision modifier on. (+greg zaal's cave wall hdri)

(i'm metaphorically tearing my hair out struggling to get renderman to consistently render hair... I render them once and it's beautiful, then I apparently change somthing somewhere and then they disappear or become anemic until the end of time no matter what I do...... why does photorealism have to be so tantalizingly out of reach!!! I need to balance it out and share something good too, so this eye render goes in your topic.)

[blindsaypatten]

I looks to me like one uses the Glass shader for solid transparent objects and Gloss just for reflections. A sphere with the Gloss shader will not distort the background behind it

While a sphere with the Glass shader will act like a lens.

An eye using Glossy with Fresnel:

Glossy Shader with Fresnel Mix Factor

An eye using the Glass shader:

Glass Shader