I was pretty much “okay” with the eyes of my character. There were some reflextions. They were maybe weak, but at least visible. But then, when trying to do a very dark scene, I suspected there being something wrong. The face was pretty much in the dark but I still wanted some small catchlight in the eyes which I couldn’t get to work.
I was already gonna post here because of this. But then I had the idea, that the scale might have to do something with this. And indeed it does. I applied the scale of the outer eye. But suddenly there is a new problem. Seems like there is too much reflection.
This was obviously not what I was looking for. So I stared tinkering about with the IOR value. The render above has a value of 1.450, which should be okay, normally.
I read about values from 1.33 to 1.38 suitable for an outer eye.
But strangly I only got acceptable results when I put it around 0.6, as you can see here:
The eye meshes have backwards normals, which causes the IOR calculation to also be backwards. If this happened when you applied scale, it was probably due to the scale being negative, applying negative scale to the normals leaves them pointing inwards instead of out.
Backwards normals result in the IOR calculation assuming light is leaving the medium instead of entering, resulting in the light speeding up. IOR below 1 results in light slowing down as it leaves the medium. 1/1.38 is ~0.72, which explains why IOR=0.6 looks right.
J_the_Ninja is correct. That “weird” look is what you get from i.e. looking from inside a water volume looking into air - at some angle you get total internal reflections and you’re seeing Snell’s window. That’s also the reason that ff you use transparency instead of refraction when building a “glass” shader (flat panes of equal thickness wouldn’t need refraction), you have to use IOR value for forward facing faces, and 1/IOR value for backward facing faces. For real glass (using refraction), you only need to make sure normals are pointing in the right direction.
IOR and glossy color (should be white) controls reflectivity, if that’s what you actually want.
However, you seem to be reflecting some quite dark wood environment.
Photographers control the lighting to get eye glints (flashes etc), maybe you want that instead. If the lighting brightens things up too much, dial down the exposure to compensate; the reflection should not be affected as much.
