[Bf-committers] ior

Daniel Barbeau DanielPGB_Vasquez at hotmail.com
Sun Apr 3 19:05:53 CEST 2005

> Of course it can !
> the ior isn't lightspeed_in_void / Lightspeed_in_material !!!
> this is the special case of an object standing in void.
> the real formula = lightspeed_in_first_material / 
> Lightspeed_in_second_material.
> if the light goes slower in the first than in the second, then the 
> ior is smaller than one.
> in the case of a bubble in water, the lightspeed is slower in the 
> water than in the air, so the ior is negative when the light
> enters the bubble, and positive when the light goes out the bubble.

three years without any optic courses at university... that stuff is 
far away.
the only thing I remember is the n= c / v   law (here it's one of 
Descartes' law)
and the sin i1 * n1 = sin i2 * n2 one, where i is the angle (the same 
as sin i1 / sin i2 = N, with N = n2 / n1)
with the normal and n the ior. Then we transformed these relations to 
get where we wanted.

So I'm a bit lost. Isn't a material's IOR (aboslute indices) 
calculated using air as a reference?
(which is close to void, at least in the approximations we did)
Then the inversions in the formulas occur logically following the 
course of the ray and the dioptre it goes through.
The user, in Blender, sets absolute IORs for the materials not N = 

So, the logical solution for me would be to place the camera in a 
world which has it's ior > 1... (1.33 for water)
Then all the rest of the objects have there normal ior, thus bubbles = 
1.0 and I'm happy with that :]

Is my case so desperate?
Am I so completely wrong?



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