# [Bf-committers] ior

Ton Roosendaal ton at blender.org
Sun Apr 3 15:52:39 CEST 2005

```Hi,

The camera is in 'void', so when it sends rays the first material hit
will be an IOR > 1.0. For every subsequent hit the IOR value is 1/ior
flipped.

For underwater render, have possibility to start with 1/ior flipped
could be useful yah. Will check on the problems that come with that! :)

-Ton-

On 3 Apr, 2005, at 15:26, Frédéric van der Essen wrote:

> Ooops...
> replace "negative" by "<=1" and "positive" by ">=1" in my post and it
> should be correct...
> Physically, Ior ranges ]0,->[
>
>
>> indeed it is not negative, if one ior was i_1 than for the opposite
>> direction the ior is i_2 = 1/i_1
>>
>> it comes out from senll's law
>>
>>
>> Anyway
>> On Sun, 2005-04-03 at 12:56 +0200, Frédéric van der Essen wrote:
>>
>>> 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.
>>>
>>>
>>> Daniel Barbeau wrote:
>>>
>>>
>>>> ior_of_material  = Lightspeed_in_void /  Lightspeed_in_material
>>>>
>>>> Lightspeed_in_void is light's maximum speed. 300 000 km/sec If i
>>>> recall well.
>>>>
>>>> Lightspeed_in_material can't be higher than Lightspeed_in_void, so
>>>> ior_of_material can't be lower than 1.
>>>>
>>>> I guess this could be an Elysiun question and an Elysiun answer.
>>>>
>>>> Dani
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------------------------------------------------------------------------
--
Ton Roosendaal  Blender Foundation ton at blender.org
http://www.blender.org

```

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