RefractionIOR below 1.0

[jop]

Hi,

I try to render air bubbles under sea surface, so I have to set the refract IOR below 1.
Corona mtl don't allow this, so I tried with a corona color map plugged into the IOR slot, but I got weird results compared to what V-Ray does.

Do you have any idea ?

Thanks,
Jérôme

[maru]

If you are rendering bubbles in water seen from above - set their IOR to 1.

If you want your camera to be under water and seeing air bubbles, it's a bit tricky... I was only able to achieve this by placing a plane in front of camera (remember about position and orientation!), assigning a 1,33 refraction IOR to that plane, and then IOR 1 to the bubbles.

[romullus]

Corona mtl don't allow this, so I tried with a corona color map plugged into the IOR slot, but I got weird results compared to what V-Ray does.

If you're using Corona version prior to v1.3, then plugging 0-1 ranged map into IOR doesn't make much sense. In v1.3 however it should behave same as Vray, AFAIK.

[maru]

Corona mtl don't allow this, so I tried with a corona color map plugged into the IOR slot, but I got weird results compared to what V-Ray does.

If you're using Corona version prior to v1.3, then plugging 0-1 ranged map into IOR doesn't make much sense. In v1.3 however it should behave same as Vray, AFAIK.

I am not sure what Vray does, but Corona does something strange indeed. A lens with IOR below 1 should not flip what is behind it upside down, and it does in Corona. I think setting it to 1/1,33=~0,75 does the same as setting it to 1,33.

[jop]

Corona mtl don't allow this, so I tried with a corona color map plugged into the IOR slot, but I got weird results compared to what V-Ray does.

If you're using Corona version prior to v1.3, then plugging 0-1 ranged map into IOR doesn't make much sense. In v1.3 however it should behave same as Vray, AFAIK.

I am not sure what Vray does, but Corona does something strange indeed. A lens with IOR below 1 should not flip what is behind it upside down, and it does in Corona. I think setting it to 1/1,33=~0,75 does the same as setting it to 1,33.

I agree with you maru, that's exactly what I tried and it gave me same result as 1.33.

I use version 1.3

[romullus]

IOR value lower than 1 in textures will now render as 1/value, so you can use LDR maps without using output manipulation. This is to improve compatibility with applications such as Substance Painter.

Isn't the same what Vray does?

[jop]

IOR value lower than 1 in textures will now render as 1/value, so you can use LDR maps without using output manipulation. This is to improve compatibility with applications such as Substance Painter.

Isn't the same what Vray does?

I don't know what's V-Ray behaviour with textures as IOR, cause I only used to input direct values below 1.

[jop]

Do you think it is possible do allow values bellow 0 romullus ?

[romullus]

You'd better ask developers about this to be sure, but AFAIK Corona doesn't support IOR <1.

[maru]

IOR lower than 1 is not supported and it looks like there is no need for it.

Answer from the developers:

you can also assign the water material (fully transparent, refraction 1,33 - no other parameters are required) to the global volume material in render setup > scene, and then assign a material with 1.0 IOR to the bubbles

[romullus]

That is interesting! So if i want to render underwater scene with visible water surface, i should model air volume above, instead of water volume where the camera is located, right? That's need to be tested :]

[dubcat]

you can also assign the water material (fully transparent, refraction 1,33 - no other parameters are required) to the global volume material in render setup > scene, and then assign a material with 1.0 IOR to the bubbles

Cool. I've always made a sphere around my camera with water material on. Need to try this method next time :)

[maru]

At least it looks correct. I just put a plane with IOR 1 as the water surface.

[romullus]

Awesome!