conversion abbe number -> dispersion coef?

[nuno1980]

Hi!

Dispersion of prism specular

Abbe number - 3 -> dispersion coefficient - ?

How do I convert this?

[nuno1980]

dispersion coeff 0.018 - is it correct??

How do you/I convert that??? - What's formula (conversion)?

[nuno1980]

Sorry but between "Abbe number" and "dispersion coefficient" aren't converted because...
eg: Abbe nr 3 seems be dispersion coef 0.018 due to the SAME refractive index by rainbow but Abbe is richer colors than dispersion coef..


Therefore, I respect Abbe number will be added for "specular" material to newer version of OR, ok?

[nuno1980]

Good idea! But yes...

In Arion, in Thea Render... -> In Octane Render

Prism by glass
IOR - 1.5 -> IOR (by rainbow) - ?
Abbe nr - 3 -> dispersion coef - ?

Water
IOR - 1.3333 -> IOR (by rainbow) - ?
Abbe nr - 55 -> dispersion coef - ?

How do you calculate "?"'s?

[nuno1980]

I'm very confused! Due to zero replies! GRRR!

[abreukers]

Hi nuno1980, So far, the dispersion in Octane is based on Cauchy’s equation, with two terms:
index of refraction (IOR)
dispersion coefficient (B)

A formula is found at http://render.otoy.com/forum/viewtopic. ... 1&p=104449 and a small explanation about dispersion can be found here: http://render.otoy.com/forum/viewtopic. ... 4&start=40

(not an expert on this so the above can't be said any better, thus I hope the links will help).

Can you tell us what you would like to simulate?

[nuno1980]

@abreukers:
I'll try test. But attention: if any object has dispersion then we should reduce ior from ior original - eg:
-ior 1.5 without dispersion -> ior 1.5
-ior 1.5 w/ dispersion ~0.045 (=Abbe nr 3) -> ior 1.32

Can you understand? Sorry, ior 1.32 and dispersion 0.045 may be not correct. But I'll test to see the difference between OR and Thea Render...


---> Tried to click http://render.otoy.com/forum/viewtopic. ... 4&start=40 but I got "You are not authorised to read this forum.", unfortunately.