Tips: TRUE specular materials and formulas for dispersion

[nuno1980]

Hello, guys. But this thread is REQUIRED!! Because most guys work to make any specular non-dispersive materials (water, glass, plastic...) for the lack of learning in Chemistry or Laboratory.


>>>>Using Octane Render, to get CORRECT (TRUE) specular settings due to the real life<<<<:

!VERY IMPORTANT!: All specular material should have the dispersion in the real life.
NOTE: You choose any specular material -> refractiveindex.info (NOTICE: not any metallic nor other materials without transmission (T = 0 is invisible as non-refraction))

-- "Reflection":
it should be 1.000 - you don't reduce reflection because lower ior (index of refraction) reduces reflection except:
>>> especial materials - you can reduce "reflection" color and greysale - few examples
- glasses with purples reflection - https://newgradoptometry.com/wp-content ... geller.jpg ;
- filter integrated with purples reflection - https://img.clasf.co.za/2014/12/20/Pric ... 204412.jpg ;
- anti-glare for glasses;
...

-- "Transmission" is 1.000 (greysale) or full color perferred for most specular materials, except water, ice... - see "transmission (T = ...)" showed from refractiveindex.info


-- "Index of refraction" and "Dispersion coefficient":

--> 3 formulas for dispersion (source web - https://en.wikipedia.org/wiki/Cauchy%27s_equation ):
!!NOTICE!! - Not "d line" as 0.58756 µm wavelength (n_d, V_d...) but YES "D line" as 0.58929 µm (n_D, V_D...) for be recommended.

-- Abbe number's formula:

Code: Select all

V_D = (n_D - 1) / (n_F - n_C)

V_D - abbe number
n_D - ior at 0.58929 µm
n_F - ior at 0.48613 µm
n_C - ior at 0.65627 µm

-- Conversion from abbe number (V_D) to dispersion coefficient (B):

Code: Select all

B = (n_D - 1) / V_D * ((0.48613^2*0.65627^2)/(0.65627^2 - 0.48613^2))

B - dispersion coefficient

-- Conversion from original n_D to n_D_dispersed formula

Code: Select all

A = n_D - B / 0.58929^2

--- A is n_D_dispersed

This conversion must enter "index of refraction" as n_D dispersion using Octane Render because you see the example of diamond material - 3 differences:

figure 1 - ior original w/o dispersion

figure 2 - ior original with dispersion -> incorrect because fig. 2 is different ior to fig. 1

figure 3 - ior dispersed (A) with dispersion -> correct because fig. 3 is as equal ior as fig. 1

Find n_D (ior at D line) and abbe number (V_D) of this material:
1- go refractiveindex.info and choose "3D - selected... artists" of "Shelf", "Crystals" of "Book" and "Diamond (C)" of "Page"
2- a) to get the number of n_D: digit "0.58929" (wavelength in µm) and click "enter" button (or press <enter> key)
b) to get n_F: digit again "0.48613" (wavelength) to enter
c) to get n_C: digit again "0.65627" (wavelength) to enter

Calculate 3 formulas of this material:
1- to get abbe number

Code: Select all

V_D = (n_D - 1) / (n_F - n_C) = (2.4166 - 1) / (2.4305 - 2.4089) = 1.4166 / 0.0216
=> V_D = 65.58

2. to get dispersion coefficient

Code: Select all

(n_D - 1) / V_D * ((0.48613^2*0.65627^2)/(0.65627^2 - 0.48613^2))
= 1.4166 / 65.58 *  ((0.48613^2*0.65627^2)/(0.65627^2 - 0.48613^2))
= 0.0216 * 0.523655 => B = 0.01131

3. to get A (= n_D_dispersed)

Code: Select all

A = n_D - B / 0.58929^2 = 2.4166 - 0.01131 / 0.58929^2 => A = 2.3840

After calculation, on Octane Render enter in specular material settings:
- "index of refraction" - 2.384 (= A = n_D_dispersed)
- "dispersion coefficient" - 0.01131


If you are any worry with any noise colored, you can disable "dispersion coefficient" as 0.000 or you need to apply new AI denoiser in new OR v4 XB1.

If you have any doubt, you can reply here.


Fantastic rendering!!

[paride4331]

Hi nuno1980,
thank you very much for your post, it is very very interesting!
Regards
Paride

[nuno1980]

Hi nuno1980,
thank you very much for your post, it is very very interesting!
Regards
Paride

Thank very much you too!!


@Admin or @moderator: I ask you pin to this thread because this thread is very important and guys find EASIER here.

[nuno1980]

Happy holidays, guys!

I change link...
from:

--> 3 formulas for dispersion (source web - http://www.luxrender.net/forum/viewtopic.php?p=84755 ):

and to:

--> 3 formulas for dispersion (source web - https://en.wikipedia.org/wiki/Cauchy%27s_equation ):

Because luxrender's forum is "dead" - my user is lost (forum).

[GXGsynth]

It would be awesome if there was a list of truly accurate Octane IORs + dispersion coefficients for basic glass + gemstones, or at least a spreadsheet that would make it easy to enter the formulas for different materials, this math is really incredible but a bit over my head and a lot of work to do!

[nuno1980]

Watch below about learn "Silverwing Long Tip: Diamond Series: The Shading" and any other specular material but on "Cinema 4D" and NOT on Octane Render (OR) standalone.



NOTICE: The Abbe Number bar is NOT available under OR standalone or plugin without any 3rd party.