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Tips: TRUE specular materials and formulas for dispersion

PostPosted: Mon Apr 16, 2018 9:56 pm
by nuno1980
Hello, guys. :D 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 - http://www.luxrender.net/forum/viewtopic.php?p=84755 ):
!!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:
ior original no dispersion.png

figure 1 - ior original w/o dispersion

ior original with dispersion.png

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

ior dispersed with dispersion.png

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!! :D

Re: Tips: TRUE specular materials and formulas for dispersion

PostPosted: Tue Apr 17, 2018 7:51 am
by paride4331
Hi nuno1980,
thank you very much for your post, it is very very interesting!
Regards
Paride

Re: Tips: TRUE specular materials and formulas for dispersion

PostPosted: Tue Apr 17, 2018 9:44 am
by nuno1980
paride4331 wrote:Hi nuno1980,
thank you very much for your post, it is very very interesting!
Regards
Paride
Thank very much you too!! :D :D


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