### Tips: TRUE specular materials and formulas for dispersion

Posted:

**Mon Apr 16, 2018 9:56 pm**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 - 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:

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):

B - dispersion coefficient

-- Conversion from original n_D to n_D_dispersed formula

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

2. to get dispersion coefficient

3. to get A (= n_D_dispersed)

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!!

>>>>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`

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!!