Testing physics proprieties of light in Octane

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FractalBuddha
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Hi,

I made some tests to see how far Octane can go at representing reality.
I am new with Octane, so I hope I did not make errors.

Pinhole photography
Worked
Theory : http://en.wikipedia.org/wiki/Pinhole_camera
I put the camera inside the box. It worked very well. The projection is blurry because the hole was relatively big.
The picture is lighted by the sun at full power.
pouiles boite noir.png
Sketchup model of Pinhole camera
Sketchup model of Pinhole camera

Refraction and total internal reflection
Worked
Theroy:
Refraction http://en.wikipedia.org/wiki/Refraction
Total internal reflection http://en.wikipedia.org/wiki/Total_internal_reflection
We can see that the blue and yellow ray are totally reflected into the glass bloc, because their incidence angle is to large.
The red and green ray passe trough the glass bloc and exit with the same angle they enter.
Forget the red, blue and yellow ray at the top right, they are passing over the bloc.
total internal relfection.png
Primary colors mix Worked
Theory http://en.wikipedia.org/wiki/Primary_color
On the left I projected on a white surface the red, blue and green lights.
On the right, a white light passe trough a yellow, cyan and magenta filter.
primary colors.png
Curved mirror Worked
Theory : http://www.physicsclassroom.com/class/refln/u13l3d.cfm
mirror 2.png
mirror.png
Diffraction Failed
Theory http://en.wikipedia.org/wiki/Diffraction
This was a though one :P . It is relative to the wave aspect of the light and I don't think it is useful for this kind of program.
A monochromatic red light is passing trough one slit.
diffraction.png
Shadows with SSS Failed
I made a quick test for leaves with a mix material, one is glossy, the other is SSS.
The two pictures are the same scene rotated by about 180°.
I don't see on the right picture, the shadow projected by L2 on L1 as I should in real life.
Feuilles.jpg

It could be fun if you want to add more tests :)

Thank you!
Last edited by FractalBuddha on Sat Dec 24, 2011 12:57 am, edited 4 times in total.
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MaTtY631990
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Not sure diffraction is supported at the moment or if like you suggested it's not a feature at the top of the list for software such as this. Also the shadow not being seen could be a bug. Their is another bug involving sunlight not passing through glass, so this could be another anomaly. :)
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gabrielefx
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MaTtY631990 wrote:Not sure diffraction is supported at the moment or if like you suggested it's not a feature at the top of the list for software such as this. Also the shadow not being seen could be a bug. Their is another bug involving sunlight not passing through glass, so this could be another anomaly. :)
missing caustics with the sun is not a bug. The cause is the difference between real emitters and the sun scale. Refractive will simulate the caustics through glasses creating a fake sun.
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FractalBuddha
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This work fine with a light source different from the sun. I have a shadow.
Leaves test with light
Leaves test with light
I don't understand what do you mean by :
gabrielefx wrote: missing caustics with the sun is not a bug. The cause is the difference between real emitters and the sun scale.
I tried different size of the same leaves without having a shadow with the sun.
Scale
Scale
Last edited by FractalBuddha on Sat Dec 24, 2011 3:22 pm, edited 1 time in total.
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FractalBuddha
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After the end of the 64000 samples of render, is it normal that my reflected and transmitted rays are so much granular ?
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Proupin
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nice tests, probably pmc is best for the prism type ones
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FractalBuddha
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I tried with pmc.
The rays are smoother but very faint compare to the power of my sources.
rayon pmc.png
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Proupin
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Weird that the yellow beam looks turned off altogether... I did some tests back when PMC just got out (dispersion), and it converged pretty nicely. You moved the prism up, I feel the previous setup (where the two upmost rays entered from the side) could explain TIR better.

Other phenomena that Octane could support include Birefringence (ice), polarized light, thin films (coatings) and anisotropy. Besides coatings that can be faked with mix material, don't even bother with the rest I think as these aren't supported afaik. Diffraction would be nice as well.
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FractalBuddha
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I just did not lit the yellow light :P
Yes, I changed the configuration of the scene to see the reflection on a wall. TIR ?

I think birefringence could be easy to add I think, they just have to add a second index in the proprieties.
I will make test, but an absorption texture mapping could maybe give the impression of anisotropy ?
I wonder how polarization could affect the render of a scene. You have to wear polarized glasses to see or hide polarized zones.

I hope someone will show me how to have shadow with SSS with sun lightning.
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Daniel
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As a physics student I enjoy seeing these test results. I, too, tried diffraction once. :P
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