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View Full Version : how to achieve dispersion?


Sincrol
06-21-2009, 10:48 PM
ok, i was trying to make some diamond but i cant manage to get the dispersion.

even with the Mib_Glossy_refraction the dispersion factor looks weird.


does someone know how to get an physically acurade light dispersion?


( sorry about my crappy english. )

MAV4d
06-22-2009, 12:09 AM
is there a reason you cant map a rainbow gradient to the refractive color to get what you want?

Sincrol
06-22-2009, 12:24 AM
thats not the way dispersion works. =(

lightcache
06-22-2009, 10:31 AM
cant u just use a chroamtical abberation texture on the bokeh lens and kind of fake it?

i know its not dispersion, but it kind of works. u get some nice results.

cbamber85
06-22-2009, 11:15 AM
mib_color_spread

InfernalDarkness
06-22-2009, 09:26 PM
...for reference, it's hard to help you.

One trick that I've used throught my mental ray career is Scale. For caustics, GI, and FG.

In the globals, turn up the scale on your caustics to something greater than one. If you're getting no caustics, try 4, then 8, then up by fours... Also, try Cone and Gaussian (I think that's the third option) in your caustics and see if that helps?

What are your raytrace settings like? What about the material you're using? We really need more info about your scene to help you...

MAV4d
06-22-2009, 09:40 PM
...for reference, it's hard to help you.

One trick that I've used throught my mental ray career is Scale. For caustics, GI, and FG.

In the globals, turn up the scale on your caustics to something greater than one. If you're getting no caustics, try 4, then 8, then up by fours... Also, try Cone and Gaussian (I think that's the third option) in your caustics and see if that helps?

What are your raytrace settings like? What about the material you're using? We really need more info about your scene to help you...

it doesnt sound like hes having that problem, i think what he wants is a physically accruate way of prisiming light.

it might be possible, but your still going to come out with a 2d image that isnt real life... so i dont understand the problem with faking it, its all the same outcome

InfernalDarkness
06-22-2009, 09:57 PM
I tried to do this awhile back, just a simple test animation. It worked fine, but my shapes were very very simple compared to an accurately modeled (Techgems, for example) diamond or actual stone. It would work just fine for those as well.

http://vids.myspace.com/index.cfm?fuseaction=vids.individual&videoid=18925010

That's how the animation came out. Sorry it's not on YouTube or something...

My point is that I used a simple Prism shader to do this. It's not physically accurate. So, I guess to re-answer the question: I have no idea how to make a physically accurate prism in mental ray.

Things to try:
1. Overmodel the diamond. Include microscopic aberrations in the model which may help to bounce the photons around. Drawback: a high ray depth of 100/100 or more may be necessary.
2. Use the others' suggestions for "faking it". The end result is what's important; if it looks right but isn't "physically accurate", you still win.

cbamber85
06-23-2009, 12:08 PM
mib_glossy_refraction/reflection has a dispersion utility as well.

Sincrol
06-24-2009, 05:47 AM
well...

what i want to do is a physically accurade dispersion...
and even if the result is the same as faking it, i think making it as perfect as possible is much more better.. as much it comes close to reality, much better it is.



what is faster and better? keying a falling box? or using dynamics?
when you have a single box.. is ok... but, if you need to animate like 400 falling boxes, i think dynamics is the best solution...

the same i want to aply to this topic. i think, the better is the physical.
ill just need to save the material and im done with that problema again... just load it and apply it to whatever i want. no need to UV map, to make textures to fake it, to worry about anything.

:[

MAV4d
06-24-2009, 06:27 AM
well...

what i want to do is a physically accurade dispersion...
and even if the result is the same as faking it, i think making it as perfect as possible is much more better.. as much it comes close to reality, much better it is.



what is faster and better? keying a falling box? or using dynamics?
when you have a single box.. is ok... but, if you need to animate like 400 falling boxes, i think dynamics is the best solution...

the same i want to aply to this topic. i think, the better is the physical.
ill just need to save the material and im done with that problema again... just load it and apply it to whatever i want. no need to UV map, to make textures to fake it, to worry about anything.

:[

Your not getting it. Once you assign the ramp to the color output for the refractions/caustics it will project it where ever the photo/raytracing bounce through the material. you dont have to uv map, and you have to make one texture once.

its really simple. export the shader out and use it again. if your normals are correct you will see the correct bouncing.

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