creating glass in mental ray

[Ken Koala]

try using a dielectric_material in the MR material shader in the SG node. Make the colour close to white. Check ignore normals.

Also apply a dielectric_material_photon node to the Photon shader. Make same changes as above.

Good luck
Ken
:beer:

Remember that final Gather photons will not got through glass because you cant change the photon depth in the interface. This can be changed in the mi file
Global Illumination photons can go though glass as u can change this setting in the globals.
Maybe this will change in Maya5.

:thumbsup:

[xn3ct]

i tried it and nothing. is there a tutorial out there for such thing?

[tumbi]

Ken Koala - you know
please tell us in depth or atach Print screen of this steps
i'm trying to to made realy good galass + caustics in mray

:love: :love: :love:

[Jozvex]

I've attached an image of the settings I use for most of my glass materials. It should give you some idea of what settings to use. I've put red spots next to the settings I've changed.

To see what sort of glass my material makes, just go to:

http://www.geocities.com/jozvex/lollies.html

or

http://www.geocities.com/jozvex/table.html

[tumbi]

Jozvex, thank you!!!
:bounce: :bounce: :bounce:

and for your tutorials :beer:

[Jozvex]

No problem!

Most of what makes glass look like glass is the environment/scene that is reflected/refracted in it. So make sure you have enough cool stuff in your scene.

:thumbsup:

[augustus]

You also need to simulate Freshnel effect to get realistic glass. Remember the high school physics lessons: if the object is transparent, amount of reflected light increases with angle. To can simulate this effect using a sampler info node and a ramp:

sampler info's facing ratio -> ramp's v coord
one of the out color channels of ramp (r, g or b) -> shader's reflectivity

Ramp should be a v ramp, say, 50% gray (bottom) to 70% gray (top).

[Jozvex]

Oh yeah I forgot that part!

And the Fresnel effect is not just for glass or transparent things, it's for all non metals I think. It depends on their refractive index how great the effect is.

Unfortunately from what I've discovered it seems like Maya doesn't take into account refractive indices over 1. Which is a shame.

Automatic Fresnel would be cool.

[augustus]

AFAIK, if the angle of incoming light is greater than a treshold angle which depends on object's and environment's IOR, light can't go into the object, and all reflect. So, object needs to be transparent I think :shrug:

Edit: But you can be right, cos all non metal objects are translucent, more or less :hmm:

[Gremlin]

sweetly... im gonna do some stuff soon (some mini-projects comin' up, specially with the ending of school) and Im gonna see if this glass material will come in handy. (maybe ill map a reflection onto it? I dunno, we'll see)

jozvex, stop trying to have more posts that me!!
hehe,
Cheers
:beer:

[Jozvex]

What........you mean like this??

Nahh, I just post if I think I can help. Hehe I probably try and help too much. One day I'll get a PM saying "Shut up already!!!"

:surprised

[Jozvex]

I forgot to reply to Augustus because I was distracted with Grelmlin...

I think we're both right and wrong. Have a look at this article on the topic by Neil Blevins:

http://www.neilblevins.com/cg_education/metal_and_refs/metal_and_refs.htm

Here's an excerpt:

Fresnel and IOR

".......This brings us to the concept of Fresnel and IOR. Materials are assigned an IOR based on how they reflect light (IOR stands for Index Of Refraction, but even non transparent objects such as metals have an IOR, usually referred to as a "complex IOR". A complex IOR measures a slightly different property then a regular IOR, but it deals with the same stuff, light reflecting or refracting off / through a surface). As a surface starts facing away from the viewer, it reflects more then a surface that is directly facing a viewer......."

I hope I'm allowed to post an excerpt like that... :shrug:

[augustus]

Thanks for the info:thumbsup:

Different materials have different IORs, some good example are air is 1.0, glass has an IOR of about 1.5, Gloss materials such as porcelain or car paint 3-5, super shiny metals like chrome a value of 10-20. The IOR controls the proportion between how much the faces pointing away from your reflect vs the faces pointing towards you. For example, a lower IOR means that the away faces will reflect a lot, and the faces facing your reflect very little, and a higher IOR will make just abut all faces of your object reflect the scene the same amount

So we don't need to worry about shiny metals anyway, because freshel effect is too small.:shrug:

[Jozvex]

Haha I guess not! Maybe you could still add just a tiny amount. Just so it's there.

It's the thought that counts in CG! Everyone know that!

:scream:

[Gremlin]

JESUS JOZ... you post so much within 1 thread its abnoxious. there is this feature called "edit" LOL, no need to post twice in row (unless you are of course tryin to post more than me)

hehe, but at the moment, i have 2 full posts more than you. hehe, which one will be the first to the 400 mark? (Im gonna be starting a thread soon, thats lotsa posts right there... cause im gonna be modeling a porsche and a blue cartoon moose)

BEWARE!
:beer:

[Jozvex]

Hehe this is my 7th post this thread!

But I'm not trying to be abnoxious! I'm just trying to help! Notice how the only off-topic messages I've posted are in reply to you!!

And now to keep things ON-topic, here are some useful links. Firstly a link to a table of refractive indices for different mediums/materials:

http://hyperphysics.phy-astr.gsu.edu/hbase/tables/indrf.html

And secondly a link to a great resource on materials in general:

http://www.neilblevins.com/cg_education/cg_education.htm

:p

[xn3ct]

strangest thing happened...

i just upgraded maya from maya 4.5 to version 5, and installed XP on my computer. Before that glass would render in mental ray not in an expected manner, if I had a glass of water in the center(where the concave region is) there would be a black area. Like this:
http://www.cgtalk.com/showthread.php?s=&threadid=58053

I was told that in standard maya reflective/refractive materials the photons would not pass through, and i had to add MR shaders to the standard one.
Now I got my upgrade and now the render is just fine, the photons seem to pass through the material like there never was a problem. You can see below:
http://www.geocities.com/marcel_pi/index.htm
Then click on the mental ray.jpg link.

Why? Why can i do now what i couldn't do then(got nothing changed)?

[Jozvex]

Maybe it's because you had some of your settings on "Derive from Maya" before, but there's no such option in Maya 5, so it just used default MRay values?

No idea..

[augustus]

I've read at somewhere (Highend 3d i think) the problem is, you cannot set photon depth for final gather within Maya, you need to alter mi file. Can you enlighten us about this issue Jozvex?

[Jozvex]

Hmm well I didn't think it could be changed!

Can you try to find where you read that augustus? I had a look around on Highend but couldn't find anything.

[Ken Koala]

Originally posted by Ken Koala
Remember that final Gather photons will not got through glass because you cant change the photon depth in the interface. This can be changed in the mi file
Global Illumination photons can go though glass as u can change this setting in the globals.
Maybe this will change in Maya5.


If you render thought the command line insert -finalgather_depth N N N
N N N represents no. for depth for reflect, refract and total
You just need to worry about refract. Set this to 2. Watch rendering times increase.

Regards
Ken
:beer:

[Jozvex]

Hey thanks Ken Koala!! Didn't know that. I must look into more command line options....

Can you edit a file so that these settings are default in Maya? Or at least used in Maya?

[Ken Koala]

Originally posted by Jozvex
Can you edit a file so that these settings are default in Maya? Or at least used in Maya?

No, well not in Maya 4.5. I don’t think it can be done in 5 either.
For command line options type -help at the prompt. This will give you all the options.

Good luck digger
:thumbsup:

[Gremlin]

good stuff in this thread... I like the table of refraction. but I have a secondary motive for posting this....
Jozvex.....OOOHHH, 400th post
thats right, I got it first... now pay up! ($19,000 just like we agreed)
Cheers,
:beer:

hey also, as far as compositing goes... dont some people just do the refraction in post (like in AE) with the glass or whatever on a layer?

[Jozvex]

"Oooh look at me! I'm from California and I have 400 posts!!"

Yeah?? Well I'm older than you by 4 years so :scream: ya little ankle biter! Hehe and I have 600+ posts over on 3DBuzz. You know what I think of when I hear "California"? I think of people rollerblading near the beach in g-strings hehe, like on the movie "The Birdcage".

And $19 000 US would end up being like $30 000 Australian dollars! Can I pay you......some other way? Errr, nevermind.

As for doing refractions in post, I'm not sure how that'd work... I haven't done much compositing yet.

And thanks again for the great info Ken Koala!

[augustus]

Thanks for the info Ken Koala:thumbsup:

[xn3ct]

yeah thx for the info, ken koala... i just don't know why they didn't include this option in the final gathering tab(or whatever). but they should have included it somewhere instead of just having to type it in the command line. lots of people don't especially use the command line(myself included), so that means that they are never going to be able to render proper looking glass with MR. how sad.

the thing i hate about MR is that it is complicated, not well documented and definitely not straight forward(as we are used from the products of alias). so i don't think the whole concept and structure of MR fits with the ALIAS|WAVEFRONT philosophy, which is clarity and ease of use. :thumbsdow

[Ken Koala]

How true xn3ct
Although at one stage we were using MentalRay as a stand alone package where everything had to be typed in (that’s right, EVERYTHING including material properties etc...). Today we still use the standalone version but only for rendering thought command line.
Don’t forget this is a physical based programmable rendering package. My major problem is that the version differences between the stand-alone package and the incorporated MR. At least Maya 5 has bridged the gap to a degree. Such a complex programme takes years to understand especially when there are few decent tutorials. I would like to see more wide ranging tutorials released by Mental Images as well as AW.


Remember that rendering in the command line will be faster than interface rendering.

Ken
:beer:

[Gremlin]

LOL...
someone seems a bit sour. *sigh* anywho, I gotta start my character modeling process soon... but I got a question. Jozvex, i'll PM it to you since your a "know-it-all" ...ya smartass.
Cheers,
:beer:

[Jozvex]

I didn't call myself a "Know-It-All"!! It just does that automatically once you reach a certain post count!

Hey Ken, do you know how to get MR to calculate volumes properly in Maya 5? (eg with a Raymarching node etc) Because it seems to treat transparent areas of a volume as being white volume, not transparent.

[Ken Koala]

Sorry mate, volumes are one thing I have been battling with.
I am assuming that you are after a non-homogeneous volume

There was a thread a few weeks back regarding volume shaders
I have not made the upgrade yet so I’m still on 4.5.
I’ve been doing my volume/fog in post if I am rendering with mr

Ken
:banghead:

[Jozvex]

Ok, thanks Ken!

I'll just have to wait for someone smarter than me to figure it out, or until a new version is released.

:surprised

[xn3ct]

ken, although the command line rendering may be faster than the interface rendering, me and most of the people for that matter aren't going to learn the commands. so we are left with the interface. another thing that i don't like about MR is that you have to learn all kinds of particular cases and exceptions to the rule... meaning that you cannot learn the rendering engine as a whole, but you have to learn different approaches to different situations. If you want to create volumetrics you have to learn how to do that, if you want to create transparency shaders you have to learn how to do that also. It seems that there isn't a general scheme and structure to MR, and each problem has to be approached in a different way, instead of knowing how to approach each problem based on a clear architecture. So instead of mastering the program in a matter of months, we have to experience all the difficulties listed above. No wonder it takes years.

I'm expecting the day when MR will be completely integrated in maya, and we are not supposed to build MR specific shaders that override the Maya shaders etc, etc. The smartest move for alias would be to create their own fully integrated rendering engine, with all the capabilities of MR, brazil, vray etc. They don't need the "help" of mental images. Hope that day will come.

[brunner]

:surprised
Yes, advanced rendering with MR is more difficult to master than other renderers. So what? Since when the quality of a renderer is measured in learning time?
That makes Renderman the crappiest renderer of all, no?

It seems that there isn't a general scheme and structure to MR, and each problem has to be approached in a different way, instead of knowing how to approach each problem based on a clear architecture
:surprised :surprised
Can you be a bit more specific on what bothers you? what "general structure, clear architecture"?
I strongly suggest you grab a book on MR, you won't find the "do kewl render" button from the other renderers here. And it seems this is a problem to you.

[brunner]

me and most of the people for that matter aren't going to learn the commands.
Why? The full power of MR is unleashed by writing your own shaders, and using the dreaded command line..

But again, maybe MR is just not suitable for your needs, not everybody likes tweaking and studying rendering techniques, some people just want the rendered to decide for them...

[xn3ct]

brunner... have you read the post at all or just dropped by to write a "well thought" reply? i have read you posts on visualart.ro and you seem to have an obssession with "do kewl render". please.

the main reason i abandoned 3dmax after 3 years of use was that it required all the plugins and all the work-arounds. it seemed it wouldn't give you the needed tools to be able to construct your scenes as you thought you would.

now maya is totally another world, and guess what... it provides the tools to do almost anything you wish. and you know that it is straight forward which means that if you encounter a problem you pretty much know how to approach it.

you misunderstood. just because i asked for the proper tools doesn't mean i'm expecting the software to do all the work for me... no way. and yes i'm willing to learn and experience new techniques, hell i'm doing that already, you're not the only one that is struggling. come on.

the situation with the MR architecture is the following... how should i put it to make it easier for you to get it?
it's like a math problem that you can solve. there are two possibilities of doing that:
I. either you actually know what you're doing and know how to solve it, you just need to work. which is great.

II. or you follow an algorythm. now if you follow an algorythm, you don't actually know what's happening, but you know it gets you there. would you not rather be in the first cathegory?

in maya even when i was a beginner i was able to see things clearly, and figure out a solution. in contrast with MR. now i don't think i can make it any clearer than that. do you get the big picture brunner? am i clear to you?

you seem to be the type of guy that appreciates the technical skills over talent. and that is just what these softwares are doing, they require you to spend far more time than necessary on learning them(and by that i don't mean i am not willing to learn, duh!), which eventually buries talent. you would admire a man that is an absolute expert in MR(or whatever software), rather than an artist that is pretty good in MR but can create images that talk to you.

so please brunner next time you reply to a post, take your time to read the whole thread, and preferably think twice about what you're saying.

regards.

[brunner]

You need to go beyond the "tutorial" style learning.
You don't have a global understanding of the way MR works, just fractionary bits of information gathered from the tutorials.
That's why you're puzzled by the approach required to do some things.
Take some time to experiment, to RTFM, get a book if you can. It will help you to understand the general picture.
Of course there will be some hacks to learn, some tricks to master, but that's the way computer software works :)

As for the "read before you post" thing, don't even go there. Why do you resort to personal attacks just because someone disagrees with you?

[xn3ct]

personal attacks... hmmm i don't think so.
at least it wasn't me who replied with the pissed off tone. and i quote:
"you won't find the "do kewl render" button from the other renderers here. And it seems this is a problem to you."
and
"But again, maybe MR is just not suitable for your needs, not everybody likes tweaking and studying rendering techniques, some people just want the rendered to decide for them..."

you were the offensive one, ok? some people?
you just got what was coming to you...

ta ta.

[Jozvex]

OK, I think a chill pill is in need right now.

Mental Ray is only new to Maya, we're still going through the rough transitioning stage where not everything is clear and integrated properly yet. It's too much to ask for it to be perfect in the first version.

All we can do right now is learn as many bits of it as we can, and look forward to the day when it's as easy and straightforward to use as the rest of Maya.

Everyone should try and make learning MRay as easy for others as possible by sharing what they know. Which is what this thread has done up until now. The more info that is shared, the easier and more fun it'll be for everyone.

[xn3ct]

that was a word from the heart jozvex... i appreciate it.

looking forward for the rest of your tutorials.
and btw what was your approach to mental ray, which path led you to where you are now?

books, tutorials, books&tutorials?

just hope MR will live up in the future to the reputation of maya.

best wishes.

[Jozvex]

Well, I had already used other advanced renderers such as Brazil and Vray for quite some time. So I already understood most of the global concepts like GI, photon mapping etc

But for learning Mental Ray specifically, I've just been experimenting a lot and reading whatever I could find on the internet. I've read a lot of the help file even though most of it is too technical for me at the moment. Mostly I would just find a hint to how I should be attempting something, rather than finding an answer.

Forums are another fantastic way to learn things too of course. Over on Highend3D there are quite a lot of good MRay threads with useful information.

And that's about it really! I haven't got any books on it, though they're something I'm considering.

:thumbsup:

[MunCHeR]

posted by Ken Koala:
try using a dielectric_material in the MR material shader in the SG node. Make the colour close to white. Check ignore normals.

Also apply a dielectric_material_photon node to the Photon shader. Make same changes as above.
----------------------------------------------------------------------------------

Would anyone be able to elaborate on this a little, I feel a little hypershade illiterate here :surprised

Thanks for your time

MunCH

[Emmortal1]

One thing I'd like to remind people of is that MR is not your standard renderer. Why do studios such as ILM run Mental Ray and Renderman? Because they both have their strong points and are extremely powerful renderers. The "other" renderers such as Vray, Brazil etc can't even come close to what Mental Ray can do in some instances. Sure you can get some nice effects with a few tweaks, but if you want specific control, forget it. Your one button "look cool" renderer falls flat on it's face.

Yes it will take some people years to master Mental Ray, there are people that have been using it since it's inception and still don't feel they've "mastered" it. Which there is absolutely nothing wrong with that, you just need to know what you have to in order to get the job done. The integration into Maya is far from intuitive, there are a lot of things that I wish they would add and fix, which I'm sure with time they will. On the other hand however, having as much control over my renders and to be able to do practically anything I want is something I wouldn't trade for anything.

There's really no reason to argue about it and no reason to complain that it's too hard of a program to learn, that's just how it is and it should be expected. It's going to be required that you put more effort into learning it, if not just go use one of those "other" renders and be happy.

EMmortal

[i-d]

To keep the flame blowing:buttrock:

Emmortal I need to totaly disagree with you on that last ting you wrote.
I never touched vray or brazil but I see people using them making some extrordinary renders.
They are studying and experimenting with their renderer very
hard, making some great images in the process.
Is it the button you press when you render, or what?

[Ken Koala]

I would take more of a harsh view about the last two posts. I'm a big believer that you could master the technical aspect of any program (obviously restricted by intellectual know-how) but the difference between a good and average image is the user. What I mean is that you need to have THE EYE (both artistic and photographically speaking). I've seen alot of images that could be improved by just altering the composition or changing the scene colours
Anyway, side tracking abit from original post, I think you shouldn’t restrict yourself to one particular package. I try to know a select few as each has its +'s and -'s. Its up to you.
Ive have been using Metalray for several years and feel I’ve just scratched the surface. As I am not a programmer I tend not to dive too deeply into MR. Hopefully one day MR (stand alone version) is totally integrated within Maya and is as easy to use as Vray etc.....Its getting better
Good luck guys and girls.

Ken

[Jackdeth]

MR isn't for everyone. Its tough as hell, but if you can smack it around, it looks amazing.

For us, the Maya rendering should be deleted and burned at the stake. But that is the opinion of my company, and others may like the the way it looks. Everybody is different, and if you dont have a great support staff, MR and Renderman might be bad choices...

If this was all easy and perfect....then what fun would it be???

[wgreenlee1]

Everybody is different, and if you dont have a great support staff, MR and Renderman might be bad choices...


that will change here shortly
more and more people are going with these accurate render engines like mray and renderman ,lightwaves renderer is falling way behind and and even for the render farm savings it doesnt mean squat when it comes down to the quality and speed ratios of these highend renderers like mray
even C4D is about to whip up on lightwave because for the money and moduals you can get just as good or better from even that
its only a matter of time before the markets are swamped with people that work mray and renderman

[joie]

I´m also trying to use Dielectric material with no success..., I connect it to the material tab of the MR atributes of the shader, change some atributes (color or IOR) and all I can get is a black hole in the render (also in alpha channel), I connected all lights in the scene as espected and nothing changes, I get the same black hole...

Please could you guys post some step by step tutorial or screengrab of an example?

This would be very kind of you if you could do it for us...

Thank´s in advance!.

[xn3ct]

well i finally got it right, don't ask how. basically i did the same thing as before only that this time it worked. by the way i'm using maya5.

copy/paste this link to see the result: http://www.geocities.com/marcel_pi/mental_ray4.jpg

enjoy!

[thematt]

here is a tut for dialectric mat..

http://www.matty3d.de/MayaTutorial/dielectric_material/index.htm


cheers

[joie]

Thank you very much, I was doing the same but now it worked..., LOL

[MunCHeR]

Thanks for the tute thematt, very useful :p

xn3ct your link doesnt work buddy, oh well cheers guys

regards

MunCH

[Emmortal1]

I-D: My point was not that Vray or Brazil were not as good renders as MR, in some aspects they are better, but in most they are not. My point was, that some seem to miss, is it's more based on the user who is using the software. Some people will pick it up faster, others will not.

Anyway, hope that clears that up. Lets try not to get off subject here with this anyway, we all have our own opinions and that's a good thing. Take care,

Emmortal

[i-d]

I agree completely. So to stay with the subject here is one older
rendering where I first tried dgs materials. It was a general chaos
because I didnt know where to put all that connections but somehow I manage to do it. Now is much easier:bounce:

http://www.i-d.hr/mr/CustomGlassWineB.jpg

As you can see glass is real fine in bottom part where is only one refraction surface
but when another is introduced (wine) lots of different problems arise.

http://www.i-d.hr/mr/CGlassWine.jpg

I would like to rerender this scene using all my bright new knowledge of dgs shading and photons
but I would like to use diffraction shader for my glass off wine.
Theres no explicit direction how to connect it in maya (believe me I tried everywhere),

btw theres a new version out, with all needed maya files.

http://animus.brinkster.net/index.html


Help

[joie]

I´ve made some test renders today and I must say that is very impressive, and you haven´t to connect any light to the shader (a time saver).

[augustus]

Theres no explicit direction how to connect it in maya (believe me I tried everywhere),

You should connect your material shader (dgs, dialectic etc.) to input of diffraction shader, and diffraction shader to mental ray material shader of shading group.

[Pixero]

Thanks for the info Augustus.
Do you think you could post a scene file for reference of your settings? A glass of wine or something.
I´ve been trying to get this to work for a while and cant really see any difference in my renderings. Should refractive index and absorption be set on both nodes and so on?

[sebast1an2]

one moment..hmm you talking about connecting a diffraction shader? but why? i though that diffractions and this "fresnell" effect are automatic computed by this shader on the physical way, and it looks as if this is calculated automatically...

:shrug:

[Jackdeth]

The defraction shader creates the prisim light splitting effect.

[Jackdeth]

The MR defraction shader creates the prisim light splitting effect. You are thinking of the Maya defraction shader. Same name, two different things.

[sebast1an2]

hmm no, i thought about the mr dielectic material...

[i-d]

Diffraction mray shader is more than "prism light splitting effect" shader,
it suppose to be advanced refraction shader, one that could behave
more predictable and "physically accurate", with many options,
some of them you dont even need (like glossy or aberation) to get a good glass,
and thats a goal (at least in this thread :) ).
But to my misery this shader is not working for me, and I dont
mean working badly but making my other shaders (dirtmap, mdsubscatter..) not loading and maya render abort.

Did anyone had simmilar problems?

[Digidim]

...nope...works good for me...however it´s fu#!ing (oops) slow...

[Digidim]

...for those still having problems with diffraction_shader/dielectric_materials...i put together a quick scene (inspired by one of the pics you find in Brazil gallery -> click (http://www.splutterfish.com/sf/sf_gen_page.php3?page=FeatureGalleries/materials))...feel free to play with it...

http://www.angelfire.com/bug/digidim/swans.jpg

Scene-File (150kb) (http://www.angelfire.com/bug/digidim/swans.mb)

[KaB]

Where did you guys get the diffraction shader? Its not showing up in my MR shader nodes.

[Digidim]

Diffraction Shader (http://animus.brinkster.net/stuff/plg_diffraction/plg_diffraction.html)

[KaB]

Thanks Digidim :)

Testing it out now.

[AniMo]

hmm i tried to install the diffraction shader
but the zip dosent icludes any .DLL !?
dont i have to insert some lines into the "rayarc" ?
in the doc is nothing discribed about htis this time

so i dled digidims szene and get bunch of erros.
also the dirtmap used by digidim doesnt shows up here i cant see its values its a blank node

and the render looks ugly

did i miss something !?

[Digidim]

After extraction...you should find the .dll here:

...\nt-x86\package\Diffraction.dll

_________

Lines to add in maya.rayc:

link "{MAYABASE}/lib/Diffraction.{DSO}"
mi "{MAYABASE}/include/Diffraction.mi"
_________

Create a new Dirtmap node and replace it with the old one...

[wgreenlee1]

im having probs also but ona fresh scene it looks ok but i cant get the fuzzy rainbow colors without adding a ramp
can someone post a pic of the settings or hypershade connections?

[KaB]

Been playing with the Swans scene that Digidim posted. I am having problems getting the Diffraction Swans to render, they always render solid black. Any ideas why?

The Diffraction file comes with a lot of XSI files. I hope I installed it right.

\Maya5.0\mentalray\lib\Diffraction.dll
\Maya5.0\mentalray\include\Diffraction.mi

Included the start up line...

mi "{MAYABASE}/include/Diffraction.mi"

in the maya.rayrc

EDIT **
Got it working, forgot to place this line in maya.rayrc
link "{MAYABASE}/lib/Diffraction.{DSO}"

Working great now :)

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