Mental Ray - Render Troubleshooting


You should increase the samples value of something. Most probably the materials’.


This is very weird - I seem to have intermittent artifacts on renders where I get what looks like a layer of bumps/embossed effects on the render.

You can see it at the edge of the shadow on the attached file.

Anyone else had this?




I have been playing around with lighting a subway car I have and am getting really long render times. It’s not a really big poly count (1/2 million or so), but as soon as I turn on shadows I am getting any where between 5 to 25 minute render times.

Subway has 2 long rows of fluorescent lights that run the length of the car.

I have tried using 2 really long photometric area lights, but don’t get the effect on the ceiling I’m looking for.
I tried using the Photo web with 4’ long tubes and instancing so I have a total of 20 lights - I get a nice result, but takes 20 minutes to render.

Any suggestions?



                         [b]Extralarge PartiVolume Caustics[/b] 
                                          (Edited: This scene don't works in Max8)

In Jeff Patton Post 169 on Page 12, there is a link to a Volume Caustics. I think that
theme was not well developped. Here is my contribution.

 In the max file (Max 7.5) you can uncheck the Diffuse Noise Map in "Caja" Material 
 to increment render speed.
  Render the Frame #0 if you want the light to the Sphere. Render Frame #25 if
  you don't want that ray.
  Use material Esfera2 (I think you must retouch it something) for a better
  glass material but very large render time.

Hey Bao2. I m wanting to make something like this scene but in Max2009. I see you had problems trying to recreate it in Max 8. Did you figure out a way to do this in later versions of Mental Ray?



Is it possible to get a truly realistic looking motion blur in Mental Ray? The effect I’m after is the rotating properller is as in the photo below. Note the really vivid highlights. I have not ever been able to get these highlights in 3D, as they simply gets smudged over the various frames. Any ideas?

NB. For the time being I am only interested in doing high-res still images like this, but ultimately a fast-rendering solution for animation would be ideal.


Hello everyone,

I work in the car vis business and having trouble with the car paint phen mat in Maya.
the hood of the car shows a moiree pattern when the flakes get to small.
we really need them to be that small but want to lose the moiree pattern.
We have tried upping the sampling, used fixed sampling, put a fractal shader on the flake component but it doesn’t go away.

Anyone have any ideas???


Mangoplukker, try to look into a different way of texture filtering. In 3DSMAX I set my textures to Summed Area filtering (opposed to the standard pyramidal one). This has solved all moiré problems for me in the past. Perhaps Maya has something similar?


FWIW, the “jitter” option is a mental ray option we can use in 3ds Max to help reduce Moiré. I have no idea what it’s called in Maya as I don’t use Maya, but it’s something to look for.


Thanks Jeff and Skyraider,

Skyraider: Texture filtering won’t help because it is a shader problem

Jeff: Tried the jitter option and it doesn’t offer a solution

Still thanks for the quick response


Hi Jeff, good to see you’re still following this thread! :wavey:
Would you have any ideas or suggestions regarding specular highlights on motion blurred objects as mentioned in my post on the previous page?

Mangoplukker, I was afraid of that. The only thing I can think of is to render bigger and downsize the render afterwards. Hopefully this smooths out the moiré. Not an ideal solution of course…


Would you have any ideas or suggestions regarding specular highlights on motion blurred objects as mentioned in my post on the previous page?

This may be of help to you:

If I remember correctly Andrew Kramer overlays the footage multiple times to create overbright highlights in the motion blurred footage.

If this is totally unrelated then I’m sorry. :slight_smile:


Nice video tut and not a bad idea at all, but it doesn’t really work for the propeller effect I’m after. The fundamental difference is that in the video there already is an existing highlight and it gets enhanced. With the motionblurred prop this highlight is non-existent unless I render static and blur in post, but I’m not a big fan of that solution (might as well overlay the highlight from a photo).
Thanks for the suggestion though. This trick might come in handy with something else in the future.


I would imagine it’s possible provided your reflections are bright enough and with the glare shader enabled. That being said, I can’t say for certain it’s possible because I haven’t personally tried because 3d motion blur in mental ray simply takes too long for me to render here on my machine so I have to avoid it like the plague. :sad:

BTW - Beautiful photo!


Thanks for your reply, Jeff. Yes my machine (3.5 year old dual Opteron) is struggling too! Time for an upgrade!

Glad you like the photo - another passion of mine! :slight_smile:
Many more can be found at -> Aircraft Photo Gallery


3d motion blur in mental ray simply takes too long for me to render here on my machine so I have to avoid it like the plague. :sad:

Thats true here even on our farm (20 machines/servers).
I really like the RealSmart Motion blur plugins. They have saved my neck on many occasions.



Anyone knows if is there any chance to change the gamma to a hole volumetric shader (vue’s one) if is not internaly implemented?


Hi everybody!
I use HABWare’s iBitmap plugin for interlaced video footage.
It works perfectly on max’s default scanline renderer, but when I move to Mental Ray, it doesn’t work anymore.

Do you know any other solution to use interlaced video footage as a map in 3dsmax/mental ?

Thank you in advance:
Lisandro Puzzolo


You could use the the pluging to convert the interlaced video separately and just composite it in post. OR, for example, if your interlaced source is 720x480 - you could open a blank max scene and setup the material using the plugin and set that to be your background image. Then re-render the the source footage to use in the other file. I’m sure there are other products that can de-interlace it as well, I just don’t know what you have at your disposal.


Thanks for your response CBoath!
I know some techniques to deinterlace the material. But I don’t want to convert an interlaced material to a non-interlaced one (I want to keep the 50 diferent images from the 25FPS interlaced video)

What I need is 3Dmax treats the footage as interlaced so it can deinterlace every field on the fly, use every field as a whole frame (in every field rendering pass), so that in the final rendered animation (field rendered) the video footage (used as a material map) doesn’t get screwed up.

This was achieved before by iBitmap very well (other software, like Premiere, or AFX handles interlaced video just like I described), but as I said, it doesn’t work with mental ray.

What I’m trying right now is to use Avisynth to convert on the fly a 25FPS interlaced footage to 50FPS uninterlaced footage and use that fake avi (via a frameserving process) on a 3dsMax map slot. (I will post the results here)

But if is there any better solution, I will be very wellcome to read it!
Thanks in advance:
Lisandro Puzzolo.


Well, for those who need to use interlaced video footage on 3dsmax/mentalray, here goes some technique:

  1. Download and install Avisynth (it’s free)
  2. Download and install ffwfv maekAVI (it’s free) from:

What we are going to do is make a ghost avi files that translates (on the fly) an interlaced video source to an uninterlaced AVI (with the double frame rate as the original, as every vide field becomes a full frame).

Create a new AVS file (with the text editor), and put this lines:


and then SAVE the AVS file.

You must replace “c:\myfile.avi” with the FULL PATH of your interlaced video source.

Then, execute makeAVIS (it’s on Start/programs/ffvfw/makeAVIS).

On the Avisynth script field, point to your recently created AVS file.
On Fake avi, point to where you want your fake avi get created.

Press the “create” button.

You now have a fake video file that plays the original video footage at (in my case) 50fps deinterlaced (every field is a full 1/50 frame).

Now on 3dsmax you can use the fake avi file.

Since in my case I will creating a 25fps interlaced animation (DV avi file), and I want to use the interlaced video footage (25fps interlaced, converted to 50fps non-interlaced), I must use a value of 2 in “playback rate”.

Now you just have to render your animation.

I hope this solves the problem to many of us!
If you have a better solution, please post it!