View Full Version : Mental Ray / Photon question

03 March 2003, 02:26 AM
I'm fairly new to caustics and mental ray. I can get the caustics to work and look good but I was wondering what kind of setting everyone else uses to get photo-realistic caustic lighting.

When I render an image now with 50,000 photons being emitted from my point light, large circles are cast onto any close surfaces, but when I kick it up to 50,000,000 photons, more realistic lighting is cast, but my render time is close to 2 hours, and there is still room for improvement.

Is there any other way of acheiving photo-realistic caustics with other settings perhaps? Any input would be appreciated as I'm clueless on this mattter.

03 March 2003, 01:11 PM
can you post an image showing your problem?

03 March 2003, 02:52 PM
ok the first image with a photon count of 50,000 and a render time of about 5-10 minutes:

And the second image with a photon count of 50,000,000 and a render time of at least 2 hours:

please help me for the love of god, I tried to render a high res 1024 image over the night while I was sleeping with 75,000,000 photons and I got an memory error from windows while maya just locked up. There must be an easier way to do this.

Oh I'm runnin on Win XP with an AMD Athlon XP 2400+ w/ 512MB of DDR

03 March 2003, 04:33 PM
:eek: So much Photos?? .. the highes i ever used was 100000 :)

did you also use final Gather?

my often used values
FG Rays: 240
Min radius: 0.4
Max Radius: 6

also by Sampling Wuality
Max Samples : 2
and Jitter on

03 March 2003, 05:36 PM
No I didn't use final gather, I'm not too familiar with all of Mental Ray's abilities yet. Would you please eplain final gather to me since I havent been succesful in getting it to do anything

03 March 2003, 05:52 PM
If you use FInal Gather your lighing going to be more "realistic" ..

i cant explain it realy good in english .. check out this tutorials =)

realy good

03 March 2003, 06:24 PM
X-Tender : I used your settings posted earlier and when I rendered although my glass shape looked a little better, the caustics did not show up at all. And although the photon count is only 50,000, render time was still 30mins+.

I'll check out this tutorial now and see what I can get from it, thanks.

03 March 2003, 06:28 PM
Although I haven't gotten the chance to mess with any of it in maya, this tutorial looks like exactly what I need.

I'll post an update image once I get the effect I was going for.
Thanks again X-Tender

03 March 2003, 08:15 PM
=) .. use for testing 320x240 ... and higher for final or check =)

/e: just a test ;)

03 March 2003, 02:51 AM
The reason you're getting such bad caustic results even with higher photon counts is because you are using a POINT light. The caustics are being sent out everywhere, when all you really need is caustics to hit your object.

Switching to a spotlight would give you a better result with only 1% to 10% the photons you're using now.

Hope that helps,


03 March 2003, 03:15 AM
GreytheSkunk: You are a genius. Such a simple solution to a problem that has caused me so much grief. Thank you !

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