Fprime's caustics


Hi !

I’ve playing with fprime’s caustics
caustics with Fprime can’t be created with standard lights, only background and light polygons

anothrer issue is that Fprime will only shoot refracted caustics not reflected ones

:lightbulb so I have found this little trick : use the transparency channel to raytrace the reflections, for this I use 0,01 as refraction indice, this force the ray to go backward, just like reflection

and it works !




great piece of info!


another one :


Reflective caustics are created by lights for the time being.
Also Refractive caustics need at least 2 light bounces or more.

Something worth mentioning is that the more directional and strong is the illuminaction source, the stronger the caustics.
Very soft illumination creates weaker caustics.
This happens in reality.

Hopefully Mr Worley will handle them soon in a future release of FPrime.


yes I hope so ! until then it may be the only way
and not a fast one

I must to say that you will need to push the light quality setting very high (20 100 or even 1000)
the smaller the light source is, the higher you will have to raise light quality



WOW thanks for the info! SUPER COOL! Never new it could do that.


Yes, thats serious.
My naive realization is that it needs this detailed scan of the environment. Worley didnt publicly comment this but I trust him

Also, something relative, currently G2-SSS is calculated based on lightsources where in reality Global Illumination contributes in the SSS effect.
I imagine of the day that I will see Fury stuff in FPrime, as well as changing a SasQ parameter and see instant feeback. Also SasQ will receive radiosity in FPrime speed :bounce:

In the future where LW and FPrime will follow a more converging route I think we will be very happy. Hope this wont take long


you’re welcome Infinite !

hey Panikos, I hope we’re not dreaming to much, but yes volumetrics with Fprime :eek: and a volumetric version of sasquatch :argh: and shaders everywhere :love: and network rendering :applause:



Did you know SkyTracer2 already works with FPrime? If not, here’s how to enable it.

  1. Open FPrime Preview (well duh :p)
  2. Open Backdrop tab, add SkyTracer2 and open its settings.
  3. If FPrime doesn’t update in this point, close SkyTracer2 settings and Backdrop tab and re-open them.
  4. Be amazed.


Hi 00!
i’m really interested in doing great caustics, but it’s not so much time that i use lightwave, so i can’t understad how have you done the trick for doing caustics:sad: … could you please explaine me in simple words?? and i also must have the FPrime plug-in? Thanks so much!!


LW renders caustics on it own, for sure, but in my experience it’s quite difficult to achieve good results using a sinlge approach or having fast rendering times!

  • In Light Properties activate “Affect Caustics” (all light sources but Distant one) for the lights that have to affect caustics

    • select “Global Illumination” option and select Enable Caustics
    • Intesity, Accuracy and Softness regulate how the renderer trace all the caustics.

    You have to know that LW caustics implementation is very sensitive to the general “scale” of the Scene.

    this is an example rendered in standard LW using 9 Point Light + 1 Spot Light


Exper you are too fast !! I preview my message and I see you have answered already !

bwt your LW causics are very impressive !!
and thanks for your invitation

Hello alberto86, Lightwave can do caustics but they are not very precise, that’s why these images were done with Fprime’s render engine ( http://www.worley.com )

within Lightwave you don’t have to use any tricks : just open the global illumination panel and check the “enable caustics” button
push the accuracy to its maximum and increase softness to 50 or 100, that should do it
you may have to increase also the intensity settings

remember that if you want some caustics to appear, the light must be concentrate by some very reflective and/or transparent surface, just like a lens or a mirror
curved shapes work better
try aiming a bright spot light towards a transparent sphere with a refraction of 1,5 or a rflective cylinder

I haven’t play recently with lightwave’s caustics, but I remember them being very soft and unable to cast precise caustics like the one Fprime can do with the trick I’ve shown, so if you are patient and willing to do sharp caustics you may need to buy Fprime
(you won’t regret)




My kyeborad is like a frying pan. :stuck_out_tongue:

Thanks! :slight_smile:
You’re FPrime trick is very impressive too! :applause:

P.S. Feel free to hop in “there” whenever you want!


Eh eh, thanks a lot for the help, but i’m not SO inexpert!:slight_smile: my problem was about a scene (not that in the following image, but similar) were i wasn’t able to do caustics with normal parameter… but now i understand! in fact, i used a caustics effect intensity of 15000% for this image! i know isn’t a great work, but i haven’t worked on it for so much time…

however, thanks thanks THANKS!!:thumbsup:


wow thanks ! I need to try that



Thanks for the heads up on the FPrime caustics trick.

Playing with it now and works well.


Had some problems getting the caustics to work on solid items. The more transparency applied controls the caustic strength, but your metal goes clear…

Add a gradient and set it to surface thickness. Then make a key at a very small value - .005mm. Set the value to 0. Make the key at 0mm 100% for starters. By reducing or increasing this key you control the caustic effect and retain the opacity.

I had refraction set to .01 for this to work…


haven’t thaught of that
maybe we could use this gradient to fake some strange reflection fallof ? I will give it a try

tho I didn’t notice any problem in my scene where the chrome objects are 100% transparent (0 diffuse 0 reflection 0 everything but transparency, I didn’t even use a gradient for the fresnel effect)



@Exper: Any time I see your piece of art I must thank you! Sorry for my partial OT


Damn, those renders at the top … :eek:

This works great with Fprime limited region also, you can just save the part with the caustic to the end.

It’d be interesting to hear a little more about things like scale, intensities, render times or if there are any particular things to watch for etc.

I got some interesting results using these reflections for fresnel on a solid object, check this:

With normal reflections, and

with reflections on the transparency channel.

All gradients and other settings as well as render time (1-2 mins) are similar. Notice (Obviously) shadow edges from raytraced spotligth and the reflection quality. The second one took much longer to arrive at quality 1 though, but seemingly caught up at the higher quality levels around 100,

Normal reflection;

And transparency reflection;

Both at maybe 15 min, I was cooking dinner …

I also tried the surface thickness trick while I was at the shop, you don’t see a very pronounced difference but I think the highligts get hotter … I think I maybe don’t have intense enough lights to get much of a caustic.

It would be great if a genious like gerardo or oo could explain what we see, this solution looks better to me with those soft edges.

  • A little clarification on this post, the renders are with monte carlo radiosity with 2 bounces which produce caustic with solids, not transparent objects with me. When panikos said 2 or more bounces, another way of saying this is that “2 might be enough, but you might need more”. Ray traced everything on in render options, radiosity intensity of 500, lightning quality of 50, and the light sphere is at intensity 200 and rather large, a kilometer or something. I think it is the relative size of light objects that can be a problem, but I just wanted to make sure it wasn’t small. Opposite Gradients with incidence on the diffuse and *either transparency or the reflection channel. And refraction for the transparency version at .001.