Caustics - V-RayIn this tutorial we are going to go over some advanced lighting techniques for creating realistic caustic effects using the V-Ray renderer.

Caustics function in V-Ray much like they function in any other 3D rendering software. As always a few settings are named differently and may be found in different locations but the ideas behind the caustic generation is very much the same.

To get you started I will be providing a simple scene which we will set up a caustic experiment in that can be downloaded here: http://tutorials.diclementi.com/start_files/causticsVray_start.max

Inside you will find a Ring, with a highly reflective Brass colored texture. A Sphere with a blue/green glass highly refractive textures, a ground plane, and a VRay sphere light.

Just as we did in Mental Ray we will have to adjust settings in 2 locations, one set at the Light source, and one set in the Render Setup window.

The V-Ray light has been set up to have a small radius which will increase the crispness of things like shadows and a high intensity which will make it brighter at the source. This kind of setup allows for tighter more condensed caustics.

If we were to reverse it and lower the intensity multiplier on the light and increase the radius at which it casts light we would get a less focused beam of light and the caustics would in turn come out wider and softer.

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Ok, so to get started we will take a look at the settings in the Render setup. If we were to take a render right now this is what we would see...

Again, we see some good lighting and some nice textures however the light without caustic effects in a scene consisting of such reflective and refractive materials is always going to look dull and fake.

So we have to turn on Caustics see what the various settings can do for us.

Open up the Render Setup by hitting F10 on your keyboards or by finding it in the Rendering menu.

First we need to go into the Indirect Illumination rollout and make sure 2 things are checked:

Both Reflective and Refractive Caustics should be enabled.

If you only have Refractive caustics in your scene then only check the one.

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We can close that rollout now and scroll down in the settings dialogue.Caustics are found on the Indirect Illumination tab for V-Ray under the rollout labeled "V-Ray:: Caustics"

Mark the Checkbox next to On to turn on caustics.

You can immediately take a render to see what happens when we simply turn them on.

Not bad, but they are pretty tame, so we need to amp things up by modifying the settings.

First thing we will talk about is the Multiplier.

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By increasing the Multiplier number you will be increasing the Intensity of the caustic effect. It will get brighter or dimmer based on how high up or down you go here. If we increase by an outrageous amount like 20. We will see how this settings changes things.

While the effect intensifies greatly it also washes everything out because the caustic lights are too bright. So we can back this down to maybe 5.

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The next setting down is the Search Distance setting.

This setting will change based on the size of your scene first of all. It is how far away from an object that VRay will search to create the caustic rays needed for an effect. The lower it is the less distance from the object to the ground plane will have to cast a caustic light shape. Increasing this number will give you more distance and more caustic light in the scene. As well as clean some of the noise and speckling of the light up. When it comes to the search distance you will reach a point where increasing it no longer actually helps your scene, so spend some time finding the right number for this one.

Here is the caustic effect with a Search distance of 20:

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and the same multiplier with a Search dist. of 1:

It becomes much less accurate and noisy. Does not look good.Taking the Search Distance above 20 in this case however does not seem to have any real noticeable effect So that is where we will keep it.

The next setting is our Max Photons value:

The lower this value the noisier but sharper the caustic lights will be. The higher the value goes the blurrier the effect will get. The trick with this one is finding a nice happy medium number that gives you crisp overall results, but less of the noise and artifacts that come along with a number that is too low.

Here is the effect with a Max photons number of 20:

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Nice and Crisp, but lots of artifacts.

Here it is set to 200:

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The Artifacts are gone, it looks a bit blurry but we haven't fixed a lot of that splotchyness yet and a little bit of blur will actually help us out to even out our reflective caustics later we can still probably meet the two somewhere in the middle for now and worry about the splotchyness in a little bit. I have gone right around 75 or so with mine and I think we will move on from there. 75 for this scene seems to combine the right amount of clarity without the artifacts and blurs enough that I think we can work with it later on well enough.

We can always come back and adjust these numbers further later.

Next we will address the splotchyness and try to smooth our effect out a bit.

The last setting in the Render Setup is the Max density value:This setting works as kind of a butterknife and spreads our speckled light out across the area of the effect. A sort of Interpolation value. Defaulted at 0.0 it has no smoothing effect, but if we increase it by increments between 0.0 and 1.0 we can find a good place to get rid of those unsightly speckles.

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Here it is at a setting of 0.4 and we can see how much it is smoothing the effect out between the splotchy bits we had previously.

Now we can go back and forth a bit, bounce around between the max density value and the max photons value and find a good balance for the end result.

Here is my 75 Max Photons with a 0.85 Max density.

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Get out of the Render Setup for now and right click on the V-Ray late for our next set of changes.

Find V-Ray properties in the Quad Menu and open up the settings dialogue.

Inside the VRay properties for the light itself you can further increase the quality of the caustics by turning up the Caustic Subdivs value.

I wouldn't go to high because this will increase render times as well, but bump it up to between 2000 and 3000 and see how it effects things.

You can also increase the Caustics Multiplier here if you would like to increase Caustic Intensity. It works separate from the Caustics Multiplier in the Render Setup so adjusting both can give you some different results.

This is also a good way to bump up the intensity of your caustics without having to change the intensity of your light itself.

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V-Ray caustics work hand in hand with both V-Ray and Standard 3D Studio lights, and the V-Ray texture sets allow for an even more powerful tool when it comes to caustics. Things like the VRayBlendMtl can incorporate several colors with minor changes to the IOR numbers and colors which can combine easily to make prisms and diamond textures which split caustics spectrums into rainbows etc. Try a few different things and see how you can make Caustics work for you!

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