Caustic effects produced when light rays reflected or refracted by the object surfaces. When the light rays are transporting from refractive surfaces to diffuse surfaces will strictly follow physical rules and cause light rays converging in one spot or diverging. In this 3D Studio Max Tutorial I want to discuss about refractive caustic effect in Vray. Creating a right material for object and setting the light is very important to show caustic effect.
Final Result Preview
Part 1: Create Glass Material
Step 1:
Open Render Setting dialog. In Assign Renderer rollout click on Production button and choose Vray from list. Here the version of Vray is not important.
Step 2:
Open Material Editor. Click on Get Material button and double click on VRayMtl in Material/Map browser. Change the name of this material to Glass_ref.
Step 3:
Change the parameters of Glass_ref material:
- Reflect color = White (R=255 , G=255 , B=255)
- Fresnel reflections = On
- Reflection Subdivs = 10
- Reflection Max Depth = 12
- Refract color = White (R=255 , G=255 , B=255)
- IOR = 1.55
- Refraction Subdivs = 10
- Refraction Max Depth = 12
- Fog Color = Light Gray (R=240 , G=240 , B=240)
- Fog Multiplier = 0.5
Finally in Options rollout check Reflect on back side
As this material is fully transparent we do not need to change Diffuse color however even if you change it, it will not have any affect in final renders. Fresnel option is check to Fresnel Physic law and let it simulate reflection naturally. if you do not check Fresnel option, then you need to change your Reflect color to a very light gray.
Max depth by default is set to 5 for both reflection and refraction. This number determines how many times the light ray can be reflected or refracted. I have sliced my glass vertically to show you how Max depth works. As you can see a ray is reflecting four times because glass object has four layers.
If Max depth be less than 4, then our final result will be very opaque. So to determine Max depth always need to see our scene reflective and refractive surfaces. For this model I chose 12 because later I want to have caustic effect which will take more energy of light. In the below picture I render Glass object once with Max depth of 12 and another time I changed it to 5. You can obviously see how glass object lost detail with Max depth of 3. Pay attention to the rendering time that it didn’t increase much.
I didn’t want to change the Glass color but I wanted to make attenuation of light as it passes through the object. So I give Fog Color a very light gray to let thicker areas become darker than thinner areas.
Under Fog color, you have Fog Multiplier. This field will let you to control the strength of the Fog color. Smaller values reduce the effect of the fog color; let more lights pass through and making the material more transparent. Larger values increase this effect and making the material more opaque. In below picture I have show you the final result with different Fog multiplier values.
Because my object has transparent material and I want it cast transparent shadow, I need to turn On Affect Shadows option. This option only works with V-Ray shadows and lights.
But in my tutorial I didn’t turn Affect shadows option On. The reason is because later I want to apply caustic effect. In Vray when you Turn on caustic effect, Affect shadows will automatically turn off. In fact Affect shadows is just a fake caustic effect.
The last option that I active it is Reflect on back side. When this option is On, reflection for back faces of object also will calculate. This affect includes internal reflections too. in Below picture I have shown the difference in result when Reflect on back is On and Off. as you can see when this option is On, increase the realism but also it take longer time for rendering.
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