Total Internal Reflection

Total Internal Reflection (TIR) lets you control the amount of TIR in a scene. When you have reflective objects such as prisms or mirrors in a scene, you can encounter situations where light rays bounce back and forth an infinite number of times within the object or between two objects. By limiting the TIR depth, you can produce realistic scenes that include a certain amount of TIR. This lets you avoid creating an infinite number of internal reflections, thus speeding up the rendering time.

To enable or disable Total Internal Reflection:

1. Click the triangle icon next to the Render Controls and select Render Options.
   
   
2. Since TIR is affected by the other Optics options, make sure they are enabled. When a checkmark appears beside the option, the option is enabled. When there is no checkmark, the option is off.
   
   
3. Click on the Total Internal Reflection (TIR) option to enable it.
   
   
4. Type a value in the Maximum TIR Depth field or leave it at the default setting of 2.
5. Click on the OK icon to accept the changes.
6. Render the scene.

For a good explanation of TIR, go to Robin Wood's site, click on Tutorials and select General 3D from the list. In addition, Robin has a "Refraction Index of Various Substances for 3D modelers." Another site with a nice listing of refraction indices is 3D Lapidary where you can also download 3D models of gemstones in a variety of cuts (one of which is used in the examples below).

Examples:

• TIR = 4
  
  
• TIR = 8
  
  
• TIR = 12
  
  

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