To create a final gathering effect
1. If necessary, specify which scene objects can cast final gathering rays, which objects are sampled by those rays, and/or which objects are invisible to final gathering rays. This is described in Setting Final Gathering Visibility Options.
2. Make sure that your scene contains at least one light with an Intensity value greater than 0.
3. Open the Render Manager and select the mental ray tab on the left side.
4. On the Optimization tab, make sure that Raytracing is selected for Primary Rays.
5. On the Final Gathering tab, select the Enable option to activate final gathering.
6. Select an Accuracy - Mode option to determine which parameters are displayed on this page and their default values. See Selecting a Final Gathering Mode for information.
7. Adjust the Accuracy values as described in Setting Accuracy Options.
8. If desired, activate the Falloff and set the Start and Stop values to limit the effect of distant objects on the final gathering calculation. See Setting the Final Gathering Falloff for information
9. If your scene contains transparent and/or reflective objects, set the Trace Depth settings to define the number of time final gathering rays are reflected and/or refracted, or bounced. See Setting the Final Gathering Trace Depth for information.
10. If desired, set the final gathering Map File options to use the map and specify its behavior. See Using the Final Gathering Map.
11. If you are rendering final gathering with global illumination, you may want to activate the Fast Lookup - Irradiance from Photon Map option. See Using Final Gathering with Global Illumination.