Maya light rays

                                  Normally we use volumetric cube or sphere to create foggy environment in Maya software. In this tutorial we use Mentalray parti_volume and mentalray physical sun and sky to create light rays.
                                  First open your scene. Open hypershade and create transpat under mentalray->materials. Create parti_volume under mentalray->volumetric. Create a new lambert material and select its shading group node(lambertSG). Go to attributes editor and find Custom Shaders section under mentalray. Drag and drop transmat to Material Shader attribute and to Shadow Shader attribute while holding middle mouse button. Drag and drop parti_volume to Volume Shader attribute.

                                   Create a polygon box which larger than your scene.

                                Assign the lambert material that we created in previous step. Select the parti_volume. Set Scatter color to dark grey. Set Extinction to 0.01. Increase the R,G1,G2 values.

                              Open render settings window. Go to Features tab and turn on Auto Volume. Set Volume Sample value to 5. Go to Quality tab and turn on Raytracing. Set Max Trace Depth value to 5.    

                              Create mentalray physical sun and sky. Select the directional light(sunShape) and turn on Use Ray Trace Shadows. Set Shadow Rays value to 5.
                              Rotate the light to suitable direction. Place your camera in proper place.

                              Render your scene..... If you have any question regarding this tutorial post it as a comment.