- Set up the base lighting of your scene to have some contrast in lighting going on - Dirt Masks respond best to light shining in to the lens so think about having some Backlighting.
- In your Camera Settings find the Dirt mask option.
- Add some imagery from your content browser in to the Dirt Mask Texture Slot.
- Adjust the Intensity and Dirt Mask Tint to adjust the subtlety of the Dirt Mask.
- Move your Camera around to see the effect the light in your scene has on your Lens.