This is my first creation for BlendSwap. The Dirty Lens Texture is packed into the .blend file and I also put it into the .zip archive. + another Hexagonal Bokeh Texture. I created the Textures with Gimp.
It's easy to just overlay a transparent Dirt-Image but in "real life" the dirt is only visible at bright areas like reflections and lamps.
It's a very simple Node Setup and beginners should be able to follow the steps. If you are woundering about all the "Reroute" Nodes, it's because I like simple and clear layouts. :) I hope you like it! Sorry for my bad English.
Really nice! Cheers, Rex