The diffuser is used to create exposures of even density over the entire of film. The light that passes through the diffuser and on to the film will create even density across the of the film. It helps to reduce hard background shadows and eliminates the red eye effect. It disperses the light over a wider area for a softer, more balanced and natural effect than you didn'for t use before. Use the diffuser by placing it flush against the front of the lens and exposing through it.