Neutral Density filters reduce the amount of light passing through the camera lens without changing the color of the scene. They are especially useful in bright light conditions to help prevent overexposure. Neutral Density filters also allow proper exposure at a wider lens opening for reduced depth-of-field to highlight a key subject by making the foreground and/or background out of focus. Tiffen filters are manufactured using ColorCore technology, a closely guarded proprietary process that entails permanently laminating the filter material in between two pieces of optical glass that are ground flat to tolerances of a ten-thousandth of an inch, then mounting them in precision metal rings.