Tiffen 6666CGN6H (6666-CGN6H) 6.6X6.6 Clear Neutral Density (ND) .6 Hard Edge Graduated Filter. Tiffen Optical Filters
Tiffen filters are manufactured using ColourCore 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. The ColourCore process allows us to control the color and density of Tiffen filters, and the characteristics of special effects filters with much greater accuracy than typical dyed-in-the-mass filters, which usually exhibit color and density .
When Tiffen filters are ground and polished, the Colourcore is unaffected, so color and density remain uniform. Indeed, when you hold a group of Tiffen filters of the same type against a white sheet of paper, they all look identical -- because they are! Try this with our competitor's filters and you're likely to see slight variations.