Circular Variable ND Coatings
Circular Variable Neutral Density coated filters is a technology used in quality optical systems to change the intensity of light from 100% to less than 0.1%. Circular Variable ND coated filters provide continuously variable, linear attenuation of light by rotating the filter with the transmitted light intensity varying as a function of optical density. As the filter rotates the beam intensity is modified due to the density variation of a gradient metallic coating around the filter. Density neutrality can be achieved for narrow band applications, such as lasers, to wide band applications, such as the spectrum of white light. The Optical Density (OD) is defined as follows: D = log10(1/T), or T = 10-D
The smooth, feathered linear transition from uncoated glass to coated glass in optical density is achieved with an Inconel alloy coating material covering 270° of the glass substrate. The coating material is a nickel variant for room temperature, low-power applications. But, the ND coating can be enhanced to increase survivability in hostel environments by the use of other common and precious metals to match the absorption, spectral, and environmental characteristics of a customized system
These filters are fully customizable in optical density gradient function, transmission gradient function, by substrate type, by coating materials, and substrate size to match an applications requirement.
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