Circular Variable ND Filters: Customizable variable density functions in a compact footprint

CVND filters linearly attenuate light as the filter rotates.

Circular Variable Filters (UV-VIS-IR) are filter wheels that linearly attenuate light as the filter is rotated. As the filter rotates, the beam intensity is customized due to the density variation of a gradient metallic coating around the filter. These filters are fully customizable in optical density gradient function, transmission gradient function, substrate type, coating materials, and size to meet customer requirements. Densities can be supplied as a standard linear or a customized gradient function.

Custom sizes and densities are available upon request.

The key features are:

• Densities can be supplied as a standard linear or a customized gradient function.

• Gradient function can be supplied from 45° to 360° of rotation.

• Coatings are used for Laser as well as Wide Band applications

• Substrates can be supplied from 1.0" (~25mm) to 8" (~200mm) in diameter

• Functional wavelengths are designed to operate from the UV to Far IR

• Custom applications are always welcomed.

In imaging systems, large aperture neutrality with constant density can be achieved by configuring two filters of equal design back-to-back. Counter-rotating the two filters allows for a variable setting of the density or transmission requirement in both the rotational and radial directions. "For large aperture imaging, the two-filter solution offers adjustment flexibility that cannot be physically achieved by any other means," says Forrest Reynard, CEO of Reynard Corporation, "High-resolution cameras can operate with full aperture while still being able to attenuate light."

These circular variable ND filters are typically specified in linear optical density or transmission. But, since all optical systems are not linear in operation, Reynard Corporation offers the capability of customizing the density gradient based on user defined functions. The filters can be made on a variety of substrates including BK-7, Fused Silica, ZnSe, and Ge, among several others. The typical coating material is a nickel variant for room temperature, low-power applications. But, the ND coating can be enhanced to increase survivability in hostile environments by the use of other common and precious metals to match the absorption, spectral, and environmental characteristics of a customized system. For more information please visit www.reynardcorp.com