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Variable Filters

Variable FiltersLVND - Linear Variable Neutral Density Filters are used to attenuate light as the filter is translated. The filters can be used with white light as well as with low power lasers. A large finite aperture can be attenuated by translating two filters in opposite directions.  The filters are available in lengths from 5mm to over 200mm. The filters are more sensitive to position at lower density values than are linear transmission filters. Our standard filters usable wavelength is from 375nm to 2000nm. We can provide any customizable range to fit your particular needs.

LVNT- Linear Variable Neutral Transmission Filters are designed to  attenuate light as a function of transmission instead of density. These filters are much more sensitive to positoin at the lower tranmission values than are linear density filters.
The relationship is: Since: D=Log10 (1/T) Then: T= 1/10D

The filters are available in lengths from 5mm to over 200mm. The filters are more sensitive to position at lower density values than are linear transmission filters. Our standard filters usable wavelength is from 375nm to 2000nm. We can provide any customizable range to fit your particular needs.

Linear Variable Spectral Filters - The variable spectral filter changes wavelength along the length of the filter. These filters have the same transmission characteristic as the standard fixed narrow bandpass filters. The undesirable secondary transmission ranges are blocked by graduated color glasses.

When the linear variable spectral filters are used with a slit on the entrance side, broadening the slit leads to a wider trasmission curve and a reduction of the maximum transmittance.  Slit widths of up to 1mm have practically no influence on the spectral characteristics. The method of manufacturing these filters leads to slight deviations in the dispersion and linearity from filter to filter.

Step Linear Filters - The Step Linear Neutral Density Filter can be used for calibration of various illumination systems.  The filter can be used from 370nm to 2600nm. The filter configuration consists of a glass substrate with a spectrally flat neutral density metallic coating. The density variations take place in discrete steps.  Filters are supplied with calibration data.

CVND - The Circular Variable Neutral Density Filter is a device to linearly attenuate light as the filter is rotated. The filter can be used for white light as well as for lasers.  A large finite aperture can be attenuated by counter rotating two filters in series.

CVNT - The Circular Variable Neutral Transmission Filter is designed to atenuate light as a function of transmission instead of density.  These filters are much more sensitive to positon at the lowser tranmission values than are linear densithy filters.

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

Circular Variable Neurtral Density FilterComplete customization of your Circular Variable Neutral Density (CVND) Filters.  This technology is best used in high quality optical systems to change the intensity of light from 100% to less than 0.1%. As the circular variable neutral density filter rotates, the beam intensity is modified due to the density variation of a gradient metallic coating around the filter. Used from the UV to the Far Infrared, density neutrality can be achieved for narrow band applications, such as lasers, to wide band applications, such as the spectrum of white light. These filters are fully customizable in optical density gradient function, transmission gradient function, substrate type, coating materials, and size to match your application requirements.

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, 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 hostel environments by the use of other common and precious metals to match the absorption, spectral, and environmental characteristics of a customized system.

A more complex variable (or gradient) filter provides a density change over a custom defined region. The variable function can be defined as linear, circular, or radial depending on the substrate needs, and in either continuous or step.

The key features are:

  • CVND's can be supplied as a linear or customized gradient function.
  • Gradient coatings can be supplied from 45° to 360° of rotation.
  • Gradient coatings are used for Laser as well as Wide Band applications
  • CVND's can be supplied from 1.0" (~25mm) to 8" (~200mm) in diameter
  • Gradient coatings and substrates can be supplied to operate from the UV to Far IR
  • Custom applications are always welcomed.

Comb Filters

CVND Comb Filter from Reynard CorporationComb filters are class of gradient filters where the coating thickness remains constant while the coating pattern changes. This is like a hair comb tongs that are not straight but rotated in a circle. Reynard Corporation manufactures two types of circular comb filters: Metallic ND's and All Dielectric Filters. These filters are used to control energy.

COMB ND FILTER.
These filters are manufactured by a photolithography process.  A photolithograph pattern is made on a glass substrate then a fixed ND coating is deposited onto the pattern. Let's assume a ND coating of 4 is deposited. The photolithograph pattern is then lifted off to produce a variable fixed ND pattern. At 0 degrees the density is 4, as the wheel is rotated the comb pattern reduces the ND coating to 0 at 270 degrees of rotation. The benefit of this type of variable ND filter is that the ND coating is thick even at the low ND area and thus is not prone to oxidation or bleaching under high heat loads. The resolution or spacing between the combs can be adjusted for specific needs.

COMB ALL DIELECTRIC COLOR FILTERS. These filters are manufactured with the same photolithography process as the Comb ND Filter. In this case the color remains constant with rotation but the intensity of the color is reduced. These filters are produced in Red, Green and Blue for the entertainment market. The three comb filters can also be used in series to produce interesting color variations with each filter rotating independently of the other filters.

The coating on Comb Filters can be any of the standard thinfilm filter designs like: Bandpass, Longwave pass, Shortwave pass, Edge Filters, etc. The coatings can also be designed to operate in the UV, Visible, NIR and Far IR.

 Comb filters from Reynard Corporation

Custom Arc Gradient Filter

Variable ARC Neutral Density FilterThe Custom ARC Gradient Filter specifcally designed  to integrate several optical functions into a single device, including:
Narrow bandpass filter 
Wide out-of-band blocking
Novel arc-gradient variable filter.

The solution is based on a combination of custom designed thin film filters, utilization of specialized filter glass, and the development of proprietary tooling for the implementation of the gradient function. The final filter meets environmental and durability requirements of MIL-PRF-13839B and MIL-C-48497A.

The gradient follows a very precise exponential function that changes optical density from OD 0 to OD 6 in less than 0.25 inches, This transition is in a radial-arc segment. Specialized coating tooling, as well as metrology instrumentation were designed and built to implement and validate the gradient function.

Bullseye® Inverted Apodizing Filters: Apodizing filters eliminate undesirable intensity variations in optical systems

Bullseye Apodizing FilterThe Bullseye® Inverted Apodizing Neutral Density Filter is part of the Bullseye® apodizer line of customizable gradient filters. These filters eliminate undesirable intensity variations in optical systems. The density of the filter increases radially from a clear center, where light is usually at its peak intensity, to the outside edge, where it can become completely opaque.

The Bullseye® apodizing filter can be designed for most distribution functions, such as a Gaussian function, regardless of the size of the beam. The distribution function, substrate type, and bandwidth are a function of the customer's specific requirements.

Key features include:

  • Density gradients can be customized to suit any application
  • The filter can be applied to a number of different substrate types
  • Can be designed to be used from the UV to the Far IR

Inserting a Bullseye® apodizing filter at the aperture stop of your imaging system modifies the intensity variations of your light source which can result inthe elimination of edge diffraction patterns.

The custom features of our Bullseye® Apodizer filters allow system designers to match the exact requirements of their instrument, whether the need is for one filter, or in production volumes.

Application examples are found in diverse industries, such as:

  • Entertainment - To make light distribution uneven for cosmetic applications.
  • Imaging - To break up diffraction patterns by the introduction of soft edges.
  • Industrial -To make sensors more sensitive in the center of the field of view
  • Photography – To create soft edged in pictures
  • Astronomy – To reduce high intensity light sources around the featured object
  • Scientific - Used as a variable phase plate when the gradient coating material has the same index of refraction as the substrate.
  • Semiconductor - Used in photolithography exposing systems to obtain perfect illumination distribution.