Bandpass Filters

• Bandpass Filters

For Industrial Applications:  Improve Contrast and Repeatability

Specially designed for industrial imaging, MidOpt Bandpass Filters are the simplest, quickest and most cost-effective way to improve the image contrast, repeatability, and long term stability of any industrial vision system.

Definition:

A bandpass filter transmits a specific portion of the spectrum while blocking shorter and longer wavelengths. Increasing signal-to-noise results in improved contrast and better control over changes that may occur over time in ambient lighting conditions.

In the case of bandpass filters, “broad” and “rugged” are necessary in most machine vision applications. This allows for use with wide angle lenses and for variations in the spectral output of LEDs and laser diodes, while providing environmental stability and mechanical durability.

MidOpt Bandpass Filters are divided into Three Series:

• BP Series   –  Broad Bandwidth. For standard machine vision and surveillance applications
• BN Series –   Narrow Bandwidth.  For outdoor applications or situations involving overwhelming ambient light
• Bi Series –     Narrow Interference Bandwidth. For laser diode or other narrow spectrum light source applications

Useful for

Industrial inspection, security, traffic control, medical and forensic applications

Multi Bandpass Filter

For Day/Night Color Camera Applications

Dual Bandpass Filters are ideal for applications that use a color camera during the day and IR illumination at night – ensuring that clear, accurate images are acquired under all lighting conditions.

Definition:

A dual bandpass filter transmits two specific wavelength ranges while blocking shorter and longer wavelengths as well as some middle portion of the spectrum. While triple bandwidth transmits three specific wavelengths ranges.

These filters in particular pass visible light and some smaller portion of the near-infrared spectrum. Blocking most of the near infrared allows for excellent color rendition while retaining the ability to pass a specific LED or laser diode wavelength used for night time illumination.

Multi Bandpass Filters

Visible + IR :  One Filter, Double the Work

Most commonly used for security and surveillance, intelligent traffic solutions and Normalized Difference Vegetation Index (NDVI) imaging.

These filters pass visible light and a narrow IR band that make viewing with commensurate IR illumination possible at night.

Features

• Pass visible light and a specific portion of the visible (VIS) and near-infrared (NIR) spectrums
• Ideal for color camera applications that utilize daytime sunlight and NIR illumination at night
• Achieve accurate color rendition by blocking interfering wavelengths
• Eliminate the need for dual sensor imaging
• Anti-reflection coated for maximum transmission
• Hard-coated, single-substrate fabrication
• Exceptional surface quality; 40/20 scratch/dig

Applications

Dual Bandpass Filters are becoming increasingly popular in NDVI aerial drone inspection, allowing for single sensor imaging and reduced operation payload. NDVI, traditionally achieved by satellite imagery, can now be obtained utilizing Dual Bandpass Filters and personal aerial imaging devices.

General Availability

• Threaded, C/CS, Slip, Unmounted
• Threaded mount sizes in M22.5 up to M82
• Custom sizes and shapes available

Longpass Filter

For Monochrome Applications:  Improve Contrast

Often referred to as a “sharp-cut” filter, Longpass Filters are specifically designed to pass a broad spectrum of longer wavelength light while blocking shorter wavelengths.

Definition:

Longpass filters transmit wavelengths longer than the specified cut-on wavelength while blocking shorter wavelengths.  They are usually used in monochromatic applications to improve contrast, where like colors will lighten like colors.  Most MidOpt longpass filters are absorptive rather than dichroic (reflective), making them well suited for wide angle applications.

Features

• Economical solution for isolating specific spectral regions
• Peak transmission ≥90%
• StablEDGE® design reduces angular dependency and minimizes short-shifting effects
• Anti-reflection coated for maximum transmission in VIS and NIR spectrums
• Can be used with Shortpass Filters for a custom, fine-tuned Bandpass Filter
• Double-side polished glass for exceptional parallelism and optical flatness
• Exceptional surface quality; 40/20 scratch/dig
• Available in wavelength ranges from 350nm to 1500nm

Applications

Longpass Filters are often used in fluorescence applications to block an excitation light source or to pass multiple emission wavelengths, improving signal to noise ratio. Longpass Filters are also commonly used in photography and astronomy.

General Availability

• VIS/IR wavelengths
• Mounting Options: Threaded, C/CS, Slip, Unmounted
• Threaded mount sizes: M25.5 up to M105

Shortpass / NIR Cut Filters

For Color or Black and White Applications

Often thought of as “IR-cut” filters, Shortpass Filters are specifically designed to pass a broad spectrum of shorter wavelength light, while blocking longer visible (VIS) and near-infrared (NIR) wavelengths.

Definition:

Shortpass filters transmit wavelengths shorter than the specified cut-off wavelength while blocking longer wavelengths. Perhaps the best example of this is the infrared blocking filter that is typically found in a color camera. In order to achieve accurate color rendition, this filter blocks longer wavelength infrared light and passes shorter wavelength visible light.

SP – Series – VIS Pass

• Separate colors in monochrome or color applications
• Improve contrast and resolution

SP Series – NIR Block/VIS Pass

• Commonly placed over the camera’s image sensor to block NIR light and achieve natural color rendition
• Used as a hot mirror to reduce unwanted heat build-up caused by IR radiation

Visible Imaging

Shortpass filters usually transition sharply from shorter wavelength transmission to reflecting longer wavelengths of light

Infrared Imaging

Several Shortpass filter types are offered which block varying amounts of visible and near-infrared light above and below 700nm. The choice of the best filter for any application is often based on the spectral characteristics of the camera sensor.

Features

• Designed to have a sharp transition between shorter wavelengths (which are passed) and longer wavelengths (which are blocked)
• Peak transmission ≥90%*
• Can be used with Longpass Filters for a custom, fine-tuned Bandpass Filter
• Anti-reflection coated for maximum transmission
• Exceptional surface quality; 40/20 scratch/dig
• Available in wavelength ranges from 340nm to 785nm

Applications

Shortpass Filters are commonly used in color imaging to achieve natural color rendering. They can also be used to protect the sensor from NIR laser damage or to reduce IR radiation or “camera bloom” created during hot metal or glass extrusion processes.

General Availability

• VIS/IR wavelengths
• Mounting Options: Threaded, C/CS, Slip, Unmounted
• Threaded Sizes: M25.5 up to M105

Neutral Density

For Light Intensity Reduction

Serves as “sunglasses” for your system and can be used with monochrome or color cameras. Designed to reduce light intensity neutrally over a specific wavelength range without affecting image color or contrast.

Definition:

Neutral density filters reduce transmission uniformly over a specific portion of the spectrum. They are defined according to their Optical Density (OD). The higher the OD, the lower the transmission. These filters can be stacked to create filters with custom ODs. They are useful when trying to image extremely bright subjects or when trying  to provide separation of subject matter from background by reducing depth of field.

ND Series – VIS, Absorptive

• Absorptive filter effective from 425-675nm
• Available in optical densities ranging from 0.10-6.0

Ni Series – VIS/NIR, Low-Reflectivity

• Low reflectivity filter effective from 400-1100nm
• Available in optical densities ranging from 0.3-1.2
• Coated on low-expansion, heat-resistant Borofloat® glass

Features

• Available in various optical densities
• Used with monochrome or color cameras operating in the visible and/0r near-IR spectrums
• Includes identical male and female filter threads on either end for stacking
• The sum of the OD’s density of two or more filters stacked together equals the total density
• Ni filters are unique in maintaining exceptional spectral neutrality over the full visible-to-near-IR range while greatly limiting undesirable back reflections over that same range.
• Excellent parallelism, optical flatness and surface quality
• Custom densities available upon request
• Useful for: attenuating bright light; exposure control of images; system protection for low power laser applications

Applications

Applications include imaging in intense lighting situations (i.e. molten metal and welding), outdoor aerial imaging and photography. Neutral Density Filters help reduce shutter speed to create blur, preventing a “jello” effect in aerial imaging.

General Availability

• UV/VIS/NIR
• Mounting Options: Threaded, C/CS, Slip, Unmounted
• Threaded sizes: M22.5 – M105
• Custom shapes and sizes available

Polarizing Filters

For Glare and Reflection Reduction

Polarizers are designed to reduce specular glare by passing only the light polarized in the direction perpendicular to the reflected light (glare). In addition, they help improve contrast, increase color saturation and detect imperfections in transparent materials. MidOpt Polarizing Filters can be easily and securely mounted to your lens and light source for maximum extinction or glare reduction.

Definition:

Light reflected from a non-metallic surface becomes polarized, sometimes to the degree that a strong glare is created. A linear polarizer rotated to pass only light polarized in the direction perpendicular to the reflected light (the glare) will absorb much of it. Aside from reducing reflections, polarizers help to improve contrast by reducing dynamic range, allow for evaluation of stress in transparent plastic and glass, and can be used in pairs to form a variable neutral density filter.

Acrylic Polarizers

 Polarizing Filters

Polarizing Filters

• Contrast ratios average up to 10,000:1
• Linear, circular and wire grid polarizers are available for visible (VIS) and near-infrared (NIR) spectrums
• Rotating mount with locking thumb screw to fine tune glare reduction
• Exceptional surface quality; 40/20 scratch/dig

 Polarizing Film

Polarizing Film

• Achieves optimal glare reduction when placed over light source
• Contrast ratios average up to 10,000:1
• Linear polarizers are available for VIS and NIR requirements
• Left and right circular polarizers are available for VIS spectrum applications
• Offered in high-temperature-resistant laminate and glass
• PSA007 and HTA008 material comes standard with self-adhesive backing

MOUNT & SIZE OPTIONS: Polarizing Filters and Films are available from stock and are ready to ship. Polarizing Filters are available in Threaded Mounts, sizes M22.5 to M105; Slip Mounts; or Unmounted. Polarizing Films are available in multiple thicknesses, and can be custom laser cut to fit any light source with a maximum usable width of 16.5″ and length up to 300′.

Applications

Polarizers are commonly used to reduce glare from non-metallic in objects with smooth surfaces or surfaces covered with grease, oil or liquid. For best results, use an optical-grade Polarizer over the lens and Polarizing Film over the light source. The PR120/PG120 offers ultra-high contrast and an anti-reflection oleophobic coating.

 

General Availability

• Use with Linear & Circular polarizing film
• VIS or Near-IR wavelengths
• Mounting Options: Threaded, Slip, Unmounted
• Threaded Sizes: M22.5 – M105

Protective Filters

For Lens Shield and Short UV Block

Protective Filters are designed to shield your lens and lighting from dirt, dust, liquids, impact and harsh environments without sacrificing image quality.

Definition:

Protective Filters typically act as windows or dust covers for lenses, filters, sensors, cameras or lighting.  Usually they will block a portion of the UV spectrum, although those used in infrared applications will often also block visible wavelengths.

• Economical solution to protect expensive lenses
• Useful for imaging in ultraviolet (UV), visible (VIS) and near-infrared (NIR) spectrums
• Available with a high-efficiency, anti-reflection coating to maximize transmission to 98% or more
• Offered in both glass and acrylic
• Exceptional surface quality; 40/20 scratch/dig

MOUNT & SIZE OPTIONS: In-stock, ready-to-ship Protective Filters are available in Threaded Mounts, sizes M13.25 to M105; 25.4® C-Mount; Slip Mounts; or Unmounted. Custom shapes and sizes are available.

PROTECTIVE FILTER APPLICATIONS:
Protective Filters are useful in all imaging applications. The LP285 can withstand high temperatures and is impact resistant (similar qualities to Pyrex).

AC Series – Acrylic Protective Longpass

LP Series – Lens Protection

Visible

• Acrylic or glass options ; anti-reflection coated or uncoated alternatives available
• Block UV wavelengths while simultaneously passing ≥90% of the visible and near-IR.
• Available in mounts or custom sizes up to 600mm (24”) dia.; can be provided with through-holes, tabs, or other features to aid in mounting.

Ultraviolet

• LP280 and LP330 will pass near-UV light, while other types block UV.
• Other materials not listed here are also available, please contact us with your specific requirements.

Infrared

• AC685, AC700 and AC760 acrylic materials are 2mm thick, shatter-resistant, and appear black; blocking visible light and passing near-IR wavelengths.
• Other listed materials pass visible light as well as the near-IR.
• Also available are materials that are not shown here.  Please contact us if you have other special needs.

Applications

Protective Filters are useful in all imaging applications. The LP285 can withstand high temperatures and is impact resistant (similar qualities to Pyrex).

General Availability

• UV/VIS/IR
• LP Series Mounting Options: Threaded, C/CS, Slip, Unmounted
• AC Series Mounting Options: Threaded, Slip, Unmounted
• Threaded Sizes: M22.5 – M105
• Custom shapes and sizes available

Acrylic Filters

For Lens Shield and Short UV Block

Acrylic Longpass Filters are a durable, lightweight and economical solution for inspection windows. They can protect a lens in environments where broken glass might pose a problem.

AC Series – Acrylic Longpass

Features

• High transmission ranging from 90 to 98%
• Available with an anti-reflection coating for maximum transmission
• Optical-grade acrylic
• Impact-resistant
• Half the weight of glass

Applications

Acrylic Longpass Filters are frequently used for lens protection and economical enclosure windows, as well as over light sources to control the wavelength emission of broad spectrum light sources. Because of their durability, they’re commonly used in Food & Drug Administration (FDA) and European Food Safety Authority (EFSA) regulated applications where glass over the inspection area is not permitted. AC370 and AC380 offer anti-abrasion, anti-reflection coating, which can also withstand harsh solvents such as alcohol, acetone or MEK.

Diffuser

Light Balancing Filters

For Color and Contrast Correction

Light Balancing Filters correct artificial lighting so colors appear more natural. These filters balance color, preventing the need for additional software processing. This allows for greater image stability and control.

Definition:

Light Balancing Filters are used to modify the color balance in LED, fluorescent, halogen, metal halide, tungsten, and other white lighting, making colors appear more natural.  The LA series (Minus Blue) reduce blue shading that often strongly predominates in white LED and xenon strobe lighting.  The LB series (Minus Red) reduces the red hue found with some tungsten and halogen lighting.

LA Series / LB Series / FL Series

Features

• Achieve accurate color images when using an artificial light source
• Increase contrast by correcting the emission spectrum of various light sources
• Exceptional surface quality; 40/20 scratch/dig
• LA series: Reduce blue shading (“warm” the scene) and commonly used with white LED and xenon strobe lighting
• LB series: Subdue the reddish hue found with some tungsten, halogen, sodium and other light sources
• FL series: Used to reduce the greenish cast created by fluorescent lighting

Applications

Commonly used in color applications (i.e. machine vision/factory automation, photography, and fluorescence imaging).

General Availability

• VIS wavelengths
• LA and LB Mounting Options: Threaded, C/CS, Slip, Unmounted
• FL550 Mounting Options: Threaded, Slip, Unmounted
• Custom shapes and sizes available