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General Filter Information & Nomenclature

If you have a question about Omega's interference filters that is not answered here, please contact us.

Omega Optical Filter Descriptors

Omega Optical uses specific descriptors to define the performance characteristics of different filter designs.


  • QM – QuantaMax™: Surface coated, single substrate designs provide steep edges, very high transmission and minimal registration shift.
  • 3RD – 3RD Millennium: Filters are manufactured using proprietary ALPHA Technology and Omega's patented, hermetic assembly.
  • AF – ALPHA Filter: Alpha filter designs are manufactured using Omega's proprietary technology resulting in extremely steep edges, precise edge placement, and theoretical attenuation >OD10.
  • DF – Discriminating Filter: These filter designs have 6 or more interfering cavities, resulting in a rectangular bandpass shape, very steep edges, and very deep blocking up to optical density (OD) 6 outside the passband.
  • WB – Wideband Filter: Wideband filters are 4 & 5 cavity designs with FWHM greater than 30nm and up to several hundred nanometers.
  • NB – Narrowband: Narrowband filters are 2-cavity designs with FWHM typically between 0.2 and 8nm.


  • DC – Dichroic: These filters provide wide regions of both transmission and reflection, exhibiting a high degree of polarization along with a somewhat shallow transition slope.
  • DR – Dichroic Reflector: These designs provide a steeper slope than typical DC filters, low polarization, a wide range of transmission and a limited region of reflection.
  • DCXR – Dichroic Extended Reflector: A design that provides extended reflection regions.
  • DCSP / DCLP / DRSP / DRLP: These designations dictate those portions of the spectrum that will be transmitted and reflected.
    The 'SP' (shortpass) nomenclature means the filter will be transmitting wavelengths below the defined cut-off region. The 'LP' (longpass) nomenclature defines the region of transmission as wavelengths above the defined cut-on region.

Longpass and Shortpass

  • LP – Longpass: These filters transmit wavelengths longer than the cut-on and reflect a range of wavelengths shorter than the cut-on.
  • SP – Shortpass: These filters transmit wavelengths shorter than the cut-off and reflect a range of wavelengths longer than the cut-off.

Multiband Filters

  • DB – Dual Band: Filters are designed to have two passbands and two rejection bands.
  • TB– Triple Band: Filters are designed to have three passbands and three rejection bands.
  • QB – Quad Band: Filters are designed to have four passbands and four rejection bands.

Filter Cleaning

Omega Optical interference filters are manufactured using state of the art technology for robustness and durability. As with all optical filters, care should be given to proper handling and cleaning.

A complete cleaning kit includes: tweezers, puffer, isopropyl dispenser, lens paper, lint free cotton swabs, finger cots and cleaning instructions.


  1. Avoid depositing oil from your hands onto filters by using finger cots. Hold filters from the edges only. For smaller filters use the tweezers provided to help with handling.
  2. Blow loose dirt and particles from the surface of the filter using the puffer. Do not blow air from your mouth as you may deposit small particles.
  3. Apply isopropyl alcohol to a lint-free cotton swab and rub the filters surface in a circular motion, working from the center to edge. Gently apply pressure. Avoid rapid side-to-side motions.
  4. Use the puffer to evaporate excess alcohol from filter surfaces.
  5. Repeat steps 3 & 4 above using a clean, lint-free cotton swab with each cleaning until all surface contamination is removed.
  6. To complete the cleaning process wipe filter surface using lens paper gently applying pressure.
  7. Return your filter to the original plastic case or envelope provided.

Note: We do not recommend the use of water, detergents or any other non-optical cleaning materials for this process.

Filter Orientation

One of the most common questions regarding completed filters is how to orient them in instrumentation. In most applications, an interference filter should be placed with the most reflective, metallic looking surface towards the light source. The second surface of the filter is distinguishable by its more colored or opaque appearance. When oriented in this manner, thermal stress on the filter is minimized.

Typically, our filters are labeled with an arrow on the edge indicating the direction of the light path. Place the arrow pointing away from the light source and towards the detector. Special markings can be made for those customers who require consistency with their custom instrument design.

Omega Optical Filter Nomenclature

Traditional & Omega-Specific Nomenclature

The accepted practice in the optics industry is to define bandpass filters by Center Wavelength (CWL) and Half Bandwidth (HBW) of Full Width at Half Maximum (FWHM). FWHM is defined as the bandwidth at 50% of the maximum transmission of the filter. Omega has used that system for many years and continues to do so with a number of developed product lines.


Bandpass filters vary in accordance with desired "edge steepness" which dictates how quickly a filter transitions from attenuation to transmission.

Bandpass Nomenclature


Note: Full Width Half Max (FWHM) is defined by the region of the passband where the transmission of the filter is 50% of the maximum transmission.


Dichroics are filters that highly reflect one specified spectral region while optimally transmitting another.

Dichroic Nomenclature


Longpass and Shortpass

Longpass and shortpass filters are defined by their cut-on and cut-off edges, where the edge is defined as the wavelength at 50% peak transmission.

LP SP Nomenclature


Note: Cut-on or cut-off wavelength is defined as the wavelength at which the filter is at 50% of its maximum transmission.

Omega-Specific Nomenclature

3rd Millennium Filter Nomenclature

3rd Millennium nomenclature utilizes the most critical feature of bandpass filter design, the transition from attenuation to transmission. By specifying the cut-on and cut-off edges for a bandpass filter we are able to achieve more precise location of band edges. The cut-on and cut-off edges are defined as the wavelength at 50% of maximum transmission. Longpass and shortpass filters continue to be defined by their cut-on and cut-off edges.

3rd Millennium Nomenclature


Catalog Stock Items

Many of our stock filters, both OEM and Fluorescence/Microscopy have standardized nomenclature used as prefixes denoting each specific product line. The following nomenclature represents each product line:

  • XA – Analytical Filters
  • XB – Bandpass Filters
  • XC – Microscope Filter Holders
  • XCC – Clinical Chemistry Filters
  • XCY – Flow Cytometry Filters
  • XF – Fluorescence Filters
  • XL – Laser Line Filters (not blocked)
  • XLD – Laser Diode Clean-up
  • XLK – Laser Line Filters (fully blocked)
  • XLL – Laser Line Filters
  • XMV – Machine Vision Filters
  • XND – Neutral Density Filters
  • XRLP – Raman Longpass Filters
  • XUV – UV Filters

Fluorescence Instrumentation & Microscopy

All of our Fluorescence Instrumentation and Microscopy filters begin with the prefix "XF" and are distinguished between excitation, dichroic and emission filters by a subsequent 4-digit code. The excitation 4-digit code begins with the number "1" followed by any 3 other digits. For dichroics, the 4-digit code begins with the number "2" and for emission filters, the 4-digit code begins with the number "3."