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2.5 OD 25mm Diameter, Reflective ND Filter

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Diameter (mm):
Angle of Incidence (°):
Optical Density OD (Average):
Substrate: Many glass manufacturers offer the same material characteristics under different trade names. Learn More
Float Glass
Surface 1: Inconel
Reflection (%):
Surface Quality:
Thickness (mm):
1.60 Nominal
Transmission (%):
Neutral Density Filter
Blocking Wavelength Range (nm):
400 - 700
Dimensional Tolerance (mm):
Clear Aperture (%):
±5% of Optical Density
Optical density values are average over specified blocking wavelength range.
Surface Flatness (P-V):
4 - 6λ

Regulatory Compliance

RoHS 2015:
Certificate of Conformance:
Reach 233:

Product Family Description

  • Spectrally Flat
  • Maximum Accuracy and Neutrality at Moderate Price
  • Use Stacks to Create Intermediate Density Values

These filters have constant density values across the surface. The transmission to reflection ratio varies with density selection. In stacks, the total density is the sum of each filter’s density. ND filters are used primarily for the attenuation of light over a wide spectral range. They are often used in laser and photometer applications, where excessive power can cause damage or inaccurate results. Orient mirrored side toward source at 0° angle of incidence.

Optical Density exhibits an additive relationship; for example, stacking filters with OD values of 0.6 and 0.9 yields a resultant density of 1.5. The optical density is related to the transmission by the following equation:
T = 10-OD x 100 = Percent Transmission.

Note: Low optical density filters (0.1, 0.15, and 0.2 OD) are coated with thin layers of Inconel and their performance may shift overtime. To prolong the lifetime of these filters, we recommend using non-contact cleaning methods (such as compressed air) to prevent damage to the coating and avoiding the use of these filters in humid environments to prevent oxidation.

Note: Due to supply chain issues, our kits may be delivered with an alternative packaging solution in place of a wooden box. For any questions, please contact

Reflective Neutral Density Filter Kits

Reflective Neutral Density Filter Kits are available with either 8 or 14 optical densities. The kits with 8 filters include our most popular filters, with densities of 0.3, 0.5, 1.0, 1.3, 1.5, 2.0, 2.5, and 3.0. The kits with 14 filters include all available densities, except for 3.0. Kits are ideal for determining precise system optical density requirements. Custom densities are available for OEM applications.