Neutral density filter


Product Description


Neutral density filters uniformly attenuate the intensity of light over a broad spectral range. Attenuation is accomplished by either absorption using light absorbing glass or by a combination of absorption and reflection using a thin-film metal coating. Neutral density filters can attenuate spectral regions selected from 250 to 2500nm. The level of attenuation can be specified from optical density (OD) 0.04 to 4.0 where OD is defined as -log10 (T).
Overall attenuation may be increased by stacking neutral density filters serially in the light path. For example, a 0.5 (OD 0.5) neutral density filter placed in series with a 0.3 (OD 0.3) neutral density filter will produce total attenuation of OD 0.8 (10-0.8) or 16% transmission. A six-filter set of 0.1, 0.3, 0.5, 1.0, 2.0, and 3.0 optical densities can achieve a graduated range of spectrally neutral attenuation from OD 0.1 to 6.9. See OD conversion table below.
Filter Description
Neutral density filters are defined by:
Optical Density—the level of neutral transmission across the wavelength region;
Optical Density—OD = -log10 (T).
smission Tolerances (at 550nm):
   For OD <1.0 ±0.05 OD from nominal
   For OD 1.0–3.0 ±0.1 OD from nominal
   For OD >3.0 ±0.2 OD from nominal
Neutrality Tolerance The variation in optical density from 400 to 700nm 
will be less than 10% of the OD measured at 550nm
Outer Dimension Tolerance +0, -0.25mm (+0, -0.01”)
Clear Aperture 4mm less than nominal outside dimension
Maximum Thickness 4mm
Substrate Material Optical quality glass or UV-grade quartz
Surface Quality 80/50 scratch/dig per Mil-O-13830A
Operating Temperature Range -60°C to +80°C
Coating Vacuum-deposited metallic alloy, if not absorption glass type
Construction Either (a) exposed, front-surface metalic coating, 
(b) metallic coating laminated and protected in a 
moisture-resistant assembly, or (c) absorption glass