Neutral Density Filter, Absorptive, 25.4 mm, 0.4 OD at 546.1 nm

The FSR-OD40 Absorptive Neutral Density Filter is a 1 inch (25.4 mm) diameter absorptive neutral density filter that has an Optical Density of 0.4 at 546.1 nm, and provides broadband attenuation for the visible to near-infrared region. This filter is precision polished for demanding research or OEM applications. The filter's Optical Density is permanently marked on the filter and is shipped with a transmission curve.

Spectrally Neutral for Visible Wavelengths

Absorptive Neutral Density Glass for Low Power Applications

These neutral density filters are made from absorptive glass. This results in a lower cost product that is somewhat less fragile compared to coated metallic ND filters. Absorptive ND filters also reflect far less light toward the source compared with metallic ND Filters, which may be beneficial. Nevertheless stacking a large number of ND filters can still result in excessive undesired reflection due to Fresnel surface reflection. Due to the absorptive nature of the filter glass, use with high power lasers should be avoided. Power levels 1-5 W/cm² are advised.

Additive Optical Densities

Optical density (OD) is given by the relationship: OD = -log(T) or T = 10(-OD) where T is transmittance (0≤T≤1). Optical Density, unlike transmittance, is additive. When multiple filters are stacked, the total density is easily found by adding up the densities of each filter in the series. For example to achieve desired transmittance of 8%, first calculate the equivalent density (OD = -log(0.08) = 1.097 ≅ 1.1), then find a combination of filters that adds to the desired number, such as a combination of an OD1 filter and an OD0.1 filter.