Hellma Analytics neutral density glass filters are made from filter materials produced by Schott AG, which were selected on account of their homogeneity and stability. Thanks to a relatively constant transmittance within the wavelength range of 405 nm to 800 nm, they have been used to check photometric accuracy and linearity in the visible wavelength range (> 405 nm) for decades.

Please note, the thickness of the filter is set at the manufacturing so that the specified nominal optical density (values from 0.04 to 3.0 Abs) obtained at 546.1 nm. This results in slightly increasing absorptions at shorter wavelengths.