ND504B Dia. 0.5 in Unmounted Reflective ND Filter; Optical Density 0.4

The ND504B is a circular, unmounted Neutral Density (ND) filter, with a diameter of 0.5 inches and a thickness of 1 millimeter, sourced from the renowned optical component manufacturer, Thorlabs. This filter is designed to reduce the intensity of incident light without altering its color composition, making it an essential tool for various optical applications.

The filter's primary function is achieved through its coating, which is uniformly applied to both the front and back surfaces. This coating, identified as 'tho nd04', provides an optical density of 0.4. Optical density is a logarithmic measure of the reduction in transmittance of light through a medium, such as this filter. In simpler terms, an optical density of 0.4 means that the filter reduces the light intensity to approximately 63% of its original value.

The ND504B filter is made from N-BK7 Schott glass, a high-quality borosilicate glass known for its excellent optical properties, including low dispersion and high homogeneity. This material ensures the filter maintains high optical performance across a wide range of wavelengths, with a specified wavelength of 633 nanometers for this particular model.

The filter's thin lens shape and unmounted design provide flexibility for integration into various optical systems. However, users should exercise caution when handling unmounted filters to prevent damage or contamination.