A high pass filter (Long pass filter) is an optical device that transmits light waves above a certain wavelength while blocking light waves below that wavelength. The amount of attenuation for each frequency depends on the filter design. Commonly used in microscopy, spectroscopy, chemical analysis, and machine vision, Edmund Optics' optical filters are available in a variety of filter types and precision levels. Vref provides a DC offset to accommodate for single-supply applications.