What is a shortpass filter?

A short-pass filter is an optical filter that only allows incident light below a certain wavelength to pass through – the so-called cut-off wavelength. It blocks light above this wavelength. In addition to the cut-off wavelength, important for the shortpass filter are the transmission band and the actual blocking band in which the short-pass filter is still permeable to a small part of light.

Short-pass filters are available both as interference filters and as coloured glass filters; the quality of blocking is usually specified in the unit of optical density (OD). One area of application for short-pass filters is, for example, to block IR radiation on camera sensors. In this case the filters are also referred to as IR cut-off filters.