Cavision 4 x 4″ Hot Mirror Filter incorporates a dielectric mirror within the filter to combat infrared light pollution that becomes noticeable when making long exposures with a digital camera. This situation is also naturally prevalent when photographing near strong sources of infrared, such as fires and at sunset. The hot mirror filter effectively cuts out infrared wavelengths but does not interfere with visible red wavelengths. This filter measures 4 x 4″ / 101.6 x 101.6mm and is constructed from 30-layer coated optical glass.