The Cavision 3x3" Hot Mirror Neutral Density 1.2 Glass Filter combines both a solid ND filter and a hot mirror filter into a single solution for greater efficiency in controlling exposures and reducing the amount of IR light contamination.
The 1.2 ND filter darkens the entire image, allowing you to photograph with longer shutter speeds or wider apertures than normally required. By providing a 4 stop reduction in exposure, this filter allows you to control depth of field and convey movement more easily. The hot mirror portion of the filter incorporates a dielectric mirror in order to filter out infrared light pollution that is common when photographing with a digital camera in strong infrared situations, helping to achieve a more neutral color balance. This filter measures 3x3" / 76.2x76.2mm and is constructed from 2mm-thick glass. By slowing your exposure time or increasing your aperture, you are able to control depth of field and convey movement more easily. Neutral density filters do not affect the coloration of the image and are ideal for pairing with other filters.
The hot mirror aspect of this 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, as well as 30-layer coating technology, effectively cuts out infrared wavelengths but does not interfere with visible red wavelengths.