The current craze in paranormal photography and video is Full Spectrum. But, what exactly is it, and why is the theory that it will work in the field to capture spirits in action.
What is Full Spectrum? It is basically the ability to capture visible and near infrared light, commonly referred to as the VNIR. Modified digital cameras can detect some UV, all of the visible and much of the near infrared spectrum, as most digital imaging sensors are sensitive from about 350 nm to 1000 nm. An off-the-shelf digital camera contains an infrared hot mirror filter that blocks most of the infrared and a bit of the ultraviolet that would otherwise be detected by the sensor, narrowing the accepted range from about 400 nm to 700 nm. Replacing a hot mirror or infrared blocking filter with an infrared pass or a wide spectrally transmitting filter allows the camera to detect the wider spectrum light at greater sensitivity. Without the hot-mirror, the red, green and blue (or cyan, yellow and magenta) elements of the color filter array placed over the sensor elements pass varying amounts of ultraviolet and infrared which may be recorded in any of the red, green or blue channels depending on the particular sensor in use and on the dyes used in the Bayer filter. A converted full-spectrum camera can be used for UV or IR with the appropriate filters.
Use within the paranormal world usually means converting a digital camera to Full Spectrum, A converted digital camera usually requires that the infrared hot mirror be removed and replaced by a wideband, spectrally flat glass of the same optical path length. Typical glass types used include Schott WG-280 and BK-7, which transmit as much as 90% from around 300 nm to past 1000 nm. Removing the hot mirror is tedious and may require special tools and clean rooms.
There are issues with this type of photography, one being with Full-spectrum photography in either film or digital photography is the chromatic aberration, produced by the wideband information. That is, different spectra, including the ultraviolet and infrared, will focus at different focal points, yielding blurry images and color edge effects, depending on the focal length used. There are specialized lenses such as the Nikon 105mm f4.5 UV-Nikkor which are designed to eliminate this chromatic aberration.
Although Full Spectrum Photography has been around since the 50’s for geological and Military functions, it hos only recently been used for “Ghost Hunting”. The theory is that perhaps spirits can be detected in this light spectrum, and therefore photographed. Until now, there has not been scientific proof that this is the case, and with as many Full Spectrum Cameras, both still and video now being used, one would think that if this technology worked in the field, we would have a plethora of evidence to back the theory up.
Perhaps there still is a wavelength that spirits can be detected in that we simply have as yet been unable to determine, so we must keep trying different techniques and theories to try and find that holy grail.