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Full-spectrum photography is a subset of
multispectral imaging Multispectral imaging captures image data within specific wavelength ranges across the electromagnetic spectrum. The wavelengths may be separated by filters or detected with the use of instruments that are sensitive to particular wavelengths, ...
, defined among photography enthusiasts as imaging with consumer cameras the full, broad spectrum of a film or
camera sensor An image sensor or imager is a sensor that detects and conveys information used to make an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of cu ...
bandwidth. In practice, specialized broadband/full-spectrum film captures visible and near
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
light, commonly referred to as the "
VNIR The visible and near-infrared (VNIR) portion of the electromagnetic spectrum has wavelengths between approximately 400 and 1100 nanometers (nm). It combines the full visible spectrum with an adjacent portion of the infrared spectrum up to the ...
".
Definition of VNIR.
Modified digital cameras can detect some
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
, 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 A hot mirror is a specialized dielectric mirror, a dichroic filter, often employed to protect optical systems by reflecting infrared light back into a light source, while allowing visible light to pass. Hot mirrors can be designed to be inserte ...
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 In digital imaging, a color filter array (CFA), or color filter mosaic (CFM), is a mosaic of tiny color filters placed over the pixel sensors of an image sensor to capture color information. The term is also used in reference to e paper devices ...
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
ultraviolet photography Ultraviolet photography is a photographic process of recording images by using radiation from the ultraviolet (UV) spectrum only. Images taken with ultraviolet radiation serve a number of scientific, medical or artistic purposes. Images may rev ...
or
infrared photography ''Top:'' tree photographed in the near infrared range. ''Bottom:'' same tree in the visible part of the spectrum. In infrared photography, the film or image sensor used is sensitive to infrared light. The part of the spectrum used is r ...
with the appropriate filters. Uses of full-spectrum photography include
fine art photography Fine-art photography is photography created in line with the vision of the photographer as artist, using photography as a medium for creative expression. The goal of fine-art photography is to express an idea, a message, or an emotion. This stand ...
,
geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
,
forensics Forensic science, also known as criminalistics, is the application of science to criminal and civil laws, mainly—on the criminal side—during criminal investigation, as governed by the legal standards of admissible evidence and crimina ...
& law enforcement, and even some claimed use in
ghost hunting Ghost hunting is the process of investigating locations that are reported to be haunted by ghosts. Typically, a ghost-hunting team will attempt to collect evidence supporting the existence of paranormal activity. Ghost hunters use a variety of ...
.


History

Full-spectrum photography has its roots in
spectral imaging Spectral imaging is imaging that uses multiple bands across the electromagnetic spectrum. While an ordinary camera captures light across three wavelength bands in the visible spectrum, red, green, and blue (RGB), spectral imaging encompasses ...
, both
multispectral Multispectral imaging captures image data within specific wavelength ranges across the electromagnetic spectrum. The wavelengths may be separated by filters or detected with the use of instruments that are sensitive to particular wavelengths, ...
and
hyperspectral imaging Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. The goal of hyperspectral imaging is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifyi ...
, which began as early as the late 1950s and early 1960s as means for geological and military
remote sensing Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Earth ...
. Wideband
panchromatic film Panchromatic emulsion is a type of black-and-white photographic emulsion that is sensitive to all wavelengths of visible light. Description A panchromatic emulsion renders a realistic reproduction of a scene as it appears to the human eye, altho ...
has been available in various forms since the 1920s, when some UV and IR sensitivity remained in commercially available emulsions. The earliest color films sometimes included wider band color than recent commercial
photographic emulsion Photographic emulsion is a light-sensitive colloid used in film-based photography. Most commonly, in silver-gelatin photography, it consists of silver halide crystals dispersed in gelatin. The emulsion is usually coated onto a substrate of g ...
s, and can be recognized by the more reddish and or limited color tones of early color prints (not to be confused with print fading). In the late 1990s enthusiastic photographers began shooting infrared with digital cameras, necessitating either long exposures or the removal of the internal
hot mirror A hot mirror is a specialized dielectric mirror, a dichroic filter, often employed to protect optical systems by reflecting infrared light back into a light source, while allowing visible light to pass. Hot mirrors can be designed to be inserte ...
. Most replaced the hot mirror with an infrared pass filter of the same
optical thickness In physics, optical depth or optical thickness is the natural logarithm of the ratio of incident to ''transmitted'' radiant power through a material. Thus, the larger the optical depth, the smaller the amount of transmitted radiant power through ...
(to retain focus) and pass only infrared light to achieve results seen with infrared B&W film. Around 2000, electro-optical engineer David Twede, already engaged in VNIR and infrared spectral remote sensing, ventured into Full-spectrum photography art, using a modified digital camera to explore broader spectral imaging and developing an artistic style using it. Around 2003, forensics photographers using engineered cameras for specific purposes began modifying off-the-shelf
digital camera A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile device ...
s to acquire less expensive tools. Full-spectrum photography is used by enthusiasts of
ghost hunting Ghost hunting is the process of investigating locations that are reported to be haunted by ghosts. Typically, a ghost-hunting team will attempt to collect evidence supporting the existence of paranormal activity. Ghost hunters use a variety of ...
, though no claims of actually photographing psychic phenomenon with Full-spectrum or infrared photography have been substantiated. Today, there are a few places that will modify digital cameras to pass broad, full-spectrum light for full spectral imaging. A few DSLR cameras such as the
Fujifilm FinePix IS Pro The FinePix IS Pro is a digital single lens reflex camera introduced by Fujifilm in 2007. It is based on a FinePix S5 Pro, which is in turn based on the Nikon D200. It has a Nikon F lens mount and can use most lenses made for 35 mm Nikon SLR cam ...
are purpose-designed for full spectrum use and respond from approximately 1000 nm (IR) to 380 nm (UV).


Basics

Digital sensor A digital sensor is an electronic or electrochemical sensor, where data is digitally converted and transmitted. Sensors are often used for analytical measurements, e.g. the measurement of chemical and physical properties of liquids. Typical measure ...
s and
photographic film Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin photographic emulsion, emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of th ...
s can be made to record non-visible ultraviolet (UV) and infrared (IR) radiation. In each case, they generally require special equipment: converted digital cameras, specific filters, highly transmitting lenses, etc. For example, most photographic lenses are made of glass and will filter out most ultraviolet light. Instead, expensive lenses made of quartz must be used. Infrared films may be shot in standard cameras using an infrared pass filters, although focus must compensate for the infrared focal point. 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 In optics, optical path length (OPL, denoted ''Λ'' in equations), also known as optical length or optical distance, is the product of the geometric length of the optical path followed by light and the refractive index of homogeneous medium through ...
. 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.
Tedious instructions on modifying a Nikon D50.
Once the camera is sensitive to the full-spectrum, external filters can be used to selectively filter portions of the UV, visible and infrared to achieve various effects. For example, a standard red #25a can be used to include red light and infrared light together, yielding particularly strong two-toned color images of a reddish nature except where the infrared is high and shows as cyan. Another example, using UV/IR filters such as the 18A or U-330 yield a two or three toned image in which blues and yellows dominate. Less common filters have been claimed to give a variety of color effects ranging from diverse pastel foliage and deep blue skies to surrealistic effects of the sky and ground, though
digital image processing Digital image processing is the use of a digital computer to process digital images through an algorithm. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing. It allo ...
is likely required to achieve the full effects. One issue with full-spectrum photography in either film or digital photography is the
chromatic aberration In optics, chromatic aberration (CA), also called chromatic distortion and spherochromatism, is a failure of a lens to focus all colors to the same point. It is caused by dispersion: the refractive index of the lens elements varies with the wave ...
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. It is important to note that while the converted camera sensor is capable of recording in both the ultraviolet and infrared region, when mixed light hits the sensor it will be the longer infrared waves that will predominate in the recording. Little or no shortwave ultraviolet light may be recorded unless selective filtering is applied to cut some or all of the infrared light. The longwave infrared light may also wash out a considerable amount of the visible light in the blue and green areas in a full spectrum photograph. Similarly if infrared light is entirely blocked, the visible light can overwhelm the recording of the ultraviolet light. So there is no truly full-spectrum photograph that can be made. Full-spectrum photography achieves various effects and surrealistic colors from the interaction of reflectivity (UV, visible, IR) of nature and man made materials and the specific spectral transmission of the red, green and blue filters on the camera. The addition of external filters will reduce and emphasize different interactions, yielding different effects.


Applications


Art

Full-spectrum photography is being used for
art photography Fine-art photography is photography created in line with the vision of the photographer as artist, using photography as a medium for creative expression. The goal of fine-art photography is to express an idea, a message, or an emotion. This stan ...
and can yield colors similar to visible color film, but with a brightness and tonality of infrared photographs. Most full-spectrum art is of landscapes. A movement is also building for artistic human photography with full-spectrum photography, that captures a real person interacting with a surreal landscape. Full-spectrum photography art is displayed at galleries in Colorado and Florida.


Science hobbyists

Hyperspectral Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. The goal of hyperspectral imaging is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifyi ...
and most
multispectral Multispectral imaging captures image data within specific wavelength ranges across the electromagnetic spectrum. The wavelengths may be separated by filters or detected with the use of instruments that are sensitive to particular wavelengths, ...
cameras are expensive and difficult to operate, requiring a computer acquisition and laborious post-processing. Modified digital cameras with the proper filtering avail some limited spectral sensing for
geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
/
mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...
,
agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...
and oceanographic purposes. Most consumer cameras retain the red, green and blue micro-filters, thus limiting their usefulness in scientific imaging.


Forensics

Forensics imaging often uses Full-spectrum cameras to emphasize non-visible materials which have more diverse reflectivities in the ultraviolet and infrared. Applications include non-visible inks (uv & ir), disturbed soil (uv & ir), gunshot residue (ir), body fluids (uv), fibers, etc. Analogous to forensics, Full-spectrum cameras are being explored to enhance photographic recordings of archeological findings.


See also

*
Infrared photography ''Top:'' tree photographed in the near infrared range. ''Bottom:'' same tree in the visible part of the spectrum. In infrared photography, the film or image sensor used is sensitive to infrared light. The part of the spectrum used is r ...
*
Ultraviolet photography Ultraviolet photography is a photographic process of recording images by using radiation from the ultraviolet (UV) spectrum only. Images taken with ultraviolet radiation serve a number of scientific, medical or artistic purposes. Images may rev ...
*
Hyperspectral imaging Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. The goal of hyperspectral imaging is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifyi ...
*
Multispectral imaging Multispectral imaging captures image data within specific wavelength ranges across the electromagnetic spectrum. The wavelengths may be separated by filters or detected with the use of instruments that are sensitive to particular wavelengths, ...
*
Full-spectrum light Full-spectrum light is light that covers the electromagnetic spectrum from infrared to near-ultraviolet, or all wavelengths that are useful to plant or animal life; in particular, sunlight is considered full spectrum, even though the solar spectral ...
* History of forensic photography * Fujifilm FinePix IS Pro full spectrum camera


References

{{Photography, date=July 2008 Photographic techniques