Ultraviolet photography

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Human skin with a sunscreen drawing: in light and ultraviolet radiation. Sunscreen on back under normal and UV light.jpg
Human skin with a sunscreen drawing: in light and ultraviolet radiation.
Earth in far ultraviolet radiation; image taken by Apollo 16 commander John W. Young. The auroral belts 13 degrees either side of the magnetic equator can be seen crossing each other on the middle of the right side of the Earth. Far-ultraviolet photo of Earth by Apollo 16 (AS16-123-19657).jpg
Earth in far ultraviolet radiation; image taken by Apollo 16 commander John W. Young. The auroral belts 13 degrees either side of the magnetic equator can be seen crossing each other on the middle of the right side of the Earth.
A false color photograph with ultraviolet radiation (335-365nm) mapped to the blue channel, green light (500-600nm) to the green channel and infrared radiation (720-850nm) to the red channel. UV-Vis-IR Homestead in Montana.jpg
A false color photograph with ultraviolet radiation (335-365nm) mapped to the blue channel, green light (500-600nm) to the green channel and infrared radiation (720-850nm) to the red channel.

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 reveal deterioration of art works or structures not apparent under light. Diagnostic medical images may be used to detect certain skin disorders or as evidence of injury. Some animals, particularly insects, use ultraviolet wavelengths for vision; ultraviolet photography can help investigate the markings of plants that attract insects, while invisible to the unaided human eye. Ultraviolet photography of archaeological sites may reveal artifacts or traffic patterns not otherwise visible.

Contents

Ultraviolet images have no color since ultraviolet radiation is invisible to human eyes.

Photographs of dyes that fluoresce under ultraviolet illumination are examples of ultraviolet fluorescence photography.

Overview

ultraviolet image of the globular cluster NGC 1851 in the southern constellation Columba. PIA07908.jpg
ultraviolet image of the globular cluster NGC 1851 in the southern constellation Columba.

Light (visible electromagnetic spectrum) covers the spectral region from about 400 to 750 nanometers. This is the radiation spectrum used in normal photography. The band of radiation that extends from about 10 nm to 400 nm is known as ultraviolet radiation. UV spectrographers divide this range into three bands:

Only near UV is of interest for UV photography, for several reasons. Ordinary air is opaque to wavelengths below about 200 nm, and most transparent lens glass is opaque below about 180 nm. UV photographers subdivide the near UV into:

(These terms should not be confused with the parts of the radio spectrum with similar names.)

There are two ways to use UV radiation to take photographs - reflected ultraviolet and ultraviolet induced fluorescence photography. Reflected ultraviolet photography finds practical use in medicine, dermatology, botany, criminology and theatrical applications.

Sunlight is the most available free UV radiation source for use in reflected UV photography, but the quality and quantity of the radiation depends on atmospheric conditions. A bright and dry day is much richer in UV radiation and is preferable to a cloudy or rainy day.

Another suitable source is electronic flash which can be used efficiently in combination with an aluminium reflector. Some flash units have a special UV absorbing glass over the flash tube, which must be removed before the exposure. It also helps to partly (90%) remove the gold coating of some flash tubes which otherwise suppresses UV.

Most modern UV sources are based on a mercury arc sealed in a glass tube. By coating the tube internally with a suitable phosphor, it becomes an effective long wave UV source.

Recently, UV-LEDs have become commercially available. Grouping several UV-LEDs can produce a strong enough source for reflected UV photography although the emission waveband is typically somewhat narrower than sunlight or electronic flash.

Special UV lamps known as "black light" fluorescence tubes or bulbs also can be used for long wave ultraviolet photography.

Equipment and techniques

Reflected UV photography

A portrait taken using only UV radiation between the wavelengths of 335 and 365 nanometres. UV Portrait.jpg
A portrait taken using only UV radiation between the wavelengths of 335 and 365 nanometres.

In reflected UV photography the subject is illuminated directly by UV emitting lamps (radiation sources) or by strong sunlight. A UV transmitting filter is placed on the lens, which allows ultraviolet radiation to pass and which absorbs or blocks all light and infrared radiation. UV filters are made from special colored glass and may be coated or sandwiched with other filter glass to aid in blocking unwanted wavelengths. Examples of UV transmission filters are the Baader-U filter or the StraightEdgeU ultraviolet bandpass filter, both of which exclude most visible and infrared radiation. Older filters include the Kodak Wratten 18A, B+W 403, Hoya U-340 and Kenko U-360 most of which need to be used in conjunction with an additional infrared blocking filter. Typically such IR blocking, UV transmissive filters are made from Schott BG-38, BG-39 and BG-40 glass. Filters for use with digital camera sensors must not have any "infrared leak" (transmission in the infrared spectrum); the sensor will pick up reflected infrared radiation as well as ultraviolet, which attenuate the contrast and may even completely obscure the details that would be resolved by ultraviolet radiation alone.

Most types of glass will allow longwave UV to pass, but absorb all the other UV wavelengths, usually from about 350 nm and below. For UV photography it is necessary to use specially developed lenses having elements made from fused quartz or quartz and fluorite. Lenses based purely on quartz show a distinct focus shift between visible and UV light, whereas the fluorite/quartz lenses can be fully corrected between visible and ultraviolet light without focus shift. Examples of the latter type are the Nikon UV-Nikkor 105 mm f/4.5, the Coastal Optics 60 mm f/4.0, the Hasselblad (Zeiss) UV-Sonnar 105 mm, and the Asahi Pentax Ultra Achromatic Takumar 85 mm f/4.5. [1]

Suitable digital cameras for reflected UV photography have been reported to be the (unmodified) Nikon D70 or D40 DSLRs, but many others are suitable after having their internal UV and IR blocking filter removed. The Fujifilm FinePix IS Pro digital SLR camera is purpose-designed for ultraviolet (and infrared) photography, with a frequency response rated from 1000 to 380 nm, although it also responds to somewhat longer and shorter wavelengths. Silicon (from which DSLR sensors are made) can respond to wavelengths between 1100 and 190 nm.

UV induced fluorescence photography

Fluorescent materials exposed to UV radiation. No filter is used to absorb violet light. Photo taken with daylight film. Www Beo cc.jpg
Fluorescent materials exposed to UV radiation. No filter is used to absorb violet light. Photo taken with daylight film.

Photography based on visible fluorescence induced by UV radiation uses the same ultraviolet illumination as in reflected UV photography. However, the glass barrier filter used on the lens must now block all ultraviolet and infrared radiation, permitting only visible radiation (light) to pass. Visible fluorescence is produced in a suitable subject when the shorter, higher energy ultraviolet wavelengths are absorbed, lose some energy and are emitted as longer, lower energy visible wavelengths.

UV induced visible fluorescence photography must take place in a darkened room, preferably with a black background. The photographer should also wear dark-colored clothes for better results. (Many light-colored fabrics also fluoresce under UV.) Any camera or lens may be used because only visible wavelengths are being recorded.

UV can also induce infrared fluorescence and UV fluorescence depending on the subject. For UV induced non-visible fluorescence photography, a camera must be modified in order to capture UV or IR images, and UV or IR capable lenses must be used.

Filters are sometimes added to the UV illumination source to narrow the illuminant waveband. This filter is called an exciter filter, and it allows only the radiation to pass which is needed to induce a particular fluorescence. As before, a barrier filter must also be placed in front of the camera lens to exclude undesired wavelengths.

Forensic use

Ultraviolet photography was used as evidence in court at least as early as 1934. [2] Photographs made with ultraviolet radiation can reveal bruises or scars not visible on the surface of the skin, in some cases long after visible healing has completed. These can serve as evidence of assault. [3] Ultraviolet imaging can be used to detect alteration of documents. [4]

See also

Related Research Articles

<span class="mw-page-title-main">Electromagnetic spectrum</span> Range of frequencies or wavelengths of electromagnetic radiation

The electromagnetic spectrum is the spectrum of electromagnetic radiation, ranging over a domain of frequencies and their respective wavelengths and photon energies.

<span class="mw-page-title-main">Infrared</span> Form of electromagnetic radiation

Infrared is electromagnetic radiation (EMR) in the spectral band between radio waves and visible light. It is invisible to the human eye. IR is generally understood to encompass wavelengths from around 1 millimeter to around 700 nanometers or 0.7 micrometers (430 terahertz).

<span class="mw-page-title-main">Ultraviolet</span> Form of electromagnetic radiation

Ultraviolet (UV) is a form of electromagnetic radiation with wavelength shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs; Cherenkov radiation; and specialized lights; such as mercury-vapor lamps, tanning lamps, and black lights.

<span class="mw-page-title-main">Visible spectrum</span> Portion of the electromagnetic spectrum that is visible to the human eye

The visible spectrum is the band of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light. The optical spectrum is sometimes considered to be the same as the visible spectrum, but some authors define the term more broadly, to include the ultraviolet and infrared parts of the electromagnetic spectrum as well.

<span class="mw-page-title-main">Ultraviolet–visible spectroscopy</span> Range of spectroscopic analysis

Ultraviolet (UV) spectroscopy or ultraviolet–visible (UV-VIS) spectrophotometry refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible regions of the electromagnetic spectrum. Being relatively inexpensive and easily implemented, this methodology is widely used in diverse applied and fundamental applications. The only requirement is that the sample absorb in the UV-Vis region, i.e. be a chromophore. Absorption spectroscopy is complementary to fluorescence spectroscopy. Parameters of interest, besides the wavelength of measurement, are absorbance (A) or transmittance (%T) or reflectance (%R), and its change with time.

<span class="mw-page-title-main">Cuvette</span> Small container used in laboratories

In laboratories, a cuvette is a small tube-like container with straight sides and a circular or square cross-section. It is sealed at one end, and made of a clear, transparent material such as plastic, glass, or fused quartz. Cuvettes are designed to hold samples for spectroscopic measurement, where a beam of light is passed through the sample within the cuvette to measure the absorbance, transmittance, fluorescence intensity, fluorescence polarization, or fluorescence lifetime of the sample. This measurement is done with a spectrophotometer.

<span class="mw-page-title-main">Infrared cut-off filter</span> Optical fiters that block near-infrared while passing visible light

Infrared cut-off filters, sometimes called IR filters or heat-absorbing filters, are designed to reflect or block near-infrared wavelengths while passing visible light. They are often used in devices with bright incandescent light bulbs to prevent unwanted heating. There are also filters which are used in solid state video cameras to block IR due to the high sensitivity of many camera sensors to near-infrared light. These filters typically have a blue hue to them as they also sometimes block some of the light from the longer red wavelengths.

<span class="mw-page-title-main">Blacklight</span> Light fixture that emits long-wave ultraviolet light and very little visible light

A blacklight, also called a UV-A light, Wood's lamp, or ultraviolet light, is a lamp that emits long-wave (UV-A) ultraviolet light and very little visible light. One type of lamp has a violet filter material, either on the bulb or in a separate glass filter in the lamp housing, which blocks most visible light and allows through UV, so the lamp has a dim violet glow when operating. Blacklight lamps which have this filter have a lighting industry designation that includes the letters "BLB". This stands for "blacklight blue". A second type of lamp produces ultraviolet but does not have the filter material, so it produces more visible light and has a blue color when operating. These tubes are made for use in "bug zapper" insect traps, and are identified by the industry designation "BL". This stands for "blacklight".

<span class="mw-page-title-main">Fused quartz</span> Glass consisting of pure silica

Fused quartz,fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which change the glasses' optical and physical properties, such as lowering the melt temperature. Fused quartz, therefore, has high working and melting temperatures, making it less desirable for most common applications.

<span class="mw-page-title-main">Spectrophotometry</span> Branch of spectroscopy

Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spectrophotometers, that can measure the intensity of a light beam at different wavelengths. Although spectrophotometry is most commonly applied to ultraviolet, visible, and infrared radiation, modern spectrophotometers can interrogate wide swaths of the electromagnetic spectrum, including x-ray, ultraviolet, visible, infrared, and/or microwave wavelengths.

<span class="mw-page-title-main">Photographic filter</span> Camera accessory consisting of an optical filter

In photography and cinematography, a filter is a camera accessory consisting of an optical filter that can be inserted into the optical path. The filter can be of a square or oblong shape and mounted in a holder accessory, or, more commonly, a glass or plastic disk in a metal or plastic ring frame, which can be screwed into the front of or clipped onto the camera lens.

<span class="mw-page-title-main">Optical filter</span> Filters which selectively transmit specific colors

An optical filter is a device that selectively transmits light of different wavelengths, usually implemented as a glass plane or plastic device in the optical path, which are either dyed in the bulk or have interference coatings. The optical properties of filters are completely described by their frequency response, which specifies how the magnitude and phase of each frequency component of an incoming signal is modified by the filter.

<span class="mw-page-title-main">Infrared photography</span> Near-infrared imaging

In infrared photography, the photographic film or image sensor used is sensitive to infrared light. The part of the spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengths used for photography range from about 700 nm to about 900 nm. Film is usually sensitive to visible light too, so an infrared-passing filter is used; this lets infrared (IR) light pass through to the camera, but blocks all or most of the visible light spectrum.

<span class="mw-page-title-main">Purple fringing</span> Type of chromatic aberration in photography

In photography, purple fringing is the term for an unfocused purple or magenta "ghost" image on a photograph. This optical aberration is generally most visible as a coloring and lightening of dark edges adjacent to bright areas of broad-spectrum illumination, such as daylight or various types of gas-discharge lamps.

A flame detector is a sensor designed to detect and respond to the presence of a flame or fire, allowing flame detection. Responses to a detected flame depend on the installation, but can include sounding an alarm, deactivating a fuel line, and activating a fire suppression system. When used in applications such as industrial furnaces, their role is to provide confirmation that the furnace is working properly; it can be used to turn off the ignition system though in many cases they take no direct action beyond notifying the operator or control system. A flame detector can often respond faster and more accurately than a smoke or heat detector due to the mechanisms it uses to detect the flame.

<span class="mw-page-title-main">Full-spectrum photography</span> Photography capturing visible and near-infrared light

Full-spectrum photography is a subset of multispectral imaging, defined among photography enthusiasts as imaging with consumer cameras the full, broad spectrum of a film or camera sensor bandwidth. In practice, specialized broadband/full-spectrum film captures visible and near infrared light, commonly referred to as the "VNIR".

<span class="mw-page-title-main">FinePix IS Pro</span> Digital single lens reflex camera

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 cameras. It replaces the Fujifilm FinePix S3 Pro UVIR.

<span class="mw-page-title-main">Non-ionizing radiation</span> Harmless low-frequency radiation

Non-ionizingradiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule. Instead of producing charged ions when passing through matter, non-ionizing electromagnetic radiation has sufficient energy only for excitation. Non-ionizing radiation is not a significant health risk. In contrast, ionizing radiation has a higher frequency and shorter wavelength than non-ionizing radiation, and can be a serious health hazard: exposure to it can cause burns, radiation sickness, many kinds of cancer, and genetic damage. Using ionizing radiation requires elaborate radiological protection measures, which in general are not required with non-ionizing radiation.

Microspectrophotometry is the measure of the spectra of microscopic samples using different wavelengths of electromagnetic radiation It is accomplished with microspectrophotometers, cytospectrophotometers, microfluorometers, Raman microspectrophotometers, etc. A microspectrophotometer can be configured to measure transmittance, absorbance, reflectance, light polarization, fluorescence of sample areas less than a micrometer in diameter through a modified optical microscope.

<span class="mw-page-title-main">Fujifilm X-T1</span> Mirrorless camera model

The Fujifilm X-T1 is a weather-resistant mirrorless interchangeable lens camera announced by Fujifilm on January 28, 2014. It uses the Fujifilm X-mount and is the first entry in the X-T lineage of DSLR-styled X series cameras.

References

  1. Medical photography; Clinical-Ultraviolet-Infrared. (1973) Gibson HL, Kodak Company, Rochester, p123-130.
  2. Larry S. Miller, Norman Marin, Police Photography, Routledge, 2014 ISBN   1317524209. page 5
  3. Ngaire E. Genge, The Forensic Casebook, Random House Publishing Group, 2002 ISBN   0345461126 page 236
  4. Donald A. Wilson,Interpreting Land Records, John Wiley & Sons, 2014, ISBN   111874683X, page 313

Further reading