by Gerald Boerner
“Infrared photography calms me. I love it.”
“…infrared photography is not the same thing as thermal imaging – the night-vision video technology used by the police and sensationalist TV shows.”
— PhotoNotes.org, “Popular Myths”
“Most films have a layer of opaque dye on the back, called an anti-halation layer, which essentially absorbs light and prevents light from bouncing around within the film itself. (this layer is washed away during film processing, which is why undeveloped film is opaque but developed film is clear.”
— PhotoNotes.org, “Popular Myths”
“Sadly, it’s true that most current Canon EOS cameras fog high-speed infrared film (Kodak HIE and EIR). However, they aren’t alone. Other camera makers use IR diodes for some of their products, including Nikon…”
— PhotoNotes.org, “Popular Myths”
“The reason why deciduous trees, grass, etc., glow white on HIE film is primarily because the structure of their living cells reflects a great deal of the sun’s infrared energy rather than absorbing it.”
— PhotoNotes.org, “Popular Myths”
[NOTE: This is the first of an occasional series of postings in this blog related to significant contributors to the technologies that enable photography in all of its forms. Today, we start out by looking at photography using “invisible light.” Please enjoy this first posting.]
Photography with Invisible Light: Robert W. Wood
Robert Williams Wood (1868 – 1955) was a physicist and inventor. He is often cited as being a pivotal contributor to the field of optics and is best known for giving birth to the so-called "black-light effect". Wood’s patents and theoretical work shed much light on the nature and physics of ultra-violet radiation and made possible the myriad of uses of uv-fluorescence which became popular after World War I.
Born in Concord, Massachusetts, Wood attended The Roxbury Latin School with the initial intent of becoming a priest. But he decided to study optics instead when he witnessed a rare glowing aurora one night and believed the effect to be caused by "invisible rays". In his pursuit to find these "invisible rays", Wood studied and earned numerous degrees from Harvard, MIT and the University of Chicago. He taught briefly at the University of Wisconsin and eventually became a full-time professor of "optical physics" at Johns Hopkins University from 1901 until his death.
His wrote many articles on spectroscopy, phosphorescence and diffraction. But it’s his work in ultra-violet light that his is most well known for.
He discovered that the darkest area of the Moon in ultraviolet light is the Aristarchus Plateau. In 1909, Wood constructed the first practical liquid mirror astronomical telescope, by spinning mercury to form a paraboloidal shape, and investigated its benefits and limitations.
Wood has been described as the "father of both infrared and ultraviolet photography". Though the discovery of electromagnetic radiation beyond the visible spectrum and the development of photographic emulsions capable of recording them pre-date Wood, he was the first intentionally to produce photographs with both infrared and ultraviolet radiation. He developed a filter, Wood’s glass, that was opaque to visible light but transparent to ultraviolet and is used in modern-day blacklites. He used it for ultraviolet photography but also suggested its use for secret communication. He was also the first person to photograph ultraviolet fluorescence. He also developed a lamp, Wood’s lamp, that radiated only ultraviolet. The slightly surreal glowing appearance of foliage in infrared photographs is called the Wood effect.
Wood also authored non-technical works. In 1915, Wood co-authored a science fiction novel, The Man Who Rocked the Earth, with Arthur Train; a sequel, The Moon Maker, was published the next year. He also wrote and illustrated two books of children’s verse, How to Tell the Birds from the Flowers (1907) and Animal Analogues (1908).
In infrared photography, the 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. Usually an "infrared filter" is used; this lets infrared (IR) light pass through to the camera, but blocks all or most of the visible light spectrum (the filter thus looks black or deep red).
When these filters are used together with infrared-sensitive film or sensors, very interesting "in-camera effects" can be obtained; false-color or black-and-white images with a dreamlike or sometimes lurid appearance known as the "Wood Effect," an effect mainly caused by foliage (such as tree leaves and grass) strongly reflecting in the same way visible light is reflected from snow. There is a small contribution from chlorophyll fluorescence, but this is marginal and is not the real cause of the brightness seen in infrared photographs. The effect is named after the infrared photography pioneer Robert W. Wood, and not after the material wood, which does not glow under infrared.
The other attributes of infrared photographs include very dark skies and penetration of atmospheric haze, caused by reduced Rayleigh scattering and Mie scattering, respectively, compared to visible light. The dark skies, in turn, result in less infrared light in shadows and dark reflections of those skies from water, and clouds will stand out strongly. These wavelengths also penetrate a few millimeters into skin and give a milky look to portraits, although eyes often look black.
Until the early 1900s, infrared photography was not possible because silver halide emulsions are not sensitive to infrared radiation without the addition of a dye to act as a color sensitizer. The first infrared photographs to be published appeared in the October 1910 edition of the Royal Photographic Society Journal to illustrate a paper by Robert W. Wood, who discovered the unusual effects that now bear his name. The RPS is co-ordinating events to celebrate the centenary of this event in 2010. Wood’s photographs were taken on experimental film that required very long exposures; thus, most of his work focused on landscapes.
Infrared-sensitive photographic plates were developed in the United States during World War I for improved aerial photography.
Infrared photography became popular with photography enthusiasts in the 1930s when suitable film was introduced commercially. By 1937 33 kinds of infrared film were available from five manufacturers including Agfa, Kodak and Ilford. Infrared movie film also available and was used to create day-for-night effects in motion pictures, a notable example being the pseudo-night aerial sequences in the James Cagney/Bette Davis movie The Bride Came COD.
False-color infrared photography became widely practiced with the introduction of Kodak Ektachrome Infrared Aero Film, Type 8443, in the 1960s.
Infrared photography became popular with a number of 1960s recording artists, because of the unusual results; Jimi Hendrix, Donovan, Frank Zappa and the Grateful Dead all issued albums with infrared cover photos. The unexpected colors and effects that infrared film can produce fit well with the psychedelic aesthetic that emerged in the late 1960s.
For some, infrared photography can easily look gimmicky, but many photographers such as Elio Ciol and Martin Reeves have made subtle use of black-and-white infrared-sensitive film. With the advent of digital infrared photography, as a part of full spectrum photography, the technique is gaining popularity and is being sold as fine art photographs in a variety of galleries worldwide.
A near-infrared photograph of
a Ringling Brothers’ train idling
near MIT in Cambridge,
Infrared light lies between the visible and microwave portions of the electromagnetic spectrum. Infrared light has a range of wavelengths, just like visible light has wavelengths that range from red light to violet. "Near infrared" light is closest in wavelength to visible light and "far infrared" is closer to the microwave region of the electromagnetic spectrum. The longer, far infrared wavelengths are about the size of a pin head and the shorter, near infrared ones are the size of cells, or are microscopic.
Most manual focus 35 mm SLR and medium format SLR lenses have a red dot, line or diamond, often with a red "R" called the infrared index mark, that can be used to achieve proper infrared focus; many autofocus lenses no longer have this mark. When a single-lens reflex (SLR) camera is fitted with a filter that is opaque to visible light, the reflex system becomes useless for both framing and focusing, one must compose the picture without the filter and then attach the filter. This requires the use of a tripod to prevent the composition from changing. A sharp infrared photograph can be done with a tripod, a narrow aperture (like f/22) and a slow shutter speed without focus compensation, however wider apertures like f/2.0 can produce sharp photos only if the lens is meticulously refocused to the infrared index mark, and only if this index mark is the correct one for the filter and film in use. However, it should be noted that diffraction effects inside a camera are greater at infrared wavelengths so that stopping down the lens too far may actually reduce sharpness.
Most apochromatic (‘APO’) lenses do not have an Infrared index mark and do not need to be refocused for the infrared spectrum because they are already optically corrected into the near-infrared spectrum. Catadioptric lenses do not require this adjustment because mirrors do not suffer from chromatic aberration.
Zoom lenses may scatter more light through their more complicated optical systems than prime lenses, that is, lenses of fixed focal length; for example, an infrared photo taken with a 50 mm prime lens may look more contrasty than the same image taken at 50 mm with a 28–80 zoom.
Some lens manufacturers such as Leica never put IR index marks on their lenses. The reason for this is because any index mark is only valid for one particular IR filter and film combination, and may lead to user error. Even when using lenses with index marks, focus testing is advisable as there may be a large difference between the index mark and the subject plane.
Many conventional cameras can be used for infrared photography, where infrared is taken to mean light of a wavelength only slightly longer than that of visible light. Photography of rather longer wavelengths is normally termed thermography and requires special equipment.
With some patience and ingenuity, most film cameras can be used. However, some cameras of the 1990s that used 35mm film have infrared sprocket-hole sensors that can fog infrared film (their manuals may warn against the use of infrared film for this reason). Other film cameras are not completely opaque to infrared light.
Black-and-white infrared film
Black-and-white infrared negative films are sensitive to wavelengths in the 700 to 900 nm near infrared spectrum, and most also have a sensitivity to blue light wavelengths. The notable halation effect or glow often seen in the highlights of infrared photographs is an artifact of Kodak High Speed Infrared (HIE) black-and-white negative film and not an artifact of infrared light. The glow or blooming is caused by the absence of an anti-halation layer on the back side of Kodak HIE film, this results in a scattering or blooming around the highlights that would usually be absorbed by the anti-halation layer in conventional films.
Digital camera sensors are inherently sensitive to infrared light, which would interfere with the normal photography by confusing the autofocus calculations or softening the image (because infrared light is focused differently than visible light), or oversaturating the red channel. Also, some clothing is transparent in the infrared, leading to unintended (at least to the manufacturer) uses of video cameras. Thus, to improve image quality and protect privacy, many digital cameras employ infrared blockers. Depending on your subject matter, infrared photography may not be practical with these cameras because the exposure times become overly long, often in the range of 30 seconds, creating noise and motion blur in the final image. However, for some subject matter the long exposure does not matter or the motion blur effects actually add to the image. Some lenses will also show a ‘hot spot’ in the centre of the image as their coatings are optimized for visible light and not for IR.
An alternative method of digital SLR infrared photography is to remove the infrared blocker in front of the CCD and replace it with a filter that removes visible light. This filter is behind the mirror, so the camera can be used normally – handheld, normal shutter speeds, normal composition through the viewfinder, and focus, all work like a normal camera. Metering works but is not always accurate because of the difference between visible and infrared reflection. When the IR blocker is removed, many lenses which did display a hotspot cease to do so, and become perfectly usable for infrared photography. Additionally, because the red, green and blue micro-filters remain and have transmissions not only in their respective color but also in the infrared, enhanced infrared color may be recorded.
Background and biographical information is from Wikipedia articles on:
Robert W. Wood that can be found at…
Infrared Photography that can be found at…
Getting Started with Infrared Photography…
Andrew Davidhazy: Infrared Photography Examples…