Digital Ultraviolet and Infrared Photography

Adrian Davies

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781315515076
• Edition: 1
• Topic: Arte
• Subtopic: Fotografía

Digital Ultraviolet and Infrared Photography discusses the growing number of applications of ultraviolet and infrared photography. Scientific and technical photographers, such as those engaged in scientific, medical, forensic, and landscape and wildlife photography routinely use ultraviolet and infrared techniques, and these techniques are growing in use in creative photography.

This is the first book to address the application and potential for both ultraviolet and infrared photography in both science and art. The author, Adrian Davies, discusses the how-to of ultraviolet and infrared digital recording with a dissection of techniques, camera requirements and camera conversion, a useful appendix of resources and equipment currently available and inspirational image examples throughout. Digital Ultraviolet and Infrared Photography is an essential read for photographers using these tools either professionally or creatively.

Chapter 1

Introduction

1.1 Introduction

Ultraviolet (UV) and infrared (IR) photography both go back to the early years of the twentieth century. They are some of the most useful photographic techniques used to make the invisible world visible to the human eye. Various techniques utilising UV and IR have and continue to be used extensively in the technical fields of medicine, geology, forensics, security, cultural heritage and botany, for example, whilst landscape, portrait, wedding and other areas of fine art photography also use the techniques extensively. UV reflectance photography has been used recently, for example, in an advertising campaign for sunscreen to illustrate its effectiveness, whilst an IR image of lions in the Serengeti won the title of Wildlife Photographer of the Year in 2014. It has often been said that photography is one of the few subjects where art and science combine, and nowhere within the genre is it more apparent than in the photography of invisible radiation.

Some of the techniques, such as UV fluorescence photography and IR photography, are relatively easy to carry out, requiring little specialist equipment, whilst others, such as UV reflectance photography, will require much research and testing of equipment to achieve high quality, repeatable results. Relatively little UV reflectance photography is carried out today, but, as we will see, there is huge scope for its application in a number of key areas, and one of the motivating forces for this book is to try and show that it can be done very successfully without the need for specialist, expensive lenses. A major new area for the subject is that of multispectral imaging where, for example, the colour vision of various animal species can be simulated by the use of filters analogous to the colour receptors in the animal’s eye.

Figure 1.1 Portrait in UV, visible and IR.

UV and IR produce completely different images of the same subject. Here, the UV record has accentuated surface detail and freckles, whilst the IR produces a smooth, virtually blemish-free record. Even lighting from two light sources has produced double shadows, particularly apparent in the UV record. (Note: The model was asked to shut his eyes for the UV record.)

Visible light shot: Nikon D800 with 105mm f/2.8 lens.

UV: Full-spectrum converted Nikon D300S with 105mm EL-Nikkor lens, with Baader U-filter. Two modified Metz full-spectrum flash guns. 1/160th second @ f/8.

IR: Full-spectrum converted Nikon D300S with 105mm Series E Nikon lens, with 720nm IR filter. Two modified Metz full-spectrum flash guns. 1/160th second @ f/11.

Images from the various techniques are often unpredictable, particularly when working outside with daylight, and often lead to surprising results. IR imaging in particular has long been popular with photographic artists; a number of record-album covers appeared in the 1960s using false colour IR images, for example, from artists such as Frank Zappa (the 1969 album Hot Rats had a now iconic false colour IR image on the front) and Jimi Hendrix. Landscape photographers have long used IR techniques to produce images with a unique, often ethereal quality. IR-sensitive cameras are now extensively used for surveillance purposes, often with invisible LED radiation sources so that criminals are unaware that they have just been photographed!

For scientific and technical photography, a meticulous approach to technique will be needed to ensure quality, consistency and repeatability. You will almost certainly need to shoot ‘control’ visible light images alongside the UV or IR images, to enable comparison between the visible light images and invisible UV and IR images.

Figure 1.2 A composite image showing a cultivated Rudbeckia flower (‘Toto Lemon’) in visible light (left), and ‘bee vision’ (right), using a filter combination to transmit UV blue and green light and absorb red and IR, to simulate the colour vision of the honey bee (Apis mellifera).

Full-spectrum Nikon D300S camera with EL-Nikkor 105mm lens.

Visible: Kolari Hot Mirror filter: Electronic flash. 1/160th @ f/16.400 ISO.

‘Bee vision’ image with Schott UG 5 and Schott S8612 filter stack. Full-spectrum electronic flash, 1/160th second @ f/11.400 ISO.

A characteristic utilised by many technical photographers is the way that UV and IR are absorbed or reflected by certain surfaces. Photographing skin or botanical subjects, for example, with UV and IR shows dramatic differences between the two. UV does not penetrate the surface but instead accentuates fine detail on the surface, whilst IR penetrates some substances such as skin by 2–3mm, enabling the visualisation of objects under the surface, such as veins under the skin or underdrawing in paintings.

The techniques also have uses in other fields of science, such as microscopy, astronomy and thermal imaging. These generally lie outside the scope of this book, though they will be discussed briefly in the appropriate section.

Some of the techniques in the book, in particular UV reflectance photography, have declined over the last few years, probably with the mistaken idea that they are more difficult to carry out with digital cameras rather than film. The main aim of this book is to enable the reader to use all of the techniques in as easy and cost-effective way as possible, whilst hopefully inspiring them to experiment to push the boundaries of these technologies further. New discoveries and applications are being made all the time, and there is huge potential for the citizen scientist to discover many more.

1.2 Historical Context

The visible light used by photographers is just one part of a range of ‘electromagnetic’ radiations. The spectrum of visible light seen in a rainbow, for example, begins at the violet or blue end of the spectrum and continues through green, yellow, orange and red as the wavelength increases. Different wavelengths produce different colours in an infinite spectrum. Blue light has a wavelength of approximately 400 nanometres (nm), green light 550nm and red approximately 700nm. The figures allotted to certain colours are only approximate – there is no hard cut-off between one colour and another. In practice there is often an overlap between the commonly defined wavebands as they gradually merge into each other.

It wasn’t until the early 1800s that other wavelengths, invisible to the human eye but visible to many other animals such as insects and birds, were discovered.

Sir William Herschel was an astronomer and composer living in Britain. He discovered the planet Uranus in 1781, a major discovery for which he was appointed court astronomer to King George III. In 1800 he was testing filters that he could use to make observations of sun spots. Part of the experiment involved placing thermometers in different regions of the visible spectrum in order to find their temperature. He used a prism to project rays of sunlight onto a table, to produce a spectrum. He then placed thermometers in different areas (colours) of the projected spectrum to measure their respective temperatures. As expected, the different colours produced different temperatures. He also placed one thermometer in the area beyond the red region of the spectrum, as a control, which he assumed would register at room temperature. To his surprise, the temperature reading was higher than that of the thermometer in the red region of the spectrum. Further experimentation led him to believe that other, invisible wavelengths were present beyond the red end of the spectrum, which he termed infrared. He called his discovery the ‘thermometric spectrum’. He published his findings in the Philosophical Transactions of the Royal Society in 1800, where he concluded that:

‘It is now evident that there was a refraction of rays coming from the sun, which, though not fit for vision, were yet highly invested with a power of occasioning heat…’¹

Sir William Herschel’s son, Sir John Herschel, also experimented with infrared wavelengths and also investigated the other end of the visible spectrum. He placed thermometers beyond the violet end of the spectrum as well, but found no temperature difference to the thermometer in the violet part of the spectrum. He concluded, erroneously, that there were no rays beyond the visible violet part of the spectrum:

By these last experiments I am sufficiently convinced that no rays, which exist outside the violet, can have any provable force, neither in the form of light nor of heat, and that these two forces prolong along the prismatic spectrum, and ends there where the farthest violets disappear.²

UV wavelengths were, however, discovered just one year later by the Polish chemist Johann Wilhelm Ritter. He was interested in the darkening of silver chloride by light and, like Herschel, used a prism to split light into its component colours. He placed vials of light-sensitive silver chloride in different regions of the spectrum to ascertain which colours had most effect on the silver chloride. He found that colours towards the blue and violet end of the spectrum had most effect, but, similar to Herschel, found that the silver chloride darkened even more quickly when placed outside the visible spectrum, beyond the violet. Ritter called these ‘Chemical Rays’, and they later became known as ultraviolet.

Other discoveries made during the early part of the twentieth century included the discovery of X-rays and gamma rays, used extensively nowadays for diagnostic medical imaging. Wavelengths longer than IR produce heat (which can be detected with thermal imaging cameras) and radio waves. Studio photographers will be familiar with the fact that a tungsten-based light bulb emits around 90 percent of its energy as heat, making it a somewhat inefficient light source.

1.3 UV Photography

Photography in the UV spectrum was possible relatively early in the history of photography, as the earliest photographic emulsions were naturally highly sensitive to both blue light and UV radiation (and the lenses in use at that time lacked modern-day UV-absorbing coatings on the glass elements, thus allowing more UV to reach the emulsion). Film emulsions required the addition of dyes to sensitise them further to green and red (and IR) wavelengths, producing orthochromatic and panchromatic emulsions respectively.

One of the first (accidental) examples of UV photography was by Hermann Vogel in 1864. Vogel was a German chemist, who later, in 1873, discovered that if he added appropriate dyes when making a photographic emulsion, the plates would respond to green light leading to the manufacture of ‘Orthochromatic’ plates.

In 1864, Vogel shot a portrait of a woman with the only available plate at the time, one sensitive to blue (and UV) light. He observed several black spots on the woman’s face – spots that were invisible to the naked eye. A few days after the photograph was taken, the woman was found to have smallpox. The significance of Vogel’s discovery was not recognised at the time and it would be another forty years or so before invisible radiation photography was fully appreciated.

The man generally credited with intentionally taking the first UV and IR images (and the first UV fluorescence images) is Professor Robert Wood, a physicist and polymath working at the Johns Hopkins University in Baltimore. His 1941 biography was aptly entitled Doctor Wood – Modern Wizard in the Laboratory.³ As well as being credited with intentionally taking the first UV and IR photographs, including UV fluorescence, and producing a UV light source, he was internationally respected for his work in optics and spectroscopy, where he undertook fundamental research in resonance radiation and in the use of absorption screens in astronomical photography.

Wood gave a lecture to the Royal Photographic Society in London in 1910, illustrated with his early applications of both UV and IR photography. He noted how chlorophyll reflected IR strongly and how blue sky recorded almost black on the IR record. He showed reflected UV photographs of both landscapes and lunar surfaces, whilst a magazine cover with various inks and dyes demonstrated the different absorbencies in UV and natural light. At the end of the lecture, Wood was credited with ‘opening up two new worlds; the worlds at each end of the spectrum, beyond the point of limit of vision’. Some of his best infrared landscapes were exhibited at the annual exhibition of the Royal Photographic Society in 1911, and were published in the Illustrated London News magazine.

In February 1903, Wood described the invention of a filter for UV transmission, which would exclude all visible light. The first version was made with nitrosodimethylaniline but this transmitted too much blue light for effective UV photography. The addition of a small amount of the dye uranine to the formula made a filter which transmitted exclusively UV. This filter became known as the Wood’s Glass filter, used by Kodak for their UV-transmi...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Foreword
• Acknowledgements
• 1. Introduction
• 2. The Electromagnetic Spectrum
• 3. Camera Conversion and Other Equipment Considerations
• 4. Ultraviolet Reflectance Photography
• 5. Ultraviolet Fluorescence Photography
• 6. Infrared Photography
• 7. Specialist Applications and Multispectral Imaging
• 8. Processing UV and IR Images
• Glossary
• Index