Adrian Davies' book, "Digital Ultraviolet and Infrared Photography", extensively covers the technical aspects of shooting both infrared and ultraviolet photography, although I will focus primarily on the infrared chapters to refine my technique.
Infrared light refers to wavelengths of electromagnetic radiation from approximately 700nm to 1,000,000nm. Davies explains that "for the purposes of photography, the near infrared (NIR) wavelengths (from around 700nm to 1100nm) are those that can be captured by conventional cameras and sensors" (Davies, 2017, p.10). Mid-range infrared is typically used for thermal imaging, which can only be captured by specialist cameras (Infiniti, 2020). The limitations of DSLR sensors mean that converted cameras cannot record mid- or long-range infrared.
A DSLR sensor is sensitive to both ultraviolet (UV) and infrared (IR) radiation but typically has a "hot mirror filter" placed in front to block out the unwanted wavelengths, recording images with colours close to what the eye naturally sees. Without this hot mirror filter, the invisible light would "give an unwanted colour cast to images" (Davies, 2017, p.13). During an infrared or full-spectrum camera conversion, this filter is removed and replaced with either an infrared filter that blocks out visible light and UV for an infrared conversion, or a plain quartz filter for a full-spectrum conversion, which allows all forms of light through (Davies, 2017, p.20). To take infrared photographs with a full-spectrum camera, you need to add another filter to the lens. Infrared filters range from approximately 520nm (allowing through a fair amount of visible light as well as IR), through 720nm (blocking most visible light), to 950nm (only IR can pass through). Full-spectrum cameras offer flexibility, whereas an infrared-converted camera with an internal 720nm filter can never capture wavelengths in the 560nm range.
Digital photography isn't the only way to visually capture infrared light; many early photographers used infrared film. Black and white IR film still exists today, but unfortunately, colour IR film is no longer available, the process of which Davies explains in detail (Davies, 2017, p.105):
With colour IR film, the three light-sensitive layers were green, red and IR (blue light was absorbed by a yellow filter incorporated into the film emulsion structure). During processing, yellow dye was produced in the green layer, magenta dye was produced in the red layer, and cyan dye was produced in the IR layer, thus shifting the colours towards the IR end of the spectrum, giving a ‘false colour’ appearance.
Using this film, the colours of various subjects shift, so healthy foliage appears red, diseased foliage is green or blue, and coniferous vegetation is recorded as purple (Davies, 2017, p.106). This film was initially used to detect disease in plants but was later adopted by photographers captivated by the vibrant, surreal colours it brought to their landscapes. Although colour film is no longer produced, its legacy endures in the digital editing techniques many artists use today.
Figures 1 and 2 (below) feature Nant Gwynan in north Wales, shot with a "Goldie" filter that allows both red light and infrared through. Figure 1 shows the original image straight from the camera, with a very orange cast. Figure 2 shows the edited image, where Davies channel-swapped the red and blue colour channels, a common technique in digital infrared photography that results in rich blue skies and yellow foliage. I have tried channel-swapping some of my previous infrared images but would like to explore this technique further. Typically, a red/blue swap sets the red channel to 100% blue and vice versa, but I am curious about the different colours I might achieve by changing these percentages.
Professor Robert Wood described "how chlorophyll reflected IR strongly and how blue sky recorded almost black on the IR record" (Davies, 2017, p.6). I was intrigued to learn that different types of rock absorb and reflect different amounts of infrared radiation. Davies explains, "Limestone such as chalk will record a pale colour, but some granites may record black, depending on their precise composition" (Davies, 2017, p.126). This could result in some interesting images when I photograph landmarks like engine houses, and I am excited to see how infrared light highlights differences that are imperceptible to the human eye.
It is not just natural rock that may appear surprisingly different in infrared, but as Figure 3 (above) demonstrates, other materials such as fabrics can look unrecognisable. These black jackets appear similar in tone initially but are vastly different hues of grey when photographed in infrared. Davies notes that "the fabric-covered buttons on the dress jacket have reflected a large amount of IR and appear very pale, whilst the plastic ones on the sleeve of the jacket next to it have recorded nearly black" (Davies, 2017, p.126). This emphasises the significant impact that material composition has on how an object is rendered in infrared.
Similarly, infrared photography alters the appearance of people, resulting in ghostly images. Walter Clark noted that in infrared portraiture, "skin appeared chalky, red lips recorded light and some lines of the face were exaggerated" (Davies, 2017, p.7). Davies elaborated that infrared creates "a translucent skin texture resembling alabaster, completely smooth, well suited to female portraiture, but perhaps not so for males. It can make acne spots disappear completely" (Davies, 2017, p.134). As evident in Figure 4, infrared portraiture tends to have a surreal tone, washing out the skin while darkening the eyes. This effect could be useful for depicting a ghostly essence while illustrating my theme of loss. Due to its youth-enhancing effects on skin, it may also be effective in photos that reference the loss of youthful innocence.
Hotspots are a common source of frustration for infrared photographers. They are bright circles in the centre of an image caused by internal reflection, which largely depends on the lens used (Davies, 2017, p.112). Using a small aperture seems to exacerbate the problem, whereas using a large aperture reduces the sharpness of the image and is not always appropriate for landscape photography. It is recommended to avoid the minimum and maximum apertures the lens allows. Davies sums this up well: "There will often be a compromise to be made, where a high-depth field is required, and a slight loss in image quality may still be acceptable" (Davies, 2017, p.17).
Infrared photographs tend to be softer than their visible light counterparts, making focus and sharpness common challenges. Focusing a converted camera using the viewfinder can produce unfocused images, as the camera has been calibrated to work with infrared light. Therefore, it is recommended to use a camera capable of Live View, which can usually display the infrared image on the screen, allowing the focus to be set more accurately (Davies, 2017, p.114). To further aid sharpness, Davies recommends assessing the image during post-processing, noting that "some sharpening is still beneficial to the image, particularly if there is a slight loss of focus due to UV/IR focus shift, or a slightly inferior lens" (Davies, 2017, p.175).
Davies' book has shown me the importance of refining my editing skills to improve my infrared photography. I look forward to experimenting with channel-swapping to craft my images. His insights have not only deepened my understanding of the technical aspects of infrared photography but have also inspired me to push the boundaries of creativity in my work. With these new techniques and knowledge, I am excited to see how my photography evolves and how I can better convey the themes of loss and surrealism in my upcoming projects.
References
Davies, A. (2017) Digital Ultraviolet and Infrared Photography. 1st edn. Routledge. Available at: https://www.perlego.com/book/1567265/digital-ultraviolet-and-infrared-photography (Accessed: 20 February 2024).
Infiniti (2020) MWIR (mid-wave infrared), Infiniti Electro-Optics. Available at: https://www.infinitioptics.com/glossary/mwir-mid-wave-infrared (Accessed: 10 June 2024).
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