Imaging the invisible using modified digital still cameras for straightforward and low-cost archaeological near-infrared photography

Abstract Analogue near-infrared (NIR) photography has already been used a lot in both scientific and medical photography, in which cases near-infrared (NIR) radiation was mostly captured by InfraRed (IR) sensitive plates or film emulsions. However, its use in archaeology has remained rather restricted, most likely due to some ignorance and/or lack of knowledge about this kind of photography, while the critical imaging process also severely limited its use. This situation could be, however, changed completely, as the image sensors used in digital still cameras (DSCs) are very sensitive to NIR wavelengths, making the quite lengthy and error-prone film-based NIR imaging process obsolete. Moreover, modifying off-the-shelf DSCs even simplifies this digital acquisition of NIR photographs to a very large extent. By starting with a general outline of the ElectroMagnetic (EM) spectrum and the specificities of NIR radiation, the base is laid out to tackle the possibilities and practicalities of archaeological NIR imaging, subsequently comparing the earlier film-based approach with the digital way of NIR shooting, showing how the latter can greatly benefit from modified compact, hybrid and small-format Single Lens Reflex (SLR) DSCs. Besides in-depth information on the technique of digital NIR photography, examples will illustrate its archaeological potential.