ABSTRACT
Much misunderstanding surrounds UV and IR photography. A number of variables are involved in obtaining a quality result with IR and UV radiation, including but not limited to the following:
• Specific wavelengths and intensity of the individual light source • The surface upon which the reacting subject rests • Type of processing completed on substrate, such as dye staining • The age and condition of subject matter • The type of camera, the quality of lens, including the amount of protective UV
coating on the lens’ glass elements • The selection and use of any barrier filters
The number of UV and IR light sources is seemingly infinite, and each light source has its own specific range of wavelengths in which it transmits energy and light. Investigators should be aware that these wavelengths may change over time as a result of the light source’s aging. Furthermore, the intensity of the light can change over time and have a direct bearing on the final result. The age of a particular stain, bite mark, or bruise may also affect the quality of the photograph captured. As the body heals or as a stain begins to fade, less material will be available to enhance through the use of UV or IR light. It is well known that a camera’s lens is a determining factor in the quality of photograph ultimately captured. This is even more the case in UV photography, because most lenses have coatings on their elements designed to block UV light. In some cases, this might be advantageous because while the exciting effect of the UV energy is blocked, the visible reaction can still be recorded on film or the digital media. On the other side of the spectrum, digital cameras have IR barrier filters covering their imaging chips. This too will affect the outcome of a photograph. Finally, the use of barrier filters, typically in the colors of yellow, orange, and red, can generate better contrast and improve the overall composition and contrast.
