Forensic dental photography 227
Focus shift is necessary because nonvisible wavelengths do not behave in the
same way as visible light as they pass through a compound lens. The focal
length of a lens is specific to a given wavelength of light. Most lenses are chro-
matically corrected to work within the 400 to 700 nm wavelengths (visible
light). When the light energy falls outside of the visible spectrum, the opti-
mal visual focus is no longer the optimally focused point for the nonvisible
light energy used to expose the film.^17 While some manufacturers have
Figure 11.28 rC Forensic blue lite pack.
Figure 11.29 e x a mple of a p or t a ble u v l i g ht s ou r c e, m a nu f a c t u r e d b y rC F or e n s ic,
las vegas, nevada (www.rcforensic.com).