When recording a night scene with IR, using a day-and-night camera without an IR-corrected lens can cause the focus to shift. This happens because IR light and visible light have different wavelengths and refract differently through the lens. An IR-corrected lens is designed to handle both types of light without causing a focus shift, ensuring sharp images in both day and night conditions. References: Axis Communications product guides on day-and-night cameras and IR-corrected lenses.