Passive autofocusing is a camera focusing system that determines focus by measuring the contrast of the subject rather than sending out a signal, as in active systems. One advantage of passive autofocus is that it is not affected by glass or other obstacles between the camera and subject, and it does not rely on knowing the exact subject distance.
However, passive autofocus struggles in low-contrast situations, such as snow scenes or dim lighting, where the lens may hunt back and forth without achieving sharp focus. Many cameras with passive autofocus offer a manual override, allowing photographers to take control and ensure precise focusing when automatic systems struggle.