The F-501 uses a through-the-lens (TTL) "passive" phase-detection autofocus method for establishing focus. Unlike active systems, which set approximate focus based on distance to the subject, the "passive" system uses a CCD to "see" the focus subject and focus in a manner similar to a human operator. This method is more precise than the active method, but requires more light to function. The F-501 has two focus modes available, single, in which focus is established and does not change so long as the operator holds down lightly on the shutter button, and continuous, in which the lens continuously re-focuses on whatever is in the focus area.