Light pattern detection for film edge following

An apparatus for positioning a read head of a photographic apparatus above a photographic filmstrip, which is supported on an apparatus top surface and has at least one data track recorded in recording material of the filmstrip, as relative movement occurs between the filmstrip and the magnetic read head, the apparatus comprising:

• an optical pattern located on the apparatus top surface beneath the photographic filmstrip such that a portion of the optical pattern is visible beyond one edge of the filmstrip;
• an optical detector that is positioned in a predetermined location relative to the read head and having a detected field of view such that a predetermined portion of the field of view is filled with the filmstrip and includes the filmstrip edge, and a remaining portion of the field of view is filled with the optical pattern that is visible beyond the filmstrip edge when the read head is properly located above the data track in the filmstrip and that produces a detector signal that indicates the relative portions of the optical detector field of view that are filled with the filmstrip and that are filled with the optical pattern as relative movement occurs between the filmstrip and the read head;
• a servo unit that receives the detector signal from the optical detector as relative movement occurs between the filmstrip and the read head and responds to the detector signal by determining if one of the portions of the optical detector field of view is increasing and then moving the read head in the direction of the corresponding portion of the optical detector field of view that is decreasing so as to maintain the relative portions of the detector signal substantially constant.