Vaginal Fatty Acids Produced by Chimpanzees during Menstrual Cycles

A focusing control system comprises a lens system having a plano-convex lens part and a cylindrical lens part formed as a unitary body such that an optical axis of the plano-convex lens and an optical axis of the cylindrical lens coincides with an optical axis of the lens system for receiving an incident optical beam reflected by the rotary recoridng medium at its one side and for transmitting the optical beam thus received to the other side of the lens system, and a photo detector array disposed so as to receive the optical beam transmitted from the lens system. The photo detector array has a quadrant detecting plane comprising four detecting sub-planes arranged in a row and column formation, and each of the sub-planes is connected to a corresponding photo detector which produces an output electrical signal when an optical beam transmitted from the lens system is irradiated on its detecting sub-plane.