Patent ID: 7251209

Claim:
An optical pickup for a recording medium comprising: a light source emitting light; an objective lens focusing an incident light to form a light spot on the recording medium; a plate beam splitter transmitting and reflecting the incident light at a predetermined ratio; a main photodetector receiving the light reflected from a recording surface of the recording medium to detect information and/or an error signal; a front photodetector arranged at one side of the plate beam splitter and receiving the light transmitted through and/or reflected from the plate beam splitter to generate an automatic power control signal to control an output power of the light source; and a collimating lens arranged between the light source and the plate beam splitter and through which the light incident thereon becomes a converging or diverging light toward the plate beam splitter, wherein denoting an incident angle of light on the collimating lens from the light source with respect to an optical axis as μ, an exit angle of light from the collimating lens as μo, and a magnifying cower of the collimating lens as m, the collimating lens satisfies the following equation: m=μ/μo 0.018 ≦|m |≦0.056.