Patent ID: 7835253

Claim:
An actuator used with an optical pickup, the actuator comprising: a lens holder in which a plurality of installation holes is formed such that a plurality of objective lenses, to record and/or reproduce optical discs having different recording densities, is installed at different heights; and a support member which movably supports the lens holder, wherein the plurality of installation holes includes: a first installation hole in which a first objective lens for a first optical disc is installed, and a second installation hole in which a second objective lens for a second optical disc is installed, wherein the second optical disc has a higher recording density than the first optical disc, wherein, when the first objective lens is used to record and/or reproduce the first optical disc, the lens holder is positioned such that a working distance from the first optical disc to the first objective lens is represented as WD 1 , wherein, when the second objective lens is used to record and/or reproduce the second optical disc, the lens holder is positioned such that a working distance from the second optical disc to the second objective lens is represented as WD 2 , wherein WD 1 ≧WD 2 , wherein, when the first objective lens is used to record and/or reproduce the first optical disc, the lens holder is positioned such that a separation distance from the first optical disc to the second objective lens equals WD 2 plus alpha, and wherein, if each respective working distance WD 1 and WD 2 is equal to or greater than a minimum of 0.6 mm, then alpha is equal to or greater than 0.1 mm.