Patent ID: 7170693
Filing Date: 2007-01-30
Classification: G11B

Abstract:
1. An objective lens unit comprising: a plurality of lenses each having a numerical aperture not less than 0.7, the plurality of lenses including a first lens and at least one secondary lens; a cylindrically-shaped lens holder configured to secure the plurality of lenses, wherein a position for seating the at least one secondary lens within said lens holder is compensated to correspond to a parallelism characteristic of an outer peripheral surface of the seated first lens; a vent formed in a surface of the lens holder, the vent positioned to coincide with a gap area between at least two lenses of the plurality of lenses; and a protector provided at an end of the lens holder in the vicinity of the first lens, wherein the protector includes a cutout at a position coincident with a path of relative motion of a recording medium the cutout being larger in breadth than a diameter of the light beam of the objective lens unit.