| 摘要 |
An optical apparatus includes a focuser for focusing and imaging a beam passing through an imaging optical system as a plurality of light spots, for recording and reproducing information on the same or adjacent tracks on a rotating optical recording medium having substantially concentric tracks; an adjuster for adjusting positions of first and second light spots with respect to a predetermined track; a tracker for positioning the first light spot with respect to an arbitrary track, using return light thereof from the medium, while keeping the relative positional relation of the light spots relative to the predetermined track; a moving device for moving the light spots in parallel with the radial direction of the medium, and a setter for setting DELTA , P, R1, R2, and d to satisfy: DELTA </=PxR1xR2/{15xdx(R2-R1)}where DELTA is the distance between the center of rotation of concentric tracks and the focus of the first light spot in the radial direction on the medium, d is the distance between the first and second light spots, R1 is an innermost radial position of the light spots from the center of rotation of the tracks, R2 is the outermost radial position of the light spots from the center of rotation of the tracks, and P is the track pitch.
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