G - Physics – 01 – J
Patent
G - Physics
01
J
88/99
G01J 1/20 (2006.01) G02B 7/32 (2006.01) G11B 7/09 (2006.01)
Patent
CA 1248796
ABSTRACT OF THE DISCLOSURE A focussing error detecting apparatus is disclosed which includes a composite lens formed of a single lens made of glass and a single lens made of plastic and a photo detector disposed behind the composite lens to oppose thereto, wherein the glass single lens has a uniform focal length, the plastic single lens is formed of a pair of lens regions divided by a flat interface including an optical axis of light incident on the composite lens, the pair of lens regions have back focal lengths different from each other and optical axes spaced apart from each other, the photo detector is placed such that its photo-detecting face is positioned at a middle point between converged points of light rays emitted from the pair of lens regions on the optical axis of the incident light when the light incident on the composite lens is in the focussed state and the photo detector is formed of first and second photo-detecting sensors for receiving light rays passed through the far-side portion and near-side portion of the first lens region of the pair of lens regions relative to the flat interface and third and fourth photo-detecting sensors for receiving light rays passed through the far-side portion and near-side portion of the second lens region of the pair of lens regions relative to the flat interface so that a focussing error signal is produced from the difference between the sum of first and fourth photo-detected signals from the first and fourth photo-detecting sensors and the sum of second and third photo-detected signals from the second and third photo-detecting sensors.
455020
Kubota Shigeo
Ohsato Kiyoshi
Gowling Lafleur Henderson Llp
Sony Corporation
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