| 摘要 |
PROBLEM TO BE SOLVED: To provide a magnetic recording device easy to assemble and adjust by arranging an object lens so that a distance between the object lens for converging a light beam on a magnetic storage medium and the magnetic storage medium differs from the focal distance of the object lens. SOLUTION: Since an object lens 17 is arranged so that a distance between the object lens 17 and a magnetic storage medium 4 is shorter than the focal distance of the object lens 17, this makes a numerical aperture larger than a theoretic numerical aperture without making a spot diameter small on the magnetic storage medium 4, and makes SN ratio higher. When the numerical aperture is enlarged, a decrease in a quantity of light, which is caused by the fact that the magnetic storage medium 4 is tilted and thereby a part of returning light of a light beam 70 is shaded by an opening 2, is reduced, therefore, this makes assembly and adjustment easier to minimize the decrease in the quantity of light by the shading. To the contrary, the distance between the object lens and the magnetic storage medium may be set to be longer than the focal distance of the object lens. Since the object lens 17 is arranged so that the distance between the object lens 17 and the magnetic storage medium 4 differs from the focal distance of the object lens 17, this makes the numerical aperture larger.
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