| US 7,394,048 B2 | ||
| Focusing device, focusing method and a pattern inspecting apparatus | ||
| Hiromu Inoue, Yokohama (Japan); Tomohide Watanabe, Yokohama (Japan); Satoshi Endo, Fuji (Japan); and Masami Ikeda, Numazu (Japan) | ||
| Assigned to Kabushiki Kaisha Toshiba, Tokyo (Japan); and NuFlare Technology, Inc., Numazu-shi (Japan) | ||
| Filed on Feb. 27, 2007, as Appl. No. 11/679,411. | ||
| Claims priority of application No. 2006-052995 (JP), filed on Feb. 28, 2006. | ||
| Prior Publication US 2007/0200051 A1, Aug. 30, 2007 | ||
| Int. Cl. G02B 7/04 (2006.01) | ||
| U.S. Cl. 250—201.2 [250/201.4] | 6 Claims |
| 1. A focusing device comprising:
first and second sensors which convert an optical image of a subject, formed on a plane of incidence, into an image signal
and output the image signal;
a first imaging optical system which forms the optical image on the first sensor;
a second imaging optical system which splits the optical image from the first imaging optical system in the direction of the
second sensor and further splits the optical image into two so that a front focus image in which the point that is in focus
is in front of the optical image on the first sensor and a back focus image in which the point that is in focus is behind
the optical image on the first sensor are formed on the second sensor;
a focus detecting circuit which detects an optimum focus position of the optical image on the first sensor by calculating
a focus evaluation value from a high-frequency component of a front sensor image in a front focus position obtained from the
second sensor and a focus evaluation value from a high-frequency component of a back sensor image in a back focus position
obtained from the second sensor and by comparing the focus evaluation values; and
a focus control circuit which controls the focusing of the first imaging optical system on the basis of the focus position
detected by the focus detecting circuit.
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