The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Oct. 05, 2004
Filed:
Jul. 21, 2003
Koji Hirata, Yokohama, JP;
Naoyuki Ogura, Ebina, JP;
Shigeru Mori, Chigasaki, JP;
Takahiro Yoshida, Miura, JP;
Kazunari Nakagawa, Ebina, JP;
Hitachi, Ltd., Tokyo, JP;
Abstract
When a projection lens system used for a rear projection type image display apparatus has a first lens group having an aspherical lens surface, a second lens group, a third lens group sharing almost all the positive refractive power of the overall system, a fourth lens group having an aspherical lens surface, a fifth lens group, and a sixth lens group including a lens having a profile of aspherical surface in which the concave surface thereof faces the screen side and the refractive power in the marginal area is weaker than the refractive power around the optical axis, a projection lens system having a large aperture ratio (low F-number), high focus, wide field angle, and sufficient marginal light amount ratio can be realized at a low cost.