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:
Nov. 03, 1998
Filed:
Oct. 06, 1997
Toshihiro Sasaya, Yokohama, JP;
Kazuo Ushida, Tokyo, JP;
Yutaka Suenaga, Yokohama, JP;
Romeo I Mercado, Fremont, CA (US);
Nikon Corporation, Tokyo, JP;
Abstract
A projection optical system that projects an image of an object in an object surface onto an image surface with a fixed reduction magnification comprises, in light path order from the object surface: a first group of lenses with positive refractive power; a second group of lenses forming an approximately afocal system; and a third group of lenses with positive refractive power. The projection optical system has a focal length F, the projection optical system has a projection magnification B, the object surface and the image surface are separated by a distance L, and a lens surface in the first group of lenses that is closest to the object surface is separated from the object surface by a distance d.sub.0. A paraxial marginal ray from an axial object point on the object surface enters the second group of lenses G.sub.2 at an entrance height h.sub.1 from an optical axis, and the paraxial marginal ray from the axial object point on the object surface emerges from the second group of lenses G.sub.2 at an emergence height h.sub.2 from the optical axis. The optical system is characterized by the following: