Patent ID: 11067782

Abstract:
An objective includes the first and second groups. The first group includes the first cemented lens with a concave surface facing the object side, the first and second single lenses having positive power, and the second cemented lens with a concave surface facing an image side. The second group includes the third cemented lens with a concave surface facing the object side and a third single lens having positive power. Each of the cemented lenses combines one positive lens with one negative lens. The objective satisfies the following expressions. 0.31≤NA<1  (1)2.2≤H/f≤3.3  (2)0<a/b≤1.2  (3)Here, NA is a numerical aperture, f is a focal length at e-line, H is a distance from an object surface to a lens surface closest to an image, a is the sum of air-gap distances in the first group, and b is a thickness of a negative lens in the second cemented lens.