Patent ID: 6822805
Filing Date: 2004-11-23
Classification: G02B

Abstract:
An objective lens having an NA of at least 0.7 and being constituted by combining a plurality of single lenses as a whole, the objective lens comprising:a first lens group having a positive meniscus lens with a convex surface facing an image side and a negative biconcave lens, which are arranged in the sequential order from the image side, so as to have negative refractive power as a whole; a second lens group having positive refractive power as a whole, lenses in the second lens group forming at least one lens pair that has a positive lens and a negative lens, which are made of media different from each other, with an air gap therebetween, a positive refractive power surface and a negative refractive power surface being arranged to face each other via the air gap; a third lens group having positive refractive power as a whole, lenses in the third lens group forming four lens pairs, each pair having a positive lens and a negative lens, which are made of media different from each other, with an air gap therebetween, a positive refractive power surface and a negative refractive power surface being arranged to face each other via the air gap; a fourth lens group having, lenses in the fourth lens group forming two lens pairs, each lens pair having a positive lens and a negative lens, which are made of media different from each other with an air gap therebetween, a positive refractive power surface and a negative refractive power surface being arranged to face each other via the air gap; a fifth lens group comprising a negative meniscus lens with a concave surface facing an object side, and having positive refractive power as a whole, lenses in the fifth lens group forming a lens pair that has a positive lens and a negative lens, which are made of media different from each other, with an air gap therebetween, a positive refractive power surface and a negative refractive power surface being arranged to face each other via the air gap; and a sixth lens group having at least one positive lens and a positive meniscus lens with a concave surface facing the object side so as to have positive refractive power as whole, wherein each of the lens pairs formed in the objective lens satisfies the following conditional expressions: d/L<0.025 0.580<1.65 where L(mm) is the overall length of the objective lens; d(mm) is the air gap inside the lens pair; and Rp and Rn are the radii of curvature of the positive refractive power surface and the negative refractive power surface facing each other via the air gap, respectively, and wherein the objective lens satisfies the following conditional expression: |DUVfpâˆ’IRfp|&lE;12 &mgr;m, where DUVfp is the image-forming position on an object side of the objective lens by light having a wavelength in a deep ultra-violet region and IRfp is the image-forming position on the object side of the objective lens by light having a wavelength in an infrared region.