Immersion-type microscope objective lens

Claim 2

An immersion-type microscope objective lens, comprising, in order from the object side: (a) a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power; (b) the first lens group comprising a planoconvex lens element as the most objectwise lens element in the first lens group, the planoconvex lens element having a refractive index n 1 and a convex surface having a curvature radius r 2 ; a negative meniscus lens element having a refractive index n 2 , a concave surface having a curvature radius r 2 cemented to the planoconvex lens element, and a convex surface oriented imagewise and having a curvature radius r 3 ; and a positive meniscus lens element having a concave surface oriented objectwise; (c) the second lens group comprising a cemented lens component including a negative lens element that is the most objectwise lens element in the second lens group, the negative lens element having a focal length f 2n ; (d) the third lens group comprising a cemented lens component having a negative refractive power and a meniscus configuration with a concave surface oriented imagewise and an overall axial thickness D 3 , the cemented lens component including a positive lens element having a refractive index n 3p cemented to a negative lens element having a refractive index n 3n and having a concave surface with curvature radius r e that is the most imagewise surface of the objective lens; (e) the objective lens having an overall focal length f and satisfying the Conditional Expressions: n.sub.2 -n.sub.1 ≧0.2 4.5≦r.sub.3 /r.sub.2 ≦5.7 5≦-f.sub.2 /f≦12 1≦D.sub.3 /f≦3 10≦r.sub.e / (n.sub.3p -n.sub.3)f!≦40.

Claim 3

The objective lens of claim 1, having a magnification of about 40×.

Claim 4

The objective lens of claim 1, exhibiting apochromatic optical performance.

Claim 5

The objective lens of claim 1, wherein n 1 is substantially the same as the refractive index of an immersion oil with which the objective lens is used.

Claim 6

The objective lens of claim 1, wherein the second lens group consists of multiple cemented lens components.

Claim 7

The objective lens of claim 5, wherein one of the cemented lens components in the second lens group consists of a negative lens cemented to a positive lens cemented to a negative lens.

Claim 8

The objective lens of claim 1, having additional characteristics as follows: a focal length f=5 mm, a magnification β=-40×, a numerical aperture N.A.=1.0, and a working distance W.D.=-0.1713 mm; values of conditional expressions as follows: n.sub.2 -n.sub.1 =0.250 r.sub.3 /r.sub.2 =5.55 |f.sub.2n /f|=6.12 D.sub.3 /f=2.5 r.sub.c / (n.sub.3p -n.sub.3n)f!=24.77; and surfaces with curvature radii (r), inter-surface axial distances (d), indices of refraction n D , and Abbe numbers ν D as follows: ______________________________________ Lens No. r (mm) d (mm) n.sub.D ν.sub.D Group ______________________________________ 1 ∞ 0.65 1.51680 64.10 G.sub.1 2 -1.031 6.0 1.76684 46.80 G.sub.1 3 -5.724 0.25 4 -16.881 4.0 1.49782 82.52 G.sub.1 5 -8.965 0.1 6 127.147 4.0 1.49782 82.52 G.sub.1 7 -17.097 1.0 8 55.240 1.5 1.75520 27.61 G.sub.2 9 16.097 6.3 1.43385 95.25 G.sub.2 10 -20.151 0.2 11 32.616 1.7 1.74000 28.19 G.sub.2 12 18.275 7.0 1.43385 95.25 G.sub.2 13 -18.275 1.7 1.52682 51.35 G.sub.2 14 188.206 12.5 15 25.968 6.9 1.61750 30.83 G.sub.3 16 -15.077 5.6 1.52682 51.35 G.sub.3 17 11.230 (R.sub.e) ______________________________________

Claim 9

The objective lens of claim 1, having additional characteristics as follows: a focal length f=5 mm, a magnification β=-40×, a numerical aperture N.A.=1.0, and a working distance W.D.=-0.1713 mm; values of conditional expressions as follows: n.sub.2 -n.sub.1 =0.252 r.sub.3 /r.sub.2 =5.31 |f.sub.2n /f=10.17 D.sub.3 /f=2.2 r.sub.e / (n.sub.3p -n.sub.3n)f!=18.10; and surfaces with curvature radii (r), inter-surface axial distances (d), indices of refraction n D , and Abbe numbers ν D as follows: ______________________________________ Lens No. r (mm) d (mm) n.sub.D ν.sub.D Group ______________________________________ 1 ∞ 0.65 1.51823 58.90 G.sub.1 2 -1.031 6.0 1.77073 50.22 G.sub.1 3 -5.477 0.25 4 -24.966 4.0 1.43385 95.25 G.sub.1 5 -8.533 0.15 6 105.261 1.5 1.62004 36.27 G.sub.1 7 27.021 6.5 1.43385 95.25 G.sub.1 8 -17.763 0.1 9 29.557 1.55 1.57501 41.42 G.sub.2 10 14.419 6.3 1.43385 95.25 G.sub.2 11 -28.320 0.15 12 42.870 1.35 1.60342 38.03 G.sub.2 13 13.468 6.75 1.43385 95.25 G.sub.2 14 -17.270 1.85 1.60342 38.03 G.sub.2 15 317.805 12.4 16 27.454 6.0 1.68893 31.08 G.sub.3 17 -16.587 5.0 1.56384 60.69 G.sub.3 18 11.319 (R.sub.e) ______________________________________

Claim 10

The objective lens of claim 1, having additional characteristics as follows: a focal length f=5 mm, a magnification β=-40×, a numerical aperture N.A.=1.0, and a working distance W.D.=-0.1713 mm; values of conditional expressions as follows: n.sub.2 -n.sub.1 =0.252 r.sub.3 /r.sub.2 =5.42 |f.sub.2n /f|=5.77 D.sub.3 /f=2.2 r.sub.c / (n.sub.3p -n.sub.3n)f!=18.21; and surfaces with curvature radii (r), inter-surface axial distances (d), indices of refraction n D , and Abbe numbers ν D as follows: ______________________________________ Lens No. r (mm) d (mm) n.sub.D ν.sub.D Group ______________________________________ 1 ∞ 0.65 1.51823 58.90 G.sub.1 2 -1.031 6.0 1.77073 50.22 G.sub.1 3 -5.584 0.2 4 -24.557 4.0 1.49782 82.52 G.sub.1 5 -8.641 0.15 6 108.446 1.5 1.60342 38.03 G.sub.1 7 19.412 5.7 1.43385 95.25 G.sub.1 8 -16.874 0.1 9 38.463 3.8 1.49782 82.52 G.sub.2 10 -44.231 1.0 1.55200 49.71 G.sub.2 11 25.052 5.0 1.43385 95.25 G.sub.2 12 -28.734 0.1 13 40.212 1.3 1.60342 38.03 G.sub.2 14 13.649 6.7 1.43385 95.25 G.sub.2 15 -17.653 1.8 1.60342 38.03 G.sub.2 16 563.685 12.4 17 26.604 6.0 1.68893 31.08 G.sub.3 18 -17.707 5.0 1.56384 60.69 G.sub.3 19 11.386 (R.sub.e) ______________________________________