Immersion objective lens system for microscope

1. An immersion objective lens system for microscope which consists, in order from the object side, of a first lens unit composed of a cemented lens component consisting of a plano-convex lens element having a planar surface on the object side and a meniscus lens element having a concave surface on the object side, a second lens unit composed of a lens component or two lens components, a third lens unit comprising at least two cemented lens components, a fourth lens unit comprising a meniscus lens component having a strongly concave surface on the image side, and a fifth lens unit comprising a meniscus lens component having a concave surface on the object side, and satisfies the following condition (1):

0.9 ≦|f 12/ f|≦ 1.3  (1)

wherein a reference symbol f 12 represents a total focal length of the first lens unit and the second lens unit, and a reference symbol f designates a focal length of the objective lens system as a whole.

2. The immersion objective lens system for microscope according to claim 1 , satisfying the following conditions (2) and (3):

0.7 ≦|R 12/ R 13|≦1.4  (2)

0.7 ≦|R 12/ f|≦ 1.3  (3)

wherein a reference symbol R 12 represents a radius of curvature on a cemented surface in the first lens unit, a reference symbol R 13 designates a radius of curvature on an image side surface of the first lens unit and a reference symbol f denotes a focal length of the objective lens system as a whole.

3. An objective lens system for microscope which consists, in order from the object side, of a first lens unit composed of a cemented meniscus lens component consisting of a plano-convex lens element and a meniscus lens element having a concave surface on the object side, a second lens unit comprising a plurality of cemented lens components and having positive refractive power, a third lens unit comprising a plurality of cemented meniscus lens components having concave surfaces on the image side and having positive refractive power, and a fourth lens unit comprising a meniscus lens component having a concave surface or more meniscus lens components having concaves surfaces on the object side, and satisfies the following conditions (4), (5) and (6):

5 <f 3 /f< 100  (4)

n d ( n )− n d ( p )<0.2  (5)

ν( p )−ν( n )>35  (6)

wherein a reference symbol f 3 represents a focal length of the third lens unit, a reference symbol f designates a focal length of the objective lens system as a whole, reference symbols n d (n) and n d (p) denote refractive indices of a negative lens element and a positive lens element respectively which compose each of the cemented lens components in the third lens unit, and reference symbols ν(p) and ν(n) represent Abbe's numbers of the positive lens element and the negative lens element respectively which compose each of the cemented lens components in the third lens unit.

4. The objective lens system for microscope according to claim 3 , satisfying the following condition (7):

0.7 <R 1 /R 2 <2  (7)

wherein reference symbols R 1 and R 2 represent radii of curvature on an object side surface and an image side surface respectively of the meniscus cemented lens component having the concave surface on the object side in the first lens unit.

5. The objective lens system for microscope according to claim 3 , comprising a cemented lens component movable along an optical axis and having weak negative refractive power in said second lens unit, and satisfying the following condition (8):

| f ( G 2 A )/ f|> 100  (8)

wherein a reference symbol f(G 2 A) represents a focal length of said lens component movable in the second lens unit.