Objective for stereomicroscopes

1. An objective for telescope-type stereomicroscopes with variable magnification, wherein the objective satisfies the conditions:

D AP ≧42 mm, and tan(ω)≧0.16,

where D AP is the diameter of the exit pupil of the objective and ω is the field angle of the objective at the lowest possible magnification setting.

2. The objective according to claim 1 whose total focal length f′ objective meets the condition:

40≦f′ objective ≦160.

3. The objective according to claim 1 , wherein the objective comprises two lens groups LG 1 and LG 2 , and the relationship of the focal length f′ LG2 of the second lens group LG 2 to the total focal length f′ objective is expressed by:

0.1−1.8723/ f′ objective ≦1 /f′ LG2 ≦0.2−1.8723/ f′ objective .

4. The objective according to claim 3 , wherein the two lens groups LG 1 and LG 2 , respectively, have a positive refractive power as a whole, the first lens group LG 1 comprises a plurality of lenses, at least two of which lenses are cemented together, and the second lens group LG 2 comprises a lens with positive refractive power and a meniscus with negative refractive power with a convex curvature toward the object, wherein the first lens group LG 1 lies closer to the object plane than the second lens group LG 2 .

5. The objective according to claim 4 , wherein the first lens group LG 1 comprises five lenses of which, considered from the object plane, the first lens ( 1 . 1 ), the third lens ( 1 . 3 ) and the fourth lens ( 1 . 4 ) have positive refractive power, the second lens ( 1 . 2 ) and the fifth lens ( 1 . 5 ) have negative refractive power, and the second lens ( 1 . 2 ) and the third lens ( 1 . 3 ) are cemented together, and the fourth lens ( 1 . 4 ) and the fifth lens ( 1 . 5 ) are cemented together.

6. The objective according to claim 4 , wherein the first lens group LG 1 comprises three lenses of which, considered from the object plane, the first lens ( 1 . 1 ) and the third lens ( 1 . 3 ) have positive refractive power, the second lens ( 1 . 2 ) has negative refractive power, and the first lens ( 1 . 1 ) and the second lens ( 1 . 2 ) are cemented together.

7. The objective according to claim 3 , wherein the second lens group LG 2 comprises three lenses ( 2 . 1 , 2 . 21 , 2 . 22 ) of which, considered from the object plane, the first lens ( 2 . 1 ) and the second lens ( 2 . 21 ) have positive refractive power, the third lens ( 2 . 22 ) has negative refractive power, and the second lens ( 2 . 21 ) is cemented to the third lens ( 2 . 22 ) to form a meniscus of negative refractive power with a convex curvature facing the object plane.

8. The objective according to claim 7 , which satisfies the condition:

0.0003/ f′ objective ≦ΔP g.F2.1 /(ν e2.1 *f′ 2.1 )+Δ P g.F2.1 /(ν e2.1 *f′ 2.21 )+Δ P g.F2.22 /(ν e2.22 *f′ 2.22 )≦0.0003 /f′ objective +0.001,

where f′ objective is the total focal length of the objective 3 , f′ 2.1 is the focal length of lens ( 2 . 1 ), f′ 2.21 is the focal length of lens ( 2 . 21 ), f′ 2.22 is the focal length of lens ( 2 . 22 ), ν e2.1 is the Abbe number of the medium of lens ( 2 . 1 ), ν e2.21 is the Abbe number of the medium of lens ( 2 . 21 ), ν e2.22 is the Abbe number of the medium of lens ( 2 . 22 ), ΔP g.F2.1 is the deviation of the medium of lens ( 2 . 1 ) from the normal line, ΔP g.F2.21 is the deviation of the medium of lens ( 2 . 21 ) from the normal line, and ΔP g.F2.22 is the deviation of the medium of lens ( 2 . 22 ) from the normal line.

9. The objective according to claim 3 , wherein lens group LG 1 includes lenses 1 . 1 , 1 . 2 , 1 . 3 , 1 . 4 and 1 . 5 and lens group LG 2 includes lenses 2 . 1 , 2 . 2 and 2 . 22 , the objective having a total focus length f′ objective =50 mm and and exit pupil with diameter D AP =47 mm and designed for magnification changers in which tan(ω)=0.18 is achieved at the lowest possible magnification, and the following constructional data indicate radii r in mm, thicknesses d in mm, distances a in mm, refractive indicies n e at a wavelength of 546.07 nm, and Abbe numbers ν e :

r

d

a

n e

ν e

Object plane

31.99693

LG1

1.1

−334.94300

13.10000

1.530190

76.58

−39.24230

10.50000

1.2

−515.78900

7.50000

1.677629

32.00

1.3

69.28260

17.25000

1.498450

81.13

−81.16600

0.15000

1.4

131.46350

17.90000

1.498450

81.13

1.5

−51.95820

6.60000

1.616640

44.27

−386.81700

0.15000

LG2

2.1

73.91790

11.50000

1.498450

81.13

−294.27300

0.92221

2.21

95.03140

8.90000

1.791789

25.89

2.22

−258.51300

5.80000

1.658030

 39.40.

39.24230

10. The objective according to claim 3 , wherein the first lens group has lenses 1 . 1 , 1 . 2 and 1 . 3 , the second group of lenses 2 . 1 , 2 . 21 and 2 . 22 , and the objective having a total focal length of f′ objective =100 mm and an exit pupil with diameter D AP =47 mm and designed for magnification changers ( 5 . 1 , 5 . 2 ) in which tan(ω)=0.18 is achieved at the lowest possible magnification, and the following constructional data indicate radii r in mm, thickness d in mm, distances a in mm, refractive indices n e at a wavelength of 546.07 nm, and Abbe numbers ν e :

r

d

a

n e

ν e

Object plane

61.80600

LG1

1.1

−258.51300

14.46000

1.487940

 8.07

1.2

−30.06750

4.00000

1.616640

44.27

−88.22520

8.15800

1.3

344.71300

16.06000

1.530190

76.58

−77.74390

0.40000

LG2

2.1

244.08300

12.00000

1.668830

35.73

−191.12700

0.05000

2.21

71.27670

12.00000

1.487940

84.07

2.22

−107.46370

4.00000

1.616640

 44.27.

51.95820