Observation optical system and optical apparatus

1 . An observation optical system comprising:

a display element; and

an eyepiece lens disposed on an eyepoint side with respect to the display element,

wherein the eyepiece lens includes a first negative lens having strongest negative refractive power among lenses included in the eyepiece lens, a first positive lens disposed adjacent to a display element side of the first negative lens, and a second positive lens disposed closest to the display element side among positive lenses disposed on the eyepoint side with respect to the first negative lens,

the number of lenses included in the eyepiece lens is greater than or equal to five,

in a case where a half value of a longest diameter of a display region in the display element is denoted by H, a focal length of the eyepiece lens in a state where diopter is −1 diopter is denoted by f, a sum of an air conversion distance on an optical axis from a display surface of the display element to a lens surface of the eyepiece lens closest to the display element side and a distance on the optical axis from the lens surface of the eyepiece lens closest to the display element side to a lens surface of the eyepiece lens closest to the eyepoint side in a state where the diopter is −1 diopter is denoted by TLA, and a refractive index of the first negative lens with respect to a d line is denoted by Nn1, Conditional Expressions (1), (2), and (3) are satisfied, which are represented by

0.355< H/f< 0.48  (1)

0.17< H/TLA< 0.285  (2)

1.5< Nn 1<1.7  (3), and

in a case where an Abbe number of the first negative lens based on the d line is denoted by νn1, Conditional Expression (11) is satisfied, which is represented by

19<ν n 1<27  (11).

2 . The observation optical system according to claim 1 ,

wherein the number of lenses included in the eyepiece lens is five or six.

3 . The observation optical system according to claim 1 ,

wherein in a case where a paraxial curvature radius of a surface of the first positive lens on the eyepoint side is denoted by Rpr, and a paraxial curvature radius of a surface of the first negative lens on the display element side is denoted by Rnf, Conditional Expression (4) is satisfied, which is represented by

0<( Rnf−Rpr )/( Rnf+Rpr )|<0.6  (4).

4 . The observation optical system according to claim 1 ,

wherein in a case where a focal length of the first positive lens is denoted by fp1, Conditional Expression (5) is satisfied, which is represented by

0< f/fp 1<1.8  (5).

5 . The observation optical system according to claim 1 ,

wherein in a case where a focal length of the first negative lens is denoted by fn1, Conditional Expression (6) is satisfied, which is represented by

−1.4< f/fn 1<−0.3  (6).

6 . The observation optical system according to claim 1 ,

wherein in a case where a focal length of the second positive lens is denoted by fp2, Conditional Expression (7) is satisfied, which is represented by

0< f/fp 2<0.9  (7).

7 . The observation optical system according to claim 1 ,

wherein in a case where a focal length of the first positive lens is denoted by fp1, Conditional Expression (8) is satisfied, which is represented by

0< H/fp 1<0.9  (8).

8 . The observation optical system according to claim 1 ,

wherein in a case where a focal length of the first negative lens is denoted by fn1, Conditional Expression (9) is satisfied, which is represented by

−0.6< H/fn 1<−0.2  (9).

9 . The observation optical system according to claim 1 ,

wherein in a case where a focal length of the second positive lens is denoted by fp2, Conditional Expression (10) is satisfied, which is represented by

0< H/fp 2<0.4  (10).

10 . The observation optical system according to claim 1 ,

wherein in a case where an Abbe number of a lens having strongest positive refractive power among the lenses included in the eyepiece lens based on the d line is denoted by νps, Conditional Expression (13) is satisfied, which is represented by

35<ν ps< 55  (13).

11 . The observation optical system according to claim 1 ,

wherein in a case where a focal length of a lens of the eyepiece lens closest to the eyepoint side is denoted by fe, Conditional Expression (15) is satisfied, which is represented by

0< f/|fe|< 0.9  (15).

12 . The observation optical system according to claim 1 ,

wherein in a case where a paraxial curvature radius of a surface, on the display element side, of a lens of the eyepiece lens closest to the eyepoint side is denoted by Ref, and a paraxial curvature radius of a surface, on the eyepoint side, of the lens of the eyepiece lens closest to the eyepoint side is denoted by Rer, Conditional Expression (16) is satisfied, which is represented by

0<( Rer−Ref )/( Rer+Ref )|<3  (16).

13 . The observation optical system according to claim 1 ,

wherein in a case where an air interval on the optical axis between a lens of the eyepiece lens closest to the eyepoint side and a second lens of the eyepiece lens from the eyepoint side in a state where the diopter is −1 diopter is denoted by dE, Conditional Expression (17) is satisfied, which is represented by

0.002< dE/TLA< 0.07  (17).

14 . The observation optical system according to claim 1 ,

wherein in a case where a focal length of a lens of the eyepiece lens closest to the display element side is denoted by fo, Conditional Expression (18) is satisfied, which is represented by

0.01< f/|fo|< 1.8  (18).

15 . The observation optical system according to claim 1 ,

wherein in a case where a paraxial curvature radius of a surface, on the display element side, of a lens of the eyepiece lens closest to the display element side is denoted by Rof, and a paraxial curvature radius of a surface, on the eyepoint side, of the lens of the eyepiece lens closest to the display element side is denoted by Ror, Conditional Expression (19) is satisfied, which is represented by

0<( Ror−Rof )/( Ror+Rof )|<10  (19).

16 . The observation optical system according to claim 1 ,

wherein in a case where an air interval on the optical axis between a lens of the eyepiece lens closest to the display element side and a second lens of the eyepiece lens from the display element side is denoted by dO, Conditional Expression (20) is satisfied, which is represented by

0< dO/TLA< 0.1  (20).

17 . An optical apparatus comprising:

the observation optical system according to claim 1 .

18 . An observation optical system comprising:

a display element; and

an eyepiece lens disposed on an eyepoint side with respect to the display element,

wherein the eyepiece lens includes a first negative lens having strongest negative refractive power among lenses included in the eyepiece lens, a first positive lens disposed adjacent to a display element side of the first negative lens, and a second positive lens disposed closest to the display element side among positive lenses disposed on the eyepoint side with respect to the first negative lens,

the number of lenses included in the eyepiece lens is greater than or equal to five,

in a case where a half value of a longest diameter of a display region in the display element is denoted by H, a focal length of the eyepiece lens in a state where diopter is −1 diopter is denoted by f, a sum of an air conversion distance on an optical axis from a display surface of the display element to a lens surface of the eyepiece lens closest to the display element side and a distance on the optical axis from the lens surface of the eyepiece lens closest to the display element side to a lens surface of the eyepiece lens closest to the eyepoint side in a state where the diopter is −1 diopter is denoted by TLA, and a refractive index of the first negative lens with respect to a d line is denoted by Nn1, Conditional Expressions (1), (2), and (3) are satisfied, which are represented by

0.355< H/f< 0.48  (1)

0.17 <H/TLA< 0.285  (2)

1.5 <Nn 1<1.7  (3), and

in a case where a refractive index of a lens having strongest positive refractive power among the lenses included in the eyepiece lens with respect to the d line is denoted by Nps, Conditional Expression (12) is satisfied, which is represented by

1.6< Nps< 2  (12).

19 . The observation optical system according to claim 18 ,

wherein in a case where an average value of refractive indexes of all lenses included in the eyepiece lens with respect to the d line is denoted by Nave, Conditional Expression (14-3) is satisfied, which is represented by

1.59628≤Nave<1.75  (14-3).

20 . The observation optical system according to claim 18 ,

wherein in a case where an air interval on the optical axis between a lens of the eyepiece lens closest to the display element side and a second lens of the eyepiece lens from the display element side is denoted by dO, Conditional Expression (20-2) is satisfied, which is represented by

0.02< dO/TLA< 0.09  (20-2).

21 . The observation optical system according to claim 18 ,

wherein in a case where an average value of refractive indexes of all lenses included in the eyepiece lens with respect to the d line is denoted by Nave, and an air interval on the optical axis between a lens of the eyepiece lens closest to the display element side and a second lens of the eyepiece lens from the display element side is denoted by dO, Conditional Expressions (14-3) and (20-2) are satisfied, which are represented by

1.59628≤Nave<1.75  (14-3)

0.02< dO/TLA< 0.09  (20-2).

22 . An optical apparatus comprising:

the observation optical system according to claim 18 .