Imaging apparatus including variable power relay optical system

1. An imaging apparatus comprising, in order from an object side:

an imaging optical system;

a variable power relay optical system arranged on an image side of the imaging optical system; and

an imaging element that images a relay image,

wherein the variable power relay optical system comprises, in order from the object side:

a front group that is arranged between the imaging optical system and a position of an image of a sample that would be formed by the imaging optical system in the absence of the variable power relay optical system, the front group forming an intermediate image formed by reducing the image; and

a rear group that forms a relay image formed by magnifying the intermediate image, the rear group comprising a plurality of lens groups, and the plurality of lens groups including lens groups that are movable along an optical axis so as to change a magnification of the rear group without changing a distance from the front group to the relay image,

wherein the front group comprises a first lens group having positive power,

wherein the rear group comprises, in order from the object side:

a second lens group having positive power;

a third lens group having negative power, the third lens group being movable along the optical axis;

a fourth lens group having positive power, the fourth lens group being movable along the optical axis; and

a fifth lens group having positive power, the fifth lens group being movable along the optical axis,

wherein the first lens group includes a meniscus lens having a convex surface on an object side of the meniscus lens, and

wherein the following conditional expression is satisfied:

0.7≤β L 1≤0.9,

where βL 1 is a magnification of the first lens group that is defined as (an image height of the intermediate image)/(an image height of the image that would be formed by the imaging optical system in the absence of the variable power relay optical system).

2. The imaging apparatus according to claim 1 , wherein:

a range of a magnification of the variable power relay optical system includes −1× at which the relay image has a the same size as that of the image that would be formed by the imaging optical system in the absence of the variable power relay optical system,

while a magnitude of the magnification of the variable power relay optical system varies from a low magnification end state in which the magnitude is smallest to a high magnification end state in which the magnitude is greatest,

the third lens group moves in a direction from the intermediate image toward the relay image, and

the fifth lens group moves toward the relay image after moving toward the intermediate image, and

the fourth lens group is located closer to the relay image in the high magnification end state than in the low magnification end state.

3. The imaging apparatus according to claim 1 , wherein:

the second lens group includes a first lens on a side of the second lens group closest to the object, the first lens having positive power,

the first lens has a convex surface on an image side thereof, the convex surface having a refractive power stronger than that of a surface on an object side of the first lens, and

the following conditional expression is satisfied:

1.4≤|β L 1−2|≤2.2,

where βL 1 −2 is a comprehensive magnification of the first lens group and the second lens group.

4. The imaging apparatus according to claim 2 , wherein:

the second lens group includes a first lens on a side of the second lens group closest to the object, the first lens having positive power,

the first lens has a convex surface on an image side thereof, the convex surface having a refractive power stronger than that of a surface on an object side of the first lens, and

the following conditional expression is satisfied:

1.4≤|β L 1−2|≤2.2,

where βL 1 −2 is a comprehensive magnification of the first lens group and the second lens group.

5. The imaging apparatus according to claim 1 , wherein the third lens group includes two lenses having concave surfaces facing each other.

6. The imaging apparatus according to claim 2 , wherein the third lens group includes two lenses having concave surfaces facing each other.

7. The imaging apparatus according to claim 3 , wherein the third lens group includes two lenses having concave surfaces facing each other.

8. The imaging apparatus according to claim 4 , wherein the third lens group includes two lenses having concave surfaces facing each other.

9. An imaging apparatus comprising, in order from an object side:

an imaging optical system;

a variable power relay optical system arranged on an image side of the imaging optical system; and

an imaging element that images a relay image,

wherein the variable power relay optical system comprises, in order from the object side:

a front group that is arranged between the imaging optical system and a position of an image of a sample that would be formed by the imaging optical system in the absence of the variable power relay optical system, the front group forming an intermediate image formed by reducing the image; and

a rear group that forms a relay image formed by magnifying the intermediate image, the rear group comprising a plurality of lens groups, and the plurality of lens groups including lens groups that are movable along an optical axis so as to change a magnification of the rear group without changing a distance from the front group to the relay image,

wherein the front group comprises a first lens group having positive power,

wherein the rear group comprises, in order from the object side:

a second lens group having positive power;

a third lens group having negative power, the third lens group being movable along the optical axis;

a fourth lens group having positive power, the fourth lens group being movable along the optical axis; and

a fifth lens group having positive power, the fifth lens group being movable along the optical axis,

wherein the second lens group includes a first lens on a side of the second lens group closest to the object, the first lens having positive power,

wherein the first lens has a convex surface on an image side thereof, the convex surface having a refractive power stronger than that of a surface on an object side of the first lens, and

wherein the following conditional expression is satisfied:

1.4≤|β L 1−2|≤2.2,

where βL 1 −2 is a comprehensive magnification of the first lens group and the second lens group, and is defined as (an image height of a relay image formed by the first lens group and the second lens group)/(an image height of the image that would be formed by the imaging optical system in the absence of the variable power relay optical system).

10. The imaging apparatus according to claim 9 , wherein:

a range of a magnification of the variable power relay optical system includes −1× at which the relay image has a the same size as that of the image that would be formed by the imaging optical system in the absence of the variable power relay optical system,

while a magnitude of the magnification of the variable power relay optical system varies from a low magnification end state in which the magnitude is smallest to a high magnification end state in which the magnitude is greatest,

the third lens group moves in a direction from the intermediate image toward the relay image, and

the fifth lens group moves toward the relay image after moving toward the intermediate image, and

the fourth lens group is located closer to the relay image in the high magnification end state than in the low magnification end state.

11. The imaging apparatus according to claim 9 , wherein the third lens group includes two lenses having concave surfaces facing each other.

12. The imaging apparatus according to claim 10 , wherein the third lens group includes two lenses having concave surfaces facing each other.