Lens system, lens apparatus, adapter apparatus, and image pickup apparatus
A lens system is disposed on the image side of an image pickup optical system and has a negative refractive power. The lens system includes, in order from an object side to the image side, a first lens unit having a positive refractive power, a second lens unit, and a third lens unit. The first lens unit consists of a single lens or a cemented lens. The second lens unit is configured to move in a direction of an optical axis to change a spherical aberration. A lateral magnification of the lens system and a lateral magnification of the second lens unit in a case where an axial ray is incident on the image pickup optical system are appropriately set.
1. A lens system to be disposed on an image side of an image pickup optical system and having a negative refractive power, the lens system comprising, in order from an object side to the image side, a first lens unit having a positive refractive power, a second lens unit, and a third lens unit,
wherein the first lens unit consists of a single lens or a cemented lens,
wherein the second lens unit is configured to move in a direction of an optical axis to change a spherical aberration, and
wherein conditional expressions
0.90<B<1.10, and
0.95<B2<1.05
are satisfied where B is a lateral magnification of the lens system in a case where an axial ray is incident on the image pickup optical system and B2 is a lateral magnification of the second lens unit in a case where an axial ray is incident on the image pickup optical system.
2. The lens system according to claim 1 ,
wherein a surface, of the second lens unit, located closest to the image side is convex toward the image side, and
wherein a surface, of the third lens unit, located closest to the object side is concave toward the object side.
3. The lens system according to claim 1 , wherein a conditional expression
1.65<ndave
is satisfied where ndave is an average refractive index of negative lenses included in the lens system.
4. The lens system according to claim 1 , wherein a conditional expression
15<vd1<40
is satisfied where vd1 is an Abbe number with respect to the d-line of a lens located closest to the object side in the first lens unit.
5. The lens system according to claim 1 , wherein a conditional expression
−5.0< f 1 /f 3<−1.0
is satisfied where f1 is a focal length of the first lens unit and f3 is a focal length of the third lens unit.
6. The lens system according to claim 1 , wherein the third lens unit consists of a single lens or a cemented lens.
7. The lens system according to claim 1 , wherein the lens system consists of four lenses.
8. The lens system according to claim 1 , wherein the second lens unit consists of two lenses.
9. A lens apparatus comprising:
an image pickup optical system; and
a lens system disposed on an image side of the image pickup optical system,
wherein the lens system has a negative refractive power, the lens system comprising, in order from an object side to the image side, a first lens unit having a positive refractive power, a second lens unit, and a third lens unit,
wherein the first lens unit consists of a single lens or a cemented lens,
wherein the second lens unit is configured to move in a direction of an optical axis to change a spherical aberration, and
wherein conditional expressions
0.90<B<1.10, and
0.95<B2<1.05
are satisfied where B is a lateral magnification of the lens system in a case where an axial ray is incident on the image pickup optical system and B2 is a lateral magnification of the second lens unit in a case where an axial ray is incident on the image pickup optical system.
10. The lens apparatus according to claim 9 ,
wherein a surface, of the second lens unit, located closest to the image side is convex toward the image side, and
wherein a surface, of the third lens unit, located closest to the object side is concave toward the object side.
11. The lens apparatus according to claim 9 , wherein a conditional expression
1.65<ndave
is satisfied where ndave is an average refractive index of negative lenses included in the lens system.
12. The lens apparatus according to claim 9 , wherein a conditional expression
15<vd1<40
is satisfied where vd1 is an Abbe number with respect to the d-line of a lens located closest to the object side in the first lens unit.
13. The lens apparatus according to claim 9 , wherein a conditional expression
−5.0< f 1 /f 3<−1.0
is satisfied where f1 is a focal length of the first lens unit and f3 is a focal length of the third lens unit.
14. An image pickup apparatus comprising:
a lens apparatus; and
an image pickup element disposed on an image plane of the lens apparatus,
wherein the lens apparatus comprises:
an image pickup optical system; and
a lens system disposed on an image side of the image pickup optical system,
wherein the lens system has a negative refractive power, the lens system comprising, in order from an object side to the image side, a first lens unit having a positive refractive power, a second lens unit, and a third lens unit,
wherein the first lens unit consists of a single lens or a cemented lens,
wherein the second lens unit is configured to move in a direction of an optical axis to change a spherical aberration, and
wherein conditional expressions
0.90<B<1.10, and
0.95<B2<1.05
are satisfied where B is a lateral magnification of the lens system in a case where an axial ray is incident on the image pickup optical system and B2 is a lateral magnification of the second lens unit in a case where an axial ray is incident on the image pickup optical system.
15. The image pickup apparatus according to claim 14 ,
wherein a surface, of the second lens unit, located closest to the image side is convex toward the image side, and
wherein a surface, of the third lens unit, located closest to the object side is concave toward the object side.
16. The image pickup apparatus according to claim 14 , wherein a conditional expression
1.65<ndave
is satisfied where ndave is an average refractive index of negative lenses included in the lens system.
17. The image pickup apparatus according to claim 14 , wherein a conditional expression
15<vd1<40
is satisfied where vd1 is an Abbe number with respect to the d-line of a lens located closest to the object side in the first lens unit.
18. The image pickup apparatus according to claim 14 , wherein a conditional expression
−5.0< f 1 /f 3<−1.0
is satisfied where f1 is a focal length of the first lens unit and f3 is a focal length of the third lens unit.
19. An adapter apparatus comprising:
a lens system; and
a mounting member configured to mount an image pickup optical system in an object side of the lens system,
wherein the lens system has a negative refractive power, the lens system comprising, in order from an object side to the image side, a first lens unit having a positive refractive power, a second lens unit, and a third lens unit,
wherein the first lens unit consists of a single lens or a cemented lens,
wherein the second lens unit is configured to move in a direction of an optical axis to change a spherical aberration, and
wherein conditional expressions
0.90<B<1.10, and
0.95<B2<1.05
are satisfied where B is a lateral magnification of the lens system in a case where an axial ray is incident on the image pickup optical system and B2 is a lateral magnification of the second lens unit in a case where an axial ray is incident on the image pickup optical system.
20. The adapter apparatus according to claim 19 , further comprising:
a mounting member configured to mount an image pickup element in an image side of the lens system.