Optical system and image pickup apparatus
An optical system according to an example embodiment includes a first lens unit that has a positive refractive power, and a second lens unit that is disposed on an image side of the first lens unit and that has a positive refractive power. The second lens unit moves when focusing from infinity to an object at near distance. The second lens unit includes, disposed in order from the object side towards an image side, a first positive lens, an aperture stop, and a second positive lens. Anomalous partial dispersibilities of the first positive lens and the second positive lens are defined.
1. An optical system comprising:
a first lens unit that has a positive refractive power; and
a second lens unit that has a positive refractive power,
wherein a distance between adjacent lens units changes during focusing,
wherein the second lens unit moves towards an object side during focusing from infinity to an object at near distance,
wherein the second lens unit includes, disposed in order from the object side towards an image side, a first positive lens, an aperture stop, and a second positive lens, and
wherein when an anomalous partial dispersibility ΔθgF of a material is represented, using an Abbe constant νd of the material, and a partial dispersion ratio θgF of the material, by
Δθ gF=θgF −(−1.665×10 −7 ×νd 3 +5.213×10 −5 ×νd 2 −5.656×10 −3 ×νd+ 7.278×10 −1 ),
the following conditional expressions are satisfied:
0.0050<Δθ gF 1<0.40: and
0.0050 <ΔθgF 2<0.40
where ΔθgF1 is an anomalous partial dispersibility of a material of the first positive lens, and ΔθgF2 is an anomalous partial dispersibility of a material of the second positive lens.
2. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.50< DL 1/ DL 2<3.00
where DL 1 is a distance, on an optical axis, between an image-side lens surface of the first positive lens and the aperture stop, and DL 2 is a distance, on the optical axis, between an object-side lens surface of the second positive lens and the aperture stop.
3. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
1.80 <nd 1<2.40
where nd1 is a refractive index of the material of the first positive lens at a d-line.
4. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
−5.00< h 1{circumflex over ( )}/ h 2{circumflex over ( )}<−0.50
where h1{circumflex over ( )} is a height through which a chief paraxial ray passes the first positive lens, and h2{circumflex over ( )} is a height through which a chief paraxial ray passes the second positive lens.
5. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
−20.0<( h 1× h 1{circumflex over ( )}/ νd 1/ fp 1Δθ gF 1)/( h 2× h 2{circumflex over ( )}/ νd 2/ fp 2×Δθ gF 2)<−0.10
where h1 is a height through which a paraxial marginal ray passes the first positive lens, h2 is a height through which a paraxial marginal ray passes the second positive lens, h1{circumflex over ( )} is a height through which a chief paraxial ray passes the first positive lens, h2{circumflex over ( )} is a height through which a chief paraxial ray passes the second positive lens, νd1 is an Abbe constant of the material of the first positive lens, νd2 is an Abbe constant of the material of the second positive lens, fp1 is a focal length of the first positive lens, and fp2 is a focal length of the second positive lens.
6. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.00 <νd 1<30.0
where νd1 is an Abbe constant of the material of the first positive lens.
7. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.00 <νd 2<30.0
wherein νd2 is an Abbe constant of the material of the second positive lens.
8. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.00< DL 1/ f< 1.00
where DL 1 is a distance, on an optical axis, between an image-side lens surface of the first positive lens and the aperture stop, and f is a focal length of the optical system.
9. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.00< DL 2/ f< 1.00
where DL 2 is a distance, on an optical axis, between an object-side lens surface of the second positive lens and the aperture stop, and f is a focal length of the optical system.
10. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.00< DL 1/ D 2<0.80
where DL 1 is a distance, on an optical axis, between an image-side lens surface of the first positive lens and the aperture stop, and D 2 is a distance, on the optical axis, between a lens surface of the second lens unit closest to an object and a lens surface of the second lens unit closest to an image.
11. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.00< DL 2/ D 2<0.80
where DL 2 is a distance, on an optical axis, between an object-side lens surface of the second positive lens and the aperture stop, and D 2 is a distance, on the optical axis, between a lens surface of the second lens unit closest to an object and a lens surface of the second lens unit closest to an image.
12. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.50< fp 1/ f 2<5.00
where fp1 is a focal length of the first positive lens, and f2 is a focal length of the second lens unit.
13. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.50< fp 2/ f 2<10.0
where fp2 is a focal length of the second positive lens, and f2 is a focal length of the second lens unit.
14. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
1.50< f 1/ f< 45.0
where f1 is a focal length of the first lens unit, and f is a focal length of the optical system.
15. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.50< f 2/ f< 1.50
where f2 is a focal length of the second lens unit, and f is a focal length of the optical system.
16. The optical system according to claim 1 ,
wherein a plurality of lens units that constitute the optical system include, are consisting of, disposed in order from the object side towards the image side, the first lens unit, the second lens unit, and a third lens unit that has a positive or a negative refractive power.
17. The optical system according to claim 16 ,
wherein the following conditional expression is satisfied:
2.00<| f 3|/ f< 35.0
where f3 is a focal length of the third lens unit, and f is a focal length of the optical system.
18. The optical system according to claim 1 ,
wherein a plurality of lens units that constitute the optical system include, are consisting of, disposed in order from the object side towards the image side, the first lens unit and the second lens unit.
19. The optical system according to claim 1 ,
wherein the following conditional expression is satisfied:
0.50 <Fno< 2.50
where Fno is an aperture ratio of the optical system during focusing to infinity.
20. The optical system according to claim 1 ,
wherein the second lens unit includes a negative lens.
21. An image pickup apparatus comprising:
an optical system; and
a light receiving element that receives an image formed by the optical system,
wherein the optical system includes
a first lens unit that has a positive refractive power; and
a second lens unit that has a positive refractive power,
wherein a distance between adjacent lens units changes during focusing,
wherein the second lens unit moves towards an object side during focusing from infinity to an object at near distance,
wherein the second lens unit includes, disposed in order from the object side towards an image side, a first positive lens, an aperture stop, and a second positive lens, and
wherein when
Δθ gF=θgF −(−1.665×10 −7 ×νd 3 +5.213×10 −5 ×νd 2 −5.656×10 −3 ×νd+ 7.278×10 −1 )
is expressed using an anomalous partial dispersibility ΔθgF of a material, an Abbe constant νd of the material, and a partial dispersion ratio θgF of the material, the following conditional expressions hold true:
0.0050 <ΔθgF 1<0.40
0.0050<Δθ gF 2<0.40
where ΔθgF1 is an anomalous partial dispersibility of a material of the first positive lens, and ΔθgF2 is an anomalous partial dispersibility of a material of the second positive lens.