Optical system and image pickup apparatus having the same
An optical system includes, in order from an object side to an image side, a front unit of a positive refractive power, a diaphragm, and a rear unit of a positive refractive power. The front unit includes, in order from the object side to the image side, a positive lens L11, a positive lens L12, and a negative lens L13. The rear unit includes, in order from the object side to the image side, a negative lens L21, a positive lens L22, and a positive lens L23. A predetermined condition is satisfied.
1. An optical system comprising, in order from an object side to an image side, a front unit of a positive refractive power, a diaphragm, and a rear unit of a positive refractive power,
wherein the front unit includes, in order from the object side to the image side, a positive lens L11, a positive lens L12, and a negative lens L13,
wherein the rear unit includes, in order from the object side to the image side, a negative lens L21, a positive lens L22, and a positive lens L23,
wherein an air lens with a convex surface on the image side is formed between the negative lens L21 and the positive lens L22, and
wherein the following conditional expressions are satisfied:
1.00< fF/fR< 2.00
1.00 <f 22 /f
( R 2 b+R 1 b )/( R 2 b−R 1 b )<−0.10
0.30< BF/f< 0.60
where fF is a focal length of the front unit, fR is a focal length of the rear unit, f22 is a focal length of the positive lens L22, f is a focal length of the optical system, R1b is a radius of curvature of a surface on the image side of the negative lens L21, R2b is a radius of curvature a surface on the object side of the positive lens L22, and BF is a distance from a lens surface closest to an image plane in the optical system to the image plane on an optical axis.
2. The optical system according to claim 1 , wherein a radius of curvature of a surface on the image side of the negative lens L21 is less than that of a surface on the object side of the negative lens L21, and
wherein the following conditional expression is satisfied:
−2.00< f 21/ f<− 0.50
where f21 is a focal length of the negative lens L21.
3. The optical system according to claim 1 , wherein the positive lens L23 has a curvature on the image side larger than that on the object side, and
wherein the following conditional expression is satisfied:
0.30< f 23/ f< 1.10
where f23 is a focal length of the positive lens L23.
4. The optical system according to claim 1 , wherein the following conditional expressions are satisfied:
| R 1 a|<|R 2 a|
0.08<( R 2 a+R 1 a )/( R 2 a−R 1 a )<0.80
where R1a is a radius of curvature of a lens surface closest to an image plane in the front unit, and
R2a is a radius of curvature of a lens surface closest to an object in the rear unit.
5. The optical system according to claim 1 , wherein the positive lens L22 is a meniscus lens with a convex surface on the image side.
6. The optical system according to claim 1 , wherein the positive lens L22 includes an aspherical surface.
7. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.60< Lst/f< 1.00
where Lst is a distance from the diaphragm to an image plane.
8. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
1.00< TTL/f< 1.40
where TTL is a distance from a lens surface closest to an object in the optical system to an image plane on an optical axis.
9. The optical system according to claim 1 , wherein the positive lens L12 and the negative lens L13 form a cemented lens.
10. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
4.50< d 12/ d 13<10.00
where d12 is a thickness of the positive lens L12 on an optical axis, and d13 is a thickness of the negative lens L13 on the optical axis.
11. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.70< N 22/ N 23<1.00
where N22 is a refractive index of the positive lens L22, and N23 is a refractive index of the positive lens L23.
12. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
1.05< NdF/NdR< 1.50
where NdF is an average refractive index of lenses included in the front unit, and NdR is an average refractive index of lenses included in the rear unit.
13. The optical system according to claim 1 , wherein the following conditional expressions are satisfied:
1.00< f 22/ f≤ 6.50
−11.35≤( R 2 b−F 1 b )/( R 2 b−R 1 b )<−0.10
14. The optical system according to claim 1 , wherein the front unit consists of the positive lens L11, the positive lens L12, and the negative lens L13.
15. The optical system according to claim 1 , wherein the rear unit consists of the negative lens L21, the positive lens L22, and the positive lens L23.
16. The optical system according to claim 1 , wherein the positive lens L12 and the negative lens L13 are cemented.
17. An image pickup apparatus comprising:
an optical system; and
an image sensor configured to receive light from the optical system,
wherein the optical system includes, in order from an object side to an image side, a front unit of a positive refractive power, a diaphragm, and a rear unit of a positive refractive power,
wherein the front unit includes, in order from the object side to the image side, a positive lens L11, a positive lens L12, and a negative lens L13,
wherein the rear unit includes, in order from the object side to the image side, a negative lens L21, a positive lens L22, and a positive lens L23,
wherein an air lens with a convex surface on the image side is formed between the negative lens L21 and the positive lens L22, and
wherein the following conditional expressions are satisfied:
1.00< fF/fR< 2.00
1.00< f 22/ f
( R 2 b+R 1 b )/( R 2 b−R 1 b )<−0.10
0.30< BF/f< 0.60
where fF is a focal length of the front unit, fR is a focal length of the rear unit, f22 is a focal length of the positive lens L22, f is a focal length of the optical system, R1b is a radius of curvature of a surface on the image side of the negative lens L21, R2b is a radius of curvature a surface on the object side of the positive lens L22, and BF is a distance from a lens surface closest to an image plane in the optical system to the image plane on an optical axis.