Optical system and imaging apparatus having the same
An optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. The second lens unit moves during focusing and a distance between adjacent lens units changes. The second lens unit includes a cemented lens closest to an object. The cemented lens includes a positive lens and a negative lens disposed on the image side of the positive lens. A predetermined condition is satisfied.
1. An optical system comprising, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power,
wherein the second lens unit moves and a distance between adjacent lens units changes during focusing,
wherein the second lens unit includes a cemented lens closest to an object,
wherein the cemented lens includes a positive lens and a negative lens disposed on the image side of the positive lens, and
wherein the following conditional expressions are satisfied:
−10.0<( r 2 LAP+r 1 LAP )/( r 2 LAP−r 1 LAP )<−1.00
0.50<( r 2 LAN+r 1 LAN )/( r 2 LAN−r 1 LAN )<10.0
where r1LAP is a radius of curvature of a surface of the positive lens on the object side, r2LAP is a radius of curvature of a surface of the positive lens on the image side, r1LAN is a radius of curvature of a surface of the negative lens on the object side, and r2LAN is a radius of curvature of a surface of the negative lens on the image side.
2. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.81<| D 12/ r 2 LAP|< 2.00
where D12 is a distance on an optical axis from a surface of the first lens unit closest to an image to a surface of the second lens unit closest to the object.
3. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.002<( nLAN−nLAP )/( nLAN+nLAP )<0.075
where nLAP is a refractive index for d-line of the positive lens, and nLAN is a refractive index for the d-line of the negative lens.
4. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
1.00< f 1/ f< 5.00
where f is a focal length of the optical system when infinity is focused, and f1 is a focal length of the first lens unit.
5. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.10< f 2/ f< 1.20
where f is a focal length of the optical system when infinity is focused, and f2 is a focal length of the second lens unit.
6. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.50< |f 3| f< 10.00
where f is a focal length of the optical system when infinity is focused, and f3 is a focal length of the third lens unit.
7. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.50< D 12/ sk< 2.50
where D12 is a distance on an optical axis from a surface of the first lens unit closest to an image to a surface of the second lens unit closest to the object, and sk is a backfocus.
8. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
1.00< td/f< 6.00
where f is a focal length of the optical system when infinity is focused, and td is an overall lens length of the optical system.
9. The optical system according to claim 1 , further comprising an aperture stop between the first lens unit and the second lens unit.
10. The optical system according to claim 1 , wherein the first lens unit includes three positive lenses.
11. The optical system according to claim 1 , wherein the first lens unit has three negative lenses.
12. The optical system according to claim 1 , wherein the second lens unit has three positive lenses.
13. An imaging apparatus comprising:
the optical system according to claim 1 ; and
an image sensor configured to receive light from the optical system.