Optical system and image pickup 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 diaphragm, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power. A distance between adjacent lens units is changed during focusing. The second lens unit is moved to the image side during focusing from an object at infinity to a short-distance object. The first lens unit includes a positive lens closest to an object and two or more negative lenses. The second lens unit consists of a single negative 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 diaphragm, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power,
wherein each distance between adjacent lens units is changed during focusing,
wherein the second lens unit is moved to the image side during focusing from an object at infinity to a short-distance object,
wherein the first lens unit includes a positive lens closest to the object and two or more negative lenses,
wherein the second lens unit consists of a single negative lens, and
wherein the following conditional expressions are satisfied:
0.2<LD1/LD<0.4,
BF/ f< 0.25, and
15<vdG1<26
where LD 1 is a distance on an optical axis from a lens surface closest to the object of the first lens unit to a lens surface closest to an image plane of the first lens unit, LD is a distance on the optical axis from the lens surface closest to the object of the first lens unit to the image plane, f is a focal length of the optical system, BF is a back focus of the optical system during focusing on the object at infinity, and vdG1 is an Abbe number of the positive lens.
2. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
LD/ f< 1.5.
3. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.50< f 1 /f< 0.85
where f1 is a focal length of the first lens unit.
4. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
−0.65< f 2/ f<− 0.35
where f2 is a focal length of the second lens unit.
5. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.65 <f 3 /f< 0.95
where f3 is a focal length of the third lens unit.
6. The optical system according to claim 1 , wherein the third lens unit consists of, in order from the object side to the image side, a first subunit having a positive refractive power, a second subunit having a negative refractive power, and a third subunit having a positive refractive power, and
wherein the second subunit is moved in a direction including a component in a direction orthogonal to the optical axis during image stabilization.
7. The optical system according to claim 1 , wherein the first lens unit and the third lens unit are stationary during focusing.
8. The optical system according to claim 1 , wherein the first lens unit includes a negative lens closest to the image side in the first lens unit.
9. An image pickup apparatus comprising:
an optical system; and
an image sensor configured to receive an image formed by the optical system,
wherein the optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a diaphragm, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power,
wherein each distance between adjacent lens units is changed during focusing,
wherein the second lens unit is moved to the image side during focusing from an object at infinity to a short-distance object,
wherein the first lens unit includes a positive lens closest to the object and two or more negative lenses,
wherein the second lens unit consists of a single negative lens, and
wherein the following conditional expressions are satisfied:
0.2<LD1/LD<0.4,
BF/ f< 0.25, and
15<vdG1<26
where LD 1 is a distance on an optical axis from a lens surface closest to the object of the first lens unit to a lens surface closest to an image plane of the first lens unit, LD is a distance on the optical axis from the lens surface closest to the object of the first lens unit to the image plane, f is a focal length of the optical system, BF is a back focus of the optical system during focusing on the object at infinity, and vdG1 is an Abbe number of the positive lens.