Optical system and optical apparatus including the optical system

1. An optical system comprising, in order from an object side to an image side:

a first lens unit having a positive refractive power;

an aperture stop; and

a rear lens group,

wherein the rear lens group includes a second lens unit configured to move during focusing,

wherein the first lens unit includes n positive lenses (n is an integer greater than 1) and one or more negative lenses, and

wherein, when i (i is an integer equal to or greater than 1) is an order of an optical member counted from the object side to the image side, Ndi and νdi are respectively a refractive index and an Abbe number of a material of an i-th positive lens of the first lens unit with respect to d-line light, max(νdi) and min (νdi) are respectively maximum and minimum values of the Abbe number νdi, min(Ndi) is a minimum value of the refractive index Ndi, fp is a focal length of the first lens unit, and f is a focal length of the entire optical system, the following conditions are satisfied:

2.2<max(ν di )/min(ν di )

min(ν di )<30.0

1.55<min( Ndi )

0.5 <fp/f< 3.7.

2. The optical system according to claim 1 , wherein, when Fno is a full-aperture F-number of the optical system during focusing on an infinitely-distant object, the following condition is satisfied:

Fno< 2.5.

3. The optical system according to claim 1 , wherein when ΔθgFi is anomalous partial dispersion of the material of the i-th positive lens of the first lens unit and fi is a focal length of the i-th positive lens, the following condition is satisfied:

3.60×10 −4 <Σ((Δθ gFi/νdi )/ fi )× fp.

4. The optical system according to claim 1 , wherein the rear lens group further includes a third lens unit located on the image side of the second lens unit and configured to be stationary during focusing.

5. The optical system according to claim 1 , wherein the optical system is configured to form an image on a photoelectric conversion element located at an image plane of the optical system.

6. An image pickup apparatus comprising:

the optical system according to claim 1 ; and

a photoelectric conversion element configured to receive an image formed by the optical system.

7. The image pickup apparatus according to claim 6 , wherein when ω is a half angle of view of the optical system, the following condition is satisfied:

6<ω<25.

8. An optical system comprising, in order from an object side to an image side:

a first lens unit having a positive refractive power, whose a refractive surface closest to the image side has a concave shape facing the image side;

an aperture stop; and

a rear lens group,

wherein the rear lens group includes a second lens unit configured to move during focusing and whose refractive surface closest to the object side has a concave shape facing the object side,

wherein the first lens unit includes n positive lenses (n is an integer greater than 1) and one or more negative lenses, and

wherein, when i (i is an integer equal to or greater than 1) is an order of an optical member counted from the object side towards the image side, νdi is an Abbe number of a material of an i-th positive lens of the first lens unit with respect to d-line light, max(νdi) and min(νdi) are respectively maximum and minimum values of the Abbe number νdi, Rp is a radius of curvature of the refractive surface of the first lens unit closest to the image side and having a concave shape facing the image side, and Rn is a radius of curvature of the refractive surface of the second lens unit closest to the object side and having a concave shape facing the object side, and f is a focal length of the entire optical system, the following conditions are satisfied:

2.2<max(ν di )/min(ν di )

min(ν di )<30.0

0.15 <Rp/f< 0.90

−15.00 <Rn/f<− 0.15.

9. The optical system according to claim 8 , wherein, when fair is a focal length of an air lens formed with refractive surfaces located at the object side and the image side of the aperture stop, the following condition is satisfied:

−0.900<fair/ f<− 0.175.

10. The optical system according to claim 8 , wherein, when Fno is a full-aperture F-number of the optical system during focusing on an infinitely-distant object, the following condition is satisfied:

Fno< 2.5.

11. The optical system according to claim 8 , wherein, when ΔθgFi is anomalous partial dispersion of the material of the i-th positive lens of the first lens unit, νdi is the Abbe number of the material of the i-th positive lens, fi is a focal length of the i-th positive lens and fp is a focal length of the first lens unit, the following condition is satisfied:

3.60×10 −4 <Σ((Δθ gFi/νdi )/ fi )× fp.

12. The optical system according to claim 8 , wherein the rear lens group further includes a third lens unit located on the image side of the second lens unit and configured to be stationary during focusing.

13. The optical system according to claim 8 , wherein the optical system is configured to form an image on a photoelectric conversion element located at an image plane of the optical system.

14. An image pickup apparatus comprising:

the optical system according to claim 8 ; and

a photoelectric conversion element configured to receive an image formed by the optical system.

15. The image pickup apparatus according to claim 14 , wherein when ω is a half angle of view of the optical system, the following condition is satisfied:

6<ω<25.