Rear attachment lens, imaging optical system and image pickup apparatus

1. A rear attachment lens detachably attached to a main lens system at an image side of the main lens system to lengthen a focal length from a focal length of the main lens system itself, the rear attachment lens comprising:

a negative lens disposed such that, when L is a distance between a lens surface closest to an object side and a lens surface closest to an image side in the rear attachment lens, the negative lens is within an area in which a distance from the lens surface closest to the object side in the rear attachment lens is in the range of 0.5 L to 1.0 L,

wherein, when νdn1 is an Abbe number of a material of the negative lens with respect to the d-line and θgFn1 is a partial dispersion ratio of the material of the negative lens with respect to the g-line and the F-line, the following conditions are satisfied:

10<νdn1<23

0.020 <θgFn 1−0.6438+0.001682 *νdn 1<0.100.

2. The rear attachment lens according to claim 1 , further comprising:

a first positive lens disposed within an area in which a distance from the lens surface closest to the object side in the rear attachment lens is in the range of 0 to 0.5 L, and

wherein, when Ndp1 and νdp1 are a refractive index and an Abbe number, respectively, of a material of the first positive lens with respect to the d-line and θgFp1 is a partial dispersion ratio of the material of the first positive lens with respect to the g-line and the F-line, the following conditions are satisfied:

1.90 <Ndp 1+0.0125 νdp 1<2.24

0.001 <θgFp 1−0.6438+0.001682 *νdp 1<0.020.

3. The rear attachment lens according to claim 1 , further comprising:

a second positive lens disposed within an area in which a distance from the lens surface closest to the object side in the rear attachment lens is in the range of 0.5 L to 1.0 L, and

wherein, when Ndp2 and νdp2 are a refractive index and an Abbe number, respectively, of a material of the second positive lens with respect to the d-line and θgFp2 is a partial dispersion ratio of the material of the second positive lens with respect to the g-line and the F-line, the following conditions are satisfied:

1.90 <Ndp 2+0.0125 νdp 2<2.24

−0.010 <θgFp 2−0.6438+0.001682*ν dp 2<0.003.

4. An imaging optical system, comprising:

a main lens system; and

the rear attachment lens according to claim 1 , the rear attachment lens being detachably attached to the main lens system at the image side of the main lens system.

5. An image pickup apparatus, comprising:

the imaging optical system according to claim 4 ; and

a light receiving unit that receives an image formed by the imaging optical system.

6. A rear attachment lens detachably attached to a main lens system at an image side of the main lens system to lengthen a focal length from a focal length of the main lens system itself, the rear attachment lens comprising:

a first lens unit having a positive refractive power and including either two lenses including a positive lens and a negative lens or a set of a single lens and a cemented lens arranged in order from an object side to the image side, the set of the single lens and the cemented lens including a positive lens and a negative lens;

a second lens unit positioned on the image side of the first lens unit and including either a cemented lens including a positive lens and a negative lens or a set of a single lens and a cemented lens arranged in order from the object side to the image side, the set of the single lens and the cemented lens including a positive lens and a negative lens;

a third lens unit positioned on the image side of the second lens unit and including a positive lens;

a fourth lens unit positioned on the image side of the third lens unit and including either two lenses including a positive lens and a negative lens or a set of a cemented lens and a single lens arranged in order from an object side to the image side, the set of the cemented lens and the single lens including a positive lens and a negative lens,

wherein, when the third lens unit includes at least one negative lens, the at least one negative lens in the third lens unit or at least one negative lens included in the fourth lens unit serves as a first negative lens, and

wherein, when ν d — N1 and Δθ gF — N1 are an Abbe number and a partial-dispersion-ratio difference, respectively, of a material of the first negative lens, f — N1 is a focal length of the first negative lens, and f is a focal length of the rear attachment lens, the following condition is satisfied:

0.00015<Δθ gF — N1 *f /(ν d — N1 *f — N1 )<0.00620.

7. The rear attachment lens according to claim 6 , wherein at least one positive lens included in the third lens unit or at least one positive lens included in the fourth lens unit serves as a first positive lens, and when ν d — P1 and Δθ gF — N1 are an Abbe number and a partial-ispersion-ratio difference, respectively, of a material of the first positive lens and f — P1 is a focal length of the first positive lens, the following condition is satisfied:

0<Δθ gF — N1 *f /(ν d — P1 *f — P1 )<0.001.

8. The rear attachment lens according to claim 6 , wherein when f3 is a focal length of the third lens unit, the following condition is satisfied:

| f/f 3|<6.5.

9. The rear attachment lens according to claim 6 , wherein when f2 is a focal length of the second lens unit, the following condition is satisfied:

−10.0 <f/|f 2|<−0.2.

10. The rear attachment lens according to claim 6 , wherein when f4 is a focal length of the fourth lens unit, the following condition is satisfied:

| f/f 4|<4.0.

11. The rear attachment lens according to claim 6 , wherein when f1 is a focal length of the first lens unit, the following condition is satisfied:

−5.5 <f/f 1<−0.05.

12. The rear attachment lens according to claim 6 , wherein when N N is a refractive index of a material of a negative lens included in the rear attachment lens, the following condition is satisfied:

1.5<N N <2.5.

13. The rear attachment lens according to claim 6 , further comprising:

at least one diffractive optical element.

14. An imaging optical system, comprising:

a main lens system; and

the rear attachment lens according to claim 6 , the rear attachment lens being detachably attached to the main lens system at the image side of the main lens system.

15. An image pickup apparatus, comprising:

the imaging optical system according to claim 14 ; and

a solid-state image pickup element that receives an image formed by the imaging optical system.

16. A rear attachment lens configured to be removably attached to a main lens system, the rear attachment lens comprising:

a first lens unit having a lens surface closest to an object side;

a second lens unit having a lens surface closest to an image side; and

a negative lens unit disposed between the first lens unit and the second lens unit along an optical axis thereof,

wherein the negative lens unit is disposed within an area in which a distance from the negative lens unit to the lens surface closest to the object side is in a range of 0.5 L to 1.0 L, where L is a distance between the lens surface closest to the object side and the lens surface closest to the image side, and

wherein,

10<νdn1<23, and

0.020 <θgFn 1−0.6438+0.001682 *νdn 1<0.100,

where νdn1 is an Abbe number of a material of the negative lens unit with respect to the d-line and θgFn1 is a partial dispersion ratio of the material of the negative lens unit with respect to the g-line and the F-line.