Optical system and image pickup apparatus
An optical system consists of a front unit and a rear unit. The front unit consists of a first lens having a positive refractive power, a second lens disposed on an image side of the first lens and having a positive refractive power, and a third lens. Each of the first lens and the second lens has a refractive index of 1.7 or higher for d-line. The rear unit consists of two or more and four or fewer lenses and includes a fourth lens having a positive refractive power and a fifth lens adjacent to the fourth lens and having a negative refractive power. Each of the fourth lens and the fifth lens is made of an organic material. A predetermined condition is satisfied.
1. An optical system consisting of a front unit and a rear unit,
wherein the front unit consists of:
a first lens having a positive refractive power;
a second lens disposed on an image side of the first lens and having a positive refractive power; and
a third lens,
wherein each of the first lens and the second lens has a refractive index of 1.7 or higher for d-line,
wherein the rear unit consists of two or more and four or fewer lenses and includes a fourth lens having a positive refractive power and a fifth lens adjacent to the fourth lens and having a negative refractive power,
wherein each of the fourth lens and the fifth lens is made of an organic material, and
wherein the following inequalities are satisfied:
0.75<ν dA/νdB< 1.30
0.75<− fA/fB< 1.30
0.50< du/BF< 1.50
where νdA is an Abbe number of the fourth lens, νdB is an Abbe number of the fifth lens, fA is a focal length of the fourth lens, fB is a focal length of the fifth lens, du is an on-axis distance from a surface vertex closest to an object to a surface vertex closest to an image plane of the rear unit, and BF is a backfocus of the optical system.
2. The optical system according to claim 1 , wherein the following inequalitys is satisfied:
α p 1<100×10{circumflex over ( )}−7
where αp1 is a linear expansion coefficient (/° C.) of the first lens.
3. The optical system according to claim 1 , wherein the following inequalitys is satisfied:
25<ν dp 1<60
where νdp1 is an Abbe number of the first lens.
4. The optical system according to claim 1 , wherein the following inequalitys expression is satisfied:
α p 2<100×10{circumflex over ( )}−7
where αp2 is a linear expansion coefficient (/° C.) of the second lens.
5. The optical system according to claim 1 , wherein the following inequalitys is satisfied:
25<ν dp 2<60
where νdp2 is an Abbe number of the second lens.
6. The optical system according to claim 1 , wherein the third lens has a negative refractive power.
7. The optical system according to claim 6 , wherein the following inequalitys is satisfied:
α n< 100×10{circumflex over ( )}−7
where αn is a linear expansion coefficient (/° C.) of the third lens.
8. The optical system according to claim 6 , wherein the following inequalitys is satisfied:
1.60< N< 2.10
where N is a refractive index of the third lens.
9. The optical system according to claim 6 , wherein the following inequalitys is satisfied:
15<ν dn <35
where νdn is an Abbe number of the third lens.
10. The optical system according to claim 1 , wherein the following inequalitys is satisfied:
1.4< fA/f< 3.5
where f is a focal length of the optical system.
11. The optical system according to claim 1 , wherein the following inequalitys is satisfied:
1.00< f/BF< 3.00
where f is a focal length of the optical system, and BF is a backfocus of the optical system.
12. The optical system according to claim 1 , wherein the following inequalitys is satisfied:
0.5<| Fu|/Fm< 25.0
where Fm is a focal length of the front unit, and Fu is a focal length of the rear unit.
13. The optical system according to claim 1 , wherein the following inequalitys is satisfied:
0.10< dA/BF< 0.60
where dA is an on-axis thickness of the fourth lens.
14. The optical system according to claim 1 , wherein the following inequalitys is satisfied:
0.05< dB/BF< 0.40
where dB is an on-axis thickness of the fifth lens, and BF is a backfocus of the optical system.
15. The optical system according to claim 1 , wherein the following inequalitys are satisfied:
50<ν dA< 60
1.45< NA< 1.60
where NA is a refractive index of the fourth lens.
16. The optical system according to claim 1 , wherein the following inequalitys are satisfied:
15<ν dA< 40
1.55< NA< 1.75
where NA is a refractive index of the fourth lens.
17. The optical system according to claim 6 , wherein the following inequalitys is satisfied:
0.20<− fn/f< 0.70
where f is a focal length of the optical system, and fn is a focal length of the third lens.
18. The optical system according to claim 1 , wherein the first lens is disposed closest to an object.
19. The optical system according to claim 1 , wherein the front unit consists of, in order from an object side to the image side, the first lens, the third lens having a negative refractive power, and the second lens.
20. An image pickup apparatus comprising:
an optical system; and
an image sensor configured to image an optical image formed by the optical system,
wherein the optical system consists of a front unit and a rear unit,
wherein the front unit consists of:
a first lens having a positive refractive power;
a second lens disposed on an image side of the first lens and having a positive refractive power; and
a third lens,
wherein each of the first lens and the second lens has a refractive index of 1.7 or higher for d-line,
wherein the rear unit consists of two or more and four or fewer lenses and includes a fourth lens having a positive refractive power and a fifth lens adjacent to the fourth lens and having a negative refractive power,
wherein each of the fourth lens and the fifth lens is made of an organic material, and
wherein the following inequalities are satisfied:
0.75<ν dA/νdB< 1.30
0.75<− fA/fB< 1.30
0.50< du/BF< 1.50
where νdA is an Abbe number of the fourth lens, νdB is an Abbe number of the fifth lens, fA is a focal length of the fourth lens, fB is a focal length of the fifth lens, du is an on-axis distance from a surface vertex closest to an object to a surface vertex closest to an image plane of the rear unit, and BF is a backfocus of the optical system.