Optical system and image pickup apparatus having the same
An optical system consists of, in order from an object side to an image side, a front unit, an aperture stop, and a rear unit having positive refractive power as a whole. The rear unit includes a final lens disposed closest to the image side and having positive refractive power. A number of inequalities relating to the spatial relationship between the lenses and their refractive powers are satisfied.
1. An optical system consisting of, in order from an object side to an image side, a front unit, an aperture stop, and a rear unit that has positive refractive power as a whole,
wherein the rear unit includes a final lens disposed closest to an image plane and having positive refractive power, and
wherein the following inequalities are satisfied:
0.5< TTL/Φi< 1.4
1.64 <PNdave <2.00
2.0<Φ p/sk< 4.0
where TTL is a distance on an optical axis from a lens surface on an object side of a lens disposed closest to an object in the optical system to the image plane, Φi is a diameter of an image circle, PNdave is an average value of refractive indices for d-line of all positive lenses included in the optical system, Φp is an effective diameter of a lens surface on the image side of the final lens, and skis an air conversion length of a distance on the optical axis from the lens surface on the image side of the final lens to the image plane.
2. The optical system according to claim 1 , wherein the following inequality is satisfied:
0.1< f/|fa|< 1.5
where fa is a focal length of the front unit, and f is a focal length of the optical system.
3. The optical system according to claim 1 , wherein the following inequality is satisfied:
0.6< fp/f< 6.0
where fp is a focal length of the final lens, and f is a focal length of the optical system.
4. The optical system according to claim 1 , wherein the following inequality is satisfied:
0.1< sk/f< 0.7
where f is a focal length of the optical system.
5. The optical system according to claim 1 , wherein the following inequality is satisfied:
0.6 <SPIP/TTL< 1.0
where SPIP is a distance on the optical axis from the aperture stop to the image plane.
6. The optical system according to claim 1 , wherein the rear unit includes at least four lenses.
7. The optical system according to claim 1 , wherein the rear unit includes a negative lens disposed on the object side of the final lens.
8. The optical system according to claim 7 , wherein the following inequality is satisfied:
0.0<( R 1+ R 2)/( R 2− R 1)<50.0
where R1 is a paraxial radius of curvature of a lens surface on the object side of the negative lens, and R2 is a paraxial radius of curvature of a lens surface on the image side of the negative lens.
9. The optical system according to claim 7 , wherein the following inequality is satisfied:
1.500< Ndn< 4.1945/ν dn+ 1.520
where Ndn is a refractive index of the negative lens for the d-line, and νdn is an Abbe number of the negative lens based on the d-line.
10. The optical system according to claim 1 , wherein the following inequality is satisfied:
0.10< fb/|fa|< 10.00
where fa is a focal length of the front unit, and fb is a focal length of the rear unit.
11. The optical system according to claim 1 , wherein the front unit includes a positive lens, and the following inequality is satisfied:
1.60 <Ndap <2.00
where Ndap is a refractive index of the positive lens for the d-line.
12. The optical system according to claim 1 , wherein the rear unit includes a positive lens, and the following inequality is satisfied:
1.60 <Ndbp <2.00
where Ndbp is a refractive index of the positive lens for the d-line.
13. The optical system according to claim 12 , wherein the rear unit includes a negative lens, and the following inequality is satisfied:
0.0 <Ndbp−Ndbn <0.4
where Ndbn is a refractive index of the negative lens for the d-line.
14. The optical system according to claim 1 , wherein the following inequality is satisfied:
1.0<Φ p/Φa< 4.0
where Φa is an effective diameter of the lens having a largest effective diameter in the front unit.
15. The optical system according to claim 1 , wherein the optical system consists of 5 or more and 8 or less lenses.
16. The optical system according to claim 1 , wherein the front unit consists of a single positive lens.
17. 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 consists of, in order from an object side to an image side, a front unit, an aperture stop, and a rear unit that has positive refractive power as a whole,
wherein the rear unit includes a final lens disposed closest to an image plane and having positive refractive power, and
wherein the following inequalities are satisfied:
0.5< TTL/Φi< 1.4
1.64 <PNdave <2.00
2.0<Φ p/sk< 4.0
where TTL is a distance on an optical axis from a lens surface on an object side of a lens disposed closest to an object in the optical system to the image plane, Φi is a diameter of an image circle, PNdave is an average value of refractive indices for d-line of all positive lenses included in the optical system, Φp is an effective diameter of a lens surface on the image side of the final lens, and skis an air conversion length of a distance on the optical axis from the lens surface on the image side of the final lens to the image plane.