Optical system and image pickup apparatus having the same
An optical system includes a first lens unit, an aperture stop, and a second lens unit having a positive refractive power. In the optical system, the first lens unit includes at least one positive lens made of a material whose Abbe number (νdGP) and relative partial dispersion (θgFGP) satisfy a predetermined condition.
1. An optical system comprising, in order from an object side to an image side:
a first lens unit;
an aperture stop; and
a second lens unit having a positive refractive power,
wherein the first lens unit includes at least one positive lens made of a material whose Abbe number (νdGP) and relative partial dispersion (θgFGP) satisfy the following conditions:
θ gFGP −(0.6438−0.001682 ×νdGP )>0.005
60<νdGP, and
wherein a back focal length when focusing on an infinitely-distant object point (BF), a focal length of the entire optical system (f), an average refractive index of materials of positive lenses included in the second lens unit (Np), and a distance from a surface of the positive lens of the first lens unit on the image side to the aperture stop on an optical axis (Lp) satisfy following conditions:
1.0 <BF/f< 3.0
1.6<Np
0.01 <Lp/f< 0.80.
2. The optical system according to claim 1 , wherein the first lens unit includes at least one negative lens made of a material whose Abbe number (νdGN) and relative partial dispersion (θgFGN) satisfy following conditions:
θ gFGN −(0.6438−0.001682 ×νdGN )<0
50 >νdGN, and
wherein a distance from a surface of the negative lens on the image side to the aperture stop on the optical axis (Ln) satisfies the following condition:
0.01 <Ln/f< 0.80.
3. The optical system according to claim 2 , wherein a distance from the aperture stop to a last lens surface of the second lens unit on the optical axis (LR) satisfies the following condition:
0.5 <LR/f< 1.5.
4. The optical system according to claim 1 , wherein the first lens unit includes at least one negative lens made of a material whose Abbe number (νdGNF) and relative partial dispersion (θgFGNF) satisfy the following condition:
θ gFGNF −(0.6438−0.001682 ×νdGNF )>0, and
wherein a distance from a surface of the at least one negative lens on the image side to the aperture stop on the optical axis (LnF) satisfies the following condition:
0.80 <LnF/f< 2.00.
5. The optical system according to claim 1 , wherein a focal length of the second lens unit (f 2 ) satisfies the following condition:
1.0 <f 2 /f< 1.5.
6. The optical system according to claim 1 , wherein the optical system is configured to form an image on a photoelectric conversion element.
7. 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.
8. An optical system comprising, in order from an object side to an image side:
a first lens unit;
an aperture stop; and
a second lens unit having a positive refractive power,
wherein the first lens unit includes at least one positive lens made of a material whose Abbe number (νdGP) and relative partial dispersion (θgFGP) satisfy the following conditions:
θ gFGP −(0.6438−0.001682 ×νdGP )>0.005
60<νdGP.