What is claimed is:
1. An optical system comprising:
- a first negative lens element disposed nearest a front side; and
- a first positive lens element whose front surface resides within a distance 0.4 L from a surface nearest the front side toward a rear side of the optical system having a total lens length L,
- wherein the first negative lens element is composed of a material satisfying the following conditions:
- description="In-line Formulae" end="lead"Ndn1>1.65description="In-line Formulae" end="tail"
- description="In-line Formulae" end="lead"θgFn1−(0.6438−0.001682×νdn1)>0.001description="In-line Formulae" end="tail"
- where Ndn1, νdn1, and θgFn1 denote a refractive index for the d-line, an Abbe number for the d-line, and a partial dispersion ratio for the g- and F-lines, respectively, of the material of the first negative lens element, and
- wherein the first positive lens element is composed of a material satisfying the following conditions:
- description="In-line Formulae" end="lead"Ndp<1.78description="In-line Formulae" end="tail"
- description="In-line Formulae" end="lead"νdp<50description="In-line Formulae" end="tail"
- description="In-line Formulae" end="lead"θgFp−(0.6438−0.001682×νdp)<0description="In-line Formulae" end="tail"
- where Ndp, νdp, and θgFp denote a refractive index for the d-line, an Abbe number for the d-line, and a partial dispersion ratio for the g- and F-lines, respectively, of the material of the first positive lens element.
2. The optical system according to claim 1, further comprising:
- an aspherical surface provided within a distance 0.3 L from the surface nearest the front side toward the rear side.
3. The optical system according to claim 1, further comprising:
- a second negative lens element whose front surface resides within a distance 0.5 L from the surface nearest the front side toward the rear side,
- wherein the second negative lens element is composed of a material satisfying the following condition:
- description="In-line Formulae" end="lead"θgFn2−(0.6438−0.001682×νdn2)>0.02description="In-line Formulae" end="tail"
where νdn2 and θgFn2 denote an Abbe number for the d-line and a partial dispersion ratio for the g- and F-lines, respectively, of the material of the second negative lens element.
4. The optical system according to claim 1, further comprising, in order from the front side to the rear side:
- a front lens unit having a negative optical power;
- an aperture stop; and
- a rear lens unit having a positive optical power,
- wherein the front lens unit includes the first negative lens element and the first positive lens element.
5. The optical system according to claim 1, further comprising:
- a plurality of lens units including a first lens unit having a negative optical power and residing at the position nearest the front side,
- wherein intervals between adjacent ones of the plurality of lens units change during zooming, and
- wherein the total lens length L is a total lens length of the optical system at a wide-angle end.
6. The optical system according to claim 5,
- wherein the plurality of lens units includes, in order from the front side to the rear side, the first lens unit, a second lens unit having a positive optical power, a third lens unit having a positive optical power, and a fourth lens unit having a positive optical power, and
- wherein the second lens unit, the third lens unit, and the fourth lens unit move during zooming.
7. An optical apparatus comprising:
- the optical system according to claim 1.
