Wide angle lens system
View Patent ↗Provided is a wide angle lens system including: a first lens group having a negative refractive power; and a second lens group having a positive refractive power, wherein the first lens group and the second lens group are provided in that order from an object to an image, and the lens system satisfies a first conditional expression: 16<| L/f |<17.5 where L denotes a distance from a lens surface of the first lens group provided closest to the object to a lens surface of the second lens group provided closest to the image, and f denotes a focal length of the wide angle lens system.
1. A wide angle lens system comprising, in an order from an object to an image:
a first lens group having a negative refractive power and comprising:
a first lens having a negative refractive power;
a second lens having a negative refractive power;
a third lens having a negative refractive power; and
a fourth lens having a positive refractive power; and
a second lens group having a positive refractive power and comprising:
a fifth lens having a positive refractive power;
a sixth lens having a negative refractive power; and
a seventh lens having a positive refractive power,
wherein the lens system satisfies a first conditional expression for improving optical performance of a half angle of view equal to or greater than 90°:
17<| L/f|< 17.5,
wherein L denotes a distance from an object-side surface of the first lens to an image side surface of the seventh lens, and f denotes a focal length of the wide angle lens system, and
wherein refractive index of the seventh lens satisfies a second conditional expression:
1.65< Nd 7 <1.78.
2. The wide angle lens system of claim 1 , wherein the second lens of the first lens group comprises at least one aspherical surface.
3. The wide angle lens system of claim 1 , wherein the second lens group comprises at least one cemented lens.
4. The wide angle lens system of claim 1 , wherein the fifth lens and the sixth lens are cemented lenses.
5. The wide angle lens system of claim 1 , wherein the seventh lens comprises at least one aspherical surface.
6. The wide angle lens system of claim 1 , wherein the seventh lens comprises two aspherical surfaces.
7. The wide angle lens system of claim 1 , satisfying a third conditional expression:
4.0< f L /f< 4.4
wherein the f denotes the focal length of the wide angle lens system and f L denotes a focal length of the second lens group.
8. The wide angle lens system of claim 1 , satisfying a fourth conditional expression:
vd 4 <25
wherein vd 4 denotes an Abbe number of the fourth lens.
9. The wide angle lens system of claim 1 , further comprising an aperture provided between the first lens group and the second lens group.
10. A photographing apparatus comprising the wide angle lens system of claim 1 .
11. The wide angle lens system of claim 1 , wherein the second lens surface corresponds to a convex surface of a lens of the second lens group, the lens provided closest to the image.
12. The wide angle lens system of claim 1 , wherein:
the first lens group comprises a first positive lens having a positive refractive power, and
the second lens group comprises a second lens having a positive refractive power, and
wherein a first thickness of the first positive lens of the first lens group is less than a second thickness of the second lens of the second lens group, the first and the second thicknesses measured along an optical axis of the wide angle lens system.