Optical lens system

Abstract

This eliminates flare when focusing at close range, ensures a larger image circle, and allows for a larger aperture ratio. [Solution] The lens consists of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, an aperture diaphragm STO, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power. When focusing at close range, the first lens group G1 and the fourth lens group G2 are fixed, the second lens group G2 moves toward the image IMG side, and the third lens group G3 moves toward the object OBJ side, satisfying 0.4 < |f2 / f| < 0.7.

Claims

1. Starting from the object side, it consists of a first lens group with positive refractive power, a second lens group with negative refractive power, an aperture diaphragm, a third lens group with positive refractive power, and a fourth lens group with negative refractive power. When focusing at close range, the first and fourth lens groups are fixed, the second lens group moves toward the image, and the third lens group moves toward the object. An optical lens system characterized in that, when the focal length of the second lens group is f2 and the focal length of the entire system is f, the condition 0.4 < |f2 / f| < 0.7 is satisfied.

2. The optical lens system according to claim 1, characterized in that the second lens group has at least one set of cemented lenses, and the third lens group has at least two sets of cemented lenses.

3. The optical lens system according to claim 1 or 2, characterized in that the cemented lens located closest to the object in the third lens group is bonded in the order of a positive lens and a negative lens from the object side, and the cemented surface faces the object side with a concave surface.

4. The optical lens system according to claim 1, characterized in that the ratio of the focal length f2 of the second lens group to the focal length f3 of the third lens group satisfies 0.7 < |f2 / f3| < 1.

2.

5. The optical lens system according to claim 4, characterized in that the difference in the number of lenses comprising the second lens group and the third lens group is one or less.

6. The optical lens system according to claim 1, characterized in that the first lens group has a negative lens with a concave surface facing the object side.

7. The optical lens system according to claim 1, characterized in that when the effective diameter of the lens surface closest to the object is φf and the effective diameter of the lens surface closest to the image is φr, the condition 0.49 < φr / φf < 0.7 is satisfied.

8. When the back focus is BF, the total focal length of the system is f, and the effective diameter of the lens surface closest to the image is φr, 0.18<BF / f<0.3 0.85<φr / 2BF<1 The optical lens system according to claim 1, characterized in that it satisfies the two formulas described above.

9. The optical lens system according to claim 1, characterized in that when the refractive index of the positive lens included in the fourth lens group is nd, nd > 1.90.

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