Search

US-20260126629-A1 - VARIABLE MAGNIFICATION IMAGING OPTICAL SYSTEM

US20260126629A1US 20260126629 A1US20260126629 A1US 20260126629A1US-20260126629-A1

Abstract

A variable magnification imaging optical system achieves reduction in size and weight, suppresses lateral chromatic aberration and on-axis chromatic aberration during magnification change, enables high-speed focusing, and has favorable optical performance from infinity to a closest distance over the entire zoom range. A variable magnification imaging optical system includes, in order from an object side, a first lens group G 1 having a positive refractive power, a second lens group G 2 having a positive refractive power, a third lens group G 3 having a negative refractive power, a middle group GM including an aperture diaphragm S consisting of one or more lens groups, a focusing group GF, and a subsequent group GR consisting of one lens group, in which a distance between adjacent lens groups changes during magnification change, and the focusing group GF moves along an optical axis during focusing from an infinite distance object to a close distance object.

Inventors

  • Yasumoto OGINOME

Assignees

  • SIGMA CORPORATION

Dates

Publication Date
20260507
Application Date
20251008
Priority Date
20241107

Claims (20)

  1. 1 . A variable magnification imaging optical system comprising, in order from an object side, a first lens group G 1 having a positive refractive power, a second lens group G 2 having a positive refractive power, a third lens group G 3 having a negative refractive power, a middle group GM including an aperture diaphragm S consisting of one or more lens groups, a focusing group GF, and a subsequent group GR consisting of one lens group, wherein a distance between adjacent lens groups changes during magnification change, and the focusing group GF moves along an optical axis during focusing from an infinite distance object to a close distance object.
  2. 2 . The variable magnification imaging optical system according to claim 1 , wherein one or more concave lenses that satisfy the following conditional expression (1) are disposed between the aperture diaphragm S and the subsequent group GR, Δ ⁢ PgFLnSr > 0.013 ( 1 ) ΔPgFLnSr: anomalous dispersion of the concave lens disposed between the aperture diaphragm S and the subsequent group GR.
  3. 3 . The variable magnification imaging optical system according to claim 1 , wherein the first lens group G 1 moves to the object side during magnification change from a wide-angle end to a telephoto end, a distance between the first lens group G 1 and the second lens group G 2 increases, and a distance between the second lens group G 2 and the third lens group G 3 decreases.
  4. 4 . The variable magnification imaging optical system according to claim 1 , wherein the second lens group G 2 moves to an image side during magnification change from a wide-angle end to a telephoto end, a distance between the first lens group G 1 and the second lens group G 2 increases, and a distance between the second lens group G 2 and the third lens group G 3 decreases.
  5. 5 . The variable magnification imaging optical system according to claim 1 , wherein the first lens group G 1 includes a concave lens that satisfies the following conditional expression (2), ndLN ⁢ 1 < 1.8 ( 2 ) ndLN1: refractive index of concave lens having a highest refractive index included in first lens group G 1 .
  6. 6 . The variable magnification imaging optical system according to claim 1 , wherein the following conditional expression (3) is satisfied, 0 . 0 ⁢ 0 ⁢ 5 < DG ⁢ 1 ⁢ G ⁢ 2 ⁢ W / DG ⁢ 1 ⁢ G ⁢ 2 ⁢ T < 0 . 4 ⁢ 0 ⁢ 0 ( 3 ) DG1G2W: distance between the first lens group G 1 and the second lens group G 2 on the optical axis at infinity wide-angle end DG1G2T: distance between the first lens group G 1 and the second lens group G 2 on the optical axis at infinity telephoto end.
  7. 7 . The variable magnification imaging optical system according to claim 1 , wherein the following conditional expression (4) is satisfied, 1. < D ⁢ G ⁢ 2 ⁢ G ⁢ 3 ⁢ W / D ⁢ G ⁢ 2 ⁢ G ⁢ 3 ⁢ T < 8 ⁢ 0 . 0 ⁢ 0 ( 4 ) DG2G3W: distance between the second lens group G 2 and the third lens group G 3 on the optical axis at infinity wide-angle end DG2G3T: distance between the second lens group G 2 and the third lens group G 3 on the optical axis at infinity telephoto end.
  8. 8 . The variable magnification imaging optical system according to claim 1 , wherein the following conditional expression (5) is satisfied, 0 . 0 ⁢ 1 < DG ⁢ 1 ⁢ G ⁢ 2 ⁢ W / DG ⁢ 2 ⁢ G ⁢ 3 ⁢ W < 2. ( 5 ) DG1G2W: distance between the first lens group G 1 and the second lens group G 2 on the optical axis at infinity wide-angle end DG2G3W: distance between the second lens group G 2 and the third lens group G 3 on the optical axis at infinity wide-angle end.
  9. 9 . The variable magnification imaging optical system according to claim 1 , wherein the following conditional expression (6) is satisfied, 2. < DG ⁢ 1 ⁢ G ⁢ 2 ⁢ T / DG ⁢ 2 ⁢ G ⁢ 3 ⁢ T < 2 ⁢ 0 ⁢ 0 . 0 ( 6 ) DG1G2T: distance between the first lens group G 1 and the second lens group G 2 on the optical axis at infinity telephoto end DG2G3T: distance between the second lens group G 2 and the third lens group G 3 on the optical axis at infinity telephoto end.
  10. 10 . The variable magnification imaging optical system according to claim 1 , wherein the following conditional expression (7) is satisfied, 1.2 < DG ⁢ 2 ⁢ Sw / DG ⁢ 2 ⁢ St < 5. ( 7 ) DG2Sw: distance from surface vertex of lens closest to the object side in the second lens group G 2 at wide-angle end to the aperture diaphragm S DG2St: distance from surface vertex of lens closest to object side in the second lens group G 2 at telephoto end to the aperture diaphragm S.
  11. 11 . The variable magnification imaging optical system according to claim 1 , wherein the second lens group G 2 satisfies the following conditional expression (8), 0.2 < g ⁢ 2 ⁢ AXhW / g ⁢ 2 ⁢ AXhT < 1.5 ( 8 ) g2AXhW: height of axial marginal ray at front surface of the second lens group G 2 at infinity wide-angle end with the diaphragm open g2AXhT: height of the axial marginal ray at front surface of the second lens group G 2 at infinity telephoto end with the diaphragm open.
  12. 12 . The variable magnification imaging optical system according to claim 1 , wherein the second lens group G 2 satisfies the following conditional expressions (9) and (10), - 1.8 < ( g ⁢ 2 ⁢ OAHW / Wih ) - ( g ⁢ 2 ⁢ OAhT / Tih ) < - 0.3 ( 9 ) 0.6 < ❘ "\[LeftBracketingBar]" g ⁢ 2 ⁢ OAhW / g ⁢ 2 ⁢ AXhT ❘ "\[RightBracketingBar]" < 2.5 ( 10 ) Wih: image height of off-axis chief ray at maximum angle of view at infinity wide-angle end Tih: image height of the off-axis chief ray at maximum angle of view at infinity telephoto end g2OAhW: height of the off-axis chief ray at maximum angle of view at front surface of second lens group G 2 at the infinity wide-angle end g2OAhT: height of the off-axis chief ray at maximum angle of view at front surface of the second lens group G 2 at infinity telephoto end g2AXhT: height of the axial marginal ray at front surface of the second lens group G 2 at infinity telephoto end with the diaphragm open.
  13. 13 . The variable magnification imaging optical system according to claim 1 , wherein the second lens group G 2 includes one or more concave lenses.
  14. 14 . The variable magnification imaging optical system according to claim 1 , wherein the second lens group G 2 includes at least one or more concave lenses that satisfy the following conditional expression (11), Δ ⁢ PgFLg ⁢ 2 > 0.009 ( 11 ) ΔPgFLg2: anomalous dispersion of concave lens having largest anomalous dispersion among concave lenses included in the second lens group G 2 .
  15. 15 . The variable magnification imaging optical system according to claim 1 , wherein the subsequent group GR includes at least one or more concave lenses that satisfy the following conditional expression (12), Δ ⁢ PgFnLr > 0.009 ( 12 ) ΔPgFnLr: anomalous dispersion of concave lens of the subsequent group GR.
  16. 16 . The variable magnification imaging optical system according to claim 1 , wherein the subsequent group GR includes at least one or more concave lenses that satisfy the following conditional expression (13), vdnLr × Δ ⁢ PgFnLr > 0.8 ( 13 ) vdnLr: Abbe number of concave lens included in the subsequent group GR ΔPgFnLr: anomalous dispersion of concave lens included in the subsequent group GR.
  17. 17 . The variable magnification imaging optical system according to claim 1 , wherein the subsequent group GR includes at least one or more convex lenses that satisfy the following conditional expression (14), Δ ⁢ PgFpLr < - 0.001 ( 14 ) ΔPgFpLr: anomalous dispersion of convex lens included in the subsequent group GR.
  18. 18 . The variable magnification imaging optical system according to claim 1 , wherein two convex lenses from an image side satisfy the following conditional expression (15), Δ ⁢ PgFprAVE < - 0.001 ( 15 ) ΔPgFprAVE: average value of anomalous dispersion of the two convex lenses from the image side.
  19. 19 . The variable magnification imaging optical system according to claim 1 , wherein the first lens group G 1 satisfies the following conditional expression (16), 0 . 1 ⁢ 8 < f ⁢ 1 / fT < 1. ( 16 ) f1: focal length of the first lens group G 1 fT: focal length of the variable magnification imaging optical system at infinity telephoto end.
  20. 20 . The variable magnification imaging optical system according to claim 1 , wherein the second lens group G 2 satisfies the following conditional expression (17), 0 . 1 < f ⁢ 2 / fT < 1.4 ( 17 ) f2: focal length of the second lens group G 2 fT: focal length of the variable magnification imaging optical system at infinity telephoto end.

Description

TECHNICAL FIELD The present invention relates to a variable magnification imaging optical system suitable for an imaging optical system used in an imaging apparatus such as a digital camera or a video camera. BACKGROUND ART In recent years, mirrorless digital cameras and video cameras have been developed, and high-performance cameras have been mounted on smartphones and mobile data terminals. Therefore, in order to differentiate digital cameras and video cameras from these mobile devices, there is an increasing demand for super telephoto zoom lenses. In addition, in recent years, the image sensor of the digital camera and the video camera has been further increased in resolution, and the demand for high performance of the imaging optical system has been further increased. Patent Documents 1 to 3 describe examples of variable magnification imaging optical system in which the half angle of view at the telephoto end is approximately 3 degrees or less. RELATED ART DOCUMENT Patent Document [Patent Document 1] JP-A-2013-167749[Patent Document 2] JP-A-2016-080825[Patent Document 3] JP-A-2019-020450 SUMMARY OF THE INVENTION In a super telephoto zoom lens in which an angle of view at a telephoto end is narrow, in order to improve usability as a zoom lens, it is necessary to achieve three points of: a large zoom ratio, a reduction in size for improving portability, and imaging performance. In order to achieve a large zoom ratio, a lens group having a positive refractive power is disposed closest to the object side, and the lens group is moved to the object side by magnification change to increase a telephoto ratio (a value obtained by dividing a total lens length by a focal length) at the telephoto end and to improve imaging performance in a telephoto state. In addition, in a telephoto type lens, aberrations generated in a lens group of a convergent system disposed on the object side are magnified by a rear lens group. In a case of a fixed focal length lens, it is possible to simply suppress aberrations generated in the convergent system on the object side based on this relationship to improve the imaging performance. However, in a zoom lens, various aberrations fluctuate due to a change in power arrangement by magnification change, and thus the improvement cannot be simply achieved as in the fixed focal length lens. In particular, in a lens in a super telephoto range having a narrow angle of view, a change in direction in which a lateral chromatic aberration by magnification change occurs is a problem. Therefore, in order to reduce the size of the optical system while suppressing the occurrence of the lateral chromatic aberration over the entire zoom range, it is important to select an optical material in accordance with the change in power arrangement by magnification change. The optical system described in Patent Document 1 is an example of a super telephoto zoom lens having a fixed total length. The various aberrations are suppressed over the entire zoom range, and the imaging performance is high. However, in a case where the zoom ratio is increased while maintaining the imaging performance in a type in which the total length is fixed, the optical system is significantly enlarged, which is not preferable. The optical system described in Patent Document 2 is an example of a super telephoto zoom lens of a type in which the total length is variable by moving out a first group. However, a back focus (distance from a final lens to an image surface) with respect to the total lens length is large, and thus the optical system is insufficient in terms of reduction in size of the optical system in view of short flange back due to mirrorless development in recent years. In addition, the change in the lateral chromatic aberration is large from the wide-angle end to the telephoto end, and the correction is insufficient. The optical system described in Patent Document 3 is an example of a super telephoto zoom lens corresponding to short flange back. However, the change in the lateral chromatic aberration is large from the wide-angle end to the telephoto end, and the correction is insufficient. In addition, the suppression of the total lens length at the wide-angle end is also insufficient. The present invention has been made in view of such problems, and an object thereof is to provide a variable magnification imaging optical system that achieves reduction in size and weight, suppresses a lateral chromatic aberration and an on-axis chromatic aberration during magnification change, enables high-speed focusing, and has favorable optical performance from infinity to a closest distance over the entire zoom range. In order to solve the above-described problem, according to an aspect of a variable magnification imaging optical system according to the present invention, the variable magnification imaging optical system consists of, in order from an object side, a first lens group G1 having a positive refractive power, a second lens g