Optical system, image projection device, and imaging device

Abstract

An optical system according to the present disclosure comprises a first lens group having negative power, a second lens group having positive power, a third lens group having positive power, and a fourth lens group having positive power, these being arranged in the above order proceeding from the enlargement side to the reduction side. When zooming from the wide angle end to the telephoto end, the interval between the first lens group and the second lens group, the interval between the second lens group and the third lens group, and the interval between the third lens group and the fourth lens group change, and the following condition (1) is satisfied. (1): G2P < G3P < G4P, where G2P is the power of the second lens group, G3P is the power of the third lens group, and G4P is the power of the fourth lens group.

Description

Optical system, image projection device and imaging device

[0001] The present disclosure relates to an optical system, and also to an image projection device and an imaging device that use such an optical system.

[0002] Patent Document 1 discloses a zoom lens. The zoom lens described in Patent Document 1 consists of, from the object side, a front group having an overall negative refractive power and a rear group having an overall positive refractive power. The rear group has at least two positive lens groups, and magnification is changed by changing the air gap between at least the front group and the two positive lens groups. In addition, in the zoom lens described in Patent Document 1, the final lens group in the rear group, located closest to the image plane, has an overall positive refractive power and includes a cemented lens made up of three lenses having two cemented surfaces, with at least one positive lens located on each of the object side and image side of the cemented lens.

[0003] Japanese Patent Application Laid-Open No. 2005-157097

[0004] The present disclosure provides an optical system that realizes a relatively long back focus while being a wide-angle zoom, ensures telecentricity, and reduces distortion fluctuations. The present disclosure also provides an image projection device and an imaging device that use such an optical system.

[0005] The optical system according to the present disclosure includes, arranged in order from the magnification side to the reduction side, a first lens group having negative power, a second lens group having positive power, a third lens group having positive power, and a fourth lens group having positive power, wherein, when zooming from the wide-angle end to the telephoto end, the distances between the first lens group and the second lens group, the distances between the second lens group and the third lens group, and the distances between the third lens group and the fourth lens group change, and the optical system satisfies the following condition (1): G2P<G3P<G4P (1) where, G2P: power of the second lens group G3P: power of the third lens group G4P: power of the fourth lens group.

[0006] An image projection device according to the present disclosure includes the above optical system and an image forming element that generates an image to be projected onto a screen via the optical system.

[0007] An imaging device according to the present disclosure includes the optical system described above and an imaging element that receives an optical image formed by the optical system and converts it into an electrical image signal.

[0008] The optical system, image projection device, and imaging device according to the present disclosure can achieve a relatively long back focus despite being a wide-angle zoom, ensure telecentricity, and reduce distortion fluctuations.

[0009]

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of well-known matters or redundant explanation of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following explanation and to facilitate understanding by those skilled in the art.

[0011] The applicant provides the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and does not intend for them to limit the subject matter described in the claims.

[0012] Below, various embodiments of the optical system according to the present disclosure will be described. In each embodiment, a case will be described in which the optical system is used in a projector (an example of an image projection device) that projects image light of an original image S, which is obtained by spatially modulating incident light using an image forming element such as a liquid crystal or a DMD (digital micromirror device) based on an image signal, onto a screen. That is, the optical system according to the present disclosure can be used to enlarge and project the original image S on an image forming element arranged on the reduction side by placing a screen (not shown) on an extension of the enlargement side.

[0013] In addition, the optical system according to the present disclosure can also be used to collect light emitted from an object located on the extension of the magnification side and form an optical image of the object on the imaging surface of an imaging element located on the reduction side.

[0014] 1 to 15C, a first embodiment of the present disclosure will be described below. Here, a zoom lens system will be described as an example of an optical system.

[0015] Figures 1, 6, and 11 show layout diagrams illustrating optical paths at the wide-angle end at an object distance of 3000 mm for the optical systems according to Examples 1 to 3. Figures 2A, 7A, and 12A show lens layout diagrams at the wide-angle end at an object distance of 3000 mm for the optical systems according to Examples 1 to 3. Figures 2B, 7B, and 12B show lens layout diagrams at intermediate positions at an object distance of 3000 mm for the optical systems according to Examples 1 to 3. Figures 2C, 7C, and 12C show lens layout diagrams at the telephoto end at an object distance of 3000 mm for the optical systems according to Examples 1 to 3.

[0016] The broken line arrows shown at the bottom of Figures 2A, 7A, and 12A are straight lines connecting the positions of the first lens group G1 to the fourth lens group G4 at the wide-angle end, the intermediate position, and the telephoto end, starting from the top of the figures. The wide-angle end and the intermediate position, and the intermediate position and the telephoto end are simply connected by straight lines, and do not represent the actual movement of each lens group G1 to G4. The symbols (+) and (-) attached to the signs of each lens group G1 to G4 indicate whether the power of each lens group G1 to G4 is positive or negative.

[0017] The wide-angle end is the shortest focal length state in which the entire system has the shortest focal length fw. The intermediate position is an intermediate focal length state between the wide-angle end and the telephoto end. The telephoto end is the longest focal length state in which the entire system has the longest focal length ft. Based on the focal length fw at the wide-angle end and the focal length ft at the telephoto end, the focal length fm at the intermediate position is defined as √(fw × ft).

[0018] In each diagram, the magnification-side imaging position (i.e., the magnification conjugate point) is located on the left, and the reduction-side imaging position (i.e., the reduction conjugate point) is located on the right. In each diagram, the straight line drawn on the most reduction side represents the position of the original image S, and optical elements P1, P2, and P3 are located on the magnification side of the original image S. The optical elements P1, P2, and P3 have zero optical power and represent optical elements such as a color separation prism, a color synthesis prism, an optical filter, a parallel plate glass, a quartz low-pass filter, and an infrared cut filter.

[0019] Regarding the zooming function, the optical systems 1 according to Examples 1 to 3 include a first lens group G1 to a fourth lens group G4. The first lens group G1 to the fourth lens group G4 are arranged in order from the enlargement side to the reduction side. The first lens group G1, the third lens group G3, and the fourth lens group G4 are movable independently of one another. The first lens group G1, the third lens group G3, and the fourth lens group G4 are movable by, for example, a cam mechanism. The second lens group G2 is fixed. When zooming from the wide-angle end to the telephoto end, the distance between the first lens group G1 and the second lens group G2, the distance between the second lens group G2 and the third lens group G3, and the distance between the third lens group G3 and the fourth lens group G4 change.

[0020] The first lens group G1 has negative power, and the second to fourth lens groups G2 to G4 have positive power.

[0021] In the optical system 1 according to Example 1, the first lens group G1 is composed of the first lens element L1 to the seventh lens element L7 and includes surfaces 1 to 14 (for surface numbers, see the numerical examples described later). The second lens group G2 is composed of the eighth lens element L8 and includes surfaces 15 and 16. The third lens group G3 is composed of the ninth lens element L9 and the tenth lens element L10 and includes surfaces 18 to 21. The fourth lens group G4 is composed of the eleventh lens element L11 to the twentieth lens element L20 and includes surfaces 23 to 42. The optical elements P1 to P3 include surfaces 43 to 48. During zooming from the wide-angle end to the telephoto end, as shown in FIGS. 2A to 2C , the first lens group G1 moves toward the reduction side, the second lens group G2 is fixed, and the third lens group G3 and the fourth lens group G4 move toward the enlargement side.

[0022] In the optical systems 1 according to Examples 2 and 3, the first lens group G1 is composed of the first lens element L1 to the seventh lens element L7 and includes surfaces 1 to 14. The second lens group G2 is composed of the eighth lens element L8 and includes surfaces 15 and 16. The third lens group G3 is composed of the ninth lens element L9 to the eleventh lens element L11 and includes surfaces 18 to 23. The fourth lens group G4 is composed of the twelfth lens element L12 to the 19th lens element L19 and includes surfaces 25 to 40. The optical elements P1 to P3 include surfaces 41 to 46. During zooming from the wide-angle end to the telephoto end, as shown in FIGS. 7A to 7C , the first lens group G1 moves toward the reduction side, the second lens group G2 is fixed, and the third lens group G3 and the fourth lens group G4 move toward the enlargement side.

[0023] FIGS. 3A, 8A, and 13A show longitudinal aberration diagrams at the wide-angle end of the optical systems according to Examples 1 to 3 at an object distance of 3000 mm. FIGS. 3B, 8B, and 13B show longitudinal aberration diagrams at an intermediate position at an object distance of 3000 mm for the optical systems according to Examples 1 to 3. FIGS. 3C, 8C, and 13C show longitudinal aberration diagrams at the telephoto end of the optical systems according to Examples 1 to 3 at an object distance of 3000 mm. FIGS. 4A, 9A, and 14A show longitudinal aberration diagrams at the wide-angle end of the optical systems according to Examples 1 to 3 at an object distance of 1800 mm. FIGS. 4B, 9B, and 14B show longitudinal aberration diagrams at the intermediate position at an object distance of 1800 mm for the optical systems according to Examples 1 to 3. FIGS. 4C, 9C, and 14C show longitudinal aberration diagrams at the telephoto end of the optical systems according to Examples 1 to 3 at an object distance of 1800 mm. Figures 5A, 10A, and 15A show longitudinal aberration diagrams at the wide-angle end at an object distance of 20,000 mm for the optical systems according to Examples 1 to 3. Figures 5B, 10B, and 15B show longitudinal aberration diagrams at the intermediate position at an object distance of 20,000 mm for the optical systems according to Examples 1 to 3. Figures 5C, 10C, and 15C show longitudinal aberration diagrams at the telephoto end at an object distance of 20,000 mm for the optical systems according to Examples 1 to 3.

[0024] Each longitudinal aberration diagram shows, from left to right, spherical aberration (SA (mm)), astigmatism (AST (mm)), and distortion (DIS (%)). In each spherical aberration diagram, the vertical axis represents pupil height, with the solid line representing the d-line characteristics, the short dashed line representing the F-line characteristics, and the long dashed line representing the C-line characteristics. In each astigmatism diagram, the vertical axis represents image height, with the solid line representing the sagittal plane (indicated by s in the diagram) and the dashed line representing the meridional plane (indicated by m in the diagram). In each distortion diagram, the vertical axis represents image height. Furthermore, distortion represents distortion relative to equidistant projection.

[0025] Regarding the focus function, the optical system 1 according to Examples 1 to 3 may include, as necessary, a force lens group that performs focus adjustment when the object distance changes, and a field curvature correction lens group that corrects field curvature aberration after the focus lens group has performed the focus adjustment.

[0026] As an example, in the optical system 1 according to Examples 1 to 3, the field curvature correction lens group is composed of a first lens element L1 and a second lens element L2. During the field curvature correction operation, the field curvature correction lens group moves along the optical axis of the optical system, and the lens positioned on the reduction side of the field curvature correction lens group is fixed.

[0027] Example 1 As shown in FIGS. 1 and 2A to 2C, an optical system 1 according to Example 1 is composed of, in order from the magnification side to the reduction side, a first lens element L1 to a twentieth lens element L20. The first lens element L1 has a negative meniscus shape with a convex surface facing the magnification side. The second lens element L2 has a positive meniscus shape with a convex surface facing the magnification side. The third lens element L3 has a negative meniscus shape with a convex surface facing the magnification side. The fourth lens element L4 has a negative meniscus shape with a convex surface facing the magnification side. The fifth lens element L5 has a negative meniscus shape with a convex surface facing the magnification side. The sixth lens element L6 has a negative meniscus shape with a convex surface facing the reduction side. The seventh lens element L7 has a positive meniscus shape with a convex surface facing the reduction side. The eighth lens element L8 has a positive meniscus shape with a convex surface facing the reduction side. The ninth lens element L9 has a negative meniscus shape with a convex surface facing the magnification side. The tenth lens element L10 has a biconvex shape. The eleventh lens element L11 has a biconcave shape. The twelfth lens element L12 has a biconvex shape. The thirteenth lens element L13 has a negative meniscus shape with a convex surface facing the reduction side. The fourteenth lens element L14 has a biconvex shape. The fifteenth lens element L15 has a negative meniscus shape with a convex surface facing the magnification side. The sixteenth lens element L16 has a biconvex shape. The seventeenth lens element L17 has a negative meniscus shape with a convex surface facing the magnification side. The eighteenth lens element L18 has a biconvex shape. The nineteenth lens element L19 has a negative meniscus shape with a convex surface facing the reduction side. The twentieth lens element L20 has a biconvex shape.

[0028] A first diaphragm A1 for cutting light rays is disposed between the eighth lens element L8 and the ninth lens element L9. The first diaphragm A1 is fixed. A second diaphragm A2 is disposed between the tenth lens element L10 and the eleventh lens element L11. The second diaphragm A2 is movable and moves in conjunction with the movement of the fourth lens group G4. Optical elements P1, P2, and P3, each having zero optical power, are disposed on the reduction side of the optical system 1.

[0029] Example 2 As shown in FIGS. 6 and 7A to 7C, an optical system 1 according to Example 2 is composed of, in order from the magnification side to the reduction side, a first lens element L1 to a nineteenth lens element L19. The first lens element L1 has a negative meniscus shape with a convex surface facing the magnification side. The second lens element L2 has a positive meniscus shape with a convex surface facing the magnification side. The third lens element L3 has a negative meniscus shape with a convex surface facing the magnification side. The fourth lens element L4 has a negative meniscus shape with a convex surface facing the magnification side. The fifth lens element L5 has a biconcave shape. The sixth lens element L6 has a biconvex shape. The seventh lens element L7 has a biconcave shape. The eighth lens element L8 has a biconvex shape. The ninth lens element L9 has a biconvex shape. The tenth lens element L10 has a negative meniscus shape with a convex surface facing the reduction side. The eleventh lens element L11 has a biconvex shape. The twelfth lens element L12 has a biconcave shape. The thirteenth lens element L13 has a biconvex shape. The fourteenth lens element L14 has a biconvex shape. The fifteenth lens element L15 has a biconvex shape. The sixteenth lens element L16 has a biconcave shape. The seventeenth lens element L17 has a biconvex shape. The eighteenth lens element L18 has a negative meniscus shape with the convex surface facing the reduction side. The nineteenth lens element L19 has a biconvex shape.

[0030] A first diaphragm A1 for cutting light rays is disposed between the eighth lens element L8 and the ninth lens element L9. The first diaphragm A1 is fixed. A second diaphragm A2 is disposed between the eleventh lens element L11 and the twelfth lens element L12. The second diaphragm A2 is movable and moves in conjunction with the movement of the fourth lens group G4. Optical elements P1, P2, and P3, each having zero optical power, are disposed on the reduction side of the optical system 1.

[0031] Example 3 As shown in FIGS. 11 and 12A to 12C, an optical system 1 according to Example 3 is composed of, in order from the magnification side to the reduction side, a first lens element L1 to a nineteenth lens element L19. The first lens element L1 has a negative meniscus shape with a convex surface facing the magnification side. The second lens element L2 has a positive meniscus shape with a convex surface facing the magnification side. The third lens element L3 has a negative meniscus shape with a convex surface facing the magnification side. The fourth lens element L4 has a negative meniscus shape with a convex surface facing the magnification side. The fifth lens element L5 has a biconcave shape. The sixth lens element L6 has a biconvex shape. The seventh lens element L7 has a biconcave shape. The eighth lens element L8 has a biconvex shape. The ninth lens element L9 has a biconvex shape. The tenth lens element L10 has a negative meniscus shape with a convex surface facing the reduction side. The eleventh lens element L11 has a biconvex shape. The twelfth lens element L12 has a biconcave shape. The thirteenth lens element L13 has a positive meniscus shape with a convex surface facing the reduction side. The fourteenth lens element L14 has a biconvex shape. The fifteenth lens element L15 has a biconvex shape. The sixteenth lens element L16 has a biconcave shape. The seventeenth lens element L17 has a biconvex shape. The eighteenth lens element L18 has a negative meniscus shape with a convex surface facing the reduction side. The nineteenth lens element L19 has a biconvex shape.

[0032] A first diaphragm A1 for cutting light rays is disposed between the eighth lens element L8 and the ninth lens element L9. The first diaphragm A1 is fixed. A second diaphragm A2 is disposed between the eleventh lens element L11 and the twelfth lens element L12. The second diaphragm A2 is movable and moves in conjunction with the movement of the fourth lens group G4. Optical elements P1, P2, and P3, each having zero optical power, are disposed on the reduction side of the optical system 1.

[0033] Next, conditions that can be satisfied by the optical system according to this embodiment will be described. Note that, although multiple conditions are specified for the optical system according to each example, it is possible to satisfy all of these multiple conditions, or to satisfy individual conditions to obtain the corresponding effects.

[0034] The optical system 1 according to Examples 1 to 3 includes, arranged in order from the magnification side to the reduction side, a first lens group G1 having negative power, a second lens group G2 having positive power, a third lens group G3 having positive power, and a fourth lens group G4 having positive power. When zooming from the wide-angle end to the telephoto end, the distance between the first lens group G1 and the second lens group G2, the distance between the second lens group G2 and the third lens group G3, and the distance between the third lens group G3, the fourth lens group G4, and the fourth lens group G4 change. The optical system 1 satisfies the following condition (1): G2P<G3P<G4P (1), where G2P is the power of the second lens group, G3P is the power of the third lens group, and G4P is the power of the fourth lens group.

[0035] With this configuration, a relatively long back focus can be achieved despite the wide-angle zoom, and telecentricity can be ensured, making it possible to reduce distortion fluctuations.

[0036] In the optical systems 1 according to Examples 1 to 3, the second lens group G2 may be fixed during zooming.

[0037] With this configuration, there is no need for a mechanism for moving the second lens group G2. Therefore, compared to an optical system in which all of the first through fourth lens groups G1 through G4 are movable, the number of mechanisms for moving the second lens group G2 can be reduced. This allows the optical system 1 to be realized with a simple configuration while reducing manufacturing costs.

[0038] In the optical systems 1 according to Examples 1 to 3, the first lens element L1, which is the first from the magnification side, may have a negative meniscus shape convex toward the object side, and the second lens element L2, which is the second from the magnification side, may be a positive lens element.

[0039] With this configuration, distortion at the wide-angle end can be reduced.

[0040] Furthermore, the optical systems 1 according to Examples 1 to 3 may include a diaphragm A1 disposed between the second lens group G2 and the third lens group G3.

[0041] This configuration makes it possible to cut out downward light rays, i.e., stray light, from the wide-angle end to the telephoto end, thereby making it possible to correct field curvature with a relatively small number of lens elements.

[0042] In the optical systems 1 according to Examples 2 and 3, the fourth lens group G4 includes at least five positive lens elements. The at least five positive lens elements may satisfy the following condition (2): dn / dt < -4 x 10^(-6) [ / K] (2), where dn / dt is the relative refractive index temperature coefficient of the positive lens element at the d-line at room temperature.

[0043] With this configuration, focus changes can be reduced when high-intensity light is incident.

[0044] Furthermore, the optical systems 1 according to Examples 1 to 3 may satisfy the following conditions (3) to (5): 6<f2 / fw<12 (3) 4<f3 / fw<10 (4) 2<f4 / fw<5 (5) where, f2: focal length of the second lens group, f3: focal length of the third lens group, f4: focal length of the fourth lens group, and fw: focal length of the entire optical system at the wide-angle end.

[0045] With this configuration, a relatively long back focus can be achieved despite the wide-angle zoom, and telecentricity can be ensured, making it possible to further reduce distortion fluctuations.

[0046] Furthermore, in the optical systems 1 according to Examples 2 and 3, the third lens element L3, which is the third from the magnification side, may be a negative lens element, and the refractive index of the negative lens element may be 2 or more, or the refractive index of all lens elements other than the third lens element L3 may be less than 2.

[0047] This configuration reduces the curvature of field at the wide-angle end. Furthermore, since the lens elements other than the third lens element L3 can be relatively inexpensive lens elements with a refractive index of less than 2, the manufacturing cost of the optical system 1 can be reduced.

[0048] In the optical systems 1 according to Examples 2 and 3, the second lens group G2 may be composed of one positive lens element. The positive lens element may satisfy the following condition (6): dn / dt < -3.5 x 10^(-6) [ / K] (6), where dn / dt is the relative refractive index temperature coefficient of the positive lens element at the d-line at room temperature.

[0049] This configuration can reduce focus changes when high-intensity light is incident, and can also reduce chromatic aberration.

[0050] Furthermore, the optical systems 1 according to Examples 1 to 3 may be configured to correct field curvature by moving the first lens element L1 and the second lens element L2 in the optical axis direction.

[0051] With this configuration, when the object distance, i.e., the distance on the magnification side, is changed, it is possible to correct the fluctuating curvature of field, and also to reduce the change in back focus due to the correction of the curvature of field.

[0052] In the optical systems 1 according to Examples 1 to 3, when zooming from the wide-angle end to the telephoto end, the distance between the first lens group G1 and the second lens group G2 may be narrowed. The distance between the second lens group G2 and the third lens group G3 may be narrowed. Furthermore, the distance between the third lens group G3 and the fourth lens group G4 may be widened.

[0053] With this configuration, it is possible to reduce the fluctuation of chromatic aberration of magnification from wide angle to telephoto.

[0054] Furthermore, the optical systems 1 according to Examples 1 to 3 may satisfy the following condition (7): BFW / fw>4 (7) where BFW is the air-equivalent back focus at the wide-angle end, and fw is the focal length of the entire optical system at the wide-angle end.

[0055] With this configuration, it is possible to achieve a back focus that corresponds to the prism length for separating blue, green, and red.

[0056] In the optical systems 1 according to Examples 1 to 3, all of the lens elements in the first lens group G1 to the fourth lens group G4 may be spherical lenses.

[0057] With this configuration, it is not necessary to use relatively expensive elements such as aspherical lens elements, and therefore manufacturing costs can be reduced.

[0058] In the optical systems 1 according to Examples 1 to 3, the second lens group G2 is fixed during zooming, but the present invention is not limited to this. For example, the second lens group G2 may be movable during zooming.

[0059] In the optical systems 1 according to Examples 1 to 3, the first aperture A1 is fixed, but the present invention is not limited to this. The first aperture A1 may be movable. For example, the first aperture A1 may move in conjunction with the movement of the third lens group G3.

[0060] In the optical systems 1 according to Examples 1 to 3, the second aperture stop A2 is movable, but the present invention is not limited to this. For example, the second aperture stop A2 may be fixed.

[0061] In the optical systems 1 according to Examples 1 to 3, all of the lens elements in the first to fourth lens groups G1 to G4 are spherical lenses, but the present invention is not limited to this. For example, the first to fourth lens groups G1 to G4 may include aspherical lenses.

[0062] (Numerical Example 1) For the optical system 1 of Numerical Example 1 (corresponding to Example 1), surface data is shown in Table 1, various data is shown in Table 2, single lens data is shown in Table 3, zoom lens group data is shown in Table 4, zoom lens group magnification is shown in Table 5, and focus data is shown in Table 6 (unit: mm).

[0063] [Table 1] Surface data Surface number rd nd vd Clear aperture Object surface ∞ 1 94.54680 4.50000 1.92286 20.9 60.491 2 75.66550 12.06260 55.164 3 128.24420 12.17380 1.83481 42.7 54.844 4 450.47270 5.00000 53.170 5 78.43150 3.50000 1.92286 20.9 38.408 6 42.19810 10.57920 31.736 7 116.72510 3.00000 1.88300 40.8 31.417 8 54.54080 8.30610 28.389 9 2429.00640 2.50000 1.88300 40.8 28.225 10 111.78450 9.31040 27.234 11 -70.59560 2.50000 1.80420 46.5 27.181 12 -758.52860 11.75120 28.123 13 -311.67280 7.02450 1.85451 25.2 30.298 14 -88.73870 Variable 30.757 15 337117.74160 6.39100 1.73800 32.3 29.299 16 -131.68200 31.00000 29.247 17 (Aperture) ∞ Variable 22.134 18 107.84250 2.00000 1.80420 46.5 17.992 19 55.66720 0.20000 17.497 20 53.15700 7.25390 1.51680 64.2 17.495 21 -114.03780 Variable 17.130 22 (Aperture) ∞ 1.81160 14.406 23 -79.38590 2.00000 1.49700 81.6 14.373 24 49.60800 3.11160 14.464 25 84.56550 7.03770 1.59270 35.4 14.888 26 -45.70010 4.07880 15.044 27 -38.98230 2.00000 1.80420 46.5 14.539 28 -1710.01420 11.51270 15.060 29 82.95410 6.84700 1.49700 81.6 17.761 30 -86.64990 0.20000 18.229 31 128.30090 2.00000 1.75500 52.3 18.676 32 50.80430 18.55590 18.710 33 90.00270 11.49540 1.45860 90.2 25.394 34 -67.44900 0.20000 25.750 35 185.89140 2.20000 1.73800 32.3 25.779 36 61.58130 3.53060 25.441 37 133.32760 10.42970 1.43700 95.1 25.571 38 -70.34130 1.22220 25.909 39 -62.04260 2.20000 1.83481 42.7 25.905 40 -112.23050 0.20000 26.825 41 113.45810 11.69950 1.43700 95.1 27.942 42 -78.14160 Variable 28.035 43 ∞ 91.00000 1.51680 64.2 35.000 44 ∞ 1.00000 35.000 45 ∞ 1.00000 1.50997 62.2 35.000 46 ∞ 1.00000 35.000 47 ∞ 3.00000 1.50847 61.2 35.000 48 ∞ 4.50000 35.000 Image plane ∞ .

[0064] [Table 2] Various data Zoom ratio 1.36435 Wide-angle Mid-range Telephoto Focal length 19.8576 23.1090 27.0928 F-number 2.49663 2.49674 2.49773 Angle of view 39.1601 34.9971 30.6887 Image height 16.0900 16.0900 16.0900 Total lens length 462.4998 443.8666 432.0107 d14 44.5298 25.8862 14.0269 d17 60.0850 44.4991 25.7624 d21 2.0000 14.4163 29.9544 d42 13.0010 16.1695 19.3811 Entrance pupil position 77.7917 77.4463 77.6310 Exit pupil position 2526.7412 2523.5727 2520.3611 Front principal point position 97.8054 100.7669 105.0150 Back principal point position 442.5141 420.5841 404.6794

[0065] [Table 3] Single lens data Lens Initial surface Focal length L1 1 -463.5878 L2 3 211.1322 L3 5 -103.7897 L4 7 -118.6266 L5 9 -132.7705 L6 11 -96.9493 L7 13 143.1070 L8 15 178.3627 L9 18 -145.5613 L10 20 71.2087 L11 23 -61.1142 L12 25 51.0815 L13 27 -49.6308 L14 29 86.4323 L15 31 -112.6547 L16 33 86.0474 L17 35 -125.7249 L18 37 107.0384 L19 39 -169.5756 L20 41 107.8899

[0066] [Table 4] Zoom lens group data Group Initial surface Focal length Lens length Front principal point Rear principal point G1 1 -42.45237 92.20780 40.35295 48.11556 G2 15 178.36266 37.39100 3.67581 6.38956 G3 18 138.40135 9.45390 3.38066 6.65652 G4 22 70.97941 102.33270 72.99697 143.11899

[0067] [Table 5] Zoom lens group magnification Group First surface Wide angle Mid-range Telephoto G1 1 0.01377 0.01377 0.01377 G2 15 4.03563 2.83833 2.38772 G3 18 -0.27819 -0.51571 -0.81768 G4 22 0.41731 0.37251 0.32740

[0068] [Table 6] Focus data Object distance: 1800mm Surface Wide Angle Medium Telephoto 4 3.500 3.250 3.000 42 13.083 16.278 19.531 Object distance: 20000mm Surface Wide Angle Medium Telephoto 4 7.000 7.000 8.000 42 12.895 16.023 19.181

[0069] (Numerical Example 2) For the optical system 1 of Numerical Example 2 (corresponding to Example 2), surface data is shown in Table 7, various data is shown in Table 8, single lens data is shown in Table 9, zoom lens group data is shown in Table 10, zoom lens group magnification is shown in Table 11, and focus data is shown in Table 12 (unit: mm).

[0070] [Table 7] Surface data Surface number rd nd vd Clear aperture Object surface ∞ 1 98.81130 4.50000 1.84666 23.8 60.495 2 60.34730 15.20290 51.009 3 100.49120 16.26180 1.73800 32.3 50.703 4 1260.83740 1.63420 49.111 5 75.26100 3.20000 2.00100 29.1 38.149 6 44.42980 11.59850 32.732 7 142.19050 2.50000 1.80420 46.5 32.281 8 51.17130 13.64860 29.328 9 -130.70200 2.20000 1.49700 81.6 29.181 10 79.84310 16.70690 29.072 11 109.19130 17.88260 1.48749 70.2 32.124 12 -56.90510 0.20000 32.188 13 -89.95500 2.20000 1.49700 81.6 30.378 14 120.29930 Variable 29.273 15 372.56590 8.34130 1.77830 23.9 28.385 16 -199.05170 23.00000 28.134 17 (Aperture) ∞ Variable 23.042 18 136.27090 10.23900 1.51742 52.4 20.125 19 -55.47420 0.57020 19.432 20 -54.52600 1.50000 1.80420 46.5 19.145 21 -318.50430 6.79420 18.934 22 425.62000 4.75040 1.51680 64.2 17.882 23 -80.98910 Variable 17.629 24 (Aperture) ∞ 1.79350 14.288 25 -79.04080 1.50000 1.48749 70.2 14.249 26 47.17180 18.59000 14.281 27 294.30900 3.38580 1.43700 95.1 17.188 28 -207.28630 26.89550 17.424 29 216.33280 7.80780 1.49700 81.6 22.981 30 -72.25650 0.20070 23.366 31 104.98040 6.28060 1.43700 95.1 23.678 32 -267.82790 0.20000 23.580 33 -375.55600 2.20000 1.80420 46.5 23.532 34 69.59600 3.21280 23.364 35 88.47060 11.75430 1.43700 95.1 24.026 36 -57.48630 0.60000 24.291 37 -64.19090 2.20000 1.80420 46.5 24.192 38 -109.89110 0.20000 24.754 39 97.68750 7.37040 1.43700 95.1 25.143 40 -262.14630 Variable 25.032 41 ∞ 91.00000 1.51680 64.2 22.940 42 ∞ 1.00000 16.686 43 ∞ 1.00000 1.47401 65.4 16.581 44 ∞ 1.00000 16.511 45 ∞ 3.00000 1.50847 61.2 16.406 46 ∞ 1.00000 16.199 Image plane ∞.

[0071] [Table 8] Various data Zoom ratio 1.38613 Wide-angle Mid-range Telephoto Focal length 19.8379 23.4070 27.4980 F-number 2.49972 2.50858 2.52120 Angle of view 39.2650 34.7738 30.5849 Image height 16.0900 16.0900 16.0900 Total lens length 463.5030 445.5917 431.9538 d14 37.7828 19.8446 6.2419 d17 51.4138 36.3597 19.8016 d23 2.6813 14.7005 26.6184 d40 16.5010 19.5348 24.1881 Entrance pupil position 74.3059 74.1206 74.1824 Exit pupil position -1235.8406 -1238.8744 -1243.5277 Front principal point position 93.8253 97.0853 101.0722 Back principal point position 443.5371 422.0064 404.2098

[0072] [Table 9] Single Lens Data Lens Initial Surface Focal Length L1 1 -193.4827 L2 3 147.0843 L3 5 -114.2811 L4 7 -100.6354 L5 9 -99.3840 L6 11 79.5452 L7 13 -103.2009 L8 15 167.7641 L9 18 77.6086 L10 20 -82.0142 L11 22 132.0822 L12 25 -60.3639 L13 27 278.8885 L14 29 109.9724 L15 31 173.4709 L16 33 -72.8504 L17 35 81.7381 L18 37 -196.1441 L19 39 163.8747

[0073] [Table 10] Zoom lens group data Group Initial surface Focal length Lens length Front principal point Rear principal point G1 1 -39.25825 107.73550 39.28424 60.96267 G2 15 167.76406 31.34130 3.07687 6.69741 G3 18 120.17806 23.85380 13.33385 18.31735 G4 24 73.10889 94.19140 68.90829 139.82056

[0074] [Table 11] Zoom lens group magnification Group Starting surface Wide angle Mid-range Telephoto G1 1 0.01275 0.01275 0.01275 G2 15 4.05482 2.82849 2.30082 G3 18 -0.24949 -0.46060 -0.77120 G4 24 0.50025 0.45837 0.39539

[0075] [Table 12] Focus data Object distance: 1800mm Surface Wide angle Medium Telephoto 4 1.334 1.284 1.234 40 16.583 19.643 24.338 Object distance: 20000mm Surface Wide angle Medium Telephoto 4 2.084 2.184 2.284 40 16.395 19.388 23.988

[0076] (Numerical Example 3) For the optical system 1 of Numerical Example 3 (corresponding to Example 3), surface data is shown in Table 13, various data is shown in Table 14, single lens data is shown in Table 15, zoom lens group data is shown in Table 16, zoom lens group magnification is shown in Table 17, and focus data is shown in Table 18 (unit: mm).

[0077] [Table 13] Surface data Surface number rd nd vd Clear aperture Object surface ∞ 1 106.09970 4.50000 1.80518 25.5 60.425 2 60.44360 14.91990 50.588 3 104.97790 15.54410 1.73800 32.3 50.426 4 1397.87420 1.69720 48.919 5 86.16110 3.20000 2.00100 29.1 39.434 6 46.68500 11.63930 33.866 7 167.57900 2.60000 1.80420 46.5 33.670 8 59.91750 12.05490 31.252 9 -179.02810 2.40000 1.49700 81.6 31.213 10 98.09030 20.64490 31.299 11 134.51410 19.42110 1.48749 70.2 35.125 12 -61.22390 0.20000 35.245 13 -107.62700 2.50000 1.49700 81.6 33.056 14 122.23120 Variable 31.792 15 412.43970 5.11250 1.77830 23.9 30.770 16 -212.52010 23.00000 30.688 17 (Aperture) ∞ Variable 25.497 18 506.52000 6.51980 1.51742 52.4 22.372 19 -74.13800 2.08840 22.109 20 -72.43080 2.00000 1.80420 46.5 21.332 21 -250.13920 18.60980 21.186 22 160.86180 4.83670 1.51680 64.2 18.481 23 -122.90270 Variable 18.175 24(Aperture) ∞ 2.02030 14.670 25 -71.08110 1.50000 1.48749 70.2 14.630 26 62.47150 33.71150 14.714 27 -713.33870 3.91320 1.43700 95.1 19.431 28 -102.29770 15.50000 19.683 29 142.61260 8.32860 1.49700 81.6 24.099 30 -85.30870 0.20000 24.359 31 92.28800 6.05900 1.43700 95.1 24.329 32 -1017.34400 0.30000 24.114 33 -517.25140 2.20000 1.80420 46.5 24.111 34 63.18860 2.55010 23.722 35 71.12250 10.90090 1.43700 95.1 24.274 36 -82.81430 0.30000 24.426 37 -77.32640 2.20000 1.80420 46.5 24.425 38 -143.47140 0.50030 24.879 39 128.16160 7.37410 1.43700 95.1 25.212 40 -152.84830 Variable 25.166 41 ∞ 91.00000 1.51680 64.2 22.922 42 ∞ 1.00000 16.681 43 ∞ 1.00000 1.50997 62.2 16.577 44 ∞ 1.00000 16.508 45 ∞ 3.00000 1.50847 61.2 16.404 46 ∞ 1.00000 16.197 Image plane ∞.

[0078] [Table 14] Various data Zoom ratio 1.38831 Wide-angle Mid-range Telephoto Focal length 19.8342 23.3785 27.5361 F-number 2.49954 2.50780 2.52410 Angle of view 39.2331 34.7960 30.5462 Image height 16.0900 16.0900 16.0900 Total lens length 484.5377 464.1321 447.8560 d14 43.5183 23.0869 6.8471 d17 52.4349 36.1299 18.0510 d23 2.0000 15.6459 29.3519 d40 17.5434 20.1981 24.5775 Entrance pupil position 73.6029 73.4177 73.5013 Exit pupil position -1215.5353 -1218.1900 -1222.5694 Front principal point position 93.1134 96.3476 100.4171 Back principal point position 464.5755 440.5757 420.0731

[0079] [Table 15] Single Lens Data Lens Initial Surface Focal Length L1 1 -182.4727 L2 3 153.0151 L3 5 -106.0959 L4 7 -117.2331 L5 9 -127.1396 L6 11 89.2082 L7 13 -114.7424 L8 15 180.8502 L9 18 125.4707 L10 20 -127.4143 L11 22 135.6016 L12 25 -67.9551 L13 27 272.7495 L14 29 108.7209 L15 31 193.9427 L16 33 -69.9016 L17 35 89.4833 L18 37 -211.6995 L19 39 160.8030

[0080] [Table 16] Zoom lens group data Group Initial surface Focal length Lens construction length Front principal point Rear principal point G1 1 -42.89454 111.32140 35.11993 56.69431 G2 15 180.85023 28.11250 1.90412 4.13135 G3 18 134.00366 34.05470 25.73350 29.57071 G4 24 75.06644 97.55800 70.56098 140.84395

[0081] [Table 17] Zoom lens group magnification Group Starting surface Wide angle Mid-range Telephoto G1 1 0.01394 0.01394 0.01394 G2 15 4.69693 3.06862 2.40572 G3 18 -0.21045 -0.41112 -0.71284 G4 24 0.46850 0.43273 0.37496

[0082] [Table 18] Focus data Object distance: 1800mm Surface Wide angle Medium Telephoto 4 1.397 1.347 1.197 40 17.625 20.311 24.734 Object distance: 20000mm Surface Wide angle Medium Telephoto 4 2.097 2.247 2.347 40 17.436 20.049 24.371

[0083] Tables 25 to 30 below show the corresponding values ​​and lens elements for each condition in each numerical example.

[0084] [Table 25]

[0085] [Table 26]

[0086] [Table 27]

[0087] [Table 28]

[0088] [Table 29]

[0089] [Table 30]

[0090] Table 31 below shows the values ​​of the variables for each condition in each numerical example.

[0091] [Table 31]

[0092] f1: focal length of the first lens group; f2: focal length of the second lens group; f3: focal length of the third lens group; f4: focal length of the fourth lens group; fw: focal length of the entire optical system at the wide-angle end; BFW: air-equivalent back focus at the wide-angle end

[0093] Table 32 below shows the glass materials used in each example.

[0094] [Table 32]

[0095] (Embodiment 2) Hereinafter, embodiment 2 of the present disclosure will be described with reference to FIG. 16 . FIG. 16 is a block diagram showing an example of an image projection device according to the present disclosure. The image projection device 100 includes the optical system 1 disclosed in embodiment 1, an image forming element 101, a light source 102, a control unit 110, and the like. The image forming element 101 is configured with a liquid crystal display (LCD), a DMD, or the like, and generates an image to be projected onto the screen SR via the optical system 1. The light source 102 is configured with an LED (light-emitting diode), a laser, or the like, and supplies light to the image forming element 101. The control unit 110 is configured with a CPU or MPU, and controls the entire device and each component. The optical system 1 may be configured as an interchangeable lens that can be detachably attached to the image projection device 100. In this case, the image projection device 100 from which the optical system 1 has been removed is an example of a main body device.

[0096] The image projection device 100 described above uses the optical system 1 according to the first embodiment to achieve a relatively long back focus despite being a wide-angle zoom, ensure telecentricity, and reduce distortion fluctuations. Furthermore, the device can be made smaller and lighter.

[0097] (Embodiment 3) Hereinafter, embodiment 3 of the present disclosure will be described with reference to FIG. 17 . FIG. 17 is a block diagram showing an example of an imaging device according to the present disclosure. The imaging device 200 includes the optical system 1 disclosed in embodiment 1, an imaging element 201, a control unit 210, and the like. The imaging element 201 is configured as a CCD (charge-coupled device) image sensor, a CMOS image sensor, or the like, and receives an optical image of an object OBJ formed by the optical system 1 and converts it into an electrical image signal. The control unit 210 is configured as a CPU or MPU, or the like, and controls the entire device and each component. The optical system 1 may be configured as an interchangeable lens that can be detachably attached to the imaging device 200. In this case, the imaging device 200 from which the optical system 1 has been removed is an example of a main body device.

[0098] The imaging device 200 described above uses the optical system 1 according to embodiment 1 to achieve a relatively long back focus despite being a wide-angle zoom, ensure telecentricity, and reduce distortion fluctuations. Furthermore, the device can be made smaller and lighter.

[0099] As described above, the embodiments have been described as disclosure of the technology in the present disclosure, and the accompanying drawings and detailed description have been provided for this purpose.

[0100] Therefore, the components shown in the accompanying drawings and detailed description may include not only essential components for solving the problem, but also components that are not essential for solving the problem in order to illustrate the above technology. Therefore, the fact that these non-essential components are shown in the accompanying drawings or detailed description should not be interpreted as immediately indicating that these non-essential components are essential.

[0101] Furthermore, since the above-described embodiments are intended to illustrate the technology of the present disclosure, various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

[0102] The present disclosure is applicable to image projection devices such as projectors and head-up displays, as well as imaging devices such as digital still cameras, digital video cameras, surveillance cameras in surveillance systems, web cameras, and in-vehicle cameras. In particular, the present disclosure is applicable to optical systems that require high image quality, such as projectors, digital still camera systems, and digital video camera systems.

[0103] 1 Optical system 100 Image projection device 101 Image forming element 102 Light source 110 Control unit 200 Imaging device 201 Imaging element 210 Control unit A1, A2 Aperture G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group L1 to L20 Lens element OBJ Object P1 to P3 Optical element S Original image SR Screen

Claims

1. An optical system comprising, arranged in order from the enlargement side to the reduction side, a first lens group having negative power, a second lens group having positive power, a third lens group having positive power, and a fourth lens group having positive power, wherein the distances between the first lens group and the second lens group, the distances between the second lens group and the third lens group, and the distances between the third lens group and the fourth lens group change when zooming from the wide-angle end to the telephoto end, and which satisfies the following condition (1): G2P<G3P<G4P (1) where, G2P: power of the second lens group G3P: power of the third lens group G4P: power of the fourth lens group.

2. The optical system according to claim 1, wherein the second lens group is fixed during the zooming.

3. The optical system according to claim 1 or 2, wherein the first lens element from the magnification side has a negative meniscus shape convex toward the object side, and the second lens element from the magnification side is a positive lens element.

4. The optical system according to claim 2, further comprising a diaphragm disposed between the second lens group and the third lens group.

5. The optical system according to any one of claims 1 to 4, wherein the fourth lens group has at least five positive lens elements, and the at least five positive lens elements satisfy the following condition (2): dn / dt < -4 x 10^(-6) [ / K] (2), where dn / dt is the relative refractive index temperature coefficient of the positive lens element at the d-line at room temperature.

6. The optical system according to any one of claims 1 to 5, which satisfies the following conditions (3) to (5): 6<f2 / fw<12 (3) 4<f3 / fw<10 (4) 2<f4 / fw<5 (5) where, f2: focal length of the second lens group, f3: focal length of the third lens group, f4: focal length of the fourth lens group, and fw: focal length of the entire optical system at the wide-angle end.

7. The optical system according to any one of claims 1 to 6, wherein a third lens element third from the magnification side is a negative lens element, the refractive index of the negative lens element is 2 or more, and the refractive index of all lens elements other than the third lens element is less than 2.

8. The optical system according to any one of claims 1 to 7, wherein the second lens group is composed of one positive lens element, and the positive lens element satisfies the following condition (6): dn / dt < -3.5 x 10^(-6) [ / K] (6), where dn / dt is the relative refractive index temperature coefficient of the positive lens element at the d-line at room temperature.

9. The optical system according to claim 3, wherein the optical system is configured to correct field curvature by moving the first lens element and the second lens element in the optical axis direction.

10. The optical system according to any one of claims 1 to 9, wherein, when zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group narrows, the distance between the second lens group and the third lens group narrows, and the distance between the third lens group and the fourth lens group widens.

11. The optical system according to any one of claims 1 to 10, which satisfies the following condition (7): BFW / fw>4 (7) where, BFW: air-equivalent back focus at the wide-angle end, fw: focal length of the entire optical system at the wide-angle end.

12. The optical system according to any one of claims 1 to 11, wherein all of the lens elements in the first to fourth lens groups are spherical lenses.

13. An image projection device comprising: an optical system according to any one of claims 1 to 12; and an image forming element that generates an image to be projected onto a screen via said optical system.

14. An imaging device comprising: an optical system according to any one of claims 1 to 12; and an imaging element that receives an optical image formed by said optical system and converts it into an electrical image signal.

Images