Lens system and imaging device

Abstract

To provide a zoom lens with which it is possible to image a compact and bright clear image.SOLUTION: A lens system 10 comprises, arranged in order from the enlargement side: a first lens group having negative refractive power and fixed in place when zooming; a second lens group having positive refractive power and movable when zooming; a third lens group provided with a diaphragm on the enlargement side and movable when zooming; a fourth lens group movable when zooming; a fifth lens group movable when zooming; and a sixth lens group having positive refractive power and fixed in place when zooming. At a wide angle end, a front group of wide angle end having negative refractive power is constituted by the first lens group, and a rear group of wide angle end having positive refractive power is constituted by the second to sixth lens groups. At a telephone end, a front group of telephoto end having positive refractive power is constituted by the first and second lens groups, an intermediate group having negative refractive power is constituted by the third to fifth lens groups, and a rear group of telephoto end having positive refractive power is constituted by the sixth lens group.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a lens system and an imaging device having the same. [Background technology]

[0002] Patent Document 1 describes a zoom lens suitable for liquid crystal projectors with a wide angle of view and a long back focus, which has good optical performance over the entire screen, corrects various aberrations associated with zooming while miniaturizing the entire lens system, and has good optical performance over the entire screen. The zoom lens includes, in order from the screen side to the liquid crystal panel side, a first lens group with negative refractive power that is stationary for zooming, a second lens group with positive refractive power, a third lens group with negative refractive power, a fourth lens group with negative or positive refractive power, a fifth lens group with negative refractive power, and a sixth lens group with positive refractive power that is stationary for zooming, and describes that the focal length of the first lens group, the air-equivalent back focus, and the focal length of the entire system at the wide-angle end satisfy certain conditions.

[0003] Patent Document 2 describes the provision of a small, lightweight wide-angle zoom lens with a small F-number (brightness), and an imaging device having the same. The zoom lens includes, in order from the object side to the image side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, a fourth lens group having positive refractive power, a fifth lens group having negative refractive power, and a sixth lens group having positive refractive power, and is configured such that the intervals between adjacent lens groups among the first, second, third, fourth, fifth, and sixth lens groups change during zooming, the first lens group does not move during zooming, the first lens group has a negative lens closest to the object, and the position difference between the second lens group in the optical axis direction between the wide-angle end and the telephoto end and the position difference between the fourth lens group in the optical axis direction between the wide-angle end and the telephoto end satisfy a predetermined condition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-62226 A [Patent Document 2] JP 2017-78771 A Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for a lens system that is compact in size for weight reduction and capable of capturing or projecting highly accurate images over the entire zoom range. [Means for solving the problem]

[0006] One aspect of the present invention is a lens system that includes, in order from the magnification side, a first lens group with negative refractive power that is fixed during zooming, a second lens group with positive refractive power that moves during zooming, a third lens group with an aperture on the magnification side that moves during zooming, a fourth lens group that moves during zooming, a fifth lens group that moves during zooming, and a sixth lens group with positive refractive power that is fixed during zooming. In this lens system, at the wide-angle end, the first lens group constitutes a front group at the wide-angle end with negative refractive power, and the second lens group, the third lens group, the fourth lens group, the fifth lens group, and the sixth lens group constitute a rear group at the wide-angle end with positive refractive power. At the telephoto end, the first lens group and the second lens group form a telephoto end front group with positive refractive power, the third lens group, the fourth lens group and the fifth lens group form an intermediate group with negative refractive power, and the sixth lens group forms a telephoto end rear group with positive refractive power.

[0007] This lens system has six lens groups, and at the wide-angle end, the second, third, fourth, fifth and sixth lens groups form a rear group with positive refractive power, and the first lens group forms a front group with negative refractive power. Therefore, as a whole, it is a two-group retrofocus type with negative-positive from the magnification side, and a lens system with a large angle of view can be provided. Furthermore, by arranging the rear group, which has a small variation in the diameter of the light beam, so that the five lens groups from the second to sixth can be regarded as one lens group, the air space between these lens groups can act as an air lens. Therefore, it is possible to provide a lens system that can significantly improve the aberration correction ability of the rear group, can satisfactorily correct aberrations generated by the wide-angle front group, and can capture or project high-precision images at a wide angle with a compact configuration.

[0008] On the other hand, at the telephoto end, the first and second lens groups form a positive front group, the third to fifth lens groups form a negative intermediate group, and the sixth lens group forms a positive rear group, so that overall, from the magnification side, it has a three-group configuration of positive-negative-positive. In this type, the magnification side is a telephoto type suitable for positive-negative telephoto, and the reduction side is a negative-positive retrofocus type. By strengthening the retrofocus property, the performance fluctuation due to the power arrangement changing to the telephoto type in which the back focus is long relative to the focal length can be appropriately corrected. Furthermore, by arranging the first and second lens groups close enough to be considered as one lens group, the air space between those lens groups can act as an air lens, and the aberration correction ability of the front group can be improved. At the same time, by moving the second lens group close to the first lens group, the distance at which the intermediate group consisting of the third to fifth lens groups can be deployed can be secured. Therefore, it is possible to provide a lens system that can capture or project high-precision images with a compact configuration even at the telephoto end.

[0009] Another aspect of the present invention is a projector having the lens system and an image forming device arranged on the conjugate plane of the reduction side. Another aspect of the present invention is an imaging device having the lens system and an image sensor arranged on the conjugate plane of the reduction side. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a lens system and an imaging apparatus. [Diagram 2] FIG. [Diagram 3] FIG. [Figure 4] FIG. 4 is a diagram showing various numerical values ​​at the wide-angle end and the telephoto end. [Diagram 5] 4A to 4C are diagrams showing various aberrations at the wide-angle end and the telephoto end. [Figure 6] FIG. 4 is a diagram showing lateral aberration at the wide-angle end. [Figure 7] FIG. 4 is a diagram showing lateral aberration at the telephoto end. [Figure 8] 1A and 1B are diagrams showing schematic configurations of different lens systems and cameras. [Figure 9] FIG. [Figure 10] FIG. [Figure 11] FIG. 4 is a diagram showing various numerical values ​​at the wide-angle end and the telephoto end. [Figure 12] 4A to 4C are diagrams showing various aberrations at the wide-angle end and the telephoto end. [Figure 13] FIG. 4 is a diagram showing lateral aberration at the wide-angle end. [Figure 14] FIG. 4 is a diagram showing lateral aberration at the telephoto end. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be further described with reference to the drawings. FIG. 1 shows an apparatus including a lens system according to an embodiment of the present invention. An example of the apparatus is an imaging apparatus (photographing apparatus, camera) 1, which has a lens system 10 and an imaging apparatus 5 arranged on a reduction side 2. The imaging apparatus 1 has a lens system 10 and an imaging element (CCD, CMOS) 5 arranged on a conjugate plane of the reduction side (image surface side) 2, and forms an image of light incident from an enlargement side (object side) 3 on the imaging element 5. Another example of an apparatus including the lens system 10 is a projector, which has an image forming device (light modulator, light valve) 8, such as a liquid crystal panel or a digital mirror device, arranged on a conjugate plane of the reduction side 2. The projector projects an image formed on the display surface of the image forming device 8 onto a screen, wall (not shown), or the like on an enlargement side (projection side) 3. The lens system 10 has the same configuration and function whether it is a lens system for an imaging apparatus or a lens system for a projector, so that hereinafter, the imaging apparatus 1 and the lens system 10 for imaging (photography) will be further described as examples.

[0012] Fig. 1(a) shows the lens arrangement of lens system 10 at the wide-angle end, and Fig. 1(b) shows the lens arrangement of lens system 10 at the telephoto end. This imaging device (camera) 1 has an optical system (imaging optical system, image-forming optical system, shooting system, lens system) 10 and an imaging element 5 arranged on the reduction side (image surface side) 2 of the optical system 10. The optical system 10 is a zoom lens system 10, and is a lens system consisting of 21 elements in 6 groups. Specifically, lens system 10 includes, arranged in order from the enlargement side (object side) 3, a first lens group G1 with negative refractive power that is fixed (does not move) during zooming, a second lens group G2 with positive refractive power that moves during zooming, a third lens group G3 that has an aperture st on the enlargement side 3 and moves during zooming, a fourth lens group G4 that moves during zooming, a fifth lens group G5 that moves during zooming, and a sixth lens group G6 with positive refractive power that is fixed (does not move) during zooming.

[0013] The lens groups G2 to G5 that move during zooming move so that, at the wide-angle end shown in Fig. 1(a), the first lens group G1 constitutes a front group Gwf at the wide-angle end, and the second lens group G2, the third lens group G3, the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6 constitute a rear group Gwe at the wide-angle end with positive refractive power. Also, at the telephoto end shown in Fig. 1(b), the lens groups G2 to G5 move so that the first lens group G1 and the second lens group G2 constitute a front group Gtf at the telephoto end with positive refractive power, the third lens group G3, the fourth lens group G4, and the fifth lens group G5 constitute a middle group Gtm with negative refractive power, and the sixth lens group G6 constitutes a rear group Gte at the telephoto end with positive refractive power.

[0014] The first lens group G1 includes a first sub-lens group G11 with negative refractive power that is fixed (does not move) during focusing, a second sub-lens group G12 with negative refractive power that moves during focusing, and a third sub-lens group G13 with positive refractive power that moves during focusing, which are arranged in order from the enlargement side 3. Therefore, the lens L11 on the most enlargement side 3 and the lens L61 on the most reduction side 2 of this lens system 10 do not move during zooming and focusing. For this reason, the total length La of the lens system 10 from the surface S1 on the enlargement side 3 of the lens L11 on the most enlargement side 3 to the surface S37 on the reduction side 2 of the lens L61 on the most reduction side 2 is fixed, resulting in a lens system 10 with a constant length.

[0015] 2 shows data for each lens that constitutes the lens system 10. The radius of curvature r is the radius of curvature (mm) of each surface S of each lens arranged in order from the magnification side 3, the surface spacing D is the distance (mm) between each lens surface, the effective diameter d is the effective diameter (diameter, mm) of each lens surface, the refractive index (n) is the refractive index (d line) of each lens, and the Abbe number (ν) is the Abbe number (d line) of each lens. The same applies below.

[0016] Fig. 3 shows the coefficients of aspheric surfaces included in the lens system 10. In this example, the surface S1 on the most enlargement side 3 of the first lens group G1 and the surface S37 on the most reduction side of the sixth lens group G6 are aspheric. The aspheric surface is expressed by the following formula (X) using the coefficients K, A, B, C, and D shown in Fig. 3, where X is the coordinate in the optical axis direction, Y is the coordinate perpendicular to the optical axis, the light traveling direction is positive, and r is the paraxial radius of curvature. The same applies to the following embodiments. Note that "en" means "10 to the nth power." X=(1 / r)Y 2 / [1+{1-(1+K)(1 / r) 2 Y 2} 1 / 2 ] +AY 4 +BY 6 +CY 8 +DY 10 (X)

[0017] FIG. 4 shows the change in the variable intervals D4, D9, D13, D20, D26, D32 and D35, and the diameter ds of the aperture st when the distance to the object is infinity (INF) and the minimum distance (413 mm) at the wide-angle end (Wide) and the telephoto end (Tele), respectively, of the lens system 10.

[0018] In the lens system 10, at the wide-angle end shown in Fig. 1(a), the first lens group G1 constitutes a front group Gwf at the wide-angle end, and the second lens group G2, the third lens group G3, the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6 constitute a rear group Gwe at the wide-angle end with positive refractive power. At the telephoto end shown in Fig. 1(b), the first lens group G1 and the second lens group G2 constitute a front group Gtf at the telephoto end with positive refractive power, the third lens group G3, the fourth lens group G4, and the fifth lens group G5 constitute an intermediate group Gtm with negative refractive power, and the sixth lens group G6 moves to constitute a rear group Gte at the telephoto end with positive refractive power.

[0019] Therefore, the distance Dg12w (the value of the distance D13 at the wide-angle end) at the wide-angle end 3 between the surface S13 on the reduction side 2 of the lens L17 at the most reduction side 2 of the first lens group G1 and the surface S14 on the enlargement side 3 of the lens L21 at the most enlargement side 3 of the second lens group G2 and the distance Dg12t (the value of the distance D13 at the telephoto end) at the telephoto end are: a distance Dg23w (a value at the wide-angle end including the distance D20 and the distance of the aperture st) between a surface S20 on the reduction side 2 of the lens L24 on the most reduction side 2 of the second lens group G2 and a surface S22 on the enlargement side 3 of the lens L31 on the most enlargement side 3 of the third lens group G3 at the wide-angle end, and a distance Dg23t (a value at the telephoto end including the distance D20 and the distance of the aperture st) at the telephoto end, a distance Dg34w (the value of the distance D26 at the wide-angle end) between a surface S26 on the reduction side 2 of the lens (cemented lens in this example) B31 on the most reduction side 2 of the third lens group G3 and a surface S27 on the enlargement side 3 of the lens (cemented lens in this example) B41 on the most enlargement side 3 of the fourth lens group G4, a distance Dg45w (the value of the distance D32 at the wide-angle end) between a surface S32 on the reduction side 2 of the lens (cemented lens in this example) B42 at the most reduction side 2 of the fourth lens group G4 and a surface S33 on the enlargement side 3 of the lens (cemented lens in this example) B51 at the most enlargement side 3 of the fifth lens group G5, Focusing on the distance Dg56w (the value of distance D35 at the wide-angle end) and the distance Dg56t (the value of distance D35 at the telephoto end) at the telephoto end between the surface S35 on the reduction side 2 of the lens (cemented lens in this example) B51 on the most reduction side 2 of the fifth lens group G5 and the surface S36 on the enlargement side 3 of the lens L61 on the most enlargement side 3 of the sixth lens group G6, the following conditions (1) to (8) may be satisfied between these distances and the thicknesses of the lenses before and after these distances (on the enlargement side and reduction side). 2.5 <Dg12w / ((Ltg1r+Ltg2f) / 2)<15 ···(1) 0 <Dg12t / ((Ltg1r+Ltg2f) / 2)<1.5···(2) 0 <Dg23w / ((Ltg2r+Ltg3f) / 2)<1.5···(3) 2.5 <Dg23t / ((Ltg2r+Ltg3f) / 2)<15 ···(4) 0 <Dg34w / ((Ltg3r+Ltg4f) / 2)<1.5···(5) 0 <Dg45w / ((Ltg4r+Ltg5f) / 2)<1.5···(6) 0 <Dg56w / ((Ltg5r+Ltg6f) / 2)<1.5···(7) 2.5 <Dg56t / ((Ltg5r+Ltg6f) / 2)<15 ···(8)

[0020] However, the lens thickness includes the thickness of the cemented lens. The lens thickness Ltg1r at the most reduction side 2 of the first lens group G1 corresponds to the thickness D12 of the lens L17, the lens thickness Ltg2f at the most enlargement side 3 of the second lens group G2 corresponds to the thickness D14 of the lens L21, the lens thickness Ltg2r at the most reduction side 2 of the second lens group G2 corresponds to the thickness D19 of the lens L24, the lens thickness Ltg3f at the most enlargement side 3 of the third lens group G3 corresponds to the thickness D22 of the lens L31, the lens thickness Ltg3r at the most reduction side 2 of the third lens group G3 corresponds to the thickness (D24+D25) of the cemented lens B31, and the lens thickness Ltg3f at the most enlargement side 3 of the third lens group G3 corresponds to the thickness D22 of the lens L31. The lens thickness Ltg4f on the large side 3 corresponds to the thickness (D27+D28) of the cemented lens B41, the lens thickness Ltg4r on the most reduction side 2 of the fourth lens group G4 corresponds to the thickness (D30+D31) of the cemented lens B42, the lens thickness Ltg5f on the most enlargement side 3 of the fifth lens group G5 corresponds to the thickness (D33+D34) of the cemented lens B51, the lens thickness Ltg5r on the most reduction side 2 of the fifth lens group G5 corresponds to the thickness (D33+D34) of the cemented lens B51, and the lens thickness Ltg6f on the most enlargement side 3 of the sixth lens group G6 corresponds to the thickness D36 of the lens L61.

[0021] When adjacent lens groups function as one lens group, the distance Dg between adjacent lenses in the adjacent lens groups may be such that the diameter of the light beam does not change significantly and the lens groups function as air lenses, that is, the distance Dg may be 1.5 times or less the average thickness of the front and rear lenses. On the other hand, when adjacent lens groups function as different lens groups, the distance Dg between adjacent lenses in the adjacent lens groups may be 2.5 times or more the average thickness of the front and rear lenses.

[0022] This lens system 10 includes six lens groups G1 to G6 arranged along an optical axis 15 with a negative-positive-negative-negative-negative-positive power configuration, and at the wide-angle end, the second, third, fourth, fifth and sixth lens groups G2 to G6 form a rear group Gwe with positive refractive power, and the first lens group G1 forms a front group Gwf with negative refractive power. Therefore, as a whole, the lens system is a negative-positive two-group retrofocus type from the enlargement side 3, and can provide a lens system with a large angle of view at the wide-angle end. Furthermore, by arranging the rear group Gwe, which has a small variation in the diameter of the light beam, close to the second to sixth lens groups G2 to G6, i.e., five lens groups, so that they can be regarded as one lens group, the air gap between these lens groups can act as an air lens. Therefore, the aberration correction capability of the rear group Gwe can be significantly improved, and the aberration generated by the wide-angle front group Gwf can be effectively corrected, thereby providing a lens system 10 with a compact configuration that can capture (photograph) or project wide-angle, high-precision images.

[0023] On the other hand, at the telephoto end, the first lens group G1 and the second lens group G2 form a positive front group Gtf, the third lens group G3, the fourth lens group G4, and the fifth lens group G5 form a negative middle group Gtm, and the sixth lens group G6 forms a positive rear group Gte. By changing (displacing) to this configuration, the lens system 10 becomes a three-group system of positive-negative-positive as a whole at the telephoto end from the enlargement side 3, the enlargement side becomes a telephoto type suitable for positive-negative telephoto, and the reduction side 2 becomes a negative-positive retrofocus type. Therefore, the enlargement side 3 has a configuration suitable for the telephoto end, while the optical performance such as the back focus that has changed on the enlargement side from the aperture can be appropriately corrected by strengthening the retrofocus property of the reduction side 2 to prevent the performance from varying due to the power arrangement changing to a telephoto type in which the back focus is longer relative to the focal length.

[0024] Furthermore, by arranging the first lens group G1 and the second lens group G2 close enough to be regarded as one lens group Gtf, the air gap between these lens groups can be made to act as an air lens, improving the aberration correction ability of the front group. At the same time, by moving the second lens group G2 close to the first lens group G1, a distance can be secured that allows the middle group Gtm consisting of the third to fifth lens groups to be deployed. Therefore, a lens system that can capture or project high-precision images with a compact configuration can be provided even at the telephoto end.

[0025] As shown in FIG. 1, in the lens system 10, at the telephoto end, the third lens group G3 and the fourth lens group G4 may form a first intermediate group Gtm1, and the fifth lens group G5 may form a second intermediate group Gtm2. At the telephoto end, the second lens group G2 and the first lens group G1 form the front group Gtf. Therefore, even in the compact lens system 10, a relatively wide space can be secured between the front group Gtf and the rear group Gte. Therefore, it is possible to dispose the fifth lens group G5 in the intermediate lens group Gtm at a distance from the other lens groups, and the aberration correction ability of the intermediate lens group Gtm can be further improved.

[0026] Therefore, the distance Dg34t (the value of the distance D26 at the telephoto end) between the surface S26 on the reduction side 2 of the lens B31 at the most reduction side 2 of the third lens group G3 and the surface S7 on the enlargement side 3 of the lens B41 at the most enlargement side 3 of the fourth lens group G4, and the distance Dg45t (the value of the distance D32 at the telephoto end) between the surface S32 on the reduction side 2 of the lens B42 at the most reduction side 2 of the fourth lens group G4 and the surface S33 on the enlargement side 3 of the lens B51 at the most enlargement side 3 of the fifth lens group G5 may satisfy the following conditions (9) and (10). 0 <Dg34t / ((Ltg3r+Ltg4f) / 2)<1.5 ···(9) 1.0 <Dg45t / ((Ltg4r+Ltg5f) / 2)<2.5···(10)

[0027] The lower limits of conditions (1), (4), and (8) may be 2.0, and the lower limit of condition (10) may be 2.0 and the upper limit may be 3.0 or 5.0, and this lens system 10 may be composed of a positive front group Gtf, a negative first intermediate group Gtm1, a negative second intermediate group Gtm2, and a positive rear group Gte at the telephoto end.

[0028] When zooming from the wide-angle end to the telephoto end, the second lens group G2 moves to the enlargement side 3, and the amount of movement MDg2 and the refractive power fg2 of the second lens group may satisfy the following condition (11). 1.2<|MDg2| / fg2<1.6 (11) If the movement distance is too short for the power of the second lens group G2, it will be impossible to ensure the distance over which the intermediate group Gtm consisting of the third lens group G3, the fourth lens group G4, and the fifth lens group G5 can expand to perform sufficient aberration correction, and if the movement distance is too large, it will be difficult to realize a compact lens system 10.

[0029] Furthermore, the movement amount MDg2 of the second lens group G2, the movement amount MDg3 of the third lens group G3, and the movement amount MDg5 of the fifth lens group G5 during zooming may satisfy the following condition (12). 1.3 <MDg5 / (MDg2-MDg3)<2.8···(12) The intermediate group Gtm, which is a moving group on the reduction side (image surface side) 2 of the second lens group G2, includes multiple negative groups, all of which are arranged adjacent to each other, and corrects the curvature of field that occurs in the second lens group G2, which is a positive variable magnification group, during zooming. All of the lens groups that make up the intermediate group Gtm move to the enlargement side (object side) 3, making it possible to accommodate air spacing and shorten the overall optical length. In addition, at the telephoto end, the distance between the intermediate group Gtm and the rear group Gte that make up the retrofocus type can be secured to be greater than the distance between the front group Gtf and the intermediate group Gtm that make up the telephoto type, and the fluctuation in back focus due to the configuration of the telephoto type on the enlargement side 3 can be more efficiently corrected by the retrofocus type on the reduction side 2.

[0030] The focal length fg2 of the second lens group G2, the focal length fg3 of the third lens group G3, the focal length fg4 of the fourth lens group G4, the focal length fg5 of the fifth lens group G5, a composite focal length fg345w of the third lens group G3, the fourth lens group G4, and the fifth lens group G5 at the wide-angle end, and a composite focal length fg345t of the third lens group G3, the fourth lens group G4, and the fifth lens group G5 at the telephoto end (the composite focal length of the middle group Gtm) may satisfy the following conditions (13) to (17). 0.02<|fg2 / fg3|<0.5 ...(13) 0.02<|fg2 / fg4|<0.5 ...(14) 0.02<|fg2 / fg5|<0.5 ...(15) 0.5<|fg2 / fg345w|<0.8···(16) 0.5<|fg2 / fg345t|<0.8···(17) The lens groups G3, G4, and G5 constituting the intermediate group Gtm may have a power sufficiently small relative to the power of the second lens group G2, while the composite focal length may be sufficiently close to that of the second lens group G2. By ensuring a certain degree of power of the intermediate group Gtm at both the wide-angle end and the telephoto end relative to the power of the second lens group G2, it is possible to ensure aberration correction capability in both telephoto and retrofocus configurations. Furthermore, by making the power of each of the lens groups G3, G4, and G5 constituting the intermediate group Gtm sufficiently small, it is possible to suppress the effect on aberration correction capability due to the difference in position when deployed as the intermediate group Gtm, and it is possible to provide a compact lens system 10 with stable aberration correction capability.

[0031] The focal length fg2 of the second lens group G2, the focal length fg3 of the third lens group G3, the focal length fg4 of the fourth lens group G4, and the focal length fg5 of the fifth lens group G5 may satisfy the following condition (18). |fg2|<|fg3|<|fg4|<|fg5|···(18) In particular, in the lens system 10 for imaging, by decreasing the power toward the reduction side 2, which is the image-forming side, it becomes easier to correct aberrations more finely, and it is possible to provide a lens system 10 that can obtain a clear image.

[0032] The first lens group G1 on the most enlargement side 3 of this lens system 10 has negative power as a whole and does not move during zooming, and functions as a three-group configuration during focusing, and includes a first sub-lens group G11 with negative refractive power fixed on the most enlargement side 3 that does not move during focusing, arranged in order from the enlargement side 3, a second sub-lens group G12 with negative refractive power that moves during focusing, and a third sub-lens group G13 with positive refractive power that moves during focusing. As shown in FIG. 4, when focusing (when in focus) when the distance to the object is changed from the closest (413 mm) to infinity, the sub-lens group G12 with negative power moves to the enlargement side 3, and the sub-lens group G13 with positive power moves to the reduction side 2. When focusing, the lens groups G12 and G13 with powers of different signs are moved to opposite sides, thereby increasing the effect of the movement and reducing the amount of movement. Moreover, by moving the lens groups G12 and G13, which have different signs, the power of these two groups as a whole can be kept small.

[0033] Furthermore, by moving the two lens groups G12 and G13 with different power signs in different directions during focusing, the fluctuation of the composite focal length caused by them can be suppressed to a small extent, and focus breathing can be reduced. Since the two lens groups G12 and G13 with different power signs are moved in different directions during focusing, the lens groups G12 and G13 can be set to have large power as focusing lens groups, and aberrations can be corrected well even if the moving distance of the lens groups is short. This contributes to the miniaturization of the entire lens system 10. In this example, the arrangement of the negative lens group G12 and the positive lens group G13 from the enlargement side 3 is adopted, and spherical aberration in particular can be corrected well.

[0034] On the other hand, the first sub-lens group G11 arranged on the most enlargement side 3, which requires the most power for wide-angle focusing, is not moved even during focusing, thereby suppressing large fluctuations in power and large fluctuations in aberration, and making it possible to correct aberration fluctuations during focusing. Also, by arranging sub-lens groups G12 and G13, which do not move during zooming but move during focusing, in the lens group G1 on the most enlargement side 3, it is possible to arrange the focusing drive mechanism 51 and the zooming drive mechanism 52 separately, as shown in Figure 1. This simplifies the overall configuration of the lens system 10, contributing to the miniaturization of the entire lens system 10.

[0035] The focal length f11 of the first sub-lens group G11, the focal length f12 of the second sub-lens group G12, and the focal length f13 of the third sub-lens group G13 may satisfy the following conditions (19) and (20). 0.6<|f12| / |f13|<0.9 (19) 0.1<|f11| / (|f12|+|f13|)<0.25···(20) The powers of the lens groups G12 and G13 that move during focusing may be close to each other, while the power of the negative lens group G12 may be greater than the power of the lens group G13 with positive refractive power so that the entire lens group G1 performs as the first lens group G1 with negative refractive power. Furthermore, the power of the lens group G11 on the most enlargement side that functions at the wide-angle end may be sufficiently greater than the average of the powers of the lens groups G12 and G13 that move during focusing.

[0036] A diameter dsw of the aperture st at the wide-angle end and a diameter dst of the aperture st at the telephoto end may satisfy the following condition (21). 0.5 <dsw / dst<0.8···(21) In this lens system 10, when zooming from the wide-angle end to the telephoto end, the aperture st always moves to the enlargement side (object side) 3 together with the third lens group G3. By moving the position of the aperture st, the movement amount of the moving groups G3, G4, and G5 of the intermediate group Gtm can be secured. Also, it is possible to appropriately respond to the change in the angle of the light ray caused by the movement of the second lens group G2. Furthermore, when zooming from the wide-angle end to the telephoto end, the aperture st always moves in one direction (the enlargement side 3) without moving even temporarily to the reduction side 2, which simplifies the mechanical configuration of the zoom mechanism 52 that moves the lens groups.

[0037] Furthermore, as shown in condition (21), when changing magnification from the wide-angle end to the telephoto end, the aperture diameter ds of the aperture st may gradually increase according to the position (or amount of movement) along the optical axis 15. By increasing the amount of light taken in on the telephoto side, it is possible to keep brightness constant over the entire range of magnification. In this example, the zoom drive mechanism 52 includes a mechanism 52s that changes the aperture diameter ds of the aperture st in response to zooming, and the aperture diameter ds of the aperture st is controlled in synchronization with the movement of the lens groups G2 to G5 during zooming.

[0038] The total length La of the lens system 10 and the effective diameter dL11 of the lens L11 on the most enlargement side 3 may satisfy the following condition (22). 2.0 <La / dL11<3.5···(22) It is possible to provide a zoom lens system 10 that has a compact configuration in which the distance (total length) La from the surface S1 on the enlargement side 3 of the lens L11 at the most enlargement side 3 to the surface S37 on the reduction side 2 of the lens (L61 in this example) at the most reduction side 2 is less than three times the effective diameter dL11 of the lens L11 that has the largest effective diameter at the most enlargement side 3, and that can obtain a clear image with a zoom ratio of about 3 or more. The lower limit of condition (22) may be 2.5, and the upper limit may be 3.0.

[0039] More specifically, in the lens system 10 shown in FIG. 1, the first lens group G1, which is arranged on the most enlargement side 3 and has a negative power as a whole, is composed of, in order from the enlargement side 3, a first sub-lens group G11 with a negative power, a second sub-lens group G12 with a negative power, and a third sub-lens group G13 with a positive power. The first sub-lens group G11 is composed of two negative-negative lenses arranged in order from the enlargement side 3, and includes negative meniscus lenses L11 and L12 that are convex on the enlargement side 3. The second sub-lens group G12 is composed of three negative-positive-negative lenses arranged in order from the enlargement side 3, and includes a negative meniscus lens L13 that is convex on the enlargement side 3, a biconvex positive lens L14, and a negative meniscus lens L15 that is convex on the reduction side 2. The two lenses L13 and L14 on the enlargement side 3 form a biconvex cemented lens B11. The third sub-lens group G13 is made up of two lenses, a positive and a negative lens, arranged in that order from the magnification side 3, and includes a biconvex positive lens L16 and a negative meniscus lens L17 that is convex toward the magnification side 3. The second sub-lens group G12 moves to the magnification side 3 when focusing from infinity to the closest distance, and the third sub-lens group G13 moves to the reduction side 2. The magnification-side surface S1 of the lens L11 closest to the magnification side 3 is aspheric.

[0040] The second lens group G2, which has positive power overall, is made up of four lenses, positive-negative-positive-positive arranged in that order from the enlargement side 3, and includes a biconvex positive lens L21, a biconcave negative lens L22, a biconvex positive lens L23, and a positive meniscus lens L24 that is convex toward the enlargement side 3. The two lenses L22 and L23 form a negative meniscus type cemented lens B21.

[0041] The third lens group G3, which has negative power overall, includes a stop st on the enlargement side 3 and is made up of three lenses arranged in order: negative-positive-negative, a biconcave negative lens L31, a convex positive meniscus lens L32 on the reduction side 2, and a biconcave negative lens L33. The two lenses L32 and L33 form a biconcave cemented lens B31.

[0042] The fourth lens group G4, which has negative power as a whole, is made up of four lenses, negative-positive-positive-negative, arranged in that order from the enlargement side 3, and includes a biconcave negative lens L41, biconvex positive lenses L42 and L43, and a negative meniscus lens L44 that is convex toward the reduction side 2. The lenses L41 and L42 form a negative-positive cemented lens B41 that is convex toward the reduction side 2, and the lenses L43 and L44 form a positive-negative biconvex cemented lens B42. These cemented lenses B41 and B42 have a symmetrical configuration and are effective for correcting chromatic and spherical aberrations.

[0043] The fifth lens group G5, which has negative power overall, is made up of two lenses, a positive lens and a negative lens, arranged in that order from the magnification side 3, including a biconvex positive lens L51 and a biconcave negative lens L52. These lenses L51 and L52 form a negative meniscus type cemented lens B51 convex toward the magnification side 3.

[0044] The sixth lens group G6 having a positive power as a whole is made up of a single positive lens, and includes a positive meniscus lens L61 convex toward the reduction side 2.

[0045] The various values ​​and conditions of this lens system 10 are as follows. The units of length and diameter are mm. F-number: Wide-angle end (infinity) 2.8, Telephoto end (infinity) 2.8 Angle of view: Wide-angle end: 84.14, Telephoto end: 31.40 Lens system 10 wide-angle focal length fw: 24.03 Telephoto focal length of lens system 10 ft: 74.99 Magnification ratio: 3.12 Total length of lens system 10 (La): 251.8 Focal length fg1 of the first lens group G1 (front group Gwf): -44.72 Focal length f11 of the first sub-lens group G11: -57.97 Focal length f12 of the second sub-lens group G12: -151.30 The focal length of the third sub-lens group G13 is f13: 201.94 Focal length of the second lens group G2 fg2: 48.05 Focal length fg3 of the third lens group G3: -147.91 The focal length of the fourth lens group G4 is fg4: -219.75 The focal length of the fifth lens group G5 (middle group Gtm2) is fg5: -1518.94 Focal length of the sixth lens group G6 fg6: 89.77 Focal length of rear group Gwe (G2-G6) at wide-angle end: 68.64 Focal length of front group Gtf (G1-G2) at telephoto end: 43.65 The focal length of the intermediate group Gtm (G3-G5) at the telephoto end is fg345t: -78.92 Focal length of G3-G5 at wide-angle end fg345w: -78.65 Focal length of the intermediate group Gtm1 (G3-G4) at the telephoto end: -86.05 Condition (1)(Dg12w / ((Ltg1r+Ltg2f) / 2)) (D13 / (D12+D14) / 2) at the wide-angle end: 12.47 Condition (2)(Dg12t / ((Ltg1r+Ltg2f) / 2) (D13 / (D12+D14) / 2) at telephoto end: 0.72 Condition (3)(Dg23w / ((Ltg2r+Ltg3f) / 2)) ((D20+D21) / (D19+D22) / 2) at the wide-angle end: 1.25 Condition (4)(Dg23t / ((Ltg2r+Ltg3f) / 2)) ((D20+D21) / (D19+D22) / 2) at telephoto end: 4.63 Condition (5)(Dg34w / ((Ltg3r+Ltg4f) / 2)) (D26 / (D24+D25+D27+D28) / 2) at the wide-angle end: 0.68 Condition (6)(Dg45w / ((Ltg4r+Ltg5f) / 2)) (D32 / (D30+D31+D33+D34) / 2) at the wide-angle end: 0.26 Condition (7)(Dg56w / ((Ltg5r+Ltg6f) / 2)) (D35 / (D33+D34+D36) / 2) at the wide-angle end: 0.55 Condition (8)(Dg56t / ((Ltg5r+Ltg6f) / 2)) (D35 / (D33+D34+D36) / 2) at telephoto end: 7.35 Condition (9)(Dg34t / ((Ltg3r+Ltg4f) / 2)) (D26 / (D24+D25+D27+D28) / 2) at telephoto end: 0.32 Condition (10) (Dg45t / ((Ltg4r+Ltg5f) / 2)) (D32 / (D30+D31+D33+D34) / 2) at telephoto end: 1.30 Condition (11)(|MDg2| / fg2)(ΔD13 / fg2):1.42 Condition (12)(MDg5 / (MDg2-MDg3))(ΔD35 / ΔD20):2.29 Condition (13)(|fg2 / fg3|):0.32 Condition (14)(|fg2 / fg4|):0.22 Condition(15)(|fg2 / fg5|):0.03 Condition(16)(|fg2 / fg345w|):0.61 Condition (17)(|fg2 / fg345t|):0.61 Condition (18) (|fg2|<|fg3|<|fg4|<|fg5|): satisfied Condition (19)(|f12| / |f13|):0.75 Condition (20)(|f11| / (|f12|+|f13|)):0.16 Condition (21) (dsw / dst): 0.63 Condition (22)(La / dL11):2.66

[0046] Furthermore, FIG. 5(a) shows the longitudinal aberration at the wide-angle end, FIG. 5(b) shows the longitudinal aberration at the telephoto end, FIG. 6 shows the transverse aberration at the wide-angle end, and FIG. 7 shows the transverse aberration at the telephoto end. The spherical aberration is shown for wavelengths of 656.2720 nm (long dashed line), 587.5620 nm (short dashed line), 546.0740 nm (solid line), 486.1330 nm (dotted line), and 435.8340 nm (dotted line). The astigmatism is shown for the tangential ray T and the sagittal ray S. The transverse aberration is shown for the same wavelengths as above for the tangential ray and the sagittal ray.

[0047] As shown in these, lens system 10 shown in FIG. 1 satisfies all of conditions (1) to (22), and is a zoom lens system with 21 elements in 6 groups arranged in a compact manner, with a zoom ratio of about 3x and an F-number that is nearly constant at the telephoto end and the wide-angle end, and is capable of capturing bright, clear images.

[0048] FIG. 8 shows another example of the imaging device 1. This imaging device 1 also includes a lens system 10 and an imaging element 5 arranged on a conjugate plane on the reduction side 2. The imaging device 1 further includes the lens system 10, a mechanism 51 that moves the second sub-lens group G12 and the third sub-lens group G13 of the first lens group G1 to perform focusing, and a mechanism 52 that performs zooming (variable magnification). The zooming mechanism 52 includes a mechanism 52s that controls the diameter ds of the aperture st. As in the example shown in FIG. 1, the lens system 10 may be a lens system for a projector that projects an image of an image generating device 8 arranged on a conjugate plane.

[0049] Fig. 9 shows data for each lens constituting the lens system 10. Fig. 10 shows coefficients of aspheric surfaces included in the lens system 10. In this example, the surface S1 on the enlargement side 3 of the lens L11 on the most enlargement side 3 of the first lens group G1 and the surface 36 on the reduction side 2 of the lens L61 on the reduction side 2 of the sixth lens group G6 are aspheric.

[0050] Fig. 11 shows various values ​​at the wide-angle end and telephoto end of lens system 10, Fig. 12 shows the spherical aberration, astigmatism, and distortion of lens system 10, and Fig. 13 and Fig. 14 show the lateral aberration of lens system 10. Fig. 12(a) and Fig. 13 show the various aberrations at the wide-angle end, and Fig. 12(b) and Fig. 14 show the various aberrations at the telephoto end.

[0051] This lens system 10 also includes 6 groups and 21 lenses L11-L17, L21-L24, L31-L33, L41-L44, L51, L52, and L61 with a negative-positive-negative-negative-negative-positive power arrangement arranged along an optical axis 15. The lens system 10 has a basic configuration in common with the lens system shown in Fig. 1. That is, at the wide-angle end shown in Fig. 8(a), the first lens group G1 constitutes a front group Gwf at the wide-angle end with negative refractive power, and the second lens group G2, the third lens group G3, the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6 constitute a rear group Gwe at the wide-angle end with positive refractive power. At the telephoto end shown in Figure 8(b), the first lens group G1 and the second lens group G2 form a front group Gtf at the telephoto end with positive refractive power, the third lens group G3, the fourth lens group G4 and the fifth lens group G5 form a middle group Gtm with negative refractive power, and the sixth lens group G6 moves to form a rear group Gte at the telephoto end with positive refractive power.

[0052] Therefore, the lens system 10 as a whole becomes a negative-positive two-group retrofocus type from the magnification side 3 at the wide-angle end, and can provide a lens system with a wide angle of view. On the other hand, at the telephoto end, the arrangement becomes a positive-negative-positive three-group arrangement from the magnification side 3, with the magnification side being a positive-negative telephoto type suitable for telephoto, and the reduction side 2 being a negative-positive retrofocus type. Therefore, the magnification side 3 has a configuration suitable for the telephoto end, while the optical performance such as the back focus that has fluctuated on the magnification side from the aperture can be appropriately corrected by strengthening the retrofocus property of the reduction side 2 to prevent performance fluctuation caused by the power arrangement changing to a telephoto type in which the back focus is longer relative to the focal length.

[0053] In this lens system 10, at the telephoto end, the third lens group G3 and the fourth lens group G4 may form a first intermediate group Gtm1, and the fifth lens group G5 may form a second intermediate group Gtm2. Furthermore, when changing magnification from the wide-angle end to the telephoto end, the aperture diameter ds of the diaphragm st may gradually increase depending on the position (or the amount of movement) in the direction of the optical axis 15.

[0054] The first lens group G1 on the most enlargement side 3 of this lens system 10 has negative power as a whole and does not move during zooming, and functions as a three-group configuration during focusing, and includes a first sub-lens group G11 with negative refractive power fixed on the most enlargement side 3 that does not move during focusing, arranged in order from the enlargement side 3, a second sub-lens group G12 with negative refractive power that moves during focusing, and a third sub-lens group G13 with positive refractive power that moves during focusing. When focusing (when in focus) when the distance to the object is changed from the closest (413 mm) to infinity, the sub-lens group G12 with negative power moves to the enlargement side 3, and the sub-lens group G13 with positive power moves to the reduction side 2. When focusing, the lens groups G12 and G13 with powers of different signs are moved to opposite sides, thereby increasing the effect of the movement and reducing the amount of movement.

[0055] In one example of the lens system 10, the first lens group G1 having a negative power as a whole and arranged closest to the enlargement side 3 has a first sub-lens group G11 having a negative power, which is made up of two negative-negative lenses arranged in order from the enlargement side 3, and includes negative meniscus lenses L11 and L12 that are convex on the enlargement side 3. The second sub-lens group G12 having a negative power has a three-element configuration of negative-positive-negative lenses arranged in order from the enlargement side 3, and includes a biconcave negative lens L13, a biconvex positive lens L14, and a negative meniscus lens L15 that is convex on the reduction side 2, and the lenses L13 and L14 form a cemented lens B11. The third sub-lens group G13 has a two-element configuration of positive-negative lenses arranged in order from the enlargement side 3, and includes a biconvex positive lens L16 and a negative meniscus lens L17 that is convex on the enlargement side 3.

[0056] The second lens group G2, which has a positive power as a whole, is made up of four lenses, positive-negative-positive-positive, arranged in that order from the enlargement side 3, and the specific configuration is the same. The third lens group G3, which has a negative power as a whole, includes a stop st on the enlargement side 3, and is made up of three lenses, negative-positive-negative, arranged in that order, including a biconcave negative lens L31, a positive meniscus lens L32 convex on the reduction side 2, and a biconcave negative lens L33, and these three lenses form a biconcave cemented lens B31. This is a lens configuration that is resistant to decentering tolerance.

[0057] The fourth lens group G4, which has negative power overall, is made up of four lenses, negative-positive-positive-negative, arranged in that order from the enlargement side 3, and has a common configuration with the above-mentioned lens system, with lenses L41 and L42 forming a negative-positive cemented lens B41 that is convex on the reduction side 2, and lenses L43 and L44 forming a positive-negative biconvex cemented lens B42. These cemented lenses B41 and B42 have a symmetrical configuration and are effective for correcting chromatic and spherical aberrations.

[0058] The fifth lens group G5, which has negative power overall, is made up of two positive and negative lenses arranged in that order from the enlargement side 3, and includes a positive meniscus lens L51 convex toward the reduction side 2, and a negative meniscus lens L52 convex toward the reduction side 2. These lenses L51 and L52 form a negative meniscus type cemented lens B51 convex toward the reduction side 2.

[0059] The sixth lens group G6 having a positive power as a whole is made up of a single positive lens, and includes a positive meniscus lens L61 convex toward the reduction side 2.

[0060] The various values ​​and conditions of this lens system 10 are as follows: F-number: Wide-angle end (infinity) 2.8, Telephoto end (infinity) 2.8 Angle of view: Wide-angle end: 83.78, Telephoto end: 31.33 The focal length of the wide-angle end of the lens system 10 (fw): 24.0 Lens System 10 Telephoto Focal Length ft: 75.2 Magnification ratio: 3.13 Total length of lens system 10 (La): 255.1 Focal length fg1 of the first lens group G1 (front group Gwf): -43.56 Focal length f11 of the first sub-lens group G11: -58.05 Focal length f12 of the second sub-lens group G12: -150.85 The focal length of the third sub-lens group G13 is f13: 211.13 Focal length of the second lens group G2 fg2: 47.58 The focal length of the third lens group G3 is fg3: -120.65 Focal length fg4 of the fourth lens group G4: -935.73 The focal length of the fifth lens group G5 (middle group Gtm2) is fg5: -361.00 Focal length of the sixth lens group G6 fg6: 83.05 Focal length of rear group Gwe (G2-G6) at wide-angle end: 78.86 Focal length of front group Gtf (G1-G2) at telephoto end: 44.31 The focal length of the intermediate group Gtm (G3-G5) at the telephoto end is fg345t: -80.75 Focal length of G3-G5 at wide-angle end fg345w: -83.42 Focal length of the intermediate group Gtm1 (G3-G4) at the telephoto end: -114.29 Condition (1)(Dg12w / ((Ltg1r+Ltg2f) / 2)) (D13 / (D12+D14) / 2) at wide-angle end: 11.04 Condition (2)(Dg12t / ((Ltg1r+Ltg2f) / 2) (D13 / (D12+D14) / 2) at telephoto end: 0.79 Condition (3)(Dg23w / ((Ltg2r+Ltg3f) / 2)) ((D20+D21) / (D19+D22+D23+D24) / 2) at the wide-angle end: 0.88 Condition (4)(Dg23t / ((Ltg2r+Ltg3f) / 2)) ((D20+D21) / (D19+D22+D23+D24) / 2) at telephoto end: 2.63 Condition (5)(Dg34w / ((Ltg3r+Ltg4f) / 2)) (D25 / (D22+D23+D24+D26+D27) / 2) at the wide-angle end: 0.38 Condition (6)(Dg45w / ((Ltg4r+Ltg5f) / 2)) (D31 / (D29+D30+D32+D33) / 2) at the wide-angle end: 0.41 Condition (7)(Dg56w / ((Ltg5r+Ltg6f) / 2)) (D34 / (D32+D33+D35) / 2) at the wide-angle end: 0.38 Condition (8)(Dg56t / ((Ltg5r+Ltg6f) / 2)) (D34 / (D32+D33+D35) / 2) at telephoto end: 4.64 Condition (9)(Dg34t / ((Ltg3r+Ltg4f) / 2)) (D25 / (D22+D23+D24+D26+D27) / 2) at telephoto end: 0.45 Condition (10) (Dg45t / ((Ltg4r+Ltg5f) / 2)) (D31 / (D29+D30+D32+D33) / 2) at telephoto end: 2.12 Condition (11)(|MDg2| / fg2)(ΔD13 / fg2):1.40 Condition (12)(MDg5 / (MDg2-MDg3))(ΔD34 / ΔD20):1.89 Condition (13)(|fg2 / fg3|):0.39 Condition (14)(|fg2 / fg4|):0.05 Condition(15)(|fg2 / fg5|):0.13 Condition(16)(|fg2 / fg345w|):0.57 Condition (17)(|fg2 / fg345t|):0.59 Condition (19)(|f12| / |f13|):0.71 Condition (20)(|f11| / (|f12|+|f13|)):0.16 Condition (21) (dsw / dst): 0.59 Condition (22)(La / dL11):2.77

[0061] As shown in these, lens system 10 shown in Fig. 8 satisfies conditions (1) to (17) and (19) to (22). Lens system 10 is a zoom lens system with 21 lenses in 6 groups arranged in a compact space, has a zoom ratio of 3.0 or more, and has an F-number that is nearly constant at the telephoto end and the wide-angle end, allowing it to capture bright, clear images. [Explanation of symbols]

[0062] 1 imaging device, 10 lens system

Claims

1. The zoom lens is made up of, arranged in order from the magnification side, a first lens group having negative refractive power and fixed during zooming, a second lens group having positive refractive power and moving during zooming, a third lens group having a stop on the magnification side and moving during zooming, a fourth lens group that moves during zooming, a fifth lens group that moves during zooming, and a sixth lens group having positive refractive power and fixed during zooming, at the wide-angle end, the first lens group constitutes a front group having negative refractive power at the wide-angle end, and the second lens group, the third lens group, the fourth lens group, the fifth lens group, and the sixth lens group constitute a rear group having positive refractive power at the wide-angle end, At the telephoto end, the first lens group and the second lens group constitute a front group at the telephoto end having positive refractive power, the third lens group, the fourth lens group and the fifth lens group constitute an intermediate group at the telephoto end having negative refractive power, and the sixth lens group constitutes a rear group at the telephoto end having positive refractive power, a distance Dg12w between a reduction-side surface of the most reduction-side lens in the first lens group and an enlargement-side surface of the most enlargement-side lens in the second lens group at a wide-angle end and a distance Dg12t between the reduction-side surface of the most enlargement-side lens in the second lens group at a telephoto end; a distance Dg23w between a reduction-side surface of the most reduction-side lens in the second lens group and an enlargement-side surface of the most enlargement-side lens in the third lens group at a wide-angle end and a distance Dg23t between the reduction-side surface of the most enlargement-side lens in the third lens group at a telephoto end; a distance Dg34w at the wide-angle end between a reduction-side surface of the most reduction-side lens in the third lens group and an enlargement-side surface of the most enlargement-side lens in the fourth lens group; a distance Dg45w at the wide-angle end between a reduction-side surface of the most reduction-side lens in the fourth lens group and an enlargement-side surface of the most enlargement-side lens in the fifth lens group; a distance Dg56w between the reduction-side surface of the most reduction-side lens in the fifth lens group and the enlargement-side surface of the most enlargement-side lens in the sixth lens group at the wide-angle end and a distance Dg56t between the reduction-side surface of the most enlargement-side lens in the sixth lens group at the telephoto end; A thickness Ltg1r of the lens on the most reduction side of the first lens group; and The thickness Ltg2f of the lens on the most enlargement side of the second lens group; and a thickness Ltg2r of the lens on the most reduction side of the second lens group; and a thickness Ltg3f of the lens on the most enlargement side of the third lens group; and a thickness Ltg3r of the lens on the most reduction side of the third lens group; and A thickness Ltg4f of the lens on the most enlargement side of the fourth lens group; and A thickness Ltg4r of the lens on the most reduction side of the fourth lens group; and a thickness Ltg5f of the lens on the most enlargement side of the fifth lens group; and a thickness Ltg5r of the lens on the most reduction side of the fifth lens group; and A lens system, wherein the thickness Ltg6f of the lens on the most enlargement side of the sixth lens group satisfies the following condition. 2.5<Dg12w / ((Ltg1r+Ltg2f) / 2)<15 0<Dg12t / ((Ltg1r+Ltg2f) / 2)<1.5 0<Dg23w / ((Ltg2r+Ltg3f) / 2)<1.5 2.5<Dg23t / ((Ltg2r+Ltg3f) / 2)<15 0<Dg34w / ((Ltg3r+Ltg4f) / 2)<1.5 0<Dg45w / ((Ltg4r+Ltg5f) / 2)<1.5 0<Dg56w / ((Ltg5r+Ltg6f) / 2)<1.5 2.5<Dg56t / ((Ltg5r+Ltg6f) / 2)<15 However, the lens thickness includes the thickness of the cemented lens.

2. In claim 1, a first intermediate group is formed by the third lens group and the fourth lens group, and a second intermediate group is formed by the fifth lens group at a telephoto end.

3. In claim 1, a distance Dg34t at a telephoto end between a reduction-side surface of the most reduction-side lens in the third lens group and an enlargement-side surface of the most enlargement-side lens in the fourth lens group; A lens system, wherein a distance Dg45t at a telephoto end between a reduction-side surface of the most reduction-side lens in the fourth lens group and a magnification-side surface of the most magnification-side lens in the fifth lens group satisfies the following condition: 0<Dg34t / ((Ltg3r+Ltg4f) / 2)<1.5 1.0<Dg45t / ((Ltg4r+Ltg5f) / 2)<2.5

4. In any one of claims 1 to 3, A lens system, in which a movement amount MDg2 of the second lens group during zooming and a refractive power fg2 of the second lens group satisfy the following condition: 1.2<MDg2 / fg2<1.6

5. In any one of claims 1 to 4, A lens system, wherein a movement amount MDg2 of the second lens group, a movement amount MDg3 of the third lens group, and a movement amount MDg5 of the fifth lens group during zooming satisfy the following condition: 1.3<MDg5 / (MDg2-MDg3)<2.8

6. In any one of claims 1 to 5, a focal length fg2 of the second lens group, a focal length fg3 of the third lens group, a focal length fg4 of the fourth lens group, a focal length fg5 of the fifth lens group, a composite focal length fg345w of the third lens group, the fourth lens group, and the fifth lens group at the wide-angle end, and a composite focal length fg345t of the third lens group, the fourth lens group, and the fifth lens group at the telephoto end, satisfy the following condition. 0.02<|fg2 / fg3|<0.5 0.02<|fg2 / fg4|<0.5 0.02<|fg2 / fg5|<0.5 0.5<|fg2 / fg345w|<0.8 0.5<|fg2 / fg345t|<0.8

7. In claim 6, A lens system, wherein a focal length fg2 of the second lens group, a focal length fg3 of the third lens group, a focal length fg4 of the fourth lens group, and a focal length fg5 of the fifth lens group satisfy the following condition: |fg2|<|fg3|<|fg4|<|fg5|

8. In any one of claims 1 to 7, The first lens group includes, arranged in order from the magnification side, a first sub-lens group having negative refractive power that is fixed during focusing, a second sub-lens group having negative refractive power that moves during focusing, and a third sub-lens group having positive refractive power that moves during focusing.

9. In any one of claims 1 to 8, The diameter dsw of the aperture at the wide-angle end and the diameter dst of the aperture at the telephoto end are as follows: A lens system that meets the above requirements. 0.5<dsw / dst<0.8

10. In any one of claims 1 to 9, A lens system in which the overall length La of the lens system and the effective diameter dL11 of the lens on the most enlargement side satisfy the following condition. 2.0<La / dL11<3.5

11. A lens system according to any one of claims 1 to 10; and an image forming device disposed at a conjugate plane of the reduction side.

12. A lens system according to any one of claims 1 to 10; and an image sensor disposed on a conjugate plane on the reduction side.

Images