Zoom lens and imaging device

Abstract

To provide a zoom lens excellent in optical performance with high variable power ratio and in a wide wavelength region.SOLUTION: The zoom lens comprises a positive first lens group immovable when zooming, a first movable lens group and a second movable lens group movable when zooming, an aperture diaphragm and a subsequent lens group. When a distance from the aperture diaphragm to a surface on an object side of a lens included in the subsequent lens group at a wide angle end is Dfs and a distance from the aperture diaphragm to an image surface at a wide angle end is Dri, the subsequent lens group includes at least one positive lens and at least one negative lens both satisfying -0.10≤Dfs / Dri≤0.24. When the Abbe number of a specific negative lens of the at lease one negative lens is νdN, average values of the Abbe numbers of the positive lens and the negative lens are νdp and νdn respectively, and average values of partial dispersion ratios are θctp and θctn, 20≤νdN≤46, -3.0×10-3≤(θctn-θctp) / (νdp-νdn)<0 are satisfied.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a zoom lens suitable for an image pickup apparatus. [Background technology]

[0002] Zoom lenses for surveillance cameras used for long-distance surveillance and the like are required to have a high zoom ratio and high optical performance from the visible region to the near-infrared region. As such a zoom lens, Patent Document 1 discloses a positive-lead type zoom lens consisting of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with negative refractive power, and a fourth lens group with positive refractive power, which are arranged in this order from the object side to the image side. In this zoom lens, a high zoom ratio of about 20 times is realized by moving the second lens group and the third lens. In addition, Patent Document 2 discloses a positive-lead type zoom lens consisting of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with positive refractive power, which are arranged in this order from the object side to the image side. In this zoom lens, a high zoom ratio of about 60 times is realized by moving the second lens group and the third lens group. The zoom lenses of Patent Documents 1 and 2 employ glass materials that are advantageous for correcting chromatic aberration in the near-infrared wavelength range for the lens groups that move during magnification variation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-95448 A [Patent Document 2] Patent Publication No. 2021-76781 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to well correct the axial chromatic aberration in the entire zoom range from the visible region to the near infrared region, a lens group with positive refractive power made of fluorophosphate glass material having low dispersion and high anomalous dispersion, or a lens group with negative refractive power made of crown glass having low dispersion and super high anomalous dispersion may be arranged in series. However, in such a configuration, the lateral chromatic aberration in the near infrared region remains large. In addition, if the axial chromatic aberration at the telephoto end is well corrected, the axial chromatic aberration in the infrared wavelength region at the wide angle end is likely to be overcorrected.

[0005] The zoom lenses disclosed in Patent Documents 1 and 2 are unable to suppress both axial chromatic aberration and lateral chromatic aberration from the visible region to the near infrared region. In particular, in order to obtain good optical performance in the near infrared wavelength region around 1000 to 2000 nm (the so-called NIR to SWIR region), it is important to more appropriately set the type of zoom lens and the lens configuration of each lens group.

[0006] The present invention provides a zoom lens having a high zoom ratio and excellent optical performance over a wide wavelength range from the visible region to the SWIR region. [Means for solving the problem]

[0007] A zoom lens according to one aspect of the present invention has a first lens group with positive refractive power arranged closest to the object and not moving during zooming, a first movable lens group with negative refractive power arranged closer to the image side than the first lens group and moving during zooming, a second movable lens group arranged closer to the image side than the first movable lens group and moving during zooming, and an aperture stop and a subsequent lens group arranged closer to the image side than the second movable lens group. When the distance on the optical axis from the aperture stop at the wide-angle end to the object-side surface of a lens included in the subsequent lens group is Dfs and the distance on the optical axis from the aperture stop at the wide-angle end to the image plane is Dri, the subsequent lens group has -0.10≦Dfs / Dri≦0.24 The optical element includes at least one positive lens and at least one negative lens, each of which satisfies the following conditions: When the Abbe number of a specific negative lens in the at least one negative lens with respect to the d-line is νdN, the average Abbe number of the at least one positive lens with respect to the d-line and the average Abbe number of the at least one negative lens with respect to the d-line are νdp and νdn, respectively, and the average partial dispersion ratio between the C-line and the t-line of the at least one positive lens and the average partial dispersion ratio between the C-line and the t-line of the at least one negative lens are θctp and θctn, respectively, 20≦νdN≦46 -3.0×10 -3 ≦(θctn-θctp) / (νdp-νdn)<0 The present invention is characterized in that the above conditions are satisfied. An image pickup apparatus including the above zoom lens also constitutes another aspect of the present invention. Effect of the Invention

[0008] According to the present invention, it is possible to provide a zoom lens having a high zoom ratio and excellent optical performance over a wide wavelength range from the visible region to the SWIR region. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of the zoom lens of Example 1 at the wide-angle end and in an infinity focused state. [Diagram 2] 5A to 5C are aberration diagrams of the zoom lens of Example 1 at (a) the wide-angle end, (b) a middle zoom position, and (c) a telephoto end and in a state focused at infinity. [Diagram 3] FIG. 11 is a cross-sectional view of the zoom lens of the second embodiment at the wide-angle end and in the infinity focused state. [Figure 4] 11A to 11C are aberration diagrams of the zoom lens of Example 2 at (a) the wide-angle end, (b) a middle zoom position, and (c) a telephoto end and in a state focused at infinity. [Diagram 5] FIG. 11 is a cross-sectional view of the zoom lens of the third embodiment at the wide-angle end and in the infinity focused state. [Figure 6]11A to 11C are aberration diagrams of the zoom lens of Example 3 at (a) the wide-angle end, (b) a middle zoom position, and (c) a telephoto end and in a state focused at infinity. [Figure 7] FIG. 11 is a cross-sectional view of the zoom lens of the fourth embodiment at the wide-angle end and in the infinity focused state. [Figure 8] 11A to 11C are aberration diagrams of the zoom lens of Example 4 at (a) the wide-angle end, (b) a middle zoom position, and (c) a telephoto end and in a state focused at infinity. [Figure 9] FIG. 13 is a cross-sectional view of the zoom lens of the fifth embodiment at the wide-angle end and in the infinity focused state. [Figure 10] 13A to 13C are aberration diagrams of the zoom lens of Example 5 at (a) the wide-angle end, (b) a middle zoom position, and (c) a telephoto end and in a state focused at infinity. [Figure 11] FIG. 23 is a cross-sectional view of the zoom lens of the sixth embodiment at the wide-angle end and in the infinity focused state. [Figure 12] 13A to 13C are aberration diagrams of the zoom lens of Example 6 at (a) the wide-angle end, (b) a middle zoom position, and (c) a telephoto end and in a state focused at infinity. [Figure 13] Distribution map of existing optical materials. [Figure 14] FIG. 1 is a diagram showing an imaging device equipped with a zoom lens according to any one of Examples 1 to 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0011] Prior to describing specific examples 1 to 6, matters common to the zoom lenses of the examples will be described. In a zoom lens, a lens group is a group of one or more lenses that move together on the optical axis during zooming between the wide-angle end and the telephoto end. That is, the distance between adjacent lens groups changes during zooming. The lens group may include an aperture stop. The wide-angle end and the telephoto end respectively indicate zoom states with the maximum angle of view (shortest focal length) and the minimum angle of view (maximum focal length) when the lens group that moves during zooming is located at both ends of the range that can be moved mechanically or controlled on the optical axis.

[0012] The zoom lens of each embodiment is a positive-lead type zoom lens in which a first lens group with positive refractive power is disposed closest to the object side. The zoom lens has two or more movable lens groups (lens groups that move during zooming) including at least one lens group with negative refractive power, an aperture stop, and a subsequent lens group, located closer to the image side than the first lens group.

[0013] In order to realize a high zoom ratio and high optical performance over the entire zoom range from the visible wavelength range to the near infrared wavelength range, the zoom lens of each embodiment has features such as the power arrangement within the zoom lens and the properties of the optical materials of the lenses constituting each lens group. As a result, a zoom lens is provided that has a zoom ratio of about 20 to 90 times and excellent correction of lateral chromatic aberration from the visible wavelength range to the near infrared wavelength range.

[0014] In the zoom lens of each embodiment, focus adjustment (focusing) is performed by moving the entirety or part of the first lens group on the optical axis.

[0015] Explaining with reference to FIG. 1, the zoom lens of each embodiment has a first lens group U1 with positive refractive power that is disposed closest to the object and does not move (fixed) during zooming. It has a first lens group U1 with positive refractive power that does not move (fixed) during zooming. It also has a first movable lens group (U2) with negative refractive power that is disposed closer to the image side than the first lens group U1 and moves during zooming, and a second movable lens group (U3) that is disposed closer to the image side than the first movable lens group and moves during zooming. It also has an aperture stop SP and a subsequent lens group (U4) that are disposed closer to the image side than the second movable lens group. In the figure, under the lens group that moves during zooming, the movement trajectory of the lens group during zooming from the wide-angle end to the telephoto end is shown. Also, under the subgroup (sub lens group) of the first lens group U1 that moves during focusing, the movement direction during focusing from the infinity side to the close distance side is shown with an arrow with "FOCUS" attached.

[0016] IP is the image plane. The image plane IP is where the image pickup surface (light receiving surface) of the image sensor and the film surface (photosensitive surface) of the silver halide film are located.

[0017] Furthermore, in the zoom lens of each embodiment, when the distance on the optical axis from the aperture stop SP at the wide-angle end to the object side surface of the lens included in the subsequent lens group is defined as Dfs, and the distance on the optical axis from the aperture stop SP at the wide-angle end to the image plane IP is defined as Dri, -0.10≦Dfs / Dri≦0.24 (1) The subsequent lens group includes at least one negative lens that satisfies the following condition. The sign of Dfs is negative when the lens included in the subsequent lens group is located on the object side of the aperture stop SP, and is positive when the lens is located on the image side. In addition, when a glass block such as a dummy glass or an optical filter that does not have refractive power is present, Dri is calculated by converting the thickness of the glass block into air.

[0018] The Abbe number of a specific negative lens of the at least one negative lens that satisfies the condition of formula (1) is defined as νdN, the average values ​​of the Abbe numbers of the at least one positive lens and the at least one negative lens that satisfies the condition of formula (1) that are defined as νdp and νdn, the average values ​​of the partial dispersion ratios from the C line to the t line of the at least one positive lens and the at least one negative lens are defined as θctp and θctn, respectively. In this case, 20≦νdN≦46 (2) -3.0×10 -3 ≦(θctn-θctp) / (νdp-νdn)<0 (3) The following conditions are satisfied.

[0019] The conditions of formulas (1) to (3) show a preferable relationship with the arrangement of at least one positive lens (lens with positive refractive power) and at least one negative lens (lens with negative refractive power) included in the subsequent lens group. The condition of formula (1) shows an appropriate arrangement of the negative lens that is advantageous for correcting axial chromatic aberration in the near-infrared wavelength region. The conditions of formulas (2) and (3) show an appropriate relationship between the Abbe number and partial dispersion ratio of at least one positive lens and negative lens (optical material forming said lens) included in the range of formula (1) in the subsequent lens group. The Abbe number and partial dispersion ratio are indexes indicating the magnitude of dispersion and the magnitude of anomalous dispersion of an optical material, respectively. The Abbe number νd based on the d-line of an optical material is defined as (Nd-1) / (NF-NC) when the refractive indices of the optical material at the d-line (wavelength 587.6 nm), C-line (wavelength 656.3 nm), and F-line (wavelength 486.1 nm) are Nd, NC, and NF, respectively. The partial dispersion ratio θct from the C-line to the t-line of an optical material is defined as (NC-Nt) / (NF-NC) where Nt is the refractive index of the optical material at the t-line (1014.0 nm). The values ​​of the Abbe number νd and the partial dispersion ratio θct can be easily confirmed from the catalogs of each glass manufacturer.

[0020] Here, the relationship between the Abbe number, partial dispersion ratio, and chromatic aberration correction will be described. As shown in FIG. 15, the partial dispersion ratio of existing optical materials is distributed in a narrow range with respect to the Abbe number, and the larger the Abbe number, the larger the partial dispersion ratio tends to be. Let the given refractive power be Φ, the positive refractive power be Φp, the negative refractive power be Φn, the Abbe numbers be νp and νn, the incidence height of the axial paraxial ray be h, and the incidence height of the pupil paraxial ray be H. In this case, the axial chromatic aberration coefficient L and the lateral chromatic aberration coefficient T of a thin close contact system consisting of two lenses, a lens Gp with a positive refractive power Φp and a lens Gn with a negative refractive power Φn, are expressed by the following formulas (a) to (c).

[0021] L = h × h × (Φp / νp + Φn / νn) (a) T = h × H × (Φp / νp + Φn / νn) (b) Φ=Φp+Φn (c) Axial paraxial rays and pupil paraxial rays are rays defined as follows. An axial paraxial ray is a paraxial ray that is incident on the optical system parallel to the optical axis at an entrance height of 1, with the focal length of the entire optical system at the wide-angle end standardized to 1. A pupil paraxial ray is a paraxial ray that is incident on the image plane at the maximum image height, with the focal length of the entire optical system at the wide-angle end standardized to 1, and passes through the intersection of the entrance pupil of the optical system and the optical axis.

[0022] The refractive power of lenses Gp and Gn is standardized so that Φ in formula (c) is 1. The same can be considered for a thin, close-contact system with three or more lenses. In formulas (a) and (b), when L=0 and T=0, the image positions of C-line and F-line coincide on the axis and on the image plane. Correcting chromatic aberration for two specific wavelengths in this way is generally called dual-wavelength achromatism (first-order spectrum correction or first-order chromatic aberration correction). In particular, in high-magnification zoom lenses, the chromatic aberration of each lens group, i.e., L and T, are corrected to approximately zero in order to suppress fluctuations in chromatic aberration that accompanies zooming.

[0023] In this case, if the amount of deviation of the axial chromatic aberration and the amount of deviation of the lateral chromatic aberration of the C-line relative to the t-line when a light beam is incident on a zoom lens with the object distance at infinity are respectively defined as the secondary spectral amount Δs of the axial chromatic aberration and the secondary spectral amount Δy of the lateral chromatic aberration, then these are expressed as follows: Δs=-h×h×(θp-θn) / (νp-νn)×f (d) Δy=-h×H×(θp-θn) / (νp-νn)×Y (e) In equations (d) and (e), f is the focal length of the entire zoom lens system, and Y is the image height. In this way, correcting chromatic aberration for three specific wavelengths by adding a specific wavelength to the two wavelengths is generally called three-wavelength achromatism (second-order spectrum correction or second-order chromatic aberration correction).

[0024] Zoom lenses used in security cameras and the like are required to have long focal lengths, and as the focal length f in formula (d) increases, the axial chromatic aberration tends to increase. In addition, as large-format image sensors that correspond to wavelengths from the visible to near-infrared range are used, the magnification chromatic aberration tends to increase as the image height Y in formula (e) increases. Therefore, it is important to appropriately determine the refractive powers of the positive and negative lens groups that make up the zoom lens and the arrangement of the optical materials to suppress the values ​​of formulas (d) and (e).

[0025] By satisfying the condition of formula (1), a negative lens using an optical material with high dispersion and high partial dispersion ratio can be arranged near the aperture stop SP with a large axial light beam diameter, and the secondary spectrum of axial chromatic aberration, particularly in the near infrared region, can be well corrected. If Dfs / Dri exceeds the upper limit of formula (1), the proportion of off-axis light rays passing through the negative lens increases, and the lateral chromatic aberration, particularly at the wide-angle end, increases, which is not preferable, and the optical performance of the zoom lens deteriorates. If Dfs / Dri falls below the lower limit of formula (1), the position of the aperture stop SP moves relatively toward the image plane, and the height of the off-axis light rays in the lens group on the object side of the aperture stop SP increases. As a result, it becomes difficult to reduce the size and weight of the lens, which is not preferable.

[0026] It is more preferable that the numerical range of formula (1) is as follows:

[0027] -0.08≦Dfs / Dri≦0.20 (1a) Moreover, it is more preferable that the numerical range of the formula (1) is as follows:

[0028] -0.05≦Dfs / Dri≦0.15 (1aa) Moreover, it is even more preferable to set the numerical range of the formula (1) as follows:

[0029] 0 <Dfs / Dri≦0.10 (1aaa) By satisfying the conditions of formulas (2) and (3), it is possible to achieve both good first-order and second-order spectral correction of axial chromatic aberration in the near-infrared wavelength region by the positive and negative lenses included in the subsequent lens group. If νdN exceeds the upper limit of formula (2), the positive and negative dispersion values ​​become too close, making first-order spectral correction difficult and chromatic aberration correction in the visible wavelength region insufficient, which is undesirable. If νdN falls below the lower limit of formula (2), the partial dispersion ratios of the positive and negative lenses differ in existing optical materials, making second-order spectral correction difficult, and it is undesirable to achieve both good correction of chromatic aberration in the visible wavelength region and near-infrared wavelength region.

[0030] It is more preferable that the numerical range of the formula (2) is as follows:

[0031] 25≦νdN≦45 (2a) Moreover, it is more preferable that the numerical range of the formula (2) is as follows:

[0032] 30≦νdN≦43 (2aa) Moreover, it is even more preferable to set the numerical range of the formula (2) as follows:

[0033] 35≦νdN≦40 (2aaa) If (θctn-θctp) / (νdp-νdn) exceeds the upper limit of formula (3), it is difficult to separate the dispersion values ​​of the positive lens and the negative lens sufficiently with existing optical materials, and the first-order spectrum correction is insufficient, which increases chromatic aberration, which is undesirable. On the other hand, if (θctn-θctp) / (νdp-νdn) falls below the lower limit of formula (3), it is undesirable because the second-order spectrum correction for the visible wavelength region and the near-infrared wavelength region is insufficient, which makes it difficult to achieve good chromatic aberration correction.

[0034] It is more preferable that the numerical range of the formula (3) is as follows:

[0035] -2.5×10 -3 ≦(θctn-θctp) / (νdp-νdn)≦-1.0×10 -4 (3a) Moreover, it is more preferable that the numerical range of the formula (3) is as follows:

[0036] -2.0×10 -3 ≦(θctn-θctp) / (νdp-νdn)≦-4.2×10 -4 (3aa) Moreover, it is even more preferable to set the numerical range of the formula (3) as follows:

[0037] -1.9×10 -3 ≦(θctn-θctp) / (νdp-νdn)≦-4.8×10 -4 (3aaa) Moreover, it is more preferable to set the numerical range of the formula (3) as follows:

[0038] -1.2×10 -3 ≦(θctn-θctp) / (νdp-νdn)≦-6.8×10 -4 (3aaaa) The zoom lens of each embodiment simultaneously satisfies the conditions of expressions (1) to (3), and thus, even though it is a high-magnification zoom lens particularly for surveillance applications, it is possible to achieve good first- and second-order spectral correction of axial chromatic aberration over the entire zoom range from the visible wavelength range to the near-infrared wavelength range.

[0039] It is preferable that the zoom lens of each embodiment satisfies at least one of the conditions of the following expressions (1) to (7) and configurations a to e.

[0040] The average values ​​of the Abbe numbers νdp and νdn based on the d-line of at least one positive lens and at least one negative lens included in the range of formula (1) in the subsequent lens group are 20≦νdp-νdn≦60 (4) It is preferable that the following conditions are satisfied.

[0041] The condition of formula (4) shows an appropriate relationship between the average values ​​of the Abbe numbers of the at least one positive lens and the negative lens. The average value is the sum of the Abbe numbers of the at least one positive lens divided by the positive lens, and the sum of the Abbe numbers of the at least one negative lens divided by the negative lens. By satisfying the condition of formula (4), it is possible to provide a dispersion characteristic that is advantageous for the first-order spectrum correction of axial chromatic aberration, particularly in the visible wavelength range to near-infrared wavelength range, in the relationship between the positive lens and the negative lens. If νdp-νdn exceeds the upper limit of formula (4), the difference in partial dispersion ratio θct becomes too large in existing optical materials, which is undesirable for the second-order spectrum correction of axial chromatic aberration. If νdp-νdn falls below the lower limit of formula (4), the Abbe numbers of the positive lens and the negative lens cannot be sufficiently separated, which is undesirable for the first-order spectrum correction of axial chromatic aberration.

[0042] It is more preferable that the numerical range of the formula (4) is as follows:

[0043] 25≦νdp-νdn≦51 (4a) Moreover, it is more preferable that the numerical range of the formula (4) is as follows:

[0044] 31≦νdp-νdn≦46 (4aa) Moreover, it is even more preferable to set the numerical range of the formula (3) as follows:

[0045] 32≦νdp-νdn≦42 (4aaa) When the partial dispersion ratio of a specific negative lens included in the subsequent lens group is θctN, 0.5566≦θctN-0.00469×νdN≦0.6566 (5) It is preferable that the following conditions are satisfied.

[0046] The condition of formula (5) indicates an appropriate partial dispersion ratio of a specific negative lens included in the subsequent lens group. By satisfying the condition of formula (5), it is possible to provide a specific negative lens with dispersion characteristics and partial dispersion properties that are advantageous for secondary spectrum correction of axial chromatic aberration, particularly in the visible to near-infrared wavelength range. When θctN-0.00469×νdN exceeds the upper limit of formula (5), an optical material with a relatively large partial dispersion ratio θctN is selected, which is undesirable because it causes inconveniences such as overcorrection of axial chromatic aberration in the near-infrared wavelength range when an appropriate power arrangement is adopted at the design reference wavelength in the visible wavelength range. Also, when θctN-0.00469×νdN falls below the lower limit of formula (5), an optical material with a relatively small partial dispersion ratio θctN is selected, which is undesirable because it causes insufficient correction of axial chromatic aberration.

[0047] It is more preferable that the numerical range of the formula (5) is as follows:

[0048] 0.5655≦θctN-0.00469×νdN≦0.6200 (5a) Moreover, it is more preferable that the numerical range of the formula (5) is as follows:

[0049] 0.5685≦θctN-0.00469×νdN≦0.5935 (5aa) Moreover, it is even more preferable to set the numerical range of the formula (5) as follows:

[0050] 0.5745≦θctN-0.00469×νdN≦0.5900 (5aaa) If the focal length of a specific negative lens in the subsequent lens group is fN and the effective diameter of the light beam is eaN, then -4.0≦fN / eaN≦-0.5 (6) It is preferable that the following conditions are satisfied.

[0051] The condition of formula (6) shows the appropriate relationship between the power and the effective diameter of a specific negative lens. The effective diameter of a lens is the maximum effective aperture of a light beam passing through the lens in the entire specification range of the zoom lens, and is shown as the "effective diameter" in the numerical examples described later. Here, the value of the effective diameter of the lens on the object side is treated as a representative value. By satisfying the condition of formula (6), the negative lens that is effective for correcting axial chromatic aberration in the near-infrared wavelength range can be given an appropriate power, and it is possible to realize good chromatic aberration correction in the visible wavelength range to the near-infrared wavelength range. If fN / eaN exceeds the upper limit of formula (6), the power of the negative lens becomes relatively excessive and the radius of curvature becomes small, which is not preferable because it causes high-order aberrations. If fN / eaN falls below the lower limit of formula (6), the negative lens cannot be given an appropriate power, and the chromatic aberration correction ability is insufficient, which is not preferable.

[0052] It is more preferable that the numerical range of the formula (6) is as follows:

[0053] -3.8≦fN / eaN≦-0.7 (6a) Moreover, it is more preferable that the numerical range of the formula (6) is as follows:

[0054] -3.5≦fN / eaN≦-0.9 (6aa) Moreover, it is even more preferable to set the numerical range of the formula (6) as follows:

[0055] -3.4≦fN / eaN≦-1.3 (6aaa) When the zoom lens is at the wide-angle end and focused on infinity (hereinafter referred to as the infinity focused state), the height of the axial paraxial ray and the height of the pupil paraxial ray in the paraxial ray tracing of the subsequent lens group are respectively h and hb. The paraxial tracing values ​​hb and h of a specific negative lens are expressed as follows: -0.10≦hb / h≦0.15 (7) It is preferable that the following conditions are satisfied.

[0056] The condition of formula (7) indicates a preferable range of paraxial tracking values ​​in a specific negative lens that is particularly effective in correcting axial chromatic aberration. Here, the paraxial tracking values ​​of the object-side surface of the lens are h and hb. By satisfying the condition of formula (7), it is possible to effectively arrange a negative lens that is particularly effective in correcting axial chromatic aberration near the position of the aperture stop SP where the axial ray is particularly high in the zoom lens. When hb / h exceeds the upper limit of formula (7), the height of the pupil paraxial ray increases relative to the height of the axial paraxial ray. As a result, a high θct lens that is effective in correcting axial chromatic aberration in the near-infrared wavelength range has the effect of increasing the secondary spectrum of the lateral chromatic aberration in the over direction at the wide-angle end, which is not preferable. When hb / h falls below the lower limit of formula (7), the axial ray height in the zoom lens of each embodiment is insufficient, and the correction ability for axial chromatic aberration is insufficient, which is not preferable.

[0057] It is more preferable that the numerical range of the formula (7) is as follows:

[0058] -0.05≦hb / h≦0.10 (7a) Moreover, it is more preferable to set the numerical range of the formula (7) as follows:

[0059] -0.02≦hb / h≦0.07 (7aa) Moreover, it is even more preferable to set the numerical range of the formula (7) as follows:

[0060] 0 <hb / h≦0.05 (7aaa) In the zoom lens of each embodiment, it is preferable that the rear lens group has positive refractive power at the wide-angle end and in the infinity focused state as configuration a, and it is preferable that the lens group B has negative refractive power as configuration b.

[0061] Each embodiment shows a high-magnification zoom lens that is small and lightweight, yet has a zoom ratio of 20 to 48 times from the wide-angle end to the telephoto end. In order to realize such a high-spec zoom lens, it is effective to arrange lens groups with negative refractive power in succession to the lens group responsible for zooming and move them in conjunction with each other. This makes it possible to efficiently increase the zoom ratio while reducing the size and weight of the lens group that moves during zooming. In addition, by arranging a lens group with positive refractive power as the subsequent lens group on the image side of the main zoom group, it becomes possible to appropriately suppress the effective diameter of the aperture stop SP and the subsequent lens group.

[0062] As a configuration c, the subsequent lens group may further have a configuration in which some of the lens groups move slightly on the optical axis to correct aberrations and reduce size and weight. As a configuration d, it is preferable that the aperture stop SP is located on the object side of the subsequent lens group or within the subsequent lens group.

[0063] Furthermore, in the configuration e, it is preferable that the distance on the optical axis from the image plane of the subsequent lens group (for example, the surface having power closest to the image side) remains unchanged during zooming.

[0064] Hereinafter, a specific description will be given of the zoom lenses of Examples 1 to 6. After Example 6, Numerical Examples 1 to 6 corresponding to Examples 1 to 6, respectively, are shown. EXAMPLES

[0065] FIG. 1 shows the configuration of a zoom lens according to the first embodiment (Numerical Example 1) at the wide-angle end and in an infinity focused state.

[0066] The zoom lens of this embodiment has a first lens group U1 with positive refractive power for focusing, which is located closest to the object and does not move during zooming. The zoom lens of this embodiment also has a second lens group U2 with negative refractive power, which is located closer to the image side than the first lens group U1 and moves toward the image side during zooming from the wide-angle end to the telephoto end. The zoom lens of this embodiment also has a third lens group U3 with negative refractive power, which is located closer to the image side than the second lens group U2 and moves toward the image side and object side in conjunction with the movement of the second lens group U2 to correct image plane fluctuations associated with zooming. In addition, the zoom lens of this embodiment has a fourth lens group U4 with positive refractive power, which is located closer to the image side than the third lens group U3 and has an image-forming action that does not move during zooming.

[0067] In this embodiment, the variable magnification system is composed of the second lens group U2 corresponding to the first movable lens group and the third lens group U3 corresponding to the second movable lens group. The subsequent lens group corresponds to the fourth lens group U4. The aperture stop SP is disposed on the object side of the fourth lens group U4 (between the third lens group U3 and the fourth lens group U2). DG in the figure is a glass block (dummy glass) such as a prism or a high-cost filter that has no refractive power.

[0068] In Numerical Example 1 corresponding to Example 1, i indicates the order of the surfaces (lens surfaces or diaphragm surfaces) counted from the object side, r indicates the radius of curvature (mm) of the i-th surface, and d indicates the distance (mm) on the optical axis between the i-th and (i+1)-th surfaces. In addition, nd, νd, and θct respectively indicate the refractive index at the d-line of the medium (optical material) between the i-th and (i+1)-th surfaces, the Abbe number based on the d-line, and the partial dispersion ratio from the C-line to the t-line.

[0069] BF stands for back focus (mm). Back focus is the distance on the optical axis from the final surface of a zoom lens (the lens surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length. The total lens length (mm) is the distance on the optical axis from the frontmost surface of a zoom lens (the lens surface closest to the object) to the final surface plus the back focus.

[0070] An "*" next to a surface number means that the surface has an aspheric shape. The aspheric shape is expressed by the following formula, where X is the displacement from the apex of the surface in the optical axis direction, H is the height from the optical axis in a direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, k is the conic constant, and A3 to A16 are aspheric coefficients. Also, "eZ" is "×10 -Z " means.

[0071]

number

[0072] The above explanation of the numerical example applies to other numerical examples.

[0073] In Numerical Example 1, the first lens group U1 corresponds to the first to the fifteenth surfaces. The second lens group U2 corresponds to the sixteenth to the twenty-fourth surfaces. The third lens group U3 corresponds to the twenty-fifth to the twenty-seventh surfaces. The twenty-eighth surface is an aperture stop SP. The fourth lens group U4 corresponds to the twenty-ninth to the forty-third surfaces. The forty-fourth to the forty-sixth surfaces are dummy glass DG. The first lens group U1 is composed of a first sub-lens group U11 with positive refractive power that does not move for focusing, and a second sub-lens group U12 with positive refractive power that moves to the object side for focusing from the infinity side to the close-up side. The first sub-lens group U11 corresponds to the first to the seventh surfaces, and the second sub-lens group U12 corresponds to the eighth to the fifteenth surfaces, respectively.

[0074] In this embodiment, the lens surfaces in the subsequent lens group that satisfy the condition of formula (1) are the 29th to 35th surfaces.

[0075] The Dfs value of the positive lens corresponding to the 29th to 30th surfaces is 0.50, the Dfs value of the positive lens corresponding to the 31st to 32nd surfaces is 5.07, and the Dfs value of the positive lens corresponding to the 33rd to 34th surfaces is 13.52. The Dfs value of the negative lens corresponding to the 34th to 35th surfaces is 18.44. Among these, a specific negative lens, which is a characteristic lens that is advantageous for chromatic aberration correction in the near-infrared wavelength region, corresponds to the 34th to 35th surfaces. This negative lens may be a cemented lens as in this embodiment, or may be a single lens. This is the same in other embodiments described later.

[0076] In Numerical Example 1, the distance Dri on the optical axis from the aperture stop SP to the image plane IP at the wide-angle end is 124.107 mm, which is the sum of the distance from surface No. 28 to surface No. 44 (87.49 mm), the air-equivalent length of the dummy glass thickness from surface No. 44 to surface No. 45 (20.5149 mm (=33.00 mm / 1.60859)), the air-equivalent length of the dummy glass thickness from surface No. 45 to surface No. 46 (8.7025 mm (=13.20 mm / 1.51680)), and the back focus of 7.40 mm.

[0077] Table 1 shows numerical values ​​corresponding to the conditions of formulas (1) to (7) in Numerical Examples 1 to 6. Numerical Example 1 satisfies all of the conditions of formulas (1) to (7), and by optimizing the chromatic aberration correction and power arrangement within the subsequent lens unit U4, it is possible to achieve high magnification and high optical performance, in particular suppression of fluctuations in and good correction of axial chromatic aberration in the infrared wavelength range.

[0078] It is desirable to satisfy all of the conditions of formulas (1) to (7), but as long as the conditions of formulas (1) to (3) are satisfied, it is not necessary to satisfy all of the conditions of formulas (4) to (7). Higher optical performance can be obtained by satisfying at least one of the conditions of formulas (4) to (7) in addition to satisfying the conditions of formulas (1) to (3).

[0079] Fig. 2(a) shows the longitudinal aberration (spherical aberration, astigmatism, distortion, and chromatic aberration) at the wide-angle end in Numerical Example 1, Fig. 2(b) shows the longitudinal aberration at the intermediate zoom position (focal length 175.0 mm) in Numerical Example 1, and Fig. 2(c) shows the longitudinal aberration at the telephoto end in Numerical Example 1. All of the figures show the longitudinal aberration when focused at infinity.

[0080] In the spherical aberration diagram, Fno indicates the F-number, the thin solid line indicates the spherical aberration for the d-line, and the two-dot chain line indicates the spherical aberration for the g-line (wavelength 435.8 nm). The dot-dash line indicates the spherical aberration for the C-line, the long dashed line indicates the spherical aberration for the F-line, the short dashed line indicates the spherical aberration for the t-line, and the thick solid line indicates the spherical aberration for a wavelength of 1700 nm. In the astigmatism diagram, the solid line S indicates the sagittal image plane, and the dashed line M indicates the astigmatism at the meridional image plane. The distortion diagram shows the distortion aberration for the d-line. The chromatic aberration diagram shows the lateral chromatic aberration at the d-line, g-line, C-line, F-line, t-line, and 1700 nm. ω is the half angle of view (°). The spherical aberration is plotted on a scale of 0.4 mm, the astigmatism on a scale of 0.4 mm, the distortion on a scale of 5%, and the lateral chromatic aberration on a scale of 0.1 mm. In each numerical embodiment, the wide-angle end and the telephoto end indicate the zoom positions when the second lens unit U2 is located at both ends of the movable range in terms of the mechanism or control. The above explanation of the aberration diagrams is the same for the other numerical embodiments. EXAMPLES

[0081] FIG. 3 shows the configuration of the zoom lens of the second embodiment (Numerical Example 2) at the wide-angle end and in the infinity focused state.

[0082] The zoom lens of this embodiment has a first lens group U1 with positive refractive power for focusing, which is disposed closest to the object side and does not move during zooming. The zoom lens of this embodiment also has a second lens group U2 with negative refractive power, which is disposed closer to the image side than the first lens group U1 and moves toward the image side during zooming from the wide-angle end to the telephoto end. Furthermore, the zoom lens of this embodiment has a third lens group U3 with negative refractive power and a fourth lens group U4 with negative refractive power, which are disposed closer to the image side than the second lens group U2 in order from the object side and move toward the image side and object side in conjunction with the movement of the second lens group U2, respectively, to correct image plane fluctuations associated with zooming. In addition, the zoom lens of this embodiment has a fifth lens group U5 with positive refractive power, which is disposed closer to the image side than the fourth lens group U4 and does not move during zooming, and has an image-forming action.

[0083] In this embodiment, the zoom system is composed of the second lens group U2, which corresponds to the first movable lens group, and the third and fourth lens groups U3 and U4, which correspond to the second movable lens group, respectively. The subsequent lens group corresponds to the fifth lens group U5. The aperture stop SP is disposed on the object side of the fifth lens group U5 (between the fourth lens group U4 and the fifth lens group U5).

[0084] The first lens group U1 corresponds to surfaces 1 to 14. The second lens group U2 corresponds to surfaces 15 to 24. The third lens group U3 corresponds to surfaces 25 to 29. The fourth lens group U4 corresponds to surfaces 30 to 31. An aperture stop SP corresponds to surface 32. The fifth lens group U5 corresponds to surfaces 33 to 50. Surfaces 51 to 53 are dummy glass DG.

[0085] The first lens group U1 is composed of a first sub-lens group U11 with positive refractive power that does not move for focusing, and a second sub-lens group U12 with positive refractive power that moves toward the object side for focusing from the infinity side to the close distance side. The first sub-lens group U11 corresponds to surfaces 1 to 8, and the second sub-lens group U12 corresponds to surfaces 9 to 14, respectively.

[0086] In this embodiment, the lens surfaces in the subsequent lens group that satisfy the formula (1) are surfaces No. 33 to No. 39. The positive lenses corresponding to surfaces No. 33 to No. 34 have a Dfs value of 0.30, the positive lenses corresponding to surfaces No. 35 to No. 36 have a Dfs value of 4.27, and the negative lenses corresponding to surfaces No. 36 to No. 37 have a Dfs value of 10.24. The negative lenses corresponding to surfaces No. 38 to No. 39 have a Dfs value of 11.44. Of these, the specific negative lenses that are characteristic lenses that are advantageous in correcting chromatic aberration in the near-infrared wavelength region correspond to surfaces No. 36 to No. 37.

[0087] In Numerical Example 2, the distance Dri on the optical axis from the aperture stop SP to the image plane IP at the wide-angle end is 120.917 mm, which is the sum of the distance from surface 32 to surface 51 (82.96 mm), the air-equivalent length of the dummy glass thickness from surface 51 to surface 52 (20.5149 mm (= 33.00 mm / 1.60859), the air-equivalent length of the dummy glass thickness from surface 52 to surface 53 (8.7025 mm (= 13.20 mm / 1.51680), and the back focus of 8.74 mm.

[0088] As shown in Table 1, Numerical Example 2 satisfies the conditions of expressions (1) to (7), and by optimizing the chromatic aberration correction and power arrangement within the subsequent lens group U5, it is possible to achieve high magnification and high optical performance, in particular suppression of fluctuations in and good correction of axial chromatic aberration in the infrared wavelength range.

[0089] Fig. 4(a) shows the longitudinal aberration at the wide-angle end in Numerical Example 2, Fig. 4(b) shows the longitudinal aberration at the intermediate zoom position (focal length 65.15 mm) in Numerical Example 2, and Fig. 4(c) shows the longitudinal aberration at the telephoto end in Numerical Example 2. All of the figures show the longitudinal aberration when focused at infinity. EXAMPLES

[0090] FIG. 5 shows the configuration of the zoom lens of the third embodiment (Numerical Example 3) at the wide-angle end and in the infinity focused state.

[0091] The zoom lens of this embodiment has a first lens group U1 with positive refractive power for focusing, which is located closest to the object and does not move during zooming. The zoom lens of this embodiment also has a second lens group U2 with negative refractive power, which is located closer to the image side than the first lens group U1 and moves toward the image side during zooming from the wide-angle end to the telephoto end. Furthermore, the zoom lens of this embodiment has a third lens group U3 with negative refractive power, which is located closer to the image side than the second lens group U2 and moves toward the image side and object side in conjunction with the movement of the second lens group U2 to correct image plane fluctuations associated with zooming. In addition, the zoom lens of this embodiment has a fourth lens group U4 with positive refractive power, which is located closer to the image side than the third lens group U3 and has an image-forming action that does not move during zooming.

[0092] In this embodiment, the zoom system is composed of the second lens group U2, which corresponds to the first movable lens group, and the third lens group U3, which corresponds to the second movable lens group. The subsequent lens group corresponds to the fourth lens group U4. The aperture stop SP is disposed on the object side of the fourth lens group U4 (between the third lens group U3 and the fourth lens group U4).

[0093] The first lens group U1 corresponds to surfaces 1 to 15. The second lens group U2 corresponds to surfaces 16 to 24. The third lens group U3 corresponds to surfaces 25 to 27. The aperture stop SP corresponds to surface 28. The fourth lens group U4 corresponds to surfaces 29 to 45. Surfaces 46 to 48 are dummy glass DG.

[0094] The first lens group U1 is composed of a first sub-lens group U11 with positive refractive power that does not move for focusing, and a second sub-lens group U12 with positive refractive power that moves toward the object side for focusing from the infinity side to the close distance side. The first sub-lens group U11 corresponds to the first to seventh surfaces, and the second sub-lens group U12 corresponds to the eighth to fifteenth surfaces, respectively.

[0095] In this embodiment, the lens surfaces in the subsequent lens group that satisfy the formula (1) are surfaces 29 to 35. The positive lenses corresponding to surfaces 29 to 30 have a Dfs value of 0.50 mm, and the positive lenses corresponding to surfaces 31 to 32 have a Dfs value of 6.72 mm. The positive lenses corresponding to surfaces 33 to 34 have a Dfs value of 16.99, and the negative lenses corresponding to surfaces 34 to 35 have a Dfs value of 23.53 mm. Of these, the specific negative lenses that are characteristic lenses that are advantageous for chromatic aberration correction in the near-infrared wavelength region correspond to surfaces 34 to 35.

[0096] In Numerical Example 3, the distance Dri on the optical axis from the aperture stop SP to the image plane IP at the wide-angle end is 121.385 mm, which is the sum of the distance from surface No. 28 to surface No. 46 (85.29 mm), the air-equivalent length of the dummy glass thickness from surface No. 46 to surface No. 47 (20.5149 mm (=33.00 mm / 1.60859)), the air-equivalent length of the dummy glass thickness from surface No. 47 to surface No. 48 (8.7025 mm (=13.20 mm / 1.51680)), and the back focus of 7.40 mm.

[0097] As shown in Table 1, Numerical Example 3 satisfies all of the conditions of expressions (1) to (7), and by optimizing the chromatic aberration correction and power arrangement within the subsequent lens unit U4, it is possible to achieve high magnification and high optical performance, in particular suppression of fluctuations in and good correction of axial chromatic aberration in the infrared wavelength range.

[0098] Fig. 6(a) shows the longitudinal aberration at the wide-angle end in Numerical Example 3, Fig. 6(b) shows the longitudinal aberration at the intermediate zoom position (focal length 175.0 mm) in Numerical Example 3, and Fig. 6(c) shows the longitudinal aberration at the telephoto end in Numerical Example 3. All of the figures show the longitudinal aberration when focused at infinity. EXAMPLES

[0099] FIG. 7 shows the configuration of the zoom lens of the fourth embodiment (numerical embodiment 4) at the wide-angle end and in the infinity focused state.

[0100] The zoom lens of this embodiment has a first lens group U1 with positive refractive power for focusing, which is located closest to the object and does not move during zooming. The zoom lens of this embodiment also has a second lens group U2 with negative refractive power that is located closer to the image side than the first lens group U1 and moves toward the image side during zooming from the wide-angle end to the telephoto end, and a third lens group U3 with negative refractive power that moves toward the image side and the object side. Furthermore, the zoom lens of this embodiment has a fourth lens group U4 with positive refractive power that is located closer to the image side than the third lens group U3 and moves toward the image side and the object side in conjunction with the movement of the second and third lens groups U2 and U3 to correct the image plane fluctuation associated with zooming. In addition, the zoom lens of this embodiment has a fifth lens group U5 with positive refractive power that is located closer to the image side than the fourth lens group U4 and has an image-forming action that does not move during zooming.

[0101] In this embodiment, the zoom system is composed of the second lens group U2 and the third lens group U3, which correspond to the first movable lens group, and the fourth lens group U4, which corresponds to the second movable lens group. The aperture stop SP is disposed on the object side of the fourth lens group U4 (between the third lens group U3 and the fourth lens group U4), and moves together with the fourth lens group U4 during zooming. The subsequent lens groups correspond to the fourth lens group U4 and the fifth lens group U5. In the fourth numerical embodiment, it is assumed that the subsequent lens groups also include a group that moves during zooming.

[0102] The first lens group U1 corresponds to surfaces 1 to 12. The second lens group U2 corresponds to surfaces 13 to 20. The third lens group U3 corresponds to surfaces 21 to 25. The fourth lens group U4 corresponds to surfaces 26 to 28, of which surface 26 is an aperture stop SP. The fifth lens group U5 corresponds to surfaces 29 to 43. Surfaces 44 to 46 are dummy glass DG.

[0103] The first lens group U1 is composed of a first sub-lens group U11 with positive refractive power that does not move for focusing, and a second sub-lens group U12 with positive refractive power that moves toward the object side for focusing from the infinity side to the close distance side. The first sub-lens group U11 corresponds to the first to sixth surfaces, and the second sub-lens group U12 corresponds to the seventh to twelfth surfaces, respectively.

[0104] In this embodiment, the lens surfaces in the subsequent lens group that satisfy the formula (1) are the 27th to 35th surfaces. The Dfs value of the positive lens corresponding to the 27th to 28th surfaces is 0.50 mm, the Dfs value of the positive lens corresponding to the 29th to 30th surfaces is 14.47 mm, and the Dfs value of the positive lens corresponding to the 31st to 32nd surfaces is 18.17 mm. The Dfs value of the negative lens corresponding to the 32nd to 33rd surfaces is 24.65 mm, and the Dfs value of the negative lens corresponding to the 34th to 35th surfaces is 28.33 mm. Among these, the specific negative lens, which is a characteristic lens that is advantageous for chromatic aberration correction in the near-infrared wavelength region, corresponds to the 34th to 35th surfaces.

[0105] In Numerical Example 4, the distance Dri on the optical axis from the aperture stop SP to the image plane IP at the wide-angle end is 121.500 mm, which is the sum of the distance from surface No. 26 to surface No. 44 (84.89 mm), the air-equivalent length of the dummy glass thickness from surface No. 45 to surface No. 46 (20.5149 mm (= 33.00 mm / 1.60859)), the air-equivalent length of the dummy glass thickness from surface No. 46 to surface No. 47 (8.7052 mm (= 13.20 mm / 1.51633)), and the back focus of 7.39 mm.

[0106] As shown in Table 1, Numerical Example 4 satisfies all of the conditions of expressions (1) to (7), and by optimizing the chromatic aberration correction and power arrangement within the subsequent lens group U5, it is possible to achieve high magnification and high optical performance, in particular suppression of fluctuations in and good correction of axial chromatic aberration in the infrared wavelength range.

[0107] Fig. 8(a) shows the longitudinal aberration at the wide-angle end in Numerical Example 4, Fig. 8(b) shows the longitudinal aberration at the intermediate zoom position (focal length 44.07 mm) in Numerical Example 4, and Fig. 8(c) shows the longitudinal aberration at the telephoto end in Numerical Example 4. All of the figures show the longitudinal aberration when focused at infinity. EXAMPLES

[0108] FIG. 9 shows the configuration of the zoom lens of the fifth embodiment (Numerical Example 5) at the wide-angle end and in the infinity focused state.

[0109] The zoom lens of this embodiment has a first lens group U1 with positive refractive power for focusing, which is disposed closest to the object side and does not move during zooming. The zoom lens of this embodiment also has a second lens group U2 with negative refractive power, which is disposed in order from the object side to the image side on the image side of the first lens group U1 and moves to the image side during zooming from the wide-angle end to the telephoto end, and a third lens group U3 and a fourth lens group U4 with negative refractive power, which move to the image side and the object side, respectively. Furthermore, the zoom lens of this embodiment has a fifth lens group U5 with positive refractive power, which is disposed closer to the image side than the fourth lens group U4 and moves to the image side and the object side in conjunction with the movement of the second to fourth lens groups U2 to U2 to correct the image plane fluctuation accompanying zooming. In addition, the zoom lens of this embodiment has a sixth lens group U6 with positive refractive power, which is disposed closer to the image side than the fifth lens group U5 and performs an image forming action that does not move during zooming.

[0110] In this embodiment, the magnification system is composed of the second lens group U2, the third lens group U3, and the fourth lens group U4, which correspond to the first movable lens group, and the fifth lens group U5, which corresponds to the second movable lens group. The subsequent lens group corresponds to the sixth lens group U6. The aperture stop SP is disposed on the object side of the sixth lens group U6 (between the fifth lens group U5 and the sixth lens group U6).

[0111] The first lens group U1 corresponds to surfaces 1 to 12. The second lens group U2 corresponds to surfaces 13 to 14. The third lens group U3 corresponds to surfaces 15 to 20. The fourth lens group U4 corresponds to surfaces 21 to 25. The fifth lens group U5 corresponds to surfaces 26 to 27. An aperture diaphragm SP corresponds to surface 28. The sixth lens group U6 corresponds to surfaces 29 to 46. Surfaces 47 to 49 are dummy glass DG.

[0112] The first lens group U1 is composed of a first sub-lens group U11 with positive refractive power that does not move for focusing, and a second sub-lens group U12 with positive refractive power that moves toward the object side for focusing from the infinity side to the close distance side. The first sub-lens group U11 corresponds to the first to sixth surfaces, and the second sub-lens group U12 corresponds to the seventh to twelfth surfaces, respectively.

[0113] In this embodiment, the lens surfaces in the subsequent lens group that satisfy the formula (1) are surfaces 29 to 35. The positive lenses corresponding to surfaces 29 to 30 have a Dfs value of 0.46 mm, the positive lenses corresponding to surfaces 31 to 32 have a Dfs value of 5.24 mm, and the negative lenses corresponding to surfaces 32 to 33 have a Dfs value of 9.57 mm. The negative lenses corresponding to surfaces 34 to 35 have a Dfs value of 13.13 mm. Among these, the specific negative lenses that are characteristic lenses that are advantageous for chromatic aberration correction in the near-infrared wavelength region correspond to surfaces 32 to 33.

[0114] In Numerical Example 5, the distance Dri on the optical axis from the aperture stop SP to the image plane IP at the wide-angle end is 103.160 mm, which is the sum of the distance from surface No. 28 to surface No. 45 (66.58 mm), the air-equivalent length of the dummy glass thickness from surface No. 45 to surface No. 46 (20.5149 mm (= 33.00 mm / 1.60859)), the air-equivalent length of the dummy glass thickness from surface No. 46 to surface No. 47 (8.7052 mm (= 13.20 mm / 1.51633)), and the back focus of 7.39 mm.

[0115] As shown in Table 1, Numerical Example 5 satisfies all of the conditions of expressions (1) to (7), and by optimizing the chromatic aberration correction and power arrangement within the subsequent lens group U6, it is possible to achieve high magnification and high optical performance, in particular suppression of fluctuations in and good correction of axial chromatic aberration in the infrared wavelength range.

[0116] Fig. 10(a) shows the longitudinal aberration at the wide-angle end in Numerical Example 5, Fig. 10(b) shows the longitudinal aberration at the intermediate zoom position (focal length 46.30 mm) in Numerical Example 5, and Fig. 10(c) shows the longitudinal aberration at the telephoto end in Numerical Example 5. All of the figures show the longitudinal aberration when focused at infinity. EXAMPLES

[0117] FIG. 11 shows the configuration of a zoom lens according to the sixth embodiment (Numerical Example 6) at the wide-angle end and in the infinity focused state.

[0118] The zoom lens of this embodiment has a first lens group U1 with positive refractive power for focusing, which is disposed closest to the object side and does not move during zooming. The zoom lens of this embodiment also has a second lens group U2 with negative refractive power, which is disposed from the object side to the image side on the image side of the first lens group U1, which moves toward the image side during zooming from the wide-angle end to the telephoto end, and a third lens group U3 with positive refractive power, which moves toward the image side and the object side. Furthermore, the zoom lens of this embodiment has a fourth lens group U4 with positive refractive power, which is disposed closer to the image side than the third lens group U3, which moves toward the image side and the object side in conjunction with the movement of the second and third lens groups U2 and U3 to correct the image plane fluctuation accompanying zooming. In addition, the zoom lens of this embodiment has a fifth lens group U5 with positive refractive power, which is disposed closer to the image side than the fourth lens group U4, which has an image forming action that does not move during zooming.

[0119] In this embodiment, the zoom system is composed of the second lens group U2 and the third lens group U3, which correspond to the first movable lens group, and the fourth lens group U4, which corresponds to the second movable lens group. The subsequent lens groups correspond to the fourth lens group U4 and the fifth lens group U5. The aperture stop SP is disposed within the fifth lens group U5.

[0120] The first lens group U1 corresponds to surfaces 1 to 14. The second lens group U2 corresponds to surfaces 15 to 24. The third lens group U3 corresponds to surfaces 25 to 29. The fourth lens group U4 corresponds to surfaces 30 to 31. The fifth lens group U5 corresponds to surfaces 32 to 49, and the aperture stop SP corresponds to surface 35. Surfaces 50 to 52 are dummy glass DG.

[0121] The first lens group U1 is composed of a first sub-lens group U11 with positive refractive power that does not move for focusing, and a second sub-lens group U12 with positive refractive power that moves toward the object side for focusing from the infinity side to the close distance side. The first sub-lens group U11 corresponds to surfaces 1 to 8, and the second sub-lens group U12 corresponds to surfaces 9 to 14, respectively.

[0122] In this embodiment, the lens surfaces in the subsequent lens group that satisfy the formula (1) are surfaces 32 to 38. The negative lens corresponding to surfaces 32 to 33 has a Dfs value of -7.77 mm, the positive lens corresponding to surfaces 33 to 34 has a Dfs value of -6.77 mm, and the positive lens corresponding to surfaces 36 to 37 has a Dfs value of 1.00 mm. The negative lens corresponding to surfaces 37 to 38 has a Dfs value of 7.23 mm. Of these, the specific negative lens, which is a characteristic lens that is advantageous for chromatic aberration correction in the near-infrared wavelength region, corresponds to surfaces 32 to 33.

[0123] Numerical Example 6 shows an example in which a specific negative lens is disposed closer to the object side than the aperture stop, and the value of formula (1) becomes a negative value.

[0124] In Numerical Example 6, the distance Dri on the optical axis from the aperture stop SP to the image plane IP at the wide-angle end is 111.877 mm, which is the sum of the distance from the 35th surface to the 50th surface (73.66 mm), the air-equivalent length of the dummy glass thickness from the 50th surface to the 51st surface (20.5149 mm (= 33.00 mm / 1.60859), the air-equivalent length of the dummy glass thickness from the 51st surface to the 52nd surface (8.7025 mm (= 13.20 mm / 1.51680), and the back focus of 9.00 mm.

[0125] As shown in Table 1, Numerical Example 5 satisfies all of the conditions of expressions (1) to (7), and by optimizing the chromatic aberration correction and power arrangement within the subsequent lens group U5, it is possible to achieve high magnification and high optical performance, in particular suppression of fluctuations in and good correction of axial chromatic aberration in the infrared wavelength range.

[0126] Fig. 12(a) shows the longitudinal aberration at the wide-angle end in Numerical Example 6, Fig. 12(b) shows the longitudinal aberration at the intermediate zoom position (focal length 117.83 mm) in Numerical Example 6, and Fig. 12(c) shows the longitudinal aberration at the telephoto end in Numerical Example 6. All of the figures show the longitudinal aberration when focused at infinity. [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd θct Effective diameter 1 134.439 11.89 1.48749 70.2 0.8924 100.00 2 -5042.410 0.19 99.48 3 284.178 3.00 1.69680 55.5 0.8330 97.63 4 85.642 12.54 1.43875 94.9 0.8373 92.91 5 340.489 0.14 92.46 6 194.606 4.21 1.43387 95.1 0.8092 91.95 7 317.708 17.08 91.37 8 188.777 10.43 1.43875 94.9 0.8373 85.97 9 -263.853 2.00 1.75500 52.3 0.8092 85.28 10 548.179 0.15 83.75 11 134.833 7.83 1.43875 94.9 0.8373 82.42 12 1975.440 2.00 1.64000 60.1 0.8645 81.74 13 180.928 0.20 79.72 14 131.859 8.70 1.59522 67.7 0.7953 79.23 15 1961.290 (variable) 78.04 16 103.601 0.90 1.75106 43.1 0.7097 26.35 17 23.391 3.52 24.26 18 83.305 5.91 1.73800 32.3 0.7154 24.07 19 -24.413 0.80 1.69930 51.1 0.7593 23.61 20 33.543 0.50 22.10 21 24.544 3.00 1.67300 38.3 0.7481 22.14 22 57.929 3.00 21.61 23 -39.443 0.80 1.59522 67.7 0.7953 21.43 24 -211.122 (variable) 21.40 25 -44.313 0.80 1.69930 51.1 0.7593 18.45 26 40.676 2.66 1.85478 24.8 0.6739 19.22 27 164.793 (variable) 19.58 28(Aperture) ∞ 0.50 31.15 29 87.018 4.50 1.59522 67.7 0.7953 32.11 30* -111.279 0.07 32.43 31 44.690 8.36 1.43875 94.7 0.8410 33.19 32 -42.039 0.09 32.98 33 -2989.843 4.92 1.43875 94.7 0.8410 30.92 34 -39.709 0.90 1.61340 44.3 0.7825 30.11 35 50.317 32.44 28.57 36 27.896 4.99 1.43875 94.9 0.8373 26.51 37 519.628 7.63 25.86 38 37.098 4.61 1.69349 50.8 0.7740 21.31 39 -42.148 0.80 1.65160 58.5 0.8525 20.34 40 21.077 7.92 18.01 41 31.531 3.96 1.51633 64.1 0.8687 16.52 42 -18.693 0.80 1.69930 51.1 0.7593 16.26 43 131.703 5.00 15.91 44 ∞ 33.00 1.60859 46.4 0.7534 40.00 45 ∞ 13.20 1.51680 64.2 0.8698 40.00 46∞7.40 40.00 Image plane ∞ Aspheric Data Page 30 K = 0.00000e+00 A 4= 4.56334e-06 A 6= 2.89109e-09 A 8= 8.03335e-13 A10 = 5.01251e-15 Various data Zoom ratio 20.00 Wide Angle Mid-Telephoto Focal length 25.00 175.00 500.00 F-number 2.90 2.90 5.00 Half angle of view (°) 12.41 1.80 0.63 Lens total length 350.00 350.00 350.00 BF 7.40 7.40 7.40 d15 5.93 77.46 92.11 d24 76.44 2.50 12.56 d27 24.28 26.70 1.99 Entrance pupil position 156.96 817.64 1623.96 Exit pupil position -103.63 -103.63 -103.63 Front principal point position 176.33 716.83 -127.56 Back principal point position -17.60 -167.60 -492.60 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 165.70 80.36 23.97 -39.74 2 16 -29.49 18.42 5.23 -7.21 3 25 -57.99 3.46 0.47 -1.42 4 29 42.49 133.70 8.36 -93.23 Single lens data Lens starting surface focal length 1 1 268.82 2 3 -177.03 3 4 256.94 4 6 1145.76 5 8 252.59 6 9 -235.67 7 11 329.40 8 12 -311.34 9 14 237.08 10 16 -40.42 11 18 26.19 12 19 -20.09 13 21 61.07 14 23 -81.63 15 25 -30.21 16 26 62.56 17 29 82.74 18 31 50.87 19 33 91.68 20 34 -36.05 21 36 66.98 22 38 29.15 23 39 -21.46 24 41 23.36 25 42 -23.36 26 44 0.00 27 45 0.00 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd θct Effective diameter 1 302.771 3.00 1.75500 52.3 0.8092 109.88 2 170.691 1.22 108.72 3 159.714 14.84 1.43387 95.1 0.8092 109.17 4 -488.916 0.47 109.04 5 533.179 3.00 1.75500 52.3 0.8092 107.87 6 131.023 2.25 105.66 7 136.123 9.60 1.43387 95.1 0.8092 106.31 8 420.426 12.02 106.23 9 151.052 10.16 1.43387 95.1 0.8092 107.38 10 1039.383 0.20 107.07 11 176.002 8.49 1.43387 95.1 0.8092 105.55 12 1072.934 1.17 104.98 13 126.198 6.99 1.43387 95.1 0.8092 100.34 14 250.173 (variable) 99.43 15 -417.619 1.40 1.69930 51.1 0.7593 45.57 16 45.511 5.72 41.07 17 55.745 11.21 1.61310 44.4 0.8010 39.24 18 -40.384 1.30 1.49700 81.5 0.8258 37.62 19 36.741 2.60 31.01 20 45.740 1.30 1.63858 55.2 0.7865 29.99 21 33.941 4.94 1.67300 38.3 0.7481 28.75 22 207.395 3.33 27.34 23 -46.677 1.20 1.59522 67.7 0.7953 26.31 24* 34.367 (variable) 24.59 25 -189.909 1.00 1.69930 51.1 0.7593 18.90 26 26.719 3.10 1.74951 35.3 0.7308 19.16 27 331.761 2.10 19.26 28 -47.103 1.00 1.59522 67.7 0.7953 19.40 29 280.028 (variable) 19.96 30* 66.475 5.65 1.59522 67.7 0.7953 28.69 31 -87.029 (variable) 29.06 32 (Aperture) ∞ 0.30 29.06 33 57.514 3.77 1.43875 94.9 0.8373 29.06 34 -241.690 0.20 28.83 35 83.098 5.97 1.43875 94.9 0.8373 28.31 36 -53.535 1.00 1.61310 44.4 0.8013 27.41 37 -1276.357 0.20 26.85 38 43.959 1.00 1.64000 60.1 0.8645 26.06 39 25.124 34.47 24.99 40 26.176 6.24 1.49700 81.5 0.8258 23.62 41 -53.487 0.20 22.84 42 58.344 5.73 1.43875 94.9 0.8373 20.89 43 -26.605 1.00 1.65160 58.5 0.8525 19.30 44 22.192 2.24 17.71 45 36.563 3.55 1.51633 64.1 0.8687 17.69 46 -39.589 1.00 2.00100 29.1 0.6838 17.43 47 33.517 2.31 17.37 48 44.048 7.91 1.78880 28.4 0.6943 18.51 49 -24.334 1.00 1.75106 43.1 0.7097 18.96 50 -46.971 4.87 19.10 51 ∞ 33.00 1.60859 46.4 0.7534 30.00 52 ∞ 13.20 1.51680 64.2 0.8698 30.00 53∞8.74 30.00 Image plane ∞ Aspheric Data Page 24 K = 0.00000e+00 A 4=-9.44296e-06 A 6=-4.94309e-10 A 8=-2.18197e-11 A10=2.87903e-13 A12=-8.53611e-16 Page 30 K =-5.07198e+00 A 4=-1.19015e-08 A 6= 3.00353e-10 A 8=-4.72391e-12 A10=2.19844e-14 A12=-3.71344e-17 Various data Zoom ratio 40.00 Wide Angle Mid-Telephoto Focal length 14.00 65.15 560.00 F-number 2.79 2.79 5.10 Half angle of view (°) 21.45 4.83 0.56 Lens total length 400.00 400.00 400.00 BF 8.74 8.74 8.74 d14 4.00 77.99 120.25 d24 89.97 7.26 12.94 d29 23.53 33.47 1.93 d31 25.33 24.11 7.71 Entrance pupil position 124.59 486.99 3090.54 Exit pupil position -182.89 -182.89 -182.89 Front principal point position 137.56 529.99 2014.04 Back principal point position -5.26 -56.41 -551.27 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 176.26 73.40 40.19 -16.25 2 15 -25.50 33.00 15.52 -5.17 3 25 -52.46 7.20 3.76 -1.28 4 30 64.20 5.65 1.56 -2.04 5 33 79.40 129.18 46.38 -71.36 Single lens data Lens starting surface focal length 1 1 -523.37 2 3 279.41 3 5 -230.82 4 7 459.27 5 9 405.95 6 11 483.87 7 13 577.10 8 15 -58.61 9 17 39.97 10 18 -38.49 11 20 -215.29 12 21 59.62 13 23 -33.07 14 25 -33.43 15 26 38.60 16 28 -67.66 17 30 64.20 18 33 106.30 19 35 75.21 20 36 -91.17 21 38 -93.56 22 40 36.31 23 42 42.52 24 43 -18.42 25 45 37.41 26 46 -18.01 27 48 20.94 28 49 -68.53 29 51 0.00 30 52 0.00 [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd θct Effective diameter 1 144.366 10.03 1.48749 70.2 0.8924 100.00 2 1362.600 0.19 99.52 3 209.517 4.00 1.69680 55.5 0.8330 97.89 4 87.719 11.92 1.43875 94.9 0.8370 93.40 5 306.061 0.14 92.91 6 164.708 3.96 1.43387 95.1 0.8092 92.24 7 229.101 18.38 91.60 8 112.805 6.26 1.43875 94.9 0.8373 85.29 9 218.585 1.40 1.75500 52.3 0.8092 84.40 10 82.623 0.91 80.98 11 80.403 12.72 1.43875 94.9 0.8373 81.06 12 3393.093 1.40 1.64000 60.1 0.9645 80.45 13 368.501 0.20 79.56 14 119.342 6.75 1.59522 67.7 0.7953 78.16 15 407.680 (variable) 77.27 16 223.760 0.90 1.75106 43.1 0.7097 22.86 17 21.609 4.15 21.06 18 -132.848 4.04 1.73800 32.3 0.7148 20.92 19 -23.288 0.80 1.72000 48.0 0.7702 20.90 20 78.402 0.50 20.81 21 30.687 3.31 1.73800 32.3 0.7148 21.07 22 -1032.038 1.27 20.77 23 -48.303 0.80 1.43875 94.7 0.8410 20.69 24 64.778 (variable) 20.32 25 -46.791 0.80 1.71700 47.9 0.7629 21.13 26 38.278 2.88 1.84666 23.8 0.6614 22.20 27 174.251 (variable) 22.55 28(Aperture) ∞ 0.50 31.04 29 59.678 6.13 1.59522 67.7 0.7953 32.54 30* -66.927 0.09 32.75 31 36.231 5.38 1.43875 94.9 0.8373 32.27 32 15957.308 4.89 31.71 33 20.481 6.54 1.43875 94.9 0.8373 26.66 34 -9359.949 0.90 1.74951 35.3 0.7308 25.32 35 17.526 34.50 22.09 36 41.849 4.21 1.59522 67.7 0.7953 20.76 37 -41.188 0.10 20.58 38 4865.022 0.80 1.65160 58.5 0.8525 19.85 39 13.682 5.43 1.56732 42.8 0.7589 18.51 40 -180.197 2.71 18.13 41 -42.228 0.80 1.72000 48.0 0.7100 17.25 42 16.794 3.24 1.48749 70.2 0.8924 17.00 43 55.422 0.65 17.17 44 25.037 3.45 1.51633 64.1 0.8687 17.69 45 -116.942 5.00 17.61 46∞ 33.00 1.60859 46.4 0.7534 40.00 47 ∞ 13.20 1.51680 64.2 0.8698 40.00 48∞7.40 40.00 Image plane ∞ Aspheric Data Page 30 K = 0.00000e+00 A 4= 2.31867e-06 A 6=-1.79873e-10 A 8= 1.38914e-12 A10=-2.86760e-15 Various data Zoom ratio 20.00 Wide Angle Mid-Telephoto Focal length 25.00 175.00 500.00 F-number 2.90 2.90 5.00 Half angle of view (°) 12.41 1.80 0.63 Lens total length 350.00 350.00 350.00 BF 7.40 7.40 7.40 d15 13.67 85.51 100.62 d24 83.73 6.42 10.70 d27 15.99 21.47 2.06 Entrance pupil position 164.40 886.21 1767.08 Exit pupil position -165.35 -165.35 -165.35 Front principal point position 185.78 883.93 819.90 Back principal point position -17.60 -167.60 -492.60 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 170.86 78.24 22.61 -40.38 2 16 -26.49 15.76 2.23 -8.69 3 25 -59.19 3.68 0.49 -1.52 4 29 49.66 131.52 24.12 -118.43 Single lens data Lens starting surface focal length 1 1 330.34 2 3 -219.51 3 4 275.66 4 6 1325.94 5 8 521.87 6 9 -176.72 7 11 187.48 8 12 -646.05 9 14 281.03 10 16 -31.91 11 18 37.67 12 19 -24.86 13 21 40.43 14 23 -62.93 15 25 -29.25 16 26 57.38 17 29 53.98 18 31 82.76 19 33 46.59 20 34 -23.34 21 36 35.55 22 38 -21.06 23 39 22.65 24 41 -16.59 25 42 48.11 26 44 40.27 27 46 0.00 28 47 0.00 [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd θct Effective diameter 1 -235.316 1.50 1.74100 52.6 0.8155 74.15 2 90.588 0.74 71.06 3 90.714 11.08 1.43387 95.1 0.8092 71.33 4 -279.590 0.20 71.29 5 174.177 6.20 1.43387 95.1 0.8092 70.60 6 -446.492 17.47 70.38 7 154.011 6.80 1.43387 95.1 0.8092 68.52 8 -332.075 0.23 68.10 9 118.293 6.54 1.43387 95.1 0.8092 66.70 10 -1013.042 0.29 66.33 11 87.542 4.64 1.43387 95.1 0.8092 63.05 12 178.505 (variable) 62.20 13* -322.998 0.60 1.78000 40.0 0.6950 26.46 14 17.623 7.21 22.83 15 -34.601 4.52 1.73800 32.3 0.7154 22.70 16 -15.913 0.80 1.75106 43.1 0.7097 23.04 17 -100.803 0.18 24.22 18 59.877 5.00 1.73800 32.3 0.7154 24.73 19 -35.386 0.60 1.75106 43.1 0.7097 24.66 20 -136.880 (variable) 24.57 21 166.124 0.50 1.59410 60.5 0.7800 17.01 22 15.085 3.06 1.74951 35.3 0.7308 16.88 23 48.840 3.12 16.69 24 -29.368 0.50 1.59522 67.7 0.7953 16.67 25 66.569 (variable) 17.14 26(Aperture) ∞ 0.50 24.10 27* 34.847 6.03 1.43875 94.7 0.8410 25.52 28 -50.262 (variable) 25.87 29 70.247 3.50 1.43875 94.9 0.8373 25.85 30 -91.848 0.20 25.69 31 25.947 6.48 1.59522 67.7 0.7953 24.46 32 -71.229 1.20 1.64000 60.1 0.8645 23.04 33 25.251 2.48 20.68 34 41.872 1.20 1.67300 38.3 0.7481 20.19 35 21.803 33.97 19.31 36 32.829 4.82 1.43875 94.9 0.8373 19.72 37 -27.547 2.45 19.64 38 -37.402 2.96 1.59522 67.7 0.7953 18.26 39 -17.181 1.00 1.91650 31.6 0.7059 18.15 40 -1179.428 0.93 18.66 41 85.570 3.43 1.75520 27.5 0.6797 19.05 42 -33.277 1.00 1.78000 40.0 0.6950 19.13 43 -51.485 4.80 19.22 44 ∞ 33.00 1.60859 46.4 0.7534 40.00 45 ∞ 13.20 1.51633 64.1 0.8687 40.00 46∞7.39 40.00 Image plane ∞ Aspheric Data Page 13 K = 2.00000e+00 A 4= 1.07319e-05 A 6= 2.07839e-08 A 8=-1.21415e-09 A10= 1.68241e-11 A12=-1.16793e-13 A14= 4.09412e-16 A16=-5.76841e-19 Page 27 K =-2.00030e+00 A 4=-5.18923e-06 A 6= 1.61568e-08 A 8=-1.64922e-10 A10=8.63258e-13 A12=-1.67142e-15 Various data Zoom ratio 26.09 Wide Angle Mid-Telephoto Focal length 11.50 44.07 300.00 F-number 2.70 2.70 4.89 Half angle of view (°) 25.56 7.11 1.05 Lens total length 300.03 300.03 300.03 BF 7.39 7.39 7.39 d12 2.54 48.68 75.27 d20 57.39 2.23 5.99 d25 19.83 21.82 2.55 d28 7.94 14.97 3.90 Entrance pupil position 65.42 213.21 1005.29 Exit pupil position 1886.15 487.11 -2773.52 Front principal point position 76.99 261.33 1272.93 Back principal point position -4.11 -36.68 -292.61 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 95.41 55.69 39.76 0.53 2 13 -27.39 18.91 -3.09 -19.90 3 21 -33.65 7.18 6.24 0.52 4 26 47.94 6.53 2.26 -2.53 5 29 67.31 116.92 56.88 -59.92 Single lens data Lens starting surface focal length 1 1 -88.10 2 3 159.30 3 5 289.67 4 7 243.53 5 9 244.57 6 11 389.94 7 13 -21.41 8 15 36.21 9 16 -25.26 10 18 30.83 11 19 -63.70 12 21 -27.96 13 22 28.03 14 24 -34.17 15 27 47.94 16 29 91.32 17 31 32.77 18 32 -28.99 19 34 -69.26 20 36 34.99 21 38 50.62 22 39 -19.03 23 41 32.13 24 42 -123.61 25 44 0.00 26 45 0.00 [Numerical Example 5] Unit: mm Surface Data Surface number rd nd νd θct Effective diameter 1 -333.604 1.50 1.75500 52.3 0.8092 72.80 2 94.281 0.67 70.07 3 93.288 9.67 1.43387 95.1 0.8092 70.19 4 -463.037 0.20 69.99 5 178.714 5.39 1.43387 95.1 0.8092 68.94 6 -704.974 14.76 68.70 7 189.224 6.53 1.43387 95.1 0.8092 67.47 8 -246.986 0.23 67.29 9 102.913 6.08 1.43387 95.1 0.8092 65.43 10 1172.136 1.49 65.00 11 87.794 5.08 1.43387 95.1 0.8092 61.98 12 227.718 (variable) 61.18 13* 2168.310 0.60 1.85920 33.0 0.6855 26.96 14 21.254 (variable) 23.99 15 -71.516 3.99 1.85478 24.8 0.6739 23.08 16 -21.254 1.00 1.59522 67.7 0.7953 23.16 17 57.975 0.18 22.32 18 26.573 5.21 1.61340 44.3 0.7825 22.30 19 -61.443 1.00 1.81600 46.6 0.7690 21.67 20 54.797 (variable) 20.88 21 144.285 0.50 1.59410 60.5 0.7800 15.60 22 18.375 2.32 1.74951 35.3 0.7308 15.60 23 49.098 2.91 15.50 24 -28.214 0.50 1.59522 67.7 0.7953 15.61 25 112.430 (variable) 16.14 26* 81.181 4.24 1.72916 54.7 0.8244 22.78 27 -53.305 (variable) 23.23 28(Aperture) ∞ 0.46 23.32 29 66.397 4.58 1.43875 94.9 0.8373 23.36 30 -32.485 0.20 23.24 31 113.201 4.33 1.43875 94.9 0.8373 21.81 32 -24.624 1.00 1.65412 39.6 0.7713 21.25 33 -111.394 2.56 20.64 34 -32.939 1.00 1.64000 60.1 0.8645 19.92 35 217.538 32.00 19.85 36 57.294 3.52 1.43875 94.9 0.8373 21.16 37 -54.470 0.20 21.20 38 35.364 4.36 1.43875 94.9 0.8373 20.80 39 -40.673 1.10 1.69930 51.1 0.7953 20.38 40 -72.695 0.29 20.11 41 93.109 1.10 1.65160 58.5 0.8525 19.40 42 18.712 2.32 18.29 43 27.952 2.69 1.51633 64.1 0.8687 18.44 44 111.020 4.87 18.18 45 ∞ 33.00 1.60859 46.4 0.7534 40.00 46 ∞ 13.20 1.51633 64.1 0.8687 40.00 47∞7.36 40.00 Image plane ∞ Aspheric Data Page 13 K = 2.00000e+00 A 4=-1.02725e-06 A 6= 2.60488e-08 A 8=-7.13861e-10 A10= 9.36626e-12 A12=-6.17750e-14 A14= 2.00894e-16 A16=-2.55993e-19 Page 26 K =-1.99983e+00 A 4=-2.00360e-06 A 6= 5.76852e-09 A 8=-8.60164e-11 A10=4.04685e-13 A12=-5.26404e-16 Various data Zoom ratio 26.09 Wide Angle Mid-Telephoto Focal length 11.50 53.59 300.00 F-number 2.70 2.70 4.89 Half angle of view (°) 25.56 5.86 1.05 Lens total length 286.04 286.04 286.04 BF 7.36 7.36 7.36 d12 2.01 52.36 73.93 d14 9.65 6.14 9.34 d20 47.02 2.79 5.60 d25 14.84 17.96 1.52 d27 18.33 12.59 1.46 Entrance pupil position 65.13 273.55 1139.78 Exit pupil position -221.15 -221.15 -221.15 Front principal point position 76.05 314.57 1045.94 Back principal point position -4.14 -46.23 -292.63 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 97.44 51.60 35.91 -1.40 2 13 -24.98 0.60 0.33 0.00 3 15 -248.04 11.38 12.49 5.72 4 21 -35.00 6.23 5.10 0.12 5 26 44.72 4.24 1.50 -0.98 6 29 60.48 112.78 44.03 -59.25 Single lens data Lens starting surface focal length 1 1 -97.21 2 3 179.90 3 5 329.21 4 7 248.06 5 9 259.58 6 11 325.74 7 13 -24.98 8 15 34.13 9 16 -26.01 10 18 30.94 11 19 -35.36 12 21 -35.50 13 22 37.95 14 24 -37.84 15 26 44.72 16 29 50.43 17 31 46.54 18 32 -48.55 19 34 -44.63 20 36 64.26 21 38 43.88 22 39 -133.94 23 41 -36.15 24 43 71.56 25 45 0.00 26 46 0.00 [Numerical Example 6] Unit: mm Surface Data Surface number rd nd νd θct Effective diameter 1 272.948 3.00 1.75500 52.3 0.8092 120.00 2 160.284 0.40 118.52 3 149.903 19.03 1.43387 95.1 0.8092 118.87 4 -343.521 -0.07 118.75 5 590.536 3.00 1.75500 52.3 0.8092 116.56 6 118.334 1.54 113.06 7 120.394 12.74 1.43387 95.1 0.8092 113.65 8 524.835 9.98 113.57 9 150.583 10.56 1.43387 95.1 0.8092 113.88 10 902.409 0.20 113.61 11 129.849 10.42 1.43387 95.1 0.8092 110.62 12 487.077 0.26 110.07 13 103.685 8.93 1.43387 95.1 0.8092 103.67 14 213.514 (variable) 102.69 15 -482.795 1.40 1.69930 51.1 0.7593 43.99 16 58.087 3.79 40.43 17 111.035 7.79 1.61310 44.4 0.8010 39.32 18 -48.485 1.30 1.49700 81.5 0.8258 38.28 19 -186.057 0.68 35.55 20 1152.395 1.30 1.63858 55.2 0.7862 33.64 21 40.533 5.59 1.67300 38.3 0.7481 30.88 22 -252.804 2.22 29.49 23 -57.059 1.20 1.59522 67.7 0.7953 28.29 24* 28.376 (variable) 25.47 25 -334.981 1.00 1.69930 51.1 0.7593 16.92 26 15.096 3.33 1.74951 35.3 0.7308 16.70 27 63.974 2.58 16.57 28 -28.126 1.00 1.59522 67.7 0.7953 16.59 29 90.850 (variable) 17.24 30* 69.372 4.76 1.59522 67.7 0.7953 26.35 31 -63.039 (variable) 26.75 32 43.960 1.00 1.63775 42.4 0.7879 26.95 33 25.973 5.27 1.43875 94.9 0.8373 26.39 34 691.109 1.50 26.21 35(Aperture) ∞ 1.00 26.03 36 45.268 6.23 1.43875 94.7 0.8410 25.68 37 111.931 1.00 1.67790 55.4 0.8271 24.34 38 42.521 33.59 23.81 39 30.747 8.50 1.49700 81.5 0.8258 22.34 40 -39.870 0.20 20.92 41 91.396 4.26 1.43875 94.9 0.8373 19.30 42 -23.346 1.00 1.65160 58.5 0.8525 18.17 43 25.753 2.72 16.84 44 245.472 3.52 1.51633 64.1 0.8687 16.94 45 -19.723 1.00 2.00100 29.1 0.6838 16.96 46 -76.606 0.17 17.54 47 58.854 4.60 1.78880 28.4 0.6943 17.88 48 -27.526 1.00 1.69930 51.1 0.7593 17.89 49 -127.462 4.87 17.81 50 ∞ 33.00 1.60859 46.4 0.7534 30.00 51 ∞ 13.20 1.51680 64.2 0.8687 30.00 52∞ 9.00 30.00 Image plane ∞ Aspheric Data Page 24 K = 0.00000e+00 A 4=-8.54695e-06 A 6=-8.72323e-09 A 8=-1.74424e-10 A10= 1.49674e-12 A12=-3.89798e-15 Page 30 K =-5.07198e+00 A 4=-5.81459e-07 A 6=-1.26791e-08 A 8= 1.64955e-10 A10=-8.83062e-13 A12= 1.70123e-15 Various data Zoom ratio 48.00 Wide Angle Mid-Telephoto Focal length 16.00 117.83 768.00 F-number 2.79 2.79 6.40 Half angle of view (°) 18.97 2.67 0.41 Lens length 388.87 388.87 388.87 BF 9.00 9.00 9.00 d14 4.01 77.50 90.47 d24 45.27 5.93 40.04 d29 28.54 26.13 1.85 d31 56.45 24.71 1.92 Entrance pupil position 140.48 954.37 5757.79 Exit pupil position -154.64 -154.64 -154.64 Front principal point position 154.92 987.35 2921.43 Back principal point position -7.00 -108.83 -759.00 Lens Group Data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 148.02 80.00 39.45 -20.65 2 15 -31.07 25.28 13.00 -3.12 3 25 -25.63 7.91 4.47 -1.18 4 30 56.24 4.76 1.59 -1.44 5 32 71.00 127.64 44.73 -69.79 Single lens data Lens starting surface focal length 1 1 -520.29 2 3 243.38 3 5 -196.55 4 7 356.69 5 9 414.82 6 11 404.49 7 13 453.43 8 15 -74.07 9 17 56.09 10 18 -132.35 11 20 -65.82 12 21 52.31 13 23 -31.67 14 25 -20.63 15 26 25.61 16 28 -35.97 17 30 56.24 18 32 -101.73 19 33 61.36 20 36 168.43 21 37 -101.74 22 39 36.38 23 41 42.87 24 42 -18.64 25 44 35.52 26 45 -26.77 27 47 24.35 28 48 -50.41 29 50 0.00 30 51 0.00

[0127] [Table 1]

[0128] (The "EM" in the value of conditional formula (3) in Table 1 means "×10-M.") FIG. 14 shows the configuration of an image pickup apparatus (television camera system) using the zoom lens of each of the above-mentioned embodiments as a photographing optical system.

[0129] 14, reference numeral 101 denotes a zoom lens according to any one of the first to sixth embodiments. Reference numeral 124 denotes a camera. The zoom lens 101 is detachable from the camera 124. Reference numeral 125 denotes an imaging device configured by mounting the zoom lens 101 on the camera 124.

[0130] The zoom lens 101 has a first lens group F, a zoom section LZ, a rear group R, etc. The first lens group F includes a first lens group U1 for focusing in each embodiment. The zoom section LZ includes a lens group (U2, etc.) that moves during zooming, and an aperture diaphragm SP. Reference numerals 114 and 115 denote driving mechanisms such as a helicoid or a cam that drive the first lens group F and the zoom section LZ in the optical axis direction, respectively. Reference numerals 116 to 118 denote actuators that electrically drive the driving mechanisms 114 and 115 and the aperture diaphragm SP. Reference numerals 119 to 121 denote detectors such as an encoder, potentiometer, or photosensor that detect the positions on the optical axis of the first lens group F, the zoom section LZ, and the aperture diaphragm SP, and the aperture diameter of the aperture diaphragm SP.

[0131] In the camera 124, reference numeral 109 denotes a glass block corresponding to an optical filter or a color separation optical system within the camera 124, and reference numeral 110 denotes a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the zoom lens 101. Reference numerals 111 and 122 denote CPUs that control various driving operations of the camera 124 and the zoom lens 101.

[0132] In this way, by using the zoom lens of each embodiment in an image pickup apparatus, it is possible to realize an image pickup apparatus having high optical performance.

[0133] The above embodiment includes the following configurations.

[0134] (Configuration 1) a first lens group having positive refractive power that is disposed closest to the object and does not move during zooming; a first movable lens group having negative refractive power, which is disposed closer to the image side than the first lens group and moves during zooming; a second movable lens group that is disposed closer to the image side than the first movable lens group and moves during zooming; an aperture stop and a subsequent lens group disposed on the image side of the second movable lens group, When the distance on the optical axis from the aperture stop at the wide-angle end to the object-side surface of the lens included in the subsequent lens group is Dfs, and the distance on the optical axis from the aperture stop at the wide-angle end to the image plane is Dri, the subsequent lens group is -0.10≦Dfs / Dri≦0.24 at least one positive lens and at least one negative lens, each of which satisfies the following conditions: Let νdN be the Abbe number based on the d-line of a specific negative lens in the at least one negative lens, νdp and νdn be the average Abbe number based on the d-line of the at least one positive lens and the average Abbe number based on the d-line of the at least one negative lens, respectively, and θctp and θctn be the average partial dispersion ratio between the C-line and the t-line of the at least one positive lens and the average partial dispersion ratio between the C-line and the t-line of the at least one negative lens, respectively. 20≦νdN≦46 -3.0e-3≦(θctn-θctp) / (νdp-νdn)<0 A zoom lens characterized by satisfying the following conditions. (Configuration 2) 20≦νdp-νdn≦60 2. The zoom lens according to claim 1, wherein the following condition is satisfied: (Configuration 3) When the partial dispersion ratio between the C-line and the t-line of the specific negative lens is θctN, 0.5566≦θctN-0.00469×νdN≦0.6566 3. The zoom lens according to configuration 1 or 2, which satisfies the following conditions: (Configuration 4) When the focal length of the specific negative lens is fN and the effective diameter of the specific negative lens is eaN, -4.0≦fN / eaN≦-0.5 4. The zoom lens according to any one of configurations 1 to 3, which satisfies the following condition: (Configuration 5) When the zoom lens is at the wide-angle end and focused on an object at infinity, the height of the axial paraxial ray and the height of the pupil paraxial ray in the paraxial tracking of the subsequent lens group are h and hb, respectively. The specific negative lens has the following characteristics: -0.10≦hb / h≦0.15 5. The zoom lens according to any one of configurations 1 to 4, which satisfies the following condition: (Configuration 6) 6. The zoom lens according to any one of configurations 1 to 5, wherein the rear lens group has positive refractive power. (Configuration 7) 7. The zoom lens according to any one of configurations 1 to 6, wherein the second movable lens group has negative refractive power. (Configuration 8) 8. A zoom lens according to any one of configurations 1 to 7, wherein the distance on the optical axis from the image plane of the subsequent lens group remains constant during zooming. (Configuration 9) 9. The zoom lens according to any one of configurations 1 to 8, wherein focusing is performed by moving all or a part of the first lens group. (Configuration 10) A zoom lens according to any one of configurations 1 to 9; and an image sensor for capturing an image of a subject through the zoom lens.

[0135] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment in implementing the present invention. [Explanation of symbols]

[0136] U1 First lens group U2 2nd lens group U3 Third lens group U4 4th lens group SP aperture stop IP image plane

Claims

1. a first lens group having a positive refractive power and disposed closest to the object side and not moving during zooming; a first movable lens group having negative refractive power, which is disposed closer to the image side than the first lens group and moves during zooming; a second movable lens group that is disposed closer to the image side than the first movable lens group and moves during zooming; an aperture stop and a subsequent lens group disposed on the image side of the second movable lens group, When the distance on the optical axis from the aperture stop at the wide-angle end to the object-side surface of the lens included in the subsequent lens group is Dfs, and the distance on the optical axis from the aperture stop at the wide-angle end to the image plane is Dri, the subsequent lens group is −0.10≦Dfs / Dri≦0.24 at least one positive lens and at least one negative lens, each of which satisfies the following conditions: Let vdN be the Abbe number of a specific negative lens in the at least one negative lens based on the d-line, vdp and vdn be the average Abbe numbers of the at least one positive lens based on the d-line and the average Abbe numbers of the at least one negative lens based on the d-line, respectively, and θctp and θctn be the average partial dispersion ratios of the at least one positive lens based on the C-line and the t-line and the average partial dispersion ratios of the at least one negative lens based on the C-line and the t-line, respectively. 20≦νdN≦46 -3.0×10 －３ ≦(θctn-θctp) / (νdp-νdn)<0 A zoom lens characterized by satisfying the following conditions.

2. 20≦νdp−νdn≦60 2. The zoom lens according to claim 1, which satisfies the following condition:

3. When the partial dispersion ratio between the C-line and the t-line of the specific negative lens is θctN, 0.5566≦θctN−0.00469×νdN≦0.6566 2. The zoom lens according to claim 1, which satisfies the following condition:

4. Let fN be the focal length of the particular negative lens, and eaN be the effective diameter of each of the at least one negative lenses, -4.0≦fN / eaN≦-0.5 2. The zoom lens according to claim 1, which satisfies the following condition:

5. When the zoom lens is at the wide-angle end and focused on an object at infinity, the height of an axial paraxial ray and the height of a pupil paraxial ray in paraxial tracking of the subsequent lens group are denoted by h and hb, respectively. The specific negative lens has the following characteristics: −0.10≦hb / h≦0.15 2. The zoom lens according to claim 1, which satisfies the following condition:

6. 2. The zoom lens according to claim 1, wherein the rear lens group has a positive refractive power.

7. 2. The zoom lens of claim 1, wherein the second movable lens group has negative refractive power.

8. 2. The zoom lens according to claim 1, wherein the distance of said subsequent lens group from the image plane on the optical axis remains constant during zooming.

9. 2. The zoom lens according to claim 1, wherein focusing is performed by moving all or a part of the first lens group.

10. A zoom lens according to any one of claims 1 to 9; and an image sensor for capturing an image of a subject through the zoom lens.

Images