Zoom lens and imaging device

Abstract

To provide a small-sized zoom lens having high optical performance in an infrared band.SOLUTION: The zoom lens consists of, in order from an object side to an image side, a first optical system having a first lens group of a positive refractive power, a second lens group of a negative refractive power, a third lens group of a positive refractive power, and a fourth lens group of a negative refractive power and a second optical system having a fifth lens group of a positive refractive power. In the first optical system, an intermediate image is formed between the first optical system and the second optical system. A distance between adjacent lens groups included in the first optical system changes for zooming. D=|ft| / Fno defined by a focal distance ft and an F value Fno of the entire system at a telephoto end, focal distances of the first and second lens groups, and a length L on an optical axis from an optical surface closest to an object to an image surface of the first lens group are appropriately set.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Known conventional infrared optical systems use wavelength bands of 3 μm to 5 μm or 8 μm to 12 μm. In particular, those in the 3 μm to 5 μm band (hereinafter also referred to as the MW (Middle Wavelength) band) are used to photograph high-temperature subjects and are widely used in situations such as defense and surveillance. In particular, variable magnification infrared optical systems are used in defense and surveillance (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-035482 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art disclosed in the above-mentioned Patent Document 1, a four-group infrared variable magnification optical system is known, which is composed of a first lens group to a fourth lens group, for the purpose of shortening the overall length of the optical system. This infrared variable magnification optical system has a problem in that the overall optical length is long relative to the focal length at the telephoto end.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a zoom lens which is compact and has high optical performance in the infrared range. [Means for solving the problem]

[0006] In order to achieve the above object, a zoom lens is composed of a first optical system composed of, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, and a second optical system composed of a fifth lens group having positive refractive power, wherein the first optical system forms an intermediate image between the first optical system and the second optical system, and a distance between adjacent lens groups included in the first optical system changes due to zooming, and when the focal length of the entire system at the telephoto end is ft and the F-number is Fno, and D is defined as D=|ft| / Fno, the focal length of the first lens group is f1, the focal length of the second lens group is f2, and the length on the optical axis from the optical surface of the first lens group closest to the object to the image plane is L, -20.00 <f1 / f2<-8.00 0.600 <D / L<1.000 The present invention is characterized in that the following condition is satisfied: Effect of the Invention

[0007] According to the present invention, it is possible to provide a zoom lens which is small in size and has high optical performance in the infrared band. [Brief description of the drawings]

[0008] [Figure 1] 3A and 3B are a cross-sectional view and a movement locus diagram of the optical system in Example 1 when focused on infinity at the wide-angle end. [Diagram 2] 4A to 4C are aberration diagrams at the wide-angle end and the telephoto end of the optical system in Example 1. [Diagram 3] 11A and 11B are a cross-sectional view and a movement locus diagram of an optical system according to a second embodiment when focused on infinity at the wide-angle end. [Figure 4] 11A to 11C are aberration diagrams at the wide-angle end and the telephoto end of the optical system in Example 2. [Diagram 5] 13A and 13B are a cross-sectional view and a movement locus diagram of an optical system according to a third embodiment when focused on infinity at the wide-angle end. [Figure 6] 11A to 11C are aberration diagrams at the wide-angle end and the telephoto end of the optical system in Example 3. [Figure 7]13A and 13B are a cross-sectional view and a movement locus diagram of an optical system according to a fourth embodiment when focused on infinity at the wide-angle end. [Figure 8] 11A to 11C are aberration diagrams at the wide-angle end and the telephoto end of the optical system in Example 4. [Figure 9] 13A and 13B are a cross-sectional view and a movement locus diagram of an optical system in Example 5 when focused on infinity at the wide-angle end. [Figure 10] 13A to 13C are aberration diagrams at the wide-angle end and the telephoto end of the optical system in Example 5. [Figure 11] 13A and 13B are a cross-sectional view and a movement locus diagram of an optical system in Example 6 when focused on infinity at the wide-angle end. [Figure 12] 13A to 13C are aberration diagrams at the wide-angle end and the telephoto end of the optical system in Example 6. [Figure 13] 13A and 13B are a cross-sectional view and a movement locus diagram of an optical system in Example 7 when focused on infinity at the wide-angle end. [Figure 14] 13A to 13C are aberration diagrams at the wide-angle end and the telephoto end of the optical system in Example 7. [Figure 15] 13A and 13B are a cross-sectional view and a movement locus diagram of an optical system in Example 8 when focused on infinity at the wide-angle end. [Figure 16] 13A to 13C are aberration diagrams at the wide-angle end and the telephoto end of the optical system in Example 8. [Figure 17] 13A and 13B are a cross-sectional view and a movement locus diagram of an optical system in Example 9 when focused on infinity at the wide-angle end. [Figure 18] 13A to 13C are aberration diagrams at the wide-angle end and the telephoto end of the optical system in Example 9. [Figure 19] FIG. 2 is a schematic diagram of an imaging device including an optical system in each embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. With reference to FIG. 1, an optical system 1a in Example 1 will be described as a representative of the other examples.

[0010] FIG. 1 is a cross-sectional view and a diagram of a movement locus of the optical system 1a in the first embodiment when focusing on infinity at the wide-angle end. The optical system 1a is an infrared optical system used in an imaging device such as a surveillance camera. In FIG. 1, the left side is the subject side (object side), and the right side is the image side. The wide-angle end and the telephoto end refer to the zoom positions when the optical system 1a is located at both ends of the range in which it can move in the direction along the optical axis due to its mechanism. The movement of each lens group from the wide-angle end to the telephoto end takes a locus like the arrow (solid line) shown in FIG. 1. The solid line and the dashed line arrows respectively indicate the movement locus when focusing on an object at infinity and a close object. The arrow F indicates the movement direction of the focus group when focusing from infinity to a close object. The above description is also applicable to each cross-sectional view of the optical system in the second to ninth embodiments.

[0011] The optical system 1a according to the first embodiment is a zoom lens having, in order from the object side to the image side, a first optical system S1 and a second optical system S2. The first optical system S1 forms an intermediate image, and the second optical system S2 forms the intermediate image on an imaging surface (image surface). The first optical system S1 is composed of a first lens group (positive lens group) L1 having positive refractive power, a second lens group L2 having negative refractive power, a third lens group L3 having positive refractive power, and a fourth lens group L4 having negative refractive power. The second optical system S2 is composed of a fifth lens group L5 having positive refractive power. IP' is a primary image formation surface (primary image formation point), and the primary image formation surface is located between the first optical system S1 and the second optical system S2. SP is an aperture stop, and is arranged on the image side (between the fifth lens group and the secondary image formation point) of the meniscus positive lens G53 that is the most image side in the optical system 1a.

[0012] G is an optical block equivalent to a window or faceplate, etc. IP is an image plane (secondary image plane, secondary image point), and when the optical system 1a is used as an imaging optical system, it corresponds to the imaging plane of a quantum MW band cooled camera such as an InSb type, MCT (Mercury Cadmium Telluride) type, or T2SL (Type-II Super Lattice) type.

[0013] In the zoom lens of the present invention, the first lens group L1, the second lens group L2, the third lens group L3, and the fourth lens group L4 constitute a first optical system S1 that forms a primary image plane IP'. The fifth lens group L5 constitutes a second optical system S2 that images the primary image plane IP' onto a secondary image plane IP.

[0014] In the optical system 1a, the spacing between adjacent lens groups included in the first optical system S1 changes during zooming. In the optical system 1a, when zooming from the wide-angle end to the telephoto end, the second lens group L2 moves toward the image side, and the third lens group L3 moves toward the object side and then moves back toward the image side, each of which moves independently. Also, when focusing from infinity to a close distance, the third lens group L3 moves toward the object side.

[0015] FIG. 2(A) is an aberration diagram of the optical system 1a in Example 1 at the wide-angle end, and FIG. 2(B) is an aberration diagram of the optical system 1a at the telephoto end. In FIG. 2(A) and (B), 4.0000 indicates a wavelength of 4 μm, 3.7000 indicates a wavelength of 3.7 μm, M indicates a meridional image plane, and S indicates a sagittal image plane. In astigmatism, the meridional image plane M and the sagittal image plane S at a wavelength of 4 μm are shown. In distortion, the wavelength of 4 μm is shown. In lateral chromatic aberration, the aberration at a wavelength of 3.7 μm for a wavelength of 4 μm is shown. The above explanation is also applicable to the aberration diagrams of the optical systems in Examples 2 to 9.

[0016] As described above, the infrared optical system of the present invention is composed of, in order from the object side, a first optical system S1 consisting of a first lens group L1 having positive refractive power, a second lens group L2 having negative refractive power, a third lens group L3 having positive refractive power, and a fourth lens group L4 having negative refractive power, and a second optical system S2 consisting of a fifth lens group L5 for secondary imaging.

[0017] This is a suitable configuration for obtaining a variable-magnification optical system having a high zoom ratio and a short optical length. In order to achieve the object of the present invention, the following conditions are specifically added and the effects are obtained.

[0018] The zoom lens of the present invention comprises, in order from the object side to the image side, a first optical system S1 consisting of a first lens group L1 having positive refractive power, a second lens group L2 having negative refractive power, a third lens group L3 having positive refractive power, and a fourth lens group L4 having negative refractive power, and a second optical system S2 consisting of a fifth lens group L5 for secondary imaging. The zoom lens of the present invention is an infrared secondary imaging variable magnification optical system that satisfies the following conditional expressions (1) and (2). -20.00 <f1 / f2<-8.00 ···(1) 0.600 <D / L<1.000 ···(2)

[0019] Here, f1 is the focal length of the first lens group L1, and f2 is the focal length of the second lens group L2. D is the focal length of the zoom lens at the telephoto end, ft is the focal length of the zoom lens at the telephoto end, and Fno is the F-number. D=|ft| / Fno L represents the length on the optical axis from the object-side surface of the lens in the first lens group closest to the object to the secondary image plane.

[0020] Conditional formula (1) specifies the relationship between the focal length of the first lens group and the focal length of the second lens group for optimally correcting the variable magnification effect and aberration of the optical system. If the upper limit of conditional formula (1) is exceeded, the power of the second lens group L2 becomes weak, the overall length of the optical system becomes long, and it becomes difficult to reduce the size. If the lower limit of conditional formula (1) is exceeded, the power of the second lens group L2 becomes too strong, and it becomes difficult to correct aberration.

[0021] Condition (2) regulates the size of the optical system. If the upper limit of condition (2) is exceeded, the overall length will be shortened and the size will be reduced, but the power of each lens group will be too strong, making it difficult to correct aberrations. If the lower limit of condition (2) is exceeded, the overall length will be too long, making it difficult to reduce the size.

[0022] In addition, in the zoom lens of the present invention, when the magnification is changed from the wide-angle end to the telephoto end, the first lens group L1, the fourth lens group L4, and the fifth lens group L5 are stationary, the second lens group L2 moves toward the image side, and the third lens group L3 moves toward the object side and then toward the image side. By performing such a moving method, the following effects can be obtained. By making the first lens group L1, which has the largest lens diameter in the entire system, stationary during the magnification change, the entire device can be made smaller and simpler. By moving the second lens group L2, which has negative refractive power, toward the image side, the magnification is changed efficiently, and the third lens group L3 moves to compensate for the change in the image point caused by the movement of the second lens group L2, thereby achieving the magnification change from the wide-angle end to the telephoto end.

[0023] The zoom lens of the present invention satisfies the following conditional expressions (3) to (7). 0.100 <f1 / |ft|<0.250 ···(3) -0.023 <f2 / |ft|<-0.010 ···(4) 0.000 <f3 / |ft|<0.050 ···(5) -1.000 <f4 / |ft|<0.000 ···(6) 40<|ft| / f5<200 ···(7)

[0024] Here, f3 is the focal length of the third lens group L3, f4 is the focal length of the fourth lens group L4, and f5 is the focal length of the fifth lens group L5. Conditional formula (3) specifies the ratio between the focal length of the first lens group L1 and the absolute value of the focal length of the entire system at the telephoto end. If the upper limit of conditional formula (3) is exceeded, the power of the first lens group L1 becomes weak and the total optical length of the entire system becomes too long, which is undesirable as it leads to an increase in the size of the entire device. If the lower limit of conditional formula (3) is exceeded, the power of the first lens group L1 becomes too strong, which is undesirable as it leads to insufficient correction of various aberrations, especially at the telephoto end.

[0025] Conditional formula (4) specifies the ratio between the focal length of the second lens group L2 and the absolute value of the focal length of the entire system at the telephoto end. If the upper limit of conditional formula (4) is exceeded, the power of the second lens group L2 becomes weak, and the total optical length of the entire system becomes too long, which is undesirable as it leads to an increase in the size of the entire device. If the lower limit of conditional formula (4) is exceeded, the power of the second lens group L2 becomes too strong, which is undesirable as it leads to insufficient correction of various aberrations, particularly at the telephoto end.

[0026] Conditional formula (5) specifies the ratio between the focal length of the third lens group L3 and the absolute value of the focal length of the entire system at the telephoto end. If the upper limit of conditional formula (5) is exceeded, the power of the third lens group L3 becomes weak, and the total optical length of the entire system becomes too long, which is undesirable since it leads to an increase in the size of the entire device. If the lower limit of conditional formula (5) is exceeded, the power of the third lens group L3 becomes too strong, which is undesirable since it leads to insufficient correction of various aberrations, particularly at the telephoto end.

[0027] Conditional formula (6) specifies the ratio between the focal length of the fourth lens group L4 and the absolute value of the focal length of the entire system at the telephoto end. If the upper limit of conditional formula (6) is exceeded, the power of the fourth lens group L4 becomes weak, and the total optical length of the entire system becomes too long, which is undesirable since it leads to an increase in the size of the entire device. If the lower limit of conditional formula (6) is exceeded, the power of the fourth lens group L4 becomes too strong, which is undesirable since it leads to insufficient correction of various aberrations, particularly at the telephoto end.

[0028] Conditional expression (7) defines the ratio between the absolute value of the focal length of the entire system at the telephoto end and the focal length of the fifth lens group L5. If the upper limit of conditional expression (7) is exceeded, the power of the fifth lens group L5 becomes too strong, which is undesirable because correction of various aberrations becomes insufficient. If the lower limit of conditional expression (7) is exceeded, the power of the fifth lens group L5 becomes too weak, which makes the total optical length of the entire system too long, which is undesirable because it leads to an increase in the size of the entire device.

[0029] Preferably, the numerical ranges of the conditional expressions (1) to (7) are as follows: -17.00 <f1 / f2<-8.30 ···(1a) 0.605 <D / L<0.990 ···(2a) 0.120 <f1 / |ft|<0.230 ···(3a) -0.023 <f2 / |ft|<-0.011 ···(4a) 0.014 <f3 / |ft|<0.050 ···(5a) -0.800 <f4 / |ft|<-0.010 ···(6a) 42<|ft| / f5<180 ···(7a)

[0030] It is even more preferable that the numerical ranges of the conditional expressions (1) to (7) are as follows: -14.00 <f1 / f2<-8.60 ···(1b) 0.610 <D / L<0.980 ···(2b) 0.140 <f1 / |ft|<0.210 ···(3b) -0.023 <f2 / |ft|<-0.012 ···(4b) 0.017 <f3 / |ft|<0.050 ···(5b) -0.700 <f4 / |ft|<-0.020 ···(6b) 44<|ft| / f5<150 ···(7b)

[0031] The zoom lens of the present invention has an aperture stop SP between the fifth lens group L5 and the secondary image point. In the case of using a cooled camera, the aperture stop SP is arranged closest to the image side of the optical system, so that the position of the exit pupil of the optical system and the position of the aperture stop SP can be matched to achieve aperture matching. In the infrared imaging device, in order to eliminate the influence of unnecessary infrared rays (e.g., self-emission of the lens barrel, etc.) emitted from other than the object to be inspected by the infrared detector, a cold shield having an opening that passes infrared rays collected by the infrared optical system is arranged between the infrared optical system and the infrared detector to block unnecessary light from the periphery of the detection surface, and the cold shield and the infrared detector are cooled to a low temperature (almost liquid nitrogen temperature) to eliminate infrared rays emitted from them as much as possible.

[0032] The zoom lens of the present invention has, in the first lens unit L1, a negative lens formed of an optical material that satisfies the following conditional expression (8). 0<ν4μm<150 (8) Here, ν4μm is the refractive index at a wavelength of 4μm, N3μm is the refractive index at a wavelength of 3μm, and N5μm is the refractive index at a wavelength of 5μm. ν4μm=(N4μm-1) / (N3μm-N5μm) ···(9) The variance is expressed by the formula:

[0033] Conditional formula (8) shows the conditional formula for the dispersion of the negative lens disposed in the first lens group L1. It is necessary to appropriately correct the axial chromatic aberration of the optical system, particularly the axial chromatic aberration of the positive lens group in an optical system with a long focal length. If the upper limit of conditional formula (8) is exceeded, it becomes difficult to correct the axial chromatic aberration due to the relationship with the dispersion of the positive lens.

[0034] It is preferable to set the numerical range of conditional expression (8) as follows: 0<ν4μm<130.0 (8a) It is even more preferable to set the numerical range of conditional expression (8a) as follows: 0<ν4μm<115.0 (8b)

[0035] Furthermore, the present invention is characterized in that it is an imaging device having a solid-state imaging element that receives an image formed by the infrared optical system of the present invention. This relates to an imaging device having an element that receives an image captured by the infrared optical system. In recent years, bolometers and collector elements have been used as thermal (uncooled) infrared sensors, and InSb, InGaAs, and T2SL types have been mainly used as quantum (cooled) infrared sensors, and the present invention is also an imaging device having a solid-state imaging element corresponding to these.

[0036] In thermal (uncooled) infrared sensors, the incoming infrared light is thermally coupled with the sensor, which detects it as heat and converts it into an electrical signal for measurement. Quantum (cooled) infrared sensors convert the incoming infrared light directly into quanta, measuring it by converting the infrared light quanta into an electrical signal proportional to the number of photons. The specific configuration of the zoom lens of each embodiment will be described in detail below. EXAMPLES

[0037] FIG. 1 is a cross-sectional view of the optical system (zoom lens) 1a in Example 1 at the wide-angle end and a diagram of the movement locus. The first lens group (positive lens group) L1 is composed of a meniscus positive lens (first positive lens) G11 having a convex shape toward the object side and a meniscus negative lens (first negative lens) G12 having a convex shape toward the object side, which are arranged in order from the object side to the image side. The second lens group L2 is composed of a negative lens G21 having a biconcave shape. The third lens group L3 is composed of a positive lens G31 having a biconvex shape. The fourth lens group L4 is composed of a meniscus negative lens G41 having a convex shape toward the object side. The fifth lens group L5 is composed of a meniscus positive lens G51 having a convex shape toward the image side, a meniscus positive lens G52 having a convex shape toward the image side, and a meniscus positive lens G53 having a convex shape toward the image side.

[0038] In addition, the opening of the cold shield is designed so that the position and size (diameter of the exit pupil) of the infrared optical system are consistent, and this state is generally called the "aperture-matched state." In this way, the cold shield is aperture-matched with the exit pupil of the infrared optical system, so that the infrared detector can efficiently suppress unnecessary infrared light other than that of the object to be examined in the infrared optical system, and can take in only the infrared light of the object to be examined. For this reason, the aperture stop SP is disposed on the image side of the meniscus positive lens G53, which is the most image side of the optical system 1a, and does not move during zooming. However, this embodiment is not limited to this, and the aperture stop SP may be movable. This point is the same in each embodiment described later.

[0039] A primary image plane IP' on the image side of the fourth lens group L4 is relay imaged by the fifth lens group L5 via the aperture stop SP onto an image plane IP (detector surface). A light receiving element (not shown) is provided on the detector surface to receive the subject image. By forming the primary image and positioning the entrance pupil on the object side of the aperture stop SP, it is possible to reduce the lens aperture on the object side of the optical system 1a.

[0040] Fig. 2A is an aberration diagram of the optical system 1a at the wide-angle end, and Fig. 2B is an aberration diagram of the optical system 1a at the telephoto end. It can be seen that the zoom lens according to Example 1 has aberrations corrected well. EXAMPLES

[0041] FIG. 3 is a cross-sectional view and a movement locus diagram of the optical system (zoom lens) 1b in the second embodiment at the wide-angle end. The configuration of the optical system 1b is approximately the same as that of the optical system 1a in the first embodiment. The first lens group (positive lens group) L1 is composed of a meniscus positive lens (first positive lens) G11 having a convex shape toward the object side, and a meniscus negative lens (first negative lens) G12 having a convex shape toward the object side. The second lens group L2 is composed of a negative lens G21 having a biconcave shape. The third lens group L3 is composed of a positive lens G31 having a biconvex shape. The fourth lens group L4 is composed of a meniscus negative lens G41 having a convex shape toward the object side. The fifth lens group L5 is composed of a meniscus positive lens G51 having a convex shape toward the image side, a meniscus positive lens G52 having a convex shape toward the image side, and a meniscus positive lens G53 having a convex shape toward the image side. The aperture stop SP is disposed closest to the image side of the optical system 1b. Aperture matching can be achieved by matching the position of the exit pupil of the optical system 1b with the position of the aperture stop SP.

[0042] Fig. 4A is a diagram showing aberrations of the optical system 1b at the wide-angle end, and Fig. 4B is a diagram showing aberrations of the optical system 1b at the telephoto end. It can be seen that the zoom lens according to Example 2 has aberrations corrected well. EXAMPLES

[0043] FIG. 5 is a cross-sectional view of the optical system (zoom lens) 1c in the third embodiment at the wide-angle end and a diagram of the movement locus. The first lens group (positive lens group) L1 is composed of a meniscus positive lens G11 having a convex shape toward the object side and a meniscus negative lens G12 having a convex shape toward the object side. The second lens group L2 is composed of a negative lens G21 having a biconcave shape. The third lens group L3 is composed of a positive lens G31 having a biconvex shape. The fourth lens group L4 is composed of a meniscus negative lens G41 having a convex shape toward the object side. The fifth lens group L5 is composed of a meniscus positive lens G51 having a convex shape toward the image side, a meniscus negative lens G52 having a convex shape toward the image side, and a meniscus positive lens G53 having a convex shape toward the image side. The aperture stop SP is disposed closest to the image side of the optical system 1c. By matching the position of the exit pupil of the optical system 1c with the position of the aperture stop SP, it is possible to obtain aperture matching.

[0044] Fig. 6A is a diagram showing aberrations of the optical system 1c at the wide-angle end, and Fig. 6B is a diagram showing aberrations of the optical system 1c at the telephoto end. It can be seen that the zoom lens according to Example 3 has aberrations corrected well. EXAMPLES

[0045] FIG. 7 is a cross-sectional view and a diagram of a movement locus of an optical system (zoom lens) 1d in Example 4 at a wide-angle end. The first lens group (positive lens group) L1 is composed of a meniscus positive lens G11 having a convex shape toward the object side and a meniscus negative lens G12 having a convex shape toward the object side. The second lens group L2 is composed of a negative lens G21 having a biconcave shape. The third lens group L3 is composed of a positive lens G31 having a biconvex shape. The fourth lens group L4 is composed of a meniscus negative lens G41 having a convex shape toward the object side. The fifth lens group L5 is composed of a meniscus positive lens G51 having a convex shape toward the image side, a meniscus negative lens G52 having a convex shape toward the image side, and a meniscus positive lens G53 having a convex shape toward the image side. The aperture stop SP is disposed closest to the image side of the optical system 1d. By matching the position of the exit pupil of the optical system 1d with the position of the aperture stop SP, it is possible to obtain aperture matching.

[0046] Fig. 8A is a diagram showing aberrations of the optical system 1d at the wide-angle end, and Fig. 8B is a diagram showing aberrations of the optical system 1d at the telephoto end. It can be seen that the zoom lens according to Example 4 has aberrations corrected well. EXAMPLES

[0047] FIG. 9 is a cross-sectional view and a diagram of a movement locus of the optical system (zoom lens) 1e in the fifth embodiment at the wide-angle end. The first lens group (positive lens group) L1 is composed of a meniscus positive lens G11 having a convex shape toward the object side and a meniscus negative lens G12 having a convex shape toward the object side. The second lens group L2 is composed of a negative lens G21 having a biconcave shape. The third lens group L3 is composed of a positive lens G31 having a biconvex shape. The fourth lens group L4 is composed of a meniscus negative lens G41 having a convex shape toward the object side. The fifth lens group L5 is composed of a meniscus positive lens G51 having a convex shape toward the image side, a meniscus positive lens G52 having a convex shape toward the image side, and a meniscus positive lens G53 having a convex shape toward the image side. The aperture stop SP is disposed closest to the image side of the optical system 1e. By matching the position of the exit pupil of the optical system 1e with the position of the aperture stop SP, it is possible to obtain aperture matching.

[0048] Fig. 10A is an aberration diagram of the optical system 1e at the wide-angle end, and Fig. 10B is an aberration diagram of the optical system 1e at the telephoto end. It can be seen that the aberration is well corrected in the zoom lens according to Example 5. EXAMPLES

[0049] FIG. 11 is a cross-sectional view of an optical system 1f in Example 6. The first lens group (positive lens group) L1 is composed of a meniscus positive lens G11 having a convex shape toward the object side and a meniscus negative lens G12 having a convex shape toward the object side. The second lens group L2 is composed of a negative lens G21 having a biconcave shape. The third lens group L3 is composed of a positive lens G31 having a biconvex shape. The fourth lens group L4 is composed of a meniscus negative lens G41 having a convex shape toward the object side. The fifth lens group L5 is composed of a meniscus positive lens G51 having a convex shape toward the image side, a meniscus positive lens G52 having a convex shape toward the image side, and a meniscus positive lens G53 having a convex shape toward the image side. The aperture stop SP is disposed closest to the image side of the optical system 1f. By matching the position of the exit pupil of the optical system 1f with the position of the aperture stop SP, it is possible to achieve aperture matching.

[0050] 12A is a diagram showing aberrations of the optical system 1f at the wide-angle end, and FIG 12B is a diagram showing aberrations of the optical system 1f at the telephoto end. It can be seen that the zoom lens according to Example 6 has aberrations corrected well. EXAMPLES

[0051] FIG. 13 is a cross-sectional view of an optical system 1g in Example 7. The first lens group (positive lens group) L1 is composed of a meniscus positive lens G11 having a convex shape toward the object side and a meniscus negative lens G12 having a convex shape toward the object side. The second lens group L2 is composed of a negative lens G21 having a biconcave shape. The third lens group L3 is composed of a positive lens G31 having a biconvex shape. The fourth lens group L4 is composed of a meniscus negative lens G41 having a convex shape toward the object side. The fifth lens group L5 is composed of a meniscus positive lens G51 having a convex shape toward the image side, a meniscus positive lens G52 having a convex shape toward the image side, and a meniscus positive lens G53 having a convex shape toward the image side. The aperture stop SP is disposed closest to the image side of the optical system 1g. Aperture matching can be achieved by matching the position of the exit pupil of the optical system 1g with the position of the aperture stop SP.

[0052] 14A is a diagram showing aberrations of the optical system 1g at the wide-angle end, and FIG 14B is a diagram showing aberrations of the optical system 1g at the telephoto end. It can be seen that the aberrations of the zoom lens according to Example 7 are well corrected. EXAMPLES

[0053] FIG. 15 is a cross-sectional view of an optical system 1h in Example 8. The first lens group (positive lens group) L1 is composed of a meniscus positive lens G11 having a convex shape toward the object side and a meniscus negative lens G12 having a convex shape toward the object side. The second lens group L2 is composed of a negative lens G21 having a biconcave shape. The third lens group L3 is composed of a positive lens G31 having a biconvex shape. The fourth lens group L4 is composed of a meniscus negative lens G41 having a convex shape toward the object side. The fifth lens group L5 is composed of a meniscus positive lens G51 having a convex shape toward the image side, a meniscus positive lens G52 having a convex shape toward the image side, and a meniscus positive lens G53 having a convex shape toward the image side. The aperture stop SP is disposed closest to the image side of the optical system 1h. Aperture matching can be achieved by matching the position of the exit pupil of the optical system 1h with the position of the aperture stop SP.

[0054] 16A is a diagram showing aberrations of the optical system 1h at the wide-angle end, and FIG 16B is a diagram showing aberrations of the optical system 1h at the telephoto end. It can be seen that the aberrations of the zoom lens according to Example 8 are well corrected. EXAMPLES

[0055] FIG. 17 is a cross-sectional view of the optical system 1i in the ninth embodiment. The first lens group (positive lens group) L1 is composed of a meniscus positive lens G11 having a convex shape toward the object side and a meniscus negative lens G12 having a convex shape toward the object side. The second lens group L2 is composed of a negative lens G21 having a biconcave shape. The third lens group L3 is composed of a positive lens G31 having a biconvex shape. The fourth lens group L4 is composed of a meniscus negative lens G41 having a convex shape toward the object side. The fifth lens group L5 is composed of a meniscus positive lens G51 having a convex shape toward the image side, a meniscus positive lens G52 having a convex shape toward the image side, and a meniscus positive lens G53 having a convex shape toward the object side. The aperture stop SP is disposed closest to the image side of the optical system 1i. Aperture matching can be achieved by matching the position of the exit pupil of the optical system 1i with the position of the aperture stop SP.

[0056] 18A is a diagram showing aberrations of the optical system 1i at the wide-angle end, and FIG 18B is a diagram showing aberrations of the optical system 1i at the telephoto end. It can be seen that the zoom lens of Example 9 has aberrations corrected well.

[0057] In each embodiment, the shape or number of lenses constituting the optical system is not limited and may be changed as appropriate. Also, some lenses and lens groups may be moved to have a component perpendicular to the optical axis OA, thereby correcting image blur caused by vibration such as camera shake. Also, distortion aberration and chromatic aberration may be corrected by an electrical correction means. Also, the angle of view and FNO (F-number) are not limited and may be changed as appropriate. Also, focusing is not limited to being performed by moving the lens groups, and may be performed by moving an imaging element such as a sensor.

[0058] Next, numerical examples corresponding to each embodiment will be shown. In each numerical example, the surface numbers are indicated in order from the object side, r is the radius of curvature, d is the spacing between optical surfaces, N3 μm, N4 μm, and N5 μm are refractive indices based on wavelengths of 3 μm, 4 μm, and 5 μm, respectively, and ν4 μm is dispersion based on a wavelength of 4 μm.

[0059] The * symbol to the right of the surface number indicates an aspheric surface. Note that the aspheric shape is expressed by the following formula, where the displacement in the optical axis direction at a position of height h from the optical axis is x with respect to the vertex of the surface.

number

[0060] In each numerical example, the notation (diffraction) to the right of the surface number means that the optical surface is a diffractive surface. The definition of a diffractive surface is expressed by the optical path difference function Ψ of the following equation (11).

number

[0061] The diffractive surface is formed by being cut in a step-like manner concentrically, and the amount of cutting with respect to the substrate surface is expressed by the following formula (12).

number

[0062] [Numerical Example 1] Unit: mm Surface Data Surface number rd N4μm v4μm 1 170.574 28.00 3.4289 233.5 2* 299.738 36.93 3 761.916 7.00 1.6979 22.5 4 410.082 (variable) 5* -246.586 3.00 4.0255 109.6 6 64.049 (variable) 7 92.564 8.00 2.4324 177.0 8*(diffraction) -110.681 (variable) 9 21.954 6.00 4.0255 109.6 10*(diffraction) 15.319 7.45 11 -17.952 5.00 4.0255 109.6 12 -15.707 13.30 13* -15.963 5.00 4.0255 109.6 14 -18.291 2.87 15 -100.777 5.00 3.4289 233.5 16 -31.219 3.00 17 ∞ 1.00 4.0255 109.6 18(Aperture) ∞ 25.00 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4= 5.13015e-09 A 6=-4.06443e-14 5th page K = 0.00000e+00 A 4= 2.25175e-06 A 6= 2.49256e-09 A 8=-1.62565e-11 Side 8 K = 0.00000e+00 A 4= 1.22466e-06 A 6=-1.10857e-10 Side 10 K = 0.00000e+00 A 4= 1.80805e-04 A 6=-8.68895e-06 A 8= 2.88566e-07 Page 13 K = 0.00000e+00 A 4=-8.17367e-05 A 6= 1.37836e-06 A 8=-5.63246e-08 Diffraction surface data Side 8 C 2=-1.22524e-04 C 4= 3.51671e-08 C 6= 9.90953e-11 C 8=-1.11176e-13 Side 10 C 2= 2.40322e-03 C 4=-3.26204e-04 C 6= 2.94960e-05 C 8=-8.02730e-07 Various data Zoom ratio 32.26 Wide-angle end Telephoto end Focal length -23.23 -749.44 F-number 4.00 4.00 Half angle of view 14.25 0.45 Image height 5.90 5.90 Lens length 305.73 305.73 BF 25.00 25.00 d 4 6.62 73.65 d 6 104.19 64.92 d 8 37.74 9.97 Zoom lens group data Group starting plane focal length 1 1 150.53 2 5 -16.68 3 7 35.71 4 9 -43.60 5 11 16.42

[0063] [Numerical Example 2] Unit: mm Surface Data Surface number rd N4μm v4μm 1 168.937 28.00 3.4289 233.5 2* 305.394 37.40 3 900.766 7.00 1.6979 22.5 4 433.739 (variable) 5* -472.351 3.00 4.0255 109.6 6 43.619 (variable) 7 62.218 8.00 2.4324 177.0 8*(diffraction) -94.013 (variable) 9 17.889 6.03 4.0255 109.6 10*(diffraction) 10.685 5.95 11 -12.416 1.38 4.0255 109.6 12 -9.749 10.47 13* -19.337 3.81 4.0255 109.6 14 -21.421 1.45 15 -44.941 2.30 3.4289 233.5 16 -19.475 3.00 17 ∞ 1.00 4.0255 109.6 18(Aperture) ∞ 25.00 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4= 6.63729e-09 A 6=-7.24715e-14 5th page K = 0.00000e+00 A 4= 4.46475e-06 A 6= 5.19759e-09 A 8=-6.42949e-11 Side 8 K = 0.00000e+00 A 4= 3.08423e-06 A 6=-5.49242e-10 Side 10 K = 0.00000e+00 A 4= 3.66223e-04 A 6=-1.81127e-06 A 8= 8.20053e-07 Page 13 K = 0.00000e+00 A 4=-1.19264e-04 A 6= 1.96458e-06 A 8=-8.22829e-08 Diffraction surface data Side 8 C 2=-1.22524e-04 C 4= 3.51671e-08 C 6= 9.90953e-11 C 8=-1.11176e-13 Side 10 C 2= 2.40322e-03 C 4=-3.26204e-04 C 6= 2.94960e-05 C 8=-8.02730e-07 Various data Zoom ratio 41.90 Wide-angle end Telephoto end Focal length -17.88 -749.30 F-number: 4.2 4.2 Half angle of view 18.26 0.45 Image height 5.90 5.90 Lens total length 269.60 269.60 BF 25.00 25.00 d 4 5.68 70.84 d 6 94.06 44.85 d 8 25.92 9.96 Zoom lens group data Group starting plane focal length 1 1 144.86 2 5 -13.14 3 7 26.77 4 9 -21.80 5 11 14.59

[0064] [Numerical Example 3] Unit: mm Surface Data Surface number rd N4μm v4μm 1 169.274 28.00 3.4289 233.5 2* 308.631 35.50 3 853.620 7.00 1.6979 22.5 4 428.469 (variable) 5* -133.343 3.00 4.0255 109.6 6 46.642 (variable) 7 41.944 8.00 2.4324 177.0 8*(diffraction) -64.087 (variable) 9 12.207 3.36 4.0255 109.6 10*(diffraction) 7.858 3.23 11 -8.547 1.40 4.0255 109.6 12 -6.643 7.56 13* -19.872 2.10 4.0255 109.6 14 -23.055 0.98 15 -29.631 2.30 3.4289 233.5 16 -13.058 3.00 17 ∞ 1.00 4.0255 109.6 18(Aperture) ∞ 25.00 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4= 6.92133e-09 A 6=-7.30712e-14 5th page K = 0.00000e+00 A 4= 7.76758e-06 A 6= 2.15888e-08 A 8=-1.34924e-10 Side 8 K = 0.00000e+00 A 4= 1.02690e-05 A 6=-3.13155e-09 Side 10 K = 0.00000e+00 A 4= 4.11159e-04 A 6= 2.20595e-04 A 8=-9.89273e-06 Page 13 K = 0.00000e+00 A 4=-3.51087e-04 A 6= 3.07285e-06 A 8=-4.73166e-08 Diffraction surface data Side 8 C 2=-1.22524e-04 C 4= 3.51671e-08 C 6= 9.90953e-11 C 8=-1.11176e-13 Side 10 C 2= 2.40322e-03 C 4=-3.26204e-04 C 6= 2.94960e-05 C 8=-8.02730e-07 Various data Zoom ratio 46.84 Wide-angle end Telephoto end Focal length -16.01 -750.02 F-number: 4.2 4.2 Half angle of view 20.23 0.45 Image height 5.90 5.90 Lens length 236.37 236.37 BF 25.00 25.00 d 4 5.01 73.47 d 6 83.21 21.36 d 8 16.59 9.99 Zoom lens group data Group starting plane focal length 1 1 143.86 2 5 -11.28 3 7 18.44 4 9 -16.33 5 11 10.56

[0065] [Numerical Example 4] Unit: mm Surface Data Surface number rd N4μm v4μm 1 165.081 28.00 3.4289 233.5 2* 312.837 29.79 3 1364.580 7.00 1.6979 22.5 4 547.149 (variable) 5* -88.853 3.00 4.0255 109.6 6 52.008 (variable) 7 36.098 7.50 2.4324 177.0 8*(diffraction) -52.270 (variable) 9 9.653 1.75 4.0255 109.6 10*(diffraction) 7.310 2.39 11 -7.744 1.40 4.0255 109.6 12 -6.006 6.09 13* -27.244 1.66 4.0255 109.6 14 -33.201 0.70 15 -19.975 3.00 3.4289 233.5 16 -10.291 3.00 17 ∞ 1.00 4.0255 109.6 18(Aperture) ∞ 25.00 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4= 8.63812e-09 A 6=-1.41093e-13 5th page K = 0.00000e+00 A 4= 1.01398e-05 A 6= 9.00453e-09 A 8= 7.91560e-11 Side 8 K = 0.00000e+00 A 4= 1.59646e-05 A 6=-3.54742e-09 Side 10 K = 0.00000e+00 A 4= 4.91002e-04 A 6= 7.19030e-04 A 8=-8.60201e-05 Page 13 K = 0.00000e+00 A 4=-7.19258e-04 A 6= 1.00068e-05 A 8=-6.44527e-08 Diffraction surface data Side 8 C 2=-3.92387e-04 C 4= 2.15329e-06 C 6=-8.63755e-09 C 8= 6.43352e-12 Side 10 C 2= 2.95703e-03 C 4= 1.75006e-03 C 6=-1.63852e-03 C 8= 3.22690e-04 Various data Zoom ratio 45.85 Wide-angle end Telephoto end Focal length -16.27 -745.85 F-number 4.5 4.5 Half angle of view 19.94 0.45 Image height 5.90 5.90 Lens total length 217.30 217.30 BF 25.00 25.00 d 4 3.97 71.55 d 6 76.27 12.93 d 8 13.91 9.67 Zoom lens group data Group starting plane focal length 1 1 134.55 2 5 -10.67 3 7 15.52 4 9 -20.36 5 11 8.68

[0066] [Numerical Example 5] Unit: mm Surface Data Surface number rd N4μm v4μm 1 164.311 28.00 3.4289 233.5 2* 310.313 28.13 3 830.220 7.00 1.4096 21.7 4 339.143 (variable) 5* -67.296 3.00 4.0255 109.6 6 56.363 (variable) 7 35.484 7.50 2.4324 177.0 8*(diffraction) -45.284 (variable) 9 9.512 1.38 4.0255 109.6 10*(diffraction) 7.132 2.48 11 -7.821 1.40 4.0255 109.6 12 -5.953 6.17 13* -60.419 0.28 4.0255 109.6 14 -48.177 0.70 15 -16.286 3.00 3.4289 233.5 16 -9.660 3.00 17 ∞ 1.00 4.0255 109.6 18(Aperture) ∞ 25.00 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4= 9.13817e-09 A 6=-1.06254e-13 5th page K = 0.00000e+00 A 4= 1.20635e-05 A 6= 2.90228e-08 A 8=-9.87391e-11 Side 8 K = 0.00000e+00 A 4= 2.01956e-05 A 6=-9.87364e-09 Side 10 K = 0.00000e+00 A 4=-2.39643e-04 A 6= 7.76152e-04 A 8=-5.86808e-05 Page 13 K = 0.00000e+00 A 4=-8.48132e-04 A 6= 1.60159e-05 A 8=-1.21419e-07 Diffraction surface data Side 8 C 2=-3.62568e-04 C 4= 9.87748e-07 C 6=-9.42339e-10 C 8=-4.70997e-12 Side 10 C 2=-2.15811e-03 C 4= 4.98746e-03 C 6=-2.18943e-03 C 8= 2.99687e-04 Various data Zoom ratio 49.19 Wide-angle end Telephoto end Focal length -15.24 -749.59 F-number: 4.2 4.2 Half angle of view 21.16 0.45 Image height 5.90 5.90 Lens length 210.87 210.87 BF 25.00 25.00 d 4 5.45 71.98 d 6 74.89 11.11 d 8 12.80 10.04 Zoom lens group data Group starting plane focal length 1 1 133.69 2 5 -9.96 3 7 14.55 4 9 -17.79 5 11 8.16

[0067] [Numerical Example 6] Unit: mm Surface Data Surface number rd N4μm v4μm 1 163.339 28.00 3.4289 233.5 2 337.601 7.34 3 501.023 7.00 4.0255 109.6 4*(diffraction) 351.237 (variable) 5* -139.035 3.00 4.0255 109.6 6 66.452 (variable) 7 77.698 14.04 2.4324 177.0 8*(diffraction) -124.201 (variable) 9 18.641 6.00 4.0255 109.6 10*(diffraction) 14.003 18.54 11 -29.168 3.00 4.0255 109.6 12 -17.626 6.85 13* -20.100 3.00 4.0255 109.6 14 -20.727 0.50 15 61.757 3.00 3.4289 233.5 16 -96.661 3.00 17 ∞ 1.00 4.0255 109.6 18(Aperture) ∞ 25.00 Image plane ∞ Aspheric Data Side 4 K = 0.00000e+00 A 4= 2.90711e-09 A 6=-1.74996e-13 5th page K = 0.00000e+00 A 4= 2.55579e-06 A 6=-7.96669e-10 A 8=-5.44388e-13 Side 8 K = 0.00000e+00 A 4= 1.29886e-06 A 6=-1.10697e-10 Side 10 K = 0.00000e+00 A 4= 1.37965e-05 A 6=-6.70000e-08 A 8= 2.09682e-09 Page 13 K = 0.00000e+00 A 4=-5.88502e-05 Diffraction surface data Side 4 C 2=-7.95872e-06 C 4=-4.42703e-10 C 6= 2.30070e-14 Side 8 C 2=-3.09547e-04 C 4= 3.56508e-07 C 6= 4.39162e-11 C 8=-1.79467e-14 Side 10 C 2= 8.46249e-04 C 4=-2.01402e-05 C 6= 2.57143e-07 C 8=-4.38929e-09 Various data Zoom ratio 51.18 Wide-angle end Telephoto end Focal length -14.66 -750.07 F-number 3.99 3.99 Half angle of view 21.93 0.45 Image height 5.90 5.90 Lens total length 280.05 280.05 BF 25.00 25.00 d 4 7.51 98.15 d 6 126.97 15.94 d 8 16.21 36.60 Zoom lens group data Group starting plane focal length 1 1 150.09 2 5 -14.70 3 7 34.12 4 9 -359.71 5 11 9.32

[0068] [Numerical Example 7] Unit: mm Surface Data Surface number rd N4μm v4μm 1 163.339 28.00 3.4289 233.5 2 337.601 7.31 3 487.662 7.00 4.0255 109.6 4*(diffraction) 351.237 (variable) 5* -126.793 3.00 4.0255 109.6 6 79.169 (variable) 7 87.769 8.14 2.4324 177.0 8*(diffraction) -99.468 (variable) 9 18.409 6.00 4.0255 109.6 10*(diffraction) 13.839 18.56 11 -28.395 3.00 4.0255 109.6 12 -17.763 7.32 13* -19.157 3.00 4.0255 109.6 14 -19.682 0.50 15 65.690 3.00 3.4289 233.5 16 -78.415 3.00 17 ∞ 1.00 4.0255 109.6 18(Aperture) ∞ 25.00 Image plane ∞ Aspheric Data Side 4 K = 0.00000e+00 A 4= 3.56040e-09 A 6=-1.70184e-13 5th page K = 0.00000e+00 A 4= 2.22108e-06 A 6=-4.91105e-10 A 8=-5.44388e-13 Side 8 K = 0.00000e+00 A 4= 1.27162e-06 A 6=-1.12492e-10 Side 10 K = 0.00000e+00 A 4= 1.05813e-05 A 6=-2.78023e-08 A 8= 2.09682e-09 Page 13 K = 0.00000e+00 A 4=-6.50792e-05 Diffraction surface data Side 4 C 2=-7.95872e-06 C 4=-4.02128e-10 C 6= 2.30070e-14 Side 8 C 2=-3.37636e-04 C 4= 4.17459e-07 C 6= 4.39162e-11 C 8=-1.79467e-14 Side 10 C 2= 8.46249e-04 C 4=-1.29837e-05 C 6= 1.50010e-07 C 8=-4.38929e-09 Various data Zoom ratio 47.12 Wide-angle end Telephoto end Focal length -15.91 -749.87 F-number 4.00 4.00 Half angle of view 20.34 0.45 Image height 5.90 5.90 Lens length 257.73 257.73 BF 25.00 25.00 d 4 4.38 94.69 d 6 114.35 6.37 d 8 15.10 32.77 Zoom lens group data Group starting plane focal length 1 1 147.07 2 5 -15.93 3 7 32.69 4 9 -499.70 5 11 9.47

[0069] [Numerical Example 8] Unit: mm Surface Data Surface number rd N4μm v4μm 1 149.717 30.00 3.4289 233.5 2 317.203 2.03 3 337.581 7.00 4.0255 109.6 4*(diffraction) 282.239 (variable) 5* -75.292 3.00 4.0255 109.6 6 78.069 (variable) 7 50.191 10.35 2.4324 177.0 8*(diffraction) -65.790 (variable) 9 14.862 6.28 4.0255 109.6 10*(diffraction) 9.733 10.56 11 96.019 2.20 4.0255 109.6 12 -78.557 5.04 13* -25.844 2.10 4.0255 109.6 14 -14.141 0.50 15 31.042 2.00 3.4289 233.5 16 212.188 3.00 17 ∞ 1.00 4.0255 109.6 18(Aperture) ∞ 25.00 Image plane ∞ Aspheric Data Side 4 K = 0.00000e+00 A 4= 1.46312e-08 A 6=-1.77446e-13 5th page K = 0.00000e+00 A 4= 5.95121e-06 A 6=-2.01987e-09 A 8=-3.21047e-12 Side 8 K = 0.00000e+00 A 4= 6.04249e-06 A 6=-1.49969e-09 Side 10 K = 0.00000e+00 A 4= 1.50631e-05 A 6= 8.04235e-07 A 8= 4.11056e-09 Page 13 K = 0.00000e+00 A 4=-1.49656e-04 Diffraction surface data Side 4 C 2=-1.17252e-05 C 4=-4.51194e-10 C 6= 2.30070e-14 Side 8 C 2=-7.01452e-04 C 4= 1.84812e-06 C 6=-2.47358e-09 C 8= 7.12987e-13 Side 10 C 2= 1.04971e-03 C 4= 1.66811e-05 C 6=-1.93884e-06 C 8= 3.00945e-08 Various data Zoom ratio 43.99 Wide-angle end Telephoto end Focal length -17.04 -749.68 F-number 4.00 4.00 Half angle of view 19.10 0.45 Image height 5.90 5.90 Lens length 199.45 199.45 BF 25.00 25.00 d 4 5.00 77.67 d 6 82.18 1.46 d 8 1.93 9.98 Zoom lens group data Group starting plane focal length 1 1 117.39 2 5 -12.48 3 7 20.44 4 9 -100.04 5 11 5.87

[0070] [Numerical Example 9] Unit: mm Surface Data Surface number rd N4μm v4μm 1 148.545 30.00 3.4289 233.5 2 311.060 0.47 3 316.549 7.00 4.0255 109.6 4*(diffraction) 280.725 (variable) 5* -76.122 3.00 4.0255 109.6 6 80.785 (variable) 7 44.554 10.42 2.4324 177.0 8*(diffraction) -71.738 (variable) 9 14.181 6.45 4.0255 109.6 10*(diffraction) 8.993 10.78 11 512.542 2.20 4.0255 109.6 12 -44.815 3.48 13* -30.895 2.10 4.0255 109.6 14 -12.925 0.50 15 46.939 2.00 3.4289 233.5 16 131.230 3.00 17 ∞ 1.00 4.0255 109.6 18(Aperture) ∞ 25.00 Image plane ∞ Aspheric Data Side 4 K = 0.00000e+00 A 4= 1.68898e-08 A 6=-1.77446e-13 5th page K = 0.00000e+00 A 4= 5.39814e-06 A 6=-1.83945e-09 A 8=-2.46883e-12 Side 8 K = 0.00000e+00 A 4= 7.01049e-06 A 6=-2.33717e-09 Side 10 K = 0.00000e+00 A 4= 7.33316e-06 A 6= 1.04574e-06 A 8= 2.35291e-10 Page 13 K = 0.00000e+00 A 4=-2.37409e-04 A 6= 7.48134e-07 A 8= 1.41637e-09 Diffraction surface data Side 4 C 2=-7.57306e-06 C 4=-8.79670e-10 C 6= 2.30070e-14 Side 8 C 2=-8.74385e-04 C 4= 2.06791e-06 C 6=-2.41424e-09 C 8= 7.12987e-13 Side 10 C 2= 1.43458e-03 C 4= 2.98729e-05 C 6=-2.64236e-06 C 8= 4.19606e-08 Various data Zoom ratio 40.61 Wide-angle end Telephoto end Focal length -18.45 -749.21 F-number 4.00 4.00 Half angle of view 17.73 0.45 Image height 5.90 5.90 Lens length 191.95 191.95 BF 25.00 25.00 d 4 3.15 73.23 d 6 80.23 1.07 d 8 0.79 9.87 Zoom lens group data Group starting plane focal length 1 1 111.53 2 5 -12.77 3 7 19.65 4 9 -99.83 5 11 5.05

[0071] The values ​​of the respective numerical examples for the above-mentioned conditional expressions (1) to (8) are shown below. [Table 1]

[0072] (Imaging device) Next, with reference to FIG. 19, an imaging device (monitoring camera) 100 using the optical system (infrared optical system) of each embodiment as an imaging optical system will be described. FIG. 19 is a configuration diagram of an imaging device 100. 11 is a surveillance camera body. 15 is an imaging optical system configured by any one of the optical systems of Examples 1 to 9. 12 is an imaging element (photoelectric conversion element) equipped with an infrared sensor such as a bolometer type, MCT type, or T2SL type, which is built into the surveillance camera body 11 and receives a subject image formed by the imaging optical system 15 (captures an image formed by the optical system). 13 is a memory (recording unit) that records information corresponding to the subject image photoelectrically converted by the imaging element 12. 14 is a network cable (transfer unit) for transferring the subject image photoelectrically converted by the imaging element 12. Note that the imaging device of each embodiment is not limited to a surveillance camera, and can also be used as other imaging devices such as a video camera or a digital camera. A system (imaging system; surveillance camera system) may be configured including the optical system of each embodiment and a control unit that controls the optical system. In this case, the control unit can control each lens group to move as described above during zooming or focusing. In this case, the control unit does not need to be configured integrally with the optical system, and the control unit may be configured separately from the optical system. For example, a configuration may be adopted in which a control unit (control device) disposed remotely from a drive unit that drives each lens of the optical system includes a transmission unit that sends a control signal (command) for controlling the optical system. Such a control unit allows the optical system to be remotely operated. According to each embodiment, for example, it is possible to provide an optical system, an imaging device, and a system that are advantageous in terms of low cost and high optical performance. Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.

[0073] The disclosure of this embodiment includes the following configuration. (Configuration 1) the first optical system is composed of, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, and a second optical system is composed of a fifth lens group having positive refractive power, the first optical system forms an intermediate image between the first optical system and the second optical system; a distance between adjacent lens groups included in the first optical system changes due to zooming; Let ft be the focal length of the entire system at the telephoto end, F-number Fno, and D = |ft| / Fno. Let f1 be the focal length of the first lens group, f2 be the focal length of the second lens group, and L be the length on the optical axis from the optical surface of the first lens group closest to the object to the image plane. -20.00 <f1 / f2<-8.00 0.600 <D / L<1.000 A zoom lens characterized by satisfying the following conditional expression. (Configuration 2) The zoom lens according to configuration 1, characterized in that, during zooming from the wide-angle end to the telephoto end, the second lens group moves toward the image side, and the third lens group moves toward the object side and then moves toward the image side. (Configuration 3) 0.100 <f1 / |ft|<0.250 3. The zoom lens according to claim 1, wherein the following condition is satisfied: (Configuration 4) -0.023 <f2 / |ft|<-0.010 4. The zoom lens according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the focal length of the third lens group is f3, 0.000 <f3 / |ft|<0.050 5. The zoom lens according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) When the focal length of the fourth lens group is f4, -1.000 <f4 / |ft|<0.000 6. The zoom lens according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) When the focal length of the fifth lens group is f5, 40<|ft| / f5<200 7. The zoom lens according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) 8. The zoom lens according to any one of configurations 1 to 7, further comprising an aperture stop disposed between the fifth lens group and a secondary image point. (Configuration 9) the first lens group includes a positive lens and a negative lens, The negative lens has a refractive index of N4 μm at a wavelength of 4 μm, a refractive index of N3 μm at a wavelength of 3 μm, and a refractive index of N5 μm at a wavelength of 5 μm, ν4μm=(N4μm-1) / (N3μm-N5μm) The dispersion ν4μm defined as 0<ν4μm<150 9. The zoom lens according to any one of configurations 1 to 8, characterized in that it is made of a material that satisfies the following conditional expression: (Configuration 10) A zoom lens according to any one of configurations 1 to 9, and an image sensor for capturing an image formed by the zoom lens. [Explanation of symbols]

[0074] L1: First lens group L2: Second lens group L3: Third lens group L4: Fourth lens group L5: Fifth lens group S1: 1st optical system S2: Second optical system

Claims

1. a first optical system including, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, and a second optical system including a fifth lens group having positive refractive power, the first optical system forms an intermediate image between the first optical system and the second optical system; a distance between adjacent lens groups included in the first optical system changes due to zooming; Let ft be the focal length of the entire system at the telephoto end, F-number Fno, and D be defined as |ft| / Fno. Let f1 be the focal length of the first lens group, f2 be the focal length of the second lens group, and L be the length on the optical axis from the optical surface of the first lens group closest to the object to the image plane. -20.00<f1 / f2<-8.00 0.600<D / L<1.000 A zoom lens characterized by satisfying the following conditional expression.

2. 2. The zoom lens according to claim 1, wherein, during zooming from the wide-angle end to the telephoto end, the second lens group moves toward the image side, and the third lens group moves toward the object side and then moves toward the image side.

3. 0.100<f1 / |ft|<0.250 2. The zoom lens according to claim 1, which satisfies the following condition:

4. -0.023<f2 / |ft|<-0.010 2. The zoom lens according to claim 1, which satisfies the following condition:

5. When the focal length of the third lens group is f3, 0.000<f3 / |ft|<0.050 2. The zoom lens according to claim 1, which satisfies the following condition:

6. When the focal length of the fourth lens group is f4, -1.000<f4 / |ft|<0.000 2. The zoom lens according to claim 1, which satisfies the following condition:

7. When the focal length of the fifth lens group is f5, 40<|ft| / f5<200 2. The zoom lens according to claim 1, which satisfies the following condition:

8. 2. The zoom lens according to claim 1, further comprising an aperture stop disposed between the fifth lens group and a secondary image point.

9. the first lens group includes a positive lens and a negative lens, The negative lens has a refractive index of N4 μm at a wavelength of 4 μm, a refractive index of N3 μm at a wavelength of 3 μm, and a refractive index of N5 μm at a wavelength of 5 μm, ν4μm=(N4μm-1) / (N3μm-N5μm) The dispersion ν4μm defined as 0<ν4μm<150 2. The zoom lens according to claim 1, which is made of a material that satisfies the following condition:

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

Images