CN113448068A - Zoom lens and imaging device - Google Patents

Abstract

The invention relates to a zoom lens and an imaging apparatus. A zoom lens as one aspect of the present invention is a zoom lens including a negative 1 st lens group and a positive 2 nd lens group arranged in this order from an object side to an image side, wherein intervals between adjacent lens groups each vary for zooming, the 2 nd lens group includes at least 2 positive lenses and at least 2 negative lenses, a negative lens located on the image side of the at least 2 negative lenses has an aspherical surface, and a focal length f of the 1 st lens group, a focal length f2 of the 2 nd lens group, an average abbe number ν d2p of the at least 2 positive lenses, and a minimum value bfwt of an air-converted back focal length at a wide-angle end satisfy a predetermined condition.

Description

Zoom lens and imaging device

Technical Field

The invention relates to a zoom lens and an imaging apparatus.

Background

As a photographing optical system in an imaging apparatus such as a surveillance camera, a digital camera, a video camera, or the like including an imaging element, an optical system having high optical performance corresponding to a high-definition imaging element is desired. In recent years, with the rapid expansion of the market of surveillance cameras, there has been a strong demand for downsizing of surveillance cameras from the viewpoint of installation and concealment. Further, an optical system which is bright (has a small F value) and can perform imaging with high optical performance even in near infrared light is required to perform imaging in a dark place. Japanese patent laid-open No. 2009-230122 discloses a 2-group zoom lens including a negative lens group and a positive lens group arranged in this order from an object side to an image side.

In the zoom lens of japanese patent laid-open No. 2009-.

Disclosure of Invention

An object of the present invention is to provide a zoom lens which is small, bright, and advantageous in terms of high optical performance from visible light to near-infrared light, for example.

A zoom lens as one aspect of the present invention is a zoom lens including a negative 1 st lens group and a positive 2 nd lens group arranged in this order from an object side to an image side, wherein intervals between adjacent lens groups each vary for zooming, the 2 nd lens group includes at least 2 positive lenses and at least 2 negative lenses, a negative lens located on the image side of the at least 2 negative lenses has an aspherical surface, and a focal length f of the 1 st lens group, a focal length f2 of the 2 nd lens group, an average abbe number ν d2p of the at least 2 positive lenses, and a minimum value bfwt of an air-converted back focal length at a wide-angle end satisfy a predetermined condition.

Further features of the invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Drawings

Fig. 1 is a diagram illustrating a cross section and a movement locus of a zoom lens at the wide-angle end of embodiment 1.

Fig. 2A to 2C are aberration diagrams of the wide angle end, the intermediate zoom position, and the telephoto end of embodiment 1.

Fig. 3 is a diagram illustrating a cross section and a movement locus of a zoom lens at the wide-angle end of embodiment 2.

Fig. 4A to 4C are aberration diagrams of the wide angle end, the intermediate zoom position, and the telephoto end of embodiment 2.

Fig. 5 is a diagram illustrating a cross section and a movement locus of a zoom lens at the wide-angle end of embodiment 3.

Fig. 6A to 6C are aberration diagrams of the wide angle end, the intermediate zoom position, and the telephoto end of embodiment 3.

Fig. 7 is a diagram illustrating a cross section and a movement locus of a zoom lens at the wide-angle end of embodiment 4.

Fig. 8A to 8C are aberration diagrams of the wide angle end, intermediate zoom position, telephoto end of embodiment 4.

Fig. 9 is a sectional view of a monitoring camera in each embodiment.

Fig. 10 is a sectional view of a monitoring camera in each embodiment.

Fig. 11A and 11B are explanatory diagrams of the monitoring camera in each embodiment.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Embodiments relate to a zoom lens which is small and has a small F-number, and has high optical performance from visible light to a near infrared region, and an imaging apparatus having the zoom lens.

Fig. 1, 3, 5, and 7 are diagrams illustrating a cross section and a movement locus of the zoom lenses 1a to 1d at the wide-angle end in embodiments 1 to 4, respectively. The zoom lenses 1a to 1d according to the embodiments are 2-group zoom lenses each including 2 lens groups, i.e., a1 st lens group L1 having a negative refractive power and a 2 nd lens group L2 having a positive refractive power, which are arranged in order from the object side to the image side. Upon zooming, the 1 st lens group L1 and the 2 nd lens group L2 both move independently and move in the direction of the arrow in the respective drawings.

In each drawing, SP is a diaphragm (aperture stop) and is disposed on the object side of the 2 nd lens group L2. G is an optical block corresponding to an optical filter, a panel, or the like. IP is an image plane, and corresponds to an image plane of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor when the zoom lenses 1a to 1d are used as an imaging optical system.

Fig. 2A to 2C, 4A to 4C, 6A to 6C, and 8A to 8C are aberration diagrams of the wide angle end, the intermediate zoom position, and the telephoto end of examples 1 to 4, respectively. In the spherical aberration, d, g, and t respectively represent a d-line (587.56nm), a g-line (435.84nm), and a t-line (1013.98 nm). In astigmatism, M, S denotes a meridional image plane and a sagittal image plane in the d-line, respectively. Distortion aberration is shown in relation to d-line. The chromatic aberration of magnification shows the aberration of g-line and t-line with respect to d-line.

Next, a method of moving each lens group constituting the zoom lenses 1a to 1d will be described with reference to fig. 1, 3, 5, and 7. Zooming from the wide angle end to the telephoto end is performed by moving the 1 st lens group L1 and the 2 nd lens group L2 independently from each other. As described above, the zoom type of the zoom lenses 1a to 1d of the respective embodiments is a 2-group structure of negative lead (negative group first). The 1 st lens group L1 is made to have negative power, and the interval between the lens groups is changed to zoom, thereby achieving a configuration suitable for a wide angle. In zooming, the positive 2 nd lens group L2 located on the image side is moved, and image plane variation accompanying this is corrected using the negative 1 st lens group L1. According to each embodiment, the lens barrel structure can be simplified by setting the number of the movable groups to 2, which contributes to downsizing. Further, focusing is performed by the movement of the 1 st lens group L1.

The zoom lenses 1a to 1d according to the embodiments each include a negative 1 st lens group L1 and a positive 2 nd lens group L2 arranged in this order from the object side to the image side, and the interval between the adjacent lens groups is changed for zooming. The 2 nd lens group L2 includes at least 2 positive lenses G21, G23 and at least 2 negative lenses G22, G24. The negative lens G24 on the image side of the at least 2 negative lenses has an aspherical surface (the negative lens G24 of each embodiment has an aspherical surface on both surfaces). The focal distance of the 1 st lens group L1 is f1, the focal distance of the 2 nd lens group L2 is f2, the average abbe number of at least 2 positive lenses G21 and G22 is vd 2p, and the minimum value of the focal length after air conversion at the wide-angle end (or the entire variable power region) is bfwt. In this case, the following conditional expressions (1) to (3) are satisfied.

-1.20<f1/f2<-0.80···(1)

68.00<νd2p<90.00···(2)

0.40<bfwt/f2<0.90···(3)

Conditional expressions (1) and (3) are conditions for obtaining high optical performance and an effect of downsizing by specifying a relationship between the 2 nd lens group L2 and the back focal length with respect to the 1 st lens group L1. The 1 st lens group L1 has relatively strong optical power (short focal length) as wide-angle zooming. The 2 nd lens group L2 is appropriately set to have power as a variable power group. The conditional expression (2) is a condition required for correcting chromatic aberration not only in visible light but also in a near infrared region, and is a condition for appropriately using glass having a good chromatic aberration correction effect.

When the refractive power of the 1 st lens group L1 exceeds the upper limit of the conditional expression (1), chromatic aberration is generated excessively, which is not preferable. On the other hand, if the refractive power exceeds the lower limit of the conditional expression (1), the refractive power of the 1 st lens group L1 becomes weak, which is not preferable for downsizing.

If the amount exceeds the upper limit of the conditional expression (2), the effect as chromatic aberration correction is obtained, but since glass satisfying this condition generally has a characteristic of a low refractive index, it is difficult to obtain the refractive power as a lens element, and it is not preferable for downsizing. On the other hand, if the lower limit of the conditional expression (2) is exceeded, the chromatic aberration correction is insufficient, which is not preferable.

Conditional expression (3) specifies the relationship between the minimum required back focal length and the power of the 2 nd lens group L2. In order to achieve downsizing, it is preferable that the 2 nd lens group L2 has a configuration in which the back focal length becomes shortest at the wide-angle end. If the upper limit of the conditional expression (3) is exceeded, the back focus becomes too long, which is not preferable for miniaturization. On the other hand, if the lower limit of the conditional expression (3) is exceeded, the tendency of the power of the 2 nd lens group L2 to become weak becomes strong, and accordingly, the moving amount for zooming of the 2 nd lens group L2 becomes excessively large, which is not preferable for downsizing.

The zoom lenses 1a to 1d of the embodiments are realized by satisfying the above configuration. In addition, in each embodiment, it is preferable that at least one of the following conditional expressions is satisfied. The following describes the respective conditional expressions and their technical meanings.

When the focal length of the negative lens G24 having an aspherical surface in the 2 nd lens group L2 is f2n _ asph, the following conditional expression is satisfied.

-4.50<f2n_asph/f2<-0.80···(4)

The conditional expression (4) is a condition for increasing the effect of downsizing by reducing the number of lenses and appropriately setting the power thereof by using an aspherical surface in the 2 nd lens group L2. If the refractive index exceeds the upper limit of conditional expression (4), the power of the negative lens having an aspherical surface becomes too strong, and characteristics such as astigmatism and field curvature deteriorate, so that high resolution at image height (MTF) cannot be obtained, which is not preferable. On the other hand, if the refractive power exceeds the lower limit of conditional expression (4), the negative lens G24 having an aspherical surface becomes too weak, and the number of glasses as an optical system cannot be reduced, which makes downsizing difficult, and is not preferable.

When the average abbe number of at least 2 positive lenses G21, G23 is vd 2p and the average abbe number of at least 2 negative lenses G22, G24 is vd 2n, the following conditional expression (5) is satisfied.

25.00<νd2p-νd2n<45.00···(5)

The conditional expression (5) is a condition for correcting chromatic aberration on axis and chromatic aberration of magnification, in particular, a condition for effectively correcting chromatic aberration of near-infrared light with respect to visible light. If the upper limit of the conditional expression (5) is exceeded, the abbe numbers of the positive lens and the negative lens in the 2 nd lens group L2 are out of balance, and therefore, the correction cannot be performed satisfactorily, which is not preferable. On the other hand, if the lower limit of the conditional expression (5) is exceeded, chromatic aberration is not sufficiently corrected, and in particular, chromatic aberration occurs on the axis of near-infrared light with respect to visible light, and the resolution is not sufficient in a light source in which visible light and near-infrared light are mixed, which is not preferable.

The 1 st lens group L1 includes at least 1 positive lens G13. When the abbe number of the positive lens G13 of the 1 st lens group L1 is vd 1p and the refractive index of the positive lens G13 of the 1 st lens group L1 is Nd1p, the following conditional expressions (6) and (7) are satisfied.

13.00<νd1p<20.00···(6)

1.85<Nd1p<2.10···(7)

Conditional expressions (6) and (7) are conditions for defining the material characteristics of the positive lens G13 of the 1 st lens group L1. The abbe number has an effect of eliminating chromatic aberration of magnification generated at the negative lenses G11, G12 located at the object side of the 1 st lens group L1 by using a relatively high dispersion material in the positive lens G13. If the upper limit of conditional expression (6) is exceeded, the correction of the chromatic aberration of magnification is insufficient, which is not preferable. On the other hand, if the lower limit of conditional expression (6) is exceeded, the correction of the chromatic aberration of magnification becomes excessive, which is not preferable. If the upper limit of the conditional expression (7) is exceeded, the balance of the petzval sum of the entire system of the zoom lenses 1a to 1d is affected, and the characteristics of the field curvature are degraded, which is not preferable. On the other hand, if the refractive index exceeds the lower limit of the conditional expression (7), the refractive index becomes low, and the lens diameter of the L1 as the 1 st lens group becomes large, which is not preferable from the viewpoint of downsizing.

The 2 nd lens group L2 is composed of, in order from the object side to the image side, a positive lens G21, a negative lens G22, a positive lens G23, and a negative lens G24. This is to define the configuration of the 2 nd lens group L2 in order to reduce the F value and to miniaturize the entire system of the zoom lenses 1a to 1 d. A stop SP is disposed on the most image side of the 2 nd lens group L2. Therefore, by setting the lens closest to the object side with the larger beam diameter as the positive lens G21, spherical aberration is effectively corrected. The subsequent group of the positive lens G21 is easy to correct the extra-axial aberration such as astigmatism together with the residual aberration of spherical aberration by the lens structure of the negative lens G22, the positive lens G23, and the negative lens G24.

In the 2 nd lens group L2, the positive lens G21 disposed closest to the object side and the negative lens G22 disposed beside the positive lens G21 are each formed of a single lens. The positive lens G12 and the negative lens G22 are separated from each other with air (air lens) interposed therebetween, and when the curvature radius on the image side of the positive lens G21 is R12 and the curvature radius on the object side of the negative lens G22 is R21, the following conditional expression (8) is satisfied.

-0.10<(R12-R21)/(R12+R21)<0.70···(8)

The conditional expression (8) is a condition for optimizing correction of spherical aberration particularly by utilizing the effect as an air lens for the shape of the air lens located closest to the object side. If the refractive power exceeds the upper limit of conditional expression (8), the refractive power as an air lens is not easily obtained, and therefore, the correction effect cannot be obtained, which is not preferable. On the other hand, if the refractive power exceeds the lower limit of conditional expression (8), the refractive power of the air lens becomes too large and excessive correction is not preferable.

In each embodiment, the following conditional expression (9) is satisfied where d2p1 is the center thickness of the positive lens G21 on the object side of the 2 positive lenses G21 and G23, and d2p2 is the center thickness of the positive lens G23 on the image side of the 2 positive lenses G21 and G23.

0.50<(d2p1+d2p2)/f2<1.20···(9)

The conditional expression (9) is a condition for correcting the on-axis aberration and the magnification chromatic aberration well. As the positive lens, a glass material having a relatively large abbe number is used, but the chromatic aberration correction effect is obtained by appropriately setting the glass thickness. If the upper limit of conditional expression (9) is exceeded, the thickness of the positive lens becomes too large, which is not preferable from the viewpoint of downsizing. On the other hand, if the lower limit of the conditional expression (9) is exceeded, the chromatic aberration correction effect cannot be obtained, which is not preferable.

In each of the embodiments, the following conditional expression (10) is satisfied where d2G represents the total center thickness of all the lenses constituting the 2 nd lens group L2, and TL2G represents the total length of the 2 nd lens group L2 (the length from the object-side surface of the lens closest to the object side to the image-side surface of the lens closest to the image side).

0.70<d2G/TL2G<0.99···(10)

The conditional expression (10) is a condition for obtaining optical performance in a small size and good quality. In order to achieve miniaturization, it is preferable to reduce the number of glasses, but this makes it difficult to correct each aberration. This can be solved by taking a balance of the optical path lengths of the glass medium and air through which the light passes. If the upper limit of conditional expression (10) is exceeded, the area through which air passes is reduced, and the optical power (optical power of glass) appropriate for aberration correction cannot be obtained, and curvature of field, astigmatism, and the like cannot be corrected, which is not preferable. On the other hand, if the lower limit of conditional expression (10) is exceeded, the power of each lens tends to be weak, and correction of astigmatism, coma aberration, and the like is not preferable.

The zoom lenses 1a to 1d of the embodiments are used for an imaging apparatus. The imaging device includes an imaging element 12 that receives (forms) an image formed by the zoom lenses 1a to 1 d. The imaging element 12 is a CCD (Charge Coupled Device) sensor, a CMOS (Complementary Metal Oxide Semiconductor) sensor, or the like for performing digital processing on an image.

In the present embodiment, it is preferable that the numerical ranges of at least one of the conditional expressions (1) to (10) are set as the following conditional expressions (1a) to (10a), respectively.

-1.15<f1/f2<-0.82···(1a)

70.00<νd2p<89.50···(2a)

0.45<bfwt/f2<0.90···(3a)

-4.00<f2n_asph/f2<-1.00···(4a)

26.50<νd2p-νd2n<43.50···(5a)

14.00<νd1p<19.50···(6a)

1.86<Nd1p<2.09···(7a)

0.05<(R12-R21)/(R12+R21)<0.65···(8a)

0.60<(d2p1+d2p2)/f2<1.15···(9a)

0.74<d2G/TL2G<0.97···(10a)

More preferably, the numerical range of at least one of the conditional expressions (1) to (10) is set as in the following conditional expressions (1b) to (10b), respectively.

-1.10<f1/f2<-0.85···(1b)

72.00<νd2p<89.00···(2b)

0.50<bfwt/f2<0.90···(3b)

-3.50<f2n_asph/f2<-1.20···(4b)

28.00<νd2p-νd2n<42.00···(5b)

15.00<νd1p<19.00···(6b)

1.88<Nd1p<2.08···(7b)

0.02<(R12-R21)/(R12+R21)<0.60···(8b)

0.70<(d2p1+d2p2)/f2<1.10···(9b)

0.78<d2G/TL2G<0.95···(10b)

Next, the lens structures of the zoom lenses 1a to 1d of the respective embodiments will be described. Hereinafter, the lens structure will be described in the order of arrangement from the object side to the image side, unless otherwise specified. In the sectional views of fig. 1, 3, 5, and 7, the left side is the object side (object side) and the right side is the image side. The wide angle end and the telephoto end refer to zoom positions of the zoom lens group at both ends of a range movable along the optical axis OA on the mechanism. The movement of each lens group from the wide angle end to the telephoto end takes a locus as indicated by an arrow (solid line) shown in each sectional view.

A solid line curve and a broken line curve of the 2 nd lens group L2 are movement loci for correcting image plane variation toward a zoom position from the wide angle end to the telephoto end upon focusing on an infinite object and a close object, respectively. For example, when focusing is performed from an infinite object to a short-distance object at a zoom position at the telephoto end, the zoom lens moves as indicated by an arrow F in each sectional view.

The stop SP is disposed in front of the 2 nd lens group L2, and moves integrally with the 2 nd lens group L2 during zooming. Further, the diaphragm SP may be independently moved, which is advantageous in that it is easy to cut off light that causes flare.

Hereinafter, the lens structure of each embodiment and the imaging apparatus having the same are described in detail. The zoom lens of each embodiment is of a 2-group structure, and is configured to have negative/positive power. Upon zooming, the 1 st lens group L1 and the 2 nd lens group L2 move. Upon zooming from the wide-angle end to the telephoto end, the 1 st lens group L1 takes a locus like a convex shape toward the image side, and the 2 nd lens group L2 moves monotonously toward the object side.

The 1 st lens group L1 is composed of a meniscus negative lens G11 having a shape convex toward the object side, a negative lens G12 having a biconcave shape, and a meniscus negative lens G13 having a shape convex toward the object side. The 2 nd lens group L2 is composed of a biconvex positive lens G21, a biconcave negative lens G22 of a meniscus shape (examples 3 and 4) convex to the image side (examples 1 and 2), a biconvex positive lens G23, and a biconcave negative lens G24. The negative lens G24 is aspheric on both surfaces, and corrects aberrations such as astigmatism and field curvature well. The aspherical surface is not limited to glass, and a plastic material having good moldability may be used. The positive lenses G21 and G23 use low dispersion glass having a large abbe number, and excellently correct chromatic aberration of magnification and chromatic aberration on axis.

Next, a monitoring camera including the zoom lenses 1a to 1d according to the embodiments will be described with reference to fig. 9 and 10. Fig. 9 is a sectional view of the monitoring camera 100 a. The monitoring camera 100a includes the zoom lens 1a (or the zoom lenses 1b to 1d of embodiments 2 to 4) of embodiment 1 and a dome 15. The dome 15 is formed of a plastic material such as polymethyl methacrylate (PMMA) or Polycarbonate (PC) to have a thickness of about several millimeters. Accordingly, when an imaging device based on a dome-attached camera is used, the various aberrations can be corrected by designing in consideration of the influence (focal length and material) of the dome 15. Fig. 10 is a sectional view of the monitoring camera 100 b. The monitoring camera 100b includes the zoom lens 1a of example 1 (or the zoom lenses 1b to 1d of examples 2 to 4) and a flat plate-shaped protective cover 17.

Next, an imaging apparatus (monitoring camera 100) using the zoom lens 1A (1B to 1d) as an imaging optical system is described with reference to fig. 11A and 11B. Fig. 11A and 11B are explanatory views of the monitoring camera 100, fig. 11A shows an external view of the monitoring camera 100, and fig. 11B shows a use example of the monitoring camera 100.

In fig. 11A, reference numeral 11 denotes a monitoring camera body, and 12 denotes an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is incorporated in the camera body 11 and receives a subject image formed by the zoom lenses 1A (1b to 1 d). Reference numeral 13 denotes a memory unit for recording information corresponding to the subject image photoelectrically converted by the imaging element 12. Reference numeral 14 denotes a network cable for transmitting the subject image photoelectrically converted by the imaging element 12. Fig. 11B shows an example of use in which the dome cover 15 is attached and the monitoring camera 100 is attached to the ceiling. Further, the imaging apparatus is not limited to the monitoring camera, and can be applied to other imaging apparatuses such as a video camera, a digital camera, and the like.

According to the embodiments, a zoom lens and an imaging apparatus which are small in size and small in F-number and have high optical performance from visible light to near infrared region can be provided.

Further, an imaging system (monitoring camera system) including the zoom lenses 1a to 1d of the embodiments and a control unit that controls the zoom lenses may be configured. In this case, the control unit can control the zoom lens so that each lens group moves as described above during zooming. In this case, the control unit does not need to be integrally configured with the zoom lens, and may be configured independently of the zoom lens. For example, a configuration may be adopted in which a control unit (control device) disposed at a distance from a drive unit that drives each lens of the zoom lens includes a transmission unit that transmits a control signal (command) for controlling the zoom lens. According to such a control unit, the zoom lens can be remotely operated.

Further, an operation unit (operation member) such as a controller or a button for remotely operating the zoom lens may be provided in the control unit, and the zoom lens may be controlled in accordance with an input to the operation unit by a user. For example, an enlargement button and a reduction button may be provided as the operation portion. In this case, the control unit may be configured to transmit a signal to the drive unit of the zoom lens so that the magnification of the zoom lens is increased if the user presses the zoom-in button and the magnification of the zoom lens is decreased if the user presses the zoom-out button.

The imaging system may have a display unit such as a liquid crystal panel that displays information (movement state) related to zooming of the zoom lens. The information on zooming of the zoom lens refers to, for example, a zoom magnification (zoom state) and a moving amount (moving state) of each lens group. In this case, the user can remotely operate the zoom lens via the operation unit while observing information on zooming of the zoom lens displayed on the display unit. In this case, the display unit and the operation unit may be integrated by using a touch panel or the like, for example.

Numerical examples 1 to 4 corresponding to examples 1 to 4 are shown below. In each numerical embodiment, the surface numbers are shown in order from the object side, r represents a radius of curvature, d represents an interval, and nd and vd represent a refractive index and an abbe number, respectively, with reference to the d-line. When refractive indices of d-line (587.6nm), F-line (486.1nm), and C-line (656.3nm) of fraunhofer line are Nd, NF, and NC, abbe number ν d of a certain material is expressed by the following formula.

νd＝(Nd-1)/(NF-NC)

In each numerical embodiment, d, the focal length (mm), the F number (F value), and the half angle of view (°) are all values when the zoom lens of each embodiment is focused on an infinitely distant object. BF (back focus) is a value obtained by expressing a distance on the optical axis from the lens final surface (the lens surface closest to the image side) to the paraxial image surface in terms of an air-converted length, and is a value in the case where no glass block is included. The "total lens length" is a length obtained by adding the back focal length to the distance on the optical axis from the foremost surface (lens surface closest to the object side) to the final surface of the zoom lens. The "lens group" is not limited to the case of being constituted by a plurality of lenses, but includes the case of being constituted by 1 lens.

In addition, when the optical surface is aspheric, a symbol of "+" is added to the right side of the surface number. When the optical axis direction is defined as the X axis, the direction perpendicular to the optical axis is defined as the h axis, the light traveling direction is defined as positive, R is defined as the paraxial radius of curvature, K is defined as the conic constant, and a4, a6, A8, a10, and a12 are respectively defined as aspheric coefficients of 4, 6, 8, 10, and 12 times, the aspheric shape is expressed by the following equation.

x＝(h2/r)/[1+{1-(1+K)(h/r)2}1/2]+A4·h4+A6·h6+A8·h8+A10·h10+A12·h12

In addition, for example, the expression "e-Z" means "10^-Z". The half angle of view is a value of the half angle of view (ω) with respect to a photographable angle of view in which distortion aberration is taken into consideration.

Table 1 shows the relationship between each numerical example and each conditional expression.

Numerical example 1

Aspheric data

The 14 th side

K＝0.00000e+000 A 4＝-7.71859e-003 A 6＝-6.95253e-005 A 8＝3.43371e-006

The 15 th surface

K＝0.00000e+000 A 4＝-5.35636e-003 A 6＝1.60144e-004 A 8＝1.17287e-005

A10＝-7.99639e-007 A12＝7.99768e-022

Various data

Focal distance of each group

1 -7.37

2 7.62

Single lens (element) focal distance

[ numerical example 2]

Aspheric data

The 14 th side

K＝0.00000e+000 A 4＝-7.81269e-003 A 6＝-1.93114e-004 A 8＝1.11847e-005

The 15 th surface

K＝0.00000e+000 A 4＝-5.39641e-003 A 6＝2.02235e-005 A 8＝3.09969e-005

A10＝-1.52457e-006 A12＝5.19989e-022

Various data

Focal distance of each group

1 -7.01

2 7.55

Single lens (element) focal distance

[ numerical example 3]

Aspheric data

The 14 th side

K＝0.00000e+000 A 4＝-7.04738e-003 A 6＝-1.93933e-004 A 8＝2.14349e-005

A10＝-8.97559e-007 A12＝5.27016e-022

The 15 th surface

K＝0.00000e+000 A 4＝-3.98411e-003 A 6＝-2.08018e-005 A 8＝3.21100e-005

Various data

Focal distance of each group

1 -7.10

2 7.09

Single lens (element) focal distance

[ numerical example 4]

Aspheric data

The 14 th side

K＝0.00000e+000 A 4＝-7.17527e-003 A 6＝-2.11347e-004 A 8＝2.12300e-005

The 15 th surface

K＝0.00000e+000 A 4＝-4.25345e-003 A 6＝-1.48874e-006 A 8＝3.03069e-005

A10＝-1.09958e-006 A12＝5.29696e-022

Various data

Focal distance of each group

1 -7.15

2 7.63

Single lens (element) focal distance

[ TABLE 1]

		Example 1	Example 2	Example 3	Example 4
						Condition (1)	f1/f2	-0.97	-0.93	-1.00	-0.94
Condition (2)	v d2p	81.54	88.32	81.54	75.89
						Condition (3)	bfwt/f2	0.76	0.81	0.62	0.77
Condition (4)	f2n_asph	-1.51	-1.79	-2.11	-2.16
						Condition (5)	vd2p-vd2n	32.01	38.60	39.91	35.30
Condition (6)	vd1p	17.98	16.48	17.47	18.90
						Condition (7)	Nd1p	1.95	1.99	1.96	1.92
Condition (8)	(R12-R21)/(R12+R21)	0.04	0.04	0.14	0.40
						Condition (9)	(d2p1+d2p2)/f2	0.93	0.90	0.81	0.81
Condition (10)	d2G/TL2G	0.94	0.94	0.84	0.88

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

For example, the shape and the number of lenses described in each embodiment are not limited to these. In each of the embodiments, it is also possible to correct image shake caused by vibration such as hand shake by moving some of the lenses and lens groups so as to have a component in a direction perpendicular to the optical axis OA. In each embodiment, the electric correction unit may correct distortion aberration, chromatic aberration, or the like.

According to the above-described embodiments, for example, a zoom lens which is small, bright, and advantageous in terms of high optical performance from visible light to near-infrared light can be provided.

Claims (13)

1. A zoom lens comprising a negative 1 st lens group and a positive 2 nd lens group arranged in this order from an object side to an image side,

the intervals of adjacent lens groups are all changed for zooming,

the 2 nd lens group includes at least 2 positive lenses and at least 2 negative lenses,

a negative lens on the image side of the at least 2 negative lenses has an aspherical surface,

when the focal distance of the 1 st lens group is f1, the focal distance of the 2 nd lens group is f2, the average abbe number of the at least 2 positive lenses is vd 2p, and the minimum value of the air converted back focal length at the wide-angle end is bfwt, the following conditional expressions are satisfied:

-1.20<f1/f2<-0.80

68.00<νd2p<90.00

0.40<bfwt/f2<0.90。

2. zoom lens according to claim 1,

when the focal length of the negative lens having the aspherical surface is f2n _ asph, the following conditional expression is satisfied:

-4.50<f2n_asph/f2<-0.80。

3. zoom lens according to claim 1,

when the average abbe number of the at least 2 positive lenses is vd 2p and the average abbe number of the at least 2 negative lenses is vd 2n, the following conditional expressions are satisfied:

25.00<νd2p-νd2n<45.00。

4. zoom lens according to claim 1,

the 1 st lens group includes a positive lens,

when the abbe number of the positive lens of the 1 st lens group is vd 1p and the refractive index of the positive lens of the 1 st lens group is Nd1p, the following conditional expressions are satisfied:

13.00<νd1p<20.00

1.85<Nd1p<2.10。

5. zoom lens according to claim 1,

the 2 nd lens group includes a positive lens, a negative lens, a positive lens, and a negative lens arranged in this order from the object side to the image side.

6. Zoom lens according to claim 1,

a positive lens disposed closest to the object side and a negative lens disposed beside the positive lens in the 2 nd lens group are each composed of a single lens, the positive lens and the negative lens are separated from each other with air interposed therebetween, and when a curvature radius of the image side of the positive lens is R12 and a curvature radius of the object side of the negative lens is R21, the following conditional expressions are satisfied:

-0.10<(R12-R21)/(R12+R21)<0.70。

7. zoom lens according to claim 1,

the 2 nd lens group is composed of 2 positive lenses,

when the center thickness of the positive lens on the object side of the 2 positive lenses is d2p1 and the center thickness of the positive lens on the image side of the 2 positive lenses is d2p2, the following conditional expressions are satisfied:

0.50<(d2p1+d2p2)/f2<1.20。

8. zoom lens according to any one of claims 1 to 7,

when the total center thickness of all the lenses constituting the 2 nd lens group is d2G and the total length of the 2 nd lens group is TL2G, the following conditional expression is satisfied:

0.70<d2G/TL2G<0.99。

9. an image forming apparatus, comprising:

a variable focus lens as claimed in any one of claims 1 to 8; and

and an imaging element that images an image formed by the zoom lens.

10. An imaging system, comprising:

the imaging device of claim 9; and

a control unit that controls the zoom lens for zooming.

11. The imaging system of claim 10,

the control unit sends a control signal to the zoom lens.

12. The imaging system of claim 10,

the control section has an operation member for operating the zoom lens.

13. The imaging system of any of claims 10 to 12, further comprising:

and a display unit that displays information regarding zooming of the zoom lens.

Images