JP7182886B2 - ZOOM LENS AND IMAGING DEVICE HAVING THE SAME - Google Patents

Description

The present invention relates to an imaging optical system and an imaging apparatus.

2. Description of the Related Art There is a demand for an imaging optical system used in an imaging apparatus (camera) to be compact as a whole, to have a wide angle of view, and to have high optical performance over the entire zoom range.

2. Description of the Related Art Conventionally, a negative lead type zoom lens in which a lens group having a negative refractive power is arranged on the object side is known as a zoom lens that can easily widen the angle of view. As a negative-lead type wide-angle zoom lens, it consists of a first lens group, a second lens group, and one or more lens groups with negative and positive refractive powers in order from the object side to the image side. A zoom lens that performs zooming by changing is known.

In this zoom lens, in order to reduce the size and weight of the focus lens group, there is known a zoom lens that uses an inner focus method in which focusing is performed by a lens group other than the lens group closest to the object (Patent References 1, 2).

In Japanese Patent Laid-Open No. 2003-100000, the zoom lens system is composed of first to fourth lens groups having negative, positive, positive, and negative refractive powers in order from the object side. discloses a zoom lens that performs In Japanese Patent Application Laid-Open No. 2002-200012, the lens system is composed of first to third lens groups having negative, positive, and negative refractive powers in order from the object side, and zooming is performed by changing the distance between adjacent lens groups, and focusing is performed by a part of the second lens group. discloses a zoom lens that performs

JP 2015-166834 A JP 2012-027311 A

In order to reduce the size of the entire zoom lens system and achieve high-speed focusing, for example, it is important to appropriately set the number of lens groups that make up the zoom lens and the refractive power of each lens group. It's going to be For example, it is important to appropriately set the lens groups that move during focusing.

Also, in order to obtain high optical performance at all object distances, it is important to appropriately set the lens configuration of the lens groups that move during focusing. In particular, it is important to appropriately set the refractive power, lens configuration, and the like of the lens groups arranged on the object side and the image side of the lens groups that move during focusing.

SUMMARY OF THE INVENTION The present invention provides a zoom lens that has a compact overall system and a wide angle of view, has little variation in aberrations during focusing, has high optical performance over the entire object distance, and is easy to focus at high speed. It is an object of the present invention to provide an imaging device having

The zoom lens of the present invention is
A zoom lens having a plurality of lens groups, wherein the distance between adjacent lens groups changes during zooming,
The plurality of lens groups includes a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens section Lp with positive refractive power, which are arranged in order from the object side to the image side. a lens group, consisting of a fourth lens group as a lens section Ln of negative refractive power, a rear group comprising one or more lens groups,
only the lens element LF, which is all or part of said lens Lp, moves during focusing,
When the radius of curvature of the lens surface on the object side of the lens element LF is R1f, the radius of curvature of the lens surface on the image side is R2f, the focal length of the lens portion Lp is fp, and the focal length of the lens portion Ln is fn ,
0.95<(R2f+R1f)/(R2f-R1f)<5.00
1.0<|fp/fn|<5.0
It is characterized by satisfying the following conditional expression:

According to the present invention, it is possible to obtain a zoom lens that is compact as a whole, has a wide angle of view, has little variation in aberrations during focusing, has high optical performance over the entire object distance, and facilitates high-speed focusing.

Cross-sectional view of the zoom lens of Example 1 Aberration diagram when focusing on infinity in Example 1 Aberration diagram of Example 1 when focusing at near and near Cross-sectional view of the zoom lens of Example 2 Aberration diagram when focusing on infinity in Example 2 Aberration diagram of Example 2 when focusing at near and near Cross-sectional view of the zoom lens of Example 3 Aberration diagram when focusing on infinity in Example 3 Aberration diagram of Example 3 at the time of focusing at near and near Cross-sectional view of the zoom lens of Example 4 Aberration diagram when focusing on infinity in Example 4 Aberration diagram of Example 4 when focusing at close distance Cross-sectional view of the zoom lens of Example 5 Aberration diagram when focusing on infinity in Example 5 Aberration diagram of Example 5 at the time of focusing at near and near Cross-sectional view of the zoom lens of Example 6 Aberration diagram when focusing on infinity in Example 6 Aberration diagram of Example 6 at the time of focusing at near and near Cross-sectional view of the zoom lens of Example 7 Aberration diagram when focusing on infinity in Example 7 Aberration diagram of Example 7 at the time of focusing at close distance FIG. 1 is a schematic diagram of an essential part of an imaging device of the present invention;

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The zoom lens of the present invention has a plurality of lens groups, and the distance between adjacent lens groups changes during zooming. The plurality of lens groups includes a first lens group with negative refractive power, a first lens group with positive refractive power, and a rear group including one or more lens groups arranged in order from the object side to the image side. have. The rear group has a negative refractive power lens portion Ln arranged closest to the image side and a positive refractive power lens portion Lp arranged adjacent to the lens portion Ln on the object side thereof.

Here, the lens group is a lens system that moves integrally during zooming, and may have one or more lenses, and does not necessarily have a plurality of lenses. The lens part Lp consists of one or more lens elements. One lens element LF of the lens portion Lp moves during focusing. Here, the lens element means an integrally formed lens such as a single lens or a cemented lens in which a plurality of lenses are cemented together.

FIG. 1 is a sectional view of the lens at the wide-angle end (short focal length end) of Example 1 of the present invention. FIGS. 2A, 2B, and 2C are aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end (long focal length end), respectively, when focusing on infinity in Example 1. FIG. 3A, 3B, and 3C are the wide-angle end (imaging magnification -0.075 times), the intermediate zoom position (imaging magnification -0.093 times), and the telephoto end (focusing magnification) of Example 1, respectively. It is an aberration diagram at an image magnification of -0.14 times. Example 1 is a zoom lens with a zoom ratio of 1.89 and an F number of 4.10 to 5.72.

FIG. 4 is a cross-sectional view of the lens at the wide-angle end of Embodiment 2 of the present invention. FIGS. 5A, 5B, and 5C are aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end (long focal length end), respectively, when focusing on infinity in Example 2. FIG. 6A, 6B, and 6C are the wide-angle end (imaging magnification -0.075 times), the intermediate zoom position (imaging magnification -0.093 times), and the telephoto end (focusing magnification) of Example 2, respectively. It is an aberration diagram at an image magnification of -0.14 times. Example 2 is a zoom lens with a zoom ratio of 1.89 and an F number of 4.10 to 5.72.

FIG. 7 is a cross-sectional view of the lens at the wide-angle end of Example 3 of the present invention. FIGS. 8A, 8B, and 8C are aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end (long focal length end) when focusing on infinity in Example 3, respectively. 9A, 9B, and 9C are the wide-angle end (imaging magnification -0.075 times), the intermediate zoom position (imaging magnification -0.093 times), and the telephoto end (focusing magnification) of Example 3, respectively. It is an aberration diagram at an image magnification of -0.14 times. Example 3 is a zoom lens with a zoom ratio of 1.89 and an F number of 4.10 to 5.72.

FIG. 10 is a cross-sectional view of the lens at the wide-angle end of Example 4 of the present invention. FIGS. 11A, 11B, and 11C are aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end (long focal length end) when focusing on infinity in Example 4, respectively. 12A, 12B, and 12C are the wide-angle end (imaging magnification -0.075 times), the intermediate zoom position (imaging magnification -0.093 times), and the telephoto end (focusing magnification) of Example 4, respectively. It is an aberration diagram at an image magnification of -0.14 times. Example 4 is a zoom lens with a zoom ratio of 1.89 and an F number of 4.10 to 5.71.

FIG. 13 is a lens cross-sectional view at the wide-angle end of Example 5 of the present invention. FIGS. 14A, 14B, and 14C are aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end (long focal length end) when focusing on infinity in Example 5, respectively. 15A, 15B, and 15C are the wide-angle end (imaging magnification -0.075 times), the intermediate zoom position (imaging magnification -0.093 times), and the telephoto end (focusing magnification) of Example 5, respectively. It is an aberration diagram at an image magnification of -0.14 times. Example 5 is a zoom lens with a zoom ratio of 1.89 and an F number of 4.10 to 5.72.

FIG. 16 is a cross-sectional view of the lens at the wide-angle end of Example 6 of the present invention. FIGS. 17A, 17B, and 17C are aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end (long focal length end) when focusing on infinity in Example 6, respectively. 18A, 18B, and 18C are the wide-angle end (imaging magnification -0.075 times), the intermediate zoom position (imaging magnification -0.093 times), and the telephoto end (focusing magnification) of Example 6, respectively. It is an aberration diagram at an image magnification of -0.14 times. Example 6 is a zoom lens with a zoom ratio of 1.89 and an F number of 4.10 to 5.72.

FIG. 19 is a lens cross-sectional view at the wide-angle end of Embodiment 7 of the present invention. FIGS. 20A, 20B, and 20C are aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end (long focal length end) when focusing on infinity in Example 7, respectively. 21A, 21B, and 21C are the wide-angle end (imaging magnification -0.075 times), the intermediate zoom position (imaging magnification -0.093 times), and the telephoto end (focusing magnification) of Example 7, respectively. It is an aberration diagram at an image magnification of -0.14 times. Example 7 is a zoom lens with a zoom ratio of 1.89 and an F number of 4.10 to 5.71. FIG. 22 is a schematic diagram of a main part of a camera (imaging device) equipped with the zoom lens of the present invention.

The zoom lens of each embodiment is an imaging optical system used in imaging devices such as video cameras, digital still cameras, surveillance cameras, and TV cameras. The zoom lens of each embodiment can also be used as a projection optical system for a projection device (projector). In the sectional view of the lens, the left side is the object side (front) and the right side is the image side (rear side). In addition, OL in the lens cross-sectional view is a zoom lens.

In the sectional view of the lens, Li indicates the i-th lens group, where i is the order of the lens groups from the object side. LR is a rear group having one or more lens groups. Arrows indicate the locus of movement of each lens group during zooming from the wide-angle end to the telephoto end. The dotted arrow indicates the locus of movement of the lens element LF during zooming from the wide-angle end to the telephoto end when focusing on a close object (very close object). The focus arrow indicates the direction of movement of the lens element LF during focusing from infinity to near.

SP is an aperture stop that determines (limits) the luminous flux of the open F-number (Fno). IP is an image plane, on which an imaging plane of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is placed when used as a photographing optical system of a video camera or a digital still camera.

In the aberration diagrams, Fno is the F number, and ω is the half angle of view (degrees), which is the angle of view according to the ray tracing value. In the spherical aberration diagrams, the solid line d is the d-line (wavelength 587.56 nm), and the two-dot chain line g is the g-line (wavelength 435.8 nm). In the astigmatism diagrams, the solid line ΔS is the sagittal image plane on the d-line, and the dotted line ΔM is the meridional image plane on the d-line. Distortion is shown for the d-line. In the chromatic aberration diagram of magnification, the two-dot chain line is the g-line. In each of the following embodiments, the wide-angle end and the telephoto end refer to zoom positions when the lens group for zooming is positioned at both ends of a range in which the lens group for zooming can move on the optical axis.

The zoom lenses OL of Example 1 of FIG. 1, Example 2 of FIG. 4, Example 3 of FIG. 7, and Example 4 of FIG. It comprises a lens group L1, a second lens group L2 with positive refractive power, and a rear group LR having one or more lens groups. The rear group LR is composed of a third lens group L3 (Lp) (LF) with positive refractive power and a fourth lens group L4 (Ln) with negative refractive power.

When zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves along a convex locus toward the image side, and the second lens unit L2, the third lens unit L3, and the fourth lens unit L4 move toward the object side in different directions. move (independently) in trajectories. The third lens unit L3 corresponds to the lens portion Lp and the lens element LF, and moves along the optical axis toward the object side as indicated by an arrow 3c during focusing from infinity to a short distance. The fourth lens group L4 corresponds to the lens section Ln. An aperture stop SP is included in the second lens group L2.

The zoom lens OL of Example 5 in FIG. 13 has a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, and one or more lens groups arranged in order from the object side to the image side. is composed of a rear group LR having The rear group LR is composed of a third lens group L3 with positive refractive power, a fourth lens group L4 (Lp) (LF) with positive refractive power, and a fifth lens group L5 (Ln) with negative refractive power. .

When zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves along a locus convex toward the image side, and the second lens unit L2, third lens unit L3, fourth lens unit L4, and fifth lens unit L5 move. move toward the object with different trajectories. The fourth lens unit L4 corresponds to the lens portion Lp and the lens element LF, and moves along the optical axis toward the object side as indicated by an arrow 4c during focusing from infinity to a short distance. The fifth lens group L5 corresponds to the lens section Ln. An aperture stop SP is arranged between the second lens group L2 and the third lens group L3.

The zoom lens OL of Example 6 in FIG. 16 has a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, and one lens group, which are arranged in order from the object side to the image side. It is composed of a rear group LR. The rear group LR is composed of a third lens group L3 with negative refractive power. The third lens unit L3 is composed of a lens portion Lp with a positive refractive power and a lens portion Ln with a negative refractive power, which are arranged in order from the object side to the image side.

During zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves along a convex trajectory toward the image side, and the second lens unit L2 and the third lens unit L3 move toward the object side along different trajectories. The lens portion Lp corresponds to the lens element LF and moves toward the object side along the optical axis during focusing from infinity to short distance. An aperture stop SP is included in the second lens group L2.

The zoom lens OL of Example 7 in FIG. 19 has a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, and one or more lens groups arranged in order from the object side to the image side. is composed of a rear group LR having The rear group LR is composed of a third lens group L3 with positive refractive power and a fourth lens group L4 with negative refractive power. The third lens unit L3 corresponds to the lens portion Lp, and is composed of a lens element L3n with negative refractive power and a lens element LF with positive refractive power, which are arranged in order from the object side to the image side.

When zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves along a convex locus toward the image side, and the second lens unit L2, the third lens unit L3, and the fourth lens unit L4 move toward the object side in different directions. move along a trajectory. The lens element LF moves along the optical axis toward the object during focusing from infinity to near. An aperture stop SP is included in the second lens group L2.

The zoom lens OL of each embodiment comprises a first lens group L1 having negative refractive power, a second lens group L2 having positive refractive power, and one or more lens groups arranged in order from the object side to the image side. It consists of a rear group LR containing. The distance between adjacent lens groups changes during zooming.

By arranging the lens group with the negative refractive power closest to the object side, a long back focus is achieved while widening the angle of view. At the telephoto end zoom position, the first lens unit L1 and the second lens unit L2 as a whole constitute a lens group with positive refractive power, and by making the entire optical system telephoto type, the lens at the telephoto end The overall length is shortened.

Here, the total lens length is the sum of the distance from the first lens surface to the final lens surface plus the value of the back focus in terms of air. The rear group LR has a lens portion Ln of negative refractive power closest to the image side and a lens portion Lp of positive refractive power adjacent to the lens portion Ln on the object side thereof, and the lens portion Lp comprises at least one lens. has an element LF. By arranging the lens portion Ln having the negative refractive power closest to the image side and appropriately setting the refractive power, the size of the entire system is reduced.

A lens element LF is a focus lens element that performs focusing by moving in the optical axis direction. During focusing, by moving the lens element LF with a positive refractive power in the optical axis direction, the size of the lens element LF is reduced, and aberration fluctuations during focusing are reduced.

In each embodiment, focusing is performed by moving one lens element LF of the lens portion Lp in the optical axis direction. Let the radius of curvature of the lens surface on the object side of the lens element LF be R1f, and the radius of curvature of the lens surface on the image side be R2f. At this time,
0.95<(R2f+R1f)/(R2f-R1f)<5.00 (1)
satisfies the following conditional expression.

Next, the technical meaning of the above conditional expression (1) will be explained. Conditional expression (1) defines the lens shape (shape factor) of the lens element LF that moves along the optical axis during focusing. If the lower limit of conditional expression (1) is exceeded, aberration fluctuations increase during focusing, particularly spherical aberration fluctuations. Spherical aberration remaining during focusing must be corrected by the lens portion Ln, which increases the number of lenses in the lens portion Ln and increases the size of the entire system, which is undesirable. If the upper limit of conditional expression (1) is exceeded, the variation in curvature of field increases when the lens element LF is moved, making it difficult to correct the curvature of field.

As described above, each embodiment is characterized by appropriately arranging each lens group and satisfying the conditional expression (1). As a result, there is obtained a zoom lens that is small in size as a whole, has a wide angle of view, has little variation in aberrations during focusing, has high optical performance over the entire object distance, and facilitates high-speed focusing.

In each embodiment, it is more preferable to set the numerical range of conditional expression (1) as follows.

1.0<(R2f+R1f)/(R2f-R1f)<4.0 (1a)

More preferably, the numerical range of conditional expression (1a) is set as follows.
1.04<(R2f+R1f)/(R2f-R1f)<3.00 (1b)

More preferably, in each embodiment, one or more of the following conditional expressions should be satisfied. Let fp be the focal length of the lens portion Lp, and fn be the focal length of the lens portion Ln. βpt is the lateral magnification of the lens element LF when focused on infinity at the telephoto end, and the lateral magnification of the lens system arranged closer to the image side than the lens element LF when focused on infinity at the telephoto end be βt. Let fw be the focal length of the zoom lens at the wide-angle end.

Dw is the distance from the most object-side lens surface of the lens element LF to the image plane at the wide-angle end when focusing on infinity, and the distance from the most object-side lens surface of the first lens unit L1 to the image plane at the wide-angle end (lens total length) is set to Lw. Dt is the distance from the most object side lens surface of the lens element LF to the image plane at the telephoto end when focusing on infinity, and the distance from the most object side lens surface of the first lens unit L1 to the image plane at the telephoto end Let Lt be (total lens length). Let ft be the focal length of the zoom lens at the telephoto end.

The lens element LF is composed of one positive lens or a cemented lens obtained by cementing one positive lens and one negative lens, and the Abbe number of the material of the positive lens is νd. Let BFw be the back focus at the wide-angle end. Let D1w be the air gap between the first lens group L1 and the second lens group L2 at the wide-angle end, and D1t be the air gap between the first lens group L1 and the second lens group L2 at the telephoto end. At this time, it is preferable to satisfy one or more of the following conditional expressions.

1.0<|fp/fn|<5.0 (2)
1.4<(1−βpt ² )×βt ² <5.0 (3)
3.0<fp/fw<8.5 (4)
0.25<Dw/Lw<0.36 (5)
0.25<Dt/Lt<0.55 (6)
1.0<|fn|/ft<10.0 (7)
1.4<βt<5.0 (8)
45≦νd (9)
0.5<BFw/fw<2.0 (10)
D1w>D1t (11)

Next, the technical meaning of each of the above conditional expressions will be explained. Conditional expression (2) defines the ratio of the focal length of the lens portion Lp to the focal length of the lens portion Ln. If the lower limit of conditional expression (2) is exceeded, the negative refractive power of the lens portion Ln becomes too weak (because the absolute value of the negative refractive power becomes too small), and the back focus cannot be shortened sufficiently. , the entire lens system becomes large, which is not good. If the upper limit of conditional expression (2) is exceeded, the negative refractive power of the lens portion Ln becomes too strong (because the absolute value of the negative refractive power becomes too large), various aberrations occurring in the lens portion Ln, In particular, chromatic aberration of magnification and off-axis coma increase, making it difficult to obtain high imaging performance.

Conditional expression (3) defines the position sensitivity of the lens element LF. Here, the position sensitivity ES is the ratio of the distance amount Δx in the optical axis direction of the lens element LF to the movement amount Δsk of the imaging position (focus position) in the optical axis direction. That is, ES=Δsk/Δx
is.

Let Δsk be the amount of change in the back focus with respect to the amount of movement of the lens element LF in the zoom lens OL. Let Δx be the amount of movement of the lens element LF. Let βP be the lateral magnification of the lens element LF, and β be the lateral magnification of the lens system arranged on the image side of the lens element LF. At that time, the amount of change Δsk is approximately represented by the following equation.

Δsk={(1−βP ² )×β ² }×Δx
According to the above formula, it can be seen that the position sensitivity ES becomes 0 when the absolute value of the lateral magnification βP of the moving lens element LF is 1, and increases as the distance from 1 increases. When the lens element LF is used as the focus lens element, it is necessary to set a sufficient distance in advance so that the lens system on the object side of the lens element LF and the lens system on the image side of the lens element LF do not interfere with each other. If the position sensitivity is low, the overall length of the lens increases, which is not good.

If the lower limit of conditional expression (3) is exceeded, the amount of movement of the lens element LF required to move the image position by a predetermined amount becomes large, making it difficult to reduce the size of the entire system. If the upper limit of conditional expression (3) is exceeded, the image position will move greatly with respect to a minute movement of the lens element LF, so high positional accuracy is required, which is not preferable.

Conditional expression (4) defines the focal length of the lens portion Lp. If the lower limit of conditional expression (4) is exceeded, the positive refracting power of the lens portion Lp becomes too strong and residual aberration of the lens portion Lp increases, which is undesirable because aberration fluctuations increase during focusing. Exceeding the upper limit of conditional expression (4) is not preferable because the positive refractive power of the lens portion Lp becomes too weak, and the amount of movement of the lens element LF during focusing increases, resulting in an increase in the total length of the lens.

Conditional expression (5) defines the distance from the most object-side lens surface of the lens element LF to the image plane when the lens is focused to infinity at the wide-angle end by the total lens length at the wide-angle end. If the lower limit of conditional expression (5) is exceeded, the incident height (absolute value of) of the off-axis light beam becomes high, so that when the lens element LF is moved, the fluctuation of the curvature of field becomes large. becomes difficult to correct. In addition, the amount of movement of the lens element LF increases during focusing, making it difficult to reduce the size of the entire system. If the upper limit of conditional expression (5) is exceeded, the incident height (absolute value of) of the axial light flux increases, making it difficult to reduce variations in spherical aberration.

Conditional expression (6) defines the distance from the lens surface closest to the object side of the lens element LF to the image plane when the lens is focused to infinity at the telephoto end by the total lens length at the telephoto end. If the lower limit of conditional expression (6) is exceeded, the incident height (absolute value of) of the off-axis luminous flux increases, so that when the lens element LF is moved, the fluctuation of the curvature of field increases, and the curvature of field increases. becomes difficult to correct. In addition, the amount of movement of the lens element LF increases during focusing, making it difficult to reduce the size of the entire system. If the upper limit of conditional expression (6) is exceeded, the incident height (absolute value of) of the axial light flux increases, making it difficult to reduce variations in spherical aberration.

Conditional expression (7) defines the focal length of the lens portion Ln by the ratio of the focal length ft of the entire system at the telephoto end. If the lower limit of conditional expression (7) is exceeded, the negative refracting power of the lens portion Ln becomes too strong, so that various aberrations, especially chromatic aberration of magnification and off-axis coma aberration occurring in the lens portion Ln increase, resulting in high imaging performance. becomes difficult to maintain. If the upper limit of conditional expression (7) is exceeded, the negative refractive power of the lens portion Ln becomes too weak, making it difficult to sufficiently shorten the back focus and increasing the size of the entire lens system. Here, the back focus is the distance from the final lens surface to the image plane expressed in air conversion length.

Conditional expression (8) defines the lateral magnification at the telephoto end of the lens system arranged closer to the image side than the lens element LF. If the lower limit of conditional expression (8) is exceeded, the amount of movement of the lens element LF increases during zooming, making it difficult to reduce the size of the entire system. If the upper limit of conditional expression (8) is exceeded, the positional sensitivity of the lens element LF increases, and high positional accuracy is required during focusing, which is not preferable. In addition, it becomes difficult to correct spherical aberration and chromatic aberration in a well-balanced manner over the entire zoom range.

Conditional expression (9) defines the Abbe number of the material of the positive lens that constitutes the lens element LF. If the material of one positive lens that constitutes the lens element LF is out of the range of conditional expression (9), the dispersion will increase, making it difficult to reduce fluctuations in chromatic aberration during zooming.

Conditional expression (10) defines the back focus BFw at the wide-angle end by the ratio of the focal lengths fw of the entire system at the wide-angle end. If the lower limit of conditional expression (10) is exceeded, the effective diameter of the lens closest to the image side will increase, making it difficult to reduce the size of the entire system. If the upper limit of conditional expression (10) is exceeded, the back focal length becomes long, and the zoom lens becomes correspondingly large, which is not good.

Conditional expression (11) defines the amount of movement of the first lens unit L1 and the second lens unit L2 during zooming. By narrowing the air space between the first lens unit L1 and the second lens unit L2 when zooming from the wide-angle end to the telephoto end, it is possible to easily achieve a retrofocus type power arrangement at the wide-angle end and a telephoto type power arrangement at the telephoto end. there is

As described above, according to each of the embodiments, there is provided a zoom lens that is small in size, has a wide angle of view, has little variation in aberrations during focusing, has high optical performance over the entire object distance, and facilitates high-speed focusing. can get.

Preferably, the numerical ranges of conditional expressions (2) to (10) are set as follows.
1.01<|fp/fn|<4.00 (2a)
1.41<(1−βpt ² )×βt ² <4.00 (3a)
3.4<fp/fw<8.4 (4a)
0.28<Dw/Lw<0.34 (5a)
0.28<Dt/Lt<0.51 (6a)
1.3<|fn|/ft<9.0 (7a)
1.42<βt<3.00 (8a)
49≦νd (9a)
0.6<BFw/fw<1.5 (10a)

More preferably, the numerical ranges of conditional expressions (2) to (10) are set as follows.
1.02<|fp/fn|<2.00 (2b)
1.42<(1−βpt ² )×βt ² <3.50 (3b)
3.50<fp/fw<8.20 (4b)
0.29<Dw/Lw<0.34 (5b)
0.30<Dt/Lt<0.51 (6b)
1.3<|fn|/ft<8.0 (7b)
1.45<βt<2.50 (8b)
49.2≦νd (9b)
0.7<BFw/fw<1.4 (10b)

More preferably, the numerical ranges of conditional expressions (4) to (10) are set as follows.
4.0<fp/fw|<4.5 (4c)
0.3<Dw/Lw<0.34 (5c)
0.3<Dt/Lt<0.50 (6c)
1.35<|fn|/ft<6.00 (7c)
2.0<βt<2.5 (8c)
60≦νd (9c)
0.7<BFw/fw<1.3 (10c)

In order to make the lens portion Lp compact and lightweight, it is desirable that it consist of one lens element LF. More preferably, the lens portion Lp is composed of a single positive lens. The lens portion Ln is preferably composed of a positive lens or a cemented lens having a positive refractive power on the side closest to the image plane. By arranging a positive lens or a cemented lens with a positive refractive power near the image plane, it becomes easy to obtain good telecentricity. Here, the cemented lens is a cemented lens in which a plurality of lenses are cemented together, and refers to a cemented lens having a positive refractive power.

In Examples 1 to 7, by moving the positive lens closest to the object side in the second lens group so as to have a component in the direction perpendicular to the optical axis, an image captured when the entire zoom lens vibrates (tilts). I am trying to compensate for blurring. In each embodiment, image blurring may be corrected by moving an arbitrary lens so as to have a component in the direction perpendicular to the optical axis.

Next, an embodiment of a digital camera (imaging device) using the zoom lens of each embodiment as an imaging optical system will be described with reference to FIG. In FIG. 22, 10 is a camera main body, and 11 is an imaging optical system configured by any one of the zoom lenses described in the first to seventh embodiments. Reference numeral 12 denotes an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor, which is built in the camera body and receives an object image formed by the imaging optical system 11 .

Although 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.

Numerical data 1 to 7 corresponding to Examples 1 to 7 are shown below. In each numerical data, i indicates the order of optical surfaces from the object side. r is the radius of curvature of the i-th optical surface, di is the lens thickness and air gap between the i-th surface and the (i+1)-th surface, and ndi and νdi are the refractive indices of the i-th optical member relative to the d-line. and the Abbe number. BF is the back focus. The aspherical shape has an X axis in the direction of the optical axis, an H axis in the direction perpendicular to the optical axis, a positive direction in which light travels, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, and A10 are the aspherical surfaces. When the coefficient is

is represented by the following formula. * means a surface having an aspherical shape. "ex" means 10 ^-x . f is the focal length, Fno is the F number, and ω is the imaging half angle of view, which is the angle of view obtained by paraxial calculation. BF is the back focus and indicates the distance from the final lens surface to the image plane. Wide-angle indicates the wide-angle end, intermediate indicates the intermediate zoom position, and telephoto indicates the telephoto end. Table 1 shows the relationship between the parameters for each conditional expression described above and each numerical embodiment corresponding to each conditional expression.

[Numeric data 1]
unit mm

Surface data surface number rd nd νd
1* 55.911 2.70 1.58313 59.4
2* 10.260 8.54
3 -58.759 1.20 1.72916 54.7
4 13.765 2.56
5 19.945 3.96 1.91082 35.3
6 227.375 (variable)
7 -574.644 2.82 1.48749 70.2
8 -28.639 1.50
9 (Aperture) ∞ 0.40
10 12.385 4.35 1.54072 47.2
11 -13.116 0.80 1.83481 42.7
12 14.614 0.69
13 11.299 4.21 1.43875 94.9
14 -13.226 0.92
15 -41.962 1.34 1.48749 70.2
16 -20.853 1.30 1.72916 54.7
17* -32.018 (variable)
18 16.704 2.34 1.48749 70.2
19 63.973 (variable)
20 77.719 0.80 1.80400 46.6
21 15.409 5.19
22 115.040 6.47 1.48749 70.2
23 -13.942 1.10 1.72916 54.7
24 -31.759 (variable)
Image plane ∞

Aspheric data 1st surface
K = 0.00000e+000 A 4= 5.33573e-005 A 6=-1.20491e-007 A 8= 4.91526e-011 A10= 2.54750e-013

2nd side
K =-9.41229e-001 A 4= 1.21515e-004 A 6= 4.48370e-007 A 8= 5.24763e-009 A10=-3.73262e-011

17th side
K = 0.00000e+000 A 4= 1.09143e-004 A 6= 1.10547e-006 A 8= 1.14921e-008 A10= 2.52199e-010

Various data Zoom ratio 1.89
Wide Angle Medium Telephoto Focal Length 11.30 14.06 21.40
F number 4.10 4.50 5.72
Half angle of view (degrees) 50.40 44.17 32.55
Image height 13.66 13.66 13.66
Overall lens length 84.52 82.26 83.53
BF 10.55 14.23 23.90

When focusing on infinity
d6 16.47 10.52 2.13
d17 3.33 3.21 2.90
d19 1.00 1.12 1.44
d24 10.55 14.23 23.90

When focusing at close range
d6 16.47 10.52 2.13
d17 2.35 1.97 0.91
d19 1.98 2.36 3.42
d24 10.55 14.23 23.90

Lens group data group Starting surface Focal length
1 1 -15.57
2 7 20.57
3 18 45.63
4 20 -35.87

[Numeric data 2]
unit mm

Surface data surface number rd nd νd
1* 91.899 2.70 1.58313 59.4
2* 11.236 8.84
3 -57.102 1.20 1.72916 54.7
4 13.363 2.60
5 19.911 3.32 1.91082 35.3
6 245.984 (variable)
7 -203.873 2.82 1.48749 70.2
8 -26.498 1.48
9 (Aperture) ∞ 0.40
10 12.385 4.20 1.56732 42.8
11 -14.717 0.80 1.83481 42.7
12 15.160 0.69
13 11.637 4.67 1.43875 94.9
14 -13.438 0.85
15 -47.445 1.98 1.53775 74.7
16 -10.359 1.30 1.80610 40.7
17* -29.294 (variable)
18 23.070 2.08 1.77250 49.6
19 78.454 (variable)
20 68.570 0.80 1.78800 47.4
21 15.902 4.25
22 220.267 7.00 1.51823 58.9
23 -12.091 1.10 1.74100 52.6
24 -29.091 (variable)
Image plane ∞

Aspheric data 1st surface
K = 0.00000e+000 A 4= 7.24007e-005 A 6=-2.11686e-007 A 8= 2.73957e-010 A10=-4.06774e-015

2nd side
K =-9.41229e-001 A 4= 1.21307e-004 A 6= 5.70865e-007 A 8= 2.26337e-009 A10=-3.52602e-011

17th side
K = 0.00000e+000 A 4= 8.50130e-005 A 6= 9.12718e-007 A 8= 6.10146e-009 A10= 8.05639e-011

Various data Zoom ratio 1.89
Wide Angle Medium Telephoto Focal Length 11.30 14.07 21.40
F number 4.10 4.50 5.72
Half angle of view (degrees) 50.40 44.15 32.55
Image height 13.66 13.66 13.66
Overall lens length 84.07 82.01 83.65
BF 10.97 14.72 24.52

When focusing on infinity
d6 15.63 9.82 1.67
d17 3.38 3.25 2.91
d19 1.00 1.13 1.46
d24 10.97 14.72 24.52

When focusing at close range
d6 15.63 9.82 1.67
d17 2.38 1.98 0.85
d19 2.00 2.40 3.52
d24 10.97 14.72 24.52

Lens group data group Starting surface Focal length
1 1 -15.24
2 7 21.01
3 18 41.62
4 20 -40.24

[Numeric data 3]
unit mm

Surface data surface number rd nd νd
1* 46.550 2.70 1.58313 59.4
2* 9.669 9.05
3 -131.893 1.20 1.72916 54.7
4 13.545 2.54
5 18.820 3.35 1.91082 35.3
6 104.092 (variable)
7 -284.041 2.72 1.48749 70.2
8 -26.473 1.46
9 (Aperture) ∞ 0.40
10 11.664 4.54 1.54072 47.2
11 -11.285 0.80 1.83481 42.7
12 15.049 0.69
13 12.094 4.87 1.43875 94.9
14 -11.129 0.87
15 -27.006 1.45 1.71300 53.9
16* -25.950 (variable)
17 17.124 2.27 1.48749 70.2
18 -60.000 0.71 1.83481 42.7
19 716.141 (variable)
20 -78.025 0.80 1.80400 46.6
21 17.003 6.44
22 95.293 3.47 1.51633 64.1
23 -46.753 (variable)
Image plane ∞

Aspheric data 1st surface
K = 0.00000e+000 A 4= 2.18227e-005 A 6=-6.00639e-008 A 8= 5.66289e-011 A10= 9.91498e-015

2nd side
K=-9.41229e-001 A 4= 9.68561e-005 A 6=-3.54794e-008 A 8= 6.53663e-009 A10=-3.96809e-011

16th side
K = 0.00000e+000 A 4= 1.22970e-004 A 6= 1.12751e-006 A 8= 1.71097e-008 A10= 1.09777e-010

Various data Zoom ratio 1.89
Wide Angle Medium Telephoto Focal Length 11.30 13.48 21.40
F number 4.10 4.44 5.72
Half angle of view (degrees) 50.40 45.38 32.55
Image height 13.66 13.66 13.66
Overall lens length 81.00 78.67 78.95
BF 10.55 13.26 23.17

When focusing on infinity
d6 16.15 11.10 1.48
d16 2.97 2.84 2.52
d19 1.00 1.14 1.45
d23 10.55 13.26 23.17

When focusing at close range
d6 16.15 11.10 1.48
d16 2.09 1.78 0.80
d19 1.88 2.19 3.17
d23 10.55 13.26 23.17

Lens group data group Starting surface Focal length
1 1 -16.11
2 7 18.79
3 17 45.82
4 20 -29.53

[Numeric data 4]
unit mm

Surface data surface number rd nd νd
1* 64.262 2.70 1.58313 59.4
2* 10.503 9.21
3 -65.110 1.20 1.72916 54.7
4 13.729 2.64
5 20.108 4.37 1.91082 35.3
6 210.405 (variable)
7 -321.132 2.81 1.48749 70.2
8 -27.881 1.48
9 (Aperture) ∞ 0.40
10 12.385 5.38 1.54072 47.2
11 -11.912 0.80 1.83481 42.7
12 14.851 0.69
13 11.579 3.74 1.43875 94.9
14 -12.182 0.87
15 -35.069 1.56 1.48749 70.2
16 -15.380 1.30 1.72916 54.7
17* -26.129 (variable)
18 16.875 1.95 1.48749 70.2
19 111.616 (variable)
20 550.804 0.80 1.80400 46.6
21 16.043 4.35
22 347.855 2.83 1.48749 70.2
23 -38.208 (Variable)
Image plane ∞

Aspheric data 1st surface
K = 0.00000e+000 A 4= 4.90439e-005 A 6=-1.40852e-007 A 8= 1.85627e-010 A10=-2.80433e-014

2nd side
K =-9.41229e-001 A 4= 1.08243e-004 A 6= 2.50033e-007 A 8= 4.28151e-009 A10=-3.47572e-011

17th side
K = 0.00000e+000 A 4= 1.09606e-004 A 6= 1.08254e-006 A 8= 1.17534e-008 A10= 2.51314e-010

Various data Zoom ratio 1.89
Wide Angle Medium Telephoto Focal Length 11.30 14.03 21.40
F number 4.10 4.50 5.71
Half angle of view (degrees) 50.40 44.23 32.55
Image height 13.66 13.66 13.66
Overall lens length 84.31 82.00 83.33
BF 15.25 18.91 28.73

When focusing on infinity
d6 15.94 9.97 1.48
d17 3.05 2.91 2.61
d19 1.00 1.14 1.44
d23 15.25 18.91 28.73

When focusing at close range
d6 15.94 9.97 1.48
d17 2.18 1.82 0.89
d19 1.87 2.22 3.16
d23 15.25 18.91 28.73

Lens group data group Starting surface Focal length
1 1 -15.50
2 7 20.74
3 18 40.51
4 20 -32.96

[Numeric data 5]
unit mm

Surface data surface number rd nd νd
1* 69.474 2.70 1.58313 59.4
2* 10.453 8.30
3 -54.599 1.20 1.72916 54.7
4 13.660 2.54
5 20.071 3.48 1.91082 35.3
6 334.946 (variable)
7 -254.680 2.82 1.48749 70.2
8 -27.271 (variable)
9 (Aperture) ∞ 0.40
10 12.385 5.05 1.54072 47.2
11 -12.115 0.80 1.83481 42.7
12 14.253 0.69
13 11.571 3.56 1.43875 94.9
14 -12.557 0.91
15 -54.288 1.34 1.48749 70.2
16 -23.298 1.30 1.72916 54.7
17* -40.792 (variable)
18 19.660 2.42 1.48749 70.2
19 400.000 (variable)
20 44.824 0.80 1.80400 46.6
21 14.972 3.25
22 -91.775 5.61 1.48749 70.2
23 -11.550 1.10 1.72916 54.7
24 -22.669 (variable)
Image plane ∞

Aspheric data 1st surface
K = 0.00000e+000 A 4= 6.81005e-005 A 6=-1.81286e-007 A 8= 1.72882e-010 A10= 1.81525e-013

2nd side
K=-9.41229e-001 A 4= 1.30061e-004 A 6= 6.80219e-007 A 8= 3.54556e-009 A10=-3.64203e-011

17th side
K = 0.00000e+000 A 4= 1.00692e-004 A 6= 1.03260e-006 A 8= 9.91225e-009 A10= 3.03667e-010

Various data Zoom ratio 1.89
Wide Angle Medium Telephoto Focal Length 11.30 14.10 21.40
F number 4.10 4.50 5.72
Half angle of view (degrees) 50.40 44.09 32.55
Image height 13.66 13.66 13.66
Overall lens length 84.11 82.11 83.58
BF 13.77 17.66 27.40

When focusing on infinity
d6 16.38 10.48 2.20
d8 1.49 1.47 1.44
d17 3.22 3.19 2.89
d19 1.00 1.04 1.39
d24 13.77 17.66 27.40

When focusing at close range
d6 16.38 10.48 2.20
d8 1.49 1.47 1.44
d17 2.26 1.97 0.90
d19 1.96 2.27 3.38
d24 13.77 17.66 27.40

Lens group data group Starting surface Focal length
1 1 -15.34
2 7 62.40
3 9 29.32
4 18 42.32
5 20 -39.00

[Numerical data 6]
unit mm

Surface data surface number rd nd νd
1* 52.830 2.70 1.58313 59.4
2* 10.181 8.60
3 -59.258 1.20 1.72916 54.7
4 13.825 2.59
5 20.078 3.65 1.91082 35.3
6 231.238 (variable)
7 -588.405 2.82 1.48749 70.2
8 -28.673 1.50
9 (Aperture) ∞ 0.40
10 12.385 4.59 1.54072 47.2
11 -13.005 0.80 1.83481 42.7
12 14.533 0.69
13 11.318 4.24 1.43875 94.9
14 -13.138 0.92
15 -41.276 1.40 1.48749 70.2
16 -19.538 1.30 1.72916 54.7
17* -30.170 (variable)
18 15.610 2.33 1.48749 70.2
19 49.850 1.00
20 65.170 0.80 1.80400 46.6
21 15.009 5.68
22 111.871 6.00 1.48749 70.2
23 -14.987 1.10 1.72916 54.7
24 -34.910 (variable)
Image plane ∞

Aspheric data 1st surface
K = 0.00000e+000 A 4= 5.31189e-005 A 6=-1.21914e-007 A 8= 4.89742e-011 A10= 2.62406e-013

2nd side
K = -9.41229e-001 A4= 1.23292e-004 A6= 4.51808e-007 A8= 4.99431e-009 A10=-3.64039e-011

17th side
K = 0.00000e+000 A 4= 1.08107e-004 A 6= 1.12667e-006 A 8= 8.54505e-009 A10= 3.02305e-010

Various data Zoom ratio 1.89
Wide Angle Medium Telephoto Focal Length 11.30 14.06 21.40
F number 4.10 4.50 5.72
Half angle of view (degrees) 50.40 44.18 32.55
Image height 13.66 13.66 13.66
Overall lens length 84.03 81.90 83.55
BF 11.08 14.62 24.01

When focusing on infinity
d6 16.40 10.54 2.30
d17 2.24 2.43 2.93
d24 11.08 14.62 24.01

When focusing at close range
d6 16.40 10.54 2.30
d17 1.30 1.23 0.96
d19 1.93 2.20 2.97
d24 11.08 14.62 24.01

Lens group data group Starting surface Focal length
1 1 -15.68
2 7 20.59
3 18 -170.94
Lp 18 45.60
Ln20 -35.34

[Numerical data 7]
unit mm

Surface data surface number rd nd νd
1* 59.225 2.70 1.58313 59.4
2* 10.006 8.26
3 -54.122 1.20 1.72916 54.7
4 14.138 2.53
5 20.646 3.51 1.91082 35.3
6 1034.167 (variable)
7 -226.812 2.49 1.48749 70.2
8 -26.151 1.47
9 (Aperture) ∞ 0.40
10 12.815 4.67 1.54072 47.2
11 -11.482 0.80 1.83481 42.7
12 14.252 0.69
13 11.703 4.24 1.43875 94.9
14 -11.801 0.94
15 -37.289 1.76 1.58573 59.7
16* -38.885 (variable)
17 20.428 1.37 1.61293 37.0
18 16.481 4.88
19 20.010 2.07 1.48749 70.2
20 64.273 (variable)
21 31.940 0.80 1.80400 46.6
22 16.774 3.09
23 177.110 6.53 1.48749 70.2
24 -13.446 1.10 1.77250 49.6
25 -29.046 (variable)
Image plane ∞

Aspheric data 1st surface
K = 0.00000e+000 A 4= 5.30425e-005 A 6=-1.43864e-007 A 8= 1.57614e-010 A10= 8.97529e-014

2nd side
K =-9.41229e-001 A 4= 1.23167e-004 A 6= 3.67689e-007 A 8= 5.51226e-009 A10=-4.00459e-011

16th side
K = 0.00000e+000 A 4= 1.10132e-004 A 6= 1.16973e-006 A 8= 1.27426e-008 A10= 3.40311e-010

Various data Zoom ratio 1.89
Wide Angle Medium Telephoto Focal Length 11.30 14.01 21.40
F number 4.10 4.50 5.71
Half angle of view (degrees) 50.40 44.28 32.55
Image height 13.66 13.66 13.66
Overall lens length 84.59 82.24 83.54
BF 10.54 14.23 24.24

When focusing on infinity
d6 16.24 10.20 1.49
d16 1.31 1.20 0.90
d20 1.00 1.11 1.41
d25 10.54 14.23 24.24

When focusing at close range
d6 16.24 10.20 1.49
d16 1.31 1.20 0.90
d18 3.05 2.55 0.92
d20 2.83 3.44 5.37
d25 10.54 14.23 24.24

Lens group data group Starting surface Focal length
1 1 -15.95
2 7 21.35
3 17 92.45
L3n 17 -160.38
LF 19 58.70
4 21 -80.47

OL zoom lens L1 first lens group L2 second lens group L3 third lens group L4 fourth lens group L5 fifth lens group LR rear group Ln lens section Lp lens section LF lens element

Claims (17)

A zoom lens having a plurality of lens groups, wherein the distance between adjacent lens groups changes during zooming,
The plurality of lens groups includes a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens section Lp with positive refractive power, which are arranged in order from the object side to the image side. A lens group, consisting of a fourth lens group as a lens portion Ln having a negative refractive power,
Only the lens element LF, which is the whole or part of the lens portion Lp, moves during focusing,
When the radius of curvature of the lens surface on the object side of the lens element LF is R1f, the radius of curvature of the lens surface on the image side is R2f, the focal length of the lens portion Lp is fp, and the focal length of the lens portion Ln is fn ,
0.95<(R2f+R1f)/(R2f-R1f)<5.00
1.0<|fp/fn|<5.0
A zoom lens characterized by satisfying the following conditional expression: A zoom lens having a plurality of lens groups, wherein the distance between adjacent lens groups changes during zooming,
The plurality of lens groups are arranged in order from the object side to the image side, a first lens group with negative refractive power, a second lens group with positive refractive power, a third lens group with positive refractive power, and a positive lens group. Consists of a fourth lens group as a lens part Lp with a refractive power and a fifth lens group as a lens part Ln with a negative refractive power,
During focusing, the lens element LF, which is the entire lens portion Lp, moves,
When the radius of curvature of the lens surface on the object side of the lens element LF is R1f, and the radius of curvature of the lens surface on the image side is R2f,
0.95<(R2f+R1f)/(R2f-R1f)<5.00
A zoom lens characterized by satisfying the following conditional expression : A zoom lens having a plurality of lens groups, wherein the distance between adjacent lens groups changes during zooming,
The plurality of lens groups consist of a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with negative refractive power, arranged in order from the object side to the image side,
The third lens group is composed of a lens portion Lp composed of a positive refractive power lens element LF that moves during focusing, and a negative refractive power lens portion Ln arranged on the image side of the lens portion Lp. ,
When the radius of curvature of the lens surface on the object side of the lens element LF is R1f, and the radius of curvature of the lens surface on the image side is R2f,
0.95<(R2f+R1f)/(R2f-R1f)<5.00
A zoom lens characterized by satisfying the following conditional expression : When the focal length of the lens portion Lp is fp and the focal length of the lens portion Ln is fn,
1.0<|fp/fn|<5.0
4. The zoom lens according to claim 2 , wherein the following conditional expression is satisfied. βpt is the lateral magnification of the lens element LF when focused on infinity at the telephoto end; When the lateral magnification is βt,
1.4<(1−βpt ² )×βt ² <5.0
5. The zoom lens according to any one of claims 1 to 4 , wherein the following conditional expression is satisfied. When the focal length of the lens portion Lp is fp and the focal length of the zoom lens at the wide-angle end is fw,
3.0<fp/fw<8.5
6. The zoom lens according to any one of claims 1 to 5 , wherein the following conditional expression is satisfied. Dw is the distance from the most object-side lens surface of the lens element LF to the image plane at the wide-angle end when focusing on infinity, and Dw is the distance from the most object-side lens surface of the first lens group to the image plane at the wide-angle end. When the distance is Lw,
0.25<Dw/Lw<0.36
7. The zoom lens according to any one of claims 1 to 6 , wherein the following conditional expression is satisfied. Dt is the distance from the most object side lens surface of the lens element LF to the image plane at the telephoto end when focusing on infinity, and Dt is the distance from the most object side lens surface of the first lens group to the image plane at the telephoto end When the distance is Lt,
0.25<Dt/Lt<0.55
8. The zoom lens according to any one of claims 1 to 7 , wherein the following conditional expression is satisfied. When the focal length of the lens portion Ln is fn and the focal length of the zoom lens at the telephoto end is ft,
1.0<|fn|/ft<10.0
9. The zoom lens according to any one of claims 1 to 8 , wherein the following conditional expression is satisfied. Let βt be the lateral magnification of the lens system arranged closer to the image side than the lens element LF when focused on infinity at the telephoto end,
1.4<βt<5.0
10. The zoom lens according to any one of claims 1 to 9 , wherein the following conditional expression is satisfied. 11. The zoom lens according to any one of claims 1 to 10 , wherein the lens portion Lp consists of one positive lens. The lens element LF is composed of one positive lens or a cemented lens in which one positive lens and one negative lens are cemented together.
45≦νd
11. The zoom lens according to any one of claims 1 to 10 , wherein the following conditional expression is satisfied. 13. The zoom lens according to any one of claims 1 to 12, wherein said second lens group includes an aperture stop. 14. The zoom lens according to any one of claims 1 to 13 , wherein the lens portion Ln has a positive lens or a cemented lens with a positive refractive power closest to the image side. When the focal length of the zoom lens at the wide-angle end is fw, and the back focus at the wide-angle end is BFw,
0.5<BFw/fw<2.0
15. The zoom lens according to any one of claims 1 to 14 , wherein the following conditional expression is satisfied. When the air gap between the first lens group and the second lens group at the wide-angle end is D1w, and the air gap between the first lens group and the second lens group at the telephoto end is D1t,
D1w>D1t
16. The zoom lens according to any one of claims 1 to 15 , wherein the following conditional expression is satisfied. An imaging apparatus comprising: the zoom lens according to any one of claims 1 to 16 ; and an imaging device for receiving an image formed by the zoom lens.

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