JP6141004B2 - Zoom lens and imaging apparatus having the same - Google Patents

Description

  The present invention relates to a zoom lens and an image pickup apparatus having the same, and is particularly suitable as an image pickup optical system used in image pickup apparatuses such as a still camera, a video camera, a digital still camera, a TV camera, and a surveillance camera.

  In recent years, an imaging optical system used in an imaging apparatus such as a video camera or a digital still camera using an imaging element has a short overall lens length (distance from the first lens surface to the image plane), the entire system is small, and has a large aperture. It is required to be a zoom lens with a ratio. As a zoom lens that satisfies these requirements, there is known a positive lead type four-group zoom lens composed of first to fourth lens units having positive, negative, positive, and positive refractive powers in order from the object side to the image side. It has been.

  In the above-described four-group zoom lens, zooming is performed by moving the second lens group, and the so-called inner focus type four-group zoom is performed in which the third lens group corrects image plane variation accompanying zooming and performs focusing. Lenses are known (Patent Documents 1 to 3).

  In general, an inner focus type zoom lens has a smaller effective diameter of the first lens group than a zoom lens that focuses by moving the first lens group, and the entire lens system can be easily downsized. Further, close-up photography, particularly close-up photography is facilitated. Further, since the small and lightweight lens group is moved during focusing, the driving force of the lens group is small, and quick focusing is easy.

JP 2006-201524 A JP 2009-86537 A JP 59-52215 A

  In recent years, with the increase in functionality and miniaturization of imaging devices, the lens system used therein has a large aperture with a high zoom ratio, the entire imaging lens system is small, and zoom with high optical performance with little chromatic aberration. There is a strong demand for lenses.

  In general, in a zoom lens, in order to reduce the size of the entire system while ensuring a high zoom ratio, the number of lenses may be reduced while increasing the refractive power of each lens group constituting the zoom lens. However, the zoom lens constructed in this manner increases the lens thickness as the refractive power of each lens surface increases, resulting in an insufficient overall shortening effect, making it difficult to miniaturize and simultaneously generating various aberrations. These corrections become difficult.

  In a positive lead type zoom lens, it is important to appropriately set each element constituting the zoom lens in order to obtain a high optical performance while ensuring a small size of the entire system and a large aperture ratio. For example, it is important to appropriately set the zoom type (the number of lens groups and the refractive power of each lens group), the movement trajectory associated with zooming of each lens group, and the variable magnification burden of each lens group. .

  If these configurations are not appropriate, the entire system becomes large when attempting to increase the diameter, and fluctuations in various aberrations associated with zooming increase, making it difficult to obtain high optical performance over the entire zoom range and the entire screen. It becomes difficult. For example, in the zoom lens disclosed in Patent Document 1, since the elements such as the lens group configuration and the refractive power sharing of each lens group are not necessarily appropriate when increasing the diameter, while maintaining the downsizing of the entire system, for example, It is difficult to make the aperture larger than F number 2.8.

  In Patent Document 1, if the magnification of the third lens group for focusing is appropriately set and the focus movement amount is optimized, the third lens group can be reduced in size. However, when the aperture is increased, the positive Petzval sum increases, and it is difficult to sufficiently improve this, and the field curvature tends to increase. In Patent Documents 2 and 3, the third lens group for focusing is composed of a plurality of lenses, the weight of the entire lens system is heavy, and rapid focusing tends to be difficult.

  The present invention provides a zoom lens having a large aperture, a small entire system, easy focusing quickly, and good optical performance over the entire zoom range from the wide-angle end to the telephoto end, and an image pickup apparatus having the zoom lens With the goal.

The zoom lens according to the present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, arranged in order from the object side to the image side. Consists of a fourth lens unit having a refractive power. During zooming from the wide-angle end to the telephoto end, the first lens unit and the fourth lens unit do not move, and the second lens unit and the third lens unit move. A zoom lens in which the interval between adjacent lens groups changes during zooming,
The distance between the first lens group and the second lens group is increased at the telephoto end compared to the wide-angle end, the third lens group is composed of one positive lens, and the zoom lens further includes an aperture stop,
The refractive index at the d-line of the positive lens material constituting the third lens group is nd3 , the focal length of the first lens group is f1, the focal length of the fourth lens group is f4, the total lens length is TL, and the telephoto end When the air-converted distance from the aperture stop to the image plane in DSP is a DSP ,
1.6 <nd3 <2.4
0.6 <f1 / f4 <2.2
0.10 <DSP / TL <0.35
It is characterized by satisfying the following conditional expression.

  According to the present invention, the zoom has a large aperture, the entire system is small, can perform quick focusing, and can easily obtain high optical performance with excellent correction of various aberrations such as spherical aberration, coma, and field curvature. A lens can be realized.

(A), (B), (C) Lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 1. (A), (B), (C) Aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 1. (A), (B), (C) Lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 2. (A), (B), (C) Aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end of Example 2. (A), (B), (C) Lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 3 (A), (B), (C) Aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end of Example 3. Schematic diagram of main parts of an imaging apparatus of the present invention Schematic diagram of main parts of an imaging apparatus of the present invention

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The zoom lens according to the present invention includes a first lens group having a positive refractive power (optical power = reciprocal of focal length), a second lens group having a negative refractive power, and a positive lens arranged in order from the object side to the image side. The third lens group has a refractive power and the fourth lens group has a positive refractive power. For zooming, the first lens group and the fourth lens group do not move, and the second lens group and the third lens group move. The distance between adjacent lens units changes during zooming.

  During zooming from the wide-angle end to the telephoto end, the second lens group moves monotonically to the image side. The third lens group moves non-linearly. In addition, the distance between the first lens group and the second lens group at the telephoto end is increased (wider) and the distance between the second lens group and the third lens group is reduced (narrowed) compared to the wide-angle end. .

  1A, 1B, and 1C are lens cross-sectional views at the wide-angle end (short focal length end), the intermediate zoom position, and the telephoto end (long focal length end) of the zoom lens according to Embodiment 1 of the present invention. is there. 2A, 2B, and 2C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively, of the zoom lens according to the first exemplary embodiment. The first embodiment is a zoom lens having a zoom ratio of 2.85, an aperture ratio of 1.85 to 2.40, and a shooting half angle of view of about 6.09 degrees to 2.14 degrees.

  3A, 3B, and 3C are lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to Embodiment 2 of the present invention. 4A, 4B, and 4C are aberration diagrams of the zoom lens of Embodiment 2 at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively. The second embodiment is a zoom lens having a zoom ratio of 2.85, an aperture ratio of 1.85 to 1.85, and a shooting half angle of view of about 8.02 degrees to 2.83 degrees.

  5A, 5B, and 5C are lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to Embodiment 3 of the present invention. 6A, 6B, and 6C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively, of the zoom lens according to the third exemplary embodiment. Example 3 is a zoom lens having a zoom ratio of 1.9, an aperture ratio of 1.34 to 2.60, and a shooting half angle of view of about 3.55 to 1.87 degrees. FIG. 7 is a schematic view of a main part of a digital video camera using the zoom lens of the present invention. FIG. 8 is a schematic view of a main part of a network camera using the zoom lens of the present invention.

  The zoom lens of each embodiment is a photographing lens system used in an imaging apparatus such as a video camera, a digital camera, a silver salt film camera, or a TV camera. The zoom lens of each embodiment can also be used as a projection optical system for an image projection apparatus (projector). In the lens cross-sectional view, the left side is the object side (front), and the right side is the image side (rear). In the lens cross-sectional view, if i is the order of the lens group from the object side, Bi indicates the i-th lens group. In the lens cross-sectional view, B1 is a first lens group having a positive refractive power, B2 is a second lens group having a negative refractive power, B3 is a third lens group having a positive refractive power, and B4 is a fourth lens having a positive refractive power. It is a lens group.

  SP is an aperture stop that determines (limits) a light beam having an open F number (Fno). G is an optical block corresponding to an optical filter, a face plate, a low-pass filter, an infrared cut filter, or the like. IP is the image plane. The image plane IP corresponds to an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor when a zoom lens is used as an imaging optical system of a video camera or a network camera. When a zoom lens is used as a photographing optical system of a silver salt film camera, it corresponds to a film surface. Arrows indicate the movement trajectory of each lens unit during zooming (variation) from the wide-angle end to the telephoto end.

  In the zoom lens of each embodiment, the distance between the first lens unit B1 and the second lens unit B2 increases during zooming from the wide-angle end to the telephoto end zoom position, and the second lens unit B2 and the third lens unit. The interval with B3 is reduced.

  Specifically, when zooming from the wide-angle end to the telephoto end as indicated by the arrow, the second lens unit B2 is moved to the image side to perform zooming, and the image plane variation caused by zooming is changed to the third lens unit B3. It is corrected by moving it in a non-linear manner. Further, focusing is performed by moving the third lens unit B3 on the optical axis. A solid curve 3a and a dotted curve 3b relating to the third lens unit B3 show image plane fluctuations accompanying zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at close distance, respectively. This is a movement locus for correction.

  Further, when focusing from an infinitely distant object to a close object at the zoom position at the telephoto end, the third lens unit B3 is retracted to the image side as indicated by an arrow 3c. In the first to third embodiments, the aperture stop SP does not move for zooming, but may be moved independently or together with other lens groups as necessary.

  In the aberration diagrams, Fno is the F number, ω is the half field angle (degrees), and the field angle based on the ray tracing value. In the spherical aberration diagram, the solid line d is the d line (wavelength 587.6 nm), and the two-dot chain line g is the g line (wavelength 435.8 nm). In the astigmatism diagram, the solid line ΔS and the dotted line ΔM are the sagittal image surface and the meridional image surface at the d line, respectively. Distortion is shown for the d-line. In the chromatic aberration diagram of magnification, g of the two-dot chain line is the g line. In the following embodiments, the wide-angle end and the telephoto end are zoom positions when the lens unit for zooming (second lens unit B2) is positioned at both ends of a range in which the lens unit can move on the optical axis. .

  In each embodiment, in order to secure a predetermined zoom ratio and correct various aberrations, the first lens unit B1 having a positive refractive power and the second lens unit having a negative refractive power are sequentially arranged from the object side to the image side. B2, a third lens unit B3 having a positive refractive power, and a fourth lens unit B4 having a positive refractive power. During zooming from the wide-angle end to the telephoto end, the first lens unit B1 is fixed with respect to the imaging surface, and the second lens unit is moved to the image side for zooming.

  By fixing the first lens unit B1 with respect to the image plane during zooming, high positional accuracy is maintained and the change in the total lens length (distance from the first lens surface to the image plane) during zooming is eliminated. ing. In addition, the number of movable lens groups is reduced, and the mechanical parts are simplified. By simplifying the mechanical parts, the generation of dust and the like can be reduced, and a zoom lens maintaining high optical performance and an imaging device using the same are configured. Further, the strength of the lens barrel when attaching an accessory such as a converter lens is increased.

  During zooming, the second lens unit B2 and the third lens unit B3 are moved to minimize the number of movable lens units, thereby reducing the size of the entire lens system and simplifying the configuration. Further, focusing is performed by moving the third lens unit B3. This suppresses aberration fluctuations during focusing from an infinitely distant object to a close object. In particular, by providing a substantially afocal refractive power arrangement between the third lens unit B3 and the fourth lens unit B4, fluctuations in various aberrations during focusing, particularly coma, are suppressed.

  In zooming, the fourth lens unit B4 is fixed with respect to the imaging surface, thereby improving the robustness while simplifying the lens barrel structure.

The third lens unit B3 is composed of one positive lens in each embodiment, the refractive index at the d-line of the material of the positive lens and nd3. At this time,
1.6 <nd3 <2.4 (1)
The following conditional expression is satisfied. By configuring the third lens unit B3 with one positive lens, the third lens unit B3 can be downsized. Conditional expression (1) defines the material of the positive lens of the third lens unit B3.

  By satisfying conditional expression (1), the refractive power of the third lens unit B3 can be determined appropriately, various aberrations, in particular, spherical aberration and coma can be easily corrected, and high imaging performance can be achieved. Have achieved. Further, by adopting a high refractive index material, an increase in the thickness of the positive lens of the third lens unit B3 is suppressed, and weight reduction is facilitated. As a result, when the third lens unit B3 is focused, a quick operation is facilitated.

  If the refractive index is too high exceeding the upper limit of conditional expression (1), in general, the greater the refractive index, the greater the dispersion and the more likely chromatic aberration occurs. For this reason, it becomes difficult to suppress fluctuations in chromatic aberration due to zooming and focusing. If the lower limit of conditional expression (1) is exceeded and the refractive index becomes too low, the radius of curvature of the lens surface becomes small to give the third lens unit B3 a predetermined refractive power, and spherical aberration and coma aberration on the telephoto side. Correction becomes difficult. In addition, it is difficult to reduce the size of the entire system. In each embodiment, the numerical range of conditional expression (1) is more preferably set as follows.

1.65 <nd3 <2.1 (1a)
By satisfying conditional expression (1a), it becomes easy to satisfactorily correct the longitudinal chromatic aberration and the variation of the spherical aberration due to zooming while reducing the overall size. More preferably, the numerical range of the conditional expression (1a) is set as follows.

1.7 <nd3 <1.9 (1b)
As described above, by appropriately configuring each lens group and satisfying conditional expression (1), the zoom has high imaging performance over the entire zoom range, a large aperture, a small overall system, and easy high-speed focusing. I have a lens.

In each embodiment, it is more preferable to satisfy one or more of the following conditional expressions. The focal length of the first lens unit B1 is f1, the focal length of the third lens unit B3 is f3, and the focal length of the fourth lens unit B4 is f4. Let the focal lengths of the entire system at the wide-angle end and the telephoto end be fW and fT, respectively. The lateral magnifications at the telephoto end of the third lens unit B3 and the fourth lens unit B4 are β3T and β4T, respectively. Further, the curvature radii of the object-side lens surface and the image-side lens surface of the positive lens included in the third lens unit B3 are R31 and R32, respectively.

The Abbe number of the material of the positive lens included in the third lens unit B3 is νd3. The total lens length is TL, and the air conversion distance from the aperture stop SP to the image plane at the telephoto end (the distance when a parallel plane plate such as a filter is removed) is DSP. At this time, it is preferable to satisfy one or more of the following conditional expressions.

0.2 <| (1-β3T ² ) × β4T ² | <1.2 (2)
-40.0 <β3T <-1.5 (3)
-1.0 <(R31 + R32) / (R31-R32) <1.0 (4)
0.8 <f1 / f3 <2.4 (5)
0.2 <f3 / fT <1.0 (6)
0.8 <f1 / fW <3.0 (7)
0.6 <f1 / f4 <2.2 (8)
0.10 <DSP / TL <0.35 (9)
35 <νd3 <65 (10)

Next, the technical meaning of each conditional expression described above will be described. Conditional expression (2) defines the position sensitivity of the third lens unit B3. By configuring the third lens unit B3 with one positive lens, the third lens unit B3 is downsized. Then, focusing (focusing operation) is performed with the positive lens, thereby reducing the weight of the focus lens and facilitating quick focusing operation. Here, the position sensitivity ES is a ratio of the movement amount Δsk in the optical axis direction of the imaging position (focus position) when the lens group is moved to the distance Δx in the optical axis direction. That is, ES = Δsk / Δx
It is.

  In order from the object side to the image side, a first lens unit B1 having a positive refractive power, a second lens unit B2 having a negative refractive power, a third lens unit B3 having a positive refractive power, and a fourth lens unit having a positive refractive power In the zoom lens composed of B4, the amount of back focus deviation with respect to the amount of movement of the third lens unit B3 is Δsk. Let the amount of movement of the third lens group be Δx. The imaging magnification of the third lens group B3 is β3, and the imaging magnification of the fourth lens group B4 is β4. At that time, the deviation amount Δsk is approximately expressed by the following equation.

Δsk = {(1−β3 ² ) × β4 ² } × Δx
From the above equation, it can be seen that the position sensitivity ES is 0 when the absolute value of the imaging magnification β3 of the moving lens group is 1, and increases as the distance from 1 increases. When the third lens unit B3 is used as a focus lens unit, the lens unit on the object side of the third lens unit B3 and the fourth lens unit B4 on the image side of the third lens unit B3 do not interfere with each other in advance. It is necessary to set a sufficient interval. If the position sensitivity is small, the total lens length increases, which is not good.

  If the upper limit of conditional expression (2) is exceeded, the image position moves greatly with respect to the minute movement of the third lens unit B3, which is not preferable because high positional accuracy is required. When the lower limit of conditional expression (2) is exceeded, the amount of movement of the third lens unit B3 required for moving the image position by a predetermined amount increases, and it becomes difficult to reduce the size of the entire system. In addition, it becomes difficult to suppress aberration variation when the third lens unit B3 is moved in order to move the image position by a predetermined amount.

  Conditional expression (3) defines the lateral magnification (imaging lateral magnification) at the telephoto end of the third lens unit B3. When the lateral magnification of the third lens unit B3 increases beyond the upper limit of conditional expression (3), the amount of movement of the third lens unit B3 during zooming increases, making it difficult to suppress fluctuations in coma during zooming. . If the lateral magnification of the third lens unit B3 is reduced beyond the lower limit of the conditional expression (3), the entire system can be easily downsized. However, the third lens unit B3 is moved and stopped by zooming, focusing, or the like. In this case, high positional accuracy is required, which is not preferable. In addition, it becomes difficult to correct spherical aberration and chromatic aberration in a balanced manner over the entire zoom range.

  Conditional expression (4) defines the lens shape (shape factor) of the positive lens of the third lens unit B3. Conditional expression (4) defines a condition for satisfactorily correcting coma while suppressing the occurrence of spherical aberration. When the upper limit of conditional expression (4) is exceeded and the radius of curvature of the lens surface on the object side becomes large, it becomes difficult to correct spherical aberration well on the wide angle side. If the radius of curvature of the lens surface on the image side increases beyond the lower limit of conditional expression (4), the spherical aberration remaining in the third lens unit B3 must be corrected by the fourth lens unit B4. The number of lenses in group B4 increases and the entire system becomes larger.

  Conditional expression (5) defines the ratio of the focal length f1 of the first lens unit B1 and the focal length f3 of the third lens unit B3. If the refractive power of the first lens unit B1 decreases beyond the upper limit of conditional expression (5), the total lens length becomes longer at the telephoto end, and the entire system becomes larger. Further, the object point with respect to the second lens unit B2 that performs zooming becomes far, and the imaging magnification of the second lens unit B2 decreases. As a result, in order to increase the zoom ratio, the amount of movement of the second lens unit B2 during zooming increases, and the entire system increases in size.

  If the refractive power of the first lens unit B1 increases beyond the lower limit of conditional expression (5), the total lens length at the telephoto end is shortened, but chromatic aberration remains on the telephoto side when the F-number is decreased. It is not preferable.

  Conditional expression (6) defines the ratio between the focal length f3 of the third lens unit B3 and the focal length fT of the entire system at the telephoto end. If the refractive power of the third lens unit B3 becomes weaker than the upper limit of conditional expression (6), the total lens length increases. Further, during focusing, the amount of movement of the third lens unit B3 becomes large, and quick focusing becomes difficult. If the lower limit of conditional expression (6) is exceeded and the refractive power of the third lens unit B3 becomes too strong, spherical aberration and coma aberration will be overcorrected over the entire zoom range, which is not preferable.

  Conditional expression (7) defines the ratio between the focal length f1 of the first lens unit B1 and the focal length fW of the entire system at the wide-angle end. If the refractive power of the first lens unit B1 decreases beyond the upper limit of conditional expression (7), it is necessary to increase the total lens length in order to achieve a high zoom ratio, which is not preferable. Increasing the refractive power of the first lens unit B1 beyond the lower limit of conditional expression (7) is advantageous for increasing the zoom ratio and shortening the total lens length, but it is possible to achieve both spherical aberration and coma correction and chromatic aberration correction. Is difficult and undesirable.

  Conditional expression (8) defines the ratio of the focal length f1 of the first lens unit B1 and the focal length f4 of the fourth lens unit B4. By satisfying conditional expression (8), the entire length of the lens is shortened while ensuring a predetermined amount of back focus. If the refractive power of the first lens unit is reduced beyond the upper limit of conditional expression (8), off-axis aberration can be reduced, but it is difficult to correct spherical aberration on the telephoto side when increasing the diameter. become.

  When the refractive power of the fourth lens unit B4 decreases beyond the lower limit of conditional expression (8), it becomes difficult to secure a predetermined amount of back focus, and an optical member such as a filter is disposed between the zoom lens and the image sensor. It becomes difficult. Furthermore, it is more preferable to satisfy the conditional expression (5) and the conditional expression (8) at the same time because it is easy to realize a refractive power arrangement that is substantially afocal between the third lens group B3 and the fourth lens group B4.

  Conditional expression (9) normalizes the position of the aperture stop SP in the zoom lens. If the upper limit of conditional expression (9) is exceeded, the entrance pupil position becomes close, and when the aperture is increased, the aperture diameter of the aperture stop SP increases in the radial direction on the wide angle side, which is not good. If the lower limit of conditional expression (9) is exceeded, the off-axis light beam incident on the first lens unit B1 is separated from the optical axis and the first lens unit B1 increases in the radial direction, particularly on the telephoto side.

Conditional expression (10) defines the Abbe number of the material of the positive lens of the third lens unit B3. The Abbe number νd is Nd, NF, NC when the refractive indices of the materials in the d-line, F-line, and C-line of the Fraunhofer line are
νd = (Nd−1) / (NF−NC)
Defined by When the third lens unit B3 is composed of one positive lens, a material outside the range of the conditional expression (10) has a large dispersion, and it is difficult to suppress fluctuations in chromatic aberration during zooming. More preferably, the numerical ranges of the conditional expressions (2) to (10) are set as follows.

0.3 <| (1-β3T ² ) × β4T ² | <1.0 (2a)
−32.0 <β3T <−2.0 (3a)
−0.7 <(R31 + R32) / (R31−R32) <0.7 (4a)
0.9 <f1 / f3 <2.0 (5a)
0.25 <f3 / fT <0.90 (6a)
1.0 <f1 / fW <2.8 (7a)
0.8 <f1 / f4 <2.0 (8a)
0.15 <DSP / TL <0.30 (9a)
40 <νd3 <60 (10a)

  By satisfying conditional expression (2a), the position sensitivity of the third lens unit B3 at the telephoto end is set more appropriately, and it becomes easy to perform high-speed and high-precision focusing. By satisfying conditional expression (3a), it becomes easy to suppress the variation of spherical aberration caused by zooming while reducing the size of the entire system. By satisfying conditional expression (4a), it becomes easy to more effectively correct spherical aberration and coma with the third lens unit B3. By satisfying conditional expression (5a), it is easier to increase the diameter and shorten the total lens length.

  By satisfying conditional expression (6a), spherical aberration and coma can be easily corrected on the telephoto side, and the number of lenses can be easily reduced. By satisfying conditional expression (7a), it is easy to increase the aperture while achieving a high zoom ratio. By satisfying the conditional expression (8a), it becomes easy to secure a predetermined amount of back focus, and it becomes easy to suppress fluctuations in lateral chromatic aberration due to zooming. By satisfying the conditional expression (9a), it is easy to suppress an increase in the diameter of the diaphragm accompanying the increase in the diameter. By satisfying conditional expression (10a), it is easy to downsize the entire system while suppressing variations in chromatic aberration associated with zooming.

  Furthermore, it is preferable to set the numerical ranges of conditional expressions (2a) to (10a) as follows.

0.35 <| (1-β3T ² ) × β4T ² | <0.70 (2b)
−26.0 <β3T <−2.4 (3b)
-0.3 <(R31 + R32) / (R31-R32) <0.3 (4b)
1.1 <f1 / f3 <1.8 (5b)
0.30 <f3 / fT <0.75 (6b)
1.1 <f1 / fW <2.5 (7b)
1.0 <f1 / f4 <1.8 (8b)
0.20 <DSP / TL <0.26 (9b)
45 <νd3 <50 (10b)

  In each embodiment, the above-described configuration achieves a high zoom ratio while shortening the total lens length at the wide-angle end and the telephoto end. Further, in each embodiment, by configuring as described above, the curvature of field is favorably corrected at the wide-angle end without using an aspheric lens.

  Next, an embodiment of a digital video camera using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG. In FIG. 7, reference numeral 10 denotes a camera body, and 11 denotes a photographing optical system constituted by any of the zoom lenses described in the first to third embodiments. Reference numeral 12 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographing optical system 11 and is built in the camera body. Reference numeral 13 denotes a viewfinder for observing a subject image formed on the solid-state image sensor 12, which includes a liquid crystal display or the like.

  An embodiment of a network camera using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG. In FIG. 8, reference numeral 20 denotes a camera body, and reference numeral 21 denotes a photographing optical system constituted by any one of the zoom lenses described in the first to third embodiments. Reference numeral 22 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographing optical system 21 and is built in the camera body. In this way, by applying the zoom lens of the present invention to an imaging apparatus such as a digital video camera or a network camera, a small-sized imaging apparatus having high optical performance can be realized.

  In addition, the zoom lens of each embodiment can also be used as a projection optical system for a projection apparatus (projector).

  Hereinafter, specific numerical data of Numerical Examples 1 to 3 corresponding to Examples 1 to 3 will be shown. In each numerical example, i indicates the number of the surface counted from the object side. ri is the radius of curvature of the i-th optical surface (i-th surface). di is the axial distance between the i-th surface and the (i + 1) -th surface. ndi and νdi are the refractive index and Abbe number of the material of the i-th optical member with respect to the d-line, respectively. The two surfaces closest to the image correspond to the glass block G.

  BF is an air equivalent back focus. Table 1 shows the relationship between the above-described conditional expressions and numerical examples. Each numerical example shows values at the F-number, half angle of view (degree), image height, total lens length, BF, etc. at three focal lengths at the wide-angle end, the intermediate zoom position, and the telephoto end. The half field angle indicates a half field angle based on the ray tracing value. Table 1 shows the correspondence between the above-described conditional expressions and the respective examples with respect to the parameters. In Table 1, f2 represents the focal length of the second lens unit B2, and β2T represents the lateral magnification at the telephoto end of the second lens unit B2.

[Numerical Example 1]
Unit mm

Surface data surface number rd nd νd
1 48.534 4.41 1.60311 60.6
2 -780.140 0.20
3 29.004 1.60 1.84666 23.8
4 19.803 6.79 1.49700 81.5
5 94.554 (variable)
6 89.689 0.80 1.83481 42.7
7 8.289 2.49 1.95906 17.5
8 13.872 2.28
9 -17.958 0.70 1.91082 35.3
10 593.130 (variable)
11 66.485 2.21 1.77250 49.6
12 -42.908 (variable)
13 24.843 2.13 1.77250 49.6
14 540.505 0.15
15 16.854 3.67 1.59522 67.7
16 -39.648 0.80 1.92286 18.9
17 30.560 4.00
18 (Aperture) ∞ 4.85
19 43.054 2.50 1.84666 23.8
20 -8.791 0.80 1.80 100 35.0
21 7.852 0.85
22 11.358 1.81 1.63636 35.4
23 -31.736 8.09
24 ∞ 2.30 1.51400 70.0
25 ∞ 1.00
Image plane ∞

Various data Zoom ratio 2.85
Wide angle Medium Telephoto focal length 28.14 58.46 80.32
F number 1.85 1.97 2.40
Half angle of view (degrees) 6.09 2.94 2.14
Image height 3.00 3.00 3.00
Total lens length 86.45 86.45 86.45
BF 10.61 10.61 10.61

d 5 11.42 18.92 20.79
d10 16.22 8.47 2.96
d12 5.16 5.42 9.06

Zoom lens group data group Start surface Focal length
1 1 48.46
2 6 -10.20
3 11 34.06
4 13 29.85
5 24 ∞

[Numerical Example 2]
Unit mm

Surface data surface number rd nd νd
1 121.088 3.55 1.62299 58.2
2 -96.851 0.20
3 26.184 1.60 1.84666 23.8
4 17.831 6.30 1.59522 67.7
5 46.571 (variable)
6 89.099 0.80 1.70154 41.2
7 10.169 2.61 1.95906 17.5
8 14.319 3.68
9 -19.663 0.70 1.83481 42.7
10 -137.956 (variable)
11 62.462 1.86 1.77250 49.6
12 -71.865 (variable)
13 25.796 2.35 1.77250 49.6
14 -252.749 0.15
15 14.752 3.64 1.59522 67.7
16 -57.273 0.80 1.95906 17.5
17 29.095 3.00
18 (Aperture) ∞ 4.65
19 21.739 2.15 1.84666 23.8
20 -11.045 0.80 1.77250 49.6
21 5.752 3.64
22 8.302 2.42 1.48749 70.2
23 -41.192 3.52
24 ∞ 2.30 1.51400 70.0
25 ∞ 1.00
Image plane ∞

Various data Zoom ratio 2.85
Wide angle Medium Tele focal length 21.30 44.06 60.63
F number 1.85 1.85 1.85
Half angle of view (degrees) 8.02 3.90 2.83
Image height 3.00 3.00 3.00
Total lens length 80.04 80.04 80.04
BF 6.04 6.04 6.04

d 5 2.66 13.56 16.29
d10 20.60 10.03 2.53
d12 5.86 5.53 10.30

Zoom lens group data group Start surface Focal length
1 1 51.52
2 6 -14.44
3 11 43.52
4 13 28.94
5 24 ∞

[Numerical Example 3]
Unit mm

Surface data surface number rd nd νd
1 38.475 5.29 1.60311 60.6
2 316.905 0.20
3 29.758 1.60 1.85478 24.8
4 19.117 7.53 1.49700 81.5
5 65.781 (variable)
6 53.697 1.00 1.77250 49.6
7 11.008 3.30 1.95906 17.5
8 15.008 5.01
9 -19.009 0.90 1.83481 42.7
10 -1071.173 (variable)
11 59.276 5.31 1.80 400 46.6
12 -43.689 (variable)
13 42.239 6.29 1.59522 67.7
14 -27.325 1.10 2.00069 25.5
15 4691.232 0.20
16 23.613 5.00 1.60311 60.6
17 -86.256 0.90 2.00069 25.5
18 266.706 7.00
19 (Aperture) ∞ 7.81
20 13.476 1.69 1.85478 24.8
21 54.125 0.80 1.80610 40.9
22 6.714 1.06
23 7.379 1.88 1.64769 33.8
24 16.618 5.78
25 ∞ 2.30 1.51400 70.0
26 ∞ 1.00
Image plane ∞

Various data Zoom ratio 1.90
Wide angle Medium Telephoto focal length 48.38 77.46 91.88
F number 1.34 2.34 2.60
Half angle of view (degrees) 3.55 2.22 1.87
Image height 3.00 3.00 3.00
Total lens length 104.17 104.17 104.17
BF 8.30 8.30 8.30

d 5 12.67 16.56 17.53
d10 14.81 6.33 2.58
d12 4.53 9.12 11.90

Zoom lens group data group Start surface Focal length
1 1 55.46
2 6 -13.24
3 11 32.02
4 13 52.60
5 25 ∞

B1 ... 1st lens group B2 ... 2nd lens group B3 ... 3rd lens group B4 ... 4th lens group

Claims (9)

A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, which are arranged in order from the object side to the image side. The first lens group and the fourth lens group do not move during zooming from the wide-angle end to the telephoto end, the second lens group and the third lens group move, and lenses adjacent to each other during zooming. A zoom lens with variable group spacing,
The distance between the first lens group and the second lens group is increased at the telephoto end compared to the wide-angle end, the third lens group is composed of one positive lens, and the zoom lens further includes an aperture stop,
The refractive index at the d-line of the positive lens material constituting the third lens group is nd3 , the focal length of the first lens group is f1, the focal length of the fourth lens group is f4, the total lens length is TL, and the telephoto end When the air-converted distance from the aperture stop to the image plane in DSP is a DSP ,
1.6 <nd3 <2.4
0.6 <f1 / f4 <2.2
0.10 <DSP / TL <0.35
A zoom lens characterized by satisfying the following conditional expression: At the time of focusing, when the third lens group moves and the lateral magnifications of the third lens group and the fourth lens group at the telephoto end are set to β3T and β4T, respectively,
0.2 <| (1-β3T ² ) × β4T ² | <1.2
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the lateral magnification of the third lens group at the telephoto end is β3T,
-40.0 <β3T <-1.5
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the curvature radii of the object-side lens surface and the image-side lens surface of the positive lens included in the third lens group are R31 and R32, respectively.
−1.0 <(R31 + R32) / (R31−R32) <1.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the front Symbol third lens group and f3,
0.8 <f1 / f3 <2.4
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the third lens group is f3 and the focal length of the entire system at the telephoto end is fT,
0.2 <f3 / fT <1.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the entire system at the wide angle end and fW,
0.8 <f1 / fW <3.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the Abbe number of the material of the positive lens included in the third lens group is νd3,
35 <νd3 <65
The zoom lens according to any one of claims 1 to 7, characterized by satisfying the conditional expression. A zoom lens according to any one of claims 1 to 8, the image pickup apparatus characterized by having an image pickup device which receives an image formed by the zoom lens.