JP5118589B2 - Zoom lens and imaging device - Google Patents

Description

  The present invention relates to a zoom lens and an imaging apparatus, and more specifically, can be suitably used for a video camera, an electronic still camera, a surveillance camera, and the like, and particularly includes a zoom lens suitable for 3CCD electronic camera use and the zoom lens. The present invention relates to an imaging apparatus.

Conventionally, as a zoom lens used for a consumer video camera or the like, many 4-group type and 5-group type zoom lenses have been proposed. For example, Patent Documents 1 and 2 disclose a zoom lens having a high zoom ratio of about 10 times and an F-number of about 1.8 in a four-group type. More specifically, the device described in Patent Document 1 has three first lens groups, three second lens groups, two third lens groups, and three fourth lens groups. Patent Document 2 describes that a composite aspherical lens in which an aspherical resin is formed on a glass spherical surface is used, and that the third lens group has a single lens structure. It is very different from the one. Conventionally, there are many proposals made up of a small number of lenses, such as about 10 to 12, as described above.
JP 2004-279726 A JP 2006-276844 A

  By the way, in recent years, zoom lenses used in consumer video cameras and the like have also become high-definition, and the demand for high-performance zoom lenses is increasing. In particular, the photographed light is divided into R (red), G (green), and B (blue) colors by a color separation prism, and images captured by three CCDs (Charge Coupled Devices) corresponding to the respective colors are superposed. There is an increasing demand for a zoom lens that can support the 3CCD system for obtaining image quality. In addition, zoom lenses in this field are also strongly required to be compact while being high performance.

  As one method for reducing the size, it is conceivable that the third lens group has a single lens configuration. However, in order to insert the color separation prism, a long back focus is required. For this purpose, it is necessary to weaken the power of the third lens group. If the third lens group is composed of one lens and its power is weakened, there is a problem that the curvature of the lens becomes small and it becomes difficult to correct aberrations.

  The one described in Patent Document 2 has a configuration in which the third lens group has one lens, but by disposing a negative lens on the most object side of the fourth lens group to obtain a negative, positive, and positive power arrangement, This prevents the curvature of the lens of the third lens group from becoming too small. However, in this configuration, because of the negative lens closest to the object side in the fourth lens group, the height of the light beam incident on the central positive lens becomes large, which is disadvantageous in terms of aberration correction.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a zoom lens capable of realizing a long back focus and good optical performance while achieving downsizing, and an imaging device including the zoom lens. It is what.

The zoom lens of the present invention has, in order from the object side, a first lens group having a positive refractive power and fixed at the time of zooming, a negative refractive power, and moving along the optical axis. A second lens group that performs zooming, a stop, a third lens group that has positive refractive power and is fixed at the time of zooming, and has a positive refractive power, and the position of the image plane associated with zooming and a fourth lens group for correcting and focusing, the first lens group comprises, in order from the object side, a cemented lens by bonding of the negative meniscus lens and a positive lens having a convex surface directed toward the object side, a positive meniscus lens The second lens group is composed of two or more negative lenses and one positive lens, and the third lens group is composed of one positive lens having at least one aspherical surface. The fourth lens group in order from the object side, positive lens, negative lens, Is composed of three lenses, the focal length of the positive lens of the third lens group and f31, the focal length of the entire system at the wide angle end and fw, the average Abbe number of the two positive lens of the fourth lens group ν4p When the Abbe number of the positive lens in the third lens group is ν31 , the following conditional expressions (1) and (2) are satisfied.
10 <f31 / fw <25 (1)
38 <ν4p−ν31 <58 (2)

  In the present invention, each “lens group” includes not only a plurality of lenses but also a lens group.

  In the present invention, a compound lens in which an aspherical resin is formed on a glass spherical surface as described above is not regarded as a “single lens”.

The zoom lens according to the present invention can be reduced in size by forming the third lens group as a single lens. Further, by arranging the fourth lens group in the order of positive, negative, and positive power from the object side, the height of the light beam incident on the central negative lens can be reduced, which is advantageous for Petzval sum and good. Aberration correction is possible. Furthermore, by satisfying conditional expression (1), it is possible to set a suitable power range of the positive lens in the third lens group, and it is possible to achieve both long back focus and good correction of various aberrations including spherical aberration. Is feasible. Satisfying conditional expression (2) makes it possible to correct chromatic aberration.

In the zoom lens of the present invention, it is preferable that the following conditional expression (3) is satisfied, where f4 is the focal length of the fourth lens group.
3.0 <f4 / fw <3.8 (3)

In the zoom lens of the present invention, either one of the two positive lenses in the fourth lens group is cemented with the negative lens in the fourth lens group, and the other not cemented is at least one non-surface. It preferably has a spherical surface. In this case, it is preferable that the following conditional expression (4) is satisfied, where the Abbe number of the other positive lens that is not cemented is ν4s.
70.0 <ν4s <83.0 (4)

  In the zoom lens of the present invention, the positive lens material of the third lens group may be made of plastic.

  The values of the conditional expressions in this specification are those at the reference wavelength of the zoom lens. For example, when the reference wavelength of the zoom lens is d-line (wavelength 587.6 nm), the values are described in the above conditional expressions. The refractive index and Abbe number are those at the d-line.

  An image pickup apparatus according to the present invention includes the zoom lens according to the present invention described above.

According to the present invention, the first lens group and the third lens group are fixed groups, and the second lens group is moved along the optical axis to perform zooming, thereby correcting and focusing the image plane position. In the zoom lens of the type in which the fourth lens group is moved, the configuration of each lens group is preferably set. In particular, the third lens group has one lens configuration, the fourth lens group has the above power arrangement, and the conditional expression (1) Since it is configured to satisfy (2) , there is provided a zoom lens capable of realizing a long back focus and good optical performance while achieving downsizing, and an imaging device including the zoom lens. be able to.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a configuration of a zoom lens according to an embodiment of the present invention, and corresponds to a zoom lens of Example 1 described later. 2 to 8 are cross-sectional views showing the configurations of zoom lenses according to Examples 2 to 8 described later, respectively. Since the basic configuration of the zoom lens shown in FIGS. 1 to 8 is the same and the method of illustration is also the same, the following description will be given mainly using FIG. 1 as an example.

  The zoom lens according to the embodiment of the present invention has, in order from the object side along the optical axis Z, a positive refractive power, a first lens group G1 fixed at the time of zooming, and a negative refractive power. A second lens group G2 that performs zooming by moving along the optical axis, an aperture stop St, a third lens group G3 that has positive refractive power and is fixed at the time of zooming, And a fourth lens group G4 that has a positive refractive power and corrects and focuses an image plane position accompanying zooming.

  Note that the aperture stop St shown in FIG. 1 does not necessarily indicate the size or shape, but indicates the position on the optical axis Z. In FIG. 1, the left side is the object side, and the right side is the image side. In FIG. 1, the upper lens arrangement is shown when focusing on infinity at the wide-angle end, the lower lens arrangement is shown when focusing on infinity at the telephoto end, and each lens group for zooming from the wide-angle end to the telephoto end. The general movement trajectory is indicated by arrows.

  In FIG. 1, the imaging position of the axial light beam from an infinite object is shown as Pim. For example, when this zoom lens is applied to an image pickup apparatus, the zoom lens is arranged so that the image pickup surface of the image pickup element is positioned at the image formation position Pim.

  When applying a zoom lens to an imaging device, depending on the configuration of the camera side on which the lens is mounted, a cover glass, prism, infrared cut filter, between the lens on the most image side and the imaging surface (imaging surface) It is preferable to arrange various filters such as a low-pass filter. In the example shown in FIG. 1, a parallel plate-shaped optical member PP that assumes these is arranged between the fourth lens group G4 and the imaging position Pim. Yes.

  In this zoom lens, at the time of zooming from the wide-angle end to the telephoto end, the first lens group G1 and the third lens group G3 are fixed on the optical axis, and the second lens group G2 is imaged along the optical axis. The zoom lens is configured to perform zooming by moving to the side, and to correct and focus the image plane position accompanying the zooming by moving the fourth lens group G4 along the optical axis. That is, the second lens group G2 functions as a variator group, and the fourth lens group G4 functions as a compensator group and a focus group.

  This zoom lens is configured as follows. In other words, the first lens group G1 is composed of three lenses including a cemented lens formed by bonding a meniscus negative lens L11 having a convex surface toward the object side and a positive lens L12, and a meniscus positive lens L13 in order from the object side. It is. The second lens group G2 has a configuration of three or more lenses including two or more negative lenses and one positive lens. The third lens group G3 has a single lens configuration including a positive lens L31 having at least one aspheric surface. The fourth lens group G4 has a three-lens configuration including a positive lens L41, a negative lens L42, and a positive lens L43 in order from the object side. The second lens group G2 may have a four-lens configuration including a negative lens L21, a negative lens L22, a positive lens L23, and a negative lens L24 in order from the object side, as in the example shown in FIG. As in the example shown in FIG. 8, a three-lens configuration including a negative lens L21, a negative lens L22, and a positive lens L23 in order from the object side may be used.

  As described above, the zoom lens according to the present invention can be configured with a small number of lenses, such as a total of 10 lenses or a total of 11 lenses, as in the examples shown in FIGS.

  In particular, the zoom lens according to the present invention is characterized in that the third lens group G3 is composed of one lens in order to reduce the size of the third lens group G3 and subsequent lenses. In the conventionally proposed 4-group type and 5-group type zoom lenses, there are lenses in which the third lens group is composed of two or three lenses, as seen in Patent Document 1 and other known examples. There are many examples in which the third lens group is composed of one lens.

  This is because, if the third lens group is composed of one lens, a problem that does not occur when the third lens group is composed of a plurality of lenses occurs, and an idea different from the conventional one is required. One is the problem of chromatic aberration. In general, in a zoom lens, achromatism is often performed by each lens group alone, and if the third lens group G3 is composed of a single lens, the third lens group alone cannot be achromatic. Therefore, in the zoom lens according to this embodiment, the third lens group G3 and the fourth lens group G4 are achromatic.

  The other problem is caused by ensuring a long back focus. As described above, in order to insert the color separation prism in the 3CCD system, a long back focus is required. For this purpose, it is necessary to weaken the power of the third lens group. If the third lens group is composed of one lens and its power is weakened, the curvature of the lens becomes small and it becomes difficult to correct aberrations.

With respect to this problem, in the zoom lens of the present invention, when the focal length of the positive lens L31 of the third lens group G3 is f31 and the focal length of the entire system at the wide angle end is fw, the following conditional expression (1) is satisfied. The solution is achieved by configuring as above.
10 <f31 / fw <25 (1)

  Conditional expression (1) defines the ratio between the focal length of the positive lens L31 (third lens group G3) and the focal length of the entire system at the wide-angle end, and is used to form the third lens group G3 as a single lens. It can also be called a condition. In order to obtain a back focus that is long enough to insert a color separation prism or the like between the optical system and the image plane, the power of the positive lens L31 is weak. If the lower limit of conditional expression (1) is not reached, the power of the positive lens L31 becomes strong and the required back focus cannot be obtained. On the contrary, if the power of the positive lens L31 is weakened so as to exceed the upper limit of the conditional expression (1), the curvature of the lens becomes small, and it becomes impossible to correct aberration, particularly spherical aberration of the entire optical system. .

  In such a long back focus and aberration correction trade-off relationship, by satisfying the conditional expression (1), both can be satisfied, and the third lens group G3 can be composed of one lens. It becomes possible to obtain a desired performance by configuring, and the performance can be maintained with a small number of lenses of about 11 as the entire system.

  In the zoom lens described in Patent Document 2, the problem caused by the long back focus is to be solved by disposing a negative lens closest to the object side of the fourth lens group. That is, in the device described in Patent Document 2, the role of lengthening the back focus is shared by the third lens group and the fourth lens group, so that the curvature of the lens of the third lens group is prevented from being reduced. ing.

  Therefore, in the thing of patent document 2, the structure of a 4th lens group becomes negative, positive, and positive power arrangement | positioning sequentially from an object side. However, since the fourth lens group has a positive, negative, and positive power arrangement like the zoom lens of the present embodiment shown in FIG. 1, the height of the light incident on the central negative lens can be reduced. This is advantageous for the Petzval sum, and good aberration correction can be performed. In addition, it is possible to prevent the fourth lens group G4 from becoming large. Considering aberration correction with the fourth lens group G4 alone, it is more advantageous to use positive, negative, and positive power arrangements as in this embodiment than with negative, positive, and positive power arrangements. Furthermore, there is an advantage that the amount of movement during zooming or focusing can be easily reduced.

  When the fourth lens group has a positive, negative, and positive power arrangement, the curvature of the positive lens L31 needs to be mainly played by one of the positive lenses L31 in the third lens group. However, in the present invention, it is possible to achieve both long back focus and good aberration correction by configuring the focal length of the positive lens L31 to satisfy the conditional expression (1). ing.

  Since the zoom lens according to the present invention has a single third lens group G3, the number of lenses in the third lens group G3 is smaller than that of the conventional example in which the third lens group G3 has two lenses as in Patent Document 1. Less. Therefore, the zoom lens according to the present invention does not necessarily have the three second lens group G2 as in the conventional example, and can have the four second lens group G2.

  The meaning of the second lens group G2 having four lenses will be described below. In order to shorten the overall length of the lens system and reduce the size, it is necessary to reduce the amount of movement during zooming. For this purpose, it is preferable to give the second lens group G2 a strong negative power. However, if the power of the lens becomes too strong, the second lens group G2 is a moving group, so that aberration fluctuations during zooming increase.

  In the conventional example of Patent Document 1, the second lens group has three negative, negative, and positive lenses. In the example of the present embodiment shown in FIG. 1, four lenses are additionally provided with one negative lens. With this configuration, even when the second lens group G2 has a strong negative power, the negative power necessary for the second lens group G2 can be dispersed. Therefore, it is possible to reduce the overall length of the lens system without increasing the intensity of power carried by each negative lens of the second lens group G2 and increasing aberration fluctuations during zooming. In the present invention, the number of lenses of the second lens group G2 is not limited to four, but may be three as shown in FIGS.

  In the example shown in FIG. 1, the second lens group G2 has two negative lenses on the object side. In this way, by distributing a large amount of negative power to the object side, the position of the object side principal point of the second lens group is brought closer to the object side, so that the principal point interval between the first lens group G1 and the second lens group G2 is increased. Can be shortened. Accordingly, the height of the off-axis light beam passing through the first lens group G1 can be reduced, and the front lens diameter (the diameter of the lens closest to the object side) can be reduced.

  Furthermore, as a preferable aspect of the second lens group G2, at least one negative lens having at least one aspheric surface is provided. In the example shown in FIG. 1, the object side surface of the negative lens L22 arranged second from the object side of the second lens group G2 is an aspherical surface. By adopting an aspherical lens in the second lens group G2, it is possible to correct distortion well, and to suppress image plane fluctuation for each angle of view and each zoom magnification.

  The above-mentioned effect by the aspherical surface can be obtained even when the second lens group G2 is provided on the negative lens L21 closest to the object side. However, the negative lens L22 has a light beam that passes through the negative lens L21. Since the height is small and the diameter can be reduced, it is advantageous in terms of cost. Further, when the negative lens L21 is an aspheric lens, the allowable amount of manufacturing error and assembly error is likely to be smaller than that of the negative lens L22. Therefore, if either one of the negative lenses L21 and L22 is an aspheric lens, it is more preferable that the negative lens L22 is an aspheric lens.

  The positive lens L31 of the third lens group G3 has an aspheric surface on at least one surface. The use of an aspheric lens is advantageous in terms of aberration correction, and it is easy to configure the third lens group G3 as a single lens.

  The material of the positive lens L31 is preferably plastic, which can realize cost reduction and weight reduction. Note that plastic is generally more affected by temperature changes than glass. However, in the zoom lens of the present embodiment, the power of the positive lens L31 is weakened to obtain a long back focus. Even for a plastic lens, the influence on the entire system due to temperature change is small.

  In addition, when the lens barrel of the applied imaging device is made of a plastic material, the expansion / contraction due to the temperature change of the lens barrel and the movement of the image position due to the temperature change of the positive lens made of the plastic material cancel each other. The change in the apparent image position due to the temperature change can be suppressed. In this respect, it can be said that the plastic lens is more advantageous for temperature change than the glass lens.

  For the fourth lens group G4, one of the two positive lenses L41 and L43 is joined to the negative lens L42, and the other unjoined positive lens has at least one aspheric surface. It is preferable to have. By using an aspheric lens for the fourth lens group G4, it is possible to satisfactorily correct spherical aberration generated by the fourth lens group G4 alone, and to reduce aberration fluctuations during zooming and focusing. .

  In addition to the above-described configuration, the zoom lens is preferably configured to satisfy the following conditional expression, whereby even better characteristics can be obtained.

More preferably, the following conditional expression (1-1) is satisfied, where f31 is the focal length of the positive lens L31 of the third lens group G3 and fw is the focal length of the entire system at the wide-angle end. By satisfying conditional expression (1-1), it becomes easier to realize long back focus and good correction of aberrations.
12 <f31 / fw <20 (1-1)

When the average Abbe number of the two positive lenses L41 and L43 of the fourth lens group G4 is ν4p and the Abbe number of the positive lens L31 of the third lens group G3 is ν31, the following conditional expression (2) is satisfied. preferable.
38 <ν4p−ν31 <58 (2)

  Conditional expression (2) defines the difference between the average Abbe number of the positive lens in the fourth lens group G4 and the Abbe number of the positive lens L31 in the third lens group G3. Although it is desirable to perform achromatization in the zoom lens in each lens group, in the present invention, the third lens group G3 is composed of one lens, and it is necessary to perform achromatization together with the fourth lens group G4. . In the fourth lens group G4, a low-dispersion material is used for the positive lens in order to suppress variation in chromatic aberration associated with zooming and focusing. Therefore, a high dispersion material that cancels chromatic aberration generated in the fourth lens group is used for the positive lens L31 of the third lens group G3.

If the lower limit of conditional expression (2) is not reached, chromatic aberration, particularly chromatic aberration from the middle range of the zoom to the telephoto end cannot be corrected sufficiently. If the upper limit of conditional expression (2) is exceeded, it is advantageous for correcting chromatic aberration. In this case, an ultra-low dispersion material is used for the positive lens of the fourth lens group G4, or a high dispersion material is used for the positive lens L31. In this case, however, it is difficult to select a material suitable for the case. In addition, the correction of chromatic aberration is biased to a specific color, and good chromatic aberration correction cannot be performed.

When the focal length of the fourth lens group G4 is f4 and the focal length of the entire system at the wide angle end is fw, it is preferable that the following conditional expression (3) is satisfied.
3.0 <f4 / fw <3.8 (3)

  Conditional expression (3) defines the ratio between the focal length of the fourth lens group G4 and the focal length of the entire system at the wide angle end. If the lower limit of conditional expression (3) is not reached, the power of each lens constituting the fourth lens group G4 becomes stronger, the lens curvature increases, and aberration fluctuations during zooming and focusing increase. . If the upper limit of conditional expression (3) is exceeded, the amount of movement of the fourth lens group G4 at the time of focusing increases, the overall length becomes longer, and the image plane is not canceled without canceling the Petzval sum generated in the second lens group G2. The curvature becomes large.

Furthermore, it is more preferable to satisfy the following conditional expression (3-1). By satisfying the conditional expression (3-1), it is easier to suppress aberration fluctuations during zooming or focusing, downsizing, and suppression of field curvature.
3.1 <f4 / fw <3.7 (3-1)

When one of the two positive lenses L41 and L43 of the fourth lens group G4 is joined to the negative lens L42, and the other positive lens that is not joined has at least one aspheric surface. When the Abbe number of the other non-joined lens is ν4s, it is preferable that the following conditional expression (4) is satisfied.
70.0 <ν4s <83.0 (4)

  Conditional expression (4) defines the Abbe number of the positive single lens of the fourth lens group G4. If the lower limit of conditional expression (4) is not reached, variations in chromatic aberration at the time of zooming or focusing become large, and chromatic aberration occurring after the third lens group G3 cannot be sufficiently corrected. If an ultra-low dispersion material exceeding the upper limit of conditional expression (4) is used, it is advantageous for chromatic aberration correction. In this case, since the refractive index is very small, the curvature becomes large, and at the time of zooming or focusing. As the aberration variation increases, the tolerance for manufacturing errors and assembly errors decreases. In addition, the center thickness must be increased in order to secure the necessary edge.

  In addition, when this zoom lens is used in harsh environments such as outdoors, the lens placed closest to the object is resistant to surface deterioration due to wind and rain, temperature changes due to direct sunlight, and oils and detergents. It is preferable to use a material resistant to chemicals, that is, a material having high water resistance, weather resistance, acid resistance, chemical resistance, and the like, and further, a material that is hard and difficult to break. From the above, as the material disposed closest to the object side, specifically, glass is preferably used, or transparent ceramics may be used.

  It is preferable to use plastic as the material of the lens on which the aspherical shape is formed. In this case, the aspherical shape can be manufactured with high accuracy, and the weight and cost can be reduced. Become.

  When the zoom lens is required to be usable in a wide temperature range, it is preferable to use a material having a small linear expansion coefficient as the material of each lens. In addition, when the zoom lens is used in a harsh environment, a protective multilayer coating is preferably applied. In addition to the protective coat, an antireflection coating film for reducing ghost light during use may be applied.

  In the example shown in FIG. 1, an example in which the optical member PP is disposed between the lens system and the imaging surface is shown, but instead of disposing a low-pass filter, various filters that cut a specific wavelength range, or the like, These various filters may be disposed between the lenses, or a coating having the same action as the various filters may be applied to the lens surface of any lens.

  As described above, according to the zoom lens of the present embodiment, the above-described preferable configuration is appropriately adopted according to required specifications and the like, while achieving a reduction in size without significantly increasing the number of lenses. Long back focus and good optical performance can be realized.

  Next, numerical examples of the zoom lens according to the present invention will be described. The lens cross-sectional views of the zoom lenses of Examples 1 to 8 are shown in FIGS.

  Table 1 shows basic lens data of the zoom lens according to Example 1, Table 2 shows data relating to zooming (magnification), and Table 3 shows aspherical data. Similarly, Tables 4 to 24 show basic data, zoom-related data, and aspherical data of the zoom lenses according to Examples 2 to 8, respectively. In the following, the meaning of the symbols in the table will be described using Example 1 as an example, but the same applies to Examples 2 to 8.

  In the basic lens data of Table 1, Si indicates the i-th (i = 1, 2, 3,...) Surface number that increases sequentially toward the image side with the most object-side component surface being first. Indicates the radius of curvature of the i-th surface, and Di indicates the surface interval on the optical axis Z between the i-th surface and the i + 1-th surface. The bottom column of the surface interval indicates the surface interval between the final surface and the image surface in the table. In the basic lens data, Ndj is the d-line (wavelength: 587.6 nm) of the j-th (j = 1, 2, 3,...) Optical element that sequentially increases toward the image side with the most object-side lens as the first lens. ), And νdj represents the Abbe number of the j-th optical element with respect to the d-line. The basic lens data includes the aperture stop St and the optical member PP. In the column of the radius of curvature of the surface corresponding to the aperture stop St, (aperture stop) is described. The radius of curvature of the basic lens data is positive when convex on the object side and negative when convex on the image side.

  In the basic lens data in Table 1, the interval changes for zooming, the interval between the first lens group G1 and the second lens group G2, the interval between the second lens group G2 and the aperture stop St, the third lens group G3. D5 (variable), D12 (variable), D15 (variable), and D20 (variable) in the columns of the distance between the fourth lens group G4 and the surface distance corresponding to the distance between the fourth lens group G4 and the optical member PP. It is described.

  The zoom-related data in Table 2 includes the focal length f of the entire system at the wide-angle end and the telephoto end, the F number Fno. , The total angle of view 2ω, and the values of the surface spacings D5, D12, D15, and D20 that change with zooming. The unit of the total angle of view 2ω is degrees.

  As the unit of Ri and Di in Table 1 and the unit of f, D5, D12, D15, and D20 in Table 2, “mm” can be used. Since the performance can be obtained, the unit is not limited to “mm”, and other appropriate units can be used.

In the basic lens data in Table 1, the surface number of the aspheric surface is marked with *, and the paraxial radius of curvature is shown as the radius of curvature of the aspheric surface. The aspherical data in Table 3 shows the sign of a lens that is an aspherical lens, the surface number of the aspherical surface, and the aspherical coefficients related to these aspherical surfaces. The aspheric coefficient is a value of each coefficient KA, RA _m (m = 3, 4, 5,... 10) in the aspheric expression expressed by the following expression (A).

Zd = C · h ² / {1+ (1−KA · C ² · h ² ) ^1/2 } + ΣRA _m · h ^m (A)
However,
Zd: Depth of aspheric surface (length of perpendicular drawn from a point on the aspherical surface of height h to a plane perpendicular to the optical axis where the aspherical vertex contacts)
h: Height (distance from the optical axis to the lens surface)
C: Reciprocal number of paraxial radius of curvature KA, RA _m : aspheric coefficient (m = 3, 4, 5,... 10)
In addition, when mm is used as the unit of Ri and Di in Table 1, the unit of Zd and h is also mm.

  In the zoom lenses of Examples 7 and 8 described below, the second lens group G2 has a negative, negative, and positive three lens structure in order from the object side, and the negative lens L22 of the second lens group G2 is double-sided. The point which is an aspherical surface is greatly different from the zoom lenses of Examples 1 to 6. The descriptions in the tables of Examples 7 and 8 correspond to these.

  Table 25 shows values corresponding to the conditional expressions (1) to (4) in Examples 1 to 8. As can be seen from Table 25, all of Examples 1 to 8 satisfy the conditional expressions (1) to (4).

  FIG. 9A to FIG. 9H show respective aberration diagrams of spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration at the wide-angle end and the telephoto end of the zoom lens of Example 1. Each aberration diagram shows the aberration with the d-line (wavelength 587.6 nm) as the reference wavelength, while the spherical aberration diagram and the magnification chromatic aberration diagram also show the aberrations for the wavelength 460.0 nm and the wavelength 615.0 nm. Fno. Of spherical aberration diagram. Means F number, and ω in other aberration diagrams means half angle of view.

  Similarly, FIGS. 10 (A) to 10 (H), FIGS. 11 (A) to 11 (H), FIGS. 12 (A) to 12 (H), and FIGS. 13 (A) to 13 (H). 14 (A) to 14 (H), 15 (A) to 15 (H), and 16 (A) to 16 (H), the wide-angle end of the zoom lenses of Examples 2 to 8 and Each aberration diagram of spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration at the telephoto end is shown.

  From the above data, the zoom lenses of Examples 1 to 8 have a magnification of about 10 times, and the F number at the wide-angle end is as small as about 1.8, and each aberration is well corrected while achieving downsizing. It can be seen that both the wide-angle end and the telephoto end have high optical performance in the visible range. These zoom lenses can be suitably used for imaging devices such as surveillance cameras, video cameras, and electronic still cameras.

  FIG. 17 shows a configuration diagram of a video camera 10 configured using the zoom lens 1 according to the embodiment of the present invention as an example of the imaging apparatus of the embodiment of the present invention. In FIG. 17, the positive first lens group G1, the negative second lens group G2, the aperture stop St, the positive third lens group G3, and the positive fourth lens group G4 included in the zoom lens 1 are schematically illustrated. Show.

  The video camera 10 shown in FIG. 17 is a so-called 3CCD type image pickup device having three image pickup devices, but the image pickup device of the present invention is not limited to this and may be one that picks up the entire wavelength band with one image pickup device. Good. The video camera 10 includes a zoom lens 1, a filter 2 having functions such as a low-pass filter and an infrared cut filter disposed on the image side of the zoom lens 1, and color separation prisms 3R and 3G disposed on the image side of the filter 2. 3B, imaging elements 4R, 4G, and 4B provided on the end faces of the color separation prisms, and a signal processing circuit 5. The image sensors 4R, 4G, and 4B convert an optical image formed by the zoom lens 1 into an electric signal, and for example, a CCD (Charge Coupled Device) can be used. The imaging elements 4R, 4G, and 4B are arranged so that their imaging surfaces coincide with the imaging surface of the zoom lens 1.

  Unnecessary light components are removed from the light transmitted through the zoom lens 1 by the filter 2 and separated into red, green, and blue light by the color separation prisms 3R, 3G, and 3B, and then imaged by the image sensors 4R, 4G, and 4B. The image is formed on the surface. Output signals from the image sensors 4R, 4G, and 4B corresponding to red, green, and blue color lights are processed by the signal processing circuit 5 to form a color image and displayed on the display device 6.

  Since the zoom lens according to the embodiment of the present invention has the above-described advantages, the imaging apparatus of the present embodiment can be compatible with the 3CCD system, can be configured in a small size, and can obtain a high-quality image.

  The present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, the values of the radius of curvature, the surface spacing, the refractive index, the Abbe number, etc. of each lens component are not limited to the values shown in the above numerical examples, but can take other values.

Sectional drawing which shows the lens structure of the zoom lens concerning Example 1 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 2 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 3 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 4 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 5 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 6 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 7 of this invention. Sectional drawing which shows the lens structure of the zoom lens concerning Example 8 of this invention. Each aberration diagram of the zoom lens according to Example 1 of the present invention Each aberration diagram of the zoom lens according to Example 2 of the present invention Each aberration diagram of the zoom lens according to Example 3 of the present invention Each aberration diagram of the zoom lens according to Example 4 of the present invention Each aberration diagram of the zoom lens according to Example 5 of the present invention Each aberration diagram of the zoom lens according to Example 6 of the present invention Each aberration diagram of the zoom lens according to Example 7 of the present invention Each aberration diagram of the zoom lens according to Example 8 of the present invention 1 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Zoom lens 2 Filter 3B, 3G, 3R Color separation prism 4B, 4G, 4R Image pick-up element 5 Signal processing circuit 6 Display apparatus 10 Video camera G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group PP Optical member St Aperture stop Z Optical axis

Claims (6)

In order from the object side, a first lens group having positive refractive power and fixed at the time of zooming, and a second lens having negative refractive power and zooming by moving along the optical axis A third lens group having a positive refracting power and fixed at the time of zooming, a first lens having a positive refracting power, and correcting and focusing the image plane position accompanying the zooming. It consists of four lens groups,
The first lens group includes, in order from the object side, a cemented lens obtained by bonding a negative meniscus lens having a convex surface toward the object side and a positive lens, and a positive meniscus lens,
The second lens group includes two or more negative lenses and one positive lens;
The third lens group is composed of one positive lens having at least one aspheric surface,
The fourth lens group is composed of a positive lens, a negative lens, and a positive lens in order from the object side,
The focal length of the positive lens of the third lens group is f31, the focal length of the entire system at the wide-angle end is fw, the average of the Abbe numbers of the two positive lenses of the fourth lens group is ν4p, A zoom lens satisfying the following conditional expressions (1) and (2) when the Abbe number of the positive lens in the three lens group is ν31 .
10 <f31 / fw <25 (1)
38 <ν4p−ν31 <58 (2) The zoom lens according to claim 1, wherein the following conditional expression (3) is satisfied when a focal length of the fourth lens group is f4.
3.0 <f4 / fw <3.8 (3) One of the two positive lenses of the fourth lens group is joined to the negative lens of the fourth lens group, and the other not joined has at least one aspherical surface. The zoom lens according to claim 1 or 2 . 4. The zoom lens according to claim 3 , wherein the following conditional expression (4) is satisfied when an Abbe number of the other positive lens not joined is ν4s.
70.0 <ν4s <83.0 (4) The zoom lens according to any one of claims 1 to 4 , wherein a material of a positive lens of the third lens group is plastic. Imaging apparatus characterized by comprising a zoom lens according to any one of claims 1 to 5.

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