JP5253997B2 - Magnification optical system and imaging device - Google Patents

Description

  The present invention relates to a variable magnification optical system used in an in-vehicle camera or a surveillance camera using an image sensor such as a CCD or CMOS, and more particularly to a variable magnification optical system suitable for a surveillance camera.

  The variable magnification optical system used for varifocal lenses for surveillance cameras has the convenience that the user can set the focal length and subject distance according to the usage environment. Yes. On the other hand, development demands for low-cost and high-performance lenses are also increasing due to intensifying development competition.

  Surveillance cameras whose main purpose is surveillance are able to cover from a high viewing angle range to a standard angle of view, and are required to withstand indoor and outdoor use, so the configuration is relatively simple and meets these conditions to some extent. Negative and positive second group zoom is often used.

  This negative positive second group zoom is widely used because it has many advantages in addition to the simplicity of the configuration, such as wide angle of view in front of the negative group and large back focus instead of short focal length. .

As such a variable magnification optical system of the negative positive second group zoom, for example, those described in the following Patent Documents 1 to 4 are known.
JP-A-01-303409 JP 2008-112000 A JP 2001-281544 A JP 2006-251437 A

  By the way, in the variable power optical system as described above, further widening of the angle and improvement of resolving power are required as the imaging element used in the imaging apparatus becomes higher in definition. However, with conventional optical systems, it has been difficult to realize a wide-angle, high-precision zoom optical system that satisfies recent requirements.

  For example, Patent Documents 1 and 2 described above do not cover the wide-angle region, and Patent Document 3 does not yet reach an angle of view of 100 degrees or more, which is the target of the present invention.

  On the other hand, Patent Document 4 has reached the target in terms of angle of view, but higher resolution is required.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an imaging apparatus including a variable magnification optical system that can cover a super-wide angle region with a wider angle and has a good resolution performance in the entire screen region. To do.

  In order to achieve a wider angle in a variable magnification optical system having a negative-positive two-group configuration, an aperture stop that defines brightness is placed between the first lens group and the second lens group with respect to the image formation point. It is preferable to dispose the first lens unit so that it does not interfere with the movement of the second lens unit at the telephoto end, so that it is possible to obtain off-axis light with a wider angle at the wide-angle end. The lens group can be prevented from increasing in diameter, and at the wide-angle end, the first and second lens groups have an asymmetric refractive power distribution with respect to the stop, and negative distortion is increased. Can be expanded.

  This is also carried out in Patent Documents 3 and 4 described above, but in the present invention, the refractive power distribution of each lens group as a whole and the constituent elements in the group is reviewed to satisfy the conditional expression described below. We have devised a variable magnification optical system suitable for the purpose.

In other words, the variable magnification optical system of the present invention includes, in order from the object side, a first lens group having negative refractive power and a second lens group having a diaphragm and a positive refractive power, with respect to aperture imaging position A variable power optical system which performs a variable power by changing a distance between a first lens group and a diaphragm and a distance between the diaphragm and the second lens group at a fixed distance, and the first lens group is located on the object side in order from the negative lens having a convex surface directed toward the object side and a biconcave lens and a positive lens, the second lens group comprises, in order from the object side, a biconvex lens, biconcave lens and a positive lens, the focal length of the first lens group FF, the focal length of the second lens group is fB, the focal length of the biconvex lens in the second lens group is f4, the focal length of the biconcave lens is f5, the focal length of the positive lens is f6 , and the entire system at the wide angle end When the focal length of fw is fw , the following conditional expression (1 ) , (2) and (3) are satisfied.
−1.30 <fB / fF <−1.10 (1)
0.90 <f6 / f4 <1.20 (2)
−0.55 <fw / f5 <−0.3 (3)

In the variable power optical system of the present invention preferably satisfies the lower Symbol conditional expression (4).
0 . 30 <fw / f6 <0.40 (4)

  An imaging apparatus according to the present invention includes the above-described variable magnification optical system and an imaging element that captures an image of a subject formed by the variable magnification optical system.

  According to the variable magnification optical system of the present invention, in order from the object side, the first lens group having a negative refractive power, the stop, and the second lens group having a positive refractive power are provided. In a variable power optical system that performs zooming by changing the distance between the first lens group and the diaphragm and the distance between the diaphragm and the second lens group, the first lens group is moved from the object side. Sequentially, a negative lens having a convex surface facing the object side, a biconcave lens, and a positive lens are provided, and a second lens group is provided in order from the object side, including a biconvex lens, a biconcave lens, and a positive lens, and the first lens group. Where fF is the focal length of the second lens group, fB is the focal length of the second lens group, f4 is the focal length of the biconvex lens in the second lens group, and f6 is the focal length of the positive lens. ) To satisfy It is possible to realize a high degree variable magnification optical system.

  Since the imaging apparatus of the present invention includes the variable magnification optical system of the present invention, it is possible to obtain a wide-angle and highly accurate image.

  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 variable magnification optical system according to an embodiment of the present invention, and corresponds to a variable magnification optical system of Example 1 described later.

  The variable magnification optical system 1 according to the embodiment of the present invention has, in order from the object side along the optical axis Z, a first lens group G1 having a negative refractive power, an aperture stop St, and a positive refractive power. The first lens group G1 includes, in order from the object side, a negative lens L1, a biconcave lens L2, and a positive lens L3 having a convex surface facing the object side. The second lens group G2 From the object side, a biconvex lens L4, a biconcave lens L5, and a positive lens L6 are included.

  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 at infinity at the wide-angle end, the middle stage is showing lens arrangement when focusing at infinity at an intermediate angle of view, and the lower stage is lens arrangement when focusing at infinity at the telephoto end. , And a schematic movement locus of each lens unit when zooming from the wide-angle end to the telephoto end is indicated by a solid line.

  In FIG. 1, the image plane is shown as 5. For example, when this zoom optical system is applied to an image pickup apparatus, the image pickup surface of the image pickup element is disposed on the image plane 5.

  When applying the variable magnification optical system to the imaging device, depending on the configuration of the camera side on which the lens is mounted, a cover glass, an ultraviolet cut filter, an infrared cut filter, between the lens on the most image side and the imaging surface, It is preferable to dispose various filters such as a low-pass filter. In FIG. 1, an example in which a parallel plate-shaped optical member PP assuming these is disposed between the lens group closest to the image side and the image surface 5 is disposed. Show.

Here, in the variable magnification optical system 1, the focal length of the first lens group G1 is fF, the focal length of the second lens group G2 is fB, and the focal length of the biconvex lens L4 in the second lens group G2 is f4, When the focal length of the positive lens L6 is set to f6, the following conditional expressions (1) and (2) are satisfied.
−1.30 <fB / fF <−1.10 (1)
0.90 <f6 / f4 <1.20 (2)

  Conditional expression (1) is a conditional expression regarding the refractive power distribution of the first lens group G1 and the second lens group G2, and if the upper limit is exceeded, the negative refractive power of the first lens group G1 becomes weak and exceeds 100 degrees. There is a problem that the super wide angle cannot be obtained, or the moving amount of each group at the time of zooming becomes large, and the lens system becomes large in diameter. If the lower limit is not reached, the negative focal length of the first lens group G1 is shortened, and the amount of movement of the second lens group G2 is further increased in order to secure the focal length of the entire system, and the brightness with respect to the image plane 5 is restricted. The second lens group G2 is too far away from the aperture stop St, and the second lens group G2 has a large diameter, or the aberration variation increases between the wide angle side and the telephoto side, resulting in deterioration in imaging performance. .

  Conditional expression (2) is a conditional expression related to the refractive power distribution in the second lens group G2. In the second lens group G2 according to the present invention, when the specification is a bright optical system of F1.4 class, the refractive power distribution of the lenses in the group is important. In the second lens group G2 including the biconvex lens L4, the biconcave lens L5, and the positive lens L6 in order from the object side, the refractive power of the second lens group G2 is restricted by the conditional expression (1). If the refractive power of the positive lens L6 is increased, the refractive power of the positive lens L6 is weakened, which is advantageous for off-axis performance. However, if the upper limit of conditional expression (2) is exceeded, the back focus of the entire system becomes shorter, and the mirror It will not be possible to meet the required flange back requirement. In order to avoid this, it is possible to increase the refractive power of the biconcave lens L5, for example, but this is not preferable because it affects chromatic aberration.

  On the contrary, if the refractive power of the biconvex lens L4 is weakened, the refractive power of the positive lens L6 becomes strong. If the refractive power falls below the lower limit value of the conditional expression (2), asymmetry of the refractive power arrangement of the entire system with the aperture stop St as the center. This is not preferable because the optical characteristics are further increased and off-axis aberrations such as field curvature and coma are deteriorated. At this time, the positive lens L6 can be aspherical, but it strongly affects both spherical aberration and off-axis aberrations, and it is difficult to maintain good imaging performance over the entire screen.

  Therefore, both the conditional expression (1) and the conditional expression (2) are satisfied, and the lenses L2 and L5 are biconcave to disperse the strong divergence in each lens group, thereby causing various aberrations on each surface. A variable power optical system that can cover a wide-angle and ultra-wide-angle range and reduce the amount of image generation over the entire screen in the entire variable power range. Can be realized.

In the variable magnification optical system 1, when the focal length of the biconcave lens in the second lens group is f5, the focal length of the positive lens is f6, and the focal length of the entire system at the wide angle end is fw, the following conditional expression ( It is preferable to satisfy 3) and (4).
−0.55 <fw / f5 <−0.3 (3)
0.30 <fw / f6 <0.40 (4)

  Conditional expression (3) is an expression relating to the refractive power of the biconcave lens L5 in the second lens group. In a bright variable power optical system such as F1.4 class which is one of the specification targets of the present invention, in order to maintain a high resolution and particularly peripheral image quality, spherical aberration, coma aberration, field curvature, chromatic aberration, etc. It is important to keep the various aberrations small in a balanced manner, but the refractive power of the biconcave lens L5 is related to any of these.

  If the lower limit of conditional expression (3) is not reached, the negative refracting power of the biconcave lens L5 will increase, the field curvature will be overcorrected, and the chromatic aberration of magnification will increase, adversely affecting imaging performance. To alleviate this, it is necessary to increase the positive refracting power of the biconvex lens L4 and the positive lens L6, but there is a limit as shown by the conditional expression (2), and it cannot be corrected sufficiently. Even if the lens is made aspherical, the second lens group fluctuates with respect to the aperture stop, so it does not improve evenly. Depending on the zoom position, it may cause performance degradation and maintain the performance in the entire zoom range. Disappear. On the other hand, if the upper limit of conditional expression (3) is exceeded, the curvature of field will be undercorrected and peripheral image quality will be impaired, or axial chromatic aberration will be undercorrected on the telephoto side, making it impossible to maintain good imaging performance.

  Conditional expression (4) is an expression relating to the refractive power of the positive lens L6 closest to the image plane. Therefore, it particularly affects the imaging performance in the vicinity. If the lower limit of conditional expression (4) is not reached, the refractive power of the positive lens L6 becomes too small to suppress the divergent force generated by the biconcave lens L5, and the field curvature is overcorrected and the peripheral performance is deteriorated. Even if the positive lens L6 is aspherical in order to solve this problem, the advantages of the wide-angle end and the telephoto end are different, and the imaging performance cannot be maintained over the entire zoom range. On the other hand, if the upper limit of conditional expression (4) is exceeded, the refractive power of the positive lens L6 becomes too strong and the curvature of field becomes insufficiently corrected, and similarly the performance over the entire zooming range cannot be maintained.

  Next, numerical examples of the variable magnification optical system of the present invention will be described.

<Example 1>
A lens cross-sectional view of the variable magnification optical system of Example 1 is shown in FIG. In addition, Table 1 shows lens data of the variable magnification optical system according to Example 1, Table 2 shows aspheric data, and Table 3 shows various data. Similarly, Tables 4 to 24 show lens data, aspheric surface data, and various data of the variable magnification optical systems 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 lens data of Table 1, the surface number increases sequentially toward the image side with the surface of the component closest to the object side being first, and the surface interval is on the optical axis Z from the corresponding surface to the next surface. The surface spacing is shown. Also, in the lens data, Nd is the first lens on the most object side, and the d-line (wavelength 587.6 nm) of the nth (n = 1, 2, 3,...) Optical element increases sequentially toward the image side. Νd represents the Abbe number of the nth 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, (stop) is described. The sign of 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 lens data in Table 1, the distance between the first lens group G1 and the aperture stop St, the distance of which changes to perform zooming, the distance between the aperture stop St and the second lens group G2, the second lens group G2 and the optical In the column of the surface interval corresponding to the interval with the member PP, D6 (variable), D7 (variable), and D13 (variable) are described, respectively.

In the 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 aspheric data in Table 2 shows surface numbers of aspheric surfaces and aspheric coefficients related to these aspheric surfaces. The aspheric coefficient is a value of each coefficient κ, A _m (m = 4, 6, 8, 10, 12) in the aspheric expression represented by the following expression (A).
X = C · h ² / (1+ (1−κ · (C · h) ² )) ^1/2 + A4 · h ⁴
+ A6 · h ⁶ + A8 · h ⁸ + A10 · h ¹⁰ + A12 · h ¹² (A)
However,
X: Depth of aspheric surface (length of perpendicular drawn from a point on the aspherical surface at 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 of paraxial radius of curvature A _m : aspheric coefficient (m = 4, 6, 8, 10, 12)

  The various data in Table 3 shows the focal length of the entire system, the back focus Bf ′ of the entire system, the F number FNO, and the total angle of view 2ω at the wide angle end, the intermediate field angle, and the telephoto end. The unit of the total angle of view 2ω is degrees.

  As the unit of the radius of curvature and the surface interval in Table 1, the aspheric depth X and the height h in the aspherical system, and the focal length of the entire system and the back focus Bf ′ of the entire system in Table 3, “mm” is used. Although the optical system can obtain the same optical performance even when the optical system is proportionally enlarged or reduced, the unit is not limited to “mm”, and other appropriate units can also be used.

<Example 2>
Table 4 shows lens data of the variable magnification optical system according to Example 2, Table 5 shows aspherical data, and Table 6 shows various data. In addition, a lens configuration diagram is shown in FIG. 2 (a schematic movement locus of each lens group is omitted).

<Example 3>
Table 7 shows lens data of the variable magnification optical system according to Example 3, Table 8 shows aspherical data, and Table 9 shows various data. Further, a lens configuration diagram is shown in FIG. 3 (a schematic movement locus of each lens group is omitted).

<Example 4>
Table 10 shows lens data of the variable magnification optical system according to Example 4, Table 11 shows aspherical data, and Table 12 shows various data. Further, a lens configuration diagram is shown in FIG. 4 (a schematic movement locus of each lens group is omitted).

<Example 5>
Table 13 shows lens data of the variable magnification optical system according to Example 5, Table 14 shows aspheric data, and Table 15 shows various data. Further, a lens configuration diagram is shown in FIG. 5 (a schematic movement locus of each lens group is omitted).

<Example 6>
Table 16 shows lens data of the variable magnification optical system according to Example 6, Table 17 shows aspherical data, and Table 18 shows various data. Further, a lens configuration diagram is shown in FIG. 6 (a schematic movement locus of each lens group is omitted).

<Example 7>
Table 19 shows lens data of the variable magnification optical system according to Example 7, Table 20 shows aspherical data, and Table 21 shows various data. In addition, a lens configuration diagram is shown in FIG. 7 (a schematic movement locus of each lens group is omitted).

<Example 8>
Table 22 shows lens data of the variable magnification optical system according to Example 8, Table 23 shows aspherical data, and Table 24 shows various data. Further, a lens configuration diagram is shown in FIG. 8 (a schematic movement locus of each lens group is omitted).

  Table 25 shows values corresponding to the conditional expressions (1), (2), (3), and (4) in the variable magnification optical systems of Examples 1 to 8. Each value in Table 25 is for d line (wavelength 587.6 nm). As can be seen from Table 25, conditional expressions (1), (2), (3), and (4) are satisfied in all of Examples 1 to 8.

  FIG. 9 shows aberration diagrams of spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration at the wide angle end, the intermediate field angle, and the telephoto end of the variable magnification optical system of Example 1. Each aberration diagram shows the aberration with the d-line (wavelength 587.6 nm) as the reference wavelength, but the spherical aberration diagram and the lateral chromatic aberration diagram show the g-line (wavelength 435.8 nm) and the c-line (wavelength 656.3 nm). The aberration for is also shown.

  Note that the distortion aberration is described in terms of TV distortion. Although the degree of distortion of the object image perpendicular to the optical axis connected by the optical system of the planar object perpendicular to the optical axis is expressed as distortion, a photographic lens, etc., generally represents the difference between the ideal image height and the real image height. Whereas the numerical value divided by the image height is expressed as a percentage, in the field of the TV lens, a different definition formula is used to distinguish it as a TV display. According to this definition, the amount of bending on the long side of the TV screen is treated as a distortion amount.

  Specifically, it is expressed as a percentage by dividing by the vertical screen length 2h of the long side bending depth Δh, and is expressed by the following equation.

DTV = Δh / 2h × 100
In the distortion diagram, assuming that the real image height Y from the optical axis is four points in the diagonal direction of the screen 4 from the optical axis center, a rectangular planar object on the object side of the planar image connected by these four points is assumed. The real image height at the center of the long side of this image is h, and the difference from the vertical height to the optical axis of the diagonal point is Δh. Accordingly, although the numerical values differ depending on the aspect ratio of the screen, in this figure, the calculation is performed at a ratio of 3: 4, which is general for a TV screen.

  Similarly, FIGS. 10 to 16 are diagrams showing spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration at the wide angle end, the intermediate field angle, and the telephoto end of the variable magnification optical systems of Examples 2 to 8, respectively. Indicates.

  From the above data, it can be seen that in the variable power optical systems of Examples 1 to 8, each aberration is corrected well and both the wide-angle end and the telephoto end have high optical performance in the visible range. These variable magnification optical systems 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 variable magnification optical system 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 negative first lens group G1, the aperture stop St, and the positive second lens group G2 included in the variable magnification optical system 1 are schematically shown.

  The video camera 10 includes a variable magnification optical system 1, a filter 6 having functions such as a low-pass filter and an infrared cut filter disposed on the image side of the variable magnification optical system 1, and an image sensor disposed on the image side of the filter 6. 7 and a signal processing circuit 8. The image sensor 7 converts an optical image formed by the variable magnification optical system 1 into an electrical signal. For example, the image sensor 7 uses a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor), or the like. be able to. The image sensor 7 is arranged such that its image plane coincides with the image plane of the variable magnification optical system 1.

  An image picked up by the variable magnification optical system 1 is formed on the image pickup surface of the image pickup device 7, and an output signal from the image pickup device 7 relating to the image is arithmetically processed by the signal processing circuit 8, and the image is displayed on the display device 9. Is displayed.

  Note that FIG. 17 illustrates a so-called single-plate type imaging apparatus using one imaging element 7, but the imaging apparatus according to the present invention is provided between the variable magnification optical system 1 and the imaging element 7. A so-called three-plate system may be used in which color separation prisms for each color such as R (red), G (green), and B (blue) are inserted and three image pickup devices corresponding to the respective colors are used.

  Since the variable magnification optical system according to the embodiment of the present invention has the above-described advantages, the imaging apparatus according to the present embodiment can obtain a wide-angle and highly accurate image.

  The present invention has been described with reference to the embodiment and examples. However, the present invention is not limited to the above embodiment and example, 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 imaging lens concerning Example 1 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 2 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 3 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 4 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 5 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 6 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 7 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 8 of this invention. Each aberration diagram of the imaging lens according to Example 1 of the present invention Each aberration diagram of the imaging lens according to Example 2 of the present invention Each aberration diagram of the imaging lens according to Example 3 of the present invention Each aberration diagram of the imaging lens according to Example 4 of the present invention Each aberration diagram of the imaging lens according to Example 5 of the present invention Each aberration diagram of the imaging lens according to Example 6 of the present invention Each aberration diagram of the imaging lens according to Example 7 of the present invention Respective aberration diagrams of the imaging lens according to the eighth embodiment 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 Variable magnification optical system 6 Filter 7 Image pick-up element 8 Signal processing circuit 9 Display apparatus 10 Imaging apparatus G1 1st lens group G2 2nd lens group L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens PP Optical member St Aperture stop Z Optical axis

Claims (3)

In order from the object side, a first lens group having a negative refractive power, a diaphragm and a second lens group having a positive refractive power ,
The stop is at a fixed distance to the imaging position;
A zooming optical system that performs zooming by changing an interval between the first lens group and the diaphragm and an interval between the diaphragm and the second lens group,
The first lens group includes, in order from the object side, a negative lens having a convex surface facing the object side, a biconcave lens, and a positive lens .
The second lens group includes, in order from the object side, a biconvex lens, a biconcave lens, and a positive lens .
The focal length of the first lens group is fF, the focal length of the second lens group is fB, the focal length of the biconvex lens in the second lens group is f4, the focal length of the biconcave lens is f5, and the positive A variable power optical system characterized by satisfying the following conditional expressions (1) , (2) and (3) , where f6 is the focal length of the lens and fw is the focal length of the entire system at the wide-angle end .
−1.30 <fB / fF <−1.10 (1)
0.90 <f6 / f4 <1.20 (2)
−0.55 <fw / f5 <−0.3 (3) Claim 1 variable magnification optical system, wherein a is satisfied under Symbol conditional expression (4).
0 . 30 <fw / f6 <0.40 (4) A variable magnification optical system according to claim 1 or 2,
An image pickup apparatus comprising: an image pickup device that picks up an image of a subject formed by the variable magnification optical system.

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