JP5006627B2 - Optical system and optical apparatus having the same - Google Patents

Description

  The present invention relates to an optical system and an optical apparatus having the optical system, and in particular, is suitable for an optical apparatus such as a video camera or a digital camera. It is.

  In recent years, various imaging devices (optical devices) such as small video cameras and digital cameras using an imaging element have been developed. As an optical system (lens system) mounted on this video camera, digital camera, etc., for example, there is known an optical system having four lenses of negative, positive, negative, and positive lenses in order from the object side (subject side) to the image side. (See Patent Documents 1 to 4).

  The optical system of Patent Document 1 includes a first lens having a negative refractive power having a convex surface on the object side and a meniscus shape, a second lens having a positive refractive power having both lens surfaces convex, and a third lens having both surfaces concave. The image-side surface is made up of four lenses that are aspherical and have a fourth lens having a positive refractive power.

  In the optical system of Patent Document 2, from the object side to the image side, the first lens having a negative refractive power and a concave surface on the image side, a second lens having a positive refractive power and a convex surface on the object side, and a concave surface on the object side. A third lens having a negative refractive power. Further, the image side is composed of an aspherical fourth lens that is convex on the image side in the paraxial region (center region) and whose positive refractive power decreases toward the periphery of the lens.

  In the optical system of Patent Document 3, in order from the subject side to the image side, a first lens having a negative refractive power having a convex surface on the subject side and a meniscus shape, a second lens having a positive refractive power having a convex surface on the object side, and a concave surface on the object side. The third lens having a negative refractive power and the fourth lens having a positive refractive power having a convex surface on the image side.

In the optical system of Patent Document 4, in order from the object side to the image side, the first lens group having a negative refractive power whose image side is concave, an aperture stop, a second lens having a positive refractive power, and both lens surfaces are concave. The third lens having a negative refractive power and the fourth lens having a positive refractive power having a convex surface on the image side.
JP 2003-195163 A JP 2003-307671 A JP 2004-53813 A JP 2004-240123 A

  In the embodiment of Patent Document 1, the thickness of the second lens having convex surfaces on both lens surfaces is larger than the focal length of the entire system, and the entire lens system tends to be large.

  In Examples 1-1 and 1-2 of Patent Document 2, compared to the focal length of the entire system, the distance between the first lens and the second lens is large, the entire lens length is increased, and the outer diameter of the first lens is also increased. Therefore, it is difficult to reduce the size of the entire lens system.

  In Examples 2-1 and 2-2, since the distance between the first lens and the second lens is too close compared to the focal length of the entire system in order to shorten the total lens length, it becomes difficult to correct various aberrations. Three aspherical surfaces are used to correct various aberrations. This increases the sensitivity to manufacturing.

  In the example of Patent Document 3, 5 to 8 aspherical surfaces are used to correct various aberrations, and the sensitivity to manufacturing increases, so that manufacturing is difficult.

  In the example of Patent Document 4, both surfaces of the final lens are aspherical. For this reason, the sensitivity with respect to manufacture may become high.

  The present invention provides a compact optical system having a relatively long back focus, low sensitivity to manufacturing, easy assembly, and excellent aberration correction from the center of the screen to the periphery of the screen, and an optical apparatus having the same. For the purpose of provision.

The optical system of the present invention includes, in order from the object side to the image side, a first lens having a negative refractive power having a concave surface on the image side and a meniscus shape, a second lens having a positive refractive power having both lens surfaces convex, and both lens surfaces An optical system composed of a concave third lens having negative refractive power and a fourth lens having positive refractive power, wherein the distance between the first lens and the second lens is D2, and the focal length of the entire system is f The focal length of the first lens is f1, the focal length of the second lens is f2 , the radius of curvature of the lens surface on the image side of the first lens is R2, and the radius of curvature of the lens surface on the object side of the second lens. Is R3 ,
0.3 <D2 / f <0.4
1.4 <| f1 / f2 | ≦ 2.1599
0.4 <R2 / R3 <1.0
It is characterized by satisfying the following conditions.

The optical instrument of the present invention is
It has the above-mentioned optical system and an image sensor for receiving an image formed by the optical system.

According to the present invention, a compact optical system that can be easily assembled with a four-lens configuration, has a short retractable length, a small front lens, and a well-corrected aberration from the center of the screen to the periphery of the screen, and An optical instrument having it can be achieved.

Embodiments of the present invention will be described below with reference to the drawings.
[Example]

Figure 1 is a lens sectional view of Example 1 of the present invention, FIG. 2 is a longitudinal aberration diagram of Example 1 of the present invention. FIG. 3 is a lens cross-sectional view of Example 1 of the present invention, and FIG. 4 is a longitudinal aberration diagram of Example 1 of the present invention. Figure 5 is a lens sectional view of a reference example 2 of the present invention, FIG. 6 is a longitudinal aberration diagram of Example 2 of the present invention. 7 is a lens cross-sectional view of Example 2 of the present invention, and FIG. 8 is a longitudinal aberration diagram of Example 2 of the present invention. FIG. 9 is a lens cross-sectional view of Example 3 of the present invention, and FIG. 10 is a longitudinal aberration diagram of Example 3 of the present invention.

  In the lens cross-sectional view, the left side is the object side (subject side) and the right side is the image side.

In each lens sectional view, GB denotes an optical system (lens system) . In order optical science system GB from the object side to the image side, a first lens G1 having a negative refractive power and a meniscus shape image side concave, a second lens having a positive refractive power of both lens surfaces is convex G2, both lens surfaces A concave third lens G3 having negative refractive power and a fourth lens G4 having positive refractive power are provided. In each example and each reference example , only an optical system composed of four lenses as described above is disclosed. The optical system of the present invention is preferably composed of only the above-described four lenses as a member having optical power (refractive lens, diffractive optical element, concave mirror, convex mirror). Of course, a member having no optical power, such as a diaphragm, a filter, a folding mirror (plane mirror), or the like, may be included.

  S is a diaphragm member (aperture diaphragm) that determines the F number, and is disposed between the first lens G1 and the second lens G2 or between the second lens G2 and the third lens G3.

  GL is an optical block corresponding to an optical filter, a face plate, a crystal low-pass filter, an infrared cut filter, or the like. IP is an image plane, and when used as a photographing optical system of a video camera or a digital still camera, a photosensitive surface corresponding to an imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is placed.

  In the longitudinal aberration diagrams, Fno is the F number, y is the image height, d is the d-line, g is the g-line, C is the C-line, and F is the F-line aberration. M is the aberration of the meridional section, and S is the aberration of the sagittal section. S. A. Is spherical aberration, AS is astigmatism, and DIST is distortion.

In each embodiment, the distance between the first lens G1 and the second lens G2 is D2, the focal length of the entire system is f, the focal length of the first lens G1 is f1, and the focal length of the second lens G2 is f2. To do. At this time,
0.3 <D2 / f <0.4 (1)
1.4 <| f1 / f2 | ≦ 2.1599 (2)
Is satisfied.

  Next, the technical meaning of each of the conditional expressions (1) to (2) will be described.

  Conditional expressions (1) and (2) are conditions relating to reduction in sensitivity to parallel and tilt decentering of the first and second lenses G1 and G2, and to miniaturization of the lens, respectively.

  When the lower limit of conditional expression (1) is exceeded, the distance between the first lens G1 and the second lens G2 becomes narrow, and it becomes difficult to mainly correct curvature of field, distortion, lateral chromatic aberration, and the like. Furthermore, it becomes difficult to maintain good optical performance from the center of the screen to the periphery of the screen. In addition, the sensitivity to manufacturing and assembly becomes high, and manufacturing and assembly become difficult.

  If the upper limit value of conditional expression (1) is exceeded, the total lens length becomes longer with respect to the focal length of the entire system, which hinders downsizing of the entire lens system. Also, when retracting is taken into account, the stroke length when retracting becomes long, so that the amount of deviation in parallel and tilt when retracting increases, leading to deterioration of optical performance.

  When the lower limit value of conditional expression (2) is exceeded, the power (refractive power) of the first lens G1 becomes strong, the sensitivity becomes high, and manufacturing and assembly become difficult. Further, a lot of curvature of field, astigmatism, etc. occur. In addition, when the first and second lenses G1 and G2 are molded, the curvature becomes large and the manufacture becomes difficult. Further, when performing the first lens G1 or the entire focus, the close focus performance is deteriorated.

  If the upper limit value of conditional expression (2) is exceeded, the power of the second lens G2 will increase, and it will be difficult to correct mainly spherical, coma, and astigmatism.

  Desirably, the numerical ranges of the conditional expressions (1) to (2) described above are preferably set as follows.

0.32 <D2 / f <0.397 (1a)
1.5 <| f1 / f2 | ≦ 2.1599 (2a)
In the present embodiment, more preferably, one or more of the following conditional expressions (3) to (8) should be satisfied.

That is, the focal length of the third lens G3 is f3, the focal length of the fourth lens G4 is f4, the radius of curvature of the image side surface of the first lens is R2, the radius of curvature of the object side surface of the second lens is R3, The radius of curvature of the image side surface is R4, the radius of curvature of the image side surface of the third lens is R6, and the center thickness of the second lens G2 is L2. At this time,
0.5 <| f3 / f4 | <0.85 (3)
0.4 <R2 / R3 <1.0 (4)
0.2 <| R3 / R4 | <0.8 (5)
0.35 <R2 / R6 <0.65 (6)
−0.9 <f4 / f1 <−0.3 (7)
0.1 <L2 / f <0.4 (8)
To satisfy the following conditions.

  Next, the technical meaning of each of the conditional expressions (3) to (8) will be described.

  Conditional expression (3) is a condition for relaxing the emission angle of the light beam from the final lens (fourth lens G4).

  As the entire lens system is reduced in size, the emission angle of light emitted from the final lens increases, and the angle incident on the image sensor increases. This causes problems such as a decrease in peripheral light amount and color shading.

  If the lower limit value of conditional expression (3) is exceeded, the positive power of the fourth lens G4 becomes strong, the back focus becomes too short, and the angle of the light ray incident on the image sensor is not good.

  If the upper limit value of conditional expression (3) is exceeded, the negative power of the third lens G3 becomes strong, the back focus becomes too long, and it becomes difficult to reduce the size of the entire lens system.

  Conditional expression (4) is a condition relating to a reduction in sensitivity to parallel eccentricity and inclination eccentricity of the first and second lenses G1 and G2 and a reduction in size of the lens.

  If the lower limit value of conditional expression (4) is exceeded, the power (refractive power) of the first and second lenses G1 and G2 will become stronger, the sensitivity will become higher, and manufacturing and assembly will become difficult. Further, a lot of curvature of field, astigmatism, etc. occur. In addition, when the first and second lenses G1 and G2 are molded, the curvature becomes large and the manufacture becomes difficult. Further, when performing the first lens G1 or the entire focus, the close focus performance is deteriorated.

  If the upper limit value of conditional expression (4) is exceeded, the total lens length and the front lens diameter become large, and the entire lens system becomes large.

  Conditional expression (5) is a conditional expression for effectively reducing the decentration / inclination sensitivity of the second lens G2 and correcting coma.

  If the lower limit of conditional expression (5) is exceeded, the radius of curvature of the object-side surface of the second lens G2 becomes small, and the sensitivity to the eccentricity / tilt with the G1 lens becomes relatively high. It becomes difficult.

If the upper limit value of conditional expression (5) is exceeded, the radius of curvature of the image plane side surface of the second lens G2 becomes small, and the sensitivity to the eccentricity and inclination of the third and fourth lenses G3 and G4 is relatively high. Since it becomes high, manufacture and assembly become difficult.

  Further, by setting the conditional expression (5) in the range, coma generated on the object side surface of the second lens G2 can be canceled out on the R4 surface of the second lens G2.

  Conditional expression (6) is a condition regarding the sensitivity to the manufacture and assembly of the first and third lenses G1 and G3.

  If the lower limit value of conditional expression (6) is exceeded, the sensitivity of the third lens G3 to manufacture and assembly becomes high, making manufacture and assembly difficult. When the upper limit value of conditional expression (6) is exceeded, the sensitivity to the manufacture and assembly of the first lens G1 increases, and the manufacture and assembly of the first lens G1 becomes difficult when the collapse of the first lens G1 is taken into consideration.

  Conditional expression (7) is a conditional expression regarding miniaturization of the lens of the light beam, relaxation of the exit angle, and correction of distortion / magnification chromatic aberration.

  The distortion is mainly corrected by the first lens G1 and the fourth lens G4. However, if the lower limit of the conditional expression (7) is exceeded, the power of the fourth lens G4 is higher than the power of the first lens G1. Strengthening, distortion and lateral chromatic aberration increase. Further, since the light emission angle is increased, there is a problem of color shading. If the upper limit of conditional expression (7) is exceeded, the power of the first lens G1 becomes stronger than the power of the fourth lens G4, and the back focus becomes longer, which hinders downsizing.

  Conditional expression (8) is a condition regarding the thickness (center thickness) of the second lens G2.

  If the lower limit value of conditional expression (8) is exceeded, the thickness of the lens becomes thin, so it is difficult to secure the edge thickness, which is not good. In addition, it becomes difficult to correct astigmatism.

  If the upper limit of conditional expression (8) is exceeded, the thickness of the lens will increase, making it difficult to reduce the size of the entire lens system.

  Further, if the conditional expression (8) is satisfied, the combination with the conditional expression (1) may increase the aperture efficiency and easily secure the peripheral light amount.

  More preferably, the numerical ranges of the conditional expressions (3) to (8) described above are set as follows.

0.5 <| f3 / f4 | <0.83 (3a)
0.4 <R2 / R3 <0.9 (4a)
0.2 <| R3 / R4 | <0.77 (5a)
0.38 <R2 / R6 <0.65 (6a)
−0.85 <f4 / f1 <−0.35 (7a)
0.1 <L2 / f <0.38 (8a)
The diaphragm member S is disposed between the second lens G2 and the third lens G3 in Reference Example 1, Examples 1 and 3. Accordingly, when the first lens G1 is retracted, the diaphragm member S can be disposed on the image side of the second lens G2, so that the retracted length of the camera is shortened, and the camera can be further downsized.

In Reference Example 2 and Example 2 , the diaphragm member S is disposed between the first lens G1 and the second lens G2. This facilitates relaxation of the emission angle and securing of the peripheral light amount.

  As described above, by appropriately setting the curvature and power (refractive power) of the lens surface, it is possible to obtain a small and small aberration optical system with a four-lens configuration of negative, positive, negative, and positive lenses. In addition, according to the present embodiment, it is possible to obtain a small optical system that can be easily assembled, has a short retractable length, has a small front lens, and has excellent aberrations corrected to the periphery of the screen. Furthermore, since the aperture efficiency of the optical system is increased and a sufficient amount of peripheral light can be secured in the lens system, a bright optical system having a relatively wide field angle can be obtained.

  Furthermore, in each embodiment, by appropriately arranging the distance between the first lens G1 and the second lens G2, a prism member or the like having a reflecting surface can be arranged between them. If the optical path is bent, the thickness direction of the camera (front and rear) Direction) can be further reduced.

  Next, an embodiment in which the optical system of the present invention is applied to a digital camera (optical apparatus) using the photographing optical system will be described with reference to FIG.

  In FIG. 11, reference numeral 20 denotes a camera body, 21 denotes a photographing optical system constituted by the optical system of the present invention, 22 denotes a CCD sensor or CMOS sensor incorporated in the camera body and receiving a subject image formed by the photographing optical system 21. A solid-state imaging device (optical conversion device). A memory 23 records information corresponding to a subject image photoelectrically converted by the solid-state imaging device 22. Reference numeral 24 denotes a finder for observing a subject image formed on the solid-state image sensor 22, which includes a liquid crystal display panel or the like.

  As described above, when the optical system of the present invention is used in a photographing optical system of a digital still camera, a small and high-performance imaging device can be realized.

Next, Numerical Examples 1 to 5 corresponding to Reference Example 1, Example 1, Reference Example 2, Example 2, and 3 of the present invention are shown. In each numerical example, f is the focal length of the entire system, fno is the F number, si (i = 1 to 10) is the i-th surface, R is the radius of curvature, D is the air spacing, and Nd is the d-line of each lens. The refractive index of the material, νd, is the Abbe number of the material of each lens.

  The interval values in the numerical examples 2, 3, and 4 are partially negative values because the positions of the members are shown in order from the object side.

The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, k is the conic coefficient (conical constant), and the aspheric coefficient is A, When B, C, and D are expressed by the following formula. E-x represents 10 ^-x .

Table 1 shows the relationship between the conditional expressions described above and the numerical values in the numerical examples.
(Numerical example 1)

Aspheric coefficient
* 8
k -8.27514
A -0.01202
B -0.002158
C -0.00043
D 5.28E-05
(Numerical example 2)

Aspheric coefficient
* 8
k -8.12166
A -0.01146
B 0.001554
C -0.00016
D 6.57E-06
(Numerical Example 3)

Aspheric coefficient
* 8
k -7.5115
A -0.01032
B 0.001397
C -0.00012
D 5.61E-06
(Numerical example 4)

Aspheric coefficient
* 8
k -4.30921
A -7.5115
B -0.01032
C 0.001397
D -0.00012
(Numerical example 5)

Aspheric coefficient
* 8
k -4.54564
A -6.77419
B -0.00854
C 0.001004
D -0.00013

Lens sectional view of Reference Example 1 of the optical system of the present invention Longitudinal aberration diagram of Numerical Example 1 corresponding to Reference Example 1 of the present invention Sectional view of the lens of Example 1 of the optical system of the present invention Longitudinal aberration diagram of Numerical Example 2 corresponding to Example 1 of the present invention Lens sectional view of Reference Example 2 of the optical system of the present invention Longitudinal aberration diagram of Numerical Example 3 corresponding to Reference Example 2 of the present invention Sectional drawing of the lens of Example 2 of the optical system of the present invention Longitudinal aberration diagram of Numerical Example 4 corresponding to Example 2 of the present invention Lens sectional view of Example 3 of the optical system of the present invention Longitudinal aberration diagram of Numerical Example 5 corresponding to Example 3 of the present invention Schematic view of essential parts of the optical apparatus (imaging device) of the present invention

GB optical system G1 first lens G2 second lens G3 third lens G4 fourth lens S stop GL optical block IP image surface A. Spherical aberration AS Astigmatism DIST Distortion aberration d d-line g g-line M Meridional image plane S Sagittal image plane
Y Half-diagonal length of imaging surface Fno F number

Claims (5)

In order from the object side to the image side, the first lens having a negative refractive power having a concave surface on the image side and a meniscus shape, the second lens having a positive refractive power having both lens surfaces convex, and the negative refractive power having both surfaces concave and convex. An optical system comprising a third lens and a fourth lens having a positive refractive power, wherein the distance between the first lens and the second lens is D2, the focal length of the entire system is f, and the focal point of the first lens When the distance is f1, the focal length of the second lens is f2 , the radius of curvature of the image side lens surface of the first lens is R2, and the radius of curvature of the object side lens surface of the second lens is R3 ,
0.3 <D2 / f <0.4
1.4 <| f1 / f2 | ≦ 2.1599
0.4 <R2 / R3 <1.0
An optical system characterized by satisfying the following conditions. When the focal length of the third lens is f3 and the focal length of the fourth lens is f4,
0.5 <| f3 / f4 | <0.85
The optical system according to claim 1, wherein the following condition is satisfied. When the radius of curvature of the lens surface on the image side of the second lens is R4 ,
0.2 <| R3 / R4 | <0.8
Optical system according to claim 1 or 2, characterized by satisfying the following condition. When the radius of curvature of the lens surface on the image side of the front Symbol third lens is R6,
0.35 <R2 / R6 <0.65
Optical system according to any one of claims 1 to 3, characterized by satisfying the following condition. An optical apparatus comprising: the optical system according to any one of claims 1 to 4, the image pickup element for receiving an image formed by the optical system.