JP2008191231A - Optical system and imaging apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical system which has a comparatively long back focus, whose entire system is miniaturized and whose aberration is satisfactorily corrected from the center of a screen to the periphery of the screen, and an imaging apparatus having the same. <P>SOLUTION: The optical system has a first lens turning its convex surface to an object side and having negative refractive power, a second lens having positive refractive power, a third lens having negative refractive power and a fourth lens having positive refractive power in order from the object side to an image side. The focal length f3 of the third lens and the focal length f of the entire system are set appropriately. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical system and an image pickup apparatus having the optical system, and is particularly suitable for a video camera, a digital camera, or the like having a short overall lens length and a relatively long back focus.

  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, or the like, there is known an optical system having a four-lens structure of negative, positive, negative, and positive lenses in order from the object side (subject side) to the image side. (See Patent Documents 1 to 6).

  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 lens 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 meniscus shape on the object side, 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.

  The photographic lens of Patent Document 4 has, in order from the object side to the image side, a first lens unit having a negative refractive power having a concave surface on the image side, an aperture stop, a second lens having a positive refractive power, and both lens surfaces having a concave surface. 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.

  All of the optical systems disclosed in Patent Documents 1 to 4 have an angle of view of 64 degrees or less.

  Patent Document 5 discloses an objective lens having a wide angle of view of an endoscope having an angle of view of 70 degrees or more.

  In Patent Document 5, a reflection member for bending an optical path is provided between the first lens and the second lens.

Patent Document 6 discloses a photographic lens having a relatively wide field angle of 68 degrees, in which a reflection member for bending an optical path is provided between a first lens and a second lens.
JP 2003-195163 A JP 2003-307671 A JP 2004-53813 A JP 2004-240123 A JP-A-10-301023 Japanese Patent Laid-Open No. 2003-161878

  The above-described optical system including the four lenses of negative, positive, negative, and positive first to fourth lenses in order from the object side to the image side can easily widen the shooting field angle. However, in order to achieve high optical performance over the entire screen with a long back focus and a wide angle of view (for example, an angle of view of 70 degrees or more) while reducing the size of the entire system, the four lens configurations should be appropriately set in a balanced manner. Becomes important.

  For example, if the lens shape of each lens, the power of the third lens (refractive power = reciprocal of focal length), the power of the fourth lens, etc. are not set appropriately, the entire system is small and has high optical performance over the entire screen. It becomes difficult to obtain an optical system.

  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.

  Since the optical system of Patent Document 5 is used for an endoscope, the distortion is 10% or more, and the field curvature and astigmatism are large.

  In Patent Document 6, the focal length of the second lens is smaller than the focal length of the entire system, the entire optical system tends to be large, and astigmatism tends to increase.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical system having a relatively long back focus, a small overall system, and having excellent aberrations corrected from the center of the screen to the periphery of the screen, and an image pickup apparatus having the optical system.

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, a second lens having a positive refractive power, a third lens having a negative refractive power, and a positive lens having a convex surface facing the object side. An optical system having a fourth lens having a refractive power of
The focal length of the third lens is f3,
When the focal length of the entire system is f, 0.8 <| f3 / f | <1.2
It is characterized by satisfying the following conditions.

  According to the present invention, an optical system having a four-lens configuration, the entire system is small, the shooting angle of view is wide, and the aberration is well corrected from the center of the screen to the periphery of the screen, and an imaging apparatus having the same. be able to.

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

  The optical system of the present invention includes, in order from the object side to the image side, a first lens G1 having a negative refractive power with a convex surface facing the object side, a second lens G2 having a positive refractive power, an aperture stop, and a negative refractive power. This is an optical system having a third lens G3 and a fourth lens G4 having a positive refractive power.

  The focal length of the third lens, the focal length of the fourth lens, and the like are set appropriately.

FIG. 1 is a lens sectional view of Example 1 of the present invention, and FIG. 2 is a longitudinal aberration diagram of Example 1 of the present invention. 3 is a lens cross-sectional view of Example 2 of the present invention, and FIG. 4 is a longitudinal aberration diagram of Example 2 of the present invention.
FIG. 5 is a lens cross-sectional view of Example 3 of the present invention, and FIG. 6 is a longitudinal aberration diagram of Example 3 of the present invention.
FIG. 7 is a lens cross-sectional view of Example 4 of the present invention, and FIG. 8 is a longitudinal aberration diagram of Example 4 of the present invention.
FIG. 9 is a lens sectional view of Example 5 of the present invention, and FIG. 10 is a longitudinal aberration diagram of Example 5 of the present invention.
FIG. 11 is an explanatory diagram of an image pickup apparatus using the optical system according to the first to third embodiments of the present invention. FIG. 12 is an explanatory diagram of an image pickup apparatus using the optical system according to Embodiments 4 and 5 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). The optical system GB of this embodiment is configured as follows in order from the object side to the image side. A first lens G1 having a negative refractive power having a convex surface on the object side and a meniscus shape, a second lens G2 having a positive refractive power having a convex surface on the object side, an aperture stop S, and a third lens G3 having a negative refractive power having both lens surfaces concave. The image side includes a fourth lens G4 having a convex surface and a positive refractive power.

  Note that the optical system of the present embodiment has a configuration having four lenses (only four lenses) having optical power (refractive power) that greatly affects the focal length of the entire optical system. Conversely, on the object side of the first lens G1 and / or the image side of the fourth lens G4, an optical member having no optical power or a very small optical power (the focal length is the focal point of the entire optical system). You may have an optical member which is 50 times or more of distance.

  S is a diaphragm member (aperture diaphragm) that determines the F number, and is disposed 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, and 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.

  7 and 9, P is a reflecting member including a reflecting surface MR for bending the optical path.

  The reflecting member P is composed of an optical block of a triangular prism, is disposed between the first lens G1 and the second lens G2, and bends the optical path on the optical axis La by 90 degrees. In this embodiment, a triangular prism is used, but a mirror may be used.

  Pa is the incident surface of the reflecting member P, Pb is the exit surface of the reflecting member, and both are perpendicular to the optical axis La. The angle formed between the normal line of the reflecting surface MR and the optical axis La is 45 degrees.

  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 aperture stop S is disposed on the image side of the second lens G2. Thereby, for example, compared with the case where the second lens G2 is disposed on the object side, a space for inserting a mechanical member such as an aperture unit can be reduced, and a reduction in thickness in the optical axis direction is achieved. At that time, the refractive power of the third lens G3 is set as follows in order to correct various aberrations, reduce the size of the entire lens system, and reduce the incident angle of the off-axis light beam on the image sensor.

  Let the focal length of the third lens G3 be f3.

Let f be the focal length of the entire system. At this time, 0.8 <| f3 / f | <1.2 (1)
Is satisfied.

  If the lower limit value of conditional expression (1) is not reached, the negative power of the third lens G3 increases. For this reason, the back focus of the entire lens system is excessively extended, the entire length of the lens at the time of photographing is extended, and it is difficult to downsize the entire lens system. Further, it becomes difficult to correct distortion. If the upper limit value of conditional expression (1) is exceeded, the negative power of the third lens G3 becomes too weak, and it becomes difficult to mainly correct spherical aberration, coma aberration, field curvature, astigmatism, and the like.

  Further, since the back focus is shortened, the incident angle of the off-axis light beam to the image sensor increases, and there is a problem that a large amount of color shading occurs.

  More preferably, the numerical range of the conditional expression (1) is set as follows.

0.82 <| f3 / f | <1.18 (1a)
As described above, according to each embodiment, it is possible to easily assemble with the configuration of four lenses by making the power of the third lens G3 appropriate, the retractable length is short, and the aberration is corrected well from the center of the screen to the periphery of the screen. Thus, a small and wide-angle optical system can be obtained.

  Furthermore, since the aperture efficiency is high and a sufficient amount of light around the screen can be secured, a bright optical system with a wide field angle exceeding 70 ° can be obtained.

  Here, only the lower limit 0.8 of the conditional expression (1) is replaced with the lower limit 0.82 of the conditional expression (1a), or only the upper limit 1.2 of the conditional expression (1) is replaced by the conditional expression (1a). The lower limit may be replaced with 1.18. That is, conditional expressions such as 0.8 <| f3 / f | <1.18 and 0.82 <| f3 / f | <1.2 are also within the application range of this embodiment.

  With the configuration as described above, the problems of the present invention can be solved. However, if at least one of the following conditional expressions (2) to (7) is satisfied, a more preferable effect is obtained. However, the conditional expressions (2) to (7) are not essential components in the sense of solving the above-described problems.

  The focal lengths of the first lens G1, the second lens G2, and the fourth lens G4 are sequentially set as f1, f2, and f4.

  However, when the fourth lens G4 is cemented with the third lens G3, it is the focal length when it is disposed in the air.

  The distance between the first lens G1 and the second lens G2 is D2.

However, when there is a reflecting member (prism P) having no refractive power as shown in FIGS. 7 and 9 between the first lens G1 and the second lens G2, the length of the reflecting member is air converted to air. The conversion length. That is, when the length of the reflecting member P in the optical axis direction is L and the refractive index of the material of the reflecting member P is N, the air equivalent length Lc of the reflecting member P is Lc = L / N
It is.

The curvature radii of the object-side and image-side surfaces of the first lens G1 are G1R1 and G1R2, respectively. At this time 0.9 <f4 / f <1.7 (2)
1.0 <D2 / f <2.5 (3)
0.8 <f2 / f <1.2 (4)
1.4 <| f1 / f | <2.3 (5)
0.65 <| f3 / f4 | <0.9 (6)
0.4 <G1R2 / G2R1 <1.2 (7)
It is more preferable to satisfy one or more of the following conditions.

  Next, technical meanings of the conditional expressions (2) to (7) will be described.

  Conditional expression (2) is for reducing the sensitivity of manufacturing and assembling of the fourth lens G4, correcting various aberrations such as distortion and lateral chromatic aberration, and reducing the incident angle of the off-axis light beam on the image sensor. Is.

  When the lower limit value of conditional expression (2) is exceeded, the positive power of the fourth lens G4 is weakened, the sensitivity of deterioration of the optical performance with respect to the accuracy in the decentering direction and the tilt direction is reduced, and manufacturing and assembly are facilitated. . If the upper limit value of conditional expression (2) is not reached, the positive power of the fourth lens G4 increases, and it becomes easy to reduce (correct) distortion aberration, lateral chromatic aberration, and the like. In addition, it is easy to reduce the incident angle of the off-axis light beam on the image sensor, and the amount of color shading can be reduced.

  Conditional expression (3) is intended to reduce the sensitivity of the first lens G1 and the second lens G2 to parallel / tilt eccentricity and to reduce the size of the entire lens system.

  If the lower limit value of conditional expression (3) is exceeded, the lens interval between the first lens G1 and the second lens G2 is widened, and correction of mainly curvature of field, distortion, lateral chromatic aberration, and the like becomes easy. For this reason, when the angle is widened, it is easy to maintain good performance up to the periphery of the screen. In addition, since the sensitivity of deterioration of the optical performance with respect to the accuracy in the eccentric direction and the tilt direction can be reduced, manufacturing and assembly are facilitated.

  If the upper limit of conditional expression (3) is not reached, the distance between the first lens G1 and the second lens G2 becomes shorter with respect to the focal length of the entire system, and the entire system can be easily reduced in size. Further, when the first lens G1 is retracted, the stroke length when retracting is shortened, so that the amount of deviation of parallelism and inclination when retracted can be reduced, so that it is easy to maintain good optical performance.

  If the lower limit of conditional expression (4) is exceeded, the power of the second lens G2 can be suppressed, and it becomes easy to mainly correct astigmatism. In addition, since the sensitivity of the second lens G2 can be reduced, manufacturing and assembly are facilitated.

  If the upper limit value of conditional expression (4) is not reached, the power of the second lens G2 can be increased and the thickness of the lens can be suppressed, so that the entire system can be easily downsized.

  Conditional expression (5) is mainly for reducing the sensitivity of the emission angle of the light beam emitted from the fourth lens G4 and the parallelism / inclination of the first lens G1.

  If the lower limit value of conditional expression (5) is exceeded, the power of the first lens G1 can be suppressed compared to the focal length of the entire system, and the sensitivity of deterioration of optical performance mainly to the parallel / tilt of the first lens G1. And the assembly becomes easy.

  Further, since the curvature of the image side surface of the first lens G1 does not become too small with respect to the effective diameter of the first lens G1, the opening angle at the time of manufacturing can be reduced, and the manufacturing becomes easy.

  Further, negative distortion can be suppressed to a small level, and this correction becomes easy.

  If the upper limit value of conditional expression (5) is not reached, the power of the first lens G1 is increased to some extent compared to the focal length of the entire system, the back focus is increased, and the incident angle of the off-axis light beam on the image sensor is reduced. Therefore, color unevenness and luminance shading can be reduced.

  Conditional expression (6) is for canceling the relative sensitivity between the third lens G3 and the fourth lens G4 and the lateral chromatic aberration between the third lens G3 and the fourth lens G4 lens.

  By making the ratio of the focal lengths of the third lens G3 and the fourth lens G4 within the range of the conditional expression (6), it is possible to effectively cancel the lateral chromatic aberration. If the lower limit of conditional expression (6) is exceeded, the sensitivity of the third lens G3 to parallelism / inclination becomes low. If the value is below the upper limit value, the sensitivity of the fourth lens G4 becomes low, and both of them are easy to manufacture and assemble.

  If the lower limit of conditional expression (7) is exceeded, the power of the first lens G1 will be weakened, the sensitivity to parallelism and tilt will be low, and manufacturing and assembly will be easy. Further, when the first lens G1 is retracted, it is possible to reduce the deterioration of the optical performance around the screen due to the parallel / tilt deviation. Also, field curvature and astigmatism can be suppressed to a small level.

  In addition, it is possible to avoid that the radius of curvature of the image side surface of the first lens G1 becomes too small, and manufacturing can be facilitated.

  Furthermore, when focusing on the first lens G1 or the entire lens, it is possible to suppress degradation of optical performance when focusing on a close object.

  If the upper limit of conditional expression (7) is not reached, the total lens length and the front lens effective diameter can be reduced, and the lens diameter can be reduced. In addition, it is possible to avoid that the amount of light around the screen becomes too small.

  It is more desirable to set the numerical ranges of the conditional expressions (2) to (7) as follows.

0.95 <f4 / f <1.65 (2a)
1.1 <D2 / f <2.3 (3a)
0.90 <f2 / f <1.17 (4a)
1.43 <| f1 / f | <2.20 (5a)
0.70 <| f3 / f4 | <0.86 (6a)
0.50 <G1R2 / G2R1 <1.18 (7a)
The upper limit values of these conditional expressions (2a) to (7a) may be used as the upper limit values of the conditional expressions (2) to (7), and the lower limit values of the conditional expressions (2a) to (7a) may be set as the conditional expressions ( It is good also as a lower limit of 2)-(7).

  The surface on the image side of the first lens G1 is preferably an aspherical shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  According to this, the angle of the light ray incident on the second lens G2 can be relaxed, and various aberrations such as coma aberration: distortion can be corrected well. In addition, the effective diameter of the lens arranged on the image side from the first lens G1 can be reduced. Further, the radius of curvature of the image side surface of the first lens G1 is reduced, the opening angle is relaxed, and the manufacture is facilitated. Further, it is possible to reduce the deterioration of the optical performance with respect to the parallel decentering and tilt decentering of the first lens G1 and the second lens G2.

  Next, a specific lens configuration of each embodiment will be described.

  The optical system GB of Numerical Example 1 in FIG. 1 includes a negative meniscus first lens G1 having a convex surface facing the object side, a positive second lens G2 having a convex surface facing the object side, an aperture stop S, both The lens surface is constituted by a negative third lens G3 having a concave shape, and both lens surfaces are constituted by a convex fourth lens G4.

  By making the image-side surface of the first lens G1 and the object-side and image-side surfaces of the fourth lens G4 aspherical, distortion is mainly corrected well, and off-axis light flux to the imaging device is mainly corrected. The incident angle is reduced.

  Also, by using the third lens G3 and the fourth lens G4 as marginal contacts, the lens barrel is simplified, and the optical performance is prevented from deteriorating due to the gap between the third lens G3 and the fourth lens G4 and the tilt eccentricity. It is easy to assemble.

  The optical system GB of Numerical Examples 2 and 3 in FIGS. 3 and 5 is as follows.

  A meniscus negative first lens G1 having a convex surface facing the object side, a positive second lens G2 having a convex surface facing the object side, an aperture stop S, a third lens G3 having concave both lens surfaces, and both lenses The surface is constituted by a cemented lens of a fourth lens G4 having a convex shape.

  By making the image-side surface of the first lens G1 and the image-side surface of the fourth lens G4 aspherical, the distortion is mainly corrected well and the incident angle of the off-axis light flux on the image sensor is adjusted. We are reducing.

  Further, the third lens G3 and the fourth lens G4 are cemented lenses to correct chromatic aberration and simplify the lens barrel. Further, the optical performance is prevented from deteriorating due to the gap between the third lens G3 and the fourth lens G4, and the tilt decentering, thereby facilitating the assembly.

  The optical system GB of Numerical Examples 4 and 5 in FIGS. 7 and 9 includes a meniscus negative first lens G1 having a convex surface facing the object side, and a reflecting member (prism) P having a reflecting surface that bends the optical path. Have.

  Further, the lens includes a positive second lens G2 having a convex surface directed toward the object side, an aperture stop S, a cemented lens of a third lens G3 having concave concave surfaces and a fourth lens G4 having convex convex surfaces. .

  The optical path on the optical axis is bent by the reflecting member P to reduce the thickness of the camera in the thickness direction. By making the image-side surface of the first lens G1 and the image-side surface of the fourth lens G4 aspherical, the distortion is mainly corrected well and the incident angle of the off-axis light flux on the image sensor is adjusted. We are reducing.

  Further, the third lens G3 and the fourth lens G4 are cemented lenses to correct chromatic aberration and simplify the lens barrel.

  Further, the optical performance is prevented from being deteriorated due to the gap between the third lens G3 and the fourth lens G4 and the eccentricity of the tilt, thereby making it easy to assemble.

  In any of the embodiments, focusing is performed by moving the first lens G1 or the entire lens.

  As described above, according to each embodiment, by appropriately setting the curvature and power (refractive power) of the lens surface, the optical system is small and has a small aberration with a four-lens configuration of negative, positive, negative, and positive lenses. Can be obtained.

  In addition, according to each embodiment, it is possible to obtain a compact 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 angle of view (for example, an angle of view of 70 degrees) can be obtained.

  Further, in Examples 4 and 5, a reflecting member made of a prism member having a reflecting surface is arranged between the first lens G1 and the second lens G2, and the optical path is bent. According to this, it is possible to further reduce the thickness of the camera in the thickness direction (front-rear direction).

  In the first to third embodiments, similarly to the fourth and fifth embodiments, a reflection member for bending the optical path may be disposed between the first lens G1 and the second lens G2.

  Next, an embodiment of a digital camera (optical apparatus) using the optical system of Embodiments 1 to 3 of the present invention as a photographing optical system will be described with reference to FIG.

  In FIG. 11, reference numeral 20 denotes a camera body, and reference numeral 21 denotes a photographing optical system constituted by the optical systems according to the first to third embodiments of the present invention. Reference numeral 22 denotes a solid-state image sensor (optical conversion element) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographing optical system 21 and is built in the camera body. A memory 23 records information corresponding to a subject image photoelectrically converted by the solid-state imaging device 22. Reference numeral 24 is 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.

  FIG. 12 is a schematic diagram of a main part of a digital camera using the optical systems of Embodiments 4 and 5 of the present invention as an imaging optical system.

  In FIG. 12, 10 is a digital camera body, and 11 is an optical system according to the present invention. Reference numeral 12 denotes a flash built in the camera body, 13 an external viewfinder, and 14 a shutter button. 15 shows a schematic optical system arrangement relationship in the camera body of the optical system according to Embodiments 4 and 5 of the present invention.

  In this way, by applying the optical system of Embodiments 4 and 5 of the present invention to a digital camera or the like, a small and high-capacity imaging device that realizes a thin camera body is realized. Yes.

  Further, in this example, the optical system is arranged so that the optical axis deflected by the reflecting member at the time of horizontal position photographing is in the vertical (vertical) direction. However, the deflected optical axis is in the horizontal (horizontal) direction. You may arrange so that it may become.

  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 the first to fifth embodiments of the present invention will be described. 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 counted from the object side, R is the radius of curvature, D is the air gap, and Nd is The refractive index of the material at the d-line of each lens, νd, is the Abbe number of the material of each lens.

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. The E-x indicates a ^{10 -x.}

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

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

Explanation of symbols

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 image plane (image height)
Fno F number

Claims (10)

In order from the object side to the image side, a first lens having a negative refractive power having a convex surface directed toward the object side, a second lens having a positive refractive power, a third lens having a negative refractive power, and a fourth lens having a positive refractive power An optical system having
The focal length of the third lens is f3,
When the focal length of the entire system is f, 0.8 <| f3 / f | <1.2
An optical system characterized by satisfying the following conditions. When the focal length of the fourth lens is f4, 0.9 <f4 / f <1.7
The optical system according to claim 1, wherein the following condition is satisfied. When the distance between the first lens and the second lens is D2, 1.0 <D2 / f <2.5
The optical system according to claim 1, wherein the following condition is satisfied. When the focal length of the second lens is f2, 0.8 <f2 / f <1.2
The optical system according to claim 1, wherein the following condition is satisfied. When the focal length of the first lens is f1, 1.4 <| f1 / f | <2.3
The optical system according to claim 1, wherein the following condition is satisfied. When the focal length of the fourth lens is f4, 0.65 <| f3 / f4 | <0.9
The optical system according to claim 1, wherein the following condition is satisfied. When the curvature radii of the object side surface and the image side surface of the first lens are G1R1 and G1R2, respectively, 0.4 <G1R2 / G2R1 <1.2
The optical system according to claim 1, wherein the following condition is satisfied.   8. The optical system according to claim 1, wherein the image-side surface of the first lens has an aspherical shape in which negative refractive power decreases as the distance from the center to the periphery of the lens increases.   9. The optical system according to claim 1, wherein a reflecting member that bends an optical path on an optical axis is disposed between the first lens and the second lens.   An imaging apparatus comprising: the optical system according to claim 1; and a solid-state imaging device that receives an image formed by the optical system.

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