Optical System and Imaging Device

Abstract

To provide a wide-angle, compact optical system which maintains high resolution from the center to the periphery of a screen.SOLUTION: An optical system comprises, in order from the object side: a first lens group (31) consisting of a first lens (L1) with negative refractive power having a convex surface on the object side and a meniscus-shaped second lens (L2) having a concave surface on the object side; and a second lens group (32) with positive refractive power. The optical system has five to ten lenses in total and satisfies specific expressions defining optical characteristics thereof.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system and an imaging device.

Background Art

[0002] In recent years, in the optical systems of digital input / output devices such as in-vehicle lenses and drone single-focus lenses, imaging devices with a zoom effect by image processing added to their functions have been rapidly spreading. For this reason, the optical system needs to maintain high resolution from the center to the periphery of the screen at a wide angle.

[0003] Regarding such an optical system, for example, an optical system is known in which, in order from the object side, the signs of the refractive powers of the respective lenses are negative, negative, positive, positive, positive, negative, and the semi-field angle is 48 degrees (see, for example, Patent Document 1).

[0004] Also, an optical system is known in which, in order from the object side, the signs of the refractive powers of the respective lenses are negative, positive, positive, positive, negative, positive, and the semi-field angle is 50 degrees (see, for example, Patent Document 2).

[0005] Also, an optical system is known in which, in order from the object side, the signs of the refractive powers of the respective lenses are negative, negative, positive, positive, negative, positive, and the semi-field angle is 59 degrees (see, for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the optical system described in Patent Document 1, there is a problem that the angle of view is as small as 48 degrees and the image plane curvature correction is insufficient. Further, in the optical systems described in Patent Documents 2 and 3, there is a problem that the correction of the image plane curvature and the distortion aberration is insufficient in the peripheral portion.

[0008] One aspect of the present invention aims to realize a wide-angle optical system and an imaging device that can maintain high resolution from the center to the periphery of the screen and is small in size.

Means for Solving the Problems

[0009] In order to solve the above problems, an optical system according to one aspect of the present invention includes, in order from the object side, a first lens group and a second lens group having a positive refractive power. The first lens group includes, in order from the object side, a first lens L1 having a convex surface on the object side and a negative refractive power, and a meniscus-shaped second lens L2 having a concave surface facing the object side. The total number of lenses is 5 or more and 10 or less, and An optical system that satisfies the following formula. 1.55 < (C L1r - C L2f ) × f < 2.55 ····· (1) 0.65 < D L12 / f < 5.00 ····· (2) However, C L1r : The curvature of the lens surface on the image plane side of the first lens L1 C L2f : The curvature of the lens surface on the object side of the second lens L2 f: The focal length when the optical system is focused at infinity D L12 : The distance on the optical axis between the lens surface on the image plane side of the first lens L1 and the lens surface on the object side of the second lens L2 when the optical system is focused at infinity

[0010] In order to solve the above problems, an optical system according to one aspect of the present invention includes, in order from the object side, a first lens group and a second lens group having a positive refractive power. The first lens group consists of a first lens L1 with a convex surface on the object side and a negative refractive power, and a meniscus-shaped second lens L2 with a concave surface facing the object side, in order from the object side. The second lens group includes a third lens L3 with a positive refractive power on the object side and an aperture on the image side of the third lens L3. The total number of lenses is 5 or more and 10 or less, and An optical system that satisfies the following formula. -2.3 < f 12 / f < -0.0 ····· (3) 1.00 < P W12 ×f < 4.00 ····· (4) -1.80 < f 1 / f < -0.10 ····· (5) However, f 12 : The combined focal length of the first lens L1 and the second lens L2 f: The focal length of the optical system when focused at infinity P W12 : (N L1 -1) / R L1r -(N L2 -1) / R L2f N L1 : The refractive index of the first lens L1 at the d-line R L1r : The radius of curvature of the lens surface on the image side of the first lens L1 N L2 : The refractive index of the second lens L2 at the d-line R L2f : The radius of curvature of the lens surface on the object side of the second lens L2 f 1 : The focal length of the first lens L1

[0011] Also, in order to solve the above problems, an imaging device according to an aspect of the present invention includes the above optical system and an imaging element provided on the image side of the optical system for converting an optical image formed by the optical system into an electrical signal.

Effects of the Invention

[0012] According to one aspect of the present invention, it is possible to realize a small-sized optical system and an imaging device that can maintain high resolution from the center to the periphery of the screen at a wide angle.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of an optical system and an imaging device according to an embodiment of the present invention will be described. More specifically, this embodiment relates to an inexpensive and lightweight optical system suitable for optical systems of in-vehicle lenses, digital input / output devices such as drone single-focus lenses, etc. using solid-state imaging devices and the like. However, the optical system and the imaging device described below are one aspect of the optical system and the imaging device according to the present invention, and the optical system and the imaging device according to the present invention are not limited to the following aspects. In this specification, a configuration expressed as "consisting of" means that it substantially includes only that configuration. Also, in this specification, a numerical range indicated by "~" means a numerical range including the numerical values at both ends.

[0015] 1. Optical System 1-1. Optical Configuration The optical system according to an embodiment of the present invention consists of a first lens group and a second lens group. The first lens group consists of, in order from the object side, a first lens L1 having a convex surface on the object side and a negative refractive power, and a meniscus-shaped second lens L2 having a concave surface facing the object side. The second lens group has a positive refractive power. Also, the total number of lenses in the optical system is 5 to 10.

[0016] Note that in this specification, a "lens group" may be composed of two or more lenses.

[0017] In addition, in this specification, the lens group may include a cemented lens. When the lens group includes a cemented lens, the number of lens elements is counted by counting the lenses that are cemented together. Examples of cemented lenses include cemented lenses in which a plurality of lenses are integrated without an air gap. In this case, only the plurality of lenses constituting the cemented lens are counted. Another example of a cemented lens is a cemented lens in which a plurality of lenses joined by an adhesive having a very thin thickness that has substantially no optical effect are integrated. In this case, the adhesive is not counted as a lens.

[0018] In addition, the lens group may include a composite lens in which a single lens element and resin are integrated. For example, a composite lens in which a single lens element and resin are integrated is counted as one lens element.

[0019] (1) First lens group The first lens group is the lens group disposed closest to the object side in the optical system. The first lens group consists of a first lens L1 and a second lens L2.

[0020] The first lens L1 is the lens disposed closest to the object side in the optical system, has a convex surface on the object side, and has a negative refractive power. The fact that the first lens L1 has a negative refractive power serves to widen the angle of view and reduce the front lens diameter (the diameter of the lens disposed closest to the object side).

[0021] The second lens L2 is the second lens from the object side in the optical system and is a meniscus-shaped lens with a concave surface facing the object side. The second lens L2 may have a negative refractive power or a positive refractive power. The fact that the second lens L2 has a negative refractive power, that is, the first lens group consists of two lenses with negative refractive powers, is preferable because it can realize a wider angle of view of the optical system and disperse the negative power between the first lens L1 and the second lens L2. By dispersing the negative power between the first lens L1 and the second lens L2, coma aberration or field curvature can be dispersed between the first lens L1 and the second lens L2.

[0022] (2) Second lens group The second lens group is a lens group disposed closer to the image plane side than the first lens group. That is, the second lens group is a lens group including all lenses from the third lens L3 to the final lens Lf, which are disposed closer to the image plane side than the second lens L2. The second lens group has a positive refractive power. The second lens group preferably has at least two lenses having a positive refractive power as long as it has a positive refractive power as a whole. The fact that the second lens group has a positive refractive power is preferable from the viewpoint of appropriately correcting the astigmatism generated in the first lens group and having an advantageous effect on wide-angle conversion.

[0023] The third lens L3 is the lens disposed closest to the object side in the second lens group. The third lens L3 preferably has a positive refractive power. The fact that the third lens L3 has a positive refractive power is preferable from the viewpoint that the light beam diameters on the optical axis and in the periphery enlarged by the first lens group having the first lens L1 with a negative refractive power can be made smaller on the image plane side than the third lens L3. Further, the fact that the third lens L3 has a positive refractive power is preferable from the viewpoint of appropriately correcting the distortion aberration or astigmatism generated in the first lens L1 with the refractive power of the second lens L2 located closer to the image side within the first lens group and having an advantageous effect on high resolution or wide-angle conversion at the peripheral image height. Further, it is preferable that the object side of the third lens L3 has a convex surface from the viewpoint of enhancing the effect.

[0024] The fact that the third lens L3 has a negative refractive power is advantageous for dispersing the necessary negative power in the first lens group and suppressing the occurrence of coma aberration.

[0025] The third lens L3 preferably has convex surfaces on both the object side and the image plane side. The fact that the third lens L3 has convex surfaces on both the object side and the image plane side is preferable from the viewpoint that when the third lens L3 has a strong power, it becomes possible to divide the power between the object side surface and the image plane side surface. By dividing the power between the object side surface and the image plane side surface, the aberration correction can be divided between the object side surface and the image plane side surface. Therefore, it has the effect of alleviating the abrupt refraction of light rays and suppressing the occurrence of higher-order aberrations.

[0026] The second lens group preferably has at least one lens with negative refractive power. The fact that the second lens group has at least one lens with negative refractive power is preferable from the viewpoint of appropriately correcting chromatic aberration. Further, the second lens group preferably has two or more lenses with positive refractive power. The fact that the second lens group has two or more lenses with positive refractive power is preferable from the viewpoint of appropriately correcting field curvature.

[0027] In the second lens group, it is preferable that a lens with negative refractive power is arranged on the object side of the lens with positive refractive power. Since arranging the entrance pupil position as close to the object side as possible leads to miniaturization in the radial direction, such an arrangement is preferable from the viewpoint of realizing miniaturization of the optical system. For this reason, in the second lens group, it is preferable to arrange a lens with negative refractive power on the object side of at least one of the lenses with positive refractive power.

[0028] Further, in the second lens group, from the viewpoint of realizing miniaturization of the optical system, the lens with negative refractive power preferably has a refractive index at d-line greater than 1.65, and more preferably greater than 1.75.

[0029] Also, in the second lens group, it is preferable to arrange a lens with negative refractive power on the image side of the lens with positive refractive power. Such an arrangement is preferable from the viewpoint of appropriately correcting chromatic aberration on the optical axis and in the vicinity of the optical axis. Among them, it is preferable to arrange a lens with positive refractive power on the object side of the lens with the most negative refractive power on the image side of the second lens group.

[0030] Among the second lens group, the third lens L3, which is the one closest to the object side, has a large difference in the incident angle characteristics between off-axis rays and on-axis rays. Therefore, the off-axis chromatic aberration correction effect is higher than that on the axis. For this reason, it is preferable that the lenses having positive refractive power included in the second lens group are made of relatively low-dispersion glass. Further, from the viewpoint of appropriately correcting chromatic aberration, the Abbe number of the lenses having positive refractive power included in the second lens group at the d-line is preferably greater than 45, and more preferably greater than 48.

[0031] The final lens Lf is the lens closest to the image plane side of the second lens group. The final lens Lf preferably has positive refractive power. The fact that the final lens Lf has positive refractive power is preferable from the viewpoint that the incident angle to the image plane can be reduced, thereby reducing the angle dependence. Also, for this reason, the peripheral light quantity can be maintained high up to the periphery.

[0032] The second lens group preferably has a pair of combined lenses on the image plane side adjacent to the aperture stop, and the combined lens preferably consists of one lens having positive refractive power and one lens having negative refractive power. The order of the lenses does not matter, as long as the two lenses are joined or the two lenses are adjacent to each other with an air gap therebetween. Such a configuration is preferable from the viewpoint of appropriately correcting axial chromatic aberration. Further, the combined lens is preferably a cemented lens from the viewpoint of reducing the assembly sensitivity and realizing the shortening of the overall optical length of the optical system.

[0033] (3) Aperture Stop The optical system preferably has a diaphragm. Here, the diaphragm refers to the diaphragm that defines the light beam diameter of the optical system, that is, the diaphragm that defines the F-number (Fno) of the optical system. The diaphragm is preferably disposed on the image plane side of the third lens L3 in the second lens group. Such an arrangement can reduce the diaphragm diameter and can make the light beam diameters on the optical axis and in the periphery smaller than the diaphragm on the image plane side. Making the light beam diameters on the optical axis and in the periphery smaller is advantageous in suppressing the aberration correction function between adjacent lenses. Further, the diaphragm is preferably disposed so as to be sandwiched between lenses having positive refractive power. Such an arrangement is preferable from the viewpoint of being able to reduce the effective diameters of the lenses on the object side and the image plane side of the diaphragm. Also, it becomes possible to make the effective diameters of both surfaces on the object side of the lens having positive refractive power on the object side of the diaphragm and on the image plane side of the lens having positive refractive power on the image plane side of the diaphragm relatively small with respect to the diaphragm surface, and it works advantageously in suppressing the aberration correction function between adjacent lenses.

[0034] (4) Lens group configuration The optical system is composed of only two lens groups, namely, a first lens group and a second lens group, in order from the object side. No other lens group is included between the first lens group and the second lens group. The optical system of the present embodiment may further include other optical elements other than the above lens groups within the range where the effects of the present embodiment can be obtained.

[0035] The total number of lenses in the optical system is 5 to 10. The fact that the optical system is composed of 5 or more lenses is preferable from the viewpoint of realizing a wide angle and high resolution. Also, the fact that the optical system is composed of 10 or fewer lenses is preferable from the viewpoint of realizing miniaturization of the optical system. The first lens group is composed of only two lenses, namely, the first lens L1 and the second lens L2, as described above. Therefore, the second lens group is composed of 3 to 8 lenses.

[0036] 1-2. Operation during focusing In the present embodiment, during focusing, the entire optical system is extended. The interval between each lens group does not change.

[0037] 1-3. Expressions Representing the Conditions of the Optical System The optical system according to the present embodiment employs the above-described configuration and preferably satisfies at least one of the following expressions.

[0038] 1.55 < (C L1r - C L2f ) × f < 2.55 ····· (1) However, C L1r : Curvature of the lens surface on the image side of the first lens L1 C L2f : Curvature of the lens surface on the object side of the second lens L2 f: Focal length when the optical system is focused at infinity

[0039] In the expression (1), (C L1r - C L2f ) is equivalent to |C L1r | + |C L2f | and represents the sum of the curvature of the lens surface on the image side of the first lens L1 and the curvature of the lens surface on the object side of the second lens L2. Note that C L1r is equivalent to the reciprocal (1 / R L1r ) of the radius of curvature of the lens surface on the image side of the first lens L1, and C L2f is equivalent to the reciprocal (1 / R L2f ) of the radius of curvature of the lens surface on the object side of the second lens L2. The expression (1) shows the value obtained by normalizing the sum of the curvature of the lens surface on the image side of the first lens L1 and the curvature of the lens surface on the object side of the second lens L2 with the focal length when the optical system is focused at infinity. Satisfying the expression (1) is preferable from the viewpoint of maintaining appropriate field curvature and realizing wide-angleization. When the lower limit of the expression (1) is exceeded, the curvature of the lens surface on the image side of the first lens L1 and the curvature of the lens surface on the object side of the second lens L2 are small, so the Petzval sum is large and it may be difficult to appropriately correct the image plane. Also, when the upper limit of the expression (1) is exceeded, the field curvature correction may become excessive.

[0040] From the viewpoint of reducing the Petzval sum and appropriately correcting the field curvature, (C L1r - C L2f)×f is more preferably greater than 1.60, and even more preferably greater than 1.63. Further, from the viewpoint of preventing an excess of field curvature correction, (C L1r -C L2f )×f is more preferably less than 2.40, and even more preferably less than 2.30.

[0041] The optical system according to the present embodiment preferably satisfies the following equation. 0.65 < D L12 / f < 5.00 ····· (2) However, D L12 : The distance on the optical axis between the lens surface on the image plane side of the first lens L1 and the lens surface on the object side of the second lens L2 when the optical system is focused at infinity f: The focal length when the optical system is focused at infinity

[0042] Equation (2) is an equation for defining the distance on the optical axis between the lens surface on the image plane side of the first lens L1 and the lens surface on the object side of the second lens L2 when the optical system is focused at infinity with respect to the focal length of the optical system when focused at infinity. Satisfying Equation (2) is preferable from the viewpoint of appropriately maintaining field curvature and reducing the Petzval sum to appropriately correct field curvature. When the lower limit of Equation (2) is exceeded, the Petzval sum may be large and it may be difficult to appropriately correct field curvature. Further, when the upper limit of Equation (2) is exceeded, field curvature correction may be excessive.

[0043] From the viewpoint of reducing the Petzval sum and appropriately correcting field curvature, D L12 / f is more preferably greater than 0.67, even more preferably greater than 0.70, and particularly preferably greater than 0.75. Further, from the viewpoint of preventing an excess of field curvature correction, D L12 / f is more preferably less than 3.50, even more preferably less than 2.80, and particularly preferably less than 2.00.

[0044] The optical system according to the present embodiment preferably satisfies the following equation. -2.3 < f 12 / f < -0.0·····(3) However, f 12 : The combined focal length of the first lens L1 and the second lens L2 f: The focal length when the optical system is focused at infinity

[0045] Equation (3) represents an equation obtained by normalizing the combined focal length of the first lens L1 and the second lens L2 with the focal length when the optical system is focused at infinity. Satisfying Equation (3) is preferable from the viewpoints of having a large negative refractive power, achieving wide-angle conversion, and appropriately correcting field curvature. When the lower limit of Equation (3) is not met, the negative refractive power may be small, making it difficult to achieve wide-angle conversion. Also, when the upper limit of Equation (3) is exceeded, it may be difficult to appropriately correct field curvature.

[0046] From the viewpoint of appropriately correcting field curvature, f 12 / f is more preferably less than -0.3, even more preferably less than -0.5, and particularly preferably less than -0.7.

[0047] The optical system according to this embodiment preferably satisfies the following equation. 1.00 < P W12 ×f < 4.00·····(4) However, P W12 : (N L1 -1) / R L1r -(N L2 -1) / R L2f N L1 : The refractive index of the first lens L1 at the d-line R L1r : The radius of curvature of the lens surface on the image side of the first lens L1 N L2 : The refractive index of the second lens L2 at the d-line R L2f : The radius of curvature of the lens surface on the object side of the second lens L2 f: The focal length when the optical system is focused at infinity

[0048] Equation (4) is an equation representing the power of the air lens between the lens surface on the image plane side of the first lens L1 and the lens surface on the object side of the second lens L2. Satisfying Equation (4) is preferable from the viewpoint that the influence of the power of the air lens becomes large and the field curvature is appropriately corrected. When it is below the lower limit of Equation (4), the influence of the power of the air lens may become small. Also, when it exceeds the upper limit of Equation (4), it may become difficult to appropriately correct the field curvature.

[0049] From the viewpoint that the influence of the power of the air lens becomes large, P W12 ×f is more preferably greater than 1.05. Also, from the viewpoint of appropriately correcting the field curvature, P W12 ×f is more preferably less than 3.00, even more preferably less than 2.70, and particularly preferably less than 2.50.

[0050] The optical system according to the present embodiment preferably satisfies the following equation. -1.80 < f 1 / f < -0.10 ····· (5) However, f 1 : Focal length of the first lens L1 f: Focal length when the optical system is focused at infinity

[0051] Equation (5) represents an equation obtained by normalizing the focal length of the first lens L1 with the focal length when the optical system is focused at infinity. Satisfying Equation (5) is preferable from the viewpoints of compensating for insufficient correction of the field curvature, realizing wide-angle conversion, reducing the effective diameter of the first lens L1, and keeping distortion small. When it is below the lower limit of Equation (5), the power of the first lens L1 becomes too weak, it becomes impossible to compensate for insufficient correction of the field curvature, it becomes difficult to realize wide-angle conversion, and the effective diameter of the first lens L1 may become too large. Also, when it exceeds the upper limit of Equation (5), the power of the first lens L1 becomes too strong, and it may become difficult to keep distortion small.

[0052] From the viewpoints of compensating for insufficient correction of the field curvature, realizing wide-angle conversion, and reducing the effective diameter of the first lens L1, f1 It is more preferable that / f is greater than -1.76, even more preferably greater than -1.72, and particularly preferably greater than -1.68. Also, from the viewpoint of keeping distortion small, f 1 / f is more preferably less than -0.80, even more preferably less than -1.20, and particularly preferably less than -1.30.

[0053] The optical system according to this embodiment preferably satisfies the following formula. -3.40 < R L2f / f < 0.00 ····· (6) However, R L2f : The radius of curvature of the lens surface on the object side of the second lens L2 f: The focal length when the optical system is focused at infinity

[0054] Equation (6) represents an equation obtained by normalizing the radius of curvature of the lens surface on the object side of the second lens L2 with the focal length when the optical system is focused at infinity. Satisfying Equation (6) is preferable from the viewpoint of appropriately correcting the field curvature generated on the lens surface on the object side of the first lens L1 and being able to increase the angle of the chief ray to the first lens L1 in advance to achieve wide-angleization. When below the lower limit of Equation (6), the power of the lens surface on the object side of the second lens L2 becomes too small, and the angle of the chief ray cannot be increased in advance, which may make it difficult to achieve wide-angleization. Also, when exceeding the upper limit of Equation (6), it may be difficult to appropriately correct the field curvature generated on the lens surface on the object side of the first lens L1.

[0055] From the viewpoint of achieving wide-angleization, R L2f / f is more preferably greater than -3.00, even more preferably greater than -1.90. Also, from the viewpoint of appropriately correcting the field curvature generated on the lens surface on the object side of the first lens L1, R L2f / f is more preferably less than -0.10, even more preferably less than -0.25.

[0056] The optical system according to this embodiment preferably satisfies the following formula. 1.30 < f 2g / f < 2.70 ····· (7) However, f 2g : Focal length of the second lens group f: Focal length when the optical system is focused at infinity

[0057] Equation (7) represents an equation obtained by normalizing the focal length of the second lens group with the focal length when the optical system is focused at infinity. Satisfying Equation (7) is preferable from the viewpoints of ensuring sufficient back focus (BF) and realizing shortening of the overall optical length of the optical system. When the lower limit of Equation (7) is exceeded, it may not be possible to ensure sufficient back focus. Also, when the upper limit of Equation (7) is exceeded, the positive refractive power of the second lens group becomes too small, and it may become difficult to realize shortening of the overall optical length of the optical system.

[0058] From the viewpoint of ensuring sufficient back focus, f 2g / f is more preferably greater than 1.40, and even more preferably greater than 1.50. Also, from the viewpoint of realizing shortening of the overall optical length of the optical system, f 2g / f is more preferably less than 2.60, and even more preferably less than 2.55.

[0059] The optical system according to this embodiment preferably satisfies the following equation. 5.0 < oal / f < 8.0 ····· (8) However, oal: Overall optical length of the optical system f: Focal length when the optical system is focused at infinity

[0060] Equation (8) represents an equation obtained by normalizing the overall optical length of the optical system with the focal length when the optical system is focused at infinity. In the present embodiment, the overall optical length of the optical system is the distance on the optical axis from the object-side surface of the first lens L1 in the optical system to the image plane. Satisfying Equation (8) is preferable from the viewpoint of ensuring sufficient back focus and realizing shortening of the overall optical length of the optical system. When the value is below the lower limit of Equation (8), it may not be possible to ensure sufficient back focus. When the value exceeds the upper limit of Equation (8), it may be difficult to realize shortening of the overall optical length of the optical system.

[0061] From the viewpoint of ensuring sufficient back focus, it is more preferable that oal / f is greater than 5.5, and further preferably greater than 5.8. From the viewpoint of realizing shortening of the overall optical length of the optical system, it is more preferable that oal / f is less than 7.0, and further preferably less than 6.7.

[0062] The optical system according to the present embodiment preferably satisfies the following equation. -2.40 < f 1g / f < -0.75 ····· (9) However, f 1g : Focal length of the first lens group f: Focal length when the optical system is focused at infinity

[0063] Equation (9) represents an equation obtained by normalizing the focal length of the first lens group with the focal length when the optical system is focused at infinity. Satisfying Equation (9) is preferable from the viewpoint of ensuring sufficient back focus and realizing shortening of the overall optical length of the optical system. When the value is below the lower limit of Equation (9), it may not be possible to ensure sufficient back focus. When the value exceeds the upper limit of Equation (9), the absolute value of the negative refractive power of the first lens group becomes too large, and it may be difficult to realize shortening of the overall optical length of the optical system.

[0064] From the viewpoint of ensuring sufficient back focus, f 1g / f is more preferably greater than -2.35. Also, from the perspective of realizing a reduction in the overall optical length of the optical system, f 1g / f is more preferably less than -0.80, and even more preferably less than -0.85.

[0065] The optical system according to this embodiment preferably satisfies the following formula. 0.50 < R L1r / f < 10.00 ····· (10) However, R L1r : The radius of curvature of the lens surface on the image plane side of the first lens L1 f: The focal length of the optical system when focused at infinity

[0066] Equation (10) represents an equation obtained by normalizing the radius of curvature of the lens surface on the image plane side of the first lens L1 with the focal length of the optical system when focused at infinity. Satisfying equation (10) is preferable from the perspective of obtaining distortion that can satisfy an appropriate projection method and realizing a reduction in the overall optical length of the optical system. When the lower limit of equation (10) is exceeded, it may be difficult to obtain distortion that can satisfy an appropriate projection method and to realize a reduction in the overall optical length of the optical system. Also, when the upper limit of equation (10) is exceeded, the positive refractive power of the lens surface on the image plane side of the first lens L1 becomes too large, and it may be difficult to realize a reduction in the overall optical length of the optical system.

[0067] From the perspective of obtaining distortion that can satisfy an appropriate projection method and realizing a reduction in the overall optical length of the optical system, R L1r / f is more preferably greater than 0.53, and even more preferably greater than 0.55. Also, from the perspective of realizing a reduction in the overall optical length of the optical system, R L1r / f is more preferably less than 2.00, and even more preferably less than 1.50.

[0068] The optical system according to this embodiment preferably satisfies the following formula. 1.70 < N L1 < 2.00 ····· (11) However, NL1 : Refractive index of the first lens L1 for the d-line

[0069] Equation (11) represents the refractive index of the first lens L1 for the d-line. Satisfying Equation (11) means that it is relatively high-refractive-index glass compared to the first lens L1 having a negative refractive power. Satisfying Equation (11) is preferable from the viewpoint of appropriately correcting the Petzval sum and appropriately correcting distortion or coma aberration. When it is below the lower limit of Equation (11), it may be difficult to appropriately correct the Petzval sum. Also, when it exceeds the upper limit of Equation (11), it may become difficult to appropriately correct distortion or coma aberration.

[0070] From the viewpoint of appropriately correcting the Petzval sum, N L1 is more preferably greater than 1.72, and even more preferably greater than 1.74. Also, N L1 is more preferably less than 1.95, and even more preferably less than 1.92.

[0071] The optical system according to the present embodiment preferably satisfies the following equation. 1.60 < N L3 < 2.00 ····· (12) N L3 : Refractive index of the third lens L3 for the d-line

[0072] Equation (12) represents the refractive index of the third lens L3 for the d-line. Satisfying Equation (12) means that the third lens L3 has a positive refractive power and is relatively high-refractive-index glass. Satisfying Equation (12) is preferable from the viewpoint of appropriately correcting the coma aberration generated in the first lens group having a negative refractive power. When it is below the lower limit of Equation (12), it may be difficult to appropriately correct the coma aberration generated in the first lens group having a negative refractive power. When it exceeds the upper limit of Equation (12), the correction of the coma aberration generated in the first lens group having a negative refractive power may become excessive.

[0073] From the viewpoint of appropriately correcting the coma aberration generated in the first lens group having a negative refractive power, NL3 is more preferably greater than 1.62, even more preferably greater than 1.64, and particularly preferably greater than 1.70. Also, from the viewpoint of preventing overcorrection of coma aberration generated in the first lens group having negative refractive power, N L3 is more preferably less than 1.96, even more preferably less than 1.94, and particularly preferably less than 1.93.

[0074] The optical system according to the present embodiment preferably satisfies the following formula. 0.01 < D L23 / f < 0.05 ····· (13) However, D L23 : The distance on the optical axis between the lens surface on the image plane side of the second lens L2 and the lens surface on the object side of the third lens L3 when the optical system is focused at infinity f: The focal length when the optical system is focused at infinity

[0075] Formula (13) represents a formula obtained by normalizing the distance on the optical axis between the lens surface on the image plane side of the second lens L2 and the lens surface on the object side of the third lens L3 when the optical system is focused at infinity by the focal length when the optical system is focused at infinity. Satisfying formula (13) is preferable from the viewpoints of maintaining a non-colliding interval during lens assembly and converging the light beam diameter that has spread too much in the first lens group with the third lens L3 on the image plane side adjacent to the second lens L2 with a close distance to appropriately correct aberrations. If it is below the lower limit of formula (13), it may not be possible to maintain a non-colliding interval during lens assembly. Also, if it exceeds the upper limit of formula (13), it may not be possible to appropriately correct aberrations by converging the light beam diameter that has spread too much in the first lens group with the third lens L3 on the image plane side adjacent to the second lens L2 with a close distance.

[0076] From the viewpoint of maintaining a non-colliding interval during lens assembly, D L23 / f is more preferably greater than 0.013, and even more preferably greater than 0.015. Further, from the viewpoint of converging the light beam diameter that has spread too much in the first lens group with the third lens L3 on the image plane side adjacent to the second lens L2 arranged at a short distance to appropriately correct aberration, D L23 / f is more preferably less than 0.030, and even more preferably less than 0.025.

[0077] The optical system according to the present embodiment preferably satisfies the following formula. 1.5 < f Lf / f < 4.5 ····· (14) However, f Lf : Focal length of the final lens Lf f: Focal length when the optical system is focused at infinity

[0078] Equation (14) represents an equation obtained by normalizing the focal length of the final lens Lf, which is the lens closest to the image plane in the second lens group, with the focal length when the optical system is focused at infinity. Satisfying equation (14) is preferable from the viewpoint of preventing the incident angle of the sensor from increasing, appropriately maintaining the peripheral light quantity, and realizing shortening of the length of the lens barrel and the overall optical length of the optical system. When the lower limit of equation (14) is exceeded, the incident angle of the sensor may become too large, making it difficult to appropriately maintain the peripheral light quantity. Also, when the upper limit of equation (14) is exceeded, it may be difficult to increase the back focus, and it may become difficult to realize shortening of the length of the lens barrel and the overall optical length of the optical system.

[0079] From the viewpoint of preventing the incident angle of the sensor from increasing and appropriately maintaining the peripheral light quantity, f Lf / f is more preferably greater than 1.9, and even more preferably greater than 2.1. Further, from the viewpoint of realizing shortening of the length of the lens barrel and the overall optical length of the optical system, f Lf / f is more preferably less than 4.0, and even more preferably less than 3.7.

[0080] 2. Imaging device Next, an imaging device according to an embodiment of the present invention will be described. The imaging device includes the optical system according to the above embodiment, and an imaging element provided on the image plane side of the optical system for converting the optical image formed by the optical system into an electrical signal. The optical system in the present embodiment is, for example, a single-focus lens.

[0081] Here, there is no limitation on the imaging element, and solid-state imaging elements such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors, silver halide films, infrared cut filters (IRCF), etc. can also be used. The imaging device according to the present embodiment is suitable for imaging devices using the above solid-state imaging elements such as FA cameras, digital cameras, and video cameras. Further, the imaging device may be a lens-fixed imaging device in which the lens is fixed to the housing, or may be an interchangeable-lens imaging device such as a single-lens reflex camera or a mirrorless single-lens camera.

[0082] FIG. 19 is a diagram schematically showing an example of the configuration of the imaging device according to the present embodiment. As shown in FIG. 19, the mirrorless single-lens camera 1 has a main body 2 and a lens barrel 3 detachably attached to the main body 2. The mirrorless single-lens camera 1 is an aspect of the imaging device.

[0083] The lens barrel 3 has an optical system 30. The optical system 30 includes a first lens group 31 and a second lens group 32, and is configured to satisfy, for example, the above-described formulas (1) and (2). Note that an aperture 33 is disposed in the second lens group 32.

[0084] The first lens group 31 includes, in order from the object side, a first lens L1 having a convex surface on the object side and a negative refractive power, and a meniscus-shaped second lens L2 having a concave surface facing the object side, and the second lens group 32 has a positive refractive power.

[0085] The main body 2 has a CCD sensor 21 as an imaging element and an infrared cut filter 22. The CCD sensor 21 is disposed at a position in the main body 2 where the optical axis OA of the optical system 30 in the lens barrel 3 attached to the main body 2 serves as the central axis. The main body 2 may have a parallel flat plate having substantially no refractive power, such as a cover glass, instead of the infrared cut filter 22.

[0086] The imaging device according to the present embodiment preferably includes an image processing unit that electrically processes the captured image data acquired by the imaging element to change the shape of the captured image, and an image correction data holding unit that holds, for example, image correction data and an image correction program used for performing zoom processing for enlarging a main part of the image on the captured image data in the image processing unit.

[0087] When the optical system is miniaturized, distortion (aberration) of the shape of the captured image formed on the imaging surface is likely to occur. At this time, it is preferable to correct the distortion of the shape of the captured image. For example, the correction can be performed by causing the image correction data holding unit to hold distortion correction data for correcting the distortion of the shape of the captured image in advance, and using the distortion correction data held in the image correction data holding unit in the image processing unit. According to such an imaging device, it is possible to further miniaturize the optical system, obtain a beautiful captured image, and miniaturize the entire imaging device.

[0088] Furthermore, in the imaging device according to the present embodiment, it is preferable to cause the image correction data holding unit to hold magnification chromatic aberration correction data in advance. Also, in the image processing unit, it is preferable to perform magnification chromatic aberration correction of the captured image using the magnification chromatic aberration correction data held in the image correction data holding unit. By correcting the magnification chromatic aberration, that is, the chromatic aberration of distortion, by the image processing unit, it is possible to reduce the number of lenses constituting the optical system. Therefore, according to such an imaging device, it is possible to further miniaturize the optical system.

[0089] The optical system according to this embodiment can be configured as a compact optical system, and in imaging, it can maintain a wide angle and high resolution from the center to the periphery of the image. Therefore, the optical system according to this embodiment is suitably used as the optical system of digital input / output devices such as in-vehicle lenses using solid-state imaging devices and drone single-focus lenses. Since the imaging device according to this embodiment includes the optical system, by providing a zoom function by image processing as necessary, it is suitably used as an imaging device for in-vehicle use or drones. Such an imaging device according to this embodiment can realize the imaging functions required for in-vehicle cameras applicable to level 3 automated driving in automobiles.

[0090] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

Example

[0091] An example of the present invention will be described below.

[0092] An example of the present invention will be described below. In the following tables, all units of length are "mm" and all units of the angle of view are "°". Also, "E-a" means "×10 -a ".

[0093] [Example 1] FIG. 1 is a diagram schematically showing the optical configuration of the optical system of Example 1 at infinite focus. The optical system of Example 1 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, a diaphragm S, a fourth lens L4 having a positive refractive power, a fifth lens L5 having a negative refractive power, and a sixth lens L6 having a positive refractive power. The sixth lens L6 corresponds to the aforementioned final lens Lf. "IMG" shown in FIG. 1 is an image plane (imaging plane), and an infrared cut filter IRCF is disposed between the sixth lens L6 and the image plane IMG.

[0094] The configurations of the respective lens groups will be described below. The first lens group is composed of a first lens L1, which is a negative meniscus lens with a convex shape on the object side, and a second lens L2, which is a negative meniscus lens with a concave shape on the object side, in order from the object side. The second lens group is composed of a third lens L3, which is a biconvex lens, a diaphragm S, a fourth lens L4, which is a biconvex lens, a fifth lens L5, which is a biconcave lens, and a sixth lens L6, which is a biconvex lens, in order from the object side. The fourth lens L4 and the fifth lens L5 are joined together.

[0095] Next, an example applying specific numerical values of the optical system will be described. Table 1 shows the surface data of the optical system of Example 1.

[0096] In the table of surface data in the examples of the present invention, "Surface No." is the order of the lens surfaces counted from the object side, "r" is the radius of curvature of the lens surface, "d" is the interval on the optical axis between the lens surfaces, "Nd" is the refractive index with respect to the d-line (wavelength λ = 587.56 nm), and "vd" represents the Abbe number with respect to the d-line. In addition, the display of "S" in the surface number indicates that it is a diaphragm, and the display of "*" indicates that the lens surface is an aspherical surface.

[0097] Note that "INF" of the radius of curvature means a plane. In Table 1, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 14 are the surface numbers of the second lens group, and No. 8 represents the diaphragm. Nos. 15 and 16 represent the infrared cut filter IRCF.

[0098] [Table 1] Surface No. r d Nd vd 1 INF 2* 8.407 1.500 1.8820 37.20 3* 3.641 6.898 4* -6.240 3.784 1.8513 40.10 5* -9.136 0.100 6* 9.267 3.921 1.7730 49.50 7* -77.737 4.088 8S 0.000 0.390 9 14.790 2.958 1.6180 63.40 10 -5.250 0.000 11 -5.250 0.900 1.8052 25.46 12 38.433 2.936 13* 7.794 3.187 1.5920 67.02 14* -100.000 0.500 15 0.000 0.500 1.5163 64.14 16 0.000 3.324

[0099] Table 2 shows the specification table of the optical system of Example 1. In the said specification table, "f" represents the focal length when the optical system is focused at infinity, "Fno." represents the F-number, "OBJ" represents the object distance, "ω" represents the semi-field angle, "Cra" represents the chief ray incidence angle, and "Y" represents the effective image height respectively.

[0100] [Table 2] f 5.331 Fno 1.850 OBJ INF ω 54.9 Cra 9.2 Y 5.17

[0101] Table 3 is a table showing the aspherical coefficients of each aspherical surface in the optical system of Example 1. The aspherical coefficients in the said table are the values when each aspherical shape is defined by the following formula.

[0102] [Formula] X(Y) = CY 2 / [1+{1-(1+Κ)·C 2 Y 2} 1 / 2 +A4·Y 4 +A6·Y 6 +A8·Y 8 +A10·Y 10

[0103] In the above formula, "X" is the displacement amount from the reference plane in the optical axis direction, "C" is the curvature at the surface vertex, "Y" is the height from the optical axis in the direction perpendicular to the optical axis, "Κ" is the conic coefficient, and "An" is the aspherical coefficient of the nth order.

[0104] [Table 3] Surface No. k A4 A6 2 0.000000 -6.661500E-04 4.611810E-06 3 0.346700 -6.387730E-04 -1.037660E-05 4 0.483500 7.346440E-04 -2.175150E-05 5 0.647200 2.211580E-04 -4.890540E-06 6 0.322400 -5.481460E-05 2.635330E-06 7 -8.900000 -8.899630E-05 8.167050E-06 13 0.787300 -4.265000E-04 1.084120E-05 14 -9.000000 -1.653140E-04 1.851110E-05 Surface No. A8 A10 2 -3.495280E-08 2.962550E-10 3 -1.071340E-07 -1.877370E-08 4 2.498880E-07 -5.519630E-09 5 3.467870E-08 -8.426310E-11 6 1.646760E-08 -4.373810E-10 7 -1.585050E-07 1.135030E-09 13 -3.107950E-07 3.922260E-09 14 -6.186870E-07 8.579220E-09

[0105] Table 4 shows the focal lengths of the respective lenses constituting the optical system of Example 1.

[0106] [Table 4] Lens No Focal Length 1 -8.542 2 -57.957 3 10.926 4 6.644 5 -5.684 6 12.349

[0107] Also, Fig. 2 is a diagram showing the longitudinal aberration at infinity focus of the optical system of Example 1. The diagrams showing the longitudinal aberration shown in each figure are, in order from the left side toward the drawing, spherical aberration (mm), astigmatism (mm), and distortion (%) respectively.

[0108] In the diagram representing spherical aberration, the vertical axis is the ratio to the open F value, and the horizontal axis is defocus. In the diagram representing spherical aberration, the solid line indicates the spherical aberration at the d line (wavelength λ = 587.6 nm), the chain line indicates the spherical aberration at the g line (wavelength λ = 435.8 nm), and the dotted line indicates the spherical aberration at the C line (wavelength λ = 656.3 nm).

[0109] In the diagram representing astigmatism, the vertical axis is the incident angle, and the horizontal axis is defocus. Note that "Angle" in the aberration diagram represents the angle of view. In the diagram representing astigmatism, the solid line indicates the sagittal image plane (S) for the d line, and the four-dot chain line indicates the meridional image plane (T) for the d line.

[0110] In the diagram representing distortion, the vertical axis is the incident angle, and the horizontal axis is %. Note that "Angle" in the aberration diagram represents the angle of view. Since the matters regarding these longitudinal aberration diagrams are the same in the longitudinal aberration diagrams shown in other examples, the description will be omitted below.

[0111] [Example 2] The optical configuration of the optical system in Example 2 at infinity focus is schematically shown in FIG. 3, and the longitudinal aberration of the optical system in Example 2 at infinity focus is shown in FIG. 4. The optical system of Example 2 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, a diaphragm S, a fourth lens L4 having a positive refractive power, a fifth lens L5 having a negative refractive power, and a sixth lens L6 having a positive refractive power. The sixth lens L6 corresponds to the aforementioned final lens Lf. An infrared cut filter IRCF is disposed between the sixth lens L6 and the image plane IMG.

[0112] Hereinafter, the configuration of each lens group will be described. The first lens group includes, in order from the object side, a first lens L1 which is a negative meniscus lens with a convex shape on the object side and a second lens L2 which is a negative meniscus lens with a concave shape on the object side. The second lens group includes, in order from the object side, a third lens L3 which is a positive meniscus lens with a convex shape on the object side, a diaphragm S, a fourth lens L4 which is a biconvex lens, a fifth lens L5 which is a negative meniscus lens with a convex shape on the image plane side, and a sixth lens L6 which is a biconvex lens. The fourth lens L4 and the fifth lens L5 are joined together.

[0113] Table 5 shows the surface data of the optical system of Example 2. In Table 5, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 14 are the surface numbers of the second lens group, and No. 8 represents the diaphragm. Nos. 15 and 16 represent the infrared cut filter IRCF.

[0114] [Table 5] Surface NO. r d Nd vd 1 INF INF 2* 9.221 1.500 1.8820 37.22 3* 3.863 7.110 4* -6.154 3.904 1.8820 37.22 5* -9.149 0.100 6* 8.127 4.031 1.8513 40.10 7 * 86.305 3.477 8S 0.000 0.100 9 19.863 3.195 1.5935 67.00 10 -4.581 0.000 11 -4.581 0.900 1.8697 20.02 12 -130.673 2.914 13 * 8.755 3.630 1.6889 31.16 14 * -100.000 0.500 15 0.000 0.500 1.5163 64.14 16 0.000 3.139

[0115] Table 6 shows the origin table of the optical system of Example 2. Table 7 is a table showing the aspherical coefficients of each aspherical surface in the optical system of Example 2. Table 8 shows the focal lengths of the respective lenses constituting the optical system of Example 2.

[0116] [Table 6] f 5.332 Fno 1.850 OBJ INF ω 54.9 Cra 9.3 Y 5.17

[0117] [Table 7] Surface No. k A4 A6 2 0.110100 -5.679470E-04 4.108850E-06 3 0.362500 -4.616820E-04 -1.076100E-05 4 0.540800 7.235910E-04 -1.735300E-05 5 0.665300 2.137450E-04 -4.615580E-06 6 0.522800 1.184160E-05 1.874130E-06 7 -9.000000 2.982540E-05 8.564620E-06 13 1.223500 -3.830780E-04 7.440420E-06 14 -2500.000 -1.399210E-04 1.598730E-05 Surface NO. A8 A10 2 -3.401790E-08 2.477320E-10 3 1.389640E-07 -1.729760E-08 4 1.513600E-07 -4.140330E-09 5 2.232200E-08 -4.656680E-12 6 2.891490E-08 -4.527540E-12 7 -1.797910E-07 1.266680E-09 13 -2.323520E-07 3.288970E-09 14 -5.587700E-07 9.439520E-09

[0118] [Table 8] Lens No Focal Length 1 -8.675 2 -54.808 3 10.294 4 6.593 5 -5.477 6 11.846

[0119] [Example 3] The optical configuration of the optical system of Example 3 at infinity focus is schematically shown in FIG. 5, and the longitudinal aberration of the optical system of Example 3 at infinity focus is shown in FIG. 6. The optical system of Example 3 is composed of, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, a diaphragm S, a fourth lens L4 having a positive refractive power, and a fifth lens L5 having a negative refractive power. The fifth lens L5 corresponds to the aforementioned final lens Lf. An infrared cut filter IRCF is disposed between the fifth lens L5 and the image plane IMG.

[0120] The configurations of the respective lens groups will be described below. The first lens group is composed of, in order from the object side, a first lens L1 which is a negative meniscus lens with a convex shape on the object side, and a second lens L2 which is a negative meniscus lens with a concave shape on the object side. The second lens group is composed of, in order from the object side, a third lens L3 which is a biconvex lens, a diaphragm, a fourth lens L4 which is a biconvex lens, and a fifth lens L5 which is a negative meniscus lens with a concave shape on the object side. The fourth lens L4 and the fifth lens L5 are joined together.

[0121] Table 9 shows the surface data of the optical system of Example 3. In Table 9, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 12 are the surface numbers of the second lens group, and No. 8 represents the diaphragm. Nos. 13 and 14 represent the infrared cut filter IRCF.

[0122] [Table 9] Surface NO. r d Nd vd 1 INF INF 2* 10.197 1.500 1.7725 49.62 3* 3.670 3.996 4* -8.083 5.449 1.9044 26.80 5* -14.518 0.100 6* 20.070 4.000 1.4970 81.61 7* -6.697 0.100 8S 0.000 8.009 9 12.018 5.000 1.6168 63.48 10 -7.500 0.000 11 -7.500 0.900 1.9229 20.88 12* -21.667 2.109 13 0.000 0.500 1.5163 64.14 14 0.000 3.337

[0123] Table 10 shows the origin table of the optical system of Example 3. Table 11 is a table showing the aspherical coefficients of each aspherical surface in the optical system of Example 3. Table 12 shows the focal lengths of the respective lenses constituting the optical system of Example 3.

[0124] [Table 10] f 5.485 Fno 1.990 OBJ INF ω 54.9 Cra 10.2 Y 5.21

[0125] [Table 11] Surface No. k A4 A6 2 2.000000 -1.074770E-03 2.622180E-05 3 0.813100 -1.797520E-03 -5.902920E-05 4 3.983300 -1.706300E-04 1.078940E-05 5 5.965300 3.458580E-04 4.963130E-06 6 1.991700 2.050880E-06 -1.963500E-05 7 0.804200 1.003330E-04 -8.712480E-06 12 2.286100 1.441920E-04 -3.753840E-06 Surface No. A8 A10 2 -3.577230E-07 1.853520E-09 3 4.245290E-06 -2.356850E-07 4 7.521900E-07 8.200190E-08 5 1.178080E-06 -5.320810E-10 6 2.001380E-06 -3.238090E-08 7 2.340480E-07 5.136970E-09 12 3.515790E-08 -3.170560E-10

[0126] [Table 12] Lens No. Focal Length 1 -8.248 2 -33.720 3 10.631 4 8.299 5 -12.820

[0127] [Example 4] The optical configuration at infinity focus of the optical system of Example 4 is schematically shown in FIG. 7, and the longitudinal aberration at infinity focus of the optical system of Example 4 is shown in FIG. 8. The optical system of Example 4 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, a diaphragm S, a fourth lens L4 having a positive refractive power, a fifth lens L5 having a negative refractive power, and a sixth lens L6 having a positive refractive power. The sixth lens L6 corresponds to the aforementioned final lens Lf. An infrared cut filter IRCF is disposed between the sixth lens L6 and the image plane IMG.

[0128] Hereinafter, the configuration of each lens group will be described. The first lens group includes, in order from the object side, a first lens L1 which is a negative meniscus lens with a convex shape on the object side and a second lens L2 which is a negative meniscus lens with a concave shape on the object side. The second lens group includes, in order from the object side, a third lens L3 which is a biconvex lens, a diaphragm S, a fourth lens L4 which is a biconvex lens, a fifth lens L5 which is a biconcave lens, and a sixth lens L6 which is a biconvex lens. The fourth lens L4 and the fifth lens L5 are joined together.

[0129] Table 13 shows the surface data of the optical system of Example 4. In Table 13, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 14 are the surface numbers of the second lens group, and No. 8 represents the diaphragm. Nos. 15 and 16 represent the infrared cut filter IRCF.

[0130] [Table 13] Surface NO. r d Nd vd 1 INF INF 2* 12.516 1.500 1.8820 37.20 3* 3.993 5.162 4* -15.729 5.934 1.8513 40.10 5* -79.099 0.100 6* 10.419 3.480 1.8881 36.18 7* -32.897 1.870 8S 0.000 0.363 9 10.906 4.495 1.6180 63.40 10 -6.000 0.000 11 -6.000 0.600 1.8080 23.82 12 20.851 1.851 13* 13.812 2.416 1.5920 67.02 14* -18.144 4.500 15 0.000 0.500 1.5163 64.14 16 0.000 2.229

[0131] Table 14 shows the origin table of the optical system of Example 4. Table 15 is a table showing the aspherical coefficients of each aspherical surface in the optical system of Example 4. Table 16 shows the focal lengths of the respective lenses constituting the optical system of Example 4.

[0132] [Table 14] f 5.421 Fno 1.850 OBJ INF ω 54.9 Cra 15.6 Y 4.95

[0133] [Table 15] Surface No. k A4 A6 2 0.000000 -6.617760E-04 5.035400E-06 3 0.492500 -3.521840E-04 -1.170940E-05 4 0.000000 5.299370E-04 -9.644310E-06 5 0.000000 1.313200E-04 -5.666370E-06 6 0.452500 -3.353340E-05 1.257310E-06 7 -9.000000 1.787490E-05 6.345430E-06 13 0.000000 -8.748250E-04 -5.621190E-06 14 2.000000 -2.139510E-04 -1.255270E-05 Plane NO. A8 A10 2 -9.720780E-09 -2.838990E-11 3 3.544680E-07 -3.215530E-08 4 1.534870E-07 -3.567140E-09 5 -2.925960E-08 4.380300E-10 6 -1.258370E-08 -5.600150E-10 7 -1.550270E-07 8.389010E-10 13 -8.742540E-07 0.000000 14 -3.790750E-07 0.000000

[0134] [Table 16] Lens No Focal Length 1 -7.247 2 -24.099 3 9.260 4 6.971 5 -5.709 6 13.630

[0135] [Example 5] The optical configuration at infinity focus of the optical system of Example 5 is schematically shown in FIG. 9, and the longitudinal aberration at infinity focus of the optical system of Example 5 is shown in FIG. 10. The optical system of Example 5 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, a diaphragm S, a fourth lens L4 having a positive refractive power, a fifth lens L5 having a negative refractive power, and a sixth lens L6 having a positive refractive power. The sixth lens L6 corresponds to the aforementioned final lens Lf. An infrared cut filter IRCF is disposed between the sixth lens L6 and the image plane IMG.

[0136] Hereinafter, the configuration of each lens group will be described. The first lens group includes, in order from the object side, a first lens L1 which is a negative meniscus lens with a convex shape on the object side and a second lens L2 which is a negative meniscus lens with a concave shape on the object side. The second lens group includes, in order from the object side, a third lens L3 which is a biconvex lens, a diaphragm S, a fourth lens L4 which is a biconvex lens, a fifth lens L5 which is a lens with a concave shape on the object side, and a sixth lens L6 which is a convex-plano lens. The fourth lens L4 and the fifth lens L5 are joined together.

[0137] Table 17 shows the surface data of the optical system of Example 5. In Table 17, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 14 are the surface numbers of the second lens group, and No. 8 represents the diaphragm. Nos. 15 and 16 represent the infrared cut filter IRCF.

[0138] [Table 17] Surface NO. r d Nd vd 1 INF INF 2* 58.490 1.500 1.7680 49.24 3* 5.457 7.151 4* -4.783 2.500 1.9520 29.80 5* -6.878 0.100 6* 9.005 4.388 1.7725 49.62 7* -53.449 5.232 8S 0.000 0.100 9 22.503 3.471 1.5930 67.00 10 -5.000 0.000 11 -5.000 0.600 2.0027 19.32 12 -15.268 4.620 13 14.901 2.300 1.9212 23.96 14 0.000 0.500 15 0.000 0.500 1.5163 64.14 16 0.000 3.075

[0139] Table 18 shows the origin table of the optical system of Example 5. Table 19 is a table showing the aspherical coefficients of each aspherical surface in the optical system of Example 5. Table 20 shows the focal lengths of the lenses constituting the optical system of Example 5.

[0140] [Table 18] f 5.435 Fno 1.850 OBJ INF ω 54.9 Cra 15.6 Y 4.95

[0141] [Table 19] Surface No. k A4 A6 2 2.000000 -1.104330E-04 3.008990E-06 3 0.712500 -2.709220E-04 -8.866030E-06 4 0.395100 2.492690E-04 -1.036640E-05 5 0.505800 1.430470E-04 -9.440480E-07 6 0.358400 -4.603160E-05 2.662070E-06 7 0.526700 -4.854810E-06 5.065450E-06 Surface NO. A8 A10 2 -3.230510E-08 1.758280E-10 3 2.763750E-07 -8.659980E-09 4 2.857530E-07 0.000000 5 5.128250E-08 0.000000 6 -2.043410E-08 1.578400E-10 7 -7.193020E-08 3.771070E-10

[0142] [Table 20] Lens No Focal Length 1 -7.934 2 -39.455 3 10.291 4 7.239 5 -7.638 6 16.176

[0143] [Example 6] The optical configuration at infinity focus of the optical system of Example 6 is schematically shown in FIG. 11, and the longitudinal aberration at infinity focus of the optical system of Example 6 is shown in FIG. 12. The optical system of Example 6 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, a fourth lens L4 having a positive refractive power, a diaphragm S, a fifth lens L5 having a positive refractive power, a sixth lens L6 having a negative refractive power, and a seventh lens L7 having a positive refractive power. The seventh lens L7 corresponds to the aforementioned final lens Lf. An infrared cut filter IRCF is disposed between the seventh lens L7 and the image plane IMG.

[0144] The configurations of the respective lens groups will be described below. The first lens group is composed of, in order from the object side, a first lens L1 which is a negative meniscus lens with a convex shape on the object side, and a second lens L2 which is a negative meniscus lens with a concave shape on the object side. The second lens group is composed of, in order from the object side, a third lens L3 which is a positive meniscus lens with a convex shape on the object side, a fourth lens L4 which is a positive meniscus lens with a convex shape on the object side, a diaphragm S, a fifth lens L5 which is a biconvex lens, a sixth lens L6 which is a meniscus lens with a concave shape on the object side, and a seventh lens L7 which is a biconvex lens. The fifth lens L5 and the sixth lens L6 are joined together.

[0145] Table 21 shows the surface data of the optical system of Example 6. In Table 21, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 16 are the surface numbers of the second lens group, and No. 10 represents the diaphragm. Nos. 17 and 18 represent the infrared cut filter IRCF.

[0146] [Table 21] Surface NO. r d Nd vd 1 INF INF 2* 34.312 1.500 1.8820 37.20 3* 6.132 4.781 4* -5.975 4.873 1.7543 50.69 5* -8.332 0.100 6* 8.297 3.102 1.6663 36.49 7* 12.102 1.300 8 13.809 1.593 1.6180 63.40 9 107.260 2.244 10S 0.000 0.100 11 11.022 4.813 1.5319 74.44 12 -6.000 0.000 13 -6.000 0.600 1.8951 21.46 14 -30.682 1.868 15 21.475 1.926 1.8830 40.81 16 -74.424 4.500 17* 0.000 0.500 1.5163 64.14 18* 0.000 1.200

[0147] Table 22 shows the origin table of the optical system of Example 6. Table 23 is a table showing the aspherical coefficients of each aspherical surface in the optical system of Example 6. Table 24 shows the focal lengths of the respective lenses constituting the optical system of Example 6.

[0148] [Table 22] f 5.559 Fno 1.850 OBJ INF ω 54.9 Cra 15.6 Y 4.95

[0149] [Table 23] Surface No. k A4 A6 2 0.000000 5.137190E-05 2.139890E-06 3 1.135900 1.637820E-04 1.027120E-06 7 0.967600 7.942720E-04 1.116260E-05 8 0.661500 3.597830E-04 -1.722780E-06 9 0.606100 -9.246350E-05 2.593290E-06 10 -6.572800 -4.845440E-05 9.418390E-06 11 0.000000 -9.576370E-04 -5.468110E-06 12 2.000000 -8.200080E-04 -4.905930E-06 Surface No. A8 A10 2 -7.954220E-08 6.188000E-10 3 7.892610E-07 -1.496300E-08 7 1.453470E-08 3.924980E-09 8 4.289570E-08 -1.089900E-09 9 -9.998790E-09 -4.200260E-10 10 -1.665500E-07 6.349930E-10 11 -4.896800E-07 0.000000 12 -2.107430E-07 0.000000

[0150] [Table 24] Lens No Focal Length 1 -8.683 2 -252.705 3 29.862 4 25.481 5 8.099 6 -8.430 7 19.054

[0151] [Example 7] The optical configuration at infinity focus of the optical system of Example 7 is schematically shown in FIG. 13, and the longitudinal aberration at infinity focus of the optical system of Example 7 is shown in FIG. 14. The optical system of Example 7 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a negative refractive power, a fourth lens L4 having a positive refractive power, a fifth lens L5 having a negative refractive power, a diaphragm S, a sixth lens L6 having a positive refractive power, a seventh lens L7 having a negative refractive power, and an eighth lens L8 having a positive refractive power. The eighth lens L8 corresponds to the aforementioned final lens Lf. An infrared cut filter IRCF is disposed between the eighth lens L8 and the image plane IMG.

[0152] The configurations of the respective lens groups will be described below. The first lens group is composed of a first lens L1, which is a negative meniscus lens with a convex shape on the object side, and a second lens L2, which is a negative meniscus lens with a concave shape on the object side, in order from the object side. The second lens group is composed of a third lens L3, which is a negative meniscus lens with a convex shape on the object side, a fourth lens L4, which is a biconvex positive lens, a fifth lens L5, which is a negative meniscus lens with a concave shape on the image side, a diaphragm S, a sixth lens L6, which is a biconvex lens, a seventh lens L7, which is a negative meniscus lens with a concave shape on the object side, and an eighth lens L8, which is a biconvex lens, in order from the object side. The sixth lens L6 and the seventh lens L7 are joined together.

[0153] Table 25 shows the surface data of the optical system of Example 7. In Table 25, No. 1 is the surface number of the object surface. No. 2 to 5 are the surface numbers of the first lens group. No. 6 to 18 are the surface numbers of the second lens group, and No. 12 represents the diaphragm. No. 19 and 20 represent the infrared cut filter IRCF.

[0154] [Table 25] Surface NO. r d Nd vd 1 INF INF 2* 16.504 1.500 1.8820 37.20 3* 5.200 4.973 4* -8.236 4.410 1.8873 28.67 5* -10.744 0.100 6 9.928 2.356 1.9229 20.88 7 8.105 1.300 8 10.695 2.729 1.8830 40.81 9 -25.106 2.123 10 18.892 0.600 1.8431 22.75 11 9.224 0.635 12S 0.000 0.767 13 107.483 2.819 1.6180 63.40 14 -5.000 0.000 15 -5.000 0.600 1.9194 21.76 16 -11.002 0.651 17 21.990 1.770 1.8830 40.81 18 -47.208 4.500 19 0.000 0.500 1.5163 64.14 20 0.000 2.667

[0155] Table 26 shows the origin table of the optical system of Example 7. Table 27 is a table showing the aspherical coefficients of each aspherical surface in the optical system of Example 7. Table 28 shows the focal lengths of the respective lenses constituting the optical system of Example 7.

[0156] [Table 26] f 5.599 Fno 1.850 OBJ INF ω 54.9 Cra 19.3 Y 4.99

[0157] [Table 27] Surface No. k A4 A6 2 1.286700 -1.303630E-04 -1.311580E-07 3 0.769500 4.850830E-05 -1.088170E-05 4 1.562300 2.767730E-04 8.137640E-06 5 1.128300 1.725830E-04 2.036530E-06 Surface No. A8 A10 2 -9.223720E-09 1.264010E-10 3 5.797910E-07 -2.243900E-08 4 -1.233300E-07 7.631740E-09 5 -4.689880E-09 1.114060E-09

[0158] [Table 28] Lens No Focal Length 1 -9.179 2 -229.813 3 -125.971 4 8.809 5 -22.002 6 7.806 7 -10.469 8 17.196

[0159] [Example 8] The optical configuration at infinity focus of the optical system of Example 8 is schematically shown in Fig. 15, and the longitudinal spherical aberration at infinity focus of the optical system of Example 8 is shown in Fig. 16. The optical system of Example 8 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, a fourth lens L4 having a positive refractive power, a fifth lens L5 having a positive refractive power, a sixth lens L6 having a negative refractive power, a diaphragm S, a seventh lens L7 having a positive refractive power, an eighth lens L8 having a negative refractive power, and a ninth lens L9 having a positive refractive power. The ninth lens L9 corresponds to the aforementioned final lens Lf. An infrared cut filter IRCF is disposed between the ninth lens L9 and the image plane IMG.

[0160] The configuration of each lens group will be described below. The first lens group includes, in order from the object side, a first lens L1 which is a negative meniscus lens with a convex shape on the object side and a second lens L2 which is a negative meniscus lens with a concave shape on the object side. The second lens group includes, in order from the object side, a third lens L3 which is a positive meniscus lens with a convex shape on the image plane side, a fourth lens L4 which is a biconvex positive lens, a fifth lens L5 which is a positive meniscus lens with a convex shape on the object side, a sixth lens L6 which is a negative meniscus lens with a concave shape on the image plane side, a diaphragm S, a seventh lens L7 which is a biconvex lens, an eighth lens L8 which is a negative meniscus lens with a concave shape on the object side, and a ninth lens L9 which is a positive meniscus lens with a convex shape on the object side. The seventh lens L7 and the eighth lens L8 are joined together.

[0161] Table 29 shows the surface data of the optical system in Example 8. In Table 29, No. 1 is the surface number of the object surface. No. 2 to 5 are the surface numbers of the first lens group. No. 6 to 20 are the surface numbers of the second lens group, and No. 14 represents the aperture stop. No. 21 and 22 represent the infrared cut filter IRCF.

[0162] [Table 29] Surface No. r d Nd vd 1 INF INF 2* 28.906 1.500 1.8820 37.20 3* 5.200 5.151 4 -8.438 3.671 1.4970 81.61 5 -11.671 0.100 6 -41.602 2.333 1.8830 40.81 7 -19.592 0.100 8 14.071 3.801 1.6666 57.57 9 -36.853 0.100 10 12.148 1.219 1.8830 40.81 11 21.659 2.743 12 20.487 0.600 1.8431 22.75 13 7.580 0.617 14S 0.000 0.333 15 16.881 3.099 1.5273 75.26 16 -5.250 0.000 17 -5.250 0.600 1.9195 21.73 18 -11.510 1.032 19 15.486 1.800 1.8830 40.81 20 178.611 4.500 21 0.000 0.500 1.5163 64.14 22 0.000 1.200

[0163] Table 30 shows the origin table of the optical system of Example 8. Table 31 is a table showing the aspherical coefficients of each aspherical surface in the optical system of Example 8. Table 32 shows the focal lengths of the respective lenses constituting the optical system of Example 8.

[0164] [Table 30] f 5.493 Fno 1.850 OBJ INF ω 54.9 Cra 11.3 Y 4.88

[0165] [Table 31] Surface No. k A4 A6 2 1.980300 -3.558770E-04 6.743390E-06 3 0.673100 -1.651480E-04 -1.044690E-05 Surface No. A8 A10 2 -8.767810E-08 4.734460E-10 3 8.900840E-07 -2.475000E-08

[0166] [Table 32] Lens No. Focal Length 1 -7.409 2 -98.366 3 39.954 4 15.746 5 29.552 6 -14.582 7 7.980 8 -11.003 9 19.103

[0167] [Example 9] The optical configuration at infinity focus of the optical system of Example 9 is schematically shown in FIG. 17, and the longitudinal aberration at infinity focus of the optical system of Example 9 is shown in FIG. 18. The optical system of Example 9 includes, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, a fourth lens L4 having a positive refractive power, a fifth lens L5 having a positive refractive power, a sixth lens L6 having a negative refractive power, a seventh lens L7 having a positive refractive power, a diaphragm S, an eighth lens L8 having a positive refractive power, a ninth lens L9 having a negative refractive power, and a tenth lens having a positive refractive power. The tenth lens L10 corresponds to the aforementioned final lens Lf. An infrared cut filter IRCF is disposed between the tenth lens L10 and the image plane IMG.

[0168] The configurations of the respective lens groups will be described below. The first lens group includes, in order from the object side, a first lens L1 which is a negative meniscus lens with a convex shape on the object side and a second lens L2 which is a negative meniscus lens with a concave shape on the object side. The second lens group includes, in order from the object side, a third lens L3 which is a biconvex lens, a fourth lens L4 which is a positive meniscus lens with a convex shape on the object side, a fifth lens L5 which is a biconvex lens, a sixth lens L6 which is a positive meniscus lens with a convex shape on the object side, a seventh lens L7 which is a biconvex lens, a diaphragm S, an eighth lens L8 which is a biconvex lens, a ninth lens L9 which is a negative meniscus lens with a concave shape on the object side, and a tenth lens L10 which is a biconvex lens. The eighth lens L8 and the ninth lens L9 are joined together.

[0169] Table 33 shows the surface data of the optical system of Example 9. In Table 33, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 22 are the surface numbers of the second lens group, and No. 16 represents the diaphragm. Nos. 23 and 24 represent the infrared cut filter IRCF.

[0170] [Table 33] Surface NO. r d Nd vd 1 INF INF 2 * 17.177 1.500 1.8820 37.20 3 * 5.200 6.135 4 -6.158 3.984 1.8830 40.81 5 -9.169 0.100 6 287.123 2.528 1.8830 40.81 7 -23.655 0.100 8 9.081 2.726 1.9229 20.88 9 14.059 0.100 10 9.887 1.809 1.4970 81.61 11 -104.284 0.100 12 45.929 0.600 1.9229 20.88 13 6.894 0.415 14 10.140 1.174 1.4970 81.61 15 -470.253 0.100 16S 0.000 0.424 17 20.941 3.123 1.4970 81.61 18 -5.250 0.000 19 -5.250 0.600 1.9229 20.88 20 -14.841 1.483 21 26.076 1.800 1.9215 21.23 22 -48.190 4.500 23 0.000 0.500 1.5163 64.14 24 0.000 1.200

[0171] Table 34 shows the origin table of the optical system of Example 9. Table 35 is a table showing the aspherical coefficients of each aspherical surface in the optical system of Example 9. Table 36 shows the focal lengths of the respective lenses constituting the optical system of Example 9.

[0172] [Table 34] f 5.604 Fno 1.850 OBJ INF ω 54.9 Cra 19.9 Y 4.93

[0173] [Table 35] Surface No. k A4 A6 2 1.070500 -4.629980E-04 1.296690E-05 3 1.080400 -6.080860E-04 -2.207820E-05 Surface No. A8 A10 2 -1.742400E-07 1.059700E-09 3 1.892430E-06 -5.997030E-08

[0174] [Table 36] Lens No. Focal Length 1 -8.983 2 -55.972 3 24.845 4 22.005 5 18.267 6 -8.855 7 19.988 8 8.794 9 -9.075 10 18.579

[0175] The calculated values obtained by the above equations in Examples 1 to 9 and the numerical values used in the equations are shown in Table 37.

[0176] [Table 37] Example 1 Example 2 Example 3 Example 4 Equation (1) (C L1r -C L2f )×f 2.318 2.247 2.173 1.702 Equation (2) D L12 / f 1.294 1.334 0.728 0.952 Equation (3) f 12 / f -1.506 -1.512 -1.286 -0.913 Equation (4) P W12×f 2.019 1.982 1.768 1.491 Equation (5) f 1 / f -1.602 -1.627 -1.504 -1.337 Equation (6) R L2f / f -1.171 -1.154 -1.474 -2.902 Equation (7) f 2g / f 2.179 2.177 2.118 1.574 Equation (8) oal / f 6.565 6.564 6.381 6.456 Equation (9) f 1g / f -1.506 -1.512 -1.286 -0.913 Equation (10) R L1r / f 0.683 0.724 0.669 0.737 Equation (11) N L1 1.882 1.882 1.773 1.882 Equation (12) N L3 1.773 1.851 1.497 1.888 Equation (13) D L23 / f 0.018 0.019 0.018 0.018 Equation (14) f Lf / f 2.316 2.222 -17.414 2.514 Example 1 Example 2 Example 3 Example 4 C L1r 0.2746 0.2589 0.2725 0.2504 C L2f -0.1602 -0.1625 -0.1237 -0.0636 f 5.331 5.332 5.485 5.421 D L12 6.898 7.110 3.996 5.162 f 12 -8.031 -8.063 -7.055 -4.952 P W12 0.3790.372 0.322 0.275 f 1 -8.542 -8.675 -8.248 -7.247 R L2f -6.240 -6.154 -8.083 -15.729 f 2g 11.615 11.615 11.615 8.533 oal 34.986 35.000 35.000 35.000 f 1g -8.031 -8.063 -7.054 -4.952 R L1r 3.641 3.863 3.670 3.993 D L23 0.100 0.100 0.100 0.100 f Lf 12.349 11.846 -12.820 13.630 Example 5 Example 6 Example 7 Example 8 Example 9 Formula (1) (C L1r -C L2f )×f 2.132 1.837 1.765 1.707 1.988 Formula (2) D L12 / f 1.316 0.860 0.888 0.938 1.095 Formula (3) f 12 / f -1.214 -1.950 -1.891 -1.320 -1.512 Formula (4) P W12 ×f 1.847 1.501 1.553 1.255 1.754 Formula (5) f 1 / f -1.460 -1.562 -1.639 -1.349 -1.603 Formula (6) R L2f / f -0.880 -1.075 -1.471 -1.536 -1.099 Formula (7) f 2g / f 2.487 2.031 1.917 1.829 1.809 Equation (8) oal / f 6.564 6.296 6.251 6.372 6.245 Equation (9) f 1g / f -1.203 -1.950 -1.951 -1.320 -1.512 Equation (10) R L1r / f 1.004 1.103 0.929 0.947 0.928 Equation (11) N L1 1.768 1.882 1.882 1.882 1.882 Equation (12) N L3 1.773 1.666 1.923 1.883 1.883 Equation (13) D L23 / f 0.018 0.018 0.018 0.018 0.018 Equation (14) f Lf / f 2.976 3.427 3.072 3.478 3.315 Example 5 Example 6 Example 7 Example 8 Example 9 C L1r 0.1833 0.1631 0.1923 0.1923 0.1923 C L2f -0.2091 -0.1674 -0.1214 -0.1185 -0.1624 f 5.435 5.559 5.599 5.493 5.604 D L12 7.151 4.781 4.973 5.151 6.13 5f 12 -6.596 -10.839 -10.588 -7.253 -8.476 P W12 0.340 0.270 0.277 0.229 0.313 f 1 -7.934 -8.683 -9.179 -7.409 -8.983 RL2f -4.783 -5.975 -8.236 -8.438 -6.158 f 2g 13.636 11.293 10.731 10.049 10.141 oal 36.008 35.000 35.000 35.000 33.800 f 1g -6.538 -10.839 -10.921 -7.253 -8.476 R L1r 5.457 6.132 5.200 5.200 5.200 D L23 0.100 0.100 0.100 0.100 0.100 f Lf 16.176 19.054 17.196 19.104 18.579

Explanation of Symbols

[0177] 1 Mirrorless Single-lens Camera 2 Body 3 Lens Barrel 21 CCD Sensor 30 Optical System 31 First Lens Group 32 Second Lens Group 33, S Diaphragm OA Optical Axis

Claims

1. It consists of a first lens group and a second lens group having a positive refractive power, in order from the object side, The first lens group consists of a first lens L1 having a convex surface on the object side and a negative refractive power, and a meniscus-shaped second lens L2 having a concave surface facing the object side, in order from the object side. The total number of lenses is 5 or more and 10 or less, and An optical system that satisfies the following formula. 1.837 ≤ (C Ｌ１ｒ - C Ｌ２ｆ ) × f < 2.55.....(1) 0.860 ≤ D Ｌ１２ / f < 5.00 ...... (2) 1.809 ≦ f2g / f < 2.70.....(7) However, C Ｌ１ｒ : The curvature of the lens surface on the image plane side of the first lens L1 C Ｌ２ｆ : Curvature of the lens surface on the object side of the second lens L2 f: Focal length when the optical system is focused at infinity D Ｌ１２ : The distance on the optical axis between the lens surface on the image plane side of the first lens L1 and the lens surface on the object side of the second lens L2 when the optical system is focused at infinity f2g: Focal length of the second lens group

2. The second lens group Has a diaphragm, Is composed of 3 or fewer lenses on the image side of the diaphragm, and The optical system according to claim 1, wherein the 3 or fewer lenses include a cemented lens of a lens having a positive refractive power and a lens having a negative refractive power.

3. The optical system according to claim 1 or 2, which satisfies the following formula. -3.40 < R Ｌ２ｆ / f < 0.00.....(6) However, R Ｌ２ｆ : The radius of curvature of the lens surface on the object side of the second lens L2

4. The optical system according to any one of claims 1 to 3, which satisfies the following formula. 5.0 < oal / f < 8.0.....(8) However, oal: Overall optical length of the optical system

5. The optical system according to any one of claims 1 to 4, wherein the second lens L2 has a negative refractive power.

6. The optical system according to any one of claims 1 to 5, which satisfies the following formula. -2.40 < f １ｇ / f < -0.75 ······ (9) However, f １ｇ : Focal length of the first lens group

7. The optical system according to any one of claims 1 to 6, which satisfies the following formula. 0.50 < R Ｌ１ｒ / f < 10.00 ...... (10) However, R Ｌ１ｒ : Radius of curvature of the lens surface on the image plane side of the first lens L1

8. The second lens group has a pair of combined lenses on the image side adjacent to the diaphragm, The optical system according to any one of claims 1 to 7, wherein the combined lens consists of a lens having a positive refractive power and a lens having a negative refractive power.

9. The optical system according to any one of claims 1 to 8, which satisfies the following formula. 1.70 < N Ｌ１ < 2.00.....(11) However, N Ｌ１ : Refractive index of the first lens L1 with respect to the d-line

10. The second lens group has a third lens L3 having a positive refractive power, The optical system according to any one of claims 1 to 9, which satisfies the following formula.

1. 60 < N Ｌ３ < 2.00 ······ (12) N Ｌ３ : Refractive index of the third lens L3 for d-line

11. The second lens group has a third lens L3 having a positive refractive power, The optical system according to any one of claims 1 to 10, which satisfies the following formula. 0.010 < D Ｌ２３ / f < 0.050 ...... (13) However, D Ｌ２３ : The distance on the optical axis between the lens surface on the image plane side of the second lens L2 and the lens surface on the object side of the third lens L3 when the optical system is focused at infinity

12. The optical system according to any one of claims 1 to 11, wherein the second lens group has a final lens Lf having a positive refractive power on the most image side.

13. The optical system according to claim 12, which satisfies the following formula. 1.5 < f Ｌｆ / f < 4.5 ····· (14) However, f Ｌｆ : Focal length of the final lens Lf

14. An imaging device comprising the optical system according to any one of claims 1 to 13, and an imaging element provided on the image plane side of the optical system for converting an optical image formed by the optical system into an electrical signal.

Images