Optical system and imaging apparatus having the same

Abstract

To provide a small-sized optical system having high optical performance.SOLUTION: An optical system comprises a front group La, an aperture stop SP, and a rear group Lb, which are arranged in order from an object side to an image side, and includes a first lens L1 having a negative refractive power arranged on the most object side, and a final lens Lp having a positive refractive power arranged on the most image side. The front group La includes a first negative lens having a concave lens surface on the object side, and a first positive lens having a concave lens surface on the image side. When the focal length of the entire system is defined as f, the distance from the lens surface on the most object side to the lens surface on the image side of the final lens Lp as D, a back focus as sk, and the focal length of the front group as fLa, the conditional expressions of 1.00<sk / D<1.80 and 0.00<f / fLa<0.50 are satisfied.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system suitable for digital video cameras, digital still cameras, broadcast cameras, cameras for silver halide film, surveillance cameras, and the like. [Background technology]

[0002] 2. Description of the Related Art In optical systems used in image pickup apparatuses, there is a demand for lenses that are compact yet have good optical performance from the center to the periphery of the screen.

[0003] Patent Document 1 discloses an optical system that is composed of a lens group with positive refractive power, an aperture stop, a lens group with positive refractive power, and a lens group with negative refractive power, which are arranged in this order from the object side to the image side, and that is capable of correcting various aberrations while reducing the overall length by using a lens having an aspheric lens surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-63676 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, due to various aberrations including pincushion distortion, the optical performance of the optical system of Patent Document 1 is insufficient at the periphery of the image plane, and a compact optical system with higher optical performance is desired.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a compact optical system having high optical performance. [Means for solving the problem]

[0007] The optical system of the present invention comprises a front group, an aperture stop, and a rear group, arranged in that order from the object side to the image side, and includes a first lens with negative refractive power arranged closest to the object side, and a final lens with positive refractive power arranged closest to the image side, the front group including a first negative lens whose lens surface on the object side is concave, and a first positive lens whose lens surface on the image side is concave, wherein f is the focal length of the entire system, D is the distance from the lens surface closest to the object side to the lens surface of the final lens on the image side, sk is the back focus, and fLa is the focal length of the front group. 1.00 <sk / D<1.80 0.00 <f / fLa<0.50 The present invention is characterized in that it satisfies the following conditions. Effect of the Invention

[0008] According to the present invention, it is possible to provide a compact optical system having high optical performance. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view of the optical system of the first embodiment. [Diagram 2] 4A to 4C are aberration diagrams of Example 1 when focusing on an object at infinity. [Diagram 3] FIG. 11 is a cross-sectional view of an optical system according to a second embodiment. [Figure 4] 11A to 11C are aberration diagrams of Example 2 when focusing on an object at infinity. [Diagram 5] FIG. 11 is a cross-sectional view of an optical system according to a third embodiment. [Figure 6] 13A to 13C are aberration diagrams of Example 3 when focusing on an object at infinity. [Figure 7] FIG. 11 is a cross-sectional view of an optical system according to a fourth embodiment. [Figure 8] 13A to 13C are aberration diagrams of Example 4 when focusing on an object at infinity. [Figure 9] FIG. 11 is a cross-sectional view of an optical system according to a fifth embodiment. [Figure 10] 13A to 13C are aberration diagrams of Example 5 when focusing on an object at infinity. [Figure 11] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that the drawings may be drawn at a scale different from the actual scale for convenience. In addition, in each drawing, the same reference numerals are used for the same components, and duplicated explanations will be omitted.

[0011] 1, 3, 5, 7, and 9 are cross-sectional views of the optical system L0 of Examples 1 to 5, respectively. In each figure, the left side is the object side (front side) and the right side is the image side (rear side). The optical system L0 of each Example is configured with multiple lenses.

[0012] In each diagram, La denotes the front group located closer to the object than the aperture stop, Lb denotes the rear group located closer to the image than the aperture stop, Lp denotes the final lens with positive refractive power located closest to the image, and Ln denotes the negative lens in the rear group that is located closest to the image.

[0013] In each figure, SP denotes an aperture stop, and IP denotes an image plane. When the optical system L0 of each embodiment is used as an imaging optical system for a digital video camera or a digital still camera, the imaging surface of a solid-state imaging element (photoelectric conversion element) is disposed on the image plane IP. A CCD (Charge Coupled Device) sensor, a CMOS (Complementary Metal Oxide Semiconductor) sensor, or the like can be used as the solid-state imaging element. When the optical system L0 of each embodiment is used as an imaging optical system for a silver halide film camera, the photosensitive surface of the film is disposed on the image plane IP.

[0014] In the optical system L0 of each embodiment, one or more lenses may be decentered so as to include a component perpendicular to the optical axis during image blur correction, thereby providing a function as an anti-vibration optical system. Also, a parallel plate with substantially no refractive power, such as a low-pass filter or an infrared cut filter, may be disposed between the lens disposed closest to the image side and the image plane.

[0015] 2, 4, 6, 8, and 10 are aberration diagrams of the optical systems of Examples 1 to 5 when focused at infinity, respectively.

[0016] In each diagram, Fno is the F-number, and ω is the imaging half angle of view (°) determined by paraxial calculation. The spherical aberration diagram shows spherical aberration at the d-line (wavelength 587.6 nm) and spherical aberration at the g-line (wavelength 435.8 nm). The astigmatism diagram shows dS the astigmatism at the d-line on the sagittal image plane, and dM the astigmatism at the d-line on the meridional image plane. The distortion diagram shows distortion at the d-line. The chromatic aberration diagram shows lateral chromatic aberration at the g-line.

[0017] The characteristic configuration of the optical system of each embodiment will be described. The optical system L0 of this embodiment is composed of a front group La, an aperture stop SP, and a rear group Lb arranged in order from the object side to the image side, and includes a first lens L1 with negative refractive power arranged closest to the object side, and a final lens Lp with positive refractive power arranged closest to the image side. The front group La includes a negative lens (first negative lens) whose lens surface on the object side is concave, and a positive lens (first positive lens) whose lens surface on the image side is concave. The optical system L0 of each embodiment suppresses the image plane incidence angle of off-axis light beams while maintaining high optical performance by a retrofocus type power arrangement. With such a configuration, a compact optical system with high optical performance can be provided.

[0018] Next, the conditions that the optical system L0 of each embodiment satisfies will be described. The optical system L0 of each embodiment satisfies the following conditional expressions (1) and (2), where D is the distance from the lens surface of the optical system L0 closest to the object side to the lens surface of the final lens Lp closest to the image side, sk is the back focus of the optical system, f is the focal length of the optical system L0, and fLa is the focal length of the front group. 1.00 <sk / D<1.80 (1) 0.00 <f / fLa<0.50 (2)

[0019] If the upper limit of conditional formula (1) is exceeded, the power arrangement of the retrofocus type becomes strong, making it difficult to correct distortion, which is undesirable. On the other hand, if the lower limit of conditional formula (1) is exceeded, the back focus becomes too short, and the effective diameter of the lens Lp arranged on the image side becomes large. As a result, the optical system becomes large in the radial direction, which is undesirable.

[0020] If the upper limit of conditional expression (2) is exceeded, the refractive power of the front group will be too strong, resulting in large pincushion distortion. As a result, it will be difficult to simultaneously correct both the curvature of field and distortion, which is undesirable. On the other hand, if the lower limit of conditional expression (2) is exceeded, the refractive power of the front group will be too weak, resulting in a long optical total length, which is undesirable.

[0021] It is more preferable that the numerical ranges of the conditional expressions (1) and (2) be the numerical ranges of the following conditional expressions (1a) and (2a). 1.05 <sk / D<1.75 (1a) 0.10 <f / fLa<0.47 (2a)

[0022] It is further preferable that the numerical ranges of the conditional expressions (1a) and (2a) be set to the numerical ranges of the following conditional expressions (1b) and (2b). 1.10 <sk / D<1.70 (1b) 0.20 <f / fLa<0.45 (2b)

[0023] Next, conditions that the optical system L0 of each embodiment preferably satisfies will be described.

[0024] The front group La in the optical system L0 preferably comprises a negative lens whose lens surface on the object side is concave, and a positive lens whose lens surface on the image side is concave. The negative lens whose lens surface on the object side is concave, and the positive lens whose lens surface on the image side is concave may be configured as a cemented lens. The cemented lens of this embodiment is bonded by applying an adhesive or the like between two or more lenses.

[0025] The rear group Lb in the optical system L0 preferably consists of a positive lens, a negative lens, and a positive lens arranged in this order from the object side to the image side. With this configuration, the rear group Lb, which is composed of a small number of lenses, can effectively correct aberrations that occur on the object side of the aperture stop SP.

[0026] The negative lens Ln, which is located closest to the image among the lenses with negative refractive power in the rear group Lb, is preferably a lens having an aspheric lens surface. If the negative lens Ln is a lens having only a spherical surface, it is not preferable because it will be difficult to suppress an increase in the angle of incidence on the image surface and the occurrence of curvature of field due to insufficient refractive power for bending off-axis light rays onto the axis.

[0027] It is preferable that the negative lens Ln, which is located closest to the image side among the lenses with negative refractive power in the rear group Lb in the optical system L0, is a lens whose material contains resin. In general, the lens closer to the image side tends to have a larger diameter. By making the negative lens Ln a lens whose material contains resin (for example, a plastic lens), the weight of the optical system can be reduced.

[0028] It is preferable that the image-side lens surface of the final lens Lp in the optical system L0 is a convex surface, which can suppress distortion.

[0029] The optical system L0 is preferably composed of five or six lenses. A lens configuration with more than six lenses is not preferred because the total lens length becomes long. On the other hand, a lens configuration with fewer than five lenses is not preferred because it becomes difficult to effectively correct various aberrations.

[0030] The front group La in the optical system L0 in each embodiment includes a negative lens having a concave lens surface on the object side, and a positive lens having a concave lens surface on the image side. When the Abbe number of the material of the negative lens having a concave lens surface on the object side is vn and the Abbe number of the material of the positive lens having a concave lens surface on the image side is vp, it is preferable to satisfy the following conditional expression (3): 0.83<νn / νp<0.95 (3)

[0031] If the upper limit of condition (3) is exceeded, it becomes difficult to correct chromatic aberration, which is undesirable. On the other hand, if the lower limit of condition (3) is not reached, the material of the positive lens has a low refractive index. As a result, it becomes difficult to suppress spherical aberration, which is undesirable.

[0032] When the average value of the refractive index of the lenses constituting the front group La in the optical system L0 of each embodiment is taken as N1ave, it is preferable that the following conditional expression (4) be satisfied. 1.65 <N1ave<1.80 (4)

[0033] If the upper limit of conditional expression (4) is exceeded, the refractive index of the lenses constituting the front group La becomes too high, resulting in large color dispersion. As a result, it is undesirable because it becomes difficult to correct axial chromatic aberration. If the lower limit of conditional expression (4) is exceeded, the refractive index of the lenses constituting the front group La becomes too low, resulting in a large Petzval sum for the entire system. As a result, it is undesirable because it becomes difficult to correct field curvature.

[0034] In the optical system L0 of each embodiment, when the focal length of the first lens L1 arranged closest to the object side is fL1, it is preferable that the following conditional expression (5) be satisfied. -4.10 <f / fL1<-2.50 (5)

[0035] If the upper limit of condition (5) is exceeded, the negative refractive power of the first lens L1 becomes too strong, which undesirably increases the overall optical length, while if the lower limit of condition (5) is exceeded, the refractive power of the front group La becomes too strong, which undesirably causes significant pincushion distortion.

[0036] When the focal length of the final lens Lp in the optical system L0 of each embodiment is fLp, it is preferable that the following conditional expression (6) be satisfied. 0.20 <f / fLp<0.45 (6)

[0037] If the upper limit of conditional expression (6) is exceeded, the refractive power of the final lens Lp becomes too strong, resulting in large barrel distortion. As a result, it becomes difficult to simultaneously correct both the curvature of field and distortion, which is undesirable. If the lower limit of conditional expression (6) is exceeded, the refractive power of the final lens Lp becomes too weak, resulting in difficult control of the image plane incidence angle, which is undesirable.

[0038] In the optical system L0 of each embodiment, when the focal length of the front group La is fLa and the focal length of the rear group Lb is fLb, it is preferable that the following conditional expression (7) be satisfied. 0.20 <fLa / fLb<4.20 (7)

[0039] If the upper limit of condition (7) is exceeded, the refractive power of the front group La becomes too strong, causing large pincushion distortion and making it difficult to simultaneously correct both the curvature of field and distortion, which is undesirable. On the other hand, if the lower limit of condition (7) is not reached, the refractive power of the rear group Lb becomes too strong, causing the total optical length to increase, which is undesirable.

[0040] It is preferable that the optical system of each embodiment satisfies the following conditional expression (8), where PD is the distance from the aperture stop SP to the image plane. 0.70 <PD / (D+sk)<1.00 (8)

[0041] If the upper limit of condition (7) is exceeded, the rear group Lb becomes large, which may result in a large diameter, whereas if the lower limit of condition (8) is not reached, the front group La becomes large, which is undesirable.

[0042] It is preferable that the following conditional expressions (3a) to (8a) be satisfied. 0.86<νn / νp<0.94 (3a) 1.68 <N1ave<1.78 (4a) -3.90 <f / fL1<-2.80 (5a) 0.22 <f / fLp<0.40 (6a) 0.50 <fLa / fLb<3.60 (7a) 0.75 <PD / (D+sk)<0.95 (8a)

[0043] It is more preferable that the following conditional expressions (3b) to (8b) be satisfied. 0.88<νn / νp<0.92 (3b) 1.72 <N1ave<1.75 (4b) -3.70 <f / fL1<-3.00 (5b) 0.25 <f / fLp<0.37 (6b) 0.80 <fLa / fLb<2.50 (7b) 0.80 <PD / (D+sk)<0.92 (8b)

[0044] The optical system L0 of each embodiment will be described in more detail below.

[0045] [Example 1] An optical system L0 according to the first embodiment will be described with reference to FIG.

[0046] In this embodiment, the front group La is composed of a first lens L1 with negative refractive power and a second lens L2 with positive refractive power, and the first lens L1 and the second lens L2 form a cemented lens. The lens surface on the object side of the first lens L1 is a concave surface, and the lens surface on the image side of the second lens L2 is a concave surface. The rear group Lb is composed of a third lens L3 with positive refractive power, a fourth lens L4 with negative refractive power, and a fifth lens L5 with positive refractive power.

[0047] In this embodiment, the negative lens Ln arranged closest to the image side among the lenses with negative refractive power in the rear group Lb is the fourth lens L4, which has an aspheric lens surface. The final lens Lp is the fifth lens L5, whose lens surface on the image side is convex.

[0048] [Example 2] Second Embodiment An optical system L0 according to a second embodiment will be described with reference to FIG.

[0049] The front group La in this embodiment is composed of a first lens L1 with negative refractive power and a second lens L2 with positive refractive power. The lens surface on the object side of the first lens L1 is concave, and the lens surface on the image side of the second lens L2 is concave. The configuration of the rear group Lb in this embodiment is the same as that in the first embodiment.

[0050] [Example 3] An optical system L0 according to the third embodiment will be described with reference to Fig. 5. The configuration of the optical system L0 in this embodiment is the same as that in the first embodiment.

[0051] [Example 4] An optical system L0 according to the fourth embodiment will be described with reference to Fig. 7. The configuration of the optical system L0 in this embodiment is the same as that in the first embodiment.

[0052] [Example 5] An optical system L0 according to the fifth embodiment will be described with reference to FIG.

[0053] The configuration of the front group La in this embodiment is the same as that of embodiment 1. The rear group Lb in this embodiment is composed of a cemented lens having a positive refractive power overall, which is composed of a third lens L3 having a positive refractive power and 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 negative lens Ln arranged closest to the image side among the lenses having negative refractive power in the rear group Lb is the fifth lens L5.

[0054] Numerical examples 1 to 5 corresponding to the first to fifth embodiments, respectively, are given below.

[0055] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial distance (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. In addition, nd represents the refractive index of each optical member with respect to the d-line, and νd represents the Abbe number of the optical member. The Abbe number νd of a certain material is a value defined by the following formula, where Nd, NF, NC, and Ng are the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), C-line (656.3 nm), and g-line (wavelength 435.8 nm) of the Fraunhofer lines. νd=(Nd-1) / (NF-NC)

[0056] In each numerical example, the focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system L0 of each example is focused on an object at infinity. The back focus BF is the distance from the lens surface on the image side of the final lens to the image surface. The total optical length (total lens length) is the value obtained by adding the back focus to the distance from the first lens surface to the lens surface on the image side of the final lens.

[0057] Furthermore, if the optical surface is aspheric, a * symbol is added to the right of the surface number. The aspheric shape can be expressed by the following formula, where X is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10, and A12 are aspheric coefficients of each order. Note that "e±XX" in each aspheric coefficient is expressed as "×10 ±XX " It means. x=(h 2 / R) / [1+{1-(1+K)(h / R) 2} 1 / 2 ]+A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12

[0058] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd vd 1 -27.121 1.50 1.62004 36.3 2 4.261 1.67 1.85150 40.8 3 58.540 (variable) 4(Aperture) ∞ 0.99 5 10.332 1.16 1.89190 37.1 6 25.198 1.11 7* -8.009 1.80 1.63540 23.9 8* -16.905 (variable) 9 208.243 1.62 1.51633 64.1 10 -40.135 (variable) Image plane ∞ Aspheric Data Side 7 K=0.00000e+00, A 4= 4.94284e-04, A 6=-3.88686e-05, A 8= 2.29406e-06 Side 8 K=0.00000e+00, A4=1.22034e-03, A 6=-8.89798e-06, A8=5.38393e-07, A10=-1.47677e-08, A12=-4.87074e-11 Focal length 21.45 F-number 8.00 Angle of view: 45.25 Image height 21.64 Lens length 27.17 BF 16.13

[0059] [Numerical Example 2] Unit: mm Surface Data Surface number rd nd vd 1 -39.352 2.18 1.63980 34.5 2 4.638 0.36 3 5.037 3.01 1.85150 40.8 4 60.596 (variable) 5(Aperture) ∞ 0.94 6 11.126 2.96 1.89190 37.1 7 24.570 1.15 8* -11.328 1.33 1.67070 19.3 9* -23.890 (variable) 10 44.002 1.74 1.51633 64.1 11 -81.936 (variable) Image plane ∞ Aspheric Data Side 8 K=0.00000e+00, A4=-1.71914e-04, A6=-9.52207e-05, A8=3.48209e-06 9th page K=0.00000e+00, A4=6.83439e-04, A6=-1.48459e-05, A8=-2.69727e-07, A10=7.39023e-08, A12=-1.83431e-09 Focal length 20.39 F-number 8.00 Angle of view: 46.70 Image height 21.64 Lens length 29.41 BF14.99

[0060] [Numerical Example 3] Unit: mm Surface Data Surface number rd nd vd 1 -23.183 1.50 1.60342 38.0 2 4.955 1.94 1.85150 40.8 3 241.544 (variable) 4(Aperture) ∞ 0.98 5 12.197 1.19 1.89190 37.1 6 96.724 0.99 7* -6.609 2.51 1.63540 23.9 8* -16.188 (variable) 9 208.243 2.17 1.51633 64.1 10 -38.757 (variable) Image plane ∞ Aspheric Data Side 7 K=0.00000e+00, A4=1.45769e-03, A6=-1.60101e-05, A8=-3.69892e-07 Side 8 K=0.00000e+00, A4=1.38395e-03, A6=2.59517e-06, A8=-4.11108e-07, A10=-5.30869e-09, A12=2.06322e-10 Focal length 20.65 F-number 8.00 Angle of view: 46.33 Image height 21.64 Lens length 27.64 BF 14.84

[0061] [Numerical Example 4] Unit: mm Surface Data Surface number rd nd vd 1 -23.361 0.74 1.60342 38.0 2 5.361 1.25 1.85150 40.8 3 196.224 (variable) 4(Aperture) ∞ 0.99 5 14.467 1.17 1.89190 37.1 6 243.323 0.90 7* -8.075 3.00 1.63540 23.9 8* -20.896 (variable) 9 208.243 1.33 1.51633 64.1 10 -83.510 (variable) Image plane ∞ Aspheric Data Side 7 K=0.00000e+00, A4= 6.52014e-04, A6=-1.17583e-05, A8=7.61621e-07 Side 8 K=0.00000e+00, A4=7.65764e-04, A6=-1.89814e-06, A8=-7.47075e-08, A10=5.32094e-09, A12=-1.85159e-10 Focal length 26.25 F-number 8.00 Angle of view 39.49 Image height 21.64 Lens length 31.98 BF 20.42

[0062] [Numerical Example 5] Unit: mm Surface Data Surface number rd nd vd 1 -28.100 1.03 1.62004 36.3 2 4.376 1.07 1.85150 40.8 3 63.362 (variable) 4(Aperture) ∞ 0.99 5 10.751 1.07 1.89190 37.1 6 16.330 1.03 1.74077 27.8 7 26.169 1.05 8* -8.840 2.28 1.67070 19.3 9* -18.648 0.85 10 208.243 2.50 1.51633 64.1 11 -30.885 (variable) Image plane ∞ Aspheric Data Side 8 K=0.00000e+00, A4=-2.55883e-04, A6=-3.14185e-05, A8=1.37367e-06 9th page K=0.00000e+00, A4=5.64074e-04, A6=-2.19562e-06, A8=3.62209e-07, A10=-8.27749e-09, A12=3.95720e-11 Focal length 21.04 F-number 8.00 Angle of view: 45.80 Image height 21.64 Lens length 26.85 BF 14.68

[0063] The various values ​​in each numerical example are summarized in Table 1 below.

[0064] [Table 1]

[0065] [Imaging device] Next, an embodiment of a digital still camera (imaging device) using the optical system L0 of the present invention as an imaging optical system will be described with reference to Fig. 11. In Fig. 11, 10 denotes a camera body, and 11 denotes an imaging optical system constituted by the optical system L0 of any one of the first to fifth embodiments. 12 denotes a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is built into the camera body and receives an optical image formed by the imaging optical system 11 and photoelectrically converts it. The camera body 10 may be a so-called single-lens reflex camera having a quick-turn mirror, or a so-called mirrorless camera having no quick-turn mirror.

[0066] In this way, by applying the optical system L0 of the present invention to an imaging device such as a digital still camera, it is possible to obtain an imaging device with a compact optical system.

[0067] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention.

[0068] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention.

[0069] The embodiments of the present invention include the following configurations.

[0070] [Configuration 1] It consists of a front group, an aperture stop, and a rear group, arranged in that order from the object side to the image side. a first lens having a negative refractive power and disposed closest to the object side, and a final lens having a positive refractive power and disposed closest to the image side; the front group includes a first negative lens having a concave lens surface on the object side and a first positive lens having a concave lens surface on the image side, Let f be the focal length of the entire system, D be the distance from the lens surface closest to the object side to the lens surface of the final lens closest to the image side, sk be the back focus, and fLa be the focal length of the front group. 1.00 <sk / D<1.80 0.00 <f / fLa<0.50 An optical system characterized in that the following condition is satisfied:

[0071] [Configuration 2] When the Abbe number of the material of the first negative lens is νn and the Abbe number of the material of the first positive lens is νp, 0.83<νn / νp<0.95 2. The optical system according to claim 1, wherein the following condition is satisfied:

[0072] [Configuration 3] 3. The optical system according to configuration 1 or 2, wherein the first negative lens is disposed closest to the object side.

[0073] [Configuration 4] When the average refractive index of the lenses constituting the front group is N1ave, 1.65 <N1ave<1.80 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied:

[0074] [Configuration 5] 5. The optical system according to any one of configurations 1 to 4, wherein the rear group comprises, in order from the object side to the image side, a positive lens, a negative lens, and a positive lens.

[0075] [Configuration 6] 5. The optical system according to any one of configurations 1 to 4, wherein the rear group comprises, in order from the object side to the image side, a positive lens, a positive lens, a negative lens, and a positive lens.

[0076] [Configuration 7] The optical system according to any one of configurations 1 to 6, wherein the lens surface on the image side of the final lens is a convex surface.

[0077] [Configuration 8] The optical system described in any one of configurations 1 to 7, characterized in that among the lenses with negative refractive power in the rear group, the negative lens arranged closest to the image side is a lens having an aspheric lens surface.

[0078] [Configuration 9] The optical system according to configuration 8, wherein the lens having the aspheric lens surface is a lens containing a resin as a material.

[0079] [Configuration 10] When the focal length of the first lens is fL1, -4.10 <f / fL1<-2.50 10. The optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied:

[0080] [Configuration 11] When the focal length of the final lens is fLp, 0.20 <f / fLp<0.45 11. The optical system according to any one of configurations 1 to 10, wherein the following condition is satisfied:

[0081] [Configuration 12] Let the focal length of the front group be fLa and the focal length of the rear group be fLb. 0.20 <fLa / fLb<4.20 12. The optical system according to any one of configurations 1 to 11, wherein the following condition is satisfied:

[0082] [Configuration 13] When the distance from the aperture stop to the image plane is PD, 0.70 <PD / (D+sk)<1.00 13. The optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied:

[0083] [Configuration 14] 14. The optical system according to any one of claims 1 to 13, characterized in that the optical system is made up of five or six lenses.

[0084] [Configuration 15] The optical system according to any one of configurations 1 to 14, an imaging device comprising an imaging element for photoelectrically converting an optical image formed by the optical system; [Explanation of symbols]

[0085] La front group SP aperture stop Lb rear group L1 First lens Lp final lens

Claims

1. It consists of a front group, an aperture stop, and a rear group, arranged in that order from the object side to the image side. a first lens having a negative refractive power and disposed closest to the object side, and a final lens having a positive refractive power and disposed closest to the image side; the front group includes a first negative lens having a concave lens surface on the object side and a first positive lens having a concave lens surface on the image side, Let f be the focal length of the entire system, D be the distance from the lens surface closest to the object side to the lens surface of the final lens closest to the image side, sk be the back focus, and fLa be the focal length of the front group. 1.00<sk / D<1.80 0.00<f / fLa<0.50 An optical system characterized in that the following condition is satisfied:

2. When the Abbe number of the material of the first negative lens is vn and the Abbe number of the material of the first positive lens is vp, 0.83<νn / νp<0.95 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. 2. The optical system according to claim 1, wherein the first negative lens is disposed closest to the object side.

4. When the average value of the refractive index of the lenses constituting the front group is N1ave, 1.65<N1ave<1.80 2. The optical system according to claim 1, wherein the following condition is satisfied:

5. 2. The optical system according to claim 1, wherein the rear group comprises, in order from the object side to the image side, a positive lens, a negative lens, and a positive lens.

6. 2. The optical system according to claim 1, wherein the rear group comprises, in order from the object side to the image side, a positive lens, a positive lens, a negative lens, and a positive lens.

7. 2. The optical system according to claim 1, wherein the lens surface on the image side of the final lens is a convex surface.

8. 2. The optical system according to claim 1, wherein, among the lenses having negative refractive power in the rear group, the negative lens arranged closest to the image side is a lens having an aspheric lens surface.

9. 9. The optical system according to claim 8, wherein the lens having the aspheric lens surface is a lens containing a resin as a material.

10. When the focal length of the first lens is fL1, -4.10<f / fL1<-2.50 2. The optical system according to claim 1, wherein the following condition is satisfied:

11. When the focal length of the final lens is fLp, 0.20<f / fLp<0.45 2. The optical system according to claim 1, wherein the following condition is satisfied:

12. Let fLa be the focal length of the front group and fLb be the focal length of the rear group. 0.20<fLa / fLb<4.20 2. The optical system according to claim 1, wherein the following condition is satisfied:

13. When the distance from the aperture stop to the image plane is PD, 0.70<PD / (D+sk)<1.00 2. The optical system according to claim 1, wherein the following condition is satisfied:

14. The optical system according to claim 1 , wherein the optical system comprises five or six lenses.

15. When the Abbe number of the material of the first negative lens is vn and the Abbe number of the material of the first positive lens is vp, 0.83<νn / νp<0.95 15. The optical system according to claim 3, wherein the following condition is satisfied:

16. 15. The optical system according to claim 4, wherein the first negative lens is disposed closest to the object side.

17. When the Abbe number of the material of the first negative lens is vn and the Abbe number of the material of the first positive lens is vp, 0.83<νn / νp<0.95 17. The optical system according to claim 16, wherein the following condition is satisfied:

18. An optical system according to any one of claims 1 to 14; an imaging device comprising an imaging element for photoelectrically converting an optical image formed by the optical system;

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