JP7605464B2 - Optical Lens System - Google Patents

Description

The present invention relates to an optical lens system that includes, in order from the object side to the image plane side, a first lens group, an aperture stop, and a second lens group.

2. Description of the Related Art There have been many proposals for the configuration of so-called double Gauss type optical lens systems for interchangeable lenses used in optical equipment for photography and videography.
For example, in Patent Document 1 (Japanese Patent No. 5217693), conditions for the lens having the highest refractive index in the first lens group are defined in order to satisfactorily correct various aberrations.
Furthermore, in Patent Document 2 (Japanese Patent No. 5,966,728), in order to reduce the number of lenses and to satisfactorily correct various aberrations, the radii of curvature and the like of two lenses in the first lens group are specified.

Patent No. 5217693 Patent No. 5966728

The optical lens systems disclosed in Patent Documents 1 and 2 are said to be able to effectively correct various aberrations with a small number of lenses, but in recent years, there has been a growing demand for miniaturization, and there is a demand for optical lens systems that are even smaller and have higher performance.

The present invention aims to provide an optical lens system that is compact and has good optical performance while shortening its overall length.

In the present invention, a first lens group having a positive refractive index, an aperture stop, and a second lens group having a positive refractive index are arranged in this order from the object side to the image forming surface side, the first lens group having, in this order from the object side to the image forming surface side, two positive meniscus lenses with convex surfaces facing the object side and a negative lens with a convex surface facing the object side, the second lens group having, in this order from the object side to the image forming surface side, a positive lens, a cemented lens consisting of a negative lens and a positive lens with a concave surface facing the object side, and a final positive lens, the refractive index at d-line of the entire system is denoted by nd and the Abbe number by vd, the two positive meniscus lenses in the first lens group and at least one positive lens in the second lens group satisfy the conditional expressions nd>1.82 and vd<44, and the optical lens system satisfies the conditional expression 0.35<BF/f<0.75, where f is a focal length of the entire system and BF is a distance from a final positive lens surface in the second lens group to the image plane.

This makes it possible to provide an optical lens system that has a shorter overall length and improved optical performance compared to optical system lenses in conventional technology.

The lens may also be characterized in that the at least one positive lens in the second lens group that satisfies the conditional expressions nd>1.82 and νd<44 includes the final positive lens.

The final lens in the second lens group may be formed to have the largest diameter in the second lens group.

Further, the present invention provides a zoom lens comprising, in order from an object side to an image forming surface side, a first lens group having a positive refractive index, an aperture stop, and a second lens group having a positive refractive index, the first lens group having, in order from the object side to the image forming surface side, two positive meniscus lenses with convex surfaces facing the object side, and a negative lens with a convex surface facing the object side, the second lens group having, in order from the object side to the image forming surface side, a positive lens, a cemented lens consisting of a negative lens and a positive lens with a concave surface facing the object side, and a final positive lens, and the first lens group includes The optical lens system is characterized in that an aberration correction lens is further disposed on the aperture stop side , and where nd is the refractive index at d-line of the entire system and vd is the Abbe number, the two positive meniscus lenses in the first lens group and at least one positive lens in the second lens group satisfy the conditional expressions nd>1.82 and vd<44, and where f is the focal length of the entire system and BF is the distance from a final positive lens surface in the second lens group to the image plane, the optical lens system satisfies the conditional expression 0.35<BF/f<0.75.
This allows for better correction of aberrations within a limited space.

The optical lens system configuration of the present invention makes it possible to reduce the overall length and improve the optical performance compared to optical lens systems with conventional structures.

FIG. 2 is a cross-sectional view of an optical lens system according to the first embodiment. FIG. 4 is a longitudinal aberration diagram of the optical lens system according to the first embodiment at infinity. FIG. 11 is a cross-sectional view of an optical lens system according to a second embodiment. FIG. 11 is a longitudinal aberration diagram of the optical lens system according to the second embodiment at infinity. FIG. 11 is a cross-sectional view of an optical lens system according to a third embodiment. 13A to 13C are longitudinal aberration diagrams of the optical lens system according to the third embodiment at infinity. FIG. 13 is a cross-sectional view of an optical lens system according to a fourth embodiment. 13A to 13C are longitudinal aberration diagrams of the optical lens system according to the fourth embodiment at infinity. FIG. 4 is a cross-sectional view of an optical lens system according to a reference embodiment.

The optical lens system in this embodiment is used in optical equipment for photography and videography, and is in particular a so-called double Gauss type optical lens system having a first lens group consisting of three lenses, an aperture stop, and a second lens group consisting of four lenses.
Each embodiment will be described below with reference to the drawings.

First Embodiment
An optical lens system 100 according to the first embodiment shown in FIG. 1 includes a first lens group G1, an aperture stop STO, and a second lens group G2, which are arranged in this order from an object OBJ toward an image plane IMG.

In this embodiment, the first lens group G1 includes, in order from the object OBJ side to the image plane IMG, a first positive meniscus lens L1, a second positive meniscus lens L2, a first negative lens L3, and an aberration correction lens L4. As is clear from Fig. 1, the second positive meniscus lens L2 (the second positive meniscus lens) and the first negative lens L3 are formed as a cemented lens. The first positive meniscus lens L1, the second positive meniscus lens L2, the first negative lens L3, and the aberration correction lens L4 are all formed as convex surfaces (curved surfaces) whose lens center side bulges out toward the object OBJ side relative to the lens outer periphery side.
The numbers of the lens surfaces (1, 2, 3, 4, 5, 6, 7) are counted from the side of the object OBJ. Thus, the first positive meniscus lens L1, the second positive meniscus lens L2, the first negative lens L3, and the aberration correction lens L4 are all arranged with their convex surfaces facing the side of the object OBJ. The first lens group G1 thus formed has a positive refractive index.

In this way, by forming all the lenses (L1 to L4) with a convex surface on the lens center side that bulges out toward the lens outer edge side and arranging them with the convex surface facing the object OBJ, it is possible to offset the lens center side of all the lenses (L1 to L4) in one direction. This has the advantage that the arrangement interval of each lens (L1 to L4) in the optical axis direction is minimized, and the optical axis direction length of the first lens group G1 can be shortened. In addition, because the second positive meniscus lens L2 and the first negative lens L3 form a cemented lens, the arrangement interval between the two lenses can be made zero, which offsets part of the increase in the optical axis direction length of the first lens group G1 due to the additional arrangement of the aberration correction lens L4.

By adopting the above-described configuration of the optical lens system 100, it is possible to shorten the overall length of the optical lens system 100 in the optical axis direction.

Next, the second lens group G2 in this embodiment will be described. The second lens group G2 is disposed at a required distance on the side of the image plane IMG from the aperture stop STO, which is disposed at a required distance on the side of the image plane IMG of the first lens group G1.
In the second lens group G2 in this embodiment, the first positive lens L5, the cemented lens L6, and the final positive lens L7 are arranged in the order listed from the object OBJ side to the image formation surface IMG side. The surface numbers of the lenses in the second lens group G2 are 9, 10, 11, 12, 13, 14, and 15 in the order from the object OBJ side to the image formation surface IMG side. The first positive lens L5 and the cemented lens L6 are arranged with a required interval, and the cemented lens L6 and the final positive lens L7 are arranged with their convex portions abutting each other. The second lens group G2 formed in this way has a positive refractive index.

The first positive lens L5 has a surface (surface number 9) on the object OBJ side formed with a radius of curvature that is substantially perpendicular to the optical axis, and a surface (surface number 10) on the image plane IMG side formed with a convex surface that bulges slightly toward the lens center toward the lens outer periphery. The cemented lens L6 in the second lens group G2 is formed of a second negative lens L6f formed with biconcave surfaces (surface numbers 11, 12), and a second positive lens L6r formed with biconvex surfaces (surface numbers 12, 13) that fits into the concave surface (surface number 12) on the image plane IMG side of the second negative lens L6f.
The cemented lens L6 thus formed is disposed with its concave surface (surface number 10) facing the object OBJ and its convex surface (surface number 13) facing the image plane IMG. The final positive lens L7, which is the final lens in the second lens group G2, is formed with biconvex surfaces (surface numbers 14 and 15) and is formed to have the largest diameter dimension in the second lens group G2.

Table 1 shows the surface data for each lens that constitutes the optical lens system 100 in this embodiment.

In Table 1, f, Fno, and ω respectively indicate the focal length, F-number, and half angle of the entire system. The surface number of the lens surface counted from the object OBJ side is i, and this surface number i corresponds to the symbol (number) shown in Figure 1. The values of the radius of curvature R(i), axial surface spacing D(i), lens refractive index nd(i), lens Abbe number νd(i), and focal length f(i) of each lens corresponding to this surface number (i) are shown in Table 1. nd(i) and νd(i) are values for the d-line (587.56 nm). The axial surface spacing D(i) indicates the lens thickness or air spacing between opposing surfaces. The units of the radius of curvature R(i) and axial surface spacing D(i) are mm. The surface number OBJ indicates the object, and the STO and IMG indicate the aperture stop and image plane, respectively.

As shown in Table 1, in the first positive meniscus lens L1 and the second positive meniscus lens L2 in this embodiment, i.e., in two positive lenses, nd and vd are set to satisfy the optical conditions of nd>1.82 and vd<44. Note that in this embodiment, the nd and vd of the aberration correction lens L4 also satisfy the optical conditions of nd>1.82 and vd<44.
For this reason, in this embodiment, the first positive meniscus lens L1 and the second positive meniscus lens L2 are made of a glass material with a high refractive index.

Furthermore, as shown in Table 1, in the respective positive lenses in the second lens group G2 of the optical lens system 100 in this embodiment, the first positive lens L5, the second positive lens L6r and the final positive lens L7 are all set to satisfy the optical conditional expressions of nd>1.82 and vd<44. That is, in this embodiment, at least one positive lens in the second lens group G2 satisfies the optical conditional expressions of nd>1.82 and vd<44.
For this reason, in this embodiment, a glass material with a high refractive index is used for the first positive lens L5, the second positive lens L6r, and the final positive lens L7.

Furthermore, in the optical lens system 100 of this embodiment, if the focal length of the optical lens system 100 is f (34.45 mm) and the distance from the surface of the final positive lens L7 in the second lens group G2 on the side of the image plane IMG (surface number 15: final lens surface) to the image plane IMG (back focus: 15.879 mm here) is BF, then BF/f = 0.461. In other words, the optical condition formula of 0.35<BF/f<0.75 is satisfied. The optical lens system 100 of this embodiment is used in an optical device equipped with a so-called APS-C size image sensor.

The longitudinal aberration in such an optical lens system 100 will be described with reference to FIG. 2. The longitudinal aberration diagrams in FIG. 2 are, from the left, (a) a spherical aberration diagram (wavelengths 656.27 nm, 587.56 nm, 435.83 nm), (b) an astigmatism diagram (wavelength 587.56 nm), and (c) a distortion aberration diagram (wavelength 587.56 nm). The horizontal axis scales in each diagram are ±0.50 mm, ±0.50 mm, and ±3.0%. In the astigmatism diagram (b), T represents the tangential plane (yz plane direction) of the focus, and S represents the sagittal plane (xz plane direction).

From FIG. 2, it can be seen that the optical lens system 100 in this embodiment provides good aberration correction in all aspects (good optical performance). In particular, this embodiment provides particularly good results in spherical aberration correction and field curvature correction, with high resolution and contrast, reduced flare, and clear peripheral images.

Second Embodiment
In the description of the optical lens system 100 of this embodiment, components common to the optical lens system 100 of the first embodiment are given the same reference numerals as in the first embodiment, and detailed descriptions thereof will be omitted here.

The first lens group G1 in this embodiment differs from the configuration of the first lens group G1 in the first embodiment in that the second positive meniscus lens L2 and the first negative lens L3 are independent and not formed as a cemented lens, and in that the aberration correction lens L4 is omitted.
According to the configuration of the first lens group G1, it is possible to shorten the length of the first lens group G1 in the optical axis direction and to shorten the distance between the first lens group G1 and the aperture stop STO. Note that, in this embodiment, the first lens group G1 also has a positive refractive index.

In the second lens group G2 in this embodiment, the second negative lens L6f and the second positive lens L6r constituting the cemented lens L6 are formed with the same outer diameter, and the diameter of the final positive lens L7 is formed with the same outer diameter as the outer diameter of the cemented lens L6 adjacent to the object OBJ side. The cemented lens L6 of the second lens group G2 in this embodiment can be made significantly thinner than the cemented lens L6 in the first embodiment, making it possible to shorten the optical axis length of the second lens group G2. Note that although the BF in the second lens group G2 in this embodiment is slightly longer than the BF in the first embodiment, the optical axis length of the second lens group G2 can be made shorter than the second lens group G2 in the first embodiment.

By adopting the above-described configuration of the optical lens system 100, it is possible to shorten the overall length of the optical lens system 100 in the optical axis direction.

Table 2 shows the surface data of each lens that constitutes the optical lens system 100 in this embodiment.

Table 2 has the same format as Table 1. As shown in Table 2, in the optical lens system 100 of this embodiment, the first positive meniscus lens L1 and the second positive meniscus lens L2 in the first lens group G1, i.e., the two positive lenses, are set so as to satisfy the optical conditional expressions of nd>1.82 and vd<44.
For this reason, in this embodiment, the first positive meniscus lens L1 and the second positive meniscus lens L2 are made of a glass material with a high refractive index.

The final positive lens L7 in the second lens group G2 is set to satisfy the optical conditions nd>1.82 and vd<44. Therefore, at least one positive lens in the second lens group G2 satisfies the optical conditions nd>1.82 and vd<44.
For this reason, in this embodiment, a glass material with a high refractive index is used for the final positive lens L7.

In this embodiment, among the positive lenses (L5, L6r, L7) in the second lens group G2, the final positive lens L7 satisfies the optical condition formulas nd>1.82 and νd<44, but it is sufficient that at least one of the first positive lens L5, the second positive lens L6r, and the final positive lens L7 satisfies the above optical condition formulas.

Furthermore, in the optical lens system 100 of this embodiment, if the focal length of the optical lens system 100 is f (38.00 mm) and the distance from the surface of the final positive lens L7 in the second lens group G2 on the image plane IMG side (surface number 14: final lens surface) to the image plane IMG (19.299 mm) is BF, then BF/f = 0.508. In other words, the optical condition formula of 0.35 < BF/f < 0.75 is satisfied. The optical lens system 100 of this embodiment is used in an optical device equipped with a so-called APS-C size image sensor.

The longitudinal aberration in such an optical lens system 100 will be described with reference to FIG. 4. The longitudinal aberration diagram in FIG. 4 is expressed in the same way as in FIG. 2. From FIG. 4, it can be seen that the optical lens system 100 in this embodiment has good aberration correction in all aspects (has good optical performance). In particular, this embodiment has good spherical aberration correction, high resolution and contrast, and can suppress the occurrence of flare.

Third Embodiment
In describing the optical lens system 100 of this embodiment, detailed descriptions of components common to the optical lens system 100 of the first and second embodiments will be omitted by assigning the same symbols as those used in the first and second embodiments.

The optical lens system 100 in this embodiment has a basic configuration common to the first embodiment as shown in FIG. 5, but the specific configuration of the cemented lens L6 in the second lens group G2 is different. That is, the cemented lens L6 in this embodiment is formed of a second negative lens L6f and a second positive lens L6r, both of which have a shape curved toward the image plane IMG on both sides (surface numbers 11, 12 and surface numbers 12, 13). The outer diameter of the second negative lens L6f is smaller than the outer diameter of the second positive lens L6r. Furthermore, the final positive lens L7 has both of its two surfaces (surface numbers 14, 15) curved toward the image plane IMG. By adopting such a configuration, the optical axis length of the second lens group G2 can be shortened. Note that both the first lens group G1 and the second lens group G2 in this embodiment have a positive refractive index.

By adopting the above-described configuration of the optical lens system 100, it is possible to shorten the overall length of the optical lens system 100 in the optical axis direction.

Table 3 shows the surface data of each lens that constitutes the optical lens system 100 in this embodiment.

Table 3 has the same format as Tables 1 and 2. As shown in Table 3, in the optical lens system 100 of this embodiment, the first positive meniscus lens L1 and the second positive meniscus lens L2 in the first lens group G1, i.e., the two positive lenses, are set so as to satisfy the optical conditional expressions of nd>1.82 and vd<44.
For this reason, in this embodiment, the first positive meniscus lens L1 and the second positive meniscus lens L2 are made of a glass material with a high refractive index.

The second positive lens L6r and the final positive lens L7 in the second lens group G2 are set to satisfy the optical conditions nd>1.82 and vd<44. That is, in the second lens group G2, at least one positive lens satisfies the optical conditions nd>1.82 and vd<44.
For this reason, in this embodiment, a glass material with a high refractive index is used for the second positive lens L6r and the final positive lens L7.

In this embodiment, among the positive lenses (L5, L6r, L7) in the second lens group G2, the second positive lens L6r and the final positive lens L7 satisfy the optical condition formulas nd>1.82 and νd<44, but it is sufficient that at least one of the first positive lens L5, the second positive lens L6r, and the final positive lens L7 satisfies the above optical condition formulas.

Furthermore, in the optical lens system 100 of this embodiment, if the focal length of the optical lens system 100 is f (36.50 mm) and the distance from the surface of the final positive lens L7 in the second lens group G2 on the image plane IMG side (surface number 15: final lens surface) to the image plane IMG is BF (20.010 mm), then BF/f = 0.548. In other words, the optical condition formula of 0.35 < BF/f < 0.75 is satisfied. The optical lens system 100 of this embodiment is used in an optical device equipped with a so-called full-size image sensor.

The longitudinal aberration in such an optical lens system 100 will be described with reference to FIG. 6. The longitudinal aberration diagram in FIG. 6 has the same format as the aberration diagrams shown in FIG. 2 and FIG. 4. From FIG. 6, it can be seen that the optical lens system 100 in this embodiment has good aberration correction in all aspects (has good optical performance). In particular, in this embodiment, distortion correction is good, making it possible to capture images that are faithful to the human visual sense.

Fourth Embodiment
In describing the optical lens system 100 of this embodiment, detailed descriptions of configurations common to the optical lens system 100 of the first to third embodiments will be omitted by assigning the same symbols as those used in the first to third embodiments.

The optical lens system 100 in this embodiment has a basic configuration common to that of the second embodiment as shown in FIG. 7, but the specific shapes of the first positive lens L5 and the final positive lens L7 in the second lens group G2 are different. That is, the first positive lens L5 in this embodiment is formed into a biconvex shape (surface numbers 8 and 9), and the outer diameter of the final positive lens L7 is formed to be larger than the outer diameter of the cemented lens in the second lens group G2. Note that both the first lens group G1 and the second lens group G2 in this embodiment have positive refractive indices.

Table 4 shows the surface data for each lens that constitutes the optical lens system 100 in this embodiment.

Table 4 has the same format as Tables 1, 2, and 3. As shown in Table 4, in the optical lens system 100 of this embodiment, the first positive meniscus lens L1 and the second positive meniscus lens L2 in the first lens group G1, i.e., the two positive lenses, are set so as to satisfy the optical conditional expressions of nd>1.82 and vd<44.
For this reason, in this embodiment, a glass material with a high refractive index is used for the first positive meniscus lens L1 and the second positive meniscus lens L2.

The second positive lens L6r and the final positive lens L7 in the second lens group G2 are set to satisfy the optical conditions nd>1.82 and vd<44. That is, in the second lens group G2, at least one positive lens satisfies the optical conditions nd>1.82 and vd<44.
For this reason, in this embodiment, a glass material with a high refractive index is used for the second positive lens L6r and the final positive lens L7.

In this embodiment, among the positive lenses (L5, L6r, L7) in the second lens group G2, the second positive lens L6r and the final positive lens L7 satisfy the optical condition formulas nd>1.82 and νd<44, but it is sufficient that at least one of the first positive lens L5, the second positive lens L6r, and the final positive lens L7 satisfies the above optical condition formulas.

Furthermore, the optical lens system 100 in this embodiment satisfies the optical condition formula of 0.35<BF/f<0.75, where BF/f=0.528, assuming that the focal length of the optical lens system 100 is f (42.00 mm) and the distance from the surface of the final positive lens L7 in the second lens group G2 on the image plane IMG side (surface number 14: final lens surface) to the image plane IMG is BF (22.180 mm). The optical lens system 100 in this embodiment is used in an optical device equipped with a so-called full-size image sensor.

By adopting the above-described configuration of the optical lens system 100, it is possible to shorten the overall length of the optical lens system 100 in the optical axis direction.

The longitudinal aberration in such an optical lens system 100 will be described with reference to FIG. 8. The longitudinal aberration diagram in FIG. 8 has the same format as FIG. 2, FIG. 4, and FIG. 6. From FIG. 8, it can be seen that the optical lens system 100 in this embodiment has good aberration correction in all aspects (has good optical performance). In particular, in this embodiment, both the spherical aberration correction and the distortion correction are extremely good, and the resolution and contrast are high, the occurrence of flare can be suppressed, and images faithful to the human visual sense can be captured.

As in the optical lens systems of the first to fourth embodiments described above, the first lens group G1 includes a first positive meniscus lens L1 and a second positive meniscus lens L2 as two high refractive index positive meniscus lenses, and the second lens group G2 includes a final positive lens L7 as one high refractive index positive lens. This means that the lenses at both ends of the object side and the image plane side of the so-called double Gauss type optical lens system are constructed with high refractive index lenses, which shortens the length in the optical axis direction of the first lens group G1 and the second lens group G2 and allows correction of spherical aberration and astigmatism.

(Reference embodiment)
Next, an optical lens system 100 in a reference embodiment will be described. In the reference embodiment, components common to the optical lens system 100 in the first to fourth embodiments will be denoted by the same reference symbols used in the first to fourth embodiments, and detailed descriptions thereof will be omitted here.

The optical lens system 100 in the reference embodiment has a basic configuration in common with the first embodiment as shown in FIG. 9, but the specific shape is different. That is, both surfaces (surface numbers 11 and 12) of the second negative lens L6f and both surfaces (surface numbers 12 and 13) of the second positive lens L6r in the cemented lens L6 are formed as convex surfaces on the side of the image plane IMG, which is a difference from the first embodiment. Note that both the first lens group G1 and the second lens group G2 in the reference embodiment have a positive refractive index.

Table 5 shows the surface data for each lens that constitutes the optical lens system 100 in this embodiment.

Table 5 has the same format as Tables 1, 2, 3, and 4. In the optical lens system 100 of the reference embodiment, only the aberration correction lens in the first lens group G1 satisfies the optical conditions of nd>1.82 and vd<44, and none of the positive lenses satisfies the optical conditions of nd>1.82 and vd<44.
Moreover, only the first positive lens L5, which is a part of the positive lenses in the second lens group G2, satisfies the optical conditions nd>1.82 and νd<44.

Incidentally, if the distance from the surface (surface number 15: final lens surface) of the final positive lens L7 in the second lens group G2 of the optical lens system 100 in the reference embodiment on the image plane IMG side to the image plane IMG is BF (15.880 mm), then BF/f = 0.432, and the optical condition formula of 0.35 < BF/f < 0.75 is satisfied. The optical lens system 100 in the reference embodiment is used in an optical device equipped with a so-called APS-C size image sensor.

Experiments on longitudinal aberration were also carried out on the optical lens system 100 in the reference embodiment in the same manner as in the first to fourth embodiments, and the results are as follows.
Regarding the spherical aberration diagram (a) (wavelengths 656.27 nm, 587.56 nm, 435.83 nm), the spherical aberration is greatly curved, the resolving power is reduced, flare occurs, and the contrast is reduced.
Regarding (b) astigmatism (wavelength 587.56 nm), the field curvature becomes large and the peripheral image is not focused on the sensor plane.
Regarding (c) distortion aberration diagram (wavelength 587.56 nm), distortion becomes large and it is not possible to take a photograph as it appears to the eye.

Furthermore, it has become clear that the following problems occur in the reference embodiment.
It is not possible to use it with APS-C or full-size image sensors because it does not have enough light to cover the sensor size.
Large coma aberration occurs, and the MTF performance deteriorates.
Magnification chromatic aberration increases, causing color bleeding in the image toward the edges of the screen.
Aberration correction is insufficient, and the above-mentioned performance degradation becomes noticeable especially on the close distance side.
The front lens diameter becomes larger, and the maximum diameter of the product becomes thicker.
The radius of curvature of the lens becomes small, which makes processing difficult or increases the production costs.
The tolerance for manufacturing errors becomes extremely small, resulting in poor productivity.

Therefore, as in the optical lens system 100 of the reference embodiment, simply satisfying the optical condition of 0.35<BF/f<0.75 by providing one positive lens each in the first lens group G1 and the second lens group G2 that satisfy nd>1.82 and νd<44 would result in the problems described above compared to the optical lens systems 100 of embodiments 1 to 4, and would not be a solution to the problems that the present invention aims to solve.

As described above, the configuration of the optical lens system 100 according to the first to fourth embodiments makes it possible to make the overall length in the optical axis direction more compact than the optical lens system 100 according to the conventional technology and the reference embodiment, and also improves aberration performance.

The configuration of the optical lens system 100 according to the present invention has been described in detail based on several embodiments, but the technical scope of the present invention is not limited to the above embodiments. It is also possible to adopt a form that appropriately combines the modified examples described in the specification and other known configurations.

100 Optical lens system G1 First lens group STO Aperture stop G2 Second lens group L1 First positive meniscus lens L2 Second positive meniscus lens L3 First negative lens L4 Aberration correction lens L5 First positive lens L6 Cemented lens L6f Second negative lens L6r Second positive lens L7 Last positive lens nd Refractive index νd at d line of entire system Abbe number f Focal length BF of entire system Distance from the last lens surface in the second lens group to the image plane (back focus)

Claims (6)

a first lens group having a positive refractive index, an aperture stop, and a second lens group having a positive refractive index are arranged in this order from the object side to the image forming surface side;
the first lens group includes, in order from the object side to the image plane side, two positive meniscus lenses each having a convex surface facing the object side and a negative lens each having a convex surface facing the object side,
the second lens group includes, in order from the object side to the image forming surface side, a positive lens, a cemented lens including a negative lens and a positive lens , the cemented lens having a concave surface facing the object side, and a final positive lens,
a cemented lens is formed by the second positive meniscus lens and the negative lens in the first lens group,
When the refractive index at the d line of the entire system is nd and the Abbe number is vd,
The two positive meniscus lenses in the first lens group and the at least one positive lens in the second lens group are
nd>1.82 and νd<44
is satisfied, and if the focal length of the entire system is f and the distance from the final positive lens surface in the second lens group to the image-forming surface is BF, then
0.35<BF/f<0.75
An optical lens system characterized in that the following condition is satisfied: The optical lens system according to claim 1, characterized in that the final positive lens is included in at least one positive lens in the second lens group that satisfies the conditions nd>1.82 and νd<44. 3. The optical lens system according to claim 1, wherein the final positive lens in the second lens group is formed to have the largest diameter in the second lens group. a first lens group having a positive refractive index, an aperture stop, and a second lens group having a positive refractive index are arranged in this order from the object side to the image forming surface side;
the first lens group includes, in order from the object side to the image plane side, two positive meniscus lenses each having a convex surface facing the object side and a negative lens each having a convex surface facing the object side,
the second lens group includes, in order from the object side to the image forming surface side, a positive lens, a cemented lens including a negative lens and a positive lens , the cemented lens having a concave surface facing the object side, and a final positive lens,
the first lens group further includes an aberration correction lens disposed on the aperture stop side;
When the refractive index at the d line of the entire system is nd and the Abbe number is vd,
The two positive meniscus lenses in the first lens group and the at least one positive lens in the second lens group are
nd>1.82 and νd<44
is satisfied, and if the focal length of the entire system is f and the distance from the final positive lens surface in the second lens group to the image-forming surface is BF, then
0.35<BF/f<0.75
An optical lens system characterized in that the following condition is satisfied: 5. The optical lens system according to claim 4 , wherein the at least one positive lens in the second lens group that satisfies the conditions nd>1.82 and νd<44 includes the final positive lens. 6. The optical lens system according to claim 4 , wherein the final positive lens in the second lens group is formed to have the largest diameter in the second lens group.