Macro lens

Abstract

To provide a macro lens that has a large-aperture ratio with a small amount of extension and is compact, adapting a front focusing method.SOLUTION: Upon focusing from infinity to a close distance in order from an object OBJ side, a macro lens has arranged first lens group G1 moving to the object OBJ side and fixed second lens group G2. The first lens group G1 has: an aperture stop STO; a first lens group G1A that is on a side closer to the object OBJ than the aperture stop STO; and a first lens group G1B that is closer to an image formation plane IMG side than the aperture stop STO. The first lens group G1A has at least, in the order from the object OBJ side, two positive lenses and one set of cemented lenses. The first lens group G1B has at least one set of cemented lenses. The second lens group G2 has at least, in the order from the object OBJ side, one set of cemented lenses and one negative lens.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a macro lens capable of photographing a close-range object.

Background Art

[0002] Among lenses used in optical devices for photographing photos and videos, there is a macro lens as a lens capable of photographing a close-range object with high resolution. While general lenses prioritize imaging performance at infinity, macro lenses are designed to obtain excellent imaging performance particularly in photographing close-range objects, but they are also used for photographing not only at close range but also at infinity and medium range. For example, Patent Document 1 (Japanese Patent No. 4986710) discloses a wide-angle macro lens system with an angle of view of about 42° to 43°, which can perform sufficient aberration correction over a wide range from infinity to high-magnification close-range photography.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the wide-angle macro lens system disclosed in Patent Document 1, when focusing from infinity to close range, it is stated that the focus adjustment mechanism can be simplified by adopting a front focus method in which the rear lens group is fixed and only the front group is moved toward the object side. However, in the digital camera market where miniaturization and weight reduction are progressing, a high-performance macro lens with a small extension amount is required.

Means for Solving the Problems

[0005] In order to achieve miniaturization, it is preferable to reduce the extension amount of the lens during close-range photography. The present invention has been made in view of the above circumstances, and an object thereof is to provide a macro lens that adopts a front focus method and has a large aperture ratio and a small size with a small extension amount.

[0006] According to the macro lens of the present invention, a first lens group that moves toward the object side and a fixed second lens group are arranged in order from the object side when focusing from infinity to a short distance. The first lens group has an aperture stop, a first lens group A on the object side of the aperture stop, and a first lens group B on the image forming surface side of the aperture stop. The first lens group A has at least two positive lenses and one set of cemented lenses in order from the object side, the first lens group B has at least one set of cemented lenses, and the second lens group has at least one set of cemented lenses and one negative lens in order from the object side. The total focal length of the system at infinity focus is f, and the distance from the lens surface closest to the object to the image plane is TL. Among the light rays that form an image at the center of the optical axis when focused at infinity, when the maximum height of the light ray on the lens surface closest to the object side is h1 and the maximum height of the light ray on the lens surface closest to the image forming surface side is h2, the following conditional expression (1) and (5) is satisfied. 1.0 <TL / f≦1.5 …(1) 0.25 < h2 / h1 …(5) By adopting this configuration, a macro lens with a large aperture ratio and a small size with a small extension amount can be obtained. If the lower limit of condition (1) is exceeded, spherical aberration cannot be corrected, resulting in a loss of resolution, and field curvature increases with changes in the distance to the object. If the upper limit of condition (1) is exceeded, spherical aberration improves, but the overall length and lens diameter of the product increase. In other words, condition (1) is a condition for suppressing the increase in product size while maintaining good optical performance, and by adopting the above configuration, macro lenses can be made smaller. When exceeding the lower limit of the conditional expression (5), it leads to an increase in the overall optical length and an increase in the outer diameter of the final lens, resulting in an increase in the size of the entire product. That is, the conditional expression (5) is a condition for suppressing the increase in the size of the product, and the macro lens can be miniaturized by adopting the above configuration.

[0008] Further, when the focal length of the first lens group at infinity focus is f1, the following conditional expression (2) is satisfied. 0.7 < f1 / f ≦ 1.2 …(2) If the lower limit of condition (2) is exceeded, the extension amount decreases, but the resolution at the edges of the image deteriorates due to coma aberration. If the upper limit of condition (2) is exceeded, the extension amount increases, and the overall length of the product becomes larger. In other words, condition (2) is a condition for suppressing the increase in extension amount while maintaining good optical performance, and by adopting the above configuration, a macro lens with a small extension amount can be made.

[0009] Furthermore, when the magnification ratio at the closest focusing point is M and the extension amount of the first lens group is X, the following condition (3) is satisfied. X≦fM …(3) For a front-focusing macro lens, it is preferable to satisfy condition (3).

[0010] Furthermore, it is characterized by satisfying the following condition (4). 0.45 <M …(4) For a macro lens, it is preferable that the condition (4) is satisfied. [Effects of the Invention]

[0012] The macro lens configuration of the present invention makes it possible to provide a macro lens with a large aperture ratio and a compact size with a small extension amount. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view of the macro lens in the first embodiment. [Figure 2] This is a schematic diagram of the optical path when the macro lens is focused at infinity in the first embodiment. [Figure 3] This is a longitudinal aberration diagram of a macro lens in the first embodiment. [Figure 4] This is a cross-sectional view of the macro lens in the second embodiment. [Figure 5] This is a longitudinal aberration diagram of the macro lens in the second embodiment. [Figure 6] This is a cross-sectional view of the macro lens in the third embodiment. [Figure 7] It is a diagram of the longitudinal aberration of the macro lens in the third embodiment.

Embodiments for Carrying Out the Invention

[0014] First, the basic configuration of the macro lens 100 will be described. In each embodiment shown in FIGS. 1, 4, and 6, the macro lens 100 includes, in order from the object OBJ side toward the imaging surface IMG side, a first lens group G1 that includes an aperture stop STO inside and has a positive refractive power, and a second lens group G2 that has a negative refractive power.

[0015] The first lens group G1 is movable along the optical axis, and the second lens group G2 is fixed. The macro lens 100 has a focusing mechanism by moving the first lens group G1. For example, when focusing from infinity to a short distance, the first lens group G1 is moved toward the object OBJ side.

[0016] The first lens group G1 includes, in order from the object OBJ side toward the imaging surface IMG side, a first lens group G1A, an aperture stop STO, and a first lens group G1B.

[0017] The first lens group G1A has at least two positive lenses and one set of cemented lenses in order from the object OBJ side. The first lens group G1B has at least one set of cemented lenses. The second lens group G2 has at least one set of cemented lenses and one negative lens in order from the object OBJ side. The above is the basic configuration of the macro lens 100 in each embodiment. Hereinafter, each embodiment will be described based on the drawings.

[0018] (First Embodiment) In the first lens group G1A in the first embodiment shown in FIG. 1, in order from the object OBJ side toward the imaging surface IMG side, there are a biconvex lens L1, a positive meniscus lens L2, and a first cemented lens L3 in which a biconcave lens L3f and a positive meniscus lens L3r are cemented.

[0019] On the image plane IMG side of the first lens group G1A, the aperture diaphragm STO is positioned at a predetermined distance from the first cemented lens L3. Furthermore, on the image plane IMG side of the aperture diaphragm STO, the first lens group G1B is positioned at a predetermined distance from the aperture diaphragm STO.

[0020] The first lens group G1B has a second cemented lens L4, which is formed by joining a negative meniscus lens L4f and a biconvex lens L4r, in order from the object OBJ side toward the image plane IMG side.

[0021] On the image plane IMG side of the first lens group G1B, the second lens group G2 is positioned at a predetermined distance from the second cemented lens L4.

[0022] The second lens group G2 includes, in order from the object OBJ side toward the image plane IMG side, a third cemented lens L5 formed by joining a positive meniscus lens L5f and a negative meniscus lens L5r, and a negative meniscus lens L6.

[0023] In the above configuration, more preferable numerical conditions will be described. When the overall focal length of the system at infinity focus is f, and the distance from the lens surface closest to the object OBJ to the image plane IMG is TL, it is preferable that the following condition (1) is satisfied. 1.0 <TL / f≦1.5 …(1) If the lower limit of condition (1) is exceeded, spherical aberration cannot be corrected, resulting in a loss of resolution, and field curvature increases with changes in the distance to the object's obj. If the upper limit of condition (1) is exceeded, spherical aberration improves, but the overall length and lens diameter of the product increase. In other words, condition (1) is a condition for suppressing the increase in product size while maintaining good optical performance.

[0024] Furthermore, when the focal length of the first lens group G1 at infinity focus is f1, it is preferable that the following condition (2) is satisfied. 0.7 <f1 / f≦1.2 …(2) When exceeding the lower limit of conditional expression (2), although the feeding amount decreases, the resolution of the peripheral part of the image deteriorates due to coma aberration. When exceeding the upper limit of conditional expression (2), the feeding amount increases and the overall length of the product becomes larger. That is, conditional expression (2) is a condition for suppressing the increase in the feeding amount while maintaining good optical performance.

[0025] Also, when the shooting magnification at the closest focusing is M and the feeding amount of the first lens group G1 is X, it is preferable to satisfy the following conditional expression (3). X≦fM …(3) As a macro lens of the front focus type, it is preferable to satisfy conditional expression (3).

[0026] Also, it is preferable to satisfy the following conditional expression (4). 0.45<M …(4) As a macro lens, it is preferable to satisfy conditional expression (4).

[0027] Also, among the light rays that form an image at the optical axis center when focused at infinity, when the maximum height of the light ray on the lens surface closest to the object OBJ side is h1 and the maximum height of the light ray on the lens surface closest to the image plane IMG side is h2 (see FIG. 2), it is preferable to satisfy the following conditional expression (5). 0.25<h2 / h1 …(5) When exceeding the lower limit of conditional expression (5), it leads to an increase in the overall optical length and an increase in the outer diameter of the final lens, and the entire product becomes larger. That is, conditional expression (5) is a condition for suppressing the enlargement of the product. Note that since these numerical conditions are the same in other embodiments, the description will be omitted below.

[0028] The optical data of this embodiment and the corresponding values of conditional expressions (1) to (5) are shown in Table 1.

[0029]

Table 1

[0030] As shown in Table 1, by adopting the lens configuration of this embodiment, all of the conditions (1) to (5) are satisfied, and a good large-aperture macro lens can be realized that is compact with a small extension amount and prevents the occurrence of spherical aberration and coma aberration.

[0031] Table 2 shows the surface data of each lens constituting the macro lens 100 in this embodiment.

[0032] [Table 2]

[0033] Table 2 shows the radius of curvature R(i), axial spacing D(i), refractive index nd(i), and Abbe number νd(i) of the lens surface corresponding to surface number i, where i is the surface number of the lens surface counted from the object OBJ side. In surface number i, OBJ indicates the object, STO indicates the aperture diaphragm, and IMG indicates the position of the image plane. The infinity of the radius of curvature R(i) is a plane. The axial spacing D(i) indicates the lens thickness or air gap between opposing surfaces. The refractive index nd(i) and Abbe number νd(i) are values ​​relative to the d line (587.56 nm), and a blank space indicates air. These matters are the same in other embodiments as well, so we will omit further explanation below.

[0034] Table 3 shows the variable focus intervals (axial plane spacing ZD0, ZD11, ZD16) of the macro lens 100 in this embodiment when it is in focus at infinity (magnification 0x) and when it is in focus at closest distance (magnification 0.50x).

[0035] [Table 3]

[0036] The longitudinal aberrations of the macro lens 100 in this embodiment will be explained with reference to Figure 3. The longitudinal aberration diagrams in Figure 3, from left to right, are spherical aberration diagrams (wavelengths 435.83 nm, 587.56 nm, 656.27 nm), astigmatism diagrams (wavelength 587.56 nm), and distortion aberration diagrams (wavelength 587.56 nm). The upper row (a) shows the case when focused at infinity, and the lower row (b) shows the case when focused at closest distance. The horizontal axis scales in each figure are ±0.50 mm, ±0.50 mm, and ±5.0%, respectively. In the astigmatism diagram, T represents the tangential plane (yz plane direction) of the focal point, and S represents the sagittal plane (xz plane direction). These matters are the same in other embodiments as well, so we will omit further explanation below.

[0037] Figure 3 shows that the macro lens 100 in this embodiment achieves good aberration correction in all aspects, regardless of the magnification (possessing good optical performance). In particular, the results for spherical aberration and astigmatism are excellent, indicating that it is a lens with high resolution and contrast.

[0038] (Second Embodiment) Next, a second embodiment will be described. In the second embodiment shown in Figure 4, the first lens group G1A has, in order from the object OBJ side toward the image plane IMG side, a biconvex lens L7, a positive meniscus lens L8, and a first cemented lens L9 formed by joining a biconcave lens L9f and a positive meniscus lens L9r.

[0039] On the image plane IMG side of the first lens group G1A, the aperture diaphragm STO is positioned at a predetermined distance from the first cemented lens L9. Furthermore, on the image plane IMG side of the aperture diaphragm STO, the first lens group G1B is positioned at a predetermined distance from the aperture diaphragm STO.

[0040] The first lens group G1B has a second cemented lens L10 formed by joining a biconvex lens L10f, a biconcave lens L10m, and a biconvex lens L10r, in order from the object OBJ side toward the image plane IMG side.

[0041] On the image plane IMG side of the first lens group G1B, the second lens group G2 is positioned at a predetermined distance from the second cemented lens L10.

[0042] The second lens group G2 includes, in order from the object OBJ side toward the image plane IMG side, a third cemented lens L11 formed by joining a positive meniscus lens L11f and a negative meniscus lens L11r, and a negative meniscus lens L12.

[0043] Table 4 shows the optical data and corresponding values ​​for conditional equations (1) to (5) in this embodiment.

[0044] [Table 4]

[0045] As shown in Table 4, by adopting the lens configuration of this embodiment, all of the conditions (1) to (5) are satisfied, and a good large-aperture macro lens can be realized that is compact with a small extension amount and prevents the occurrence of spherical aberration and coma aberration.

[0046] Table 5 shows the surface data of each lens constituting the macro lens 100 in this embodiment.

[0047] [Table 5]

[0048] Table 6 shows the variable focus intervals (axial plane spacing ZD0, ZD12, ZD17) of the macro lens 100 in this embodiment when it is in focus at infinity (magnification 0x) and when it is in focus at closest distance (magnification 0.50x).

[0049] [Table 6]

[0050] Figure 5 shows the longitudinal aberration diagram of the macro lens 100 in this embodiment. Regardless of the magnification, good aberration correction is achieved in all aspects (indicating excellent optical performance). In particular, the results for spherical aberration and astigmatism are excellent, indicating that this lens boasts high resolution and contrast.

[0051] (Third embodiment) Next, a third embodiment will be described. In the third embodiment shown in Figure 6, the first lens group G1A includes, in order from the object OBJ side toward the image plane IMG side, a biconvex lens L13, a positive meniscus lens L14, and a first bonded lens L15 formed by joining a biconcave lens L15f and a positive meniscus lens L15r.

[0052] On the image plane IMG side of the first lens group G1A, the aperture diaphragm STO is positioned at a predetermined distance from the first cemented lens L15. Furthermore, on the image plane IMG side of the aperture diaphragm STO, the first lens group G1B is positioned at a predetermined distance from the aperture diaphragm STO.

[0053] The first lens group G1B has a second cemented lens L16 formed by joining a negative meniscus lens L16f and a biconvex lens L16r, in order from the object OBJ side toward the image plane IMG side.

[0054] On the image plane IMG side of the first lens group G1B, the second lens group G2 is positioned at a predetermined distance from the second cemented lens L16.

[0055] The second lens group G2 includes, in order from the object OBJ side toward the image plane IMG side, a third cemented lens L17 formed by joining a biconvex lens L17f and a biconcave lens L17r, and a negative meniscus lens L18.

[0056] Table 7 shows the optical data and corresponding values ​​for conditional equations (1) to (5) in this embodiment.

[0057] [Table 7]

[0058] As shown in Table 7, by adopting the lens configuration of this embodiment, all of the conditions (1) to (5) are satisfied, and a good large-aperture macro lens can be realized that is compact with a small extension amount and prevents the occurrence of spherical aberration and coma aberration.

[0059] Table 8 shows the surface data of each lens constituting the macro lens 100 in this embodiment.

[0060] [Table 8]

[0061] Table 9 shows the variable focus intervals (axial plane spacing ZD0, ZD11, ZD16) of the macro lens 100 in this embodiment when it is in focus at infinity (magnification 0x) and when it is in focus at closest distance (magnification 0.50x).

[0062] [Table 9]

[0063] Figure 7 shows the longitudinal aberration diagram of the macro lens 100 in this embodiment. Regardless of the magnification, good aberration correction is achieved in all aspects (indicating excellent optical performance). In particular, the results for spherical aberration and astigmatism are excellent, indicating that this lens boasts high resolution and contrast.

[0064] As described above, the configuration of the macro lens 100 according to the first to third embodiments makes it possible to realize a macro lens that employs a front focusing method, has a large aperture ratio with a small extension amount, and is compact in size.

[0065] Although the configuration of the macro lens 100 according to the present invention has been described in detail based on several embodiments, the technical scope of the present invention is not limited to these embodiments. It is also possible to adopt modified forms described in the specification or forms that combine other known configurations as appropriate. [Explanation of symbols]

[0066] 100 Macro Lens G1 First Lens Group G1A First lens group A G1B First lens group B G2 2nd lens group IMG imaging plane L1 Biconvex Lens L2 positive meniscus lens L3 First cemented lens L3f biconcave lens L3r positive meniscus lens L4 Second Bonded Lens L4f Negative Meniscus Lens L4r biconvex lens L5 Third-Glare Lens L5f positive meniscus lens L5r Negative Meniscus Lens L6 Negative Meniscus Lens L7 Biconvex Lens L8 positive meniscus lens L9 First cemented lens L9f biconcave lens L9r positive meniscus lens L10 Second Bonded Lens L10f biconvex lens L10m Biconcave Lens L10r biconvex lens L11 Third-Glare Lens L11f positive meniscus lens L11r Negative Meniscus Lens L12 Negative Meniscus Lens L13 Biconvex Lens L14 positive meniscus lens L15 First Bonded Lens L15f biconcave lens L15r positive meniscus lens L16 Second Bonded Lens L16f Negative Meniscus Lens L16r biconvex lens L17 Third-bonded lens L17f biconvex lens L17r Biconcave Lens L18 Negative Meniscus Lens OBJ object STO aperture diaphragm

Claims

1. Starting from the object side, the lens system is arranged with a first lens group that moves toward the object when focusing from infinity to near distance, and a second lens group that remains fixed. The first lens group comprises an aperture diaphragm, a first lens group A on the object side of the aperture diaphragm, and a first lens group B on the image plane side of the aperture diaphragm. The first lens group A has, in order from the object side, at least two positive lenses and one set of cemented lenses. The first lens group B has at least one set of cemented lenses, The second lens group comprises, in order from the object side, at least one set of cemented lenses and one negative lens. A macro lens characterized by satisfying the following conditions (1) and (5), where f is the total focal length of the system when focused at infinity, TL is the distance from the lens surface closest to the object to the image plane, and h1 is the maximum height of the light ray imaged at the center of the optical axis when focused at infinity, and h2 is the maximum height of the light ray at the lens surface closest to the object. 1.0<TL / f≦1.5 (1) 0.25<h2 / h1...(5)

2. The macro lens according to claim 1, characterized in that when the focal length of the first lens group at infinity focus is f1, the following condition (2) is satisfied. 0.7<f1 / f≦1.2…(2)

3. The macro lens according to claim 1 or 2, characterized in that when the magnification at the closest focusing point is M and the extension amount of the first lens group is X, the following condition (3) is satisfied. X ≤ fM …(3)

4. A macro lens according to any one of items 1 to 3, characterized in that it satisfies the following condition (4). 0.45<M…(4)

Images