JP7484149B2 - Teleconverter lenses, optical systems and optical instruments - Google Patents

Description

The present invention relates to a teleconverter lens, an optical system , and an optical device.

Conventionally, a method has been known in which a teleconverter lens with a negative focal length is inserted between the master lens and the camera body to extend the focal length of the photographing lens (see, for example, Patent Document 1). However, Patent Document 1 has an issue in that further improvements in optical performance are required.

JP 2017-62317 A

A teleconverter lens according to a first aspect of the present invention is a teleconverter lens that is arranged on the image side of a master lens and extends the focal length of the entire optical system including the master lens, and has a diffractive surface that is formed on a positive single lens that satisfies the condition of the following equation:
40.00 < νp < 100.00
1.40 < np < 1.90
however,
νp: Abbe number for the d-line of the medium of the positive single lens
np: refractive index of the medium of the positive single lens with respect to the d line

An optical system according to a first aspect of the present invention has a diffractive surface on the lens closest to the image side, and the lens closest to the image side is a positive single lens that satisfies the following condition:
40.00 < νp < 70.00
1.40 < np ≦ 1.517420
however,
νp: Abbe number of the medium of the positive single lens for the d line np: refractive index of the medium of the positive single lens for the d line

1 is a cross-sectional view of a camera equipped with a teleconverter lens according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the lens configuration of a master lens (when a teleconverter lens is not attached). 4A to 4C are diagrams showing various aberrations of the master lens. FIG. 2 is a cross-sectional view showing a lens configuration of an optical system consisting of a master lens and a teleconverter lens according to the first example. 3A to 3C are diagrams showing various aberrations of an optical system including a master lens and a teleconverter lens according to Example 1. FIG. 11 is a cross-sectional view showing the lens configuration of an optical system consisting of a master lens and a teleconverter lens according to a second example. 11A to 11C are diagrams showing various aberrations of an optical system including a master lens and a teleconverter lens according to the second example. FIG. 11 is a cross-sectional view showing the lens configuration of an optical system consisting of a master lens and a teleconverter lens according to a third example. 13A to 13C are diagrams showing various aberrations of an optical system including a master lens and a teleconverter lens according to the third example. 4 is a flowchart for explaining a method of manufacturing the teleconverter lens.

A preferred embodiment will be described below with reference to the drawings. As shown in FIG. 1, the teleconverter lens TCL according to this embodiment is disposed on the image side of the master lens ML, and is configured so that the combined focal length with this master lens ML is longer than the focal length of the master lens ML. Specifically, the description will be based on a camera 10, which is an optical device equipped with the teleconverter lens TCL according to this embodiment, as shown in FIG. 1. This camera 10 is a so-called mirrorless camera with interchangeable lenses that has a master lens ML as the photographing lens 2. The teleconverter lens 3 (TCL) is attached between the photographing lens 2, which is the master lens ML, and the camera body 1 that has the imaging unit 4.

In this camera 10, light from an object (subject) (not shown) is collected by the photographing lens 2 and teleconverter lens 3, and passes through an OLPF (Optical low pass filter) FL to form a subject image on the imaging surface of the imaging unit 4. The subject image is then photoelectrically converted by a photoelectric conversion element provided in the imaging unit 4 to generate an image of the subject. This image is displayed on an EVF (Electronic view finder) 5 provided in the camera body 1. This allows the photographer to observe the subject through the EVF 5.

When the photographer presses a release button (not shown), the image photoelectrically converted by the imaging unit 4 is stored in a memory (not shown). In this way, the photographer can photograph the subject using the camera 10. Note that, although an example of a mirrorless camera has been described in this embodiment, the same effects as the camera 10 can be achieved even if the teleconverter lens TCL according to this embodiment is mounted on a single-lens reflex type camera that has a quick-return mirror in the camera body and observes the subject through a viewfinder optical system.

The teleconverter lens TCL according to this embodiment is disposed on the image side of the master lens ML as shown in FIG. 2, and extends the focal length of the master lens ML.

Conventionally, a rear converter that has a negative refractive power and is arranged on the image side of a master lens to expand the focal length is known. However, in the lenses for recent mirrorless cameras, the back focus of the master lens is short, so the distance between the focal plane of the master lens and the rear converter is short, and the refractive power (power) of the lens group of the rear converter (converter lens group) is strong, making it difficult to correct both the Petzval sum and the chromatic aberration. That is, since the converter lens group has a strong negative power as a whole, it is necessary to lower the refractive index of the medium of the positive lens and to increase the refractive index of the medium of the negative lens in order to bring the Petzval sum closer to zero. On the other hand, in order to correct chromatic aberration, the Abbe number of the medium of the positive lens needs to be small and the Abbe number of the medium of the negative lens needs to be large, but in general optical glass, the Abbe number tends to decrease as the refractive index increases, making this correction difficult.

In contrast, a diffractive lens with a diffractive surface does not affect the Petzval sum, and while it has positive refractive power (power), it has the strong achromatic effect of a negative lens with an Abbe number equivalent of -3.453. Therefore, by arranging the diffractive surface D, the teleconverter lens TCL of this embodiment achieves extremely excellent image plane flatness and chromatic aberration correction while being small in size and mainly used as a rear converter for mirrorless cameras, due to the properties of the diffractive lens (diffractive surface). Note that in this embodiment, the diffractive lens (diffractive surface) is used as an optical element with negative refractive power (power), and has the achromatic effect of a strong positive lens.

It is desirable for the teleconverter lens TCL according to this embodiment to satisfy the following conditional expression (1).

0.010 < f / fpf < 0.100 (1)
however,
f: focal length of teleconverter lens TCL fpf: focal length of diffractive surface D

Conditional formula (1) specifies the ratio of the focal length of the teleconverter lens TCL to the focal length of the diffractive surface D. By satisfying this conditional formula (1), good optical performance can be obtained. Exceeding the range of conditional formula (1) is undesirable because it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration, especially secondary spectrum. In order to ensure the effect of conditional formula (1), it is more preferable to set the lower limit of conditional formula (1) to 0.011, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, and even more preferable to set it to 0.025. In addition, in order to ensure the effect of conditional formula (1), it is more preferable to set the upper limit of conditional formula (1) to 0.099, 0.095, 0.090, 0.085, 0.080, 0.078, 0.075, 0.073, and even more preferable to set it to 0.070.

It is desirable for the teleconverter lens TCL according to this embodiment to satisfy the following conditional expression (2).

1.10 < β < 2.50 (2)
however,
β: Magnification of teleconverter lens TCL

Conditional formula (2) specifies the magnification of the teleconverter lens TCL. By satisfying this conditional formula (2), good optical performance can be obtained. If the lower limit of conditional formula (2) is exceeded, that is, if the magnification of the teleconverter lens TCL is low, the total length of the teleconverter lens TCL becomes relatively large compared to the increase in the focal length of the optical system when the teleconverter lens TCL is attached, and the back focus of the optical system when the teleconverter lens TCL is attached becomes insufficient, which is not preferable. In order to ensure the effect of conditional formula (2), it is more preferable to set the lower limit of conditional formula (2) to 1.20, and even more preferable to set it to 1.30. In addition, if the upper limit of conditional formula (2) is exceeded, that is, if the magnification of the teleconverter lens TCL is high, performance cannot be obtained even if the diffractive surface D is used, and the lens becomes large, which is not preferable. In order to ensure the effect of conditional formula (2), it is more preferable to set the upper limit of conditional formula (2) to 2.40, 2.30, 2.20, and even more preferable to set it to 2.10.

It is desirable for the teleconverter lens TCL according to this embodiment to satisfy the following conditional expression (3).

10.00 mm < L < 49.00 mm (3)
however,
L: the distance on the optical axis from the image plane of the master lens ML when the teleconverter lens TCL is not attached to the master lens ML to the lens surface of the teleconverter lens TCL closest to the object when the teleconverter lens TCL is attached

Conditional formula (3) specifies the distance on the optical axis from the image plane of the master lens ML when the teleconverter TCL is not attached to the master lens ML to the lens surface of the teleconverter lens TCL closest to the object side when the teleconverter lens TCL is attached. Optically, this L corresponds to the object distance for the teleconverter TCL. By satisfying this conditional formula (3), good optical performance can be obtained. If the lower limit of conditional formula (3) is exceeded, the refractive power (power) of the teleconverter TCL becomes too strong, making it difficult to correct the curvature of field, which is not preferable. In order to ensure the effect of conditional formula (3), it is more preferable to set the lower limit of conditional formula (3) to 12.50, 15.00, 16.50, 18.00, 20.00, 21.50, 22.00, 23.00, 23.50, 24.00, 24.50, and even 25.00. Furthermore, if the upper limit value of conditional expression (3) is exceeded, the effect of diffractive surface D cannot be exhibited, which is undesirable. In order to ensure the effect of conditional expression (3), it is more preferable to set the upper limit value of conditional expression (3) to 47.50, 45.00, 42.50, 40.00, 37.50, 35.00, 33.00, 32.50, 32.00, 31.50, 31.00, 30.50, and even more preferably 30.00.

It is desirable for the teleconverter lens TCL according to this embodiment to have at least one positive lens (hereinafter referred to as the "specific positive lens") that satisfies the following conditional expressions (4) and (5).

40.00 < vp < 100.00 (4)
1.40 < np < 1.90 (5)
however,
νp: Abbe number of a specific positive lens medium for the d line np: refractive index of a specific positive lens medium for the d line

Conditional formula (4) and conditional formula (5) stipulate the Abbe number and refractive index for the d-line of the medium of the specific positive lens included in the teleconverter lens TCL. By providing the specific positive lens that satisfies conditional formula (4) and conditional formula (5) in the teleconverter lens TCL, axial chromatic aberration and lateral chromatic aberration can be effectively corrected.

If the range of conditional expression (4) is exceeded, it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration, which is undesirable. In order to ensure the effect of conditional expression (4), it is more preferable to set the lower limit of conditional expression (4) to 41.00, 42.50, 44.00, 45.00, 46.00, 47.00, 48.00, 49.00, and even more preferable to set the upper limit of conditional expression (4) to 95.00, 90.00, 85.00, 80.00, 75.00, 70.00, 65.00, 63.00, 60.00, 58 ...55.00.

If the lower limit of conditional formula (5) is exceeded, the curvature of the lens surface of the specific positive lens becomes too sharp, which is undesirable as it deteriorates aberration correction and workability. In order to ensure the effect of conditional formula (5), it is more preferable to set the lower limit of conditional formula (5) to 1.42, 1.45, 1.48, or even 1.50. In addition, if the upper limit of conditional formula (5) is exceeded, it is undesirable as it becomes difficult to correct the Petzval sum. In order to ensure the effect of conditional formula (5), it is more preferable to set the upper limit of conditional formula (5) to 1.80, 1.75, 1.70, 1.65, 1.60, 1.58, or even 1.55.

In the teleconverter lens TCL according to this embodiment, it is desirable that the diffractive surface D is formed on the specific positive lens described above. With this configuration, the effect of the diffractive surface D can be fully exerted.

It is desirable for the teleconverter lens TCL according to this embodiment to satisfy the following conditional expression (6).

0.15 < Lpf/TL < 0.75 (6)
however,
Lpf: the distance on the optical axis from the diffraction surface D to the image plane when the teleconverter lens TCL is attached to the master lens ML. TL: the distance on the optical axis from the lens surface closest to the object of the teleconverter lens TCL to the image plane when the teleconverter lens TCL is attached to the master lens ML.

Conditional formula (6) specifies the ratio of the distance on the optical axis from the diffractive surface D to the image plane to the distance on the optical axis from the lens surface closest to the object of the teleconverter lens TCL to the image plane when the teleconverter lens TCL is attached to the master lens ML. By satisfying this conditional formula (6), good optical performance can be obtained. If the lower limit of conditional formula (6) is exceeded, the correction of chromatic aberration by the diffractive surface D is not sufficiently obtained, but if the refractive power (power) of the diffractive surface D is increased to obtain a correction effect, the correction of the chromatic aberration of magnification becomes strong, and the balance between the chromatic aberration of magnification and the axial chromatic aberration becomes lost, which is not preferable. In order to ensure the effect of this conditional formula (6), it is more preferable to set the lower limit of conditional formula (6) to 0.16, 0.18, 0.20, 0.23, 0.25, 0.28, 0.30, 0.32, 0.34, and further 0.35. Moreover, exceeding the upper limit of conditional expression (6) is undesirable because the correction of axial chromatic aberration becomes too strong, resulting in a loss of balance between lateral chromatic aberration and axial chromatic aberration. Also, the angle of the light passing through the diffractive surface (diffraction grating) D varies greatly depending on the angle of view, lowering the diffraction efficiency, and undesirable diffracted light degrades image quality, which is undesirable. In order to ensure the effect of conditional expression (6), it is more preferable to set the upper limit of conditional expression (6) to 0.73, 0.70, 0.68, 0.65, 0.63, 0.60, 0.58, or even 0.55.

It is desirable for the teleconverter lens TCL according to this embodiment to satisfy the following conditional expression (7).

1/rpf≦0.00 mm ⁻¹ (7)
however,
rpf: radius of curvature of the reference sphere of the diffractive surface D when the convex surface on the object side is positive

Conditional expression (7) defines the radius of curvature of the reference sphere of diffractive surface D. If conditional expression (7) is satisfied, diffractive surface D will be concave on the object side. If the upper limit of conditional expression (7) is exceeded, that is, if diffractive surface D is convex on the object side, molding will be difficult, which is not preferable. Also, if diffractive surface D is concave on the image side, reflected light from the imaging surface will cause ghosts and flares, degrading image quality, which is not preferable.

It is desirable for the teleconverter lens TCL according to this embodiment to satisfy the following conditional expression (8).

0.80 < {f/(fpf × β^2)} × 100 < 5.00 (8)
however,
f: focal length of the entire system of the teleconverter lens TCL fpf: focal length of the diffraction surface D β: magnification of the teleconverter lens TCL

Conditional formula (8) specifies the relationship between the focal length, magnification, and focal length of the diffractive surface D of the teleconverter lens TCL. By satisfying this conditional formula (8), good optical performance can be obtained. If the lower limit of conditional formula (8) is exceeded, the effect of the diffractive surface D becomes insufficient, making it difficult to correct chromatic aberration, which is undesirable. In order to ensure the effect of conditional formula (8), it is more preferable to set the lower limit of conditional formula (8) to 0.85, 0.90, 0.95, 1.00, 1.05, or even 1.10. In addition, if the upper limit of conditional formula (8) is exceeded, the effect of the diffractive surface D becomes too strong, making it difficult to correct the secondary spectrum, which is undesirable. In order to ensure the effect of conditional formula (8), it is more preferable to set the upper limit of conditional formula (8) to 4.95, 4.90, 4.80, 4.50, 4.25, 4.00, 3.80, or even 3.50.

The teleconverter lens TCL according to this embodiment preferably has one diffractive surface D. Providing multiple diffractive surfaces on the teleconverter lens TCL is not preferable because the higher-order diffracted light generated on each diffractive surface becomes unnecessary flare light in the design, which deteriorates the imaging performance.

In the teleconverter lens TCL according to this embodiment, it is preferable that the diffraction surface D is formed on a single lens. If the diffraction surface D is to be formed on the surface of a cemented lens, a UV curing resin for forming the diffraction surface D and a UV adhesive for bonding the lenses are required, but it is not preferable because it is difficult to use these UV curing resin and UV adhesive together. In addition, if the diffraction surface D is formed on the cemented surface of a cemented lens, unless both of the two lenses to be bonded have a glass material with a high UV transmittance, the temperature change occurs due to UV absorption during molding of the UV curing resin, and the surface accuracy deteriorates due to thermal stress, which is not preferable. On the other hand, if glass materials with high UV transmittance are used to avoid the above problem, there are many optical design constraints and the optical performance is deteriorated, which is not preferable. Specifically, when a cemented lens is formed by bonding a positive lens and a negative lens, a glass material with a high refractive index has a poor UV transmittance, so the refractive index of the negative lens cannot be increased, making it difficult to correct the Petzval sum.

It is desirable for the teleconverter lens TCL according to this embodiment to satisfy the following conditional expression (9).

0.05 < (BF/TL)/β < 0.25 (9)
however,
BF: Back focus when the teleconverter lens TCL is attached to the master lens ML TL: Distance on the optical axis from the lens surface of the teleconverter lens TCL closest to the object to the image plane when the teleconverter lens TL is attached to the master lens ML β: Magnification of the teleconverter lens TCL

Conditional formula (9) specifies the relationship between the magnification of the teleconverter lens and the back focus and total optical length (the distance on the optical axis from the lens surface closest to the object of the teleconverter lens TCL to the image surface) when the teleconverter lens TCL is attached to the master lens ML. By satisfying this conditional formula (9), good optical performance can be obtained. If the lower limit of conditional formula (9) is not met, the lens diameter closest to the image side must be set to a size close to the maximum image height, otherwise the appropriate exit pupil position cannot be obtained for the image sensor, and the entire optical system becomes bloated in the radial direction, which is undesirable. In order to ensure the effect of conditional formula (9), it is more preferable to set the lower limit of conditional formula (9) to 0.06, 0.08, 0.10, 0.12, or even 0.15. In addition, if the upper limit of conditional formula (9) is exceeded, it becomes impossible to arrange a positive lens with a strong refractive power (power) on the image side, the Petzval sum deteriorates, and the entire optical system becomes bloated in the optical axis direction, which is undesirable because it becomes difficult to achieve the miniaturization required mainly for mirrorless cameras. In order to ensure the effect of conditional expression (9), it is more desirable to set the upper limit of conditional expression (9) to 0.24, 0.23, or even 0.22.

As described above, by appropriately setting the position and refractive power of the diffractive surface D in the teleconverter lens TCL, it is possible to achieve extremely excellent field flatness and chromatic aberration correction while still being compact, primarily as a rear converter for mirrorless cameras.

The above-mentioned configuration and conditional expressions can be applied even if the master lens ML and the teleconverter lens TCL attached to this master lens ML are integrated into an optical system OL, and the effects of each configuration and conditional expression can be obtained.

When the master lens ML and the teleconverter lens TCL are integrated into an optical system OL, it is desirable to have the diffractive surface D on the lens closest to the image side. With this configuration, the effect of the diffractive surface D can be fully exerted, and good optical performance can be obtained.

In addition, in the optical system OL, it is preferable that the diffractive surface D is formed on a specific positive lens.

In the case of the optical system OL, TL is the distance on the optical axis from the lens surface closest to the object of the optical system OL to the image plane, and BF is the back focus of the optical system OL.

The conditions and configurations described above each provide the above-mentioned effects, and are not limited to those that satisfy all of the conditions and configurations. The above-mentioned effects can be obtained by satisfying any of the conditions or configurations, or any combination of the conditions or configurations.

The contents described below can be adopted as appropriate as long as they do not impair optical performance.

In this embodiment, the teleconverter lens TCL is configured as one group, but the above configuration conditions can be applied to other group configurations such as two groups or three groups. For example, the optical system may be one in which the magnification can be changed by moving some of the lens groups in the teleconverter lens TCL in the optical axis direction, or one in which the magnification can be changed by replacing or attaching/detaching some of the lens groups. In addition, a configuration in which a lens or lens group is added to the most object side, or a configuration in which a lens or lens group is added to the most image side may be used. Specifically, a configuration in which a lens group whose position relative to the image surface is fixed when changing magnification or focusing is added to the most image side is considered. In addition, a lens group refers to a portion having at least one lens separated by an air gap that changes when changing magnification or focusing. In addition, a lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

The lens surface may be spherical or flat, or aspheric. A spherical or flat lens surface is preferable because it facilitates lens processing and assembly adjustment, and prevents deterioration of optical performance due to errors in processing and assembly adjustment. It is also preferable because there is little deterioration in depiction performance even if the image plane is shifted. If the lens surface is aspheric, the aspheric surface may be any of the following aspheric surfaces: an aspheric surface formed by grinding, a glass molded aspheric surface in which glass is formed into an aspheric shape using a mold, and a composite aspheric surface in which resin is formed into an aspheric shape on the surface of glass. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

In addition, each lens surface may be coated with an anti-reflection coating that has high transmittance over a wide wavelength range to reduce flare and ghosting and achieve high-contrast optical performance.

The teleconverter lens TCL of this embodiment has a magnification of approximately 1.2 to 3.0 times.

Below, an outline of the manufacturing method for the teleconverter lens TCL according to this embodiment will be described with reference to FIG. 10. First, each lens is arranged to prepare each lens component of the teleconverter lens TCL (step S100). Next, a lens component having a diffractive surface is arranged (step S200). Then, each lens component is arranged so as to satisfy a condition according to a predetermined conditional formula (for example, the above-mentioned conditional formula (1)) (step S300).

Specifically, in this embodiment, as shown in FIG. 4, for example, the teleconverter lens TCL is prepared by, in order from the object side, a biconvex positive lens L1, a biconcave negative lens L2 with an aspheric lens surface on the object side, a cemented lens formed by cementing a biconvex positive lens L3 and a negative meniscus lens L4 with a concave surface facing the object side, and a diffractive lens L5 which is a positive meniscus lens with a concave surface facing the object side and has a diffractive surface D formed on the lens surface on the object side, and arranging them in the above-mentioned procedure to manufacture the teleconverter lens TCL.

The above configuration makes it possible to provide a teleconverter lens, optical system, optical device, and method for manufacturing a teleconverter lens with good imaging performance.

Each embodiment of the present application will be described below with reference to the drawings. Note that FIG. 2 is a cross-sectional view showing the configuration of the master lens ML, and FIGS. 4, 6, and 8 are cross-sectional views showing the configuration of the teleconverter lens TCL (TCL1 to TCL3) in each embodiment.

Each embodiment also shows the master lens ML to which each teleconverter lens TCL1 to TCL3 is attached. In each embodiment, the teleconverter lenses TCL1 to TCL3 are attached to a master lens ML with the same specifications.

In each embodiment, the aspheric surface is expressed by the following formula (a), where y is the height in the direction perpendicular to the optical axis, S(y) is the distance along the optical axis from the tangent plane of the apex of each aspheric surface at height y to each aspheric surface (amount of sag), r is the radius of curvature (paraxial radius of curvature) of the reference spherical surface, K is the conic constant, and An is the n-th order aspheric coefficient. Note that in the following embodiments, "E-n" represents "×10 ^-n ".

S(y) = (y ² /r) / {1 + (1 - K x y ² /r ² ) ^1/2 }
+ A4 x ^y4 + A6 x ^y6 + A8 x ^y8 + A10 x ^y10 (a)

In each example, the second-order aspheric coefficient A2 is 0. In the table for each example, aspheric surfaces are marked with an * to the right of the surface number.

In each embodiment, the phase shape ψ of the diffractive surface is expressed by the following equation (b):

ψ(h,n) = (2π/(n × λ0)) × ( ^C2h2 + ^C4h4 ) (b)
however,
h: Height perpendicular to the optical axis n: Order of diffracted light λ0: Design wavelength Ci: Phase coefficient (i = 2, 4)

Furthermore, the refractive power φD of the diffractive optical surface expressed by equation (b) for an arbitrary wavelength λ and an arbitrary diffraction order m is expressed as the following equation (c) using the lowest-order phase coefficient C2.

φD(λ,n) = -2×C2×n×λ/λ0 (c)

In the tables for each example, diffractive surfaces are marked with a # to the right of the surface number.

[Master lens]
As shown in FIG. 2, the master lens ML includes, in order from the object side, a cemented positive lens formed by cementing together a negative meniscus lens M1 with a convex surface facing the object side and a plano-convex positive lens M2 with a convex surface facing the object side, a positive meniscus lens M3 with a convex surface facing the object side, a negative meniscus lens M4 with a convex surface facing the object side, a biconcave negative lens M5, a positive meniscus lens M6 with a convex surface facing the object side, a biconcave negative lens M7, a positive meniscus lens M8 with a convex surface facing the object side, a biconvex positive lens M9, a positive meniscus lens M10 with a convex surface facing the object side, an aperture stop S, a biconvex negative lens L11, and a biconvex positive lens L12 cemented together. The lens element is made up of a cemented negative lens having a convex surface facing the object side, a negative meniscus lens L13 with a convex surface facing the object side, a cemented positive lens having a biconvex positive lens L14 with its object-side lens surface formed into an aspheric shape and a negative meniscus lens L15 with a concave surface facing the object side, a positive meniscus lens L16 with a convex surface facing the object side, a positive meniscus lens L17 with a concave surface facing the object side, a negative meniscus lens L18 with a convex surface facing the object side, a biconvex positive lens L19, a negative meniscus lens L20 with its object-side lens surface formed into an aspheric shape, and a negative meniscus lens L21 with a concave surface facing the object side.

The following Table 1 lists the values of the specifications of the master lens ML. In this Table 1, fm, which is shown in the overall specifications, represents the focal length of the entire system, FNOm represents the F-number, ωm represents the half angle of view [°], Y represents the maximum image height, BFm represents the air-equivalent back focus, and TLm represents the air-equivalent total optical length. Here, the back focus BF indicates the distance on the optical axis from the lens surface closest to the image side (surface No. 40 in this embodiment) to the image surface I, and the total optical length TL indicates the distance on the optical axis from the lens surface closest to the object side (surface No. 1 in this embodiment) to the image surface I. In addition, the first column m in the lens data indicates the order (surface number) of the lens surfaces from the object side along the direction in which the light ray travels, the second column r indicates the radius of curvature of each lens surface, the third column d indicates the distance on the optical axis from each optical surface to the next optical surface (surface spacing), and the fourth column νd and the fifth column nd indicate the Abbe number and refractive index for the d line (λ = 587.6 nm). Also, a radius of curvature of 0.0000 indicates a flat surface, and the refractive index of air, 1.000000, has been omitted.

The focal length f, radius of curvature r, surface spacing d, and other length units listed in the following specifications are generally in "mm," but this is not limited to this because the optical system provides the same optical performance even when proportionally enlarged or reduced. The explanations of these symbols and the specifications table also apply to the following examples.

(Table 1) Master lens [overall specifications]
fm = 196.000
FNOm = 2.878
ωm = 6.136°
Y = 21.70
BFm = 32.547
TLm = 232.433

[Lens data]
m r d ν d nd
Surface ∞
1 116.2423 2.8000 29.12 2.001000
2 85.0631 9.7000 82.57 1.497820
3 0.0000 0.1000
4 92.0132 7.7000 95.25 1.433852
5 696.9876 49.5274
6 59.5059 1.9000 65.44 1.603000
7 31.9138 10.3000
8 -185.1020 1.6000 82.57 1.497820
9 108.1171 0.8000
10 41.1067 3.7000 27.35 1.663819
11 64.1222 5.5000
12 -71.7484 1.9000 82.57 1.497820
13 88.6525 1.6071
14 69.5450 3.2000 17.98 1.945950
15 201.9972 2.3656
16 126.1730 4.7000 82.57 1.497820
17 -126.1730 0.1000
18 47.6776 3.8500 82.57 1.497820
19 122.6982 8.1230
20 0.0000 3.5000 Aperture S
21 -84.8430 1.8000 20.88 1.922860
22 51.8412 5.0000 82.57 1.497820
23 -171.0866 1.4835
24 110.4711 1.7000 32.35 1.850260
25 60.9020 2.0000
26* 58.6240 7.7000 66.89 1.592010
27 -57.5104 1.7000 36.40 1.620040
28 -95.6311 1.3000
29 58.4576 2.7000 34.92 1.801000
30 135.4103 4.1032
31 -369.9204 2.0000 17.98 1.945950
32 -98.7678 0.8000
33 1320.8593 1.2500 53.96 1.713000
34 37.1386 27.7126
35 119.5718 3.8500 35.77 1.902650
36 -119.5718 3.9138
37* -80.2212 1.9000 63.84 1.516120
38 -307.4896 4.1000
39 -55.1271 1.9000 60.71 1.563840
40 -276.4823 32.5472
Image plane ∞

In this master lens ML, surfaces 26 and 37 are formed aspheric. Table 2 below shows the aspheric data, i.e., the conic constant K and the values of each of the aspheric constants A4 to A10.

(Table 2)
[Aspheric data]
Face K A4 A6 A8 A10
26 1.0000 -2.02109E-06 9.22834E-10 -6.78340E-12 2.57624E-14
37 1.0000 1.26934E-06 1.09611E-09 -5.25758E-12 2.06460E-14

The spherical aberration, astigmatism, distortion, chromatic aberration, and coma diagrams of this master lens ML are shown in Figure 3. In each aberration diagram, FNO indicates the F-number, and Y indicates the image height. In the spherical aberration diagram, the F-number value corresponding to the maximum aperture is shown, in the astigmatism diagram and distortion diagram, the maximum value of the image height is shown, and in the coma diagram, the value of each image height is shown. d indicates the d-line (λ = 587.6 nm), g indicates the g-line (λ = 435.8 nm), F indicates the F-line (λ = 486.1 nm), and C indicates the C-line (λ = 656.3 nm). In the astigmatism diagram, the solid line indicates the sagittal image surface, and the dashed line indicates the meridional image surface. In the coma diagram, the solid line indicates the meridional coma, and the dashed line indicates the Y direction (meridional) and Z direction (sagittal) of the skew ray, respectively. Additionally, the same symbols as in this embodiment are used in the aberration diagrams of each embodiment shown below. From these aberration diagrams, it can be seen that the master lens ML has various aberrations well corrected.

[First embodiment]
FIG. 4 is a diagram showing the configuration of an optical system OL1 in which a teleconverter lens TCL1 according to the first embodiment is attached to the master lens ML described above.

The teleconverter lens TCL1 that constitutes the optical system OL1 is composed of, in order from the object side, a biconvex positive lens L1, a biconcave negative lens L2 whose object side lens surface is formed into an aspheric shape, a cemented negative lens formed by cementing a biconvex positive lens L3 and a negative meniscus lens L4 whose concave surface faces the object side, and a diffractive lens L5 in which a diffractive surface D is formed on the object side lens surface of a positive meniscus lens (specified positive lens) whose concave surface faces the object side.

The following Table 3 lists the values of the specifications of the teleconverter lens TCL1 in the first embodiment. In this Table 3, f in the overall specifications represents the focal length of the entire system of the teleconverter lens TCL1, fa represents the focal length of the optical system OL1 (composite focal length of the master lens ML and the teleconverter lens TCL1), FNOa represents the F-number (composite F-number) of the optical system OL1, ωa represents the half angle of view of the optical system OL1, Y represents the maximum image height of the optical system OL1, Bfa represents the air-equivalent back focus of the optical system OL1, and TLa represents the air-equivalent total optical length of the optical system OL1. The explanation of these symbols is the same in the following embodiments.

In addition, since the lens data of the master lens ML is already shown in Table 1, the lens data in Table 3 shows the values of the 40th surface of the master lens ML, which is the surface closest to the image side, and the values of the subsequent teleconverter lenses TCL1 when the teleconverter lens TCL1 is attached to the master lens ML. Therefore, the lens data of the optical system OL1 when the teleconverter lens TCL1 is attached to the master lens ML is represented by the data of the 1st to 39th surfaces shown in Table 1, and the data of the 40th and subsequent surfaces shown in Table 3.

(Table 3) First Example [Overall Specifications]
f = -101.095
f a = 274.123
FNOa = 4.025
ωa = 4.374°
Y = 21.70
BFa = 10.055
TLa = 247.986

[Lens data]
m r d ν d nd
40 -276.4823 3.9922
41 162.0565 4.0500 22.74 1.808090
42 -66.8770 4.0897
43* -40.6283 1.2500 37.23 1.882020
44 29.3716 11.9646 35.27 1.592700
45 -20.1549 1.2500 26.94 2.050898
46 -96.2968 4.2680
47# -56.6787 7.1805 52.20 1.517420
48 -27.2719 10.0547
Image plane ∞

In this teleconverter lens TCL1, surface 43 is formed aspherically. Table 4 below shows the aspheric data, i.e., the conic constant K and the values of each aspheric constant A4 to A10.

(Table 4)
[Aspheric data]
Face K A4 A6 A8 A10
43 1.0000 5.56880E-06 -9.20130E-09 7.90410E-11 -3.08340E-13

In this teleconverter lens TCL1, surface 47 is a diffractive surface. Table 5 below shows the diffractive surface data, i.e., the design wavelength λ0, the order n, and the values of each phase coefficient C2 and C4.

(Table 5)
[Diffraction surface data]
m λ0 n C2 C4
47 587.6 1.0 1.45000E-04 4.43000E-07

Figure 5 shows the spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration diagrams of the optical system OL1 consisting of the master lens ML and the teleconverter lens TCL1. From these aberration diagrams, it can be seen that the optical system OL1 including the teleconverter lens TCL1 has various aberrations well corrected.

[Second embodiment]
FIG. 6 is a diagram showing the configuration of an optical system OL2 in which a teleconverter lens TCL2 according to the second embodiment is attached to the master lens ML described above.

The teleconverter lens TCL2 constituting the optical system OL2 is composed of, in order from the object side, a biconvex positive lens L1, a cemented negative lens formed by cementing a biconcave negative lens L2 and a biconvex positive lens L3, a negative meniscus lens L4 with its concave surface facing the object side and its lens surface on the object side and its lens surface on the image side formed with aspheric shapes, and a diffractive lens L5 with a diffractive surface D formed on the object side lens surface of a plano-convex positive lens (specified positive lens) with a flat surface facing the object side.

Table 6 below lists the values of the specifications of the teleconverter lens TCL2 in the second embodiment. Note that since the lens data of the master lens ML has already been shown in Table 1, the lens data in Table 6 shows the values of the 40th surface of the master lens ML, which is the surface closest to the image side, and the values of the subsequent teleconverter lenses TCL2 when the teleconverter lens TCL2 is attached to the master lens ML. Therefore, the lens data of the optical system OL2 when the teleconverter lens TCL2 is attached to the master lens ML is represented by the data of the 1st to 39th surfaces shown in Table 1, and the data of the 40th and subsequent surfaces shown in Table 6.

(Table 6) Second Example [Overall Specifications]
f = -110.158
f a = 274.127
FNOa = 4.250
ωa = 4.388°
Y = 21.70
BFa = 13.372
TLa = 249.177

[Lens data]
m r d ν d nd
40 -276.4823 4.0000
41 94.3781 4.1630 20.36 1.892860
42 -67.0448 3.1379
43 -41.5374 1.2000 26.94 2.050898
44 19.6703 8.7114 27.51 1.755199
45 -221.8166 2.8804
46* -42.0485 1.4000 29.83 1.951499
47* -6317.6373 0.7711
48# 0.0000 9.6550 64.14 1.516800
49 -26.3976 13.3722
Image plane ∞

In this teleconverter lens TCL2, surfaces 46 and 47 are aspheric. Table 7 below shows the aspheric data, i.e., the conic constant K and the values of each aspheric constant A4 to A10.

(Table 7)
[Aspheric data]
Face K A4 A6 A8 A10
46 -15.6386 -1.71660E-05 3.44620E-08 -1.32520E-10 1.96330E-13
47 -0.2923E+06 4.67600E-06 -5.11750E-08 1.06390E-10 -1.56130E-13

In this teleconverter lens TCL2, surface 48 is a diffractive surface. Table 8 below shows the diffractive surface data, i.e., the design wavelength λ0, the order n, and the values of each phase coefficient C2 and C4.

Table 8
[Diffraction surface data]
m λ0 n C2 C4
48 587.6 1.0 2.65000E-04 4.02000E-07

Figure 7 shows the spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration diagrams of the optical system OL2 consisting of the master lens ML and the teleconverter lens TCL2. From these aberration diagrams, it can be seen that the optical system OL2 including the teleconverter lens TCL2 has various aberrations well corrected.

[Third Example]
FIG. 8 is a diagram showing the configuration of an optical system OL3 in which a teleconverter lens TCL3 according to the third embodiment is attached to the master lens ML described above.

The teleconverter lens TCL3 constituting the optical system OL3 is composed of, in order from the object side, a biconvex positive lens L1, a cemented negative lens formed by cementing a biconcave negative lens L2 with an aspheric lens surface on the object side to a biconvex positive lens L3, a cemented negative lens formed by cementing a biconcave negative lens L4, a biconvex positive lens L5 and a negative meniscus lens L6 with a concave surface facing the object side, a negative meniscus lens L7 with a concave surface facing the object side, and a diffractive lens L8 in which a diffractive surface D is formed on the object side lens surface of a positive meniscus lens (specified positive lens) with a concave surface facing the object side.

Table 9 below lists the values of the specifications of the teleconverter lens TCL3 in the third embodiment. Note that since the lens data of the master lens ML has already been shown in Table 1, the lens data in Table 9 shows the values of the 40th surface of the master lens ML, which is the surface closest to the image side, and the values of the subsequent teleconverter lenses TCL3 when the teleconverter lens TCL3 is attached to the master lens ML. Therefore, the lens data of the optical system OL3 when the teleconverter lens TCL3 is attached to the master lens ML is represented by the data of the 1st to 39th surfaces shown in Table 1, and the data of the 40th and subsequent surfaces shown in Table 9.

(Table 9) Third Example [Overall Specifications]
f = -66.558
f a = 391.997
FNOa = 5.756
ωa = 3.129°
Y = 21.70
BFa = 9.156
TLa = 261.766

[Lens data]
m r d ν d nd
40 -276.4823 3.9922
41 70.2166 4.1000 30.05 1.698950
42 -56.8450 3.0327
43* -32.8691 1.0000 40.39 1.854000
44 16.0992 8.2000 28.46 1.728250
45 -47.0798 1.1597
46 -40.9426 1.0000 26.94 2.050898
47 24.9501 11.7078 30.13 1.698947
48 -14.4836 1.1000 26.94 2.050898
49 -52.0176 2.4551
50 -53.0373 1.4000 26.94 2.050898
51 -168.8728 1.0000
52# -273.3168 12.5762 52.20 1.517420
53 -22.8743 9.1556
Image plane ∞

In this teleconverter lens TCL3, surface 43 is formed aspherically. Table 10 below shows the aspheric data, i.e., the conic constant K and the values of each aspheric constant A4 to A10.

(Table 10)
[Aspheric data]
Face K A4 A6 A8 A10
43 1.0000 1.35720E-05 -3.41470E-08 3.73080E-10 -2.61940E-12

In this teleconverter lens TCL3, surface 52 is a diffractive surface. Table 11 below shows the diffractive surface data, i.e., the design wavelength λ0, the order n, and the values of each phase coefficient C2 and C4.

Table 11
[Diffraction surface data]
m λ0 n C2 C4
52 587.6 1.0 4.60000E-04 -1.35000E-07

Figure 9 shows the spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration diagrams of the optical system OL3 consisting of the master lens ML and the teleconverter lens TCL3. From these aberration diagrams, it can be seen that the optical system OL3 including the teleconverter lens TCL3 has various aberrations well corrected.

[Conditional expression corresponding value]
The values of conditional expressions (1) to (9) of the first embodiment (teleconverter lens TCL1 and optical system OL1) to the third embodiment (teleconverter lens TCL3 and optical system OL3) are listed below.
(1) f/fpf
(2) β
(3) L
(4) vp
(5) np
(6) Lpf/TL
(7) 1/rpf
(8) {f/(fpf×β^2)}×100
(9) (BF/TL)/β

First Example Second Example Third Example fpf -3448.276 -1886.792 -1086.957
Lpf 17.235 23.027 21.732

(1) 0.029 0.058 0.061
(2) 1.399 1.399 2.000
(3) 28.555 28.563 28.555
(4) 52.20 64.14 52.20
(5) 1.517420 1.516800 1.517420
(6) 0.358 0.467 0.351
(7) -0.01764 0.00000 -0.00337
(8) 1.499 2.985 1.531
(9) 0.149 0.194 0.074

1 Camera (optical equipment) OL1-OL3 Optical system ML Master lens TCL (TCL1-TCL3) Teleconverter lens D Diffraction surface

Claims (13)

A teleconverter lens is disposed on the image side of a master lens and expands the focal length of an entire optical system including the master lens,
It has a diffractive surface,
The diffractive surface is formed on a positive single lens that satisfies the following condition:
40.00 < νp < 100.00
1.40 < np < 1.90
however,
νp: Abbe number of the medium of the positive single lens for the d line np: refractive index of the medium of the positive single lens for the d line 2. The teleconverter lens according to claim 1, which satisfies the following condition:
0.010 < f/fpf < 0.100
however,
f: focal length of the teleconverter lens fpf: focal length of the diffractive surface 3. The teleconverter lens according to claim 1, which satisfies the following condition:
1.10 < β < 2.50
however,
β: Magnification of the teleconverter lens 4. The teleconverter lens according to claim 1, which satisfies the following condition:
10.00mm < L < 49.00mm
however,
L: the distance on the optical axis from the image plane of the master lens when the teleconverter lens is not attached to the master lens to the lens surface of the teleconverter lens closest to the object when the teleconverter lens is attached 5. The teleconverter lens according to claim 1, which satisfies the following condition:
0.15 < Lpf/TL < 0.75
however,
Lpf: the distance on the optical axis from the diffraction surface to the image plane when the teleconverter lens is attached to the master lens. TL: the distance on the optical axis from the lens surface of the teleconverter lens closest to the object to the image plane when the teleconverter lens is attached to the master lens. 6. The teleconverter lens according to claim 1, which satisfies the following condition:
1/rpf≦0.00mm
however,
rpf: radius of curvature of the reference sphere of the diffractive surface when the convex surface on the object side is positive 7. The teleconverter lens according to claim 1, which satisfies the following condition:
0.80 < {f/(fpf x β^2)} x 100 < 5.00
however,
f: focal length of the entire system of the teleconverter lens, fpf: focal length of the diffractive surface, β: magnification of the teleconverter lens. The teleconverter lens according to any one of claims 1 to 7, which has one diffractive surface. 9. The teleconverter lens according to claim 1, which satisfies the following condition:
0.05 < (BF/TL)/β < 0.25
however,
BF: back focus when the teleconverter lens is attached to the master lens TL: distance on the optical axis from the lens surface of the teleconverter lens closest to the object to the image plane when the teleconverter lens is attached to the master lens β: magnification of the teleconverter lens The lens closest to the image has a diffractive surface.
The optical system in which the lens closest to the image side is a positive single lens that satisfies the following condition:
40.00 < νp < 70.00
1.40 < np ≦ 1.517420
however,
νp: Abbe number of the medium of the positive single lens for the d line np: refractive index of the medium of the positive single lens for the d line 11. The optical system according to claim 10 , which satisfies the following condition:
0.05 < Lpf/TL < 0.50
however,
Lpf: distance on the optical axis from the diffractive surface to the image plane TL: distance on the optical axis from the lens surface closest to the object side of the optical system to the image plane 12. The optical system according to claim 10, which satisfies the following condition:
1/rpf≦0.00mm
Where rpf: radius of curvature of the reference sphere of the diffractive surface when the convex surface facing the object side is positive An optical device comprising a teleconverter lens according to any one of claims 1 to 9.

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