JP7218469B2 - converter lens, interchangeable lens, and imaging device - Google Patents

Description

The present invention relates to a converter lens, an interchangeable lens, and an imaging device.

A rear converter lens is known that can increase the focal length of the entire system by being arranged between an imaging device and an interchangeable lens including a master lens.

In the case of the rear converter lens, there is an advantage that the entire lens system can be made more compact than when it is arranged on the object side of the master lens. However, since the residual aberration of the master lens is increased in proportion to the magnification, the image quality tends to deteriorate. Therefore, in order to maintain good aberrations of the entire system even when the rear converter lens is arranged on the image side of the master lens, it is necessary to correct various aberrations of the rear converter lens itself.

Patent Document 1 describes a rear converter lens that can be used with a master lens having a relatively short back focus.

WO2017/134928

A rear converter lens that increases the focal length of the entire system has a negative refractive power. That is, the Petzval sum with a large negative component tends to occur in the rear converter lens. Therefore, when the lens is arranged on the image side of the master lens, the curvature of field tends to be particularly large. In addition, the aperture stop included in the master lens is often used instead of placing an aperture stop in the rear converter lens. , passes through a position radially away from the optical axis. This is also a factor in increasing the curvature of field.

Furthermore, especially when the back focus of the master lens is short, the lens diameter of the rear converter lens arranged on the image side of the master lens tends to be large, and it tends to be difficult to secure a space for arranging many lenses. Therefore, it is difficult to construct a compact converter lens and to correct field curvature and lateral chromatic aberration. Although it is possible to reduce the size by using an aspherical lens as in Japanese Patent Laid-Open No. 2002-200013, there is a demand for further improvement in terms of chromatic aberration of magnification.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a converter lens having high optical performance when arranged on the image side of a master lens.

A converter lens according to an embodiment of the present invention has a negative refractive power and is arranged on the image side of the master lens to make the focal length of the entire system longer than the focal length of the master lens alone. A lens comprising: a first lens element arranged closest to the object side of the converter lens; a second lens element arranged adjacent to the image side of the first lens element with a space therebetween; and the converter lens. a lens element arranged closest to the image side, wherein the second lens element comprises a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented, arranged in order from the object side to the image side, The lens element has a positive refractive power, f is the focal length of the converter lens, na1 is the refractive index in the d-line of the material forming the image-side lens surface of the first lens element, and na1 is the second lens element. na2 is the refractive index at the d-line of the material constituting the object-side lens surface of , ra1 is the radius of curvature of the image-side lens surface of the first lens element, and ra1 is the radius of curvature of the object-side lens surface of the second lens element is ra2, the focal length of the first lens element is f1,
the focal length fa of the space between the first lens element and the second lens element,
fa = 1/[{(1/ra1) x (1-na1)/na2}-{(1/ra2) x (1-na2)/na2}]
When expressed as
1.45<|fa/f|<8.55
-80.0<(ra2+ra1)/(ra2-ra1)<-2.00
0.01<|f1/fa|≦0.195
It is characterized by satisfying the following conditional expression.

ADVANTAGE OF THE INVENTION According to this invention, the converter lens which has high optical performance when arrange|positioned at the image side of a master lens can be obtained.

4 is a cross-sectional view of a master lens and a converter lens; FIG. FIG. 4 is an aberration diagram of the master lens when focusing on an object at infinity. 4 is a cross-sectional view of the converter lens of Example 1. FIG. FIG. 10 is an aberration diagram when focusing on an object at infinity when the converter lens of Example 1 is arranged on the image side of the master lens; FIG. 10 is a cross-sectional view of a converter lens of Example 2; FIG. 10 is an aberration diagram when focusing on an infinite distance object when the converter lens of Example 2 is arranged on the image side of the master lens; FIG. 11 is a cross-sectional view of a converter lens of Example 3; FIG. 10 is an aberration diagram when focusing on an infinite distance object when the converter lens of Example 3 is arranged on the image side of the master lens; FIG. 11 is a cross-sectional view of a converter lens of Example 4; FIG. 10 is an aberration diagram when focusing on an infinite distance object when the converter lens of Example 4 is arranged on the image side of the master lens; FIG. 11 is a cross-sectional view of a converter lens of Example 5; FIG. 11 is an aberration diagram when focusing on an infinite distance object when the converter lens of Example 5 is arranged on the image side of the master lens; FIG. 11 is a cross-sectional view of a converter lens of Example 6; FIG. 12 is an aberration diagram when focusing on an infinite distance object when the converter lens of Example 6 is arranged on the image side of the master lens; It is a figure which shows the structure of an imaging system.

Hereinafter, a rear converter lens (hereinafter referred to as a converter lens) and an imaging device according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the converter lens RCL of the embodiment of the present invention is arranged on the image side of a master lens ML (main lens system) such as an interchangeable lens, thereby providing a photographing system composed of the master lens ML and the converter lens RCL. The focal length of the optical system (whole system) is made longer than when only the master lens ML is used as the imaging optical system.

Note that the master lens ML is a photographing lens system used in an image pickup apparatus such as a digital video camera, digital camera, silver salt film camera, and TV camera.

In the cross-sectional view of the master lens ML shown in FIG. 1 and the cross-sectional views of the converter lens RCL shown in FIGS. (rear). The aperture stop SP determines (limits) the light flux at the open F-number (Fno).

When the imaging device is a digital video camera, a digital camera, or the like, the image plane IP corresponds to the imaging plane of an imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor. If the imaging device is a silver halide film camera, the image plane IP corresponds to the film plane.

FIG. 2 is an aberration diagram of the master lens ML, and FIGS. 4, 6, 8, 10, 12, and 14 are aberration diagrams of the converter lens RCL of each example described later. In the spherical aberration diagrams, the solid line indicates the d-line, and the two-dot chain line indicates the g-line. In the astigmatism diagrams, the dashed line ΔM indicates the amount of aberration on the meridional image plane, and the solid line ΔS indicates the amount of aberration on the sagittal image plane. Distortion is shown for the d-line. Lateral chromatic aberration is shown for the g-line. ω is a half angle of view (degrees), which is an angle of view obtained by paraxial calculation. Fno is the F number.

The converter lens RCL according to the embodiment is a converter lens that has negative refractive power and is arranged on the image side of the master lens to make the focal length of the entire system longer than the focal length of the master lens alone. .

It also has a first lens element L1 arranged closest to the object side of the converter lens RCL, and a second lens element L2 arranged adjacent to the image side of the first lens element with a space therebetween. Here, the term "lens element" refers to a single lens or a cemented lens composed of a plurality of lenses. The space between the first lens element L1 and the second lens element L2 is also referred to herein as an air lens. That is, the air lens between the first lens element L1 and the second lens element L2 is also the air lens arranged closest to the object side in the converter lens RCL. Even when the first lens element L1 and the second lens element L2 are partially cemented together, if there is an interval on the optical axis, they are regarded as an air lens.

Further, na1 is the refractive index for the d-line of the material forming the image-side lens surface of the first lens element L1, na2 is the refractive index for the d-line of the material forming the object-side lens surface of the second lens element L2, When the radius of curvature of the image-side lens surface of the first lens element L1 is ra1, and the radius of curvature of the object-side lens surface of the second lens element L2 is ra2,
The focal length fa of the air lens is
fa = 1/[{(1/ra1) x (1-na1)/na2}-{(1/ra2) x (1-na2)/na2}]
is represented.

However, when the first lens element L1 is composed of a cemented lens, the material of the lens arranged closest to the image side of the first lens element L1 has a refractive index na1 at the d-line. When the second lens element L2 is composed of a cemented lens, the material of the lens located closest to the object side of the second lens element L2 has a refractive index na2 for the d-line.

If the lens surface is aspherical, the radius of curvature means the base radius of curvature (paraxial radius of curvature).

When the lens surface is aspherical, for example, k is the eccentricity, A4, A6, A8, A10, and A12 are the aspherical coefficients, and the optical axis direction at the position of the height h from the optical axis with reference to the vertex of the lens surface. When the displacement is x, the aspherical shape is
x=(h ² /R)/[1+{1−(1+k)(h/R) ² } ^1/2 ]+A4h ⁴ +A6h ⁶ +A8h ⁸ +A10h ¹⁰ +A12h ¹²
is expressed as where R is the paraxial radius of curvature. The radius of curvature component of this equation is
(h ² /R)/[1+{1−(1+k)(h/R) ² } ^1/2 ]
is. When calculating the focal length fa of the air lens,
r′=[R−{R ² −(1+k)R ² } ^1/2 ]/(1+k)
Calculate as Here, the height h from the optical axis is calculated from the maximum image height h of the master lens or the converter lens as a representative value of the converter lens.

Moreover, when k>0, the calculation is performed as k=0.

At this time, the following conditional expressions (1) and (2) are satisfied. Note that the focal length of the converter lens RCL is f, and the focal length fa and the radii of curvature ra1 and ra2 are as described above.
1.45<|fa/f|<8.55 (1)
-80.0<(ra2+ra1)/(ra2-ra1)-2.00 (2)

The refracting power and shape of the air lens closest to the object side are important factors for correcting the image plane characteristics well and increasing the degree of freedom in material selection for the lens adjacent to the air lens to reduce the Petzval sum. be.

Conditional expression (1) defines the degree of preferable refractive power of the air lens closest to the object side of the converter lens RCL by the focal length of the air lens with respect to the focal length of the converter lens RCL.

When the upper limit of conditional expression (1) is exceeded and the focal length of the air lens becomes longer (the absolute value of the focal length becomes larger) and the refractive power of the air lens becomes weaker, the first lens element L1 and the second lens element L2 It is not preferable because it becomes difficult to correct off-axis coma at . If the lower limit of conditional expression (1) is exceeded and the focal length of the air lens becomes short (the absolute value of the focal length becomes small) and the refractive power of the air lens becomes strong, the curvature of field varies for each wavelength. I don't like it.

Conditional expression (2) defines a preferable shape factor of the air lens. By satisfying conditional expression (2), curvature of field, chromatic aberration of magnification, and distortion can be satisfactorily corrected, and high optical performance can be obtained.

When the upper limit of conditional expression (2) is exceeded and the shape of the image-side lens surface of the first lens element L1 and the shape of the object-side lens surface of the second lens element L2 approach the same shape, the aberration correction function of the air lens is insufficient, making it difficult to satisfactorily correct lateral chromatic aberration and distortion. If the lower limit of conditional expression (2) is exceeded and the degree of the meniscus shape of the air lens becomes large, the curvature of field becomes large and the dispersion of the curvature of field for each wavelength becomes large, which is not preferable.

Thus, according to the present invention, a converter lens RCL having high optical performance can be obtained. Depending on the focal length of the converter lens RCL, the converter lens RCL can be configured to be small. In particular, the converter lens RCL of the present invention is suitable for a converter device arranged between a mirrorless camera and an interchangeable lens detachable from the camera and having a relatively short back focus.

It is preferable to set the numerical ranges of conditional expressions (1) and (2) as follows.
1.47<|fa/f|<8.52 (1a)
−75.0<(ra2+ra1)/(ra2−ra1)<−3.00 (2a)

It is more preferable to set the numerical ranges of conditional expressions (1) and (2) as follows.
1.48<|fa/f|<8.50 (1b)
−70.0<(ra2+ra1)/(ra2−ra1)<−4.40 (2b)

Furthermore, it is preferable that the converter lens satisfy one or more of the following conditional expressions (3) to (11).
1.58<nAP<1.80 (3)
1.80<nAN<2.20 (4)
0.01<|f1/fa|<0.40 (5)
0.15<|f1/f|<0.70 (6)
26.0<νAN<45.0 (7)
0.02<rl/f<0.32 (8)
1.75<nd1<2.00 (9)
0.04<f2/f<1.10 (10)
1.00<ra2/rl<3.40 (11)

When the converter lens RCL has at least one positive lens, let nAP be the average refractive index at the d-line of the materials of all the positive lenses included in the converter lens RCL. When the converter lens RCL has at least one negative lens, let nAN be the average refractive index at the d-line of the materials of all the negative lenses included in the converter lens RCL.

Let f1 be the focal length of the first lens element L1, and f2 be the focal length of the second lens element L2.

Also, when the converter lens RCL has at least one negative lens, let νAN be the average Abbe number of the materials of all the negative lenses included in the converter lens RCL with respect to the d-line. Incidentally, the Abbe number νi of a certain material is given by
νi = (Nd-1)/(NF-NC)
is represented by

When the lens surface of the converter lens RCL closest to the image side is convex toward the image side, let rl be the radius of curvature of the lens surface.

When the converter lens RCL has at least one positive lens, let nd1 be the refractive index for the d-line of the material of the positive lens Lp arranged closest to the object side among all the positive lenses included in the converter lens RCL.

When the first lens element L1 has positive refractive power and the second lens element L2 has negative refractive power, let rl be the radius of curvature of the lens surface of the converter lens RCL closest to the image side.

Conditional expression (3) defines the average refractive index of the materials of all the positive lenses included in the converter lens RCL. By satisfying the conditional expression (3), longitudinal chromatic aberration and curvature of field can be particularly well corrected.

If the average refractive index is higher than the upper limit of conditional expression (3), the absolute value of the Petzval sum increases and the curvature of field increases, which is not preferable. Alternatively, if the number of lenses is increased in order to correct the curvature of field, it is difficult to reduce the size of the converter lens RCL, which is not preferable. If the lower limit of conditional expression (3) is exceeded, the average refractive index becomes low and the Abbe number of the material becomes large, it is not preferable because it becomes difficult to correct longitudinal chromatic aberration.

Conditional expression (4) is an expression that defines the average refractive index of the materials of all the negative lenses included in the converter lens RCL. By satisfying the conditional expression (4), it is possible to satisfactorily correct lateral chromatic aberration and field curvature.

In general, the Abbe number tends to decrease as the refractive index of the material of the negative lens increases. Therefore, if the upper limit of conditional expression (4) is exceeded and the average refractive index becomes high and the Abbe's number becomes small, the primary chromatic aberration correction becomes insufficient, making it difficult to correct the chromatic aberration of magnification. If the average refractive index is lower than the lower limit of conditional expression (4), the negative component of the Petzval sum increases and the curvature of field increases, which is not preferable. Alternatively, if the number of lenses is increased in order to correct the curvature of field, it is difficult to reduce the size of the converter lens RCL, which is not preferable.

Conditional expression (5) defines the focal length of the first lens element L1 by the focal length of the air lens. By satisfying conditional expression (5), the lens on the image side of the first lens element L1 can be made smaller, or aberrations such as curvature of field can be satisfactorily corrected.

When the upper limit of conditional expression (5) is exceeded and the focal length of the first lens element L1 increases (the absolute value of the focal length increases) and the refractive power of the first lens element L1 decreases, the first lens element L1 The angle from the optical axis of the chief ray of the off-axis light flux emitted from the increases. As a result, the diameter of the lens arranged closer to the image side than the first lens element L1 becomes large, making it difficult to reduce the size of the converter lens RCL, which is not preferable. Furthermore, curvature of field and chromatic aberration of magnification increase, which is not preferable. When the lower limit of conditional expression (5) is exceeded and the focal length of the first lens element L1 becomes shorter (the absolute value of the focal length becomes smaller) and the refractive power of the first lens element L1 becomes stronger, the spherical aberration becomes negative. It is not preferable because it becomes large.

Conditional expression (6) defines the focal length of the first lens element L1 by the focal length of the converter lens RCL. By satisfying conditional expression (6), the refracting power of the first lens element L1 is strengthened to reduce the size of the converter lens RCL, and the negative refracting power of the converter lens RCL is weakened to satisfactorily correct field curvature. be able to.

When the upper limit of conditional expression (6) is exceeded and the focal length of the first lens element L1 increases (the absolute value of the focal length increases) and the refractive power of the first lens element L1 decreases, the entire converter lens RCL becomes Negative refractive power becomes too strong. As a result, the Petzval sum increases in the negative direction, making it difficult to correct curvature of field, which is not preferable. When the lower limit of conditional expression (6) is exceeded and the focal length of the first lens element L1 becomes short (the absolute value of the focal length becomes small) and the refractive power of the first lens element L1 becomes strong, the first lens element L1 This is not preferable because it becomes difficult to correct the longitudinal chromatic aberration that occurs with a lens arranged closer to the image side than the first lens element L1. Alternatively, the number of lenses must be increased in order to correct the longitudinal chromatic aberration, which makes it difficult to reduce the size of the converter lens RCL, which is not preferable.

Conditional expression (7) defines the average Abbe number of the materials of all the negative lenses included in the converter lens RCL. In a high-refractive region with a refractive index of 1.80 or more, the partial dispersion ratio tends to increase as the Abbe number decreases. In order to suppress the secondary spectrum of the chromatic aberration of magnification, it is preferable to use a material having high refraction and relatively high dispersion characteristics (low Abbe number). However, if the Abbe number is out of the appropriate range, such as when the upper limit of conditional expression (7) is exceeded or the lower limit is not reached, correction of first-order chromatic aberration becomes difficult, and field curvature and This is not preferable because correction of chromatic aberration of magnification becomes difficult.

Conditional expression (8) defines the radius of curvature rl of the lens surface closest to the image side of the converter lens RCL by the focal length of the converter lens RCL. In order to suppress the occurrence of various aberrations caused by the off-axis rays incident on the image plane IP, each off-axis ray should be concentric with the exit pupil so that the converter lens RCL is located at the maximum position. It must be incident on the lens surface on the image side. Therefore, in an optical system in which the exit pupil position is close to the image plane IP, it is important to set the radius of curvature appropriately while making the lens surface closest to the image side convex toward the image side.

When the absolute value of the radius of curvature of the lens surface of the converter lens RCL closest to the image side is large (the curvature is small) with respect to the negative refractive power of the converter lens RCL exceeding the upper limit of conditional expression (8), field curvature This is not preferable because it leads to insufficient correction of distortion and distortion. When the lower limit of conditional expression (8) is exceeded, the absolute value of the radius of curvature of the lens surface of the converter lens RCL closest to the image side becomes small (the curvature becomes large) with respect to the negative refractive power of the converter lens RCL, and the lens surface If the half-open angle of is large, it is not preferable because processing such as polishing and coating becomes difficult.

Conditional expression (9) defines the refractive index of the material of the positive lens Lp closest to the object side among the positive lenses included in the converter lens RCL. By satisfying conditional expression (9), it is possible to reduce the size of the converter lens RCL and reduce the occurrence of spherical aberration and coma.

When the refractive index of the material of the positive lens Lp increases beyond the upper limit of conditional expression (9), the difference between the refractive power for the on-axis light beam and the refractive power for the off-axis light beam in the lens Lp becomes small, resulting in curvature of field and magnification. This is not preferable because it causes insufficient correction of chromatic aberration. If the lower limit of conditional expression (9) is not reached and the refractive index of the material of the positive lens Lp becomes low, high-order spherical aberration and coma aberration will occur significantly, making it difficult to correct them.

Conditional expression (10) defines the focal length of the second lens element L2 by the focal length of the converter lens RCL. The first lens element L1 with positive refractive power refracts the angle of the principal ray of the off-axis light flux so as to approach the direction parallel to the optical axis, and the second lens element L1 with strong negative refractive power is directed toward the image side of the first lens element L1. By arranging the lens element L2, the curvature of field can be corrected satisfactorily.

When the upper limit of conditional expression (10) is exceeded and the focal length of the second lens element L2 increases (the absolute value of the focal length increases) and the refractive power of the second lens element L2 decreases, off-axis coma aberration occurs. This is not preferable because it makes it difficult to make good corrections. When the lower limit of conditional expression (10) is exceeded, the focal length of the second lens element L2 becomes short (the absolute value of the focal length becomes small), the refractive power of the second lens element L2 becomes strong, and If the angle of the principal ray of the emitted off-axis light flux with respect to the optical axis increases, the diameter of the lens arranged closer to the image side than the second lens element L2 increases, making it difficult to reduce the size of the converter lens RCL, which is preferable. do not have.

Conditional expression (11) defines the radius of curvature of the object-side lens surface of the second lens element L2 by the radius of curvature of the most image-side lens surface of the converter lens RCL. Conditional expression (11) indicates that both the most image-side lens surface of the converter lens RCL and the object-side lens surface of the second lens element L2 are convex in the same direction. By satisfying the conditional expression (11), the off-axis ray emitted from the first lens element L1 is incident on the image plane IP at an appropriate angle, and the field curvature, distortion aberration, and lateral chromatic aberration can be satisfactorily corrected. can.

When the absolute value of the radius of curvature of the object-side lens surface of the second lens element L2 becomes large (the curvature becomes small) exceeding the upper limit of conditional expression (11), field curvature, distortion, and other aberrations occur. This is not preferable because correction of aberration becomes difficult. When the absolute value of the radius of curvature of the object-side lens surface of the second lens element L2 decreases (the curvature increases) below the lower limit value of conditional expression (11), field curvature, distortion, and other aberrations occur. This is not preferable because it results in overcorrection of aberrations.

It is preferable to set the numerical ranges of conditional expressions (3) to (11) as follows.
1.60<nAP<1.75 (3a)
1.84<nAN<2.00 (4a)
0.10<|f1/fa|<0.35 (5a)
0.01<|f1/fa|≦0.195 (5a′)
0.02<|f1/f|<0.55 (6a)
30.0<νAN<42.0 (7a)
0.04<rl/f<0.28 (8a)
1.78<nd1<1.90 (9a)
0.07<f2/f<0.80 (10a)
1.10<ra2/rl<3.00 (11a)

More preferably, the numerical ranges of conditional expressions (3) to (11) are set as follows.
1.62<nAP<1.73 (3b)
1.86<nAN<1.95 (4b)
0.03<|f1/fa|<0.31 (5b)
0.27<|f1/f|<0.53 (6b)
34.5<νAN<39.0 (7b)
0.06<rl/f<0.24 (8b)
1.80<nd1<1.86 (9b)
0.10<f2/f<0.60 (10b)
1.30<ra2/rl<2.80 (11b)

By satisfying at least one of the above conditional expressions, various aberrations such as curvature of field and chromatic aberration of magnification can be satisfactorily corrected, and high optical performance can be obtained. Furthermore, it becomes possible to configure the converter lens RCL in a small size.

Furthermore, a preferred configuration of the converter lens RCL will be described.

As in Examples 1 and 3 to 6, which will be described later, it is preferable that the second lens element L2 is composed of a cemented lens in which a negative lens, a positive lens, and a negative lens are cemented and arranged from the object side to the image side. As a result, the Petzval sum can be brought close to zero, and the curvature of field can be favorably corrected.

It is preferable that the lens surface closest to the object side of the second lens element L2 be concave toward the object side. Furthermore, it is preferable that the lens surface closest to the image side of the second lens element L2 be concave toward the image side. This can reduce the occurrence of astigmatism.

It is preferable that the lens element (one cemented lens or one lens in which a plurality of lenses are cemented together) arranged closest to the image side of the converter lens RCL has a positive refractive power. This makes it easier to correct field curvature.

Furthermore, it is preferable that all the lenses constituting the converter lens RCL are spherical lenses. By not using an aspherical lens, it becomes possible to manufacture the converter lens RCL at low cost.

Next, the master lens ML of the example and the converter lens RCL of the example will be described. Examples 2 to 6 are examples corresponding to this embodiment, and Example 1 is a reference example.

[Master lens]
In this specification, the configuration of the master lens ML is common to Examples 1 to 6 of the converter lens RCL.

FIG. 1 is a cross-sectional view of the master lens ML when focusing on an infinite distance object, and FIG. 2 is an aberration diagram of the master lens ML when focusing on an infinite distance object. The master lens ML has an F number of 2.90, a half angle of view of 3.16 degrees, and a back focus of 39 mm. It should be noted that the configuration of the master lens ML given in the example is merely an example, and other optical systems may be used as long as they are optical systems capable of forming an image on the image plane IP.

[Converter lens]
Next, converter lenses of Examples 1 to 6 will be described.

[Example 1]
FIG. 3 is a cross-sectional view of the converter lens RCL of Example 1. FIG. FIG. 4 is an aberration diagram when focusing on an object at infinity when the converter lens RCL of Example 1 is arranged on the image side of the master lens ML.

In the converter lens RCL of Example 1, the first lens element L1 is the positive lens Lp arranged closest to the object side of the converter lens RCL. The second lens element L2 is a cemented lens of a negative lens placed second from the object side of the converter lens RCL and a positive lens placed adjacent to the image side of the negative lens.

[Example 2]
FIG. 5 is a cross-sectional view of the converter lens RCL of Example 2. FIG. FIG. 6 is an aberration diagram when focusing on an object at infinity when the converter lens RCL of Example 2 is arranged on the image side of the master lens ML.

In the converter lens RCL of Example 2, the first lens element L1 is a cemented lens of a negative lens arranged closest to the object side of the converter lens RCL and a positive lens Lp arranged adjacent to the image side of the negative lens. is. Also, the second lens element L2 is a cemented lens of a negative lens arranged third from the object side of the converter lens RCL and a positive lens arranged adjacent to the image side of the negative lens.

[Example 3]
FIG. 7 is a cross-sectional view of the converter lens RCL of Example 3. FIG. FIG. 8 is an aberration diagram when focusing on an object at infinity when the converter lens RCL of Example 3 is arranged on the image side of the master lens ML.

In the converter lens RCL of Example 3, the first lens element L1 is the positive lens Lp arranged closest to the object side of the converter lens RCL. The second lens element L2 is a cemented lens composed of three lenses, a negative lens, a positive lens, and a negative lens, arranged second to fourth from the most object side of the converter lens RCL.

[Example 4]
FIG. 9 is a cross-sectional view of the converter lens RCL of Example 4. FIG. FIG. 10 is an aberration diagram when focusing on an object at infinity when the converter lens RCL of Example 4 is arranged on the image side of the master lens ML.

In the converter lens RCL of Example 4, the first lens element L1 is the positive lens Lp arranged closest to the object side of the converter lens RCL. The second lens element L2 is a cemented lens composed of three lenses, a negative lens, a positive lens, and a negative lens, arranged second to fourth from the most object side of the converter lens RCL.

[Example 5]
FIG. 11 is a cross-sectional view of the converter lens RCL of Example 5. FIG. FIG. 12 is an aberration diagram when focusing on an object at infinity when the converter lens RCL of Example 5 is arranged on the image side of the master lens ML.

In the converter lens RCL of Example 5, the first lens element L1 is the positive lens Lp arranged closest to the object side of the converter lens RCL. The second lens element L2 is a cemented lens composed of three lenses, a negative lens, a positive lens, and a negative lens, arranged second to fourth from the most object side of the converter lens RCL.

[Example 6]
FIG. 13 is a cross-sectional view of the converter lens RCL of Example 6. FIG. FIG. 14 is an aberration diagram when focusing on an object at infinity when the converter lens RCL of Example 6 is arranged on the image side of the master lens ML.

In the converter lens RCL of Example 6, the first lens element L1 is the positive lens Lp arranged closest to the object side of the converter lens RCL. The second lens element L2 is a cemented lens composed of three lenses, a negative lens, a positive lens, and a negative lens, arranged second to fourth from the most object side of the converter lens RCL.

By satisfying the conditional expressions (1) to (11) described above, all of Examples 1 to 6 achieve high optical performance while miniaturizing the converter lens RCL.

[Numerical example]
Numerical examples 1 to 6 corresponding to numerical examples of the master lens ML and converter lenses RCL of examples 1 to 6 are shown.

Also, in each numerical example, the surface numbers indicate the order of the optical surfaces from the object side. r is the radius of curvature of the optical surface (mm), d in the surface number i is the distance (mm) between the i-th optical surface and the i+1-th optical surface, nd is the refractive index of the material of the optical member on the d line, νd is the Abbe number of the material of the optical member with respect to the d-line. The definition of the Abbe number is the same as above,
νd = (Nd-1)/(NF-NC)
is.

BF indicates back focus. The back focus in the numerical examples of the master lens ML is the distance on the optical axis from the surface closest to the image side to the paraxial image plane expressed in air conversion length.

The total lens length of the master lens ML in the numerical examples is the distance on the optical axis from the most object-side surface (first lens surface) of the master lens ML to the most image-side surface (final lens surface) of the master lens ML. This is the length including the back focus. The total lens length in the numerical examples of the converter lens RCL is the distance on the optical axis from the lens surface closest to the object (first lens surface) to the lens surface closest to the image (final lens surface) of the converter lens RCL.

The lens interval between the master lens ML and the converter lens RCL is the distance on the optical axis from the most image side surface of the master lens ML to the most object side surface of the converter lens RCL. The distance between the master lens ML and the converter lens RCL is represented by the air conversion length.

The front principal point position is the distance from the most object side surface to the front principal point, and the rear principal point position is the distance from the most image side surface to the rear principal point. Each numerical value for the front principal point position and the rear principal point position is a paraxial amount, and the sign is positive in the direction from the object side to the image side.

[Table 1] shows the physical quantities used in the above conditional expressions in each of Numerical Examples 1 to 6, and [Table 2] shows the values corresponding to the above conditional expressions.

SFa in [Table 2] means the value of (ra2+ra1)/(ra2-ra1) in conditional expression (2).

[Master Lens] - Common to Numerical Examples 1 to 6 of Converter Lenses -
unit mm

Surface data surface number rd nd νd θgF
1 147.291 15.31 1.59522 67.74 0.5442
2 497.553 135.95
3 93.917 15.46 1.43700 95.10 0.5326
4 -169.659 1.50 1.80610 33.27 0.5881
5 85.058 2.78
6 81.980 11.17 1.43700 95.10 0.5326
7 ∞ 30.12
8 64.700 7.23 1.89286 20.36 0.6393
9 117.746 0.20
10 53.244 2.00 1.83400 37.16 0.5776
11 34.348 8.98 1.43700 95.10 0.5326
12 71.295 7.95
13 (Aperture) ∞ 5.00
14 -424.241 1.60 1.61800 63.40 0.5395
15 56.377 38.46
16 192.506 1.40 1.89286 20.36 0.6393
17 120.766 4.96 1.51742 52.43 0.5564
18 -71.885 1.00
19 61.529 4.26 1.80610 33.27 0.5881
20 -244.681 1.20 1.53775 74.70 0.5392
21 29.916 6.46
22 -88.814 1.20 1.72916 54.68 0.5444
23 62.251 2.54
24 94.888 4.00 1.65412 39.68 0.5737
25 -343.957 6.25
26 45.503 9.29 1.64769 33.79 0.5938
27 -81.900 1.70 1.80810 22.76 0.6307
28 81.305 6.55
29 64.484 5.47 1.56732 42.82 0.5731
30 294.428 39.00
Image plane ∞

Various data Focal length 392.00
F number 2.90
Half angle of view (degrees) 3.16
Image height 21.64
Lens length 379.01
BF 39.00

[Converter lens]
[Numerical Example 1]
unit mm

Surface data surface number rd nd νd
1 800.000 3.97 1.85478 24.8
2 -64.600 5.05
3 -41.053 1.50 1.88300 40.8
4 109.415 7.84 1.53172 48.8
5 -33.368 0.67
6 -43.314 1.50 1.90043 37.4
7 176.343 10.11 1.51742 52.4
8 -22.583 1.60 1.90043 37.4
9 -125.408 2.17
10 -84.365 7.82 1.63980 34.5
11 -30.377

Various data focal length -152.43
Lens length 42.24
Front principal point position -10.55
Rear principal point position -50.64
Lateral magnification 1.400

Distance between the master lens and the converter lens of Numerical Example 1: 6.00

[Numerical Example 2]
unit mm

Surface data surface number rd nd νd
1 364.337 1.50 1.90043 37.4
2 75.135 4.30 1.85478 24.8
3 -108.452 3.59
4 -81.339 1.50 1.90043 37.4
5 45.855 8.57 1.62004 36.3
6 -31.329 3.00
7 -24.851 1.50 2.05090 26.9
8 -202.363 5.73
9 -99.050 1.70 1.90043 37.4
10 252.137 11.91 1.67300 38.3
11 -29.905

Various data focal length -379.68
Lens length 43.29
Front principal point position -75.48
Rear principal point position -141.87
Lateral magnification 1.400

Distance between master lens and converter lens of Numerical Example 2 6.00

[Numerical Example 3]
unit mm

Surface data surface number rd nd vd
1 ∞ 3.32 1.85478 24.8
2 -58.256 3.22
3 -56.595 1.30 1.77250 49.6
4 68.517 6.43 1.60342 38.0
5 -42.322 1.30 2.00100 29.1
6 -351.582 3.55
7 -61.010 9.54 1.51742 52.4
8 -20.182 1.65 1.95375 32.3
9 -73.911 2.85
10 -70.983 7.36 1.63980 34.5
11 -28.545

Various data focal length -204.04
Total lens length -232.83
Lens length 40.52
Front principal point position -25.29
Rear principal point position -69.31
Lateral magnification 1.400

Distance between master lens and converter lens of Numerical Example 3: 6.00

[Numerical Example 4]
unit mm

Surface data surface number rd nd νd
1 159.417 3.91 1.80518 25.5
2 -68.675 3.95
3 -50.952 1.20 1.90043 37.4
4 16.198 9.93 1.66565 35.6
5 -32.188 1.20 1.83481 42.7
6 37.352 0.46
7 31.866 5.03 1.72047 34.7
8 -260.827 5.20
9 -75.715 1.50 1.91082 35.3
10 30.495 10.24 1.67300 38.3
11 -41.863 1.60 2.05090 26.9
12 -917.130 1.18
13 544.949 12.25 1.54814 45.8
14 -26.693

Various data focal length -115.57
Lens length 57.65
Front principal point position -24.78
Rear principal point position -102.30
Lateral magnification 2.000

Distance between master lens and converter lens of Numerical Example 4 6.00

[Numerical Example 5]
unit mm

Surface data surface number rd nd νd
1 230.983 3.76 1.80518 25.5
2 -61.821 4.05
3 -47.109 1.20 1.90043 37.4
4 16.833 11.39 1.62004 36.3
5 -28.332 1.20 1.81600 46.6
6 54.014 0.30
7 33.307 5.48 1.72047 34.7
8 -288.920 5.02
9 -100.495 1.50 1.88300 40.8
10 29.178 12.81 1.60342 38.0
11 -42.699 0.00
12 -42.699 1.80 1.89286 20.4
13 449.449 11.49 1.56732 42.8
14 -27.219

Various data focal length -126.12
Lens length 59.99
Front principal point position -30.06
Rear principal point position -113.01
Lateral magnification 2.000

Distance between master lens and converter lens of Numerical Example 5: 6.00

[Numerical Example 6]
unit mm

Surface data surface number rd nd νd
1 102.255 3.69 1.80518 25.5
2 -76.294 3.24
3 -61.063 1.20 1.90043 37.4
4 16.888 10.64 1.60342 38.0
5 -34.524 1.20 1.81600 46.6
6 37.047 0.46
7 26.804 6.35 1.66565 35.6
8 -95.813 3.46
9 -35.439 1.50 1.90043 37.4
10 26.155 13.21 1.66565 35.6
11 -37.965 0.25
12 -56.043 1.80 1.92286 20.9
13 1008.919 12.42 1.51742 52.4
14 -26.712

Focal length -133.43
Lens length 59.42
Front principal point position -33.72
Rear principal point position -120.50
Lateral magnification 2.000

Distance between master lens and converter lens of Numerical Example 6: 6.00

[Embodiment of Imaging Device]
FIG. 10 is a diagram showing the configuration of an imaging device (digital camera) 10. As shown in FIG. FIG. 10(a) is a perspective view, and FIG. 10(b) is a side view. The imaging device 10 photoelectrically converts an image formed by the camera body 13, the master lens ML, the converter lens RCL which is the same as in any of the first to sixth embodiments, and the master lens ML and the converter lens RCL. A light receiving element (imaging element) 12 is provided. As the light receiving element 12, an imaging element such as a CCD sensor or a CMOS sensor can be used. The master lens ML and the converter lens RCL may be configured integrally with the camera body 13, or may be configured to be detachable from the camera body 13, respectively. When the master lens ML and the converter lens RCL are configured integrally with the camera body 13, the converter lens RCL is configured to be removable on the optical axis.

[Example of Interchangeable Lens]
The present invention can also be applied to an interchangeable lens in which the master lens ML and the converter lens RCL are configured in the same lens barrel and which can be attached to and detached from the imaging apparatus. The master lens ML may be a single focus lens or a zoom lens. In this case, the converter lens RCL is configured to be insertable and removable on the optical axis. The converter lens RCL is arranged on or off the optical axis according to instructions from the user via the operation member or the user interface.

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

RCL converter lens ML master lens L1 first lens element L2 second lens element

Claims (17)

A converter lens that has a negative refractive power and is arranged on the image side of the master lens to make the focal length of the entire system longer than the focal length of the master lens alone,
a first lens element arranged closest to the object side of the converter lens;
a second lens element arranged adjacent to the image side of the first lens element via a space;
a lens element arranged closest to the image side of the converter lens,
the second lens element comprises a cemented lens formed by cementing a negative lens, a positive lens, and a negative lens arranged in order from the object side to the image side;
the lens element has a positive refractive power,
f is the focal length of the converter lens, na1 is the refractive index at the d-line of the material forming the image-side lens surface of the first lens element, and d is the material forming the object-side lens surface of the second lens element. na2 is the refractive index at the line, ra1 is the radius of curvature of the image-side lens surface of the first lens element, ra2 is the radius of curvature of the object-side lens surface of the second lens element, and the focal length of the first lens element is Let f1
the focal length fa of the space between the first lens element and the second lens element,
fa = 1/[{(1/ra1) x (1-na1)/na2}-{(1/ra2) x (1-na2)/na2}]
When expressed as
1.45<|fa/f|<8.55
-80.0<(ra2+ra1)/(ra2-ra1)<-2.00
0.01<|f1/fa|≦0.195
A converter lens characterized by satisfying the following conditional expression: The converter lens has at least one positive lens,
When nAP is the average refractive index at the d-line of all positive lens materials included in the converter lens,
1.58<nAP<1.80
2. The converter lens according to claim 1, wherein the following condition is satisfied. The converter lens has at least one negative lens,
When nAN is the average refractive index at the d-line of all negative lens materials included in the converter lens,
1.80<nAN<2.20
3. The converter lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the first lens element is f1,
0.15<|f1/f|<0.70
4. The converter lens according to any one of claims 1 to 3, wherein the following condition is satisfied. A converter lens that has a negative refractive power and is arranged on the image side of the master lens to make the focal length of the entire system longer than the focal length of the master lens alone,
a first lens element arranged closest to the object side of the converter lens;
a second lens element arranged adjacent to the image side of the first lens element via a space;
a lens element arranged closest to the image side of the converter lens,
the lens element has a positive refractive power,
f is the focal length of the converter lens, na1 is the refractive index at the d-line of the material forming the image-side lens surface of the first lens element, and d is the material forming the object-side lens surface of the second lens element. na2 is the refractive index at the line, ra1 is the radius of curvature of the image-side lens surface of the first lens element, ra2 is the radius of curvature of the object-side lens surface of the second lens element, and the focal length of the first lens element is Let f1
the focal length fa of the space between the first lens element and the second lens element,
fa = 1/[{(1/ra1) x (1-na1)/na2}-{(1/ra2) x (1-na2)/na2}]
When expressed as
1.45<|fa/f|<8.55
-80.0<(ra2+ra1)/(ra2-ra1)<-2.00
0.01<|f1/fa|≦0.195
0.15<|f1/f|<0.70
A converter lens characterized by satisfying the following conditional expression: The converter lens has at least one negative lens,
When νAN is the average Abbe number of all negative lens materials included in the converter lens with respect to the d-line,
26.0<νAN<45.0
6. The converter lens according to any one of claims 1 to 5 , wherein the following condition is satisfied. The lens surface closest to the image side of the converter lens has a convex shape toward the image side, and when the radius of curvature of the lens surface is rl,
0.02<rl/f<0.32
7. The converter lens according to any one of claims 1 to 6 , wherein the following condition is satisfied. A converter lens that has a negative refractive power and is arranged on the image side of the master lens to make the focal length of the entire system longer than the focal length of the master lens alone,
a first lens element arranged closest to the object side of the converter lens;
a second lens element arranged adjacent to the image side of the first lens element via a space;
a lens element arranged closest to the image side of the converter lens,
the lens element has a positive refractive power,
f is the focal length of the converter lens, na1 is the refractive index at the d-line of the material forming the image-side lens surface of the first lens element, and d is the material forming the object-side lens surface of the second lens element. na2 is the refractive index at the line, ra1 is the radius of curvature of the image-side lens surface of the first lens element, ra2 is the radius of curvature of the object-side lens surface of the second lens element, and the focal length of the first lens element is f1, let rl be the radius of curvature of the lens surface closest to the image side of the converter lens,
the focal length fa of the space between the first lens element and the second lens element,
fa = 1/[{(1/ra1) x (1-na1)/na2}-{(1/ra2) x (1-na2)/na2}]
When expressed as
1.45<|fa/f|<8.55
-80.0<(ra2+ra1)/(ra2-ra1)<-2.00
0.01<|f1/fa|≦0.195
0.02<rl/f<0.32
A converter lens characterized by satisfying the following conditional expression: The converter lens has at least one positive lens,
Let nd1 be the refractive index at the d-line of the material of the positive lens located closest to the object side among all the positive lenses included in the converter lens,
1.75<nd1<2.00
9. The converter lens according to any one of claims 1 to 8 , wherein the following condition is satisfied. the first lens element has a positive refractive power and the second lens element has a negative refractive power;
When the focal length of the second lens element is f2,
0.04<f2/f<1.10
10. The converter lens according to any one of claims 1 to 9 , wherein the following condition is satisfied. When the curvature radius of the image side lens surface of the lens closest to the image side of the converter lens is rl,
1.00<ra2/rl<3.40
11. The converter lens according to any one of claims 1 to 10 , wherein the following condition is satisfied. A converter lens that has a negative refractive power and is arranged on the image side of the master lens to make the focal length of the entire system longer than the focal length of the master lens alone,
a first lens element arranged closest to the object side of the converter lens;
a second lens element arranged adjacent to the image side of the first lens element via a space;
a lens element arranged closest to the image side of the converter lens,
the lens element has a positive refractive power,
f is the focal length of the converter lens, na1 is the refractive index at the d-line of the material forming the image-side lens surface of the first lens element, and d is the material forming the object-side lens surface of the second lens element. na2 is the refractive index at the line, ra1 is the radius of curvature of the image-side lens surface of the first lens element, ra2 is the radius of curvature of the object-side lens surface of the second lens element, and the focal length of the first lens element is f1, let rl be the radius of curvature of the image-side lens surface of the lens closest to the image side of the converter lens,
the focal length fa of the space between the first lens element and the second lens element,
fa = 1/[{(1/ra1) x (1-na1)/na2}-{(1/ra2) x (1-na2)/na2}]
When expressed as
1.45<|fa/f|<8.55
-80.0<(ra2+ra1)/(ra2-ra1)<-2.00
0.01<|f1/fa|≦0.195
1.00<ra2/rl<3.40
A converter lens characterized by satisfying the following conditional expression: 13. The converter lens according to any one of claims 1 to 12, wherein the object-side lens surface of the second lens element is concave toward the object side. 14. The converter lens according to any one of claims 1 to 13, wherein the image-side lens surface of the second lens element is concave toward the image side. 15. The converter lens according to any one of claims 1 to 14, wherein all lenses constituting the converter lens are spherical lenses. An interchangeable lens comprising a master lens and the converter lens according to any one of claims 1 to 15 . master lens and
A converter lens according to any one of claims 1 to 16 ;
An image pickup device comprising an image pickup device that receives an image formed by the converter lens.

Images