JP7129001B2 - Rear converter lens and optical equipment - Google Patents

Description

The present invention relates to rear converter lenses and optical instruments.

Conventionally, there is known a method of increasing the focal length of a photographing lens by inserting a rear converter lens having a negative focal length between a master lens and a camera body (for example, see Patent Document 1). However, Patent Document 1 has a problem that further improvement in optical performance is demanded.

JP 2013-235217 A

A rear converter lens according to a first aspect of the present invention is a rear converter lens that is arranged on the image side of a master lens and has a combined focal length with the master lens that is longer than the focal length of the master lens. A first lens component disposed on the object side and having a positive refractive power, a specific cemented lens having a negative refractive power composed of at least a cemented negative lens, a positive lens, and a negative lens, and a cemented lens disposed closest to the image side, a third lens component having positive refractive power, wherein the first lens component is a biconvex positive lens and the third lens component is a single lens satisfying the following condition:
1.90 < nspn
however,
nspn: Refractive index of the medium of the negative lens having the highest refractive index among the negative lenses constituting the specific cemented lens with respect to the d-line The lens component refers to a single lens or a cemented lens.

A rear converter lens according to a second aspect of the present invention is a rear converter lens that is arranged on the image side of a master lens and has a combined focal length with the master lens that is longer than the focal length of the master lens. A first lens component disposed on the object side and having a positive refractive power, a specific cemented lens having a negative refractive power composed of at least a cemented negative lens, a positive lens, and a negative lens, and a cemented lens disposed closest to the image side, and a third lens component having a positive refractive power, satisfying the following condition.
2.02 < nspn
20.00 < νspn
however,
nspn: the refractive index for the d-line of the medium of the negative lens having the highest refractive index among the negative lenses constituting the specific cemented lens
νspn: the Abbe number for the d-line of the medium of the negative lens with the highest refractive index among the negative lenses constituting the specific cemented lens
A lens component refers to a single lens or a cemented lens.

1 is a cross-sectional view of a camera equipped with a rear converter lens according to this embodiment; FIG. FIG. 3 is a cross-sectional view showing the lens configuration of the optical system including the master lens and the rear converter lens according to the first example, in a state in which the lens is in focus at infinity. FIG. 10 is a diagram showing various aberrations of the optical system composed of the master lens and the rear converter lens according to the first embodiment in an infinity focused state; FIG. 11 is a cross-sectional view showing the lens configuration of the optical system including the master lens and the rear converter lens according to the second embodiment in a state of being in focus at infinity. FIG. 10 is a diagram of various aberrations of an optical system composed of a master lens and a rear converter lens according to the second embodiment in an infinity focused state; FIG. 12 is a cross-sectional view showing the lens configuration of the optical system including the master lens and the rear converter lens according to the third embodiment, in a state in which the lens is in focus at infinity. FIG. 10 is a diagram of various aberrations of the optical system composed of the master lens and the rear converter lens according to the third embodiment in an infinity focused state; FIG. 11 is a cross-sectional view showing the lens configuration of the optical system including the master lens and the rear converter lens according to the fourth embodiment in an infinity focused state; FIG. 11 is a diagram of various aberrations of the optical system composed of the master lens and the rear converter lens according to the fourth embodiment in an infinity focused state; FIG. 12 is a cross-sectional view showing the lens configuration of the optical system including the master lens and the rear converter lens according to the fifth embodiment in an infinity focused state; FIG. 11 is a diagram of various aberrations of an optical system composed of a master lens and a rear converter lens according to the fifth embodiment in an infinity focused state; 4 is a flowchart for explaining a method of manufacturing the rear converter lens;

Preferred embodiments are described below with reference to the drawings. As shown in FIG. 1, the rear converter lens RCL according to this embodiment is arranged on the image side of the master lens ML, and 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 made based on the camera 10, which is an optical device including the rear converter lens RCL according to the present embodiment, shown in FIG. This camera 10 is a lens interchangeable so-called mirrorless camera that has a master lens ML as a photographing lens 2 . The rear converter lens 3 (RCL) is attached between the taking lens 2 which is the master lens ML and the camera body 1 having the imaging section 4 .

In this camera 10, light from an object (subject) (not shown) is condensed by a photographing lens 2 and a rear converter lens 3, passes through an OLPF (Optical low pass filter) FL, and passes through an imaging unit 4. A subject image is formed on the imaging plane. Then, the subject image is photoelectrically converted by the 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 EVF5.

Further, when a release button (not shown) is pressed by the photographer, an image photoelectrically converted by the imaging section 4 is stored in a memory (not shown). In this manner, the photographer can photograph the subject with the camera 10. FIG. In the present embodiment, an example of a mirrorless camera has been described. , the same effects as those of the camera 10 can be obtained.

The rear converter lens RCL according to the present embodiment is arranged closest to the object side and is composed of a first lens component LC1 having positive refractive power and at least a cemented negative lens, a positive lens, and a negative lens, and has negative refractive power. and a third lens component LC3 disposed closest to the image side and having positive refractive power. With this configuration, spherical aberration, longitudinal chromatic aberration, lateral chromatic aberration, and especially the Petzval sum can be corrected satisfactorily in spite of the fact that the rear converter lens as a whole is a strong negative lens system.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (1).

1.50 < nspn (1)
however,
nspn: Refractive index for the d-line of the medium of the negative lens with the highest refractive index among the negative lenses constituting the specific cemented lens SPL

Conditional expression (1) defines the refractive index for the d-line of the medium of the negative lens having the highest refractive index among the negative lenses included in the specific cemented lens SPL. By arranging a negative lens that satisfies conditional expression (1) in the specific cemented lens SPL, it is possible to obtain an optical system in which the Petzval sum is well corrected while being compact. It is suitable for an optical system with a very short back focus. If the lower limit of conditional expression (1) is not reached, correction of the Petzval sum becomes difficult, which is not preferable. In addition, in order to ensure the effect of conditional expression (1), the lower limit of conditional expression (1) is 1.60, and further 1.70, 1.80, 1.85, 1.90, 1 More preferably, 0.95, 1.97, 1.99, 2.00, 2.02, 2.03, 2.04.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (2).

20.00 < νspn (2)
however,
νspn: Abbe number for the d-line of the medium of the negative lens with the highest refractive index among the negative lenses that make up the specific cemented lens SPL

Conditional expression (2) defines the Abbe number for the d-line of the medium of the negative lens having the highest refractive index among the negative lenses included in the specific cemented lens SPL. By arranging a negative lens that satisfies conditional expression (2) in the specific cemented lens SPL, it is possible to achieve both correction of the Petzval sum and correction of longitudinal chromatic aberration and lateral chromatic aberration. If the lower limit of conditional expression (2) is not reached, it is difficult to correct axial chromatic aberration and chromatic aberration of magnification, which is not preferable. In order to ensure the effect of conditional expression (2), the lower limit of conditional expression (2) is set to 20.50, and further to 21.00, 21.50, 22.00, 22.50, 23.00. 00, 23.50, 24.00, 24.50, 25.00, 25.50, and 26.00 are more desirable. In order to ensure the effect of conditional expression (2), it is more desirable to set the upper limit of conditional expression (2) to 40.00, more preferably 38.00 and 35.00.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (3).

Bfa/L/β < 0.50 (3)
however,
Bfa: Air-converted back focus of the optical system in which the rear converter lens RCL is attached to the master lens ML L: Distance on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the rear converter lens RCL β: Magnification of rear converter lens RCL

Conditional expression (3) defines the air-converted back focus with respect to the distance on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the rear converter lens RCL. By satisfying conditional expression (3), the rear converter lens RCL according to this embodiment can be applied to a mirrorless camera with a short back focus relative to the total lens length of the master lens ML. If the upper limit of conditional expression (3) is exceeded, the total length of the rear converter lens RCL (the distance on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the rear converter lens RCL) ) is too short, it becomes difficult to correct the Petzval sum, axial chromatic aberration, and lateral chromatic aberration. In order to ensure the effect of the conditional expression (3), the upper limit of the conditional expression (3) is set to 0.48, 0.45, 0.43, 0.40, 0.38, 0.48, 0.45, 0.43, 0.40, 0.38, 0.48. 37, 0.36, 0.35 and 0.34 are more desirable.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (4).

νL1p < 45.00 (4)
however,
νL1p: Abbe number for the d-line of the medium of the positive lens forming the first lens component LC1

Conditional expression (4) defines the Abbe number for the d-line of the medium of the positive lens forming the first lens component LC1. If the positive lens constituting the first lens component LC1 satisfies the conditional expression (4), longitudinal chromatic aberration can be satisfactorily corrected. Exceeding the upper limit of conditional expression (4) is not preferable because it becomes difficult to correct axial chromatic aberration. In order to ensure the effect of conditional expression (4), the upper limit of conditional expression (4) is set to 44.00, and further to 43.00, 42.00, 41.00, 40.00, 39.50, 39.00, 38.50, 38.00, and 26.00 are more desirable.

Further, in the rear converter lens RCL according to this embodiment, it is desirable that the first lens component LC1 be a single lens. If the first lens component LC1 is a cemented lens in which a positive lens is cemented with a negative lens, the dispersion of the positive lens system will decrease, making it difficult to correct axial chromatic aberration, which is not preferable.

Further, in the rear converter lens RCL according to this embodiment, the first lens component LC1 is preferably a biconvex positive lens. If the first lens component LC1 has a shape other than biconvex, correction of spherical aberration becomes difficult, which is not preferable.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (5).

nspp < 1.80 (5)
however,
nspp: refractive index for the d-line of the medium of the positive lens that constitutes the specific cemented lens SPL

Conditional expression (5) defines the refractive index for the d-line of the medium of the positive lens that constitutes the specific cemented lens SPL. By arranging a positive lens that satisfies conditional expression (5) in the specific cemented lens SPL, it is possible to obtain an optical system in which the Petzval sum is favorably corrected while being compact. Exceeding the upper limit of conditional expression (5) is not preferable because correction of the Petzval sum becomes difficult. In order to ensure the effect of conditional expression (5), the upper limit of conditional expression (5) should be set to 1.79, and further to 1.78, 1.77, 1.76, and 1.60. is more desirable.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (6).

νspp < 45.00 (6)
however,
νspp: Abbe number for the d-line of the medium of the positive lens that constitutes the specific cemented lens SPL

Conditional expression (6) defines the Abbe number for the d-line of the medium of the positive lens that constitutes the specific cemented lens SPL. By disposing a positive lens that satisfies conditional expression (6) in the specific cemented lens SPL, it is possible to satisfactorily correct longitudinal chromatic aberration and lateral chromatic aberration. If the upper limit of conditional expression (6) is exceeded, it becomes difficult to correct axial chromatic aberration and chromatic aberration of magnification, which is not preferable. In order to ensure the effect of conditional expression (6), the upper limit of conditional expression (6) is set to 44.00, and further to 43.00, 42.00, 41.50, 41.00, 40.00. 50, 40.00, 39.50, 39.00, 38.50 and 38.00 are more desirable.

Further, in the rear converter lens RCL according to the present embodiment, it is desirable that the lens surface closest to the image side of the third lens component LC3 be convex toward the image side. If the lens surface closest to the image side of the third lens component LC3 is not convex toward the image side, correction of curvature of field becomes difficult, which is undesirable. In addition, for a camera equipped with an image pickup device equipped with an on-chip microlens, the exit pupil must be somewhat distant, and it is desirable that the lens surface closest to the image side of the third lens component LC3 be convex toward the image side. If the lens surface on the side is not convex toward the image side, it is difficult to correct the pupil position, which is not preferable.

Further, in the rear converter lens RCL according to this embodiment, it is desirable that the third lens component LC3 has a biconvex shape. If the third lens component does not have a biconvex shape, correction of curvature of field becomes difficult, which is undesirable. Further, if the third lens component is not biconvex, it is not preferable because it becomes difficult to correct the pupil position.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfy the following conditional expression (7).

nL3p < 1.630 (7)
however,
nL3p: refractive index for the d-line of the medium of the positive lens forming the third lens component LC3

Conditional expression (7) defines the refractive index for the d-line of the medium of the positive lens that constitutes the third lens component LC3. By arranging a positive lens that satisfies conditional expression (7) as the third lens component LC3, it is possible to obtain an optical system in which the Petzval sum is favorably corrected while being compact. Exceeding the upper limit of conditional expression (7) is not preferable because it becomes difficult to correct the Petzval sum. In order to ensure the effect of the conditional expression (7), the upper limit of the conditional expression (7) is set to 1.625, 1.620, 1.615, 1.610, 1.608, 1.625, 1.615, 1.610, 1.608, 1.625. 605 and 1.595 are more desirable.

Further, in the rear converter lens RCL according to this embodiment, it is desirable that the third lens component LC3 be a single lens. If the third lens component LC3 is not composed of a single lens, the optical system becomes large, and forcibly reducing the size makes it difficult to correct curvature of field and the Petzval sum, which is not preferable.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (8).

0.40 < fL3/fL1 < 1.80 (8)
however,
fL1: focal length of first lens component LC1 fL3: focal length of third lens component LC3

Conditional expression (8) defines the ratio of the focal length of the third lens component LC3 to the focal length of the first lens component LC1. By satisfying the conditional expression (8), the rear converter lens RCL can obtain an optical system in which the Petzval sum is well corrected while being compact. Suitable for short optical systems. Outside the range of conditional expression (8), it is difficult to correct lateral chromatic aberration, which is not preferable. In order to ensure the effect of the conditional expression (8), the lower limit of the conditional expression (8) is set to 0.45, 0.50, 0.55, 0.60, 0.65, 0.50, 0.55, 0.60, 0.65, 0.45. 70, 0.75, 0.78 and 0.80 are more desirable. In order to ensure the effect of conditional expression (8), the upper limit of conditional expression (8) is set to 1.75, 1.70, 1.65, 1.60, 1.55, 1.50, 1.45, 1.42, 1.40 and 1.38 are more desirable.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (9).

1.20 < fL1/(-fsp) < 4.50 (9)
however,
fL1: focal length of first lens component LC1 fsp: focal length of specific cemented lens SPL

Conditional expression (9) defines the ratio of the focal length of the first lens component LC1 to the focal length of the specific cemented lens SPL. Outside the range of conditional expression (9), it is difficult to correct curvature of field, Petzval sum, chromatic aberration of magnification, and longitudinal chromatic aberration, which is not preferable. In order to ensure the effect of conditional expression (9), the lower limit of conditional expression (9) is set to 1.25, further 1.30, 1.35, 1.40, 1.45, 1.25 More preferably 50, 1.55, 1.58, 1.60, 1.62, 1.65. Also, in order to ensure the effect of conditional expression (9), the upper limit of conditional expression (9) is set to 4.40, 4.30, 4.20, 4.10, 4.00, 3 0.95, 3.90, 3.85 and 3.80 are more desirable.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (10).

0.70 < fL3/(-fsp) < 5.50 (10)
however,
fL3: focal length of the third lens component LC3 fsp: focal length of the specific cemented lens SPL

Conditional expression (10) defines the ratio of the focal length of the third lens component LC3 to the focal length of the specific cemented lens SPL. Outside the range of conditional expression (10), it is difficult to correct curvature of field, Petzval sum, chromatic aberration of magnification, and longitudinal chromatic aberration, which is not preferable. In order to ensure the effect of conditional expression (10), the lower limit of conditional expression (10) is set to 0.75, 0.80, 0.85, 0.90, 0.95, 1. 00, 1.05, 1.10, 1.15, 1.20, 1.25 and 1.30 are more desirable. Further, in order to ensure the effect of conditional expression (10), the upper limit of conditional expression (10) is set to 5.40, 5.30, 5.20, 5.10, 5.05, and 5.05. More preferably, 0.00, 4.95, 4.90, 4.88, 4.85, 4.83.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (11).

Bfa/(-f)/β < 0.25 (11)
however,
Bfa: Air conversion back focus of the optical system in which the rear converter lens RCL is attached to the master lens ML f: Focal length of the rear converter lens RCL β: Magnification of the rear converter lens RCL

Conditional expression (11) defines the ratio of the air-converted back focus to the focal length of the entire system of the rear converter lens RCL. If the upper limit of conditional expression (11) is exceeded, the back focus becomes too large with respect to the focal length of the entire system of the rear converter lens RCL, and the negative lens becomes too strong. This is not preferable because correction of chromatic aberration becomes difficult. In order to ensure the effect of conditional expression (11), the upper limit of conditional expression (11) is set to 0.23, 0.20, 0.18, 0.16, 0.15, and 0.23. .14 is more desirable.

Further, in the rear converter lens RCL according to the present embodiment, it is desirable that the lens surface closest to the object side of the specific cemented lens SPL is an aspherical surface. By making the lens surface closest to the object side of the specific cemented lens SPL an aspherical surface, it is possible to satisfactorily correct curvature of field.

Further, it is desirable that the rear converter lens RCL according to this embodiment has a specific positive lens Lp that satisfies the following conditional expressions (12) to (14). The specific positive lens Lp corresponds to, for example, the biconvex positive lens L22 included in the second lens group G2 of the rear converter lens RCL3 according to the third embodiment shown in FIG.

22.00 < vp < 30.00 (12)
0.01×νp+np<2.02 (13)
0.604<0.00168×νp+θgFp (14)
however,
np: refractive index of the medium of the specific positive lens Lp for the d-line νp: Abbe number of the medium of the specific positive lens Lp for the d-line θgFp: partial dispersion ratio of the medium of the specific positive lens Lp

Conditional expression (12) defines the refractive index for the d-line of the medium of the specific positive lens Lp. If the rear converter lens RCL according to this embodiment has the specific positive lens Lp that satisfies the conditional expression (12), it is possible to suppress curvature of field while minimizing deterioration of longitudinal chromatic aberration and lateral chromatic aberration. can be done. In order to ensure the effect of conditional expression (12), the lower limit of conditional expression (12) is set to 22.30, and further to 22.50, 22.80, 23.00, 23.30, 23.00. 50, 23.80 and 24.00 are more desirable. Further, in order to ensure the effect of conditional expression (12), the upper limit of conditional expression (12) is set to 29.50, and further to 29.00, 28.50, 28.30, 28.00, 27. 80, 27.50, 27.30 and 27.00 are more desirable.

Conditional expression (13) defines the relationship between the refractive index of the medium of the specific positive lens Lp for the d-line and the Abbe number for the d-line. If the rear converter lens RCL according to the present embodiment has the specific positive lens Lp that satisfies the conditional expression (13), it is possible to suppress curvature of field while minimizing deterioration of longitudinal chromatic aberration and lateral chromatic aberration. can be done. In order to ensure the effect of conditional expression (13), the upper limit of conditional expression (13) is set to 2.01, 2.00, 1.99, 1.98, 1.97, 1. 96 and 1.95 are more desirable.

Conditional expression (14) defines the relationship between the Abbe number for the d-line of the medium of the specific positive lens Lp and the partial dispersion ratio. Here, the partial dispersion ratio θgFp is defined by the following equation, where ng is the refractive index for the g-line of the medium of the specific positive lens Lp, nF is the refractive index for the F-line, and nC is the refractive index for the C-line.

θgFp = (ng-nF)/(nF-nC)

If the rear converter lens RCL according to the present embodiment has the specific positive lens Lp that satisfies the conditional expression (14), it is possible to suppress curvature of field while minimizing deterioration of longitudinal chromatic aberration and chromatic aberration of magnification. can be done. In order to ensure the effect of conditional expression (14), the lower limit of conditional expression (14) is set to 0.605, 0.610, 0.615, 0.620, 0.625, 0.605, 0.610, 0.615, 0.620, 0.625, 0.605. 630, 0.635, 0.640, 0.645, 0.650, 0.655, 0.660 are more desirable.

Further, the rear converter lens RCL according to this embodiment includes a first lens group G1 including a first lens component LC1, a second lens group G2 including a specific cemented lens SPL, and a third lens including a third lens component LC3. It is desirable to have groups G3 and . With this configuration, spherical aberration, longitudinal chromatic aberration, lateral chromatic aberration, and especially the Petzval sum can be corrected satisfactorily in spite of the fact that the rear converter lens as a whole is a strong negative lens system.

In addition, in the rear converter lens RCL according to this embodiment, it is desirable that the first lens group G1 is composed only of the first lens component LC1. By configuring in this way, the rear converter lens RCL can be miniaturized, and the Petzval sum and longitudinal chromatic aberration can be satisfactorily corrected. If the number of lenses constituting the first lens group G1 is increased, the size of the optical system will increase.

Further, in the rear converter lens RCL according to this embodiment, it is desirable that the third lens group G3 is composed only of the third lens component LC3. By configuring in this way, the rear converter lens RCL can be miniaturized, and chromatic aberration of magnification and the Petzval sum can be satisfactorily corrected. If the number of lenses constituting the third lens group G3 is increased, the size of the optical system will increase.

Further, in the rear converter lens RCL according to the present embodiment, it is desirable that the specific cemented lens SPL is arranged closest to the image side of the second lens group G2. By configuring in this way, the size of the rear converter lens RCL can be reduced.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (15).

0.05 < f1/(-f) < 2.00 (15)
however,
f1: focal length of the first lens group G1 f: focal length of the rear converter lens RCL

Conditional expression (15) defines the ratio of the focal length of the first lens group G1 to the focal length of the rear converter lens RCL. Outside the range of conditional expression (15), it is difficult to correct curvature of field, Petzval sum, chromatic aberration of magnification, and longitudinal chromatic aberration, which is not preferable. In order to ensure the effect of conditional expression (15), the lower limit of conditional expression (15) is set to 0.10, 0.15, 0.20, 0.25, 0.30, 0.10, 0.15, 0.20, 0.25, 0.30, 0.10. 35, 0.40, 0.45, 0.50, 0.55, 0.58 and 0.60 are more desirable. Further, in order to ensure the effect of conditional expression (15), the upper limit of conditional expression (15) is set to 1.80, further 1.60, 1.50, 1.40, 1.30, 1.60, 1.50, 1.40, 1.30, 1.80. 20, 1.10, 1.00, 0.90 and 0.80 are more desirable.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (16).

0.03 < f2/f < 0.50 (16)
however,
f2: focal length of the second lens group G2 f: focal length of the rear converter lens RCL

Conditional expression (16) defines the ratio of the focal length of the second lens group G2 to the focal length of the rear converter lens RCL. If the conditional expression (16) is out of range, it is difficult to correct field curvature, Petzval sum, lateral chromatic aberration, and axial chromatic aberration, which is not preferable. In order to ensure the effect of conditional expression (16), the lower limit of conditional expression (16) is set to 0.05, 0.06, 0.08, 0.10, 0.11, 0. 12, 0.13, 0.14, 0.15 and 0.16 are more desirable. Further, in order to ensure the effect of conditional expression (16), the upper limit of conditional expression (16) is set to 0.48, and further 0.45, 0.42, 0.40, 0.38, 0.48, 0.45, 0.42, 0.40, 0.38, 0.48, 0.45, 0.42, 0.40, 0.38, 0.48, 0.45, 0.42, 0.40, 0.38, 0.48 35, 0.33, 0.30, 0.29, 0.28 and 0.27 are more desirable.

Moreover, it is desirable that the rear converter lens RCL according to the present embodiment satisfies the following conditional expression (17).

0.05 < f3/(-f) < 3.00 (17)
however,
f3: focal length of the third lens group G3 f: focal length of the rear converter lens RCL

Conditional expression (17) defines the ratio of the focal length of the third lens group G3 to the focal length of the rear converter lens RCL. Outside the range of conditional expression (17), it is difficult to correct curvature of field, Petzval sum, chromatic aberration of magnification, and longitudinal chromatic aberration, which is not preferable. In order to ensure the effect of conditional expression (17), the lower limit of conditional expression (17) is set to 0.10, 0.15, 0.20, 0.25, 0.30, 0.10, 0.10, 0.15, 0.20, 0.25, 0.30, 0.10, 0.15, 0.20, 0.25, 0.30, 0.10. 35, 0.40, 0.43, 0.45, 0.48, 0.50 and 0.53 are more desirable. Further, in order to ensure the effect of conditional expression (17), the upper limit of conditional expression (17) is set to 2.80, and further 2.50, 2.30, 2.00, 1.80, 1. 50, 1.40, 1.30, 1.20 and 1.00 are more desirable.

In addition, the conditions and configurations described above exhibit the effects described above, and are not limited to those that satisfy all the conditions and configurations. It is possible to obtain the above-described effects even if the conditions or combinations of the above conditions are satisfied.

Also, the contents described below can be appropriately adopted within a range that does not impair the optical performance.

In this embodiment, the rear converter lens RCL having a three-group configuration is shown, but the above configuration conditions and the like are also applicable to other group configurations such as a four-group configuration and a five-group configuration. Also, a configuration in which a lens or lens group is added closest to the object side, or a configuration in which a lens or lens group is added closest to the image side may be used. Specifically, a configuration is conceivable in which a lens group, which is positioned closest to the image side and has a fixed position with respect to the image plane during zooming or focusing, is added. Also, a lens group refers to a portion having at least one lens separated by an air gap that changes during zooming or focusing. A lens component refers to a single lens or a cemented lens in which a plurality of lenses are cemented together.

Also, a single lens group, a plurality of lens groups, or a partial lens group may be moved in the optical axis direction to serve as a focusing group for focusing from an object at infinity to an object at a short distance. In this case, the focusing group can also be applied to autofocus, and is suitable for driving a motor (such as an ultrasonic motor) for autofocus. At least part of the lens group of this embodiment may be used as a focusing group, and the other lenses may be fixed in position with respect to the image plane during focusing. Considering the load on the motor, it is preferable that the focusing group consist of a single lens.

In addition, the lens group or partial lens group is moved so as to have a displacement component in the direction perpendicular to the optical axis, or rotated (oscillated) in the in-plane direction including the optical axis to correct image blur caused by camera shake. It is good also as a vibration-proof group which carries out. At least part of the lens group in this embodiment may be an anti-vibration group.

Also, the lens surface may be spherical, planar, or aspherical. If the lens surface is spherical or flat, it is preferable because it facilitates lens processing and assembly adjustment and prevents deterioration of optical performance due to errors in processing and assembly adjustment. Also, even if the image plane is deviated, there is little deterioration in rendering performance, which is preferable. If the lens surface is aspherical, the aspherical surface can be ground aspherical, glass-molded aspherical, which is formed into an aspherical shape from glass, or composite aspherical, which is formed into an aspherical shape from resin on the surface of glass. Any aspheric surface may be used. Further, the lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

Further, each lens surface may be provided with an antireflection film having high transmittance in a wide wavelength range in order to reduce flare and ghost and achieve high contrast and high optical performance.

Further, the rear converter lens RCL of this embodiment has a magnification of about 1.2 to 3.0 times.

The outline of the method for manufacturing the rear converter lens RCL according to this embodiment will be described below with reference to FIG. First, a first lens component LC1 having a positive refractive power of the rear converter lens RCL by arranging each lens, a specific cemented lens SPL having a negative refractive power and comprising at least a cemented negative lens, a positive lens and a negative lens, and A third lens component LC3 having positive refractive power is prepared (step S100). Next, the first lens component LC1 is arranged closest to the object (step S200), the specific cemented lens SPL is arranged (step S300), and the third lens component LC3 is arranged closest to the image (step S400). Then, each lens component is arranged so as to satisfy a predetermined conditional expression (for example, conditional expression (1) or conditional expression (3) described above) (step S500).

Specifically, in this embodiment, for example, as shown in FIG. 2, as the rear converter lens RCL, a biconvex positive lens L11 is arranged in order from the object side as the first lens component LC1, and the lens surface on the object side A cemented lens obtained by cementing a biconcave negative lens L21 formed in an aspherical shape, a biconvex positive lens L22, and a plano-concave lens L23 having a concave surface facing the object side is arranged as a specific cemented lens SPL, and a biconvex A positive lens L31 is arranged as a third lens component LC3. Then, the rear converter lens RCL is manufactured by arranging the lens components prepared in this manner in accordance with the procedure described above.

With the configuration as described above, it is possible to provide a rear converter lens, an optical device, and a method for manufacturing a rear converter lens having excellent imaging performance.

Each embodiment of the present application will be described below with reference to the drawings. 2, 4, 6, 8, and 10 are sectional views showing the configuration and refractive power distribution of the rear converter lens RCL (RCL1 to RCL5) according to each example.

Each embodiment also shows the master lens ML to which the respective rear converter lenses RCL1 to RCL5 are attached. In any of the examples, rear converter lenses RCL1 to RCL5 are attached to master lens ML having the same specifications.

The master lens ML is, as shown in FIG. A negative meniscus negative lens M3 with a convex surface facing the object side, a biconcave negative lens M4, a positive meniscus lens M5 with a convex surface facing the object side, an aperture stop S, and an object a double-convex positive lens M6 having an aspherical lens surface on the side, a cemented positive lens in which a negative meniscus lens M7 having a convex surface facing the object side and a double-convex positive lens M8 are cemented together, a double-concave negative lens A cemented negative lens M9 and a biconvex positive lens M10 cemented together, a negative meniscus lens M11 with a concave surface facing the object side, a biconvex positive lens M12 with an aspherical lens surface on the image side, and an object It is composed of a positive meniscus-shaped positive lens M13 with a concave surface on the side and a biconcave negative lens M14.

In each embodiment, the aspherical surface has a height y in the direction perpendicular to the optical axis, and the distance along the optical axis from the tangent plane of the vertex of each aspherical surface at height y to each aspherical surface (amount of sag) is S(y), r is the radius of curvature of the reference sphere (paraxial radius of curvature), K is the conic constant, and An is the n-th order aspherical surface coefficient. . In the following examples, "En" indicates "×10 ^-n ".

S(y)=(y ² /r)/{1+(1−K×y ² /r ² ) ^1/2 }
+A4×y4+A6× ^y6 +A8× ^y8 +A10× ^y10 +A12× ^{y12 (} a)

In each embodiment, the second-order aspheric coefficient A2 is zero. In addition, in the tables of each example, an asterisk (*) is attached to the right side of the surface number of an aspherical surface.

[First embodiment]
FIG. 2 is a diagram showing the configuration of an optical system OL1 in which the rear converter lens RCL1 according to the first embodiment is attached to the master lens ML described above. The rear converter lens RCL1 constituting this optical system OL1 has, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a positive refractive power. and a third lens group G3.

The first lens group G1 is composed of a biconvex positive lens L11. The biconvex positive lens L11 corresponds to the first lens component LC1.

The second lens group G2 includes, in order from the object side, a biconcave negative lens L21 having an aspheric lens surface on the object side, a biconvex positive lens L22, and a plano-concave negative lens having a concave surface facing the object side. It is composed of a specific cemented lens SPL which is a cemented negative lens cemented with L23.

The third lens group G3 is composed of a biconvex positive lens L31. The biconvex positive lens L31 corresponds to the third lens component LC3.

A filter FL is arranged between the rear converter lens RCL1 and the image plane I in the optical system OL1 according to the first embodiment.

Table 1 below shows the values of the specifications of the optical system OL1 composed of the master lens ML and the rear converter lens RCL1 shown in the first embodiment. In Table 1, fa shown in the overall specifications is the focal length of the optical system OL1 in focus at infinity (composite focal length of the master lens ML and the rear converter lens RCL1), FNOa is the F number (composite F number), Y represents the maximum image height, and Bfa represents the back focus. Here, the back focus Bfa indicates the air-converted value of the distance on the optical axis from the lens surface closest to the image side (the 34th surface in FIG. 2) to the image plane I. Also, fm represents the focal length of the master lens ML, and FNOm represents the F-number of the master lens ML.

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 light rays travel, the second column r indicates the radius of curvature of each lens surface, and the third column d is the distance (surface distance) on the optical axis from each optical surface to the next optical surface, and the fourth column nd and fifth column νd are the refractive index and Abbe number for the d-line (λ = 587.6 nm). is shown. A radius of curvature of 0.0000 indicates a flat surface, and the refractive index of air of 1.000000 is omitted.

In Table 1, the 1st to 26th surfaces correspond to the master lens ML, the 27th to 34th surfaces correspond to the rear converter lens RCL1, and the 35th to 36th surfaces correspond to the filter FL. .

Here, the focal length f, radius of curvature r, surface spacing d, and other lengths listed in all the specifications below are generally expressed in units of "mm". The same optical performance can be obtained even if the size is reduced, so the size is not limited to this. Further, the explanation of these symbols and the explanation of the specification table are the same in the following embodiments.

(Table 1) First embodiment [overall specifications]
fa = 94.967
FNOa = 5.61
Y = 22.34
BFa = 14.113
fm = 67.902
FNOm = 4.00

[Lens data]
m r d nd νd
object ∞
1 73.0481 2.1500 1.846660 23.80
2 47.7610 8.6000 1.755000 52.34
3 425.2719 31.0971
4 399.4019 1.8000 1.743890 49.53
5* 16.7883 8.8100
6 -133.6662 1.3500 1.755000 52.34
7 55.4226 1.6300
8 38.8003 3.7000 2.000690 25.46
9 330.4685 2.7610
10 0.0000 1.5000 Aperture diaphragm S
11* 25.4945 4.2500 1.553320 71.67
12 -336.5410 0.3000
13 54.2840 1.0000 1.834810 42.73
14 25.8310 3.8000 1.618000 63.34
15 -109.2461 3.7700
16 -34.4612 1.0000 1.816000 46.59
17 16.8999 7.1600 1.593190 67.90
18 -23.6417 10.9493
19 -23.1238 1.0000 1.801000 34.92
20 -43.0157 0.1000
21 58.4301 6.0000 1.59 2010 67.05
22* -26.8720 2.0000
23 -37.0646 3.4500 1.589130 61.24
24* -22.7817 5.8600
25 -24.0379 1.4000 1.618000 63.34
26 116.2419 7.3200
27 121.7597 4.0500 1.808090 22.74
28 -59.9022 3.8578
29* -30.1138 1.2500 1.882020 37.23
30 34.8289 12.0728 1.592701 35.31
31 -20.2211 1.2500 2.050900 26.95
32 0.0000 0.1000
33 154.9881 8.4139 1.592701 35.31
34 -34.5581 12.9580
35 0.0000 1.6000 1.516800 64.14
36 0.0000 0.0998
Image plane ∞

In this optical system OL1, the fifth, eleventh, twenty-second, and twenty-fourth surfaces of the master lens ML and the twenty-ninth surface of the rear converter lens RCL1 are aspherical. Table 2 below shows the data of the aspheric surface, namely the values of the conic constant K and each of the aspheric constants A4-A12.

(Table 2)
[Aspheric data]
5th surface K=0.0000
A4 = 2.19138E-05 A6 = 4.38276E-08 A8 = -4.21622E-11
A10= 5.08044E-13 A12= 0.00000E+00
11th surface K= 1.0000
A4 = -5.47924E-06 A6 = 5.09592E-10 A8 = 6.44602E-11
A10 = -4.66596E-13 A12 = 0.00000E+00
22nd surface K=1.0000
A4 = 1.44646E-05 A6 = -1.62650E-08 A8 = -3.71277E-11
A10 = -1.25784E-13 A12 = 0.00000E+00
24th surface K=1.0000
A4 = 4.38057E-06 A6 = 3.06382E-08 A8 = 8.17585E-12
A10= 3.01361E-13 A12= 0.00000E+00
29th surface K=1.0000
A4 = 1.39380E-05 A6 = -1.18850E-08 A8 = 1.02570E-10
A10 = -3.98840E-13 A12 = 0.66334E-15

Table 3 below shows values corresponding to each conditional expression in the rear converter lens RCL1. In this Table 3, nspp and νspp are the refractive index and Abbe number for the d-line of the medium of the negative lens having the highest refractive index among the negative lenses constituting the specific cemented lens SPL, Bfa is the air conversion back focus, L is the distance on the optical axis from the lens surface closest to the object side of the rear converter lens RCL to the lens surface closest to the image side, β is the magnification of the rear converter lens RCL, and νL1p is the positive lens constituting the first lens component LC1. nspp and νspp are the refractive index and Abbe number for the d-line of the medium of the positive lens constituting the specific cemented lens SPL, nL3p is the medium of the positive lens constituting the third lens component LC3 fL1 is the focal length of the first lens component LC1, fsp is the focal length of the specific cemented lens SPL, fL3 is the focal length of the third lens component LC3, f is the rear converter lens RCL np and νp are the refractive index and Abbe number for the d-line of the medium of the specific positive lens Lp, θgFp is the partial dispersion ratio of the medium of the specific positive lens Lp, and f1 is the focal length of the first lens group G1. , f2 represents the focal length of the second lens group G2, and f3 represents the focal length of the third lens group G3. The description of these symbols is the same for the following embodiments. Note that the rear converter lens RCL1 according to the first example does not have the specific positive lens Lp.

(Table 3)
f = -80.670
f1 = 50.185
fL1 = 50.185
f2 = -14.849
fsp = -14.849
f3 = 48.476
fL3 = 48.476
L = 30.995
β = 1.4

(1) nspn = 2.050900
(2) νspn = 26.95
(3) Bfa/L/β=0.326
(4) νL1p = 22.74
(5) nspp = 1.592701
(6) νspp = 35.31
(7) nL3p = 1.592701
(8) fL3/fL1 = 0.966
(9) fL1/(-fsp) = 3.380
(10) fL3/(-fsp) = 3.265
(11) Bfa/(-f)/β=0.125
(12) to (14) No specific positive lens Lp (15) f1/(-f) = 0.622
(16) f2/f = 0.184
(17) f3/(-f) = 0.601

Thus, the rear converter lens RCL1 satisfies the conditional expressions (1) to (11) and (15) to (17).

FIG. 3 shows spherical aberration diagrams, astigmatism diagrams, distortion aberration diagrams, lateral chromatic aberration diagrams, and coma aberration diagrams of the optical system OL1 composed of the master lens ML and the rear converter lens RCL1 when in focus at infinity. . In each aberration diagram, FNO indicates F number and Y indicates image height. The spherical aberration diagram shows the F-number value corresponding to the maximum aperture, the astigmatism diagram and the distortion diagram show the maximum image height, and the coma aberration diagram shows the value of each image height. d indicates d-line (λ=587.6 nm), g indicates g-line (λ=435.8 nm), F indicates F-line (λ=486.1 nm), and C indicates C-line (λ=656.3 nm). . In the astigmatism diagrams, the solid line indicates the sagittal image plane, and the dashed line indicates the meridional image plane. In the coma aberration diagrams, the solid line indicates the meridional coma, and the dashed lines indicate the Y direction (meridional) and Z direction (sagittal) of the skew ray. Further, in the aberration diagrams of each example shown below, the same reference numerals as in this example are used. From these aberration diagrams, it can be seen that the optical system OL1 including the rear converter lens RCL1 is satisfactorily corrected for various aberrations.

[Second embodiment]
FIG. 4 is a diagram showing the configuration of an optical system OL2 in which a rear converter lens RCL2 according to the second embodiment is attached to the master lens ML described above. The rear converter lens RCL2 constituting this optical system OL2 has, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a positive refractive power. and a third lens group G3.

The first lens group G1 is composed of a biconvex positive lens L11. The biconvex positive lens L11 corresponds to the first lens component LC1.

The second lens group G2 includes, in order from the object side, a cemented negative lens in which a biconcave negative lens L21 having an aspherical lens surface on the object side cemented with a biconvex positive lens L22, and a biconcave lens. It is composed of a specific cemented lens SPL which is a cemented negative lens obtained by cementing a negative lens L23, a biconvex positive lens L24, and a negative meniscus lens L25 having a concave surface facing the object side.

The third lens group G3 is composed of, in order from the object side, a biconcave negative lens L31 and a biconvex positive lens L32. The biconvex positive lens L32 corresponds to the third lens component LC3.

A filter FL is arranged between the rear converter lens RCL2 and the image plane I in the optical system OL2 according to the second embodiment.

Table 4 below lists values of specifications of the rear converter lens RCL2 in the optical system OL2 of the second embodiment. The values of the specifications of the master lens ML are the same as those of the first embodiment. In Table 4, the 27th to 39th surfaces correspond to the rear converter lens RCL2, and the 40th to 41st surfaces correspond to the filter FL.

(Table 4) Second embodiment [overall specifications]
fa = 135.803
FNOa = 8.03
Y = 22.08
BFa = 9.155

[Lens data]
m r d nd νd
object ∞
1-26 Master lens ML
27 84.2581 4.1629 1.592700 35.27
28 -39.8516 2.2305
29* -33.4716 1.0000 1.772500 49.49
30 15.4911 8.4899 1.666800 33.05
31 -59.6128 1.2887
32 -47.1321 1.0000 2.050900 26.95
33 27.1804 10.1575 1.752110 25.05
34 -16.4648 1.1000 2.050900 26.95
35 -69.4425 3.9358
36 -56.1615 1.4000 2.050900 26.95
37 153.2053 0.0500
38 108.8458 14.6000 1.517420 52.20
39 -22.9140 8.0000
40 0.0000 1.6000 1.516800 64.14
41 0.0000 0.0997
Image plane ∞

In the rear converter lens RCL2, the 29th surface is formed in an aspherical shape. Table 5 below shows the data of the aspheric surface, namely the values of the conic constant K and each of the aspheric constants A4-A12.

(Table 5)
[Aspheric data]
29th surface K=1.0000
A4 = 5.02790E-06 A6 = -2.56160E-08 A8 = 1.68730E-10
Ａ10＝-3.15170E-13 Ａ12＝-0.16286E-14

Table 6 below shows values corresponding to each conditional expression in the rear converter lens RCL2. Note that the rear converter lens RCL2 according to the second example does not have the specific positive lens Lp.

(Table 6 )
f = -66.557
f1 = 46.224
fL1 = 46.224
f2 = -16.483
fsp = -27.329
f3 = 151.808
fL3 = 38.020
L = 49.415
β = 2.0

(1) nspn = 2.050900
(2) νspn = 26.95
(3) Bfa/L/β=0.093
(4) νL1p = 35.27
(5) nspp = 1.752110
(6) νspp = 25.05
(7) nL3p = 1.517420
(8) fL3/fL1 = 0.823
(9) fL1/(-fsp) = 1.691
(10) fL3/(-fsp) = 1.391
(11) Bfa/(-f)/β=0.069
(12) to (14) No specific positive lens Lp (15) f1/(-f) = 0.695
(16) f2/f = 0.248
(17) f3/(-f) = 2.281

Thus, the rear converter lens RCL2 satisfies the conditional expressions (1) to (11) and (15) to (17).

FIG. 5 shows spherical aberration diagrams, astigmatism diagrams, distortion aberration diagrams, lateral chromatic aberration diagrams, and coma aberration diagrams of the optical system OL2 consisting of the master lens ML and the rear converter lens RCL2 when in focus at infinity. . From these aberration diagrams, it can be seen that the optical system OL2 including the rear converter lens RCL2 is satisfactorily corrected for various aberrations.

[Third embodiment]
FIG. 6 is a diagram showing the configuration of an optical system OL3 in which a rear converter lens RCL3 according to the third embodiment is attached to the master lens ML described above. The rear converter lens RCL3 constituting this optical system OL3 has, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a positive refractive power. and a third lens group G3.

The first lens group G1 is composed of a biconvex positive lens L11. The biconvex positive lens L11 corresponds to the first lens component LC1.

The second lens group G2 includes, in order from the object side, a biconcave negative lens L21 having an aspheric lens surface on the object side, a biconvex positive lens L22, and a plano-concave negative lens having a concave surface facing the object side. It is composed of a specific cemented lens SPL which is a cemented negative lens cemented with L23.

The third lens group G3 is composed of a cemented positive lens in which a biconvex positive lens L31 and a negative meniscus lens L32 having a concave surface facing the object are joined in order from the object side. The cemented positive lens corresponds to the third lens component LC3.

A filter FL is arranged between the rear converter lens RCL3 and the image plane I in the optical system OL3 according to the third embodiment.

Table 7 below lists values of specifications of the rear converter lens RCL3 in the optical system OL3 of the third embodiment. The values of the specifications of the master lens ML are the same as those of the first embodiment. In Table 7, the 27th to 35th surfaces correspond to the rear converter lens RCL3, and the 36th to 37th surfaces correspond to the filter FL.

(Table 7) Third embodiment [overall specifications]
fa = 94.967
FNOa = 5.61
Y = 22.38
BFa = 9.640

[Lens data]
m r d nd νd
object ∞
1-26 Master lens ML
27 84.8837 4.0500 1.698950 30.13
28 -72.4695 4.7045
29* -33.0742 1.2500 1.882020 37.23
30 24.3545 13.1369 1.659398 26.87
31 -20.2211 1.2500 2.050900 26.95
32 0.0000 0.1000
33 496.8472 9.3665 1.516800 64.14
34 -25.2365 1.2300 1.698950 30.13
35 -30.5238 8.4853
36 0.0000 1.6000 1.516800 64.14
37 0.0000 0.0996
Image plane ∞

In the rear converter lens RCL3, the 29th surface is formed in an aspherical shape. Table 8 below shows the data of the aspheric surface, namely the values of the conic constant K and each of the aspheric constants A4-A12.

(Table 8)
[Aspheric data]
29th surface K=1.0000
A4 = 1.28300E-05 A6 = -1.03110E-08 A8 = 7.20140E-11
A10 = -2.30770E-13 A12 = 0.26141E-15

Table 9 below shows values corresponding to each conditional expression in the rear converter lens RCL3. The specific positive lens Lp is the biconvex positive lens L22 of the second lens group G2.

(Table 9)
f = -77.804
f1 = 56.530
fL1 = 56.530
f2 = -16.343
fsp = -16.343
f3 = 59.802
fL3 = 59.802
L = 35.088
β = 1.4
np = 1.659398
θgFp = 0.632707

(1) nspn = 2.050900
(2) νspn = 26.95
(3) Bfa/L/β=0.196
(4) νL1p = 30.13
(5) nspp = 1.659398
(6) νspp = 26.87
(7) nL3p = 1.516800
(8) fL3/fL1 = 1.058
(9) fL1/(-fsp) = 3.459
(10) fL3/(-fsp) = 3.659
(11) Bfa/(-f)/β=0.089
(12) νp = 26.87
(13) 0.01 x vp + np = 1.928
(14) 0.00168 x νp + θgFp = 0.678
(15) f1/(-f) = 0.727
(16) f2/f = 0.210
(17) f3/(-f) = 0.769

Thus, the rear converter lens RCL3 satisfies all of the above conditional expressions (1) to (17).

FIG. 7 shows spherical aberration diagrams, astigmatism diagrams, distortion aberration diagrams, lateral chromatic aberration diagrams, and coma aberration diagrams of the optical system OL3 composed of the master lens ML and the rear converter lens RCL3 when in focus at infinity. . From these aberration diagrams, it can be seen that the optical system OL3 including the rear converter lens RCL3 is satisfactorily corrected for various aberrations.

[Fourth embodiment]
FIG. 8 is a diagram showing the configuration of an optical system OL4 in which a rear converter lens RCL4 according to the fourth embodiment is attached to the master lens ML described above. The rear converter lens RCL4 constituting this optical system OL4 has, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a positive refractive power. and a third lens group G3.

The first lens group G1 is composed of a biconvex positive lens L11 having an aspherical lens surface on the object side and an aspherical lens surface on the image side. The positive lens L11 corresponds to the first lens component LC1.

The second lens group G2 includes, in order from the object side, a specific cemented lens SPL, which is a cemented negative lens obtained by cementing a biconcave negative lens L21, a biconvex positive lens L22, and a biconcave negative lens L23, and a biconvex positive lens L24. and a negative meniscus lens L25 having a concave surface facing the object side.

The third lens group G3 is composed of, in order from the object side, a biconcave negative lens L31 and a biconvex positive lens L32. The biconvex positive lens L32 corresponds to the third lens component LC3.

A filter FL is arranged between the rear converter lens RCL4 and the image plane I in the optical system OL4 according to the fourth embodiment.

Table 10 below lists values of specifications of the rear converter lens RCL4 in the optical system OL4 of the fourth example. The values of the specifications of the master lens ML are the same as those of the first embodiment. In Table 10, the 27th to 39th surfaces correspond to the rear converter lens RCL4, and the 40th to 41st surfaces correspond to the filter FL.

(Table 10) Fourth embodiment [overall specifications]
fa = 136.028
FNOa = 7.98
Y = 22.33
BFa = 9.168

[Lens data]
m r d nd νd
object ∞
1-26 Master lens ML
27* 34.6680 3.7582 1.802440 25.55
28* -878.5075 3.2748
29 -33.3780 1.2000 2.050900 26.95
30 14.8417 9.3092 1.784720 25.64
31 -23.4558 1.2000 1.755000 52.34
32 27.0093 0.2000
33 26.1066 10.0659 1.603420 38.03
34 -16.1711 1.3000 2.050900 26.95
35 -128.6960 4.3463
36 -174.1699 1.3000 2.050900 26.95
37 105.0415 0.1000
38 91.1486 12.8876 1.603420 38.03
39 -26.5862 8.0000
40 0.0000 1.6000 1.516800 64.14
41 0.0000 0.1133
Image plane ∞

In the rear converter lens RCL4, the 27th and 28th surfaces are aspherical. Table 11 below shows the data of the aspheric surface, namely the values of the conic constant K and each of the aspheric constants A4-A12.

(Table 11)
[Aspheric data]
27th surface K=1.0000
A4 = 1.62030E-05 A6 = -1.37440E-07 A8 = 2.99200E-09
A10 = -2.29940E-11 A12 = 0.65180E-13
28th surface K=1.0000
A4 = 1.84150E-07 A6 = -1.70930E-07 A8 = 3.18560E-09
A10 = -2.78130E-11 A12 = 0.83812E-13

Table 12 below shows values corresponding to each conditional expression in the rear converter lens RCL4. Note that the rear converter lens RCL4 according to the fourth example does not have the specific positive lens Lp.

(Table 12)
f = -66.716
f1 = 41.639
fL1 = 41.639
f2 = -11.616
fsp = -11.796
f3 = 66.146
fL3 = 35.576
L = 48.942
β = 2.0

(1) nspn = 2.050900
(2) νspn = 26.95
(3) Bfa/L/β=0.094
(4) νL1p = 25.55
(5) nspp = 1.784720
(6) νspp = 25.64
(7) nL3p = 1.603420
(8) fL3/fL1 = 0.854
(9) fL1/(-fsp) = 3.530
(10) fL3/(-fsp) = 3.016
(11) Bfa/(-f)/β=0.069
(12) to (14) No specific positive lens Lp (15) f1/(-f)=0.624
(16) f2/f = 0.174
(17) f3/(-f) = 0.991

Thus, the rear converter lens RCL4 satisfies the conditional expressions (1) to (11) and (15) to (17).

FIG. 9 shows spherical aberration diagrams, astigmatism diagrams, distortion aberration diagrams, lateral chromatic aberration diagrams, and coma aberration diagrams of the optical system OL4 composed of the master lens ML and the rear converter lens RCL4 when in focus at infinity. . From these aberration diagrams, it can be seen that the optical system OL4 including the rear converter lens RCL4 is satisfactorily corrected for various aberrations.

[Fifth embodiment]
FIG. 10 is a diagram showing the configuration of an optical system OL5 in which a rear converter lens RCL5 according to the fifth embodiment is attached to the master lens ML described above. The rear converter lens RCL5 constituting this optical system OL5 has, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a positive refractive power. and a third lens group G3.

The first lens group G1 is composed of a cemented positive lens in which a negative meniscus lens L11 having a convex surface facing the object side and a biconvex positive lens L12 are cemented in order from the object side. The cemented positive lens corresponds to the first lens component LC1.

The second lens group G2 is a cemented negative lens formed by cementing, in order from the object side, a biconcave negative lens L21 having an aspherical lens surface on the object side, a biconvex positive lens L22, and a biconcave negative lens L23. It is composed of a specific cemented lens SPL, which is a lens.

The third lens group G3 is composed of a biconvex positive lens L31. The biconvex positive lens L31 corresponds to the third lens component LC3.

A filter FL is arranged between the rear converter lens RCL5 and the image plane I in the optical system OL5 according to the fifth embodiment.

Table 13 below lists values of specifications of the rear converter lens RCL5 in the optical system OL5 of the fifth embodiment. The values of the specifications of the master lens ML are the same as those of the first embodiment. In Table 13, the 27th to 35th surfaces correspond to the rear converter lens RCL5, and the 36th to 37th surfaces correspond to the filter FL.

(Table 13) Fifth embodiment [overall specifications]
fa = 94.967
FNOa = 5.59
Y = 22.40
BFa = 9.154

[Lens data]
m r d nd νd
object ∞
1-26 Master lens ML
27 76.6553 1.0000 1.755000 52.34
28 33.0718 6.6303 1.698947 30.13
29 -58.2961 3.7648
30* -29.0755 1.2500 1.882020 37.23
31 24.9005 13.0211 1.592701 35.31
32 -20.8622 1.2500 2.050900 26.95
33 8672.6899 0.1159
34 461.2494 9.0106 1.603420 38.03
35 -28.8707 8.0000
36 0.0000 1.6000 1.516800 64.14
37 0.0000 1.1546
Image plane ∞

In the rear converter lens RCL5, the 30th surface is formed in an aspherical shape. Table 14 below shows the data of the aspheric surface, namely the values of the conic constant K and each of the aspheric constants A4-A12.

(Table 14)
[Aspheric data]
30th surface K=1.0000
A4 = 1.51410E-05 A6 = -3.82990E-08 A8 = 3.72570E-10
A10 = -1.69370E-12 A12 = 0.29241E-14

Table 15 below shows values corresponding to each conditional expression in the rear converter lens RCL5. Note that the rear converter lens RCL5 according to the fifth example does not have the specific positive lens Lp.

(Table 15)
f = -81.649
f1 = 50.751
fL1 = 50.751
f2 = -13.824
fsp = -13.824
f3 = 45.340
fL3 = 45.340
L = 36.043
β = 1.4

(1) nspn = 2.050900
(2) νspn = 26.95
(3) Bfa/L/β=0.182
(4) νL1p = 30.13
(5) nspp = 1.592701
(6) νspp = 35.31
(7) nL3p = 1.603420
(8) fL3/fL1 = 0.893
(9) fL1/(-fsp) = 3.671
(10) fL3/(-fsp) = 3.280
(11) Bfa/(-f)/β=0.080
(12) to (14) No specific positive lens Lp (15) f1/(-f) = 0.622
(16) f2/f = 0.169
(17) f3/(-f) = 0.555

Thus, the rear converter lens RCL5 satisfies the conditional expressions (1) to (11) and (15) to (17).

FIG. 11 shows spherical aberration diagrams, astigmatism diagrams, distortion aberration diagrams, lateral chromatic aberration diagrams, and coma aberration diagrams of the optical system OL5 composed of the master lens ML and the rear converter lens RCL5 when in focus at infinity. . From these aberration diagrams, it can be seen that the optical system OL5 including the rear converter lens RCL5 is satisfactorily corrected for various aberrations.

10 Camera (optical equipment) OL1 to OL5 Optical system ML Master lens RCL (RCL1 to RCL5) Rear converter lens G1 First lens group LC1 First lens component G2 Second lens group SPL Specified cemented lens Lp Specified positive lens G3 Third lens Group LC3 third lens component

Claims (21)

A rear converter lens arranged on the image side of a master lens and having a combined focal length with the master lens longer than the focal length of the master lens,
a first lens component disposed closest to the object side and having positive refractive power;
a specific cemented lens composed of at least a cemented negative lens, a positive lens and a negative lens and having a negative refractive power;
a third lens component disposed closest to the image side and having a positive refractive power;
The first lens component is a biconvex positive lens,
the third lens component is a single lens,
A rear converter lens that satisfies the following conditions.
1.90 < nspn
however,
nspn: Refractive index of the medium of the negative lens having the highest refractive index among the negative lenses constituting the specific cemented lens with respect to the d-line The lens component refers to a single lens or a cemented lens. A rear converter lens arranged on the image side of a master lens and having a combined focal length with the master lens longer than the focal length of the master lens,
a first lens component disposed closest to the object side and having positive refractive power;
a specific cemented lens composed of at least a cemented negative lens, a positive lens and a negative lens and having a negative refractive power;
a third lens component disposed closest to the image side and having a positive refractive power;
A rear converter lens that satisfies the following conditions.
2.02 < nspn
20.00 < νspn
however,
nspn: the refractive index for the d-line of the medium of the negative lens having the highest refractive index among the negative lenses constituting the specific cemented lens
νspn: the Abbe number for the d-line of the medium of the negative lens with the highest refractive index among the negative lenses constituting the specific cemented lens
A lens component refers to a single lens or a cemented lens. 2. A rear converter lens according to claim 1 , wherein the following condition is satisfied.
20.00 < νspn
however,
νspn: the Abbe number for the d-line of the medium of the negative lens with the highest refractive index among the negative lenses constituting the specific cemented lens 4. The rear converter lens according to any one of claims 1 to 3, which satisfies the following conditions.
νL1p < 45.00
however,
νL1p: Abbe number for the d-line of the medium of the positive lens constituting the first lens component 5. The rear converter lens according to any one of claims 1 to 4, which satisfies the following conditions.
nspp < 1.80
however,
nspp: refractive index for the d-line of the medium of the positive lens that constitutes the specific cemented lens 6. The rear converter lens according to any one of claims 1 to 5, which satisfies the following conditions.
νspp < 45.00
however,
νspp: Abbe number for the d-line of the medium of the positive lens constituting the specific cemented lens The rear converter lens according to any one of claims 1 to 6, wherein a lens surface closest to the image side of the third lens component is convex toward the image side. The rear converter lens according to any one of claims 1 to 7, wherein the third lens component has a biconvex shape. 9. The rear converter lens according to any one of claims 1 to 8, which satisfies the following conditions.
nL3p < 1.630
however,
nL3p: refractive index for the d-line of the medium of the positive lens constituting the third lens component 10. The rear converter lens according to any one of claims 1 to 9, which satisfies the following conditions.
0.40 < fL3/fL1 < 1.80
however,
fL1: focal length of the first lens component fL3: focal length of the third lens component 11. The rear converter lens according to any one of claims 1 to 10, which satisfies the following conditions.
1.20 < fL1/(-fsp) < 4.50
however,
fL1: focal length of the first lens component fsp: focal length of the specific cemented lens 12. The rear converter lens according to any one of claims 1 to 11, which satisfies the following formula.
0.70 < fL3/(-fsp) < 5.50
however,
fL3: focal length of the third lens component fsp: focal length of the specific cemented lens The rear converter lens according to any one of claims 1 to 12, wherein the lens surface closest to the object side of the specific cemented lens is an aspherical surface. 14. The rear converter lens according to any one of claims 1 to 13, having a specific positive lens that satisfies the following condition.
22.00 < vp < 30.00
0.01×νp+np<2.02
0.604 < 0.00168 x νp + θgFp
however,
np: refractive index of the medium of the specific positive lens with respect to the d-line νp: Abbe number of the medium of the specific positive lens with respect to the d-line θgFp: partial dispersion ratio of the medium of the specific positive lens a first lens group comprising the first lens component;
a second lens group including the specific cemented lens;
15. The rear converter lens according to any one of claims 1 to 14, comprising substantially three lens groups with a third lens group comprising said third lens component. 16. The rear converter lens according to claim 15 , wherein the specific cemented lens is arranged closest to the image side of the second lens group. 17. A rear converter lens according to claim 15 or 16 , wherein the following condition is satisfied.
0.05 < f1/(-f) < 2.00
however,
f1: focal length of the first lens group f: focal length of the rear converter lens 18. The rear converter lens according to any one of claims 15 to 17, which satisfies the following formula.
0.03 < f2/f < 0.50
however,
f2: focal length of the second lens group f: focal length of the rear converter lens 19. The rear converter lens according to any one of claims 15 to 18, which satisfies the following formula.
0.05 < f3/(-f) < 3.00
however,
f3: focal length of the third lens group f: focal length of the rear converter lens master lens,
and the rear converter lens according to any one of claims 1 to 19 arranged on the image side of the master lens. 21. The optical instrument according to claim 20 , wherein the following condition is satisfied.
Bfa/(-f)/β < 0.25
however,
Bfa: Air conversion back focus of the optical system f: Focal length of the rear converter lens β: Magnification of the rear converter lens

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