JP2018004884A - Sub optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sub optical system which can maintain a high level of optical performance of an entire optical system even when applied to a main optical system with a large image circle that encompasses the Leica size, for example, and can be reduced in size.SOLUTION: A sub optical system to be disposed on the object side of a main optical system is provided, consisting of a negative first optical element, a second optical element, a third optical element, and a positive fourth optical element, the second optical element having a concave surface on the first optical element side. The sub optical system satisfies the following conditional expression (1): -2.5<(L2Ra+L3Rb)/(L2Ra-L3Rb)<0 ...(1), where L2Ra represents a curvature radius of the first optical element-side surface of the second optical element, and L3Rb represents a curvature radius of a fourth optical element-side surface of the third optical element.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sub optical system.

  Located on the object side of the main optical system, the combined focal length with the main optical system (focal length of the combined optical system, focal length of the entire system) is converted (longer or longer) to the focal length of the main optical system alone A sub-optical system (conversion optical system, teleconverter lens system, or wide converter lens system) is known.

  Patent Document 1 discloses a wide converter lens system in which the focal length of the entire system is 0.82 times the focal length of the main optical system. However, when the wide converter lens system is attached to the main optical system in the wide angle state (half field angle w = 38.2 ° state), the distortion aberration is remarkably increased.

  Patent Document 2 discloses a wide converter lens system in which the focal length of the entire system is 0.70 times the focal length of the main optical system. However, the length of the wide converter lens system and the total lens length combined with the main optical system become too large.

  The wide converter lens system of Patent Document 3 has good optical performance up to the image height (radius of image circle) y = 9.1 targeted by the main optical system, and the wide converter lens system of Patent Document 4 is The optical performance is good up to a range of image height (radius of image circle) y = 4.0 targeted by the main optical system. However, when the wide converter lens systems of Patent Documents 3 and 4 are applied to, for example, the main optical system of a high image circle including Leica size, an increase in size is inevitable.

JP 2008-26779 A JP 2000-241700 A JP 2005-31354 A Japanese Patent Laid-Open No. 63-1000041

  The present invention has been made on the basis of the above problem awareness. For example, even when applied to the main optical system of a high image circle including the Leica size, the optical performance of the entire system is high. An object of the present invention is to obtain a secondary optical system capable of maintaining and miniaturizing.

The sub optical system of the present embodiment is a sub optical system disposed on the object side of the main optical system, and includes a negative first optical element, a second optical element, a third optical element, and a positive fourth optical element. The second optical element is provided with a concave surface on the surface of the second optical element on the first optical element side, and satisfies the following conditional expression (1).
(1) −2.5 <(L2Ra + L3Rb) / (L2Ra−L3Rb) <0
However,
L2Ra: radius of curvature of the surface of the second optical element on the side of the first optical element,
L3Rb: radius of curvature of the surface of the third optical element on the side of the fourth optical element,
It is.

  The sub-optical system includes the negative first optical element, the second optical element, the third optical element, and the positive fourth optical element in order from the object side toward the main optical system. The combined focal length of the main optical system and the sub optical system can be converted to be shorter than the single focal length of the main optical system.

The conversion optical system of the present embodiment preferably satisfies the following conditional expression (2).
(2) d2 / LD> 0.37
However,
d2: distance on the optical axis between the first optical element and the second optical element (between the surface of the first optical element on the second optical element side and the surface of the second optical element on the first optical element side) Air distance),
LD: distance on the optical axis from the first optical element to the fourth optical element (total length on the optical axis of the conversion optical system),
It is.

It is preferable that one of the second optical element and the third optical element is a positive optical element and the other is a negative optical element, and satisfies the following conditional expression (3).
(3) νp> νn
However,
νp: Abbe number of the positive optical element among the second optical element and the third optical element,
νn: Abbe number of the negative optical element among the second optical element and the third optical element,
It is.

It is preferable that one of the second optical element and the third optical element is a positive optical element and the other is a negative optical element, and satisfies the following conditional expression (4).
(4) ν1>νp>νn> ν4
However,
v1: Abbe number of the first optical element,
νp: Abbe number of the positive optical element among the second optical element and the third optical element,
νn: Abbe number of the negative optical element among the second optical element and the third optical element,
ν4: Abbe number of the fourth optical element,
It is.

  The second optical element and the third optical element may be composed of one positive optical element and the other negative optical element, and may be bonded to each other.

  The focal length of the sub optical system alone can be made almost infinite.

  The position of the imaging point where the infinite object is imaged by the main optical system and the sub optical system should be substantially equal to the position of the imaging point where the infinite object is imaged by the main optical system alone. Can do.

  The sub optical system sequentially moves the negative first optical element, the second optical element, the third optical element, and the positive fourth optical element from the main optical system toward the object side. The combined focal length of the main optical system and the sub optical system can be converted longer than the single focal length of the main optical system.

  According to the present invention, it is possible to maintain the optical performance of the entire optical system at a high level and achieve downsizing even when applied to the main optical system of a high image circle that includes, for example, the Leica size. An auxiliary optical system that can be obtained is obtained.

It is a lens block diagram of all the optical systems which attached the wide converter lens system of Numerical Example 1 to the object side of the master lens system. 2A to 2D are graphs showing various aberrations in the configuration shown in FIG. 3A to 3D are lateral aberration diagrams in the configuration of FIG. It is a lens block diagram of all the optical systems which attached the wide converter lens system of Numerical Example 2 to the object side of the master lens system. 5A to 5D are graphs showing various aberrations in the configuration of FIG. 6A to 6D are lateral aberration diagrams in the configuration of FIG. It is a lens block diagram of all the optical systems which attached the wide converter lens system of Numerical Example 3 to the object side of the master lens system. 8A to 8D are graphs showing various aberrations in the configuration of FIG. 9A to 9D are lateral aberration diagrams in the configuration of FIG. It is a lens block diagram of all the optical systems which attached the wide converter lens system of Numerical Example 4 to the object side of the master lens system. 11A to 11D are graphs showing various aberrations in the configuration of FIG. 12A to 12D are lateral aberration diagrams in the configuration of FIG. It is a lens block diagram of all the optical systems which attached the wide converter lens system of Numerical Example 5 to the object side of the master lens system. 14A to 14D are graphs showing various aberrations in the configuration shown in FIG. 15A to 15D are lateral aberration diagrams in the configuration of FIG.

  The sub optical system (hereinafter referred to as a conversion optical system) of this embodiment is arranged on the object side of the main optical system and converts the focal length of the entire system. Numerical Example 1-5 illustrates a wide converter lens system WL that is arranged on the object side of the master lens system (main optical system) ML and changes the focal length of the entire system to the shorter side (wide angle side). This wide converter lens system WL is suitable for mounting on, for example, a single-focus lens system having a focal length of 35 m and other lens systems.

  The wide converter lens system (conversion optical system) WL is detachable from the master lens system (main optical system) ML. The wide converter lens system WL has a substantially infinite focal length in a single optical system. Here, “substantially infinite” means that the absolute value is 1000 times or more as compared with the single focal length of the master lens system ML (−1000 times to infinity to +1000 times). The wide converter lens system WL is a so-called “afocal optical system”, but there is substantially no problem even if it is not a complete afocal optical system. In addition, since it is easy to change a complete afocal optical system to an incomplete afocal optical system, this can be referred to as a “substantially afocal optical system”.

  The master lens system (main optical system) ML is, for example, as described in Example 4 of Japanese Patent Laid-Open No. 2000-235145, and can function alone as an imaging optical system. The master lens system ML is corrected for aberrations as a single unit, and can focus on a subject at infinity or a predetermined short distance (can be focused) as a single unit. The position of the image formation point on the object (object) at infinity by the master lens system ML alone is the image formation point on the object (object) at infinity when the wide converter lens system WL is disposed on the object side of the master lens system ML. Is almost the same. For example, back focus fB = 37.93 in Example 4 of Japanese Patent Laid-Open No. 2000-235145 is substantially the same as back focus fB in Numerical Example 1-5 of the present application described later. Here, “substantially the same” is considered to be, for example, within 3 times the spherical aberration of the master lens system ML. However, even if the position of each imaging point changes more than that, it is sufficient to focus again. In the case of a camera, there is no practical problem even if it changes by several millimeters. The half angle of view W of the master lens system ML of numerical value example 1-5 of the present application described later is W = 32.2 °, but the wide converter lens system WL of the present embodiment is about the same or larger than the above-mentioned angle of view. It can be applied to a master lens with a narrow angle of view.

  In Numerical Example 1-4, the wide converter lens system WL of the present embodiment includes a negative first lens (first optical element) WL1 and a positive second lens (second optical element) WL2 in order from the object side. And a negative third lens (third optical element) WL3 and a positive fourth lens (fourth optical element) WL4. The image-side surface of the second lens WL2 and the object-side surface of the third lens WL3 are joined (this joining is not an essential configuration). A concave surface is provided on the surface of the second lens WL2 on the first lens WL1 side.

  In Numerical Example 5, the wide converter lens system WL according to this embodiment includes a negative first lens (first optical element) WL1 ′ and a negative second lens (second optical element) WL2 ′ in order from the object side. And a positive third lens (third optical element) WL3 ′ and a positive fourth lens (fourth optical element) WL4 ′. The image side surface of the second lens WL <b> 2 ′ and the object side surface of the third lens WL <b> 3 ′ are joined (this joining is not an essential configuration). A concave surface is provided on the surface of the second lens WL2 'on the first lens WL1' side.

  The master lens system ML of the present embodiment includes, through all numerical examples 1-5, in order from the object side, a negative fifth lens (fifth optical element) ML5 and a positive sixth lens (sixth optical element) ML6. A negative seventh lens (seventh optical element) ML7, a negative eighth lens (eighth optical element) ML8, a positive ninth lens (ninth optical element) ML9, and a positive tenth lens ( (10th optical element) ML10. The image side surface of the sixth lens ML6 and the object side surface of the seventh lens ML7 are cemented. An aspheric surface is formed on the object side surface of the tenth lens ML10.

  The wide converter lens system WL of this embodiment has a single focal length that is substantially infinite. Further, the position of the imaging point at which an infinite object is imaged by the master lens system ML and the wide converter lens system WL is substantially the same as the position of the imaging point at which the infinite object is imaged by the master lens system ML alone. Are equal. Here, “substantially equal” is considered to be, for example, within 3 times the spherical aberration of the master lens system ML. However, even if the position of each imaging point changes more than that, it is sufficient to focus again. In the case of a focus type camera, there is no practical problem even if it changes by several millimeters.

  Even if the wide converter lens system WL of the present embodiment is applied to, for example, a master optical system ML of a high image circle that includes Leica size, the master optical system ML and, in addition, the wide converter lens system WL combined therewith While maintaining the optical performance of the optical system at a high level, it is possible to achieve miniaturization.

  More specifically, the wide converter lens system WL of the present embodiment obtains excellent optical performance over the range of image height (radius of image circle) y = 21.6 targeted by the master lens system ML. Can do.

  In general, when the image height (radius of the image circle) targeted by the master lens system increases, the master lens system and the wide converter lens system used in combination therewith tend to increase in size. It is preferable to make it as small as possible by bringing it as close as possible to the master lens system.

  However, when the wide converter lens system is brought close to the master lens system, the off-axis light beam passes near the center of the first lens of the wide converter lens system, so that it becomes difficult to correct distortion aberration by the first lens, and it is impossible. Attempting to correct distortion will increase coma and astigmatism. That is, the correction balance of distortion, coma and astigmatism is broken.

  Therefore, in this embodiment, in order to correct distortion aberration, coma aberration, and astigmatism in a well-balanced manner, the shapes of the second lens and the third lens of the wide converter lens system are optimally set, and these two lenses are used. It takes on the role of positive aberration correction.

Conditional expression (1) defines the relationship between the radius of curvature of the second lens side surface of the second lens and the radius of curvature of the third lens side surface of the fourth lens. In other words, the conditional expression (1) defines a shape factor when the second lens and the third lens are viewed as a whole (when regarded as one lens). By satisfying conditional expression (1), it is possible to correct distortion, coma and astigmatism with a good balance.
When the upper limit of conditional expression (1) is exceeded, the radius of curvature of the surface of the second lens on the first lens side becomes too loose compared to the radius of curvature of the surface of the third lens on the fourth lens side, resulting in distortion. Aberration correction will be insufficient.
If the lower limit of conditional expression (1) is exceeded, the radius of curvature of the surface of the second lens on the side of the first lens becomes too large compared to the radius of curvature of the surface of the third lens on the side of the fourth lens, resulting in a coma. Aberration and astigmatism correction will be insufficient.

Conditional expression (2) indicates that the distance on the optical axis between the first lens and the second lens (the air distance between the master lens system side surface of the first lens and the object side surface of the second lens) and The relationship with the distance on the optical axis from the first lens to the fourth lens (the total length on the optical axis of the wide converter lens system) is defined. By satisfying conditional expression (2), it is possible to correct distortion, coma and astigmatism with a good balance.
When the lower limit of the conditional expression (2) is exceeded, the first lens and the second lens are too close to the total length on the optical axis of the wide converter lens system, so that it becomes difficult to correct distortion. Although it is possible to burden the first lens with correction of distortion, in that case, coma and astigmatism are greatly generated.

  In the wide converter lens system of the present embodiment, one of the second lens and the third lens has a positive power and the other has a negative power. Conditional expression (3) defines the magnitude relationship between the Abbe numbers of the second lens and the third lens in this configuration. By satisfying conditional expression (3), the lateral chromatic aberration can be corrected well. If conditional expression (3) is not satisfied, it will be difficult to correct lateral chromatic aberration.

  In the wide converter lens system of the present embodiment, the first lens has negative power, the fourth lens has positive power, one of the second lens and the third lens is positive power, and the other is negative. Has power. Conditional expression (4) defines the magnitude relation of the Abbe numbers of the first lens, the second lens, the third lens, and the fourth lens in this configuration. By satisfying conditional expression (4), the lateral chromatic aberration can be satisfactorily corrected. If conditional expression (4) is not satisfied, it will be difficult to correct lateral chromatic aberration.

Next, specific numerical value examples 1-5 will be described. In the various aberration diagrams and lateral aberration diagrams and tables, d-line, g-line and C-line are aberrations for each wavelength, S is sagittal, M is meridional, FNO. Is F-number, f is the focal length of the whole system, W Is half field angle (°), Y is image height, fB Is the back focus, LD is the total lens length, fs is the focal length of the wide converter lens system (conversion optical system) alone, R is the radius of curvature, d is the lens thickness or lens interval, N is the refractive index, and ν is the Abbe number. The back focus is a distance from the most image side surface of the entire lens system to the designed image surface I. The unit of length is [mm].
A rotationally symmetric aspherical surface is defined by the following equation.
x = cy ² / [1+ [1- (1 + K) c ² y ² ] ^1/2 ] + A3y ³ + A4y ⁴ + A6y ⁶ + A8y ⁸ + A10y ¹⁰ + A12y ¹² ...
(Where c is the curvature (1 / r), y is the height from the optical axis, K is the conic coefficient, A4, A6, A8,... Are the aspheric coefficients of each order, and x is the sag amount)
The Abbe number ν is defined by the following equation.
ν = (nd-1) / (nF-nC)
nd: Refractive index for d-line (587.56nm)
nF: Refractive index for F-line (486.13nm)
nC: Refractive index for C-line (656.27nm)

[Numerical Example 1]
FIG. 1 is a lens configuration diagram of an entire optical system in which the wide converter lens system (conversion optical system) of Numerical Example 1 is mounted on the object side of the master lens system (main optical system), and FIGS. 2A to 2D are graphs showing various aberrations thereof. 3A to 3D are lateral aberration diagrams thereof. Table 1 shows surface data, Table 2 shows various data, and Table 3 shows aspherical data.

  The wide converter lens system WL of Numerical Example 1 is mounted on the object side of the master lens system ML and has a function of changing the focal length of the entire system to the shorter side (wide angle side). This function of the wide converter lens system WL is the same in Numerical Example 2-5 described later.

  The wide converter lens system WL is, in order from the object side, a first lens (first optical element) WL1 composed of a negative meniscus lens having a convex surface facing the object side, and a second meniscus lens composed of a positive meniscus lens having a convex surface facing the image side. The lens (second optical element) WL2, a third lens (third optical element) WL3 composed of a biconcave negative lens, and a fourth lens (fourth optical element) WL4 composed of a biconvex positive lens. . The image side surface of the second lens WL2 and the object side surface of the third lens WL3 are cemented.

  The master lens system ML includes, in order from the object side, a fifth lens (fifth optical element) ML5 composed of a negative meniscus lens having a convex surface facing the object side, and a sixth lens (sixth optical element) composed of a biconvex positive lens. ML6, a seventh lens (seventh optical element) ML7 composed of a negative meniscus lens having a convex surface facing the image side, and an eighth lens (eighth optical element) ML8 composed of a negative meniscus lens having a convex surface facing the image side A ninth lens (9th optical element) ML9 composed of a positive meniscus lens having a convex surface facing the image side, and a tenth lens (tenth optical element) ML10 composed of a positive meniscus lens having a convex surface facing the image side. Has been. The image side surface of the sixth lens ML6 and the object side surface of the seventh lens ML7 are cemented. An aspheric surface is formed on the object side surface of the tenth lens ML10. This configuration of the master lens system ML is the same in Numerical Example 2-5 described later.

(Table 1)
Surface data surface number R d N ν
1 84.915 3.00 1.74320 49.3
2 47.598 17.48
3 -161.224 11.00 1.72047 34.7
4 -47.991 2.50 1.80000 29.8
5 903.940 0.15
6 75.676 9.80 1.72825 28.5
7 -290.179 10.36
8 146.963 1.50 1.51823 59.0
9 18.423 14.68
10 28.642 8.40 1.77250 49.6
11 -28.642 1.40 1.60342 38.0
12 -381.090 12.95
13 -17.426 1.38 1.80518 25.4
14 -150.390 0.42
15 -74.060 4.40 1.80400 46.6
16 -21.222 0.10
17 * -216.808 3.10 1.66910 55.4
18 -35.520-
* Is a rotationally symmetric aspherical surface.
(Table 2)
Various data
FNO. 2.2
f 28.85
W 38.9
Y 21.64
fB 37.92
LD 140.54
fs -1.2E08 (nearly infinite)
(Table 3)
Aspheric data surface number K A4 A6 A8
17 0.000 -0.1172E-04 -0.5051E-08 -0.7061E-10

[Numerical Example 2]
FIG. 4 is a lens configuration diagram of the entire optical system in which the wide converter lens system (conversion optical system) of Numerical Example 2 is mounted on the object side of the master lens system (main optical system), and FIGS. 5A to 5D are graphs showing various aberrations thereof. 6A to 6D are lateral aberration diagrams thereof. Table 4 shows surface data, Table 5 shows various data, and Table 6 shows aspherical data.

The lens configuration of the wide converter lens system WL in Numerical Example 2 is the same as the lens configuration of the wide converter lens system WL in Numerical Example 1 except for the following points.
(1) The third lens WL3 is not a biconcave negative lens but a negative meniscus lens having a convex surface facing the image side.

(Table 4)
Surface data surface number R d N ν
1 99.894 3.00 1.74100 52.6
2 53.703 17.30
3 -135.513 11.00 1.72047 34.7
4 -48.287 2.50 1.80000 29.8
5 -3824.009 0.15
6 83.372 10.00 1.72151 29.2
7 -258.790 10.89
8 146.963 1.50 1.51823 59.0
9 18.423 14.68
10 28.642 8.40 1.77250 49.6
11 -28.642 1.40 1.60342 38.0
12 -381.090 12.95
13 -17.426 1.38 1.80518 25.4
14 -150.390 0.42
15 -74.060 4.40 1.80400 46.6
16 -21.222 0.10
17 * -216.808 3.10 1.66910 55.4
18 -35.520-
* Is a rotationally symmetric aspherical surface.
(Table 5)
Various data
FNO. 2.2
f 28.86
W 39.4
Y 21.64
fB 37.92
LD 141.09
fs -1.5E08 (nearly infinite)
(Table 6)
Aspheric data surface number K A4 A6 A8
17 0.000 -0.1172E-04 -0.5051E-08 -0.7061E-10

[Numerical Example 3]
FIG. 7 is a lens configuration diagram of the entire optical system in which the wide converter lens system (conversion optical system) of Numerical Example 3 is mounted on the object side of the master lens system (main optical system), and FIGS. 8A to 8D are graphs showing various aberrations thereof. 9A to 9D are lateral aberration diagrams. Table 7 shows surface data, Table 8 shows various data, and Table 9 shows aspherical data.

  The lens configuration of the wide converter lens system WL in Numerical Example 3 is the same as the lens configuration of the wide converter lens system WL in Numerical Example 2.

(Table 7)
Surface data surface number R d N ν
1 96.034 3.00 1.77250 49.6
2 52.526 17.30
3 -147.140 11.00 1.72047 34.7
4 -50.415 2.50 1.80000 29.8
5 -2000.000 0.15
6 84.242 10.00 1.72825 28.5
7 -305.837 10.73
8 146.963 1.50 1.51823 59.0
9 18.423 14.68
10 28.642 8.40 1.77250 49.6
11 -28.642 1.40 1.60342 38.0
12 -381.090 12.95
13 -17.426 1.38 1.80518 25.4
14 -150.390 0.42
15 -74.060 4.40 1.80400 46.6
16 -21.222 0.10
17 * -216.808 3.10 1.66910 55.4
18 -35.520-
* Is a rotationally symmetric aspherical surface.
(Table 8)
Various data
FNO. 2.2
f 28.89
W 39.1
Y 21.64
fB 37.92
LD 140.93
fs -1.1E08 (nearly infinite)
(Table 9)
Aspheric data surface number K A4 A6 A8
17 0.000 -0.1172E-04 -0.5051E-08 -0.7061E-10

[Numerical Example 4]
FIG. 10 is a lens configuration diagram of an entire optical system in which the wide converter lens system (conversion optical system) of Numerical Example 4 is mounted on the object side of the master lens system (main optical system), and FIGS. 11A to 11D are graphs showing various aberrations thereof. 12A to 12D are lateral aberration diagrams. Table 10 shows surface data, Table 11 shows various data, and Table 12 shows aspheric data.

  The lens configuration of the wide converter lens system WL in Numerical Example 4 is the same as the lens configuration of the wide converter lens system WL in Numerical Examples 2 and 3.

(Table 10)
Surface data surface number R d N ν
1 108.168 3.00 1.88300 40.8
2 58.773 18.04
3 -137.016 9.97 1.72047 34.7
4 -50.153 2.50 1.80000 29.8
5 -4538.934 0.15
6 77.210 10.03 1.76182 26.5
7 -380.206 10.32
8 146.963 1.50 1.51823 59.0
9 18.423 14.68
10 28.642 8.40 1.77250 49.6
11 -28.642 1.40 1.60342 38.0
12 -381.090 12.95
13 -17.426 1.38 1.80518 25.4
14 -150.390 0.42
15 -74.060 4.40 1.80400 46.6
16 -21.222 0.10
17 * -216.808 3.10 1.66910 55.4
18 -35.520-
* Is a rotationally symmetric aspherical surface.
(Table 11)
Various data
FNO. 2.2
f 28.84
W 39.5
Y 21.64
fB 37.78
LD 140.11
fs 7.0E03 (nearly infinite)
(Table 12)
Aspheric data surface number K A4 A6 A8
17 0.000 -0.1172E-04 -0.5051E-08 -0.7061E-10

[Numerical Example 5]
FIG. 13 is a lens configuration diagram of the entire optical system in which the wide converter lens system (conversion optical system) of Numerical Example 5 is mounted on the object side of the master lens system (main optical system), and FIGS. 14A to 14D are graphs showing various aberrations thereof. 15A to 15D are lateral aberration diagrams. Table 13 shows surface data, Table 14 shows various data, and Table 15 shows aspherical data.

The lens configuration of the wide converter lens system WL in Numerical Example 5 is entirely different from the lens configuration of the wide converter lens system WL in Numerical Example 1-4, and is specifically as follows.
(1) The wide converter lens system WL includes, in order from the object side, a first lens (first optical element) WL1 ′ composed of a negative meniscus lens having a convex surface facing the object side, and a second lens composed of a biconcave negative lens ( (Second optical element) WL2 ′, a third lens (third optical element) WL3 ′ composed of a biconvex positive lens, and a fourth lens (fourth optical element) WL4 ′ composed of a biconvex positive lens. Yes. The image side surface of the second lens WL2 ′ and the object side surface of the third lens WL3 ′ are cemented.

(Table 13)
Surface data surface number R d N ν
1 102.742 3.00 1.61272 58.7
2 50.378 18.50
3 -94.613 2.50 1.80000 29.8
4 105.194 7.65 1.72047 34.7
5 -257.096 0.15
6 93.227 7.65 1.69895 30.1
7 -222.838 10.73
8 146.963 1.50 1.51823 59.0
9 18.423 14.68
10 28.642 8.40 1.77250 49.6
11 -28.642 1.40 1.60342 38.0
12 -381.090 12.95
13 -17.426 1.38 1.80518 25.4
14 -150.390 0.42
15 -74.060 4.40 1.80400 46.6
16 -21.222 0.10
17 * -216.808 3.10 1.66910 55.4
18 -35.520-
* Is a rotationally symmetric aspherical surface.
(Table 14)
Various data
FNO. 2.2
f 28.81
W 39.6
Y 21.64
fB 38.02
LD 136.53
fs -1.0E04 (nearly infinite)
(Table 15)
Aspheric data surface number K A4 A6 A8
17 0.000 -0.1172E-04 -0.5051E-08 -0.7061E-10

Table 16 shows values for the conditional expressions of the numerical examples.
(Table 16)
Example 1 Example 2 Example 3
Conditional expression (1) -0.70 -1.00 -1.16
Conditional expression (2) 0.398 0.394 0.394
Conditional expression (3)
νp 34.7 34.7 34.7
νn 29.5 29.8 29.8
Conditional expression (4)
ν1 49.3 52.6 49.6
νp 34.7 34.7 34.7
νn 29.5 29.8 29.8
ν4 28.5 29.2 28.5
Example 4 Example 5
Conditional expression (1) -1.06 -2.16
Conditional expression (2) 0.413 0.469
Conditional expression (3)
νp 25.7 34.7
νn 27.5 29.8
Conditional expression (4)
ν1 40.8 58.7
νp 25.7 34.7
νn 27.5 29.8
ν4 64.1 30.1

  As apparent from Table 16, Numerical Example 1 to Numerical Example 5 satisfy the conditional expression (1), and the various aberrations and lateral aberration are compared, as is clear from the various aberration diagrams and lateral aberration diagrams. Correctly corrected.

  In the above numerical example 1 to numerical example 5, the wide converter lens system that changes the focal length of the entire system to the shorter side (wide angle side) has been described as an example. However, the conversion optical system of the present embodiment can also be applied to a teleconverter lens system that changes the focal length of the entire system to the longer side (telephoto side). In this case, the first lens, the second lens, the third lens, and the fourth lens may be sequentially arranged from the master lens system (main optical system) toward the object side (Numerical Example 1-Numerical Example 5 and Reverse order).

ML Master lens system (main optical system)
WL Wide converter lens system (sub optical system, conversion optical system)
WL1 negative first lens (first optical element)
WL2 positive second lens (second optical element)
WL3 negative third lens (third optical element)
WL4 positive fourth lens (fourth optical element)
WL1 ′ negative first lens (first optical element)
WL2 ′ negative second lens (second optical element)
WL3 ′ positive third lens (third optical element)
WL4 ′ positive fourth lens (fourth optical element)
I Design image plane

Claims (8)

A sub optical system arranged on the object side of the main optical system,
A negative first optical element, a second optical element, a third optical element, and a positive fourth optical element;
A concave surface is provided on a surface of the second optical element on the first optical element side;
A sub-optical system that satisfies the following conditional expression (1):
(1) −2.5 <(L2Ra + L3Rb) / (L2Ra−L3Rb) <0
However,
L2Ra: radius of curvature of the surface of the second optical element on the side of the first optical element,
L3Rb: radius of curvature of the surface of the third optical element on the side of the fourth optical element. In the sub optical system according to claim 1,
The sub-optical system includes the negative first optical element, the second optical element, the third optical element, and the positive fourth optical element in order from the object side toward the main optical system. A sub-optical system that is arranged and converts a combined focal length of the main optical system and the sub-optical system to be shorter than a single focal length of the main optical system. The sub optical system according to claim 1 or 2,
A sub optical system that satisfies the following conditional expression (2).
(2) d2 / LD> 0.37
However,
d2: a distance on the optical axis between the first optical element and the second optical element,
LD: distance on the optical axis from the first optical element to the fourth optical element. The sub optical system according to any one of claims 1 to 3,
The second optical element and the third optical element are sub optical systems in which one is a positive optical element and the other is a negative optical element and satisfies the following conditional expression (3).
(3) νp> νn
However,
νp: Abbe number of the positive optical element among the second optical element and the third optical element,
νn: Abbe number of the negative optical element among the second optical element and the third optical element. The sub optical system according to any one of claims 1 to 4,
The second optical element and the third optical element are sub optical systems in which one is a positive optical element and the other is a negative optical element and satisfies the following conditional expression (4).
(4) ν1>νp>νn> ν4
However,
v1: Abbe number of the first optical element,
νp: Abbe number of the positive optical element among the second optical element and the third optical element,
νn: Abbe number of the negative optical element among the second optical element and the third optical element,
ν4: Abbe number of the fourth optical element. The sub optical system according to any one of claims 1 to 5,
The second optical element and the third optical element are sub-optical systems in which one is a positive optical element and the other is a negative optical element and is bonded to each other. The sub optical system according to any one of claims 1 to 6,
A sub optical system in which the focal length of a single unit of the sub optical system is substantially infinite. The sub optical system according to any one of claims 1 to 7,
The position of the image point at which an infinite object is imaged by the main optical system and the sub optical system is substantially equal to the position of the image point at which an infinite object is imaged by the main optical system alone. Sub-optical system characterized.

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