JP7576231B2 - Optical systems and optical instruments - Google Patents

Description

The present invention relates to an optical system and an optical instrument.

In recent years, there has been a demand for optical systems with short overall optical lengths (see, for example, Patent Document 1). However, there is a demand for further improvement in the optical performance of Patent Document 1.

JP 2013-195587 A

An optical system according to a first aspect of the present invention comprises, in order from the object side, a front group, a stop, and a rear group having positive refractive power, the rear group comprising a second lens group having positive refractive power, or, in order from the object side, the second lens group having positive refractive power and a third lens group having negative refractive power, the front group is fixed with respect to an image plane during focusing and the second lens group moves in the direction of an optical axis, and satisfies the condition of the following formula :
0.100 < LA/LB ≦ 0.264
however,
LA: the distance on the optical axis from the lens surface of the front group closest to the object to the lens surface of the rear group closest to the image when focusing at infinity LB: the distance on the optical axis from the lens surface of the rear group closest to the object to the lens surface of the rear group closest to the image when focusing at infinity
The rear group includes a negative lens NR having the largest refractive power among the negative lenses satisfying the condition of the following formula, and a negative lens NF having the largest refractive power among the negative lenses satisfying the condition of the following formula,
0.000 < LNRL/LB < 0.400
0.800 < R2NR/Bfa < 3.000
0.600 < LNFL/LB ≦ 1.000
-3.000 < R1NF/Bfa < -0.500
however,
LB: the distance on the optical axis from the lens surface of the rear group closest to the object to the lens surface closest to the image when focusing at infinity
LNRL: the distance on the optical axis from the image-side lens surface of the negative lens NR to the lens surface of the rear group closest to the image side when focusing at infinity
R2NR: radius of curvature of the image-side lens surface of the negative lens NR
LNFL: the distance on the optical axis from the object side lens surface of the negative lens NF to the lens surface of the rear group closest to the image side when focusing at infinity
R1NF: radius of curvature of the lens surface on the object side of the negative lens NF
Bfa: Back focus (air equivalent length) of the optical system when focused at infinity
The front group has at least one negative lens N1, and the rear group has at least one negative lens NL on the image side of the negative lens NR, and satisfies the following condition:
0.300 < fN1/fNL < 1.200
however,
fN1: focal length of the negative lens N1
fNL: focal length of the negative lens NL

FIG. 2 is a cross-sectional view showing a lens configuration of the optical system according to the first example when focused on infinity. 5A and 5B are diagrams showing various aberrations in the optical system according to the first example, where FIG. 5A shows the case where the optical system is focused on an infinity object, and FIG. 5B shows the case where the optical system is focused on a close distance. FIG. 11 is a cross-sectional view showing a lens configuration of an optical system according to a second example when focused on infinity. 13A and 13B are diagrams showing various aberrations in the optical system according to Example 2, in which FIG. 13A shows the case where the optical system is focused on an infinity object, and FIG. FIG. 11 is a cross-sectional view showing the lens configuration of the optical system according to Example 3 when focused at infinity. 13A and 13B are diagrams showing various aberrations in the optical system according to Example 3, in which FIG. 13A shows the case where the optical system is focused on an infinity object, and FIG. FIG. 13 is a cross-sectional view showing the lens configuration of the optical system according to Example 4 when focused on infinity. 13A and 13B are diagrams showing various aberrations in the optical system according to Example 4, in which FIG. 13A shows the case where the optical system is focused on an infinity object, and FIG. FIG. 13 is a cross-sectional view showing the lens configuration of the optical system according to Example 5 when focused on infinity. 13A and 13B are diagrams showing various aberrations in the optical system according to Example 5, in which FIG. 13A shows the case where the optical system is focused on an infinity object, and FIG. FIG. 2 is a cross-sectional view of a camera equipped with the optical system. 4 is a flowchart illustrating a method for manufacturing the optical system.

A preferred embodiment will now be described with reference to the drawings. As shown in FIG. 1, the optical system OL according to this embodiment is configured to include, in order from the object side, a front group GA, a diaphragm S, and a rear group GB having positive refractive power. With this configuration, it is possible to effectively suppress various aberrations while shortening the overall optical length of the optical system OL.

It is desirable for the optical system OL of this embodiment to satisfy the following condition (1).

0.100 < LA/LB < 0.400 (1)
however,
LA: the distance on the optical axis from the lens surface of the front group GA closest to the object to the lens surface closest to the image when focusing at infinity LB: the lens surface of the rear group GB closest to the object when focusing at infinity Distance on the optical axis from to the lens surface closest to the image

Conditional formula (1) specifies the ratio of the length of the front group GA (the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image) to the length of the rear group GB of the optical system OL when focusing at infinity (the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image). By satisfying this conditional formula (1), the length of the rear group GB becomes longer than the length of the front group GA, that is, the optical system on the image side from the aperture stop S becomes longer, so that good correction of field curvature and astigmatism can be realized in the optical system OL with a short optical total length. In order to ensure the effect of conditional formula (1), it is more preferable to set the upper limit value of conditional formula (1) to 0.350, and more preferably 0.320. In addition, in order to ensure the effect of conditional formula (1), it is more preferable to set the lower limit value of conditional formula (1) to 0.130, and more preferably 0.150.

Furthermore, it is desirable for the optical system OL according to this embodiment to satisfy the following conditional expression (2).

0.070 < LAS/LAB < 0.300 (2)
however,
LAS: the distance on the optical axis from the lens surface of the front group GA closest to the object to the aperture stop S when focusing at infinity LAB: the distance on the optical axis from the lens surface of the front group GA closest to the object to the lens surface of the rear group GB when focusing at infinity Distance on the optical axis to the lens surface closest to the image

Conditional expression (2) specifies the ratio of the length of the optical system OL (the distance on the optical axis from the lens surface of the front group GA closest to the object to the lens surface of the rear group GB closest to the image) to the length of the optical system OL when focusing at infinity (the distance on the optical axis from the lens surface of the front group GA closest to the object to the lens surface of the rear group GB closest to the image). By satisfying this conditional expression (2), the optical system on the object side of the aperture S becomes shorter than the length of the optical system OL, so that the entrance pupil of the optical system OL approaches the object side, and good correction of field curvature, astigmatism, and distortion can be realized. In order to ensure the effect of conditional expression (2), it is more preferable to set the upper limit value of conditional expression (2) to 0.280, and more preferably 0.260. In addition, in order to ensure the effect of conditional expression (2), it is more preferable to set the lower limit value of conditional expression (2) to 0.100, and more preferably 0.130.

In addition, in the optical system OL according to this embodiment, it is desirable for the rear group GB to have a negative lens NR that satisfies the following conditional expression (3).

0.000 < LNRL/LB < 0.500 (3)
however,
LB: the distance on the optical axis from the lens surface of the rear group GB closest to the object to the lens surface closest to the image when focusing at infinity. LNRL: the distance on the optical axis from the lens surface of the negative lens NR closest to the image when focusing at infinity. The distance on the optical axis to the lens surface of the rear group GB closest to the image

Conditional formula (3) specifies the ratio of the length (distance on the optical axis) from the image side lens surface of the negative lens NR to the lens surface of the rear group GB closest to the image side to the length of the rear group GB. By satisfying this conditional formula (3), the negative lens NR is disposed on the image side of the rear group GB, that is, near the image surface I, and the total optical length of the optical system OL can be shortened while suppressing various aberrations such as curvature of field, astigmatism, and distortion aberration. In order to ensure the effect of conditional formula (3), it is more preferable to set the upper limit value of conditional formula (3) to 0.450, and more preferably 0.400, 0.360, or 0.320. In addition, in order to ensure the effect of conditional formula (3), it is more preferable to set the lower limit value of conditional formula (3) to 0.070, and more preferably 0.150.

It is also desirable for the negative lens NR to satisfy the following condition (4).

0.800 < R2NR/Bfa < 3.000 (4)
however,
R2NR: radius of curvature of the lens surface on the image side of the negative lens NR Bfa: back focus (air equivalent length) of the optical system OL when focused at infinity

Conditional expression (4) specifies the ratio of the radius of curvature of the image-side lens surface of the negative lens NR to the back focus of the optical system OL. By satisfying conditional expression (3) and placing the negative lens NR near the image surface I, the negative lens NR satisfies conditional expression (4), and good correction of field curvature, astigmatism, and distortion can be realized. In order to ensure the effect of conditional expression (4), it is more preferable to set the upper limit of conditional expression (4) to 2.700, and more preferably 2.400. In addition, in order to ensure the effect of conditional expression (4), it is more preferable to set the lower limit of conditional expression (4) to 0.850, and more preferably 0.900.

In addition, in the optical system OL of this embodiment, it is desirable for the rear group GB to have a negative lens NF that satisfies the following conditional expression (5).

0.600 < LNFL/LB ≦ 1.000 (5)
however,
LB: the distance on the optical axis from the lens surface of the rear group GB closest to the object to the lens surface closest to the image when focusing at infinity. LNFL: the distance on the optical axis from the lens surface of the negative lens NF closest to the object when focusing at infinity. The distance on the optical axis to the lens surface of the rear group GB closest to the image

Conditional formula (5) specifies the ratio of the length (distance on the optical axis) from the object side lens surface of the negative lens NF to the lens surface of the rear group GB closest to the image side to the length of the rear group GB. By satisfying this conditional formula (5), the negative lens NF is disposed on the object side of the rear group GB, that is, near the aperture stop S, and the total optical length of the optical system OL can be shortened while effectively suppressing various aberrations such as spherical aberration, axial chromatic aberration, and curvature of field. In order to ensure the effect of conditional formula (5), it is more preferable to set the lower limit of conditional formula (5) to 0.700, and even more preferably 0.800.

It is also desirable for the negative lens NF to satisfy conditional expression (6) below.

-3.000 < R1NF/Bfa < -0.500 (6)
however,
R1NF: radius of curvature of the lens surface on the object side of the negative lens NF Bfa: back focus (air equivalent length) of the optical system OL when focused at infinity

Conditional expression (6) specifies the ratio of the radius of curvature of the object-side lens surface of the negative lens NF to the back focus of the optical system OL. By satisfying conditional expression (5) and arranged near the aperture stop S, the negative lens NF satisfies conditional expression (6), and good correction of spherical aberration, field curvature, and axial chromatic aberration can be realized. In order to ensure the effect of conditional expression (6), it is more preferable to set the upper limit value of conditional expression (6) to -0.600, and even more preferable to set it to -0.700. In order to ensure the effect of conditional expression (6), it is more preferable to set the lower limit value of conditional expression (6) to -2.500, and even more preferable to set it to -2.000.

In the following description, when the rear group GB contains multiple negative lenses that satisfy conditional expressions (3) and (4), the negative lens with the greatest refractive power among those negative lenses is referred to as the negative lens NR. When the rear group GB contains multiple negative lenses that satisfy conditional expressions (5) and (6), the negative lens with the greatest refractive power among those negative lenses is referred to as the negative lens NF.

In the optical system OL of this embodiment, it is desirable that the negative lens NR and the negative lens NF satisfy the following conditional expression (7).

-0.800<(R1NF+R2NR)/(R1NF-R2NR)<0.800 (7)
however,
R1NF: Radius of curvature of the lens surface on the object side of the negative lens NF R2NR: Radius of curvature of the lens surface on the image side of the negative lens NR

Conditional formula (7) specifies the shape factor from the object side lens surface of the negative lens NF to the image side lens surface of the negative lens NR. Satisfying conditional formula (7) indicates that the absolute values of the radii of curvature of the object side lens surface of the negative lens NF and the image side lens surface of the negative lens NR are close to each other. By satisfying this conditional formula (7), the symmetry of the negative lenses included in the rear group GB is increased, and as a result, good correction of spherical aberration, field curvature, axial chromatic aberration, astigmatism, distortion, and other aberrations can be achieved with good balance. In order to ensure the effect of conditional formula (7), it is more preferable to set the upper limit of conditional formula (7) to 0.600, and more preferably to 0.400 or 0.200. In addition, in order to ensure the effect of conditional formula (7), it is more preferable to set the lower limit of conditional formula (7) to -0.600, and more preferably to -0.400 or -0.200.

Furthermore, in the optical system OL of this embodiment, it is desirable that the negative lens NR and the negative lens NF satisfy the following conditional expression (8).

0.200 < fNF/fNR < 1.200 (8)
however,
fNF: focal length of negative lens NF fNR: focal length of negative lens NR

Conditional formula (8) specifies the ratio of the focal length of the negative lens NF to the focal length of the negative lens NR. By satisfying this conditional formula (8), the refractive power of the negative lens NF and the refractive power of the negative lens NR become close to each other, so that the symmetry of the refractive power of the negative lens as the rear group GB is high, and as a result, a well-balanced and good correction of field curvature, astigmatism, distortion, etc. can be realized. In order to ensure the effect of conditional formula (8), it is more preferable to set the upper limit value of conditional formula (8) to 1.000, and more preferably 0.900 or 0.800. In addition, in order to ensure the effect of conditional formula (8), it is more preferable to set the lower limit value of conditional formula (8) to 0.300, and more preferably 0.400.

In addition, in the optical system OL according to this embodiment, it is desirable for the rear group GB to have at least two positive lenses between the negative lens NF and the negative lens NR. By configuring in this way, good aberration correction can be easily performed. In particular, spherical aberration, axial chromatic aberration, curvature of field, astigmatism, etc. can be corrected well.

In addition, in the optical system OL of this embodiment, the front group GA has at least one negative lens N1, and the rear group GB has at least one negative lens NL on the image side of the negative lens NR, and it is desirable that the following conditional expression (9) be satisfied.

0.300 < fN1/fNL < 1.200 (9)
however,
fN1: focal length of negative lens N1 fNL: focal length of negative lens NL

Conditional formula (9) specifies the ratio of the focal length of the negative lens N1 included in the front group GA to the focal length of the negative lens NL included in the rear group GB. By arranging negative lenses that satisfy conditional formula (9), that is, negative lenses N1 and NL with similar refractive powers, on the object side of the negative lens NF and the image side of the negative lens NR and sandwiching the negative lenses NF and NR, the symmetry of the negative lenses is increased in the optical system as a whole, and as a result, better correction of curvature of field, astigmatism, distortion, etc. can be realized with a better balance. In order to ensure the effect of conditional formula (9), it is more preferable to set the upper limit of conditional formula (9) to 1.100, and more preferably 1.000 or 0.900. In addition, in order to ensure the effect of conditional formula (9), it is more preferable to set the lower limit of conditional formula (9) to 0.330, and more preferably 0.360.

In addition, in the optical system OL according to this embodiment, the rear group GB has an aspheric lens having an aspheric surface formed on at least one of the object-side lens surface and the image-side lens surface, and it is desirable that the following conditional expression (10) is satisfied.

0.100 < LASI/LAB < 0.600 (10)
however,
LASI: the distance on the optical axis from the aspheric surface located closest to the image in the rear group GB to the image surface when focusing at infinity. LAB: the lens closest to the object in the front group GA when focusing at infinity. The distance on the optical axis from the surface to the lens surface of the rear group GB closest to the image side.

Conditional expression (10) specifies the ratio of the length (distance on the optical axis) from the aspherical surface arranged closest to the image side to the image surface to the length of the optical system OL. By satisfying this conditional expression (10), the aspherical surface arranged closest to the image side in the rear group GB is located close to the image surface I, so that the curvature of field, astigmatism, and distortion can be corrected well. In order to ensure the effect of conditional expression (10), it is more preferable to set the upper limit value of conditional expression (10) to 0.550, and even more preferable to set it to 0.500. In addition, in order to ensure the effect of conditional expression (10), it is more preferable to set the lower limit value of conditional expression (10) to 0.200, and even more preferable to set it to 0.300.

In addition, in the optical system OL according to this embodiment, the rear group GB has an aspheric lens having an aspheric surface formed on at least one of the object-side lens surface and the image-side lens surface, and it is desirable that the following conditional expression (11) is satisfied.

0.000 ≦ LASL/LAB < 0.150 (11)
however,
LASL: The distance on the optical axis from the aspherical surface located closest to the image side in the rear group GB to the lens surface closest to the image side in the rear group GB when focusing at infinity. LAB: The distance on the optical axis from the aspherical surface located closest to the image side in the rear group GB when focusing at infinity. The distance on the optical axis from the lens surface of the group GA closest to the object to the lens surface of the rear group GB closest to the image

Conditional expression (11) specifies the ratio of the length (distance on the optical axis) from the aspherical surface arranged closest to the image to the surface of the rear group GB closest to the image to the length of the optical system OL. By satisfying this conditional expression (11), the aspherical surface arranged closest to the image in the rear group GB is located close to the image surface I, so that the curvature of field, astigmatism, and distortion can be corrected well. In order to ensure the effect of conditional expression (11), it is more preferable to set the upper limit of conditional expression (11) to 0.120, and more preferably 0.100. In order to ensure the effect of conditional expression (11), it is more preferable to set the lower limit of conditional expression (11) to 0.007.

Furthermore, it is desirable for the optical system OL in this embodiment to satisfy the following condition (12).

0.800 < fB/f < 1.600 (12)
however,
fB: focal length of the rear group GB when focusing at infinity f: focal length of the entire optical system OL when focusing at infinity

Conditional expression (12) specifies the ratio of the focal length of the rear group GB to the focal length of the entire system. By satisfying this conditional expression (12), the total optical length of the optical system OL can be shortened while effectively suppressing various aberrations such as spherical aberration, coma aberration, curvature of field, and astigmatism. In order to ensure the effect of conditional expression (12), it is more preferable to set the upper limit value of conditional expression (12) to 1.500, and more preferably 1.400. In addition, in order to ensure the effect of conditional expression (12), it is more preferable to set the lower limit value of conditional expression (12) to 0.900, and more preferably 0.950.

It should be noted that the conditions and configurations described above each provide the effects described above, and are not limited to those that satisfy all of the conditions and configurations; the effects described above can be obtained by satisfying any one of the conditions or configurations, or any combination of the conditions or configurations.

Next, a camera, which is an optical device equipped with the optical system OL according to this embodiment, will be described with reference to FIG. 11. This camera 1 is a so-called mirrorless camera with interchangeable lenses, equipped with the optical system OL according to this embodiment as the photographing lens 2. In this camera 1, light from an object (subject) (not shown) is collected by the photographing lens 2 and forms a subject image on the imaging surface of the imaging unit 3 via an OLPF (Optical low pass filter) (not shown). The subject image is then photoelectrically converted by a photoelectric conversion element provided in the imaging unit 3 to generate an image of the subject. This image is displayed on an EVF (Electronic view finder) 4 provided in the camera 1. This allows the photographer to observe the subject through the EVF 4.

Furthermore, when the photographer presses a release button (not shown), the image photoelectrically converted by the imaging unit 3 is stored in a memory (not shown). In this way, the photographer can photograph the subject using the camera 1. Note that, although an example of a mirrorless camera has been described in this embodiment, the same effect as the camera 1 can be achieved even if the optical system OL according to this embodiment is mounted on a single-lens reflex type camera that has a quick-return mirror in the camera body and observes the subject through a viewfinder optical system.

Below, an outline of the manufacturing method for the optical system OL of this embodiment is explained with reference to Figure 12.

First, the lenses are positioned to prepare the front group GA, the aperture stop S, and the rear group GB of the optical system OL (step S100). Then, the front group GA, the aperture stop S, and the rear group GB are positioned so as to satisfy a predetermined condition (for example, the above-mentioned condition (1)) (step S200).

With the above-described configuration, it is possible to provide an optical system OL with a short overall optical length and in which various aberrations are effectively suppressed, an optical device having this optical system OL, and a method for manufacturing the optical system OL.

Each embodiment of the present application will be described below with reference to the drawings. Note that Figures 1, 3, 5, 7, and 9 are cross-sectional views showing the configuration and refractive power distribution of the optical system OL (OL1 to OL5) in each embodiment.

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

S(y)=(y ² /r)/{1+(1-K×y ² /r ² ) ^1/2 }
+A4×y ⁴ +A6×y ⁶ +A8×y ⁸ +A10×y ¹⁰ +A12×y ¹² (a)

In addition, in each embodiment, the second-order aspheric coefficient A2 is 0.

Furthermore, the following examples show a specific example of the present invention, and the present invention is not limited to these.

[First embodiment]
1 is a diagram showing the configuration of an optical system OL1 according to Example 1. This optical system OL1 is composed of, from the object side, a front group GA, an aperture stop S, and a rear group GB having positive refractive power. The front group GA is composed of a first lens group G1 having negative refractive power, and the rear group GB is composed of, from the object side, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power.

The first lens group G1 is composed of, in order from the object side, a negative meniscus lens L11 with a convex surface facing the object side, a biconcave negative lens L12, and a biconvex positive lens L13. The second lens group G2 is composed of, in order from the object side, a positive meniscus lens L21 with a convex surface facing the object side, a cemented negative lens formed by cementing a biconcave negative lens L22 and a biconvex positive lens L23, a biconvex positive lens L24, a cemented positive lens formed by cementing a biconvex positive lens L25 and a biconcave negative lens L26, and an aspheric positive lens L27 that has a positive meniscus shape with a concave surface facing the object side and has an aspheric lens surface on the object side and an aspheric lens surface on the image side. The third lens group G3 is composed of a biconcave negative lens L31. An optical filter FL is disposed between the rear group GB and the image surface I.

In this optical system OL1, the negative meniscus lens L11 is the negative lens N1, the biconcave negative lens L22 is the negative lens NF, the biconcave negative lens L26 is the negative lens NR, and the biconcave negative lens L31 is the negative lens NL.

In addition, in this optical system OL1, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the object.

The values of the specifications of optical system OL1 are listed in Table 1 below. In the overall specifications in Table 1, f represents the focal length of the entire optical system OL1, FNO represents the F-number, ω represents the half angle of view [°], Y represents the maximum image height, TL represents the total length, and BF represents the back focus value. Here, the total length TL indicates the distance on the optical axis (actual distance) from the lens surface closest to the object (surface 1) to the image surface I when focused at infinity. In addition, the back focus BF indicates the distance on the optical axis (actual distance and air-equivalent length) from the lens surface closest to the image surface (surface 21) to the image surface I when focused at infinity. In addition, the first column m in the lens data indicates the order (surface number) of the lens surfaces from the object side along the direction in which the light travels, the second column r indicates the radius of curvature of each lens surface, the third column d indicates the distance on the optical axis from each optical surface to the next optical surface (surface spacing), and the fourth column nd and the fifth column vd indicate the refractive index and Abbe number for the d-line (λ=587.6 nm). In addition, a radius of curvature of 0.00000 indicates a flat surface, and the refractive index of air of 1.00000 is omitted. The lens group focal length indicates the surface number and focal length of the first surface of each lens group.

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

(Table 1) First Example [Overall Specifications]
f 18.66
FNO 1.88
ω [°] 39.7
Y 14.50
TL 50.948
BF 14.138
BF (air equivalent length) 13.593

[Lens data]
m r d nd νd
Surface ∞
1 30.88470 0.800 1.51680 63.9
2 10.13359 3.253
3 -19.53734 0.800 1.51680 63.9
4 61.77677 0.200
5 28.44452 1.786 1.88300 40.7
6 -44.24172 2.161
7 0.00000 D7 Aperture S
8 25.03904 1.406 1.67790 55.4
9 71.55004 2.029
10 -17.74480 0.800 1.73800 32.3
11 17.70671 4.036 1.72916 54.6
12 -57.28104 0.200
13 44.58187 4.546 1.77250 49.6
14 -26.47919 0.200
15 24.68842 4.741 1.77250 49.6
16 -41.92740 0.800 1.73800 32.3
17 28.22236 3.986
18* -340.64532 1.217 1.53113 55.8
19* -28.19344 D19
20 -49.63870 0.800 1.51680 63.9
21 102.44757 11.540
22 0.00000 1.600 1.51680 64.1
23 0.00000 0.998
Image plane ∞

[Lens group focal length]
Lens group First surface Focal length First lens group G1 1 -76.08
Second lens group G2 8 17.43
Third lens group G3 20 -64.58

In this optical system OL1, the lens surfaces No. 18 and No. 19 are formed aspherically. The following Table 2 shows the surface number m and the aspheric data, i.e., the conic constant K and the values of each aspheric constant A4 to A12.

(Table 2)
[Aspheric data]
Face 18 K = 1.00000e+00
A4 = -1.34226e-04 A6 = 4.64940e-06 A8 = -3.86730e-08
A10= 0.00000e+00 A12= 0.00000e+00
Face 19 K = 1.00000e+00
A4 = -2.70832e-06 A6 = 5.26276e-06 A8 = -3.87365e-08
A10= 0.00000e+00 A12= 0.00000e+00

In this optical system OL1, the axial air spacing D7 between the first lens group G1 and the second lens group G2, and the axial air spacing D19 between the second lens group G2 and the third lens group G3 change during focusing. Table 3 below shows the variable spacings when focusing at infinity and when focusing at close ranges. Note that D0 indicates the distance on the optical axis from the object to the lens surface (first surface) of the optical system OL1 closest to the object, β indicates the magnification, and f indicates the focal length of the entire system. The explanations of these symbols are the same in the following examples.

(Table 3)
Infinity Near distance D0 ∞ 188.54
β - -0.1000
f 18.66 -
D7 1.878 0.541
D19 1.170 2.508

Figure 2 shows the spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and coma diagrams of this optical system OL1 when focusing at infinity and at close distances. In each aberration diagram, FNO indicates the F-number, NA indicates the numerical aperture, and Y indicates the image height. In the spherical aberration diagram, the F-number or numerical aperture value corresponding to the maximum aperture is shown, in the astigmatism diagram and the distortion diagram, the maximum value of the image height is shown, and in the coma diagram, the value of each image height is shown. d indicates the d-line (λ = 587.6 nm), and g indicates the g-line (λ = 435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal image surface, and the dashed line indicates the meridional image surface. In the aberration diagrams of each embodiment shown below, the same symbols as in this embodiment are used. From these aberration diagrams, it can be seen that various aberrations are well corrected in this optical system OL1.

[Second embodiment]
3 is a diagram showing the configuration of an optical system OL2 according to Example 2. This optical system OL2 is composed of, from the object side, a front group GA, an aperture stop S, and a rear group GB having positive refractive power. The front group GA is composed of a first lens group G1 having positive refractive power, and the rear group GB is composed of, from the object side, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power.

The first lens group G1 is composed of, in order from the object side, a negative meniscus lens L11 with a convex surface facing the object side, and a positive meniscus lens L12 with a convex surface facing the object side. The second lens group G2 is composed of, in order from the object side, a cemented negative lens in which a biconcave negative lens L21 and a biconvex positive lens L22 are cemented together, a biconvex positive lens L23, a cemented negative lens in which a positive meniscus lens L24 with a convex surface facing the object side and a negative meniscus lens L25 with a convex surface facing the object side are cemented together, and an aspheric positive lens L26 with a concave surface facing the object side and an aspheric positive lens L26 with an aspheric surface formed on the object side and the lens surface on the image side. The third lens group G3 is composed of a biconcave negative lens L31. An optical filter FL is disposed between the rear group GB and the image surface I.

In this optical system OL2, the negative meniscus lens L11 is the negative lens N1, the biconcave negative lens L21 is the negative lens NF, the negative meniscus lens L25 is the negative lens NR, and the biconcave negative lens L31 is the negative lens NL.

In addition, in this optical system OL2, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the object.

The values of the specifications of the optical system OL2 are shown in Table 4 below. Note that the third surface in the lens data is a virtual surface, but is not shown in the cross-sectional view of Figure 3.

(Table 4) Second Example [Overall Specifications]
f 24.21
FNO 1.76
ω［°］ 30.5
Y 14.50
TL 50.004
BF 14.096
BF (air equivalent length) 13.551

[Lens data]
m r d nd νd
Surface ∞
1 26.24690 0.800 1.60311 60.7
2 12.59482 1.700
3 0.00000 0.400
4 15.67302 1.691 1.80400 46.6
5 30.29814 1.833
6 0.00000 D6 Aperture S
7 -12.84018 0.800 1.73800 32.3
8 75.53056 4.818 1.75500 52.3
9 -16.73420 0.200
10 36.79732 4.800 1.72916 54.6
11 -47.51982 0.200
12 18.21772 3.700 1.72916 54.6
13 41.67744 2.081 1.67300 38.1
14 14.30567 3.803
15* -60.75531 1.465 1.53110 55.9
16* -21.32052 D16
17 -58.67999 0.800 1.75520 27.6
18 120.38649 11.496
19 0.00000 1.600 1.51680 64.1
20 0.00000 1.000
Image plane ∞

[Lens group focal length]
Lens group First surface Focal length First lens group G1 1 474.50
Second lens group G2 7 19.56
Third lens group G3 17 -52.14

In this optical system OL2, the lens surfaces No. 15 and No. 16 are formed aspherically. Table 5 below shows the surface number m and aspheric data, i.e., the conic constant K and the values of each aspheric constant A4 to A12.

(Table 5)
[Aspheric data]
Face 15 K = 1.00000e+00
A4 = -4.27043e-05 A6 = 3.35775e-07 A8 = 1.40921e-08
A10= 0.00000e+00 A12= 0.00000e+00
Face 16 K = 1.00000e+00
A4 = 5.80487e-05 A6 = 4.09696e-07 A8 = 1.64474e-08
A10= 0.00000e+00 A12= 0.00000e+00

In this optical system OL2, the axial air spacing D6 between the first lens group G1 and the second lens group G2, and the axial air spacing D16 between the second lens group G2 and the third lens group G3 change during focusing. The following Table 5 shows the variable spacings when focusing at infinity and when focusing at close range.

Table 6
Infinity Near distance D0 ∞ 243.98
β - -0.1000
f 24.21 -
D6 5.818 4.309
D16 1.000 2.509

Figure 4 shows the spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and coma aberration diagrams for this optical system OL2 when focused at infinity and when focused at a close distance. From these aberration diagrams, it can be seen that the various aberrations of this optical system OL2 are well corrected.

[Third Example]
5 is a diagram showing the configuration of an optical system OL3 according to Example 3. This optical system OL3 is composed of, from the object side, a front group GA, an aperture stop S, and a rear group GB having positive refractive power. The front group GA is composed of a first lens group G1 having positive refractive power, and the rear group GB is composed of, from the object side, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power.

The first lens group G1 is composed of, in order from the object side, a negative meniscus lens L11 with a convex surface facing the object side, and a positive meniscus lens L12 with a convex surface facing the object side. The second lens group G2 is composed of, in order from the object side, a cemented negative lens formed by cementing a negative meniscus lens L21 with a concave surface facing the object side and a positive meniscus lens L22 with a convex surface facing the object side, a biconvex positive lens L23, a positive meniscus lens L24 with a convex surface facing the object side, a negative meniscus lens L25 with a convex surface facing the object side, and an aspheric positive lens L26 with a concave surface facing the object side and an aspheric lens surface on the object side and an aspheric lens surface on the image side formed in an aspheric shape. The third lens group G3 is composed of an aspheric negative lens L31 with a biconcave shape and an aspheric lens surface on the object side and an aspheric lens surface on the image side formed in an aspheric shape. In addition, an optical filter FL is disposed between the rear group GB and the image plane I.

In this optical system OL3, the negative meniscus lens L11 is the negative lens N1, the negative meniscus lens L21 is the negative lens NF, the negative meniscus lens L25 is the negative lens NR, and the aspheric negative lens L31 is the negative lens NL.

In addition, in this optical system OL3, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the object.

The values of the specifications of the optical system OL3 are listed in Table 7 below. Note that the third surface of the lens data is a virtual surface, but is not shown in the cross-sectional view of Figure 5.

(Table 7) Third Example [Overall Specifications]
f 23.99
FNO 1.74
ω [°] 30.1
Y 14.50
TL 49.992
BF 12.990
BF (air equivalent length) 12.445

[Lens data]
m r d nd νd
Surface ∞
1 25.94000 0.800 1.60311 60.7
2 14.70210 2.017
3 0.00000 0.780
4 19.62856 1.510 1.80400 46.6
5 40.55492 1.609
6 0.00000 D6 Aperture S
7 -11.09774 0.800 1.73800 32.3
8 -71.62023 4.000 1.75500 52.3
9 -15.17987 0.000
10 2312.74590 3.823 1.72916 54.6
11 -26.33558 0.200
12 18.26036 5.535 1.72916 54.6
13 137.30289 0.200
14 49.24547 1.572 1.76182 26.6
15 16.62297 4.616
16* -12.37612 0.919 1.53113 55.8
17* -11.35573 D17
18* -128.13552 0.800 1.64000 60.2
19* 104.42083 10.390
20 0.00000 1.600 1.51680 64.1
21 0.00000 1.000
Image plane ∞

[Lens group focal length]
Lens group First surface Focal length First lens group G1 1 198.61
Second lens group G2 7 22.16
Third lens group G3 18 -89.78

In this optical system OL3, the lens surfaces No. 16, No. 17, No. 18, and No. 19 are formed aspherically. Table 8 below shows the surface number m and aspheric data, i.e., the conic constant K and the values of each aspheric constant A4 to A12.

Table 8
[Aspheric data]
Face 16 K = 1.00000e+00
A4 = 3.18413e-04 A6 = 1.91924e-06 A8 = -8.92961e-09
A10= 0.00000e+00 A12= 0.00000e+00
Face 17 K = 1.00000e+00
A4 = 4.58812e-04 A6 = 7.66215e-07 A8 = 3.67698e-09
A10= 0.00000e+00 A12= 0.00000e+00
Face 18 K = 1.00000e+00
A4 = -5.32694e-07 A6 = -8.50693e-07 A8 = 4.38809e-09
A10= 0.00000e+00 A12= 0.00000e+00
Face 19 K = 1.00000e+00
A4 = -3.35211e-05 A6 = 2.16253e-07 A8 = 0.00000e+00
A10= 0.00000e+00 A12= 0.00000e+00

In this optical system OL3, the axial air spacing D6 between the first lens group G1 and the second lens group G2, and the axial air spacing D17 between the second lens group G2 and the third lens group G3 change during focusing. The following Table 9 shows the variable spacing when focusing at infinity and when focusing at close range.

Table 9
Infinity Near distance D0 ∞ 242.49
β - -0.1000
f 23.99 -
D6 6.793 4.946
D17 1.028 2.875

Figure 6 shows the spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and coma aberration diagrams for this optical system OL3 when focused at infinity and when focused at a close distance. From these aberration diagrams, it can be seen that the various aberrations of this optical system OL3 are well corrected.

[Fourth embodiment]
7 is a diagram showing the configuration of an optical system OL4 according to Example 4. This optical system OL4 is composed of, from the object side, a front group GA, an aperture stop S, and a rear group GB having positive refractive power. The front group GA is composed of a first lens group G1 having positive refractive power, and the rear group GB is composed of, from the object side, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power.

The first lens group G1 is composed of, in order from the object side, a negative meniscus lens L11 with a convex surface facing the object side, and a biconvex positive lens L12. The second lens group G2 is composed of, in order from the object side, a negative meniscus lens L21 with a concave surface facing the object side, a positive meniscus lens L22 with a concave surface facing the object side, an aspheric positive lens L23 with a biconvex shape and an aspheric shape formed on the lens surface on the object side and the lens surface on the image side, and a cemented negative lens in which a positive meniscus lens L24 with a convex surface facing the object side and a negative meniscus lens L25 with a convex surface facing the object side are cemented together. The third lens group G3 is composed of an aspheric negative lens L31 in which a resin layer provided on the lens surface on the object side of the biconcave negative lens is formed into an aspheric shape. An optical filter FL is arranged between the rear group GB and the image surface I.

In this optical system OL4, the negative meniscus lens L11 is the negative lens N1, the negative meniscus lens L21 is the negative lens NF, the negative meniscus lens L25 is the negative lens NR, and the aspheric negative lens L31 is the negative lens NL.

In addition, in this optical system OL4, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the object.

The values of the specifications of the optical system OL4 are shown in Table 10 below. Note that the third and eleventh surfaces in the lens data are virtual surfaces, but are not shown in the cross-sectional view of FIG.

(Table 10) Fourth Example [Overall Specifications]
f 24.64
FNO 1.75
ω [°] 30.3
Y 14.50
TL 50,000
BF 13.012
BF (air equivalent length) 12.467

[Lens data]
m r d nd νd
Surface ∞
1 95.72479 0.800 1.69680 55.5
2 30.29508 3.511
3 0.00000 -0.700
4 26.01082 1.945 1.77250 49.6
5 -349.67569 1.000
6 0.00000 D6 Aperture S
7 -10.06582 0.800 1.72825 28.4
8 -42.33130 0.901
9 -35.35053 5.000 1.77250 49.6
10 -13.06203 -0.500
11 0.00000 0.600
12* 34.65982 4.800 1.69350 53.3
13* -52.08174 0.200
14 30.12605 2.885 1.77250 49.6
15 101.41586 2.700 1.78472 25.6
16 23.50659 D16
17* -212.49838 0.100 1.56093 36.6
18 -125.18463 1.100 1.51680 63.9
19 54.07182 10.412
20 0.00000 1.600 1.51680 63.9
21 0.00000 1.000
Image plane ∞

[Lens group focal length]
Lens group First surface Focal length First lens group G1 1 57.07
Second lens group G2 7 25.23
Third lens group G3 17 -84.30

In this optical system OL4, the lens surfaces No. 12, No. 13, and No. 17 are formed aspherically. Table 11 below shows the surface number m and aspheric data, i.e., the conic constant K and the values of each aspheric constant A4 to A12.

Table 11
[Aspheric data]
Face 12 K = 1.00000e+00
A4 = 2.63231e-05 A6 = -2.91715e-08 A8 = 1.91541e-10
A10= 0.00000e+00 A12= 0.00000e+00
Face 13 K = 1.00000e+00
A4 = 5.30867e-05 A6 = -5.02435e-08 A8 = 0.00000e+00
A10= 0.00000e+00 A12= 0.00000e+00
Face 17 K = 1.00000e+00
A4 = 6.34469e-06 A6 = -2.28171e-07 A8 = 1.47869e-10
A10=-6.83855e-12 A12=0.00000e+00

In this optical system OL4, the axial air spacing D6 between the first lens group G1 and the second lens group G2, and the axial air spacing D16 between the second lens group G2 and the third lens group G3 change during focusing. The following Table 12 shows the variable spacings when focusing at infinity and when focusing at close range.

(Table 12)
Infinity Near distance D0 ∞ 162.24
β - -0.1500
f 24.64 -
D6 7.809 4.719
D16 4.037 7.127

Figure 8 shows the spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and coma aberration diagrams for this optical system OL4 when focused at infinity and when focused at a close distance. From these aberration diagrams, it can be seen that the various aberrations of this optical system OL4 are well corrected.

[Fifth Example]
9 is a diagram showing the configuration of an optical system OL5 according to Example 5. This optical system OL5 is composed of, in order from the object side, a front group GA, an aperture stop S, and a rear group GB having positive refractive power. The front group GA is composed of a first lens group G1 having positive refractive power, and the rear group GB is composed of a second lens group G2 having positive refractive power.

The first lens group G1 is composed of, in order from the object side, a negative meniscus lens L11 with a convex surface facing the object side, and a positive meniscus lens L12 with a convex surface facing the object side. The second lens group G2 is composed of, in order from the object side, a negative meniscus lens L21 with a concave surface facing the object side, a positive meniscus lens L22 with a concave surface facing the object side, an aspherical positive lens L23 with a biconvex shape and with aspherical shapes on the object side lens surface and the image side lens surface, a cemented positive lens in which a positive meniscus lens L24 with a convex surface facing the object side and a negative meniscus lens L25 with a convex surface facing the object side are cemented together, and an aspherical negative lens L26 in which a resin layer provided on the object side lens surface of the biconcave negative lens is formed into an aspherical shape. An optical filter FL is arranged between the rear group GB and the image surface I.

In this optical system OL5, the negative meniscus lens L11 is the negative lens N1, the negative meniscus lens L21 is the negative lens NF, the negative meniscus lens L25 is the negative lens NR, and the aspheric negative lens L26 is the negative lens NL.

In addition, in this optical system OL5, focusing from infinity to a close-distance object is performed by moving the second lens group G2 toward the object.

The values of the specifications of the optical system OL5 are listed in Table 13 below. Note that the third and eleventh surfaces in the lens data are virtual surfaces, but are not shown in the cross-sectional view of FIG.

(Table 13) Fifth Example [Overall Specifications]
f 24.28
FNO 1.74
ω［°］ 30.0
Y 14.50
TL 50,000
BF 13.413
BF (air equivalent length) 12.868

[Lens data]
m r d nd νd
Surface ∞
1 50.00000 0.800 1.69680 55.5
2 17.24209 2.151
3 0.00000 -0.700
4 19.58974 2.153 1.77250 49.6
5 205.71020 1.601
6 0.00000 D6 Aperture S
7 -10.35061 0.800 1.72825 28.4
8 -32.62394 0.335
9 -40.55777 5.000 1.77250 49.6
10 -13.65162 -0.800
11 0.00000 0.900
12* 32.69590 4.800 1.69350 53.3
13* -281.19271 0.259
14 21.08477 3.700 1.77250 49.6
15 152.39896 2.700 1.78472 25.6
16 22.00000 3.177
17* 280.88096 0.100 1.56093 36.6
18 -134.95915 1.100 1.51680 64.1
19 40.00000 D19
20 0.00000 1.600 1.51680 64.1
21 0.00000 1.000
Image plane ∞

[Lens group focal length]
Lens group First surface Focal length First lens group G1 1 93.85
Second lens group G2 7 28.46

In this optical system OL5, the lens surfaces No. 12, No. 13, and No. 17 are formed aspherically. Table 14 below shows the surface number m and aspheric data, i.e., the conic constant K and the values of each aspheric constant A4 to A12.

(Table 14)
[Aspheric data]
Face 12 K = 1.00000e+00
A4 = 2.55005e-05 A6 = 2.68082e-07 A8 = -4.15521e-09
A10= 1.91843e-11 A12=-7.32920e-14
Face 13 K = 1.00000e+00
A4 = 2.69977e-05 A6 = 2.93612e-07 A8 = -3.82736e-09
A10= 0.00000e+00 A12= 0.00000e+00
Face 17 K = 1.00000e+00
A4 =-8.70020e-05 A6 =-1.11329e-08 A8 =-4.28635e-09
A10=-1.69867e-11 A12=0.00000e+00

In this optical system OL5, the axial air spacing D6 between the first lens group G1 and the second lens group G2, and the axial air spacing D19 between the second lens group G2 and the filter group FL change during focusing. The following Table 15 shows the variable spacings when focusing at infinity and when focusing at close range.

Table 15
Infinity Near distance D0 ∞ 168.61
β - -0.1500
f 24.28 -
D6 8.511 4.746
D19 10.813 14.578

Figure 10 shows the spherical aberration, astigmatism, distortion, chromatic aberration of magnification, and coma aberration diagrams for this optical system OL5 when focused at infinity and when focused at a close distance. From these aberration diagrams, it can be seen that the various aberrations of this optical system OL5 are well corrected.

[Conditional expression corresponding value]
The corresponding values of the conditional expressions (1) to (12) in the first to fifth embodiments are shown in Table 16 below.

Table 16
(1) LA/LB
(2) LAS/LAB
(3) LNRL/LB
(4) R2NR/Bfa
(5) LNFL/LB
(6) R1NF/Bfa
(7) (R1NF+R2NR)/(R1NF-R2NR)
(8) fNF/fNR
(9) fN1/fNL
(10) LASI/LAB
(11) LASL/LAB
(12) fB/f

1st Example 2nd Example 3rd Example 4th Example 5th Example f 18.663 24.208 23.987 24.645 24.278
fB 19.882 25.239 26.058 33.313 28.463
fNR -22.746 -33.387 -33.640 -39.597 -33.066
fNF -11.895 -14.814 -17.895 -18.325 -21.138
fN1 -29.572 -41.054 -57.817 -63.929 -38.152
fNL -64.585 -52.138 -89.777 -84.301 -94.584
LA 6.839 4.591 5.107 5.556 4.404
LB 25.931 23.667 23.493 22.623 22.071
LAB 36.809 35.903 37.002 36.988 36.587
LAS 9.000 6.424 6.716 6.556 6.005
LASI 15.563 15.351 12.445 13.667 14.068
LASL 1.970 1.800 0.000 1.200 1.200
Bfa 13.593 13.551 12.445 12.467 12.868
LNRL 7.173 7.068 7.363 5.237 4.377
R2NR 28.222 14.306 16.623 23.507 22.000
LNFL 22.496 23.667 23.493 22.623 22.071
R1NF -17.745 -12.840 -11.098 -10.066 -10.351

(1) 0.264 0.194 0.217 0.246 0.200
(2) 0.245 0.179 0.182 0.177 0.164
(3) 0.277 0.299 0.313 0.231 0.198
(4) 2.076 1.056 1.336 1.886 1.710
(5) 0.868 1.000 1.000 1.000 1.000
(6) -1.305 -0.948 -0.892 -0.807 -0.804
(7) -0.228 -0.054 -0.199 -0.400 -0.360
(8) 0.523 0.444 0.532 0.463 0.639
(9) 0.458 0.787 0.644 0.758 0.403
(10) 0.423 0.428 0.336 0.369 0.385
(11) 0.054 0.050 0.000 0.032 0.033
(12) 1.065 1.043 1.086 1.352 1.172

In addition, the contents described below can be adopted as appropriate to the extent that they do not impair optical performance.

In this embodiment, an optical system OL having a two-group or three-group configuration is shown, but the above configuration conditions can also be applied to other group configurations such as four groups or five groups. 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 also be used. Specifically, a configuration in which a lens group whose position relative to the image surface is fixed when zooming or focusing is added closest to the image side can be considered. A lens group refers to a portion having at least one lens separated by an air gap that changes when zooming or focusing. A lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

In addition, a single or multiple lens groups, or a partial lens group, may be moved in the optical axis direction to form a focusing group that focuses from an infinitely distant object to a close-distance object. In this case, the focusing group can also be applied to autofocusing, and is also suitable for driving a motor (such as an ultrasonic motor) for autofocusing. In particular, it is preferable to use the second lens group G2 as the focusing group, and to fix the positions of the other lenses relative to the image plane when focusing, but the entire optical system OL may be moved in the optical axis direction to focus. Considering the load on the motor, it is preferable for the focusing group to be composed of a single lens.

In addition, a lens group or a partial lens group may be moved so as to have a displacement component perpendicular to the optical axis, or rotated (rocked) in a plane including the optical axis to serve as an anti-vibration group that corrects image blur caused by camera shake. In particular, it is preferable to use at least a part of the first lens group G1 or the second lens group G2 as an anti-vibration group.

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

It is preferable that the aperture stop S be disposed between the first lens group G1 and the second lens group G2, but it is also possible to use the lens frame to fulfill this role without providing a component serving as an aperture stop.

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

1 Camera (optical device) OS (OS1 to OS5) Optical system GA Front group GB Rear group S Aperture (aperture stop)

Claims (9)

From the object side,
The front group and
Aperture and
a rear group having positive refractive power;
the rear group is composed of a second lens group having positive refractive power, or, in order from the object side, a second lens group having positive refractive power and a third lens group having negative refractive power;
During focusing, the front lens group is fixed relative to an image plane, and the second lens group moves in the optical axis direction.
The following condition is satisfied :
0.100 < LA/LB ≦ 0.264
however,
LA: the distance on the optical axis from the lens surface of the front group closest to the object to the lens surface of the front group closest to the image when focusing at infinity LB: the distance on the optical axis from the lens surface of the rear group closest to the object to the lens surface of the rear group closest to the image when focusing at infinity
The rear group is
a negative lens NR having the largest refractive power among the negative lenses satisfying the condition of the following formula;
and a negative lens NF having the largest refractive power among the negative lenses satisfying the condition of the following formula:
0.000 < LNRL/LB < 0.400
0.800 < R2NR/Bfa < 3.000
0.600 < LNFL/LB ≦ 1.000
-3.000 < R1NF/Bfa < -0.500
however,
LB: the distance on the optical axis from the lens surface of the rear group closest to the object to the lens surface closest to the image when focusing at infinity
LNRL: the distance on the optical axis from the image-side lens surface of the negative lens NR to the lens surface of the rear group closest to the image side when focusing at infinity
R2NR: radius of curvature of the image-side lens surface of the negative lens NR
LNFL: the distance on the optical axis from the object side lens surface of the negative lens NF to the lens surface of the rear group closest to the image side when focusing at infinity
R1NF: radius of curvature of the lens surface on the object side of the negative lens NF
Bfa: Back focus (air equivalent length) of the optical system when focused at infinity
the front group has at least one negative lens N1,
the rear group has at least one negative lens NL on the image side of the negative lens NR,
An optical system that satisfies the following condition:
0.300 < fN1/fNL < 1.200
however,
fN1: focal length of the negative lens N1
fNL: focal length of the negative lens NL 2. The optical system according to claim 1, which satisfies the following condition:
-0.800<(R1NF+R2NR)/(R1NF-R2NR)<0.800
however,
R1NF: radius of curvature of the lens surface on the object side of the negative lens NF R2NR: radius of curvature of the lens surface on the image side of the negative lens NR 3. The optical system according to claim 1, which satisfies the following condition:
0.200 < fNF/fNR < 1.200
however,
fNF: focal length of the negative lens NF fNR: focal length of the negative lens NR 4. The optical system according to claim 1, wherein the rear group has at least two positive lenses between the negative lens NF and the negative lens NR. 5. The optical system according to claim 1, which satisfies the following condition:
0.070 < LAS/LAB < 0.300
however,
LAS: the distance on the optical axis from the lens surface of the front group closest to the object to the aperture when focusing at infinity LAB: the distance on the optical axis from the lens surface of the front group closest to the object to the lens surface of the rear group closest to the image when focusing at infinity the rear group includes an aspheric lens;
6. The optical system according to claim 1, which satisfies the following condition:
0.100 < LASI/LAB < 0.600
however,
LASI: the distance on the optical axis from the aspheric surface located closest to the image side in the rear group to the image surface when focusing at infinity. LAB: the distance on the optical axis from the lens surface of the front group closest to the object side to the lens surface of the rear group closest to the image side when focusing at infinity. the rear group includes an aspheric lens;
7. The optical system according to claim 1, which satisfies the following condition:
0.000 ≦ LASL/LAB < 0.150
however,
LASL: the distance on the optical axis from the aspheric surface located closest to the image in the rear group to the lens surface closest to the image in the rear group when focusing at infinity. LAB: the distance on the optical axis from the lens surface closest to the object in the front group to the lens surface closest to the image in the rear group when focusing at infinity. 8. The optical system according to claim 1, which satisfies the following condition:
0.800 < fB/f < 1.600
however,
fB: focal length of the rear group when focusing at infinity f: focal length of the entire system when focusing at infinity An optical instrument comprising the optical system according to any one of claims 1 to 8 .

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