JP2013025175A - Optical system, optical device having the same, and method for manufacturing optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system having excellent optical performance, an optical device having the optical system, and a method for manufacturing the optical system.SOLUTION: An optical system OS used for a camera 1 or the like comprises, in order from an object side: a first lens group G1 having a positive refractive power; a second lens group G2 having a positive refractive power; and a third lens group G3 having a positive refractive power. The second lens group G2 has an aperture stop S and a front group G2F comprising at least one lens disposed at the object side of the aperture stop S and having a positive refractive power. In focusing, the first lens group G1 and the third lens group G3 are fixed with respect to an image plane, and the second lens group G2 moves along the optical axis.

Description

  The present invention relates to an optical system, an optical apparatus having the optical system, and a method for manufacturing the optical system.

  2. Description of the Related Art Conventionally, an inner focus type optical system suitable for shortening the autofocus speed of a photographic camera, an electronic still camera, a video camera, or the like has been proposed (for example, see Patent Document 1).

Japanese Patent Laid-Open No. 7-199066

  However, the conventional optical system has a problem that the power arrangement between the in-focus group and the other groups is not optimized, and good optical performance cannot be achieved from infinity to the closest distance.

  The present invention has been made in view of such a problem, and an object thereof is to provide an optical system having good optical performance, an optical apparatus having the optical system, and a method for manufacturing the optical system.

In order to solve the above problems, an optical system according to the present invention has, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a positive refractive power. A third lens group, and the second lens group includes an aperture stop, and a front group that includes at least one lens disposed on the object side of the aperture stop and has a positive refractive power; In focusing, the first lens group and the third lens group are fixed with respect to the image plane, and the second lens group moves along the optical axis, and satisfies the following conditional expression: And
0.50 <f21 / f2 <18.00
However,
f21: Focal length of the front group f2: Focal length of the second lens group

Such an optical system preferably satisfies the following conditional expression.
0.50 <f21 / f <20.00
However,
f: Focal length of the entire system when focusing on infinity

Such an optical system preferably satisfies the following conditional expression.
0.20 <f3 / f2 <7.80
However,
f3: focal length of the third lens unit

Such an optical system preferably satisfies the following conditional expression.
0.30 <f3 / f <6.00
However,
f3: focal length of the third lens group f: focal length of the entire system when focusing on infinity

Such an optical system preferably satisfies the following conditional expression.
0.50 <f2 / f <2.00
However,
f: Focal length of the entire system when focusing on infinity

Such an optical system preferably satisfies the following conditional expression.
1.90 <f1 / f <50.00
However,
f1: Focal length of the first lens unit f: Focal length of the entire system when focusing on infinity

Such an optical system preferably satisfies the following conditional expression.
0.40 <f1 / f3 <20.00
However,
f1: Focal length of the first lens group f3: Focal length of the third lens group

  In such an optical system, it is preferable that the second lens group has a positive lens closest to the object side.

Such an optical system preferably satisfies the following conditional expression.
0.30 <r1 / f2 <15.00
However,
r1: radius of curvature of the object side surface of the positive lens of the second lens group

  In such an optical system, it is preferable that the first lens group has two positive lenses in order from the object side.

  In such an optical system, it is preferable that the most image side lens of the second lens group has a biconvex shape.

  In such an optical system, it is preferable that all lens surfaces be spherical or flat.

  An optical apparatus according to the present invention includes any one of the above optical systems.

The optical system manufacturing method according to the present invention includes a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens having a positive refractive power in order from the object side. A first lens group, and an aperture stop and at least one lens disposed on the object side of the aperture stop, and has a positive refractive power. A second lens group having a front group and a third lens group are arranged, and in focusing, the first lens group and the third lens group are fixed with respect to the image plane, and the second lens group is placed on the optical axis. It arrange | positions so that it may move along, and it arrange | positions so that the following conditional expressions may be satisfied.
0.50 <f21 / f2 <18.00
However,
f21: Focal length of the front group f2: Focal length of the second lens group

  ADVANTAGE OF THE INVENTION According to this invention, the optical system which has favorable optical performance, the optical apparatus which has this optical system, and the manufacturing method of an optical system can be provided.

It is sectional drawing which shows the structure of the optical system which concerns on 1st Example. FIG. 5A is a diagram illustrating various aberrations of the optical system according to Example 1, where (a) shows an infinite focus state and (b) shows a short distance focus state (D0 = 700 mm). It is sectional drawing which shows the structure of the optical system which concerns on 2nd Example. FIG. 5A is a diagram illustrating various aberrations of the optical system according to Example 2, wherein (a) shows an infinite focus state and (b) shows a short distance focus state (D0 = 700 mm). It is sectional drawing which shows the structure of the optical system which concerns on 3rd Example. FIG. 6A is a diagram illustrating various aberrations of the optical system according to Example 3, wherein (a) shows an infinitely focused state, and (b) shows a short-range focused state (D0 = 700 mm). It is sectional drawing which shows the structure of the optical system which concerns on 4th Example. FIG. 7A is a diagram illustrating various aberrations of the optical system according to Example 4, where (a) shows an infinitely focused state, and (b) shows a short-range focused state (D0 = 700 mm). It is sectional drawing which shows the structure of the optical system which concerns on 5th Example. FIG. 7A is a diagram illustrating various aberrations of the optical system according to Example 5, wherein (a) shows an infinite focus state, and (b) shows a short distance focus state (D0 = 700 mm). 1 is a cross-sectional view of a camera equipped with an optical system according to the present embodiment. It is a flowchart for demonstrating the manufacturing method of the optical system which concerns on this embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the optical system OS according to this embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a positive And a third lens group G3 having refractive power. The second lens group G2 includes an aperture stop S, and a front group G2F that includes at least one lens disposed on the object side of the aperture stop S and has a positive refractive power. With this configuration, it is possible to satisfactorily correct the downsizing of the lens barrel and each aberration. In the optical system OS, when focusing on an object at a short distance from infinity, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane, and the second lens group G2 is along the optical axis. Move. With such a configuration, it is possible to satisfactorily correct the aberration variation of the lens barrel and focusing.

  Moreover, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (1).

0.50 <f21 / f2 <18.00 (1)
However,
f2: Focal length of second lens group G2 f21: Focal length of front group G2F

  Conditional expression (1) defines the ratio of the focal length f21 of the front group G2F having the positive refractive power disposed on the most object side of the second lens group G2 and the focal length f2 of the second lens group G2. It is. This optical system OS can realize good optical performance by satisfying conditional expression (1).

  If the upper limit value of the conditional expression (1) is exceeded, the refractive power of the front group G2F arranged closest to the object side of the second lens group G2 becomes strong, and the spherical aberration is overcorrected when focusing on a close object. Therefore, the field curvature is insufficiently corrected, and it becomes difficult to simultaneously correct the spherical aberration and the field curvature. Further, the refractive power of the second lens group G2 becomes weak, the amount of focusing movement increases, and the total length of the optical system increases, which is not preferable. Note that the effect of the present application can be ensured by setting the upper limit of conditional expression (1) to 15.00. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (1) to 12.00.

  If the lower limit value of conditional expression (1) is not reached, the refractive power of the front group G2F arranged closest to the object side of the second lens group G2 becomes weak, and spherical aberration is corrected when focusing on an object at close range. Insufficient field curvature is overcorrected, making it difficult to correct spherical aberration and field curvature simultaneously. The effect of the present application can be ensured by setting the lower limit value of conditional expression (1) to 0.60. More preferably, the effect of this application can be made more reliable by setting the lower limit value of conditional expression (1) to 0.70.

  Moreover, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (2).

0.50 <f21 / f <20.00 (2)
However,
f21: Focal length of the front group G2F of the second lens group G2 f: Focal length of the entire system when focusing on infinity

  Conditional expression (2) is a ratio of the focal length f21 of the front group G2F having the positive refractive power disposed on the most object side of the second lens group G2 and the focal length f of the entire system in the infinite focus state. It prescribes. This optical system OS can realize good optical performance by satisfying conditional expression (2).

  If the upper limit value of the conditional expression (2) is exceeded, the refractive power of the front group G2F disposed closest to the object side of the second lens group G2 becomes strong, and the spherical aberration is overcorrected when focusing on a close object. Therefore, the field curvature is insufficiently corrected, and it becomes difficult to simultaneously correct the spherical aberration and the field curvature. In addition, the refractive power of the second lens group G2 is weakened, and the amount of focusing movement is increased, which increases the total length of the optical system OS, which is not preferable. The effect of the present application can be ensured by setting the upper limit value of conditional expression (2) to 18.00. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (2) to 15.00.

  If the lower limit value of conditional expression (2) is not reached, the refractive power of the front group G2F arranged closest to the object side of the second lens group G2 becomes weak, and spherical aberration is corrected when focusing on a close-range object. Insufficient field curvature is overcorrected, making it difficult to correct spherical aberration and field curvature simultaneously. The effect of the present application can be ensured by setting the lower limit of conditional expression (2) to 0.80. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (2) to 1.00.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (3).

0.20 <f3 / f2 <7.80 (3)
However,
f2: Focal length of the second lens group G2 f3: Focal length of the third lens group G3

  Conditional expression (3) defines the ratio between the focal length f3 of the third lens group G3 and the focal length f2 of the second lens group G2. This optical system OS can realize good optical performance by satisfying conditional expression (3).

  If the upper limit value of the conditional expression (3) is exceeded, the refractive power of the second lens group G2 becomes strong, and when focusing on a close object, the spherical aberration is overcorrected and the field curvature is undercorrected. It becomes difficult to correct the curvature of field at the same time. Note that the effect of the present application can be ensured by setting the upper limit of conditional expression (3) to 7.10. More preferably, the effect of the present application can be further ensured by setting the upper limit of conditional expression (3) to 6.40.

  If the lower limit of conditional expression (3) is not reached, the refractive power of the third lens group G3 becomes strong, and when focusing on a close object, the spherical aberration is insufficiently corrected and the curvature of field becomes excessively corrected. It becomes difficult to correct aberration and curvature of field simultaneously. In addition, the refractive power of the second lens group G2 is weakened, and the amount of focusing movement is increased, which increases the total length of the optical system OS, which is not preferable. The effect of the present application can be ensured by setting the lower limit of conditional expression (3) to 0.60. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (3) to 1.00.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (4).

0.30 <f3 / f <6.00 (4)
However,
f3: focal length of the third lens group G3 f: focal length of the entire system when focusing on infinity

  Conditional expression (4) defines the ratio between the focal length f2 of the second lens group G2 and the focal length f of the entire system in the infinitely focused state. The present optical system OS can realize good optical performance from infinity to the closest distance by satisfying conditional expression (4).

  If the lower limit value of the conditional expression (4) is not reached, the refractive power of the third lens group G3 becomes strong, and when focusing on an object at a close distance, the spherical aberration is insufficiently corrected and the field curvature becomes excessively corrected. It becomes difficult to correct the curvature of field at the same time. The effect of the present application can be ensured by setting the lower limit of conditional expression (4) to 0.80. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (4) to 1.30.

  If the upper limit of conditional expression (4) is exceeded, the refractive power of the third lens group G3 becomes weak, and when focusing on an object at a close distance, the spherical aberration is overcorrected and the field curvature is undercorrected. It becomes difficult to correct aberration and curvature of field simultaneously. The effect of the present application can be ensured by setting the upper limit value of conditional expression (4) to 5.50. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (4) to 5.00.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (5).

0.50 <f2 / f <2.00 (5)
However,
f2: focal length of the second lens group G2 f: focal length of the entire system when focusing on infinity

  Conditional expression (5) defines the ratio between the focal length f2 of the second lens group G2 and the focal length f of the entire system in the infinitely focused state. The present optical system OS can realize good optical performance from infinity to a close range by satisfying conditional expression (5).

  If the lower limit value of conditional expression (5) is not reached, the refractive power of the second lens group G2 becomes strong, and it becomes difficult to correct the variation in spherical aberration during focusing. Note that the effect of the present application can be ensured by setting the lower limit of conditional expression (5) to 0.60. More preferably, the effect of this application can be made more reliable by setting the lower limit value of conditional expression (5) to 0.70.

  If the upper limit of conditional expression (5) is exceeded, the refractive power of the second lens group G2 becomes weak, the amount of focusing movement increases, and the overall length of the optical system OS increases. In addition, it becomes difficult to correct spherical aberration and curvature of field. Note that the effect of the present application can be ensured by setting the upper limit of conditional expression (5) to 1.70. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (5) to 1.50.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (6).

1.90 <f1 / f <50.00 (6)
However,
f1: Focal length of the first lens group G1 f: Focal length of the entire system when focusing on infinity

  Conditional expression (6) defines the ratio between the focal length f1 of the first lens group G1 and the focal length f of the entire system in the infinitely focused state. This optical system OS can realize good optical performance by satisfying conditional expression (6).

  If the upper limit value of the conditional expression (6) is exceeded, the refractive power of the first lens group G1 becomes weak, and it becomes difficult to correct focusing fluctuations of spherical aberration and field curvature. Note that the effect of the present application can be ensured by setting the upper limit of conditional expression (6) to 20.00. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (6) to 10.00.

  On the other hand, if the lower limit of conditional expression (6) is not reached, the refractive power of the first lens group G1 becomes strong and it becomes difficult to correct spherical aberration. In addition, the effect of this application can be made reliable by making the lower limit of conditional expression (6) into 2.00. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (6) to 2.10.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (5).

0.40 <f1 / f3 <20.00 (7)
However,
f1: Focal length of the first lens group G1 f3: Focal length of the third lens group G3

  Conditional expression (7) defines the ratio between the focal length f1 of the first lens group G1 and the focal length f3 of the third lens group G3. This optical system OS can realize good optical performance by satisfying conditional expression (7).

  If the upper limit of conditional expression (7) is exceeded, the refractive power of the third lens group G3 becomes strong, and when focusing on a close-range object, the spherical aberration is insufficiently corrected and the curvature of field becomes excessively corrected. It becomes difficult to correct the curvature of field at the same time. In addition, the effect of this application can be made reliable by making the upper limit of conditional expression (7) into 12.00. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (7) to 5.00.

  On the other hand, if the lower limit of conditional expression (7) is not reached, the refractive power of the first lens group G1 becomes strong and it becomes difficult to correct spherical aberration. Note that the effect of the present application can be ensured by setting the lower limit of conditional expression (7) to 0.45. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (7) to 0.50.

  In the optical system OS according to the present embodiment, it is desirable that the second lens group G2 has a positive lens closest to the object side (for example, a positive meniscus lens L21 in FIG. 1). With such a configuration, it is possible to satisfactorily correct spherical aberration fluctuations accompanying focusing.

  In addition, it is desirable that the optical system OS according to the present embodiment satisfies the following conditional expression (8).

0.30 <r1 / f2 <15.00 (8)
However,
r1: radius of curvature of the object side surface of the positive lens arranged closest to the object side in the second lens group G2 f2: focal length of the second lens group G2

  Conditional expression (8) defines the ratio between the radius of curvature r1 of the object side surface of the positive lens disposed closest to the object side of the second lens group G2 and the focal length f2 of the second lens group G2. This optical system OS can realize good optical performance by satisfying conditional expression (8).

  If the upper limit value of conditional expression (8) is exceeded, it will be difficult to correct variations in spherical aberration and coma due to focusing. Note that the effect of the present application can be ensured by setting the upper limit of conditional expression (8) to 10.00. More preferably, the effect of this application can be made more reliable by setting the upper limit of conditional expression (8) to 5.00.

  If the lower limit of conditional expression (8) is not reached, it will be difficult to correct fluctuations in spherical aberration and coma due to focusing. The effect of the present application can be ensured by setting the lower limit value of conditional expression (8) to 0.40. More preferably, the effect of this application can be made more reliable by setting the lower limit of conditional expression (8) to 0.50.

  Further, it is desirable that the first lens group G1 of the optical system OS according to the present embodiment has two positive lenses in order from the object side (for example, a positive meniscus lens L11 and a positive meniscus lens L12 in FIG. 1). With such a configuration, it is possible to satisfactorily correct spherical aberration, field curvature, and coma.

  In addition, it is desirable that the most image side lens of the second lens group G2 of the optical system OS according to the present embodiment has a biconvex shape (for example, a biconvex lens L24 in FIG. 1). With such a configuration, spherical aberration and coma can be favorably corrected.

  In addition, it is desirable that all lens surfaces of the optical system OS according to the present embodiment be spherical or flat. With such a configuration, lens processing is facilitated, and aberration fluctuations due to processing errors can be reduced.

  Next, a camera equipped with the optical system OS of the present application will be described with reference to FIG. FIG. 11 is a diagram illustrating a configuration of a camera including the optical system OS of the present application. As shown in FIG. 11, the camera 1 is a so-called mirrorless camera of an interchangeable lens provided with the above-described optical system OS as a photographing lens 2. In the camera 1, light from an object (subject) (not shown) is collected by the photographing lens 2 and is on the imaging surface of the imaging unit 3 via an OLPF (Optical low pass filter) (not shown). A subject image is formed on the screen. Then, the subject image is photoelectrically converted by the 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. Thus, the photographer can observe the subject via the EVF 4.

  Further, when a release button (not shown) is pressed by the photographer, an image photoelectrically converted by the imaging unit 3 is stored in a memory (not shown). In this way, the photographer can shoot the subject with the camera 1. In this embodiment, an example of a mirrorless camera has been described. However, an optical system OS according to this embodiment is mounted on a single-lens reflex camera that has a quick return mirror in the camera body and observes a subject using a finder optical system. Even in this case, the same effect as the camera 1 can be obtained.

  The contents described below can be appropriately adopted as long as the optical performance is not impaired.

  In the present embodiment, the optical system OS having the three-group configuration is shown, but the above-described configuration conditions and the like can be applied to other group configurations such as the fourth group and the fifth group. Further, a configuration in which a lens or a lens group is added to the most object side, or a configuration in which a lens or a lens group is added to the most image side may be used. The lens group refers to a portion having at least one lens separated by an air interval that changes during focusing.

  The second lens group G2, which is the focusing lens group described above, can also be applied to autofocus and is also suitable for driving a motor for autofocus (using an ultrasonic motor or the like).

  Also, by moving the lens group or partial lens group so that it has a component in the direction perpendicular to the optical axis, or rotating (swinging) in the in-plane direction including the optical axis, image blur caused by camera shake is corrected. An anti-vibration lens group may be used. In particular, it is preferable that at least a part of the two lenses on the image side from the aperture stop S of the second lens group G2 is an anti-vibration lens group.

  The lens surface may be formed as an aspheric surface. When the lens surface is an aspheric surface, the aspheric surface is an aspheric surface by grinding, a glass mold aspheric surface made of glass with an aspheric shape, or a composite aspheric surface made of resin with an aspheric shape on the glass surface. Any aspherical surface may be used. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

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

  Hereinafter, an outline of a method for manufacturing the optical system OS of the present embodiment will be described with reference to FIG. First, each lens is arranged and a lens group is prepared (step S100). Specifically, in this embodiment, for example, as shown in FIG. 1, in order from the object side, a positive meniscus lens L11 having a convex surface facing the object side, a positive meniscus lens L12 having a convex surface facing the object side, A positive meniscus lens L13 having a convex surface and a negative meniscus lens L14 having a convex surface facing the object side are arranged as a first lens group G1, and a positive meniscus lens L21 having a convex surface facing the object side is sequentially arranged from the object side. The arranged front group G2F, an aperture stop S, a biconcave lens L22, a positive meniscus lens L23 having a convex surface facing the image side, and a rear group G2R having a biconvex lens L24 are arranged to form a second lens group G2. A cemented negative lens CL31 composed of a positive meniscus lens L31 having a convex surface facing the object side and a negative meniscus lens L32 having a convex surface facing the object side, and a convex surface facing the object side The third lens group G3 are arranged meniscus lens L33. The lens groups prepared in this way are arranged to manufacture the optical system OS.

  At this time, in focusing, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane, and the second lens group G2 is arranged to move along the optical axis (step S200). In addition, the first lens group G1, the second lens group G2, and the third lens group G3 are arranged so that the conditional expression (1) is satisfied (step S300).

  Hereinafter, each example of the present application will be described with reference to the drawings. 1, 3, 5, 7, and 9 show the configuration of the optical system OS (OS1 to OS5) according to each embodiment and each lens group in the change of the focusing state from infinity to a close object. It is sectional drawing which shows the mode of movement of.

[First embodiment]
FIG. 1 is a diagram illustrating a configuration of an optical system OS1 according to the first example. The optical system OS1 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, It is comprised. The first lens group G1, in order from the object side, includes a positive meniscus lens L11 having a convex surface directed toward the object side, a positive meniscus lens L12 having a convex surface directed toward the object side, a positive meniscus lens L13 having a convex surface directed toward the object side, and It is composed of a negative meniscus lens L14 having a convex surface facing the object side. The second lens group G2 includes, in order from the object side, a front group G2F having a positive refractive power, an aperture stop S, and a rear group G2R. The front group G2F has a positive surface with a convex surface facing the object side. Consists of a meniscus lens L21, and the rear group G2R includes, in order from the object side, a biconcave lens L22, a positive meniscus lens L23 having a convex surface facing the image side, and a biconvex lens L24. The third lens group G3 includes, in order from the object side, a cemented negative lens CL31 including a positive meniscus lens L31 having a convex surface facing the object side and a negative meniscus lens L32 having a convex surface facing the object side, and a convex surface facing the object side. From the positive meniscus lens L33.

  Thus, in the optical system OS1 according to the first example, the first lens group G1 includes two positive lenses (a positive meniscus lens L11 and a positive meniscus lens L12) arranged in order from the object side. In the second lens group G2, the positive lens (positive meniscus lens L21) is disposed closest to the object side, and the lens closest to the image side has a biconvex shape (biconvex lens L24). Further, all lens surfaces of the optical system OS1 are constituted by spherical surfaces or flat surfaces.

  A filter group FL is disposed between the optical system OS1 and the image plane I.

  In the optical system OS1 according to the first example having such a configuration, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane, and the second lens group G3 is fixed at the time of focusing from infinity to a close object. The lens group G2 moves in the object direction along the optical axis. The aperture stop S moves together with the second lens group G2 when focusing.

  Table 1 below lists values of specifications of the optical system OS1 according to the first example. In the overall specifications of Table 1, f is the focal length of the entire system, FNO is the F number, ω is the half field angle, Y is the image height, TL is the full length, and Bf is the back focus. Note that the total length TL indicates the distance on the optical axis from the most object side lens surface (first surface) to the image plane I when focusing on infinity, and the back focus is the most image side lens surface (22nd lens surface). The distance on the optical axis from the surface) to the image plane I is shown. In the lens data, the first column m indicates the order (surface number) of the lens surfaces from the object side along the light traveling direction, the second column r indicates the curvature radius of each optical surface, and the third column d. Indicates the distance (surface distance) on the optical axis from each optical surface to the next optical surface, and the fourth column nd and the fifth column νd indicate the refractive index and Abbe number for the d-line (λ = 587.6 nm), respectively. ing. The surface numbers 1 to 24 shown in Table 1 correspond to the numbers 1 to 24 shown in FIG. A curvature radius of 0.0000 indicates a plane on the lens surface and an aperture on the aperture stop S. Further, the refractive index of air of 1.0000 is omitted. The lens group focal length indicates the surface number and focal length of the start surface of each of the first to third lens groups G1 to G3. Here, “mm” is generally used for the focal length, the radius of curvature, the surface interval, and other length units listed in all the following specifications, but the optical system is proportionally enlarged or reduced. However, the same optical performance can be obtained, and the present invention is not limited to this. The description of these symbols and the description of the specification table are the same in the following embodiments.

(Table 1)
[Overall specifications]
f = 32.30
FNO = 1.23
ω = 13.97
Y = 8.00
TL = 61.93
Bf = 14.10

[Lens data]
m r d nd νd
1 58.9509 2.7624 1.81600 46.63
2 296.6226 0.1000
3 30.8042 2.7169 1.83481 42.72
4 68.4943 0.1000
5 20.8894 2.8130 1.83400 37.17
6 21.5342 2.5000
7 56.1565 1.7000 1.78472 25.68
8 16.3967 d1
9 99.9914 1.3939 1.72916 54.66
10 961.1485 1.6042
11 0.0000 3.6310 Aperture stop S
12 -15.7157 1.2000 1.69895 30.13
13 40.0528 1.4252
14 -307.9409 2.5406 1.88300 40.77
15 -39.7561 0.1000
16 61.5510 4.0998 1.81600 46.63
17 -24.1299 d2
18 18.9404 3.4997 1.83481 42.72
19 78.3470 1.5000 1.74077 27.79
20 14.0997 2.2371
21 33.6753 2.2809 1.90265 35.71
22 215.9000 10.8099
23 0.0000 2.7900 1.51680 64.12
24 0.0000 0.5000

[Lens focal length]
Lens group Start surface Focal length 1st lens group 1 126.08
Second lens group 9 42.03
Third lens group 18 59.00

  In the first example, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 are from infinity. Changes when focusing on short-range objects. Table 2 below shows variable intervals when focusing on infinity and focusing on a short-distance object. In Table 2, D0 represents the distance from the lens surface (first surface) closest to the object of the optical system OS1 to the object. The description of this variable interval is the same in the following embodiments.

(Table 2)
Infinity Short distance D0 ∞ 700.0000
d1 8.5270 4.3965
d2 1.1000 5.2305

  Table 3 below shows values corresponding to the respective conditions of the optical system OS1 according to the first example. In Table 3, f is the focal length of the entire system, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, and f21 is the front group of the second lens group G2. G2F represents the focal length, f3 represents the focal length of the third lens group G3, and r1 represents the radius of curvature of the object side surface of the positive lens disposed closest to the object side of the second lens group G2. The description of the above symbols is the same in the following embodiments.

(Table 3)
f21 = 153.0
(1) f21 / f2 = 3.64
(2) f21 / f = 4.74
(3) f3 / f2 = 1.40
(4) f3 / f = 1.83
(5) f2 / f = 1.30
(6) f1 / f = 3.90
(7) f1 / f3 = 2.14
(8) r1 / f2 = 2.38

  Note that r1 in the conditional expression (6) corresponds to the radius of curvature of the ninth surface. Thus, the optical system OS1 according to the first example satisfies all the conditional expressions (1) to (8).

  FIG. 2 shows spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration in the infinite focus state and the short distance object focus state (D0 = 700 mm) of the optical system OS1 according to the first embodiment. The aberration diagrams of are shown. In each aberration diagram, FNO is the F number, NA is the numerical aperture, Y is the image height with respect to the half field angle, d is the d-line (λ = 587.6 nm), and g is the g-line (λ = 435.6 nm). ) Respectively. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. Further, the coma aberration diagram shows the aberration with respect to the image height Y. The explanation of these aberration diagrams is the same in the following examples. As apparent from the respective aberration diagrams shown in FIG. 2, in the optical system OS1 according to the first example, various aberrations are satisfactorily corrected in each state from the infinitely focused state to the short-distance object focused state, It can be seen that the imaging performance is excellent.

[Second Embodiment]
FIG. 3 is a diagram illustrating a configuration of the optical system OS2 according to the second embodiment. The optical system OS2 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, It is comprised. The first lens group G1 includes, in order from the object side, a biconvex lens L11, a positive meniscus lens L12 having a convex surface facing the object side, and a negative meniscus lens L13 having a convex surface facing the object side. The second lens group G2 includes a front group G2F having a positive refractive power, an aperture stop S, and a rear group G2R in order from the object side. The front group G2F is arranged in order from the object side to the object side. The rear lens group G2R is composed of a cemented positive lens CL21 of a biconcave lens L23 and a biconvex lens L24, and a biconvex lens L25 in this order from the object side. The The third lens group G3 includes, in order from the object side, a cemented negative lens CL31 including a positive meniscus lens L31 having a convex surface directed toward the image side and a biconcave lens L32, and a biconvex lens L33.

  Thus, in the optical system OS2 according to the second example, in the first lens group G1, two positive lenses (biconvex lens L11 and positive meniscus lens L12) are arranged in order from the object side. In the second lens group G2, the positive lens (positive meniscus lens L21) is disposed closest to the object side, and the lens closest to the image side has a biconvex shape (biconvex lens L25). Further, all lens surfaces of the optical system OS2 are constituted by spherical surfaces or flat surfaces.

  A filter group FL is disposed between the optical system OS2 and the image plane I.

  In the optical system OS2 according to the second example having such a configuration, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane when focusing from infinity to a close object, and the second The lens group G2 moves in the object direction along the optical axis. The aperture stop S moves together with the second lens group G2 when focusing.

  Table 4 below lists values of specifications of the optical system OS2 according to the second example. The surface numbers 1 to 24 shown in Table 4 correspond to the numbers 1 to 24 shown in FIG.

(Table 4)
[Overall specifications]
f = 31.50
FNO = 1.23
ω = 14.33
Y = 8.00
TL = 54.30
Bf = 13.70

[Lens data]
m r d nd νd
1 36.5576 4.5395 1.51680 64.10
2 -179.0694 0.1000
3 15.9667 4.5519 1.83480 42.72
4 30.4447 0.6098
5 37.6030 1.8631 1.67270 32.11
6 10.5289 d1
7 29.2292 1.6293 1.80400 46.58
8 74.2437 1.6887
9 -24.1013 1.0000 1.64768 33.80
10 23.7658 2.0921
11 0.0000 1.1570 Aperture stop S
12 -173.1509 1.1997 1.67270 32.11
13 23.8072 2.9707 1.83480 42.72
14 -41.4088 0.1000
15 32.6245 3.0534 1.77249 49.61
16 -41.4025 d2
17 -55.0447 1.9311 1.90366 31.27
18 -19.3923 1.5000 1.67270 32.11
19 16.7526 1.2805
20 21.3864 3.1896 1.83480 42.72
21 -85.7704 10.4124
22 0.0000 2.7900 1.51680 64.12
23 0.0000 0.5000

[Lens focal length]
Lens group Start surface Focal length 1st lens group 1 69.77
Second lens group 7 25.22
Third lens group 17 135.82

  In the second embodiment, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 are from infinity. Changes when focusing on short-range objects. Table 5 below shows variable intervals when focusing on infinity and focusing on a short-distance object.

(Table 5)
Infinity Short distance D0 ∞ 700.0000
d1 6.0410 4.3247
d2 0.1000 1.8162

  Table 6 below shows values corresponding to the respective conditions of the optical system OS2 according to the second example.

(Table 6)
f21 = 59.0
(1) f21 / f2 = 2.34
(2) f21 / f = 1.87
(3) f3 / f2 = 5.38
(4) f3 / f = 4.31
(5) f2 / f = 0.80
(6) f1 / f = 2.21
(7) f1 / f3 = 0.51
(8) r1 / f2 = 1.16

  Note that r1 in the conditional expression (8) corresponds to the radius of curvature of the seventh surface. As described above, the optical system OS2 according to the second example satisfies all the conditional expressions (1) to (8).

  FIG. 4 shows spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration in the infinite focus state and the short distance object focus state (D0 = 700 mm) of the optical system OS2 according to the second embodiment. The aberration diagrams of are shown. As apparent from the respective aberration diagrams shown in FIG. 4, in the optical system OS2 according to the second example, various aberrations are satisfactorily corrected in each state from the infinitely focused state to the short-distance object focused state, It can be seen that the imaging performance is excellent.

[Third embodiment]
FIG. 5 is a diagram illustrating a configuration of the optical system OS3 according to the third embodiment. The optical system OS3 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, It is comprised. The first lens group G1, in order from the object side, includes a positive meniscus lens L11 having a convex surface facing the object side, a positive meniscus lens L12 having a convex surface facing the object side, and a negative meniscus lens L13 having a convex surface facing the object side. Composed. The second lens group G2 includes, in order from the object side, a front group G2F having a positive refractive power, an aperture stop S, and a rear group G2R. The front group G2F includes a biconvex lens L21, and a rear lens group G21. The group G2R includes, in order from the object side, a biconcave lens L22, a positive meniscus lens L23 having a convex surface facing the image side, and a biconvex lens L24. The third lens group G3 includes, in order from the object side, a cemented negative lens CL31 of a biconvex lens L31 and a biconcave lens L32, and a positive meniscus lens L33 having a convex surface facing the object side.

  Thus, in the optical system OS3 according to the third example, the first lens group G1 includes two positive lenses (a positive meniscus lens L11 and a positive meniscus lens L12) arranged in order from the object side. In the second lens group G2, the positive lens (biconvex lens L21) is disposed closest to the object side, and the lens closest to the image side has a biconvex shape (biconvex lens L24). Further, all lens surfaces of the optical system OS3 are constituted by spherical surfaces or flat surfaces.

  A filter group FL is disposed between the optical system OS3 and the image plane I.

  In the optical system OS3 according to the third example having such a configuration, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane when focusing from infinity to a short distance object, and the second The lens group G2 moves in the object direction along the optical axis. The aperture stop S moves together with the second lens group G2 when focusing.

  Table 7 below provides values of specifications of the optical system OS3 according to the third example. The surface numbers 1 to 22 shown in Table 7 correspond to the numbers 1 to 22 shown in FIG.

(Table 7)
[Overall specifications]
f = 31.99
FNO = 1.23
ω = 14.11
Y = 8.00
TL = 64.25
Bf = 14.30

[Lens data]
m r d nd νd
1 31.5954 4.3000 1.83481 42.73
2 221.2096 0.1000
3 28.0000 3.2000 1.83400 37.18
4 39.0000 2.7000
5 182.5453 1.2000 1.75520 27.57
6 17.8832 d1
7 54.5012 2.2000 1.77250 49.62
8 -121.1911 1.4000
9 0.0000 3.5000 Aperture stop S
10 -17.5587 1.2000 1.68893 31.16
11 32.6949 1.5000
12 -123.2970 2.3000 1.88300 40.66
13 -53.0000 1.7000
14 75.1287 4.8000 1.81600 46.59
15 -23.0269 d2
16 21.5035 3.9500 1.95400 33.46
17 -714.3048 1.3000 1.80518 25.45
18 14.8026 1.2000
19 24.9460 2.5000 1.88300 40.66
20 55.6297 11.0102
21 0.0000 2.7900 1.51680 64.12
22 0.0000 0.5000

[Lens focal length]
Lens group Start surface Focal length 1st lens group 1 210.36
Second lens group 7 39.09
Third lens group 16 68.51

  In the third example, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 are from infinity. Changes when focusing on short-range objects. Table 8 below shows variable intervals when focusing on infinity and focusing on a short-distance object.

(Table 8)
Infinity Short distance D0 ∞ 700.0000
d1 9.3000 5.7083
d2 1.6000 5.1916

  Table 9 below shows values corresponding to the respective conditions of the optical system OS3 according to the third example.

(Table 9)
f21 = 48.9
(1) f21 / f2 = 1.25
(2) f21 / f = 1.53
(3) f3 / f2 = 1.75
(4) f3 / f = 2.14
(5) f2 / f = 1.22
(6) f1 / f = 6.57
(7) f1 / f3 = 3.07
(8) r1 / f2 = 1.39

  Note that r1 in the conditional expression (8) corresponds to the radius of curvature of the seventh surface. As described above, the optical system OS3 according to the third example satisfies all the conditional expressions (1) to (8).

  FIG. 6 shows spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration in the infinite focus state and the short distance object focus state (D0 = 700 mm) of the optical system OS3 according to the third embodiment. The aberration diagrams of are shown. As is apparent from the respective aberration diagrams shown in FIG. 6, in the optical system OS3 according to the third example, various aberrations are satisfactorily corrected in each state from the infinitely focused state to the short-distance object focused state, It can be seen that the imaging performance is excellent.

[Fourth embodiment]
FIG. 7 is a diagram illustrating a configuration of an optical system OS4 according to the fourth example. The optical system OS4 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power, It is comprised. The first lens group G1 includes, in order from the object side, a biconvex lens L11, a positive meniscus lens L12 having a convex surface directed toward the object side, a positive meniscus lens L13 having a convex surface directed toward the object side, and a negative having a convex surface directed toward the object side. It comprises a meniscus lens L14. The second lens group G2 includes, in order from the object side, a front group G2F having a positive refractive power, an aperture stop S, and a rear group G2R. The front group G2F has a positive surface with a convex surface facing the object side. The rear group G2R is composed of a meniscus lens L21, and in order from the object side, is composed of a biconcave lens L22, a positive meniscus lens L23 having a convex surface facing the image side, and a biconvex lens L24. The third lens group G3 includes, in order from the object side, a biconvex lens L31, and a cemented negative lens CL31 including a biconcave lens L32 and a positive meniscus lens L33 having a convex surface facing the object side.

  Thus, in the optical system OS4 according to the fourth example, in the first lens group G1, two positive lenses (a biconvex lens L11 and a positive meniscus lens L12) are arranged in order from the object side. In the second lens group G2, the positive lens (positive meniscus lens L21) is disposed closest to the object side, and the lens closest to the image side has a biconvex shape (biconvex lens L24). Further, all lens surfaces of the optical system OS4 are constituted by spherical surfaces or flat surfaces.

  A filter group FL is disposed between the optical system OS4 and the image plane I.

  In the optical system OS4 according to the fourth example having such a configuration, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane when focusing from infinity to a close object, and the second lens group G3 is fixed to the image plane. The lens group G2 moves in the object direction along the optical axis. The aperture stop S moves together with the second lens group G2 when focusing.

  Table 10 below lists values of specifications of the optical system OS4 according to the fourth example. The surface numbers 1 to 24 shown in Table 10 correspond to the numbers 1 to 24 shown in FIG.

(Table 10)
[Overall specifications]
f = 31.50
FNO = 1.23
ω = 14.24
Y = 8.00
TL = 55.00
Bf = 13.70

[Lens data]
m r d nd νd
1 57.7937 3.8669 1.60311 60.67
2 -152.7504 0.1000
3 21.6543 3.7584 1.60311 60.67
4 41.5111 0.1000
5 30.0061 2.7318 1.83480 42.72
6 49.8338 0.8669
7 127.2755 1.4984 1.67270 32.11
8 16.5082 d1
9 20.0297 1.1782 1.83480 42.72
10 20.7248 2.4693
11 0.0000 2.9702 Aperture stop S
12 -14.3410 1.0000 1.64768 33.80
13 40.2723 1.4672
14 -56.8420 2.1002 1.83480 42.72
15 -23.2653 0.1000
16 42.7022 3.8131 1.77249 49.61
17 -24.2988 d2
18 59.8262 2.5837 1.83480 42.72
19 -31.8636 0.5731
20 -27.0382 1.3000 1.68893 31.07
21 20.7059 2.5815 1.83480 42.72
22 63.7424 10.4100
23 0.0000 2.7900 1.51680 64.12
24 0.0000 0.5000

[Lens focal length]
Lens group Start surface Focal length 1st lens group 1 70.00
Second lens group 9 36.83
Third lens group 18 100.83

  In the fourth example, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 are from infinity. Changes when focusing on short-range objects. Table 11 below shows variable intervals when focusing on infinity and focusing on a short-distance object.

(Table 11)
Infinity Short distance D0 ∞ 700.0000
d1 6.1423 3.0681
d2 0.1000 3.1741

  Table 12 below shows values corresponding to the respective conditions of the optical system OS4 according to the fourth example.

(Table 12)
f21 = 403.9
(1) f21 / f2 = 10.97
(2) f21 / f = 12.82.
(3) f3 / f2 = 2.74
(4) f3 / f = 3.20
(5) f2 / f = 1.17
(6) f1 / f = 2.22
(7) f1 / f3 = 0.75
(8) r1 / f2 = 0.54

  Note that r1 in the conditional expression (8) corresponds to the radius of curvature of the ninth surface. As described above, the optical system OS4 according to the fourth example satisfies all the conditional expressions (1) to (8).

  FIG. 8 shows spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration in the infinite focus state and the short distance object focus state (D0 = 700 mm) of the optical system OS4 according to the fourth embodiment. The aberration diagrams of are shown. As is apparent from the respective aberration diagrams shown in FIG. 8, in the optical system OS4 according to the fourth example, various aberrations are satisfactorily corrected in each state from the infinite focus state to the short distance object focus state, It can be seen that the imaging performance is excellent.

[Fifth embodiment]
FIG. 9 is a diagram illustrating a configuration of an optical system OS5 according to the fifth example. The optical system OS5 includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, a third lens group G3 having a positive refractive power, It is comprised. The first lens group G1, in order from the object side, includes a positive meniscus lens L11 having a convex surface facing the object side, a positive meniscus lens L12 having a convex surface facing the object side, and a negative meniscus lens L13 having a convex surface facing the object side. Composed. The second lens group G2 includes a front group G2F having positive refractive power, an aperture stop S, and a rear group G2R in order from the object side. The front group G2F includes a biconvex lens L21 in order from the object side. The rear group G2R includes, in order from the object side, a biconcave lens L23, a positive meniscus lens L24 having a convex surface facing the image side, and a biconvex lens L25. The third lens group G3 includes, in order from the object side, a cemented negative lens CL31 of a biconvex lens L31 and a biconcave lens L32, and a positive meniscus lens L33 having a convex surface facing the object side.

  Thus, in the optical system OS5 according to the fifth example, the first lens group G1 includes two positive lenses (a positive meniscus lens L11 and a positive meniscus lens L12) arranged in order from the object side. In the second lens group G2, the positive lens (biconvex lens L21) is disposed closest to the object side, and the lens closest to the image side has a biconvex shape (biconvex lens L25). Further, all lens surfaces of the optical system OS5 are constituted by spherical surfaces or flat surfaces.

  A filter group FL is disposed between the optical system OS5 and the image plane I.

  In the optical system OS5 according to the fifth example having such a configuration, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane when focusing from infinity to a close object, and the second The lens group G2 moves in the object direction along the optical axis. The aperture stop S moves together with the second lens group G2 when focusing.

  Table 13 below provides values of specifications of the optical system OS5 according to the fifth example. The surface numbers 1 to 24 shown in Table 13 correspond to the numbers 1 to 24 shown in FIG.

(Table 13)
[Overall specifications]
f = 32.00
FNO = 1.23
ω = 14.28
Y = 8.00
TL = 66.45
Bf = 12.89

[Lens data]
m r d nd νd
1 32.2742 4.3000 1.83481 42.73
2 211.6960 0.1000
3 29.1133 3.2000 1.83400 37.18
4 40.6849 2.7000
5 180.5106 1.2000 1.75520 27.57
6 18.6131 d1
7 98.6239 2.0000 1.77250 49.62
8 -180.0796 0.4000
9 107.3684 2.0000 1.78800 47.35
10 -1504.7540 1.4000
11 0.0000 3.5000 Aperture stop S
12 -17.1756 1.2000 1.68893 31.16
13 33.6239 1.5000
14 -112.0910 2.3000 1.88300 40.66
15 -53.2261 1.7000
16 83.2714 4.8000 1.81600 46.59
17 -22.5820 d2
18 20.6232 3.9500 1.95400 33.46
19 -230.0863 1.3000 1.80518 25.45
20 14.3197 1.2000
21 24.2925 2.5000 1.88300 40.66
22 55.6297 9.4000
23 0.0000 2.7900 1.51680 64.12
24 0.0000 0.7000

[Lens focal length]
Lens group Start surface Focal length 1st lens group 1 216.32
Second lens group 7 41.62
Third lens group 18 61.28

  In the fifth example, the axial air distance d1 between the first lens group G1 and the second lens group G2 and the axial air distance d2 between the second lens group G2 and the third lens group G3 are from infinity. Changes when focusing on short-range objects. Table 14 below shows variable intervals when focusing on infinity and focusing on a short-distance object.

(Table 14)
Infinity Short distance D0 ∞ 700.0000
d1 9.3000 5.3227
d2 1.5000 5.4773

  Table 15 below shows values corresponding to the respective conditions of the optical system OS5 according to the fifth example.

(Table 15)
f21 = 50.4
(1) f21 / f2 = 1.21
(2) f21 / f = 1.58
(3) f3 / f2 = 1.47
(4) f3 / f = 1.91
(5) f2 / f = 1.30
(6) f1 / f = 6.76
(7) f1 / f3 = 3.53
(8) r1 / f2 = 2.37

  Note that r1 in the conditional expression (8) corresponds to the radius of curvature of the seventh surface. Thus, the optical system OS5 according to the fifth example satisfies all the conditional expressions (1) to (8).

  FIG. 10 shows spherical aberration, astigmatism, distortion, lateral chromatic aberration, and coma aberration when the optical system OS5 according to the fifth embodiment is in focus at infinity and in focus at short distance (D0 = 700 mm). The aberration diagrams of are shown. As is apparent from the respective aberration diagrams shown in FIG. 10, in the optical system OS5 according to the fifth example, various aberrations are satisfactorily corrected in each state from the infinity in-focus state to the short-distance object in-focus state, It can be seen that the imaging performance is excellent.

OS (OS1 to OS5) Optical system G1 First lens group L11 Positive meniscus lens L12 Positive meniscus lens G2 Second lens group G2F Front group S Aperture stop L21 Positive meniscus lens L24 Biconvex lens G3 Third lens group 1 Camera (optical equipment)

Claims (14)

From the object side,
A first lens group having a positive refractive power;
A second lens group having a positive refractive power;
A third lens group having a positive refractive power,
The second lens group includes an aperture stop, and a front group that includes at least one lens disposed on the object side of the aperture stop and has a positive refractive power,
Upon focusing, the first lens group and the third lens group are fixed with respect to the image plane, and the second lens group moves along the optical axis,
An optical system satisfying the following conditional expression:
0.50 <f21 / f2 <18.00
However,
f21: Focal length of the front group f2: Focal length of the second lens group The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.50 <f21 / f <20.00
However,
f: Focal length of the entire system when focusing on infinity The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.20 <f3 / f2 <7.80
However,
f3: focal length of the third lens group The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.30 <f3 / f <6.00
However,
f3: focal length of the third lens group f: focal length of the entire system when focusing on infinity The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.50 <f2 / f <2.00
However,
f: Focal length of the entire system when focusing on infinity The optical system according to claim 1, wherein the following conditional expression is satisfied.
1.90 <f1 / f <50.00
However,
f1: Focal length of the first lens group f: Focal length of the entire system when focusing on infinity The optical system according to claim 1, wherein the following conditional expression is satisfied.
0.40 <f1 / f3 <20.00
However,
f1: Focal length of the first lens group f3: Focal length of the third lens group   The optical system according to claim 1, wherein the second lens group includes a positive lens closest to the object side. The optical system according to claim 8, wherein the following conditional expression is satisfied.
0.30 <r1 / f2 <15.00
However,
r1: radius of curvature of the object side surface of the positive lens included in the second lens group   The optical system according to claim 1, wherein the first lens group includes two positive lenses in order from the object side.   The optical system according to any one of claims 1 to 10, wherein a lens closest to the image side of the second lens group has a biconvex shape.   All the lens surfaces are spherical surfaces or planes, The optical system as described in any one of Claims 1-11 characterized by the above-mentioned.   An optical apparatus comprising the optical system according to claim 1. An optical system manufacturing method including a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power in order from the object side. And
The first lens group, the second lens group having a front lens group having a positive refractive power, which includes an aperture stop and at least one lens disposed on the object side of the aperture stop, and the third lens unit. A lens group, and
In focusing, the first lens group and the third lens group are fixed with respect to the image plane, and the second lens group is arranged to move along the optical axis,
A method of manufacturing an optical system, wherein the optical system is arranged so as to satisfy the following conditional expression:
0.50 <f21 / f2 <18.00
However,
f21: Focal length of the front group f2: Focal length of the second lens group

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