JP5157401B2 - Imaging lens, imaging apparatus and focusing method therefor - Google Patents

Description

  The present invention relates to a photographic lens, and more particularly to an internal focus type photographic lens in which the entire length of the lens is invariable, an imaging apparatus, and a focusing method according to the photographic lens.

  Conventionally, a photographing lens for close-up photography has been proposed (see, for example, Patent Document 1). Unlike normal photographic lenses, close-up lenses focus on subjects from infinity to close-up subjects at the same magnification or near the same magnification, so the amount of movement of the lens group that moves during focusing increases. There was a tendency to be unsuitable for focus. Further, when focusing from infinity to equal magnification is performed by a method in which only one lens unit is extended, a large amount of movement as much as the focal length is required. Then, the fluctuation of spherical aberration and the fluctuation of the image plane become large and the optical performance deteriorates. Therefore, the focus lens system is divided into a plurality of groups, and each group has a different speed along the optical axis at the time of focusing. There are many close-up lenses that employ a so-called floating system that can be moved by the lens and maintain sufficient optical performance when focusing on a short-distance object.

JP 2005-4041 A

  However, the floating close-up lens as described above still has a relatively large amount of movement of the lens group and is not suitable for high-speed autofocus. In recent years, there has been a demand for such a close-up lens to reduce not only aberration performance but also ghost and flare, which are factors that impair optical performance.

  The present invention has been made in view of such problems, and is a high-performance photographic lens in which focusing is performed in an in-focus manner, the amount of movement of the focusing lens group is small, and ghost and flare are further reduced. It is an object of the present invention to provide a photographing apparatus and a focusing method.

In order to achieve such an object, the photographing lens of the present invention includes first to fourth lens groups arranged in order from the object side along the optical axis, and the photographing magnification is from 0 times to at least -1.0 times. In a photographing lens capable of photographing, during focusing, the first lens group and the fourth lens group are fixed with respect to the image plane, the second lens group and the third lens group are moved in the optical axis direction, An antireflection film is provided on at least one of the optical surfaces in the third lens group and the fourth lens group, and the antireflection film is composed of a plurality of layers, at least one of which is formed by a wet process, The layer formed using the wet process satisfies the condition of the following formula nd ≦ 1.30 when the refractive index with respect to the d-line is nd, and the side of the second lens group in the infinitely focused state. When the ratio is β0 and the lateral magnification of the second lens group in the equal magnification in-focus state is β1, the following conditions are satisfied: 1.5 <β0 <2.3 and 0.3 <β1 <0.9 It is characterized by satisfaction .

  The antireflection film is preferably a multilayer film, and the outermost surface layer of the multilayer film is preferably a layer formed using the wet process.

  Moreover, it is preferable that the optical surface provided with the antireflection film has a concave surface facing the image side.

  Moreover, it is preferable to have at least one aspherical surface.

  Further, it is preferable that the first lens group is composed of three or less lenses.

  The fourth lens group is preferably composed of at least three lenses.

  Moreover, it is preferable that each of the first lens group and the second lens group has at least one aspheric lens.

  In addition, an imaging apparatus according to the present invention includes the above-described photographing lens.

In addition, the focusing method of the present invention includes first to fourth lens groups arranged in order from the object side along the optical axis, and focusing of a photographing lens capable of photographing from a photographing magnification of 0 to at least −1.0 times. In the method, an antireflection film is provided on at least one of the optical surfaces of the third lens group and the fourth lens group, and the antireflection film is composed of a plurality of layers, and at least one of them is formed by a wet process. The layer formed using the wet process satisfies the condition of the following formula nd ≦ 1.30 when the refractive index for the d-line is nd, and the second lens in an infinitely focused state When the lateral magnification of the group is β0 and the lateral magnification of the second lens group in the same magnification in-focus state is β1, the following expressions 1.5 <β0 <2.3 and 0.3 <β1 <0.9 satisfy the conditions, Four In Thing, the first lens group and the fourth lens group is fixed with respect to the image plane, and wherein the moving the second lens group and the third lens group in the optical axis direction.

  As described above, according to the present invention, it is suitable for an optical apparatus such as a film camera and an electronic still camera, can be focused with autofocus, and a high-quality image with reduced ghost and flare can be obtained. It is possible to provide an in-focus type photographing lens, a photographing apparatus including the same, and a focusing method.

  Hereinafter, preferred embodiments will be described with reference to the drawings. As shown in FIG. 1, a digital single-lens reflex camera 1 (imaging device) provided with a photographic lens according to the present embodiment is configured so that light from an object (subject) (not shown) is condensed by a photographic lens 2 An image is formed on the light collector 4 via the return mirror 3. The light imaged on the focusing screen 4 is reflected a plurality of times in the pentaprism 5 and guided to the eyepiece lens 6. Thus, the photographer can observe the object (subject) image as an erect image through the eyepiece 6.

  Further, when a release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted out of the optical path, and light of an object (subject) (not shown) condensed by the photographing lens 2 is captured on the image sensor 7. Form an image. Thereby, the light from the object (subject) is captured by the image sensor 7 and recorded as an object (subject) image in a memory (not shown). In this way, the photographer can shoot an object (subject) with the camera 1.

  The photographing lens for close-up photography according to the present embodiment (hereinafter also referred to as a close-up photography lens) used for the photographing lens 2 is first to fourth lenses arranged in order from the object side along the optical axis. The first lens group G1 and the fourth lens group G4 are fixed with respect to the image plane, and the second lens group G4 is fixed to the image plane during focusing. The lens group G2 and the third lens group G3 are moved in the optical axis direction, and at least one layer formed by using a wet process is formed on at least one of the optical surfaces in the third lens group G3 and the fourth lens group G4. An antireflection film including a layer is provided. With such a configuration, close-up photography can be performed at a large magnification without changing the overall lens length. Note that the in-focus state at an imaging magnification of 0 indicates an infinitely-focused state.

  In addition, the close-up lens according to the present embodiment includes first to fourth lens groups G1 to G4 arranged in order from the object side along the optical axis, and the photographing magnification is 0 to at least −1.0 times. In focusing, the first lens group G1 and the fourth lens group G4 are fixed with respect to the image plane, the second lens group G2 and the third lens group G3 are moved in the optical axis direction, and the third lens group An antireflection film including at least one layer formed by a wet process is provided on at least one of the optical surfaces in G3 and the fourth lens group G4, and the second lens group G2 in the infinitely focused state is provided. Is set to β0, and the horizontal magnification of the second lens group G2 in the equal magnification in-focus state is set to β1, the following expressions (1) and (2) are satisfied. Note that the in-focus state at the photographing magnification of -1.0 times indicates an equal-magnification in-focus state (or a close-in distance in-focus state).

1.5 <β0 <2.3 (1)
0.3 <β1 <0.9 (2)

  Conditional expression (1) defines an appropriate lateral magnification of the second lens group G2 in the infinitely focused state. In this conditional expression (1), if the upper limit value is exceeded, the focal length of the second lens group G2 becomes short, and both spherical aberration and field curvature are overcorrected. On the other hand, if the lower limit value of the conditional expression (1) is not reached, the focal length of the second lens group G2 becomes long, and both spherical aberration and field curvature are insufficiently corrected. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (1) to 2.10. In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to 1.70.

  Conditional expression (2) defines an appropriate lateral magnification of the second lens group G2 in the equal magnification in-focus state. In this conditional expression (2), if the upper limit is exceeded, the combined focal length in the same magnification state of the first lens group G1 and the second lens group G2 becomes short, and various aberrations such as spherical aberration from infinity to equal magnification It is difficult to suppress fluctuations. On the other hand, if the lower limit of conditional expression (2) is not reached, the combined focal length in the same magnification state of the first lens group G1 and the second lens group G2 becomes long, so that both the spherical aberration and the curvature of field are insufficiently corrected. This is not preferable. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (2) to 0.8. In order to secure the effect of the present invention, it is preferable to set the lower limit of conditional expression (2) to 0.5.

  In the above close-up lens, the antireflection film provided on at least one of the optical surfaces in the third lens group G3 and the fourth lens group G4 is a multilayer film (in this embodiment, a seven-layer structure), The outermost surface layer of this multilayer film (in this embodiment, a seventh layer 101g of the antireflection film 101 described later) is preferably a layer formed using a wet process. With this configuration, since the difference in refractive index between the lens and air can be reduced, it is possible to reduce the reflection of light in this close-up lens and further reduce ghosts and flares. Can do.

  In the above close-up lens, it is preferable that the following formula (3) is satisfied, where nd is the refractive index of the layer formed using the wet process with respect to the d-line.

  nd ≦ 1.30 (3)

  Conditional expression (3) appropriately defines the refractive index nd with respect to the d-line of a layer (in this embodiment, the seventh layer 101g of the antireflection film 101) formed by using a wet process. By satisfying this conditional expression (3), the difference in refractive index between the lens and air can be reduced. Therefore, in this close-up photographing lens, the reflection of light can be further reduced, and ghost and flare can be reduced. Can be further reduced.

  In the above close-up lens, it is preferable that the optical surface provided with the antireflection film has a concave surface directed toward the image side. In this way, in this close-up lens, ghosts and flares can be effectively reduced by applying the antireflection film to the optical surface with the concave surface facing the image surface where ghosts are likely to occur. When the optical surface provided with the antireflection film is disposed on the image side of the aperture stop, it is possible to effectively suppress the reflected light that becomes ghost and flare generated from the optical surface of the rear group, More preferred.

  In the above close-up lens, it is preferable to have at least one aspherical surface. With such a configuration, various aberrations such as spherical aberration and coma can be corrected well.

  In the above close-up lens, the first lens group G1 is preferably composed of three or less lenses. With such a configuration, the movable range of the second lens group G2, which is a focusing lens, can be widened while correcting spherical aberration and coma aberration, so that variations in various aberrations such as spherical aberration accompanying focusing can be reduced. Can do.

  In the above close-up lens, it is preferable that the fourth lens group G4 includes at least three lenses. With such a configuration, various aberrations such as curvature of field can be favorably corrected.

  In the above close-up lens, each of the first lens group G1 and the second lens group G2 preferably includes at least one aspheric lens. With such a configuration, various aberrations such as spherical aberration and coma can be corrected well.

  Further, the focusing method of the above-mentioned close-up lens including the first to fourth lens groups G1 to G4 arranged in order from the object side along the optical axis and capable of photographing from 0 times to at least −0.5 times. In the third lens group G3 and the fourth lens group G4, an antireflection film including at least one layer formed using a wet process is provided on at least one of the optical surfaces of the third lens group G3 and the fourth lens group G4. The group G1 and the fourth lens group G4 are fixed with respect to the image plane, and the second lens group G2 and the third lens group G3 are moved in the optical axis direction. With such a focusing method, the close-up lens can obtain a high-quality image with little ghost and flare up to the same magnification as that at infinity. It is preferable that an aperture stop is disposed between the second lens group G2 and the third lens group G3, and the aperture stop is fixed during focusing.

  Further, the close-up lens focusing method described above includes first to fourth lens groups G1 to G4 arranged in order from the object side along the optical axis, and capable of photographing from 0 times to at least -1.0 times. In the third lens group G3 and the fourth lens group G4, an antireflection film including at least one layer formed by a wet process is provided on at least one of the optical surfaces in the third lens group G3 and the fourth lens group G4. When the lateral magnification of the second lens group G2 is β0 and the lateral magnification of the second lens group G2 in the equal magnification in-focus state is β1, the following expressions 1.5 <β0 <2.3 and 0.3 < The first lens group G1 and the fourth lens group G4 are fixed with respect to the image plane, and the second lens group G2 and the third lens group G4 are aligned in the optical axis direction during focusing, satisfying the condition of β1 <0.9. Configured to move . By this focusing method, the photographing lens can obtain a high-quality image with little ghost and flare up to the same magnification as that at infinity.

  Embodiments according to the present application will be described with reference to the accompanying drawings. Tables 1 to 8 are shown below, but these are tables of specifications in the first to eighth examples. In [Overall specifications], f indicates a focal length, FNO indicates an F number, and Bf indicates a back focus. In [Lens data], the surface number is the order of the lens surfaces from the object side along the direction in which the light beam travels, r is the radius of curvature of each lens surface, and d is the next optical surface from each optical surface (or The distance between the surfaces, which is the distance on the optical axis to the image plane), nd is the refractive index with respect to the d line (wavelength 587.6 nm), and νd is the Abbe number with respect to the d line. [Variable interval data] indicates the value of each variable interval with respect to the photographing magnification β. In [conditional expression], values corresponding to the conditional expressions (1) to (3) are shown.

  In the table, “mm” is generally used as the unit of focal length f, radius of curvature r, surface interval d, and other lengths. However, since the optical system can obtain the same optical performance even when proportionally enlarged or proportionally reduced, the unit is not limited to “mm”, and other appropriate units can be used. In the table, the radius of curvature “∞” indicates a plane or an opening, and the air refractive index “1.00000” is omitted.

Also, in the table, the aspherical surface marked with * is the optical axis from the tangential plane at the apex of the aspherical surface to the position on the aspherical surface at the height y, where y is the height in the direction perpendicular to the optical axis. When the distance along the sag (sag amount) is S (y), the radius of curvature of the reference sphere (paraxial radius of curvature) is r, the cone coefficient is K, and the nth-order aspheric coefficient is An, It is represented by (a). In each example, the secondary aspheric coefficient A2 is 0, and the description thereof is omitted. Further, En represents × 10 ^n. For example, 1.234E-05 = 1.234 × 10 ⁻⁵ .

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 ... (a)

(First embodiment)
1st Example of this application is described using FIG.2, FIG.3, FIG.4 and Table 1. FIG. The close-up photographing lens according to the present embodiment, as shown in FIG. 2, has a first lens group G1 having a positive refractive power, arranged in order from the object side along the optical axis, and a negative refractive power. A second lens group G2 having an aperture stop S for adjusting the amount of light, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. Configured. The image plane I is formed on an image sensor (not shown), and the image sensor is composed of a CCD, a CMOS, or the like.

  The above-described photographing lens has the first lens group G1, the fourth lens group G4, and the aperture stop S with respect to the image plane I during focusing from the infinity to the closest distance (equal magnification state). The second lens group G2 is moved to the image plane I side along the optical axis, and the third lens group G3 is moved to the object side along the optical axis.

  The first lens group G1 is arranged in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface on the object side and an aspheric surface on the image side lens surface, and a positive meniscus having a convex surface on the object side. The lens L12 is composed of a biconvex positive lens L13. The second lens group G2 is arranged in order from the object side along the optical axis, and includes a negative meniscus lens L21 having a convex surface on the object side and an aspheric surface on the image side lens surface, a biconcave negative lens L22, and both It is composed of a cemented lens with a convex positive lens L23. The third lens group G3 is formed by joining a biconvex positive lens L31, a biconvex positive lens L32, and a negative meniscus lens L33 having a concave surface facing the object side, which are arranged in order from the object side along the optical axis. It consists of a lens. The fourth lens group G4 includes, in order from the object side along the optical axis, a negative meniscus lens L41 having a convex surface directed toward the object side, a negative meniscus lens L41 having a convex surface directed toward the object side, and a positive meniscus having a convex surface directed toward the object side. It comprises a cemented lens with a meniscus lens L42.

  As shown in FIG. 3, when the light beam BM from the object side is incident on the photographing lens, the light is reflected by the image plane I (first ghost generation surface) and then the object side lens of the positive lens L31. The light is reflected again by the surface (the second ghost generation surface and corresponds to the surface number 13 in Table 1 below) and reaches the image surface I to generate a ghost. Therefore, an antireflection film corresponding to a wider wavelength range and a wide incident angle is formed on the surface on which the concave surface is directed with respect to the image surface I where ghost is likely to occur, in this embodiment, on the object side lens surface of the positive lens L31. By doing so, the ghost is effectively reduced. Although the antireflection film will be described in detail later, the antireflection film according to each example has a multi-layer structure including seven layers, and the seventh layer of the outermost surface layer is formed by using a wet process, and is applied to the d line. The refractive index is 1.26 (see Table 9 below).

  Table 1 shows a table of specifications in the first embodiment. The surface numbers 1 to 22 in Table 1 correspond to the surfaces 1 to 22 shown in FIG. In the first embodiment, the lens surfaces of the second surface and the eighth surface are both aspherical.

  In the table, the axial air space between the first lens group G1 and the second lens group G2 is D6, the axial air space between the second lens group G2 and the aperture stop S is D11, and the aperture stop S The axial air gap between the third lens group G3 and the third lens group G3 and the fourth lens group G4 is D17. These on-axis air spacings, ie D6, D11, D12 and D17, change during focusing.

(Table 1)
[Overall specifications]
f = 54.9, FNO = 2.88, Bf = 36.33
[Lens specifications]
Surface number r d nd νd
1 53.6481 1.2235 1.834000 37.17
2 * 23.7149 3.0444
3 55.1154 2.3000 1.677900 55.43
4 154.6254 0.0943
5 50.0781 2.7389 1.834807 42.71
6 -176.5486 (D6 = variable)
7 106.1229 1.1868 1.516120 64.03
8 * 19.4713 4.9300
9 -25.1250 1.7346 1.620040 36.30
10 37.9551 5.8886 1.883000 40.77
11-30.3977 (D11 = variable)
12 Aperture stop S (D12 = variable)
13 316.1763 2.9215 1.497820 82.56
14 -42.6285 0.0456
15 55.1820 4.3365 1.603000 65.47
16 -38.7234 1.0955 1.846660 23.78
17 -139.0482 (D17 = variable)
18 155.9225 1.0955 1.805180 25.43
19 28.9155 1.5520
20 68.4642 1.1868 1.801000 34.96
21 17.8157 5.6603 1.846660 23.78
22 126.0536 (Bf)
[Aspherical data]
Second side
K = -5.0082, A4 = 6.42810E-05, A6 = -1.62540E-07, A8 = 6.11660E-10, A10 = -9.13480E-13
8th page
K = 1.9410, A4 = -3.17360E-05, A6 = -1.34580E-07, A8 = 1.79850E-10, A10 = -4.47290E-12
[Variable interval data]
β 0 times -0.5 times -1.0 times D6 2.50446 6.29642 13.40000
D11 10.38771 6.59575 0.10000
D12 21.88818 11.54539 1.64821
D17 3.51915 13.86323 23.75911
[Conditional expression]
(1) β0 = 2.00
(2) β1 = 0.63
(3) nd = 1.26

  As can be seen from the table of specifications shown in Table 1, it can be seen that the photographic lens according to the present example satisfies all the conditional expressions (1) to (3).

  4A and 4B are graphs showing various aberrations of the first embodiment. FIG. 4A is a diagram showing various aberrations when the photographing magnification is 0, that is, in an infinite focus state, and FIG. FIG. 4C is a diagram illustrating various aberrations in the close focus state at a photographing magnification of −1.0 times.

  In each aberration diagram, FNO is the F number, Y is the image height, NA is the numerical aperture, D is the d-line (wavelength 587.6 nm), G is the g-line (wavelength 435.8 nm), and C is the C-line (wavelength) 656.3 nm), and F represents F line (wavelength 486.1 nm). In the aberration diagrams showing astigmatism, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. The explanation of the above aberration diagrams is the same in the other examples, and the explanation is omitted.

  As is apparent from the respective aberration diagrams, in the first embodiment, various aberrations are well corrected from the photographing magnification of 0 times (focused at infinity) to the photographing magnification of -1.0 times, and excellent results are obtained. It can be seen that it has image performance.

  As a result, by mounting the photographic lens of the first embodiment, excellent optical performance can be ensured even in a digital single-lens reflex camera (photographing apparatus, see FIG. 1).

(Second embodiment)
A second embodiment of the present application will be described with reference to FIGS. As shown in FIG. 5, the photographic lens according to the present embodiment includes a first lens group G1 having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the object side along the optical axis. It comprises a group G2, an aperture stop S for adjusting the amount of light, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. Yes.

  In the photographic lens having the above-described configuration, the first lens group G1, the fourth lens group G4, and the aperture stop S are located on the image plane I during focusing from the infinity to the closest distance (equal magnification state). The second lens group G2 is moved to the image plane I side along the optical axis, and the third lens group G3 is moved to the object side along the optical axis.

  The first lens group G1 is arranged in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface on the object side and an aspheric surface on the image side lens surface, and a positive meniscus having a convex surface on the object side. The lens L12 is composed of a biconvex positive lens L13. The second lens group G2 is arranged in order from the object side along the optical axis, and includes a negative meniscus lens L21 having a convex surface on the object side and an aspheric surface on the image side lens surface, a biconcave negative lens L22, and both It is composed of a cemented lens with a convex positive lens L23. The third lens group G3 is formed by joining a biconvex positive lens L31, a biconvex positive lens L32, and a negative meniscus lens L33 having a concave surface facing the object side, which are arranged in order from the object side along the optical axis. It consists of a lens. In this embodiment, an antireflection film, which will be described later, is formed on the object side lens surface (surface number 15) of the positive lens L32 to effectively reduce the ghost. The fourth lens group G4 includes, in order from the object side along the optical axis, a negative meniscus lens L41 having a convex surface directed toward the object side, a negative meniscus lens L41 having a convex surface directed toward the object side, and a positive meniscus having a convex surface directed toward the object side. It comprises a cemented lens with a meniscus lens L42. In this embodiment, an antireflection film described later is formed on the object side lens surface of the positive meniscus lens L32 (corresponding to the surface number 15 shown in Table 2 below) to effectively reduce the ghost.

  Table 2 shows a table of specifications in the second embodiment. The surface numbers 1 to 22 in Table 2 correspond to the surfaces 1 to 22 shown in FIG. In the second embodiment, the lens surfaces of the second surface and the eighth surface are both aspherical.

  In the table, the axial air space between the first lens group G1 and the second lens group G2 is D6, the axial air space between the second lens group G2 and the aperture stop S is D11, and the aperture stop S The axial air gap between the third lens group G3 and the third lens group G3 and the fourth lens group G4 is D17. These on-axis air spacings, ie D6, D11, D12 and D17, change during focusing.

(Table 2)
[Overall specifications]
f = 58.0, FNO = 2.88, Bf = 37.45
[Lens specifications]
Surface number r d nd νd
1 68.8358 1.3514 1.804400 39.57
2 * 25.1596 3.1598
3 50.5680 3.0890 1.638540 55.48
4 726.7885 0.0997
5 61.6542 2.8959 1.834807 42.71
6 -213.3350 (D6 = variable)
7 114.0007 1.2549 1.516120 64.03
8 * 21.4584 5.2000
9 -25.9781 1.8341 1.620040 36.30
10 45.0791 6.2262 1.883000 40.77
11 -31.6859 (D11 = variable)
12 Aperture stop S (D12 = variable)
13 279.3330 3.0890 1.497820 82.56
14 -45.8650 0.0483
15 55.7141 4.5852 1.603000 65.47
16 -42.3441 1.1584 1.846660 23.78
17 -171.5862 (D17 = variable)
18 202.8956 1.1584 1.805180 25.43
19 30.8234 1.6410
20 90.5377 1.2549 1.801000 34.96
21 18.9814 5.9849 1.846660 23.78
22 242.9593 (Bf)
[Aspherical data]
Second side
K = -5.3148, A4 = 5.58040E-05, A6 = -1.43070E-07, A8 = 5.02630E-10, A10 = -7.75980E-13
8th page
K = 2.1218, A4 = -2.69280E-05, A6 = -9.47080E-08, A8 = 9.70030E-11, A10 = -2.56360E-12
[Variable interval data]
β 0 times -0.5 times -1.0 times D6 2.62569 6.63506 13.83349
D11 12.29619 8.28682 1.08839
D12 23.27238 12.33659 1.87196
D17 4.49094 15.42810 25.89136
[Conditional expression]
(1) β0 = 2.00
(2) β1 = 0.64
(3) nd = 1.26

  As can be seen from the table of specifications shown in Table 2, it can be seen that the photographic lens according to the present example satisfies all the conditional expressions (1) to (3).

  6A and 6B are graphs showing various aberrations of the second example. FIG. 6A is a diagram showing various aberrations when the photographing magnification is 0, that is, in an infinitely focused state, and FIG. FIG. 6C is a diagram illustrating various aberrations in the close focus state at a photographing magnification of −1.0 times.

  As is apparent from the respective aberration diagrams, in the second embodiment, various aberrations are well corrected from the shooting magnification of 0 times (focused at infinity) to the shooting magnification of -1.0 times, and excellent results are obtained. It can be seen that it has image performance.

  As a result, by mounting the photographic lens of the second embodiment, excellent optical performance can be ensured even in a digital single-lens reflex camera (photographing apparatus; see FIG. 1).

(Third embodiment)
A third embodiment of the present application will be described with reference to FIGS. As shown in FIG. 7, the photographing lens according to the present embodiment includes a first lens group G1 having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the object side along the optical axis. It comprises a group G2, an aperture stop S for adjusting the amount of light, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. Yes.

  The above-described photographing lens has the first lens group G1, the fourth lens group G4, and the aperture stop S with respect to the image plane I during focusing from the infinity to the closest distance (equal magnification state). The second lens group G2 is moved to the image plane I side along the optical axis, and the third lens group G3 is moved to the object side along the optical axis.

  The first lens group G1 is arranged in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface on the object side and an aspheric surface on the image side lens surface, a biconvex positive lens L12, And a positive meniscus lens L13 having a convex surface facing the object side. The second lens group G2 is composed of a biconcave negative lens L21 and a cemented lens of a biconcave negative lens L22 and a biconvex positive lens L23 arranged in order from the object side along the optical axis. Is done. The third lens group G3 is formed by joining a biconvex positive lens L31, a biconvex positive lens L32, and a negative meniscus lens L33 having a concave surface facing the object side, which are arranged in order from the object side along the optical axis. It consists of a lens. The fourth lens group G4 is arranged in order from the object side along the optical axis, and is a cemented lens of a positive meniscus lens L41 having a concave surface facing the object side and a biconcave negative lens L42, and a concave surface facing the object side. The positive meniscus lens L43 and a cemented lens of a negative meniscus lens L44 having a concave surface facing the object side. In this embodiment, an antireflection film, which will be described later, is formed on the image side lens surface of the negative lens L42 (corresponding to the surface number 20 in Table 3 below) to effectively reduce ghosts.

  Table 3 shows a table of specifications in the third embodiment. The surface numbers 1 to 23 in Table 3 correspond to the surfaces 1 to 23 shown in FIG. In the third embodiment, the second lens surface is formed in an aspherical shape.

  In the table, the axial air space between the first lens group G1 and the second lens group G2 is D6, the axial air space between the second lens group G2 and the aperture stop S is D11, and the aperture stop S The axial air gap between the third lens group G3 and the third lens group G3 and the fourth lens group G4 is D17. These on-axis air spacings, ie D6, D11, D12 and D17, change during focusing.

(Table 3)
[Overall specifications]
f = 60.0, FNO = 2.92, Bf = 37.96
[Lens specifications]
Surface number r d nd νd
1 60.3817 1.1000 1.834000 37.17
2 * 22.6018 3.0297
3 3399.2300 2.4000 1.755000 52.32
4 -75.0211 0.1000
5 28.2032 3.4000 1.696797 55.53
6 1042.1457 (D6 = variable)
7 -234.0513 1.5000 1.883000 40.77
8 34.3647 4.2931
9 -29.2081 1.2000 1.617720 49.82
10 36.5790 7.6000 1.883000 40.77
11 -31.1199 (D11 = variable)
12 Aperture stop S (D12 = variable)
13 91.5369 4.0626 1.603000 65.47
14 -45.3779 0.1018
15 47.5342 4.9554 1.603000 65.47
16 -31.3415 1.4000 1.846660 23.78
17 -223.9687 (D17 = variable)
18 -4996.8991 2.7000 1.846660 23.78
19 -37.4608 1.4000 1.720000 43.69
20 28.1629 2.7000
21 -103.6322 3.5000 1.595510 39.23
22 -24.1631 1.3000 1.883000 40.77
23 -60.5172 (Bf)
[Aspherical data]
Second side
K = -2.0292, A4 = 3.42730E-05, A6 = -3.44480E-08, A8 = 1.29790E-10, A10 = -1.21790E-13
[Variable interval data]
β 0 times -0.5 times -1.0 times D6 2.50000 6.38544 13.10605
D11 13.17882 9.29338 2.57277
D12 16.48970 10.27593 3.94864
D17 2.10000 8.31377 14.64137
[Conditional expression]
(1) β0 = 3.03
(2) β1 = -0.22
(3) nd = 1.26

  As can be seen from the table of specifications shown in Table 3, it can be seen that the photographic lens according to the present example satisfies all the conditional expressions (1) to (3).

  8A and 8B are graphs showing various aberrations of the third embodiment. FIG. 8A is a diagram showing various aberrations when the shooting magnification is 0, that is, in the infinite focus state, and FIG. FIG. 8C is a diagram illustrating various aberrations in the close focus state at a photographing magnification of −1.0 times.

  As is apparent from the respective aberration diagrams, in the second embodiment, various aberrations are well corrected from an imaging magnification of 0 times, that is, from an infinitely focused state to an imaging magnification of -1.0 times, and excellent imaging. It can be seen that it has performance.

  As a result, by mounting the photographic lens of the third embodiment, excellent optical performance can be secured even in a digital single-lens reflex camera (photographing apparatus, see FIG. 1).

(Fourth embodiment)
A fourth embodiment of the present application will be described with reference to FIGS. 9 and 10 and Table 4. FIG. As shown in FIG. 9, the photographing lens according to the present embodiment includes a first lens group G1 having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the object side along the optical axis. It comprises a group G2, an aperture stop S for adjusting the amount of light, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. Yes.

  The above-described photographing lens has the first lens group G1, the fourth lens group G4, and the aperture stop S with respect to the image plane I during focusing from the infinity to the closest distance (equal magnification state). The second lens group G2 is moved to the image plane I side along the optical axis, and the third lens group G3 is moved to the object side along the optical axis.

  The first lens group G1 is arranged in order from the object side along the optical axis, the negative meniscus lens L11 having a convex surface facing the object side, the positive lens L12 having a biconvex shape, and the positive meniscus having a convex surface facing the object side. Lens L13. The second lens group G2 is arranged in order from the object side along the optical axis, a negative lens L21 having a biconcave shape and an aspheric surface on the image side lens surface, and a negative meniscus lens L22 having a concave surface facing the object side. And a cemented lens with a positive meniscus lens L23 having a concave surface directed toward the object side. The third lens group G3 includes a biconvex positive lens L31, and a cemented lens of a biconvex positive lens L32 and a biconcave negative lens L33, which are arranged in order from the object side along the optical axis. . The fourth lens group G4 is arranged in order from the object side along the optical axis, a cemented lens L42 of a positive meniscus lens L41 having a concave surface facing the object side and a biconcave negative lens, and a convex surface facing the object side. And a positive meniscus lens L43. In this embodiment, an antireflection film described later is formed on the object side lens surface of the positive meniscus lens L43 (corresponding to the surface number 21 in Table 4 below) to effectively reduce the ghost.

  Table 4 shows a table of specifications in the fourth embodiment. In addition, the surface numbers 1-22 in Table 4 respond | correspond to the surfaces 1-22 shown in FIG. In the fourth embodiment, the lens surface of the eighth surface is formed in an aspheric shape.

  In the table, the axial air space between the first lens group G1 and the second lens group G2 is D6, the axial air space between the second lens group G2 and the aperture stop S is D11, and the aperture stop S The axial air gap between the third lens group G3 and the third lens group G3 and the fourth lens group G4 is D17. These on-axis air spacings, ie D6, D11, D12 and D17, change during focusing.

(Table 4)
[Overall specifications]
f = 64.9, FNO = 2.88, Bf = 37.83
[Lens specifications]
Surface number r d nd νd
1 73.1911 1.1897 1.749497 35.28
2 23.7843 4.6333
3 89.9396 3.2000 1.677900 50.74
4 -69.3425 0.1081
5 32.2463 3.4000 1.640000 60.09
6 119.8334 (D6 = variable)
7 -452.8613 1.2979 1.744000 44.79
8 * 42.2438 5.3891
9 -23.9371 2.2712 1.658440 50.88
10 -451.4167 6.3000 1.883000 40.77
11 -27.2977 (D11 = variable)
12 Aperture stop S (D12 = variable)
13 113.4847 3.8657 1.620410 60.29
14 -50.6983 0.1081
15 53.8201 5.1041 1.603000 65.47
16 -35.6935 1.2978 1.761820 26.52
17 345.1147 (D17 = variable)
18 -1814.3448 3.2109 1.755200 27.51
19 -42.2202 1.7000 1.743200 49.32
20 25.3684 0.8470
21 25.6333 3.4346 1.568830 56.32
22 55.0236 (Bf)
[Aspherical data]
8th page
K = -0.0421, A4 = -1.60920E-06, A6 = -5.10530E-09, A8 = 1.78050E-11, A10 = -9.31080E-14
[Variable interval data]
β 0 times -0.5 times -1.0 times D6 2.34559 5.84062 11.23623
D11 14.06385 10.56882 5.17320
D12 21.92885 12.96078 4.11221
D17 1.88582 10.85389 19.70246
[Conditional expression]
(1) β0 = 3.20
(2) β1 = -0.17
(3) nd = 1.26

  As can be seen from the table of specifications shown in Table 4, it can be seen that the photographic lens according to the present example satisfies all the conditional expressions (1) to (3).

  10A and 10B are graphs showing various aberrations of the fourth embodiment. FIG. 10A is a diagram showing various aberrations when the shooting magnification is 0, that is, in the infinite focus state, and FIG. FIG. 10C is a diagram illustrating various aberrations in the close focus state at a photographing magnification of −1.0 times.

  As is apparent from the respective aberration diagrams, in the fourth embodiment, various aberrations are corrected well from the photographing magnification of 0 times, that is, from the infinite focus state to the photographing magnification of -1.0 times, and excellent imaging. It can be seen that it has performance.

  As a result, by mounting the photographing lens of the fourth embodiment, excellent optical performance can be ensured even in a digital single-lens reflex camera (photographing apparatus, see FIG. 1).

(5th Example)
A fifth embodiment of the present application will be described with reference to FIGS. As shown in FIG. 11, the photographing lens according to the present embodiment includes a first lens group G1 having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the object side along the optical axis. It comprises a group G2, an aperture stop S for adjusting the amount of light, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. Yes.

  The above-described photographing lens has the first lens group G1, the fourth lens group G4, and the aperture stop S with respect to the image plane I during focusing from the infinity to the closest distance (equal magnification state). The second lens group G2 is moved to the image plane I side along the optical axis, and the third lens group G3 is moved to the object side along the optical axis.

  The first lens group G1 includes, in order from the object side along the optical axis, a negative 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 biconvex positive The negative meniscus lens L11 closest to the object side is provided with a resin layer on the glass lens surface on the image side to form an aspherical surface. The second lens group G2 is arranged in order from the object side along the optical axis, and includes a negative meniscus lens L21 having a convex surface on the object side and an aspheric surface on the image side lens surface, a biconcave negative lens L22, and both It is composed of a cemented lens with a convex positive lens L23. The third lens group G3 includes, in order from the object side along the optical axis, a positive meniscus lens L31 having a concave surface facing the object side, a positive lens L32 having a biconvex shape, and a negative meniscus lens having a concave surface facing the object side. It consists of a cemented lens with L33. The fourth lens group G4 is arranged in order from the object side along the optical axis. The negative meniscus lens L41 has a convex surface facing the object side, the negative meniscus lens L42 has a convex surface facing the object side, and the convex surface faces the object side. And a cemented lens with a positive meniscus lens L43. In the present embodiment, although details will be described later, the object side lens surface of the positive lens L32 (corresponding to surface number 16 in Table 5 below) and the object side lens surface of the negative meniscus lens L41 (surface number in Table 5). 19), an antireflection film described later is formed to effectively reduce the ghost.

  Table 5 shows a table of specifications in the fifth embodiment. The surface numbers 1 to 23 in Table 5 correspond to the surfaces 1 to 23 shown in FIG. In the fifth embodiment, each of the third and ninth lens surfaces is formed in an aspheric shape.

  In the table, the axial air space between the first lens group G1 and the second lens group G2 is D7, the axial air space between the second lens group G2 and the aperture stop S is D12, and the aperture stop S The axial air gap between the third lens group G3 and the third lens group G3 and the fourth lens group G4 is D18. These on-axis air spacings, D7, D12, D13 and D18, change during focusing.

(Table 5)
[Overall specifications]
f = 50.75, FNO = 2.80, Bf = 35.00
[Lens specifications]
Surface number r d nd νd
1 72.3338 1.2394 1.834810 42.72
2 20.5000 0.2000 1.553890 38.09
3 * 21.7574 3.6262
4 49.4081 2.8000 1.729157 54.68
5 322.3365 0.0443
6 43.9944 3.2000 1.816000 46.63
7 -215.5926 (D7 = variable)
8 89.5564 1.2394 1.516120 64.03
9 * 21.0795 5.6430
10 -24.8795 1.6821 1.620040 36.30
11 53.7747 5.7101 1.883000 40.77
12 -29.6576 (D12 = variable)
13 Aperture stop S (D13 = variable)
14 -164.6300 2.5000 1.497820 82.56
15 -43.8195 0.0443
16 48.5362 5.0000 1.618000 63.38
17 -31.5106 1.0624 1.846660 23.78
18 -87.1486 (D18 = variable)
19 87.4674 1.1509 1.805180 25.43
20 27.5622 1.5139
21 56.1194 1.2837 1.801000 34.96
22 17.5250 6.0000 1.846660 23.78
23 76.8622 (Bf)
[Aspherical data]
Third side
K = 1.5218, A4 = -4.94910E-07, A6 = 1.58790E-08, A8 = -6.47580E-11, A10-3.02540E-13
9th page
K = -2.3833, A4 = 3.22620E-05, A6 = -1.31840E-07, A8 = 5.38320E-10, A10 = -1.90480E-12
[Variable interval data]

β 0 times -0.5 times -1.0 times D7 2.73230 6.40936 13.01116
D12 11.62011 7.94305 1.34125
D13 20.51008 10.48069 0.88340
D18 2.96672 12.99737 22.59339
[Conditional expression]
(1) β0 = 1.79
(2) β1 = 0.74
(3) nd = 1.26

  As can be seen from the table of specifications shown in Table 5, it can be seen that the photographic lens according to the present example satisfies all the conditional expressions (1) to (3).

  12A and 12B are graphs showing various aberrations of the fifth example. FIG. 12A is a diagram showing various aberrations when the shooting magnification is 0, that is, in an infinite focus state, and FIG. FIG. 12C is a diagram illustrating various aberrations in the close focus state at a photographing magnification of −1.0 times.

  As is apparent from the respective aberration diagrams, in the fifth embodiment, various aberrations are well corrected from an imaging magnification of 0 times, that is, from an infinitely focused state to an imaging magnification of -1.0 times, and excellent imaging. It can be seen that it has performance.

  As a result, by mounting the photographing lens of the fifth embodiment, excellent optical performance can be ensured even in a digital single lens reflex camera (photographing apparatus, see FIG. 1).

(Sixth embodiment)
A sixth embodiment of the present application will be described with reference to FIGS. 13 and 14 and Table 6. FIG. As shown in FIG. 13, the photographic lens according to the present example includes a first lens group G1 having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the object side along the optical axis. It comprises a group G2, an aperture stop S for adjusting the amount of light, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. Yes.

  The above-described photographing lens has the first lens group G1, the fourth lens group G4, and the aperture stop S with respect to the image plane I during focusing from the infinity to the closest distance (equal magnification state). The second lens group G2 is moved to the image plane I side along the optical axis, and the third lens group G3 is moved to the object side along the optical axis.

  The first lens group G1 is arranged in order from the object side along the optical axis. The negative meniscus lens L11 having a convex surface facing the object side, the positive lens L12 having a biconvex shape, and the negative meniscus having a convex surface facing the object side. The lens L13 includes a biconvex positive lens L14. The second lens group G2 is composed of a biconcave negative lens L21 and a cemented lens of a biconcave negative lens L22 and a biconvex positive lens L23 arranged in order from the object side along the optical axis. Is done. The third lens group G3 is formed by joining a biconvex positive lens L31, a biconvex positive lens L32, and a negative meniscus lens L33 having a concave surface facing the object side, which are arranged in order from the object side along the optical axis. It consists of a lens. The fourth lens group G4 includes a cemented lens of a biconvex positive lens L41 and a biconcave negative lens L42 arranged in order from the object side along the optical axis, and a positive meniscus lens having a concave surface facing the object side. L43 and a negative meniscus lens L44 having a concave surface facing the object side. In this embodiment, at least one of the object side lens surface of the positive lens L31 (corresponding to surface number 15 in Table 6 below) and the image side lens surface of the negative lens L42 (corresponding to surface number 22 in Table 6). An antireflection film, which will be described later, is formed on one surface to effectively reduce ghosts.

  Table 6 shows a table of specifications in the sixth embodiment. In addition, the surface numbers 1-26 in Table 6 respond | correspond to the surfaces 1-26 shown in FIG.

  In the table, the axial air space between the first lens group G1 and the second lens group G2 is D8, the axial air space between the second lens group G2 and the aperture stop S is D13, and the aperture stop S The axial air gap between the third lens group G3 and the third lens group G3 and the fourth lens group G4 is D19. These on-axis air spacings, D8, D13, D14 and D19, change during focusing.

(Table 6)
[Overall specifications]
f = 60.0, FNO = 2.88, Bf = 35.07
[Lens specifications]
Surface number r d nd νd
1 49.6392 2.0000 1.883000 40.77
2 24.1735 4.5000
3 107.0994 3.2000 1.834810 42.72
4 -118.9379 0.1000
5 23.9586 2.2000 1.487490 70.24
6 22.1799 1.7000
7 43.4010 3.5000 1.563840 60.69
8 -804.1163 (D8 = variable)
9 -81.7637 1.6000 1.883000 40.77
10 49.2732 3.4322
11 -35.4331 2.1000 1.720000 43.69
12 32.3118 8.0000 1.883000 40.77
13 -30.3900 (D13 = variable)
14 Aperture stop S (D14 = variable)
15 69.6837 4.5000 1.497000 81.61
16 -45.6572 0.1000
17 63.7316 5.3000 1.487490 70.24
18 -33.6688 1.6000 1.846660 23.78
19 -91.3448 (D19 = variable)
20 661.9601 4.5000 1.846660 23.78
21 -27.3275 1.8000 1.755200 27.51
22 36.2356 2.6000
23 -215.2877 2.8000 1.846660 23.78
24 -38.5091 0.9000
25 -28.6608 1.5000 1.755000 52.32
26 -121.5032 (Bf)
[Variable interval data]
β 0 times -0.5 times -1.0 times D7 2.73230 6.40936 13.01116
D6 2.62569 6.63506 13.83349
D8 3.53723 7.45531 13.98947
D13 12.82448 8.90640 2.37224
D14 21.64645 12.66373 3.44637
D19 3.17811 12.16083 21.37819
[Conditional expression]
(1) β0 = 3.93
(2) β1 = -0.34
(3) nd = 1.26

  As can be seen from the table of specifications shown in Table 6, it can be seen that the photographic lens according to the present example satisfies all the conditional expressions (1) to (3).

  14A and 14B are graphs showing various aberrations of the sixth example. FIG. 14A is a diagram showing various aberrations when the shooting magnification is 0, that is, in the infinite focus state, and FIG. 14B is a shooting magnification of -0.5. FIG. 14C is a diagram illustrating various aberrations in the close focus state at a photographing magnification of −1.0 times.

  As is apparent from the respective aberration diagrams, in the sixth embodiment, various aberrations are satisfactorily corrected from an imaging magnification of 0 times, that is, from an infinitely focused state to an imaging magnification of -1.0 times, and excellent imaging. It can be seen that it has performance.

  As a result, by mounting the photographic lens of the sixth embodiment, excellent optical performance can be secured even in a digital single-lens reflex camera (photographing apparatus, see FIG. 1).

(Seventh embodiment)
A seventh embodiment of the present application will be described with reference to FIGS. 15 and 16 and Table 7. FIG. As shown in FIG. 15, the photographing lens according to the present embodiment includes a first lens group G1 having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the object side along the optical axis. It comprises a group G2, an aperture stop S for adjusting the amount of light, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. Yes.

  The above-described photographing lens has the first lens group G1, the fourth lens group G4, and the aperture stop S with respect to the image plane I during focusing from the infinity to the closest distance (equal magnification state). The second lens group G2 is moved to the image plane I side along the optical axis, and the third lens group G3 is moved to the object side along the optical axis.

  The first lens group G1 is arranged in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface on the object side and an aspheric surface on the image side lens surface, a biconvex positive lens L12, It is composed of a cemented lens composed of a negative meniscus lens L13 having a convex surface facing the object side and a positive meniscus lens L14 having a convex surface facing the object side. The second lens group G2 is composed of a biconcave negative lens L21 and a cemented lens of a biconcave negative lens L22 and a biconvex positive lens L23 arranged in order from the object side along the optical axis. Is done. The third lens group G3 is formed by joining a biconvex positive lens L31, a biconvex positive lens L32, and a negative meniscus lens L33 having a concave surface facing the object side, which are arranged in order from the object side along the optical axis. It consists of a lens. The fourth lens group G4 includes, in order from the object side along the optical axis, a positive meniscus lens L41 having a concave surface facing the object side, a negative lens L42 having a biconcave shape, and a positive meniscus having a concave surface facing the object side. The lens L43 and a negative meniscus lens L44 having a concave surface facing the object side. In this embodiment, the object side lens surface of the positive lens L31 (corresponding to surface number 14 in Table 7 below), the object side lens surface of the positive lens L32 (corresponding to surface number 16 in Table 7), and the negative lens An antireflection film described later is formed on at least one of L42 image side lens surfaces (corresponding to surface number 22 in Table 7) to effectively reduce ghosts.

  Table 7 shows a table of specifications in the seventh embodiment. The surface numbers 1 to 26 in Table 7 correspond to the surfaces 1 to 26 shown in FIG. In the seventh embodiment, the second lens surface is formed in an aspherical shape.

  In the table, the axial air space between the first lens group G1 and the second lens group G2 is D7, the axial air space between the second lens group G2 and the aperture stop S is D12, and the aperture stop S The axial air gap between the third lens group G3 and the third lens group G3 and the fourth lens group G4 is D18. These on-axis air spacings, D7, D12, D13 and D18, change during focusing.

(Table 7)
[Overall specifications]
f = 57.6, FNO = 2.88, Bf = 36.95
[Lens specifications]
Surface number r d nd νd
1 99.7242 1.3446 1.834000 37.17
2 * 25.2586 2.9500
3 162.4990 3.2654 1.755000 52.32
4 -63.3696 0.0960
5 37.5818 1.5366 1.846660 23.78
6 27.4223 3.4574 1.883000 40.77
7 269.9034 (D7 = variable)
8 -204.9659 1.1525 1.804000 46.58
9 31.9916 4.4699
10 -26.4063 1.2965 1.639300 44.89
11 38.5096 7.4431 1.883000 40.77
12 -28.3376 (D12 = variable)
13 Aperture stop S (D13 = variable)
14 88.2222 3.4574 1.438750 94.97
15 -40.8526 0.0978
16 54.7952 4.5139 1.497000 81.61
17 -29.6922 1.2485 1.846660 23.78
18 -63.2238 (D18 = variable)
19 -59.1213 1.9208 1.846660 23.78
20 -32.4933 0.5282
21 -45.9203 1.3446 1.701540 41.24
22 41.5215 2.4970
23 -56.7820 2.8812 1.639800 34.47
24 -28.5627 1.2485
25 -18.5941 1.3446 1.640000 60.09
26 -26.8640 (Bf)
[Aspherical data]
Second side
K = 0.5089, A4 = 4.78110E-06, A6 = 1.77850E-09, A8 = 3.09600E-11, A10 = -7.17800E-15
[Variable interval data]
β 0 times -0.5 times -1.0 times D7 2.26762 5.23755 10.56946
D12 11.02008 8.05013 3.19843
D13 19.08376 11.23975 3.59710
D18 1.91404 9.75805 17.40070
[Conditional expression]
(1) β0 = 2.59
(2) β1 = -0.20
(3) nd = 1.26

  As can be seen from the table of specifications shown in Table 7, it can be seen that the photographic lens according to the present example satisfies all the conditional expressions (1) to (3).

  FIGS. 16A and 16B are graphs showing various aberrations of the seventh example. FIG. 16A is a diagram showing various aberrations when the shooting magnification is 0, that is, in the infinite focus state, and FIG. FIG. 16C is a diagram illustrating various aberrations in the close focus state at a photographing magnification of −1.0 times.

  As is apparent from the respective aberration diagrams, in the seventh embodiment, various aberrations are well corrected from an imaging magnification of 0 times, that is, from an infinitely focused state to an imaging magnification of -1.0 times, and excellent imaging. It can be seen that it has performance.

  As a result, by mounting the photographing lens of the seventh embodiment, excellent optical performance can be ensured even in a digital single-lens reflex camera (photographing apparatus, see FIG. 1).

(Eighth embodiment)
An eighth embodiment of the present application will be described with reference to FIGS. As shown in FIG. 17, the photographic lens according to the present example includes a first lens group G1 having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the object side along the optical axis. It comprises a group G2, an aperture stop S for adjusting the amount of light, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. Yes.

  The above-described photographing lens has the first lens group G1, the fourth lens group G4, and the aperture stop S with respect to the image plane I during focusing from the infinity to the closest distance (equal magnification state). The second lens group G2 is moved to the image plane I side along the optical axis, and the third lens group G3 is moved to the object side along the optical axis.

  The first lens group G1 includes a negative meniscus lens L11 having a convex surface facing the object side, a biconvex positive lens L12, and a biconvex positive lens L13, which are arranged in order from the object side along the optical axis. Composed. The second lens group G2 is arranged in order from the object side along the optical axis, a negative lens L21 having a biconcave shape and an aspheric surface on the image side lens surface, a biconcave negative lens L22, and a biconvex shape. It consists of a cemented lens with a positive lens L23. The third lens group G3 includes a biconvex positive lens L31, and a cemented lens of a biconvex positive lens L32 and a biconcave negative lens L33, which are arranged in order from the object side along the optical axis. . The fourth lens group G4 includes, in order from the object side along the optical axis, a cemented lens of a biconvex positive lens L41 and a biconcave negative lens L42, and a positive meniscus lens having a convex surface facing the object side. L43. In this embodiment, the object side lens surface of the positive lens L31 (corresponding to surface number 13 in Table 8 below), the object side lens surface of the positive lens L32 (corresponding to surface number 15 in Table 8), and the negative lens An antireflection film to be described later is provided on at least one of the image side lens surface of L42 (corresponding to surface number 20 in Table 8) and the object side lens surface of positive meniscus lens L43 (corresponding to surface number 21 in Table 8). Forming and effectively reducing ghosting.

  Table 8 shows a table of specifications in the eighth embodiment. In addition, the surface numbers 1-22 in Table 8 respond | correspond to the surfaces 1-22 shown in FIG. In the eighth example, the lens surface of the eighth surface is formed in an aspheric shape.

  In the table, the axial air space between the first lens group G1 and the second lens group G2 is D6, the axial air space between the second lens group G2 and the aperture stop S is D11, and the aperture stop S The axial air gap between the third lens group G3 and the third lens group G3 and the fourth lens group G4 is D17. These on-axis air spacings, ie D6, D11, D12 and D17, change during focusing.

(Table 8)
[Overall specifications]
f = 60.0, FNO = 2.89, Bf = 43.16
[Lens specifications]
Surface number r d nd νd
1 61.8055 1.1000 1.749497 35.28
2 21.7357 4.5000
3 178.0125 2.8000 1.677900 50.74
4 -81.1807 0.1000
5 31.8030 3.4000 1.640000 60.09
6 -430.0858 (D6 = variable)
7 -93.9735 1.2001 1.744000 44.79
8 * 43.2422 4.7000
9 -26.6717 2.1000 1.658440 50.88
10 225.7682 5.4000 1.883000 40.77
11 -26.6715 (D11 = variable)
12 Aperture stop S (D12 = variable)
13 76.1926 3.5744 1.620410 60.29
14 -51.5727 0.1000
15 57.2625 4.7195 1.603000 65.47
16 -31.6111 1.2000 1.761820 26.52
17 518.3373 (D17 = variable)
18 1121.7328 2.9689 1.755200 27.51
19 -43.1177 1.8000 1.743200 49.32
20 23.2742 0.7437
21 23.6785 3.1758 1.568830 56.32
22 47.1230 (Bf)
[Aspherical data]
8th page
K = 0.1631, A4 = -2.60650E-06, A6 = -2.93000E-09, A8 = -1.25040E-11, A10 = -3.46030E-14
[Variable interval data]
β 0 times -0.5 times -1.0 times D6 3.86985 7.10150 12.09051
D11 13.24131 10.00966 5.02065
D12 20.36812 12.07586 3.89411
D17 1.18069 9.47295 17.65470
[Conditional expression]
(1) β0 = 3.20
(2) β1 = -0.23
(3) nd = 1.26

  As can be seen from the table of specifications shown in Table 8, it can be seen that the photographic lens according to the present example satisfies all the conditional expressions (1) to (3).

  18A and 18B are graphs showing various aberrations of the eighth embodiment. FIG. 18A is a diagram showing various aberrations when the shooting magnification is 0, that is, in the infinite focus state, and FIG. 18B is a shooting magnification being −0.5 times. FIG. 18C is a diagram illustrating various aberrations in the close focus state at a photographing magnification of −1.0 times.

  As is apparent from the respective aberration diagrams, in the eighth embodiment, various aberrations are satisfactorily corrected from the photographing magnification of 0 times, that is, from the infinitely focused state to the photographing magnification of -1.0 times, and excellent imaging. It can be seen that it has performance.

  As a result, by mounting the photographing lens of the eighth embodiment, excellent optical performance can be secured even in a digital single-lens reflex camera (photographing apparatus, see FIG. 1).

  In the above-described embodiment, the four-group configuration is shown as the photographing lens, but the present invention can be applied to other group configurations such as a five-group configuration.

  Alternatively, the lens group or the partial lens group may be vibrated in a direction perpendicular to the optical axis to correct the image blur caused by camera shake. In particular, it is preferable that the whole or part of the fourth lens group G4 is a vibration-proof lens group.

  In the photographic lens according to the present application, each lens surface may be aspherical. The aspherical surface may be any one of an aspherical surface by grinding, a glass mold aspherical surface in which glass is formed into an aspherical shape, and a composite aspherical surface in which a resin provided on the glass surface is formed in an aspherical shape.

  Here, the antireflection film used for the photographing lens of the above embodiment will be described. As shown in FIG. 19, the antireflection film 101 is composed of seven layers (first layer 101a to seventh layer 101g), and is formed on the optical surface of the optical member 102 of the photographing lens. In each embodiment, the number of lens surfaces on which the antireflection film is formed is not limited, and a larger number is preferable from the viewpoint of optical performance.

  The first layer 101a is formed of aluminum oxide deposited by a vacuum deposition method. A second layer 101b made of a mixture of titanium oxide and zirconium oxide deposited by a vacuum deposition method is formed on the first layer 101a. Subsequently, a third layer 101c made of aluminum oxide deposited by vacuum deposition is formed on the second layer 101b, and a mixture of titanium oxide and zirconium oxide deposited by vacuum deposition on the third layer 101c. A fourth layer 101d made of is formed. Further, a fifth layer 101e made of aluminum oxide deposited by a vacuum deposition method is formed on the fourth layer 101d, and a mixture of titanium oxide and zirconium oxide deposited by a vacuum deposition method on the fifth layer 101e. A sixth layer 101f is formed. Then, a seventh layer 101g made of a mixture of silica and magnesium fluoride is formed on the sixth layer 101f by a wet process.

  The seventh layer 101g is formed using a sol-gel method that is a kind of wet process. In the sol-gel method, a sol, which is an optical thin film material, is applied on the optical surface of an optical member, the gel film is deposited, and then immersed in a liquid. This is a method for producing a film by vaporizing and drying. However, the wet process is not limited to the sol-gel method, and a method of obtaining a solid film without going through a gel state may be used.

  As described above, the antireflection film 101 is formed by electron beam evaporation as a dry process from the first layer 101a to the sixth layer 101f, and the seventh layer 101g which is the outermost surface layer (uppermost layer) is formed of hydrofluoric acid / It is formed by a wet process using a sol solution prepared by the magnesium acetate method.

  Next, a procedure for forming the antireflection film 101 having the above configuration will be described. First, using a vacuum deposition apparatus on the lens film formation surface (the optical surface of the optical member 102 described above) in advance, an aluminum oxide layer to be the first layer 101a, a titanium oxide-zirconium oxide mixed layer to be the second layer 101b, An aluminum oxide layer to be the third layer 101c, a titanium oxide-zirconium oxide mixed layer to be the fourth layer 101d, an aluminum oxide layer to be the fifth layer 101e, and a titanium oxide-zirconium oxide mixed layer to be the sixth layer 101f are formed in this order. . Then, after the optical member 102 is taken out from the vacuum deposition apparatus, a sol solution prepared by the hydrofluoric acid / magnesium acetate method is added with a binder component by a spin coating method, and the silica and fluorine to form the seventh layer 101g are applied. A layer comprising a mixture of magnesium halide is formed. Here, the reaction formula when prepared by the hydrofluoric acid / magnesium acetate method is shown in the following formula (b).

2HF + Mg (CH ₃ COO) ² → MgF ₂ + 2CH ₃ COOH (b)

The sol solution used for the film formation is used for film formation after mixing raw materials and subjecting to an autoclave at 140 ° C. for 24 hours at a high temperature and pressure. After the film formation of the seventh layer 101g is completed, the optical member 102 is completed by heat treatment in the atmosphere at 160 ° C. for 1 hour. More specifically, by using the sol-gel method described above, MgF ₂ particles having a size of several nanometers to several tens of nanometers can be formed, and further, secondary particles are formed by collecting several of these particles. By depositing these secondary particles, the seventh layer 101g is formed.

The optical performance of the antireflection film 101 formed as described above will be described using the spectral characteristics shown in FIG. FIG. 20 shows the spectral characteristics when the light ray is vertically incident when the antireflection film 101 is designed under the conditions shown in Table 9 below when the reference wavelength λ is 550 nm. Table 9 shows aluminum oxide as Al ₂ O ₃ , titanium oxide-zirconium oxide mixture as ZrO ₂ + TiO ₂ , silica and magnesium fluoride as SiO ₂ + MgF _2, and reference wavelength λ of 550 nm. In some cases, the respective design values are shown when the refractive index of the substrate is 1.46, 1.62, 1.74 and 1.85.

(Table 9)
Substance Refractive index Optical film thickness Optical film thickness Optical film thickness Optical film thickness Medium Air 1.00
7th layer SiO ₂ + MgF ₂ 1.26 0.275λ 0.268λ 0.271λ 0.269λ
6th layer ZrO ₂ + TiO ₂ 2.12 0.045λ 0.057λ 0.054λ 0.059λ
5th layer Al ₂ O ₃ 1.65 0.212λ 0.171λ 0.178λ 0.162λ
4th layer ZrO ₂ + TiO ₂ 2.12 0.077λ 0.127λ 0.13λ 0.158λ
3rd layer Al ₂ O ₃ 1.65 0.288λ 0.122λ 0.107λ 0.08λ
Second layer ZrO ₂ + TiO ₂ 2.12 0 0.059λ 0.075λ 0.105λ
1st layer Al ₂ O ₃ 1.65 0 0.257λ 0.03λ 0.03λ
Substrate refractive index 1.46 1.62 1.74 1.85

  From FIG. 20, it can be seen that the reflectance is suppressed to 0.2% or less over the entire wavelength range of 420 nm to 720 nm.

  In the photographic lens of the first example, since the refractive index of the positive lens L31 is 1.497820, an antireflection film corresponding to the refractive index of the substrate of 1.46 is used on the object-side lens surface of the positive lens L31. Is possible.

  In the photographic lens of the second embodiment, since the refractive index of the positive lens L32 is 1.603000, an antireflection film corresponding to a refractive index of the substrate corresponding to 1.62 is used on the object side lens surface of the positive lens L32. Is possible.

  In the photographic lens of the third example, since the refractive index of the negative lens L42 is 1.720000, an antireflection film corresponding to the refractive index of the substrate corresponding to 1.74 is used on the image side lens surface of the negative lens L42. Is possible.

  In the photographic lens of the fourth example, since the refractive index of the positive meniscus lens L43 is 1.568830, an antireflection film corresponding to a refractive index of the substrate of 1.62 is provided on the object side lens surface of the positive meniscus lens L43. It is possible to use.

  In the photographing lens of the fifth example, since the refractive index of the positive lens L32 is 1.618000, an antireflection film corresponding to a refractive index of the substrate corresponding to 1.62 is used on the object side lens surface of the positive lens L32. Is possible. Further, in the photographing lens of the fifth example, since the refractive index of the negative meniscus lens L41 is 1.805180, an antireflection film corresponding to the refractive index of the substrate of 1.85 is provided on the object side lens surface of the negative meniscus lens L41. It is possible to use.

  In the photographic lens of the sixth example, the refractive index of the positive lens L31 is 1.497000, and an antireflection film corresponding to the refractive index of the substrate of 1.46 is used for the object-side lens surface of the positive lens L31. Is possible. Further, in the photographic lens of the sixth example, since the refractive index of the negative lens L42 is 1.755200, an antireflection film corresponding to the refractive index of the substrate corresponding to 1.74 is used for the lens surface on the image plane side of the negative lens L42. It is possible.

  In the photographing lens of the seventh example, the refractive index of the positive lens L31 is 1.438750, and an antireflection film corresponding to the refractive index of the substrate of 1.46 is used for the lens surface on the object side of the positive lens L31. Is possible. The refractive index of the positive lens L32 is 1.4977000, and an antireflection film corresponding to the refractive index of the substrate of 1.46 can be used on the object-side lens surface of the positive lens L32. Further, since the refractive index of the biconcave lens L42 is 1.701540, it is possible to use an antireflection film corresponding to the refractive index of the substrate of 1.74 on the image side lens surface of the biconcave lens L42.

  In the photographing lens of the eighth example, the refractive index of the positive lens L31 is 1.620410, and an antireflection film corresponding to the refractive index of the substrate of 1.62 is used on the object-side lens surface of the positive lens L31. It is possible. The refractive index of the positive lens L32 is 1.603000, and an antireflection film corresponding to the refractive index of the substrate of 1.62 can be used on the object side lens surface of the positive lens L32. The negative lens L42 has a refractive index of 1.743200, and an antireflection film corresponding to a refractive index of the substrate of 1.74 can be used for the image surface side lens surface of the negative lens L42. Further, since the refractive index of the positive meniscus lens L43 is 1.568830, it is possible to use an antireflection film corresponding to the refractive index of the substrate of 1.62 on the object side lens surface of the positive meniscus lens L43.

  In this way, by applying the antireflection film 101 of this embodiment to each of the photographing lenses of the first to eighth examples, focusing from an infinite object to an equal magnification object is performed in-focus, and the focusing lens. Focusing is possible with autofocus using a drive motor such as an ultrasonic motor with a small movement amount of the group, and ghosts and flares can be further reduced to obtain a high-quality image. A photographic lens, a photographic device including the photographic lens, and a focusing method suitable for optical devices such as film cameras and electronic still cameras having a number of about 2.8 to 3.0 and a focal length of about 50 to 60 can be provided. .

  The antireflection film 101 can be used as an optical element provided on the optical surface of a plane-parallel plate, or can be used provided on the optical surface of a lens formed in a curved surface. is there.

  Next, a modified example of the antireflection film 101 will be described. The antireflection film of this modification is composed of five layers and is configured under the conditions shown in Table 10 below. Note that the sol-gel method described above is used to form the fifth layer. Table 10 shows design values when the reference wavelength λ is 550 nm and the refractive index of the substrate is 1.52.

(Table 10)
Material Refractive index Optical film thickness Medium Air 1.00
5th layer Mixture of silica and magnesium fluoride 1.26 0.269λ
4th layer Titanium oxide-zirconium oxide mixture 2.12 0.043λ
3rd layer Aluminum oxide 1.65 0.217λ
Second layer Titanium oxide-zirconium oxide mixture 2.12 0.066λ
1st layer Aluminum oxide 1.65 0.290λ
Board BK7 1.52

  FIG. 21 shows spectral characteristics when light is vertically incident on the antireflection film of the modification. FIG. 21 shows that the reflectance is suppressed to 0.2% or less over the entire wavelength range of 420 nm to 720 nm. FIG. 22 shows the spectral characteristics when the incident angles are 30, 45, and 60 degrees.

  For comparison, FIG. 23 shows the spectral characteristics at the time of vertical incidence of a multilayer broadband antireflection film formed by only a dry process such as a conventional vacuum deposition method and configured under the conditions shown in Table 11 below. FIG. 24 shows the spectral characteristics when the incident angles are 30, 45, and 60 degrees.

(Table 11)
Material Refractive index Optical film thickness Medium Air 1.00
7th layer MgF ₂ 1.39 0.243λ
6th layer Titanium oxide-zirconium oxide mixture 2.12 0.119λ
5th layer Aluminum oxide 1.65 0.057λ
4th layer Titanium oxide-zirconium oxide mixture 2.12 0.220λ
3rd layer Aluminum oxide 1.65 0.064λ
Second layer Titanium oxide-zirconium oxide mixture 2.12 0.057λ
1st layer Aluminum oxide 1.65 0.193λ
Board BK7 1.52

  When the spectral characteristics of the modification shown in FIGS. 21 and 22 are compared with the spectral characteristics of the conventional example shown in FIGS. 23 and 24, the low reflectance of the antireflection film according to the modification can be clearly seen.

  In addition, in order to make this invention easy to understand, it has been described with the configuration requirements of the above embodiment, but it goes without saying that the present invention is not limited to this.

It is a figure which shows the structure of the imaging device (camera) provided with the imaging lens which concerns on this invention. It is sectional drawing which shows the lens structure in the infinite point focusing state of the imaging lens which concerns on 1st Example. FIG. 6 is a diagram for explaining how incident light rays are reflected by a first ghost generation surface (image surface I) and a second ghost generation surface in the photographing lens according to the first example. FIG. 3A is a diagram illustrating various aberrations of the photographing lens according to the first example. FIG. 9A is a diagram illustrating various aberrations in the infinite focus state (photographing magnification is 0 times), and FIG. , And (c) show various aberration diagrams at an imaging magnification of -1.0. It is sectional drawing which shows the lens structure in the infinite point focusing state of the imaging lens which concerns on 2nd Example. FIG. 4 is a diagram illustrating various aberrations of the photographing lens according to Example 2, wherein (a) illustrates various aberrations in the infinite focus state (photographing magnification of 0 times), and (b) illustrates various aberrations at the photographing magnification of −0.5 times. , And (c) show various aberration diagrams at an imaging magnification of -1.0. It is sectional drawing which shows the lens structure in the infinite point focusing state of the imaging lens which concerns on 3rd Example. FIG. 6 is a diagram illustrating various aberrations of the photographing lens according to Example 3, wherein (a) illustrates various aberrations in the infinite focus state (photographing magnification of 0 times), and (b) illustrates various aberrations at the photographing magnification of −0.5 times. , And (c) show various aberration diagrams at an imaging magnification of -1.0. It is sectional drawing which shows the lens structure in the infinite point focusing state of the imaging lens which concerns on 4th Example. FIG. 6A is a diagram illustrating various aberrations of the photographing lens according to Example 4, wherein FIG. 9A illustrates various aberrations in the state of focusing on infinity (photographing magnification 0 ×), and FIG. 9B illustrates various aberrations at a photographing magnification of −0.5 ×. FIGS. 4A and 4C show various aberration diagrams at a photographing magnification of −1.0 times. It is sectional drawing which shows the lens structure in the infinite point focusing state of the imaging lens which concerns on 5th Example. FIG. 7A is a diagram illustrating various aberrations of the photographing lens according to Example 5, wherein FIG. 9A is a diagram illustrating various aberrations in an infinitely focused state (a photographing magnification of 0 ×), and FIG. , And (c) show various aberration diagrams at an imaging magnification of -1.0. It is sectional drawing which shows the lens structure in the infinite point focusing state of the imaging lens which concerns on 6th Example. FIG. 9A is a diagram illustrating various aberrations of the photographing lens according to Example 6. FIG. 10A is a diagram illustrating various aberrations in the infinite focus state (photographing magnification of 0 ×), and FIG. , And (c) show various aberration diagrams at an imaging magnification of -1.0. It is sectional drawing which shows the lens structure in the infinite point focusing state of the imaging lens which concerns on 7th Example. FIG. 9A is a diagram illustrating various aberrations of the taking lens according to Example 7, wherein FIG. 9A is a diagram illustrating various aberrations in the infinite focus state (shooting magnification is 0 times), and FIG. , And (c) show various aberration diagrams at an imaging magnification of -1.0. It is sectional drawing which shows the lens structure in the infinite point focusing state of the imaging lens which concerns on 8th Example. FIG. 9A is a diagram illustrating various aberrations of the taking lens according to Example 8, wherein FIG. 9A is a diagram illustrating various aberrations in the infinite focus state (shooting magnification is 0 times), and FIG. , And (c) show various aberration diagrams at an imaging magnification of -1.0. It is explanatory drawing which shows the structure of the anti-reflective film concerning a present Example. It is a graph which shows the spectral characteristic of the anti-reflective film concerning a present Example. It is a graph which shows the spectral characteristics of the antireflection film concerning a modification. It is a graph which shows the spectral characteristics of the antireflection film concerning a modification. It is a graph which shows the spectral characteristic of the anti-reflective film produced with the prior art. It is a graph which shows the spectral characteristic of the anti-reflective film produced with the prior art.

Explanation of symbols

G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group S Aperture stop I Image plane 1 Camera (imaging device) 2 Shooting lens 3 Quick return mirror 4 Focus plate 5 Pentaprism 6 Eyepiece lens 7 Imaging Element 101 Antireflection film 101a 1st layer 101b 2nd layer 101c 3rd layer 101d 4th layer 101e 5th layer 101f 6th layer 101g 7th layer 102 Optical member

Claims (9)

In a photographing lens that includes first to fourth lens groups arranged in order from the object side along the optical axis, and capable of photographing from 0 times to at least −1.0 times,
At the time of focusing, the first lens group and the fourth lens group are fixed with respect to the image plane, the second lens group and the third lens group are moved in the optical axis direction,
An antireflection film is provided on at least one of the optical surfaces of the third lens group and the fourth lens group;
The antireflection film is composed of a plurality of layers, at least one of which is formed by a wet process,
The layer formed by using the wet process has the following formula when the refractive index for d-line is nd.
nd ≦ 1.30
Satisfy the conditions of
When the lateral magnification of the second lens group in the infinitely focused state is β0 and the lateral magnification of the second lens group in the equal magnification focused state is β1,
1.5 <β0 <2.3
0.3 <β1 <0.9
A photographic lens characterized by satisfying the above conditions . The antireflection film is a multilayer film,
The outermost layer of the multilayer film, the imaging lens according to claim 1, wherein a layer formed using a wet process. The optical surface on which the antireflection film is provided, the imaging lens according to claim 1 or 2, characterized in that towards the concave to the image side. Photographing lens according to any one of claims 1 to 3, characterized in that at least one aspherical surface. The photographic lens according to any one of claims 1 to 4 , wherein the first lens group includes three or less lenses. The fourth lens group, the imaging lens according to any one of claims 1 to 5, characterized in that it is composed of at least three or more lenses. The first lens group and the second lens group, the imaging lens according to any one of claims 1 to 6, characterized in that it has at least one aspherical lens, respectively. Imaging apparatus characterized by comprising a photographing lens according to any one of claims 1-7. In a focusing method of a photographing lens that includes first to fourth lens groups arranged in order from the object side along the optical axis, and capable of photographing from 0 times to at least -1.0 times,
An antireflection film is provided on at least one of the optical surfaces of the third lens group and the fourth lens group ;
The antireflection film is composed of a plurality of layers, at least one of which is formed by a wet process,
The layer formed by using the wet process has the following formula when the refractive index for d-line is nd.
nd ≦ 1.30
Satisfy the conditions of
When the lateral magnification of the second lens group in the infinitely focused state is β0 and the lateral magnification of the second lens group in the equal magnification focused state is β1, the following formula 1.5 <β0 <2. 3 and 0.3 <β1 <0.9 are satisfied,
In focusing, the first lens group and the fourth lens group are fixed with respect to the image plane, and the second lens group and the third lens group are moved in the optical axis direction. Method.

Images