JP5403411B2 - Converter lens and optical apparatus having the same - Google Patents

Description

  The present invention relates to a converter lens and an optical device having the converter lens.

  Conventionally, a detachable converter lens that changes the focal length of the entire lens system has been proposed in order to increase the focal length of a telephoto lens or the like (see, for example, Patent Document 1). In recent years, with respect to this type of converter lens, not only aberration performance but also ghost and flare, which are one of the factors that impair optical performance, have become increasingly strict, and are therefore applied to the lens surface. Higher performance is also required for antireflection films, and multilayer film design techniques and multilayer film formation techniques continue to advance to meet the demands (see, for example, Patent Document 2).

JP 63-201624 A JP 2000-356704 A

  However, the conventional converter lens cannot be said to have sufficient imaging performance. In addition to this, the conventional converter lens also has a problem in that reflected light that becomes a ghost or flare that affects the optical performance is likely to be generated from the optical surface.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a converter lens capable of further reducing ghosts and flares and achieving good optical performance, and an optical apparatus having the same. To do.

  In order to achieve such an object, the present invention is a detachable converter lens that is used by being attached to the image side of a master lens, and is a positive lens including at least a positive lens, a negative lens, and a positive lens. An antireflective film including at least one layer formed using a wet process is applied to at least one of optical surfaces constituting the converter lens having a cemented lens having a refractive power.

  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, when the refractive index in the d-line of the layer formed by using the wet process is nd, it is preferable that the condition of the following formula nd ≦ 1.30 is satisfied.

  Further, it is preferable to have a first lens having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the most object side.

  The first lens group and the second lens group arranged in order from the object side, and a distance from the most image side surface of the first lens group to the most object side surface of the second lens group Is D, and TL is the distance on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the converter lens, the following condition is satisfied: 0.01 <D / TL <0.25 It is preferable to satisfy.

  Further, when the combined focal length of the cemented lens is fc and the focal length of the negative lens constituting the cemented lens is fn, the following condition is satisfied: 0.02 <(− fn) / fc <2.00 It is preferable to satisfy.

  Further, when the refractive index of the d-line of the negative lens constituting the cemented lens is Nn, and the refractive index Np1 of the d-line of the positive lens on the object side joined to the negative lens constituting the cemented lens. It is preferable to satisfy the following formula: 0.75 <Np1 / Nn <0.95.

  Further, the refractive index of d-line of the negative lens constituting the cemented lens is Nn, and the refractive index of d-line of the positive lens on the image side cemented to the negative lens constituting the cemented lens is Np2. At this time, it is preferable to satisfy the following condition: 0.70 <Np2 / Nn <0.95.

  Further, when the magnification of the converter lens is β, it is preferable to satisfy the following formula 1.40 ≦ β.

  Moreover, it is preferable to have an aspherical surface.

  Moreover, it is preferable that the aspheric surface is disposed on the image side of the cemented lens.

  An optical device according to the present invention includes any of the above converter lenses.

  ADVANTAGE OF THE INVENTION According to this invention, a ghost and flare can be reduced more and the converter lens which can achieve favorable optical performance, and an optical apparatus which has this can be provided.

It is a figure which shows the structure which mounted | wore the master lens ML with the converter lens CL which concerns on 1st Example. FIG. 6 is a diagram illustrating various aberrations of the converter lens CL according to Example 1 when focused on infinity. It is a figure explaining a mode that incident light is reflected in the 1st ghost generating surface and the 2nd ghost generating surface in an optical system with which converter lens CL concerning the 1st example was equipped to master lens ML. It is a figure which shows the structure which mounted | wore the master lens ML with the converter lens CL which concerns on 2nd Example. FIG. 12 is a diagram illustrating various aberrations of the converter lens CL according to Example 2 when focusing on infinity. It is a figure which shows the structure which mounted | wore the master lens ML with the converter lens CL which concerns on 3rd Example. FIG. 12 is a diagram illustrating various aberrations of the converter lens CL according to Example 3 when focusing on infinity. It is a figure which shows the structure which mounted | wore the master lens ML with the converter lens CL which concerns on 4th Example. FIG. 11 is a diagram illustrating all aberrations when the converter lens CL according to Example 4 is in focus at infinity. It is a figure which shows the structure which mounted | wore the master lens ML with the converter lens CL which concerns on 5th Example. FIG. 12 is various aberration diagrams of the converter lens CL according to Example 5 when focusing on infinity. It is an aberration diagram of the master lens ML when focusing on infinity. It is a figure which shows the structure of the optical apparatus (camera) provided with the converter lens CL which concerns on 1st Example. 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.

  Hereinafter, embodiments of the present invention will be described.

  In general, the converter lens not only increases the focal length of the master lens, but also increases the aberration of the master lens at the same time, so it is difficult to correct the aberration. This becomes more prominent as the magnification is higher. Therefore, the higher the magnification of the converter lens, the better the optical performance.

  The converter lens according to the present embodiment is used by being attached to the image side of the master lens, and is a detachable converter lens, which has at least a positive refractive power composed of a positive lens, a negative lens, and a positive lens. This is a configuration having a lens. With this configuration, it is possible to increase the power of the negative lens constituting the cemented lens, and the Petzval sum can be reduced, so that a good image surface with little field curvature can be formed. Further, coma and spherical aberration can be corrected well.

  An antireflection film including at least one layer formed by a wet process is applied to at least one of the optical surfaces constituting the converter lens according to the present embodiment based on the above configuration. .

  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. With this configuration, since the difference in refractive index with air can be reduced, the reflection of light can be further reduced, and ghosts and flares can be further reduced.

  Further, in the converter lens according to the present embodiment, when the refractive index at the d-line (wavelength 587.6 nm) of the layer formed using the wet process is nd, the condition of the following formula nd ≦ 1.30 is satisfied. It is preferable. By satisfying this conditional expression, the difference in refractive index with air can be reduced, so that the reflection of light can be further reduced, and ghosts and flares can be further reduced.

  The antireflection film is not limited to a wet process, and may include at least one layer having a refractive index of 1.30 or less (by a dry process or the like). Even if comprised in this way, the effect similar to the case where a wet process is used can be acquired. At this time, the layer having a refractive index of 1.30 or less is preferably the outermost surface layer among the layers constituting the multilayer film.

  The converter lens according to the present embodiment preferably includes a first lens having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the most object side. With this configuration, spherical aberration can be corrected satisfactorily.

  In addition, the converter lens according to the present embodiment includes a first lens group and a second lens group arranged in order from the object side, and the most of the second lens group from the most image side surface of the first lens group. When the distance to the object side surface is D and the distance on the optical axis from the most object side lens surface of the converter lens to the image side lens surface is TL, the following conditional expression (1) is satisfied. It is desirable.

  0.01 <D / TL <0.25 (1)

  Conditional expression (1) indicates that the distance from the most image side surface of the first lens group to the most object side surface of the second lens group, and the most object side lens surface of the converter lens to the most image side lens surface. It is a relational expression with the distance on the optical axis to (total length of a converter lens). If the lower limit of conditional expression (1) is not reached, the correction of coma will be insufficient. If the upper limit of conditional expression (1) is exceeded, the diameter of the cemented lens will increase, and converse aberration will increase greatly. Also, correction of spherical aberration becomes difficult.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to 0.03. In order to further secure the effect of the present embodiment, it is more preferable to set the lower limit of conditional expression (1) to 0.05.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (1) to 0.20. In order to further secure the effect of the present embodiment, it is more preferable to set the upper limit of conditional expression (1) to 0.15.

  Further, the converter lens according to the present embodiment satisfies the following conditional expression (2), where fc is the combined focal length of the cemented lens and fn is the focal length of the negative lens constituting the cemented lens. It is desirable.

  0.02 <(− fn) / fc <2.00 (2)

  The conditional expression (2) is a relational expression between the combined focal length of the cemented lens and the focal length of the negative lens of the cemented lens. If the lower limit of conditional expression (2) is not reached, it will be difficult to correct coma. On the other hand, if the upper limit of conditional expression (2) is exceeded, the negative power of the cemented lens will be weakened, making it difficult to correct the Petzval sum.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (2) to 0.03.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (2) to 1.80. In order to further secure the effect of the present embodiment, it is more preferable to set the upper limit of conditional expression (2) to 1.70.

  Further, in the converter lens according to the present embodiment, the refractive index of the d-line of the negative lens that constitutes the cemented lens is Nn, and d of the positive lens on the object side that is cemented to the negative lens that constitutes the cemented lens. When the refractive index of the line is Np1, it is desirable to satisfy the following conditional expression (3).

  0.75 <Np1 / Nn <0.95 (3)

  The conditional expression (3) is a relational expression of the refractive index of the glass material used for the negative lens constituting the cemented lens and the object side positive lens. If the lower limit of conditional expression (3) is not reached, an expensive glass material is used, and the manufacturing cost increases. Further, the Petzval sum increases, and field curvature and coma are deteriorated. If the upper limit of conditional expression (3) is exceeded, the Petzval sum will decrease, and field curvature and coma will deteriorate.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to 0.80. In order to further secure the effect of the present embodiment, it is more preferable to set the lower limit value of conditional expression (3) to 0.84.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (3) to 0.935. In order to further secure the effect of the present embodiment, it is more preferable to set the upper limit of conditional expression (3) to 0.92.

  Further, in the converter lens according to the present embodiment, the refractive index of the d-line of the negative lens constituting the cemented lens is Nn, and d of the positive lens on the image side joined to the negative lens constituting the cemented lens. When the refractive index of the line is Np2, it is desirable that the following conditional expression (4) is satisfied.

  0.70 <Np2 / Nn <0.95 (4)

  Conditional expression (4) is a relational expression of the refractive index of the glass material used for the negative lens constituting the cemented lens and the image side positive lens. If the lower limit of conditional expression (4) is not reached, an expensive glass material is used, and the manufacturing cost increases. Further, the Petzval sum increases, and field curvature and coma are deteriorated. If the upper limit of conditional expression (4) is exceeded, the Petzval sum will decrease, and field curvature and coma will deteriorate.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.75. In order to further secure the effect of the present embodiment, it is more preferable to set the lower limit value of conditional expression (4) to 0.80.

  In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (4) to 0.90. In order to further secure the effect of the present embodiment, it is more preferable to set the upper limit value of conditional expression (4) to 0.85.

  The converter lens according to the present embodiment preferably satisfies the following conditional expression (5), where β is the magnification of the converter lens.

  1.40 ≦ β (5)

  Conditional expression (5) defines the magnification at which the converter lens enlarges the focal length of the master lens in the infinitely focused state. If the lower limit of conditional expression (5) is not reached, the magnification becomes insufficient and the lens does not function as a converter lens.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (5) to 1.50. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (5) to 1.70.

  In addition, the converter lens according to the present embodiment desirably has an aspherical surface. By using an aspherical surface, the effect of correcting spherical aberration and field curvature is particularly improved.

  In the converter lens according to the present embodiment, it is desirable that the aspherical surface is disposed on the image side from the cemented lens. With this configuration, it is possible to particularly favorably correct curvature of field.

  Hereinafter, each embodiment will be described with reference to the drawings. Tables 1 to 5 shown below are tables of specifications in the first to fifth examples. In [Surface data], the object surface is the object surface, 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 from each optical surface. The surface interval, which is the distance on the optical axis to the next optical surface (or image surface), nd represents the refractive index at the d-line (wavelength 587.6 nm), and νd represents the Abbe number at the d-line. When the lens surface is an aspherical surface, the surface number is marked with * and the paraxial radius of curvature is shown in the column of the radius of curvature r. The curvature radius “∞” indicates a plane. The description of the refractive index “1.00000” of air is omitted.

In [Aspherical data], the shape of the aspherical surface shown in [Surface data] is shown by the following equation (a). That is, y is the height in the direction perpendicular to the optical axis, and S (y) is the distance (sag amount) along the optical axis from the tangent plane of each aspheric surface at the height y to each aspheric surface. When the radius of curvature of the reference spherical surface (paraxial radius of curvature) is r, the conic coefficient is κ, and the nth-order aspherical coefficient is An, the following equation (a) is given. In each example, the secondary aspheric coefficient A2 is 0, and the description thereof is omitted. “E-n” represents “× 10 ⁻ⁿ ”. For example, 1.234E-05 = 1.234 × 10 ⁻⁵ .

S (y) = (y ² / r) / {1+ (1−κ · y ² / r ² ) ^1/2 }
^{+ A4 × y 4 + A6 ×} y 6 + A8 × y 8 + A10 × y 10 ... (a)

  In [various data], f (ML) is the focal length of the master lens ML, FNO (ML) is the F number of the master lens ML, R is the shooting distance, S is the aperture diameter, and f1 is the first lens group. G1 is the combined focal length of the second lens group G2, f (ML + CL) is the combined focal length when the converter lens CL is attached to the master lens ML, and FNO is the F number of the converter lens CL. 2ω is the angle of view (unit: “°”) of the converter lens CL, Y is the image height of the converter lens CL, Bf is the back focus, and D is the first image from the surface closest to the image side of the first lens group G1. TL is the distance on the optical axis from the lens surface closest to the object side of the converter lens CL to the lens surface closest to the image side (the total length of the converter lens CL). Fc is the combined focal length of the cemented lens, fn is the focal length of the negative lens constituting the cemented lens, and Np1 is the refractive index of the d-line of the positive lens on the object side cemented to the negative lens constituting the cemented lens. Nn represents the refractive index of the d-line of the negative lens constituting the cemented lens, and Np2 represents the refractive index of the d-line of the positive lens on the image side joined to the negative lens constituting the cemented lens.

  [Conditional Expression Corresponding Value] indicates the corresponding value of each conditional expression.

  In addition, in all the following specification values, the focal lengths (f (ML), f1, f2, etc.), the radius of curvature r, the surface interval d, and other units of length other than those described are as follows. In general, “mm” is used. However, since the optical system can obtain the same optical performance even if it is proportionally enlarged or reduced, the unit is not limited to “mm”, and other appropriate units can be used.

  The above description is the same in each embodiment, and the description below is omitted.

(First embodiment)
The converter lens CL according to the first example will be described with reference to FIGS. FIG. 1 is a diagram illustrating a configuration in which a converter lens CL according to the first example is mounted on a master lens ML. As shown in FIG. 1, the converter lens CL according to the first example includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side. .

  The first lens group G1 includes a biconvex positive lens L1 (first lens) and a biconcave negative lens L2 (second lens) arranged in order from the object side.

  The second lens group G2 includes a cemented positive lens of a biconvex positive lens L3, a biconcave negative lens L4, and a biconvex positive lens L5 arranged in order from the object side, and a concave surface facing the object side. The positive meniscus lens L6 and a negative biconcave lens L7.

  Table 1 below lists specifications of the master lens ML and the converter lens CL according to the first example attached to the image side of the master lens ML. The surface numbers 1 to 37 in Table 1 correspond to the surfaces 1 to 37 shown in FIG. Surface numbers 1 to 25 indicate the master lens ML, and surface numbers 26 and after indicate the converter lens CL.

(Table 1)
[Surface data]
Surface number r d nd νd
Object ∞ ∞
1 ∞ 4.00 1.51680 64.10
2 ∞ 0.60
3 173.866 12.00 1.49782 82.52
4 -978.065 0.20
5 133.636 15.00 1.49782 82.52
6 -464.694 5.00 1.80411 46.54
7 332.918 46.30
8 99.554 3.50 1.74400 45.00
9 55.631 15.90 1.49782 82.52
10 -1371.060 29.55
11 -169.969 2.70 1.51680 64.10
12 67.285 4.51
13 -192.927 7.00 1.80384 33.89
14 -43.081 2.80 1.58913 61.09
15 83.887 19.21
16 ∞ 1.70 (Aperture)
17 194.039 5.80 1.51860 69.98
18 -90.958 3.10
19 -43.595 3.50 1.79504 28.56
20 -64.790 7.60
21 -175.804 6.70 1.48749 70.41
22 -53.035 14.50
23 ∞ 3.63
24 ∞ 2.00 1.51680 64.10
25 ∞ 38.62
26 56.424 5.00 1.62004 36.30
27 -92.429 1.20
28 -125.333 1.50 1.80400 46.58
29 26.565 6.00
30 37.489 9.60 1.62004 36.30
31 -20.065 2.00 1.88300 40.77
32 32.015 8.80 1.57501 41.49
33 -32.015 6.60
34 -48.625 6.50 1.58913 61.18
35 -25.283 0.10
36 -52.195 2.50 1.88300 40.77
37 158.210 (Bf)
Image plane ∞

[Various data]
f (ML) = 294.001
FNO (ML) = 2.89
f (ML + CL) = 585.3
R = ∞
S = 38.7
f1 = -59.1
f2 = 309.1
FNO = 5.7
2ω = 4.2
Y = 21.6
Bf = 45.6
D = 6.00
TL = 49.80
fc = 79.41
fn = -43.74
Np1 = 1.62004
Nn = 1.88300
Np2 = 1.57501

[Conditional expression values]
(1) D / TL = 0.120
(2) (-fn) / fc = 0.551
(3) Np1 / Nn = 0.860
(4) Np2 / Nn = 0.836
(5) β = 1.99

  FIG. 2 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion aberration, coma aberration, and lateral chromatic aberration) when the converter lens CL according to the first example is focused at infinity. In each aberration diagram, FNO represents an F number, Y represents an image height, and A represents a half angle of view (unit: “°”). D represents an aberration curve of d-line (wavelength 587.6 nm), and g represents a g-line (wavelength 435.8 nm) aberration curve. In the spherical aberration diagram and the astigmatism diagram, 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 each aberration diagram, it can be seen that the converter lens CL according to Example 1 has various aberrations corrected well and has excellent imaging performance.

  FIG. 3 shows an image plane in which an incident light beam BM is reflected by a first ghost generation surface and a second ghost generation surface in an optical system in which the converter lens CL according to the first example is mounted on the master lens ML. It shows how I reached I and became a ghost or flare. As shown in FIG. 3, when the light beam BM from the object side enters the converter lens CL, the light is the object side lens surface (the first ghost generation surface in the negative lens L7 and corresponds to the surface number 36. ), The reflected light is reflected again by the object side lens surface of the positive lens L3 (second ghost generating surface, corresponding to surface number 30) and reaches the image surface I, and the ghost is reflected. It will be generated. A ghost can be effectively reduced by forming an antireflection film corresponding to a wide incident angle in a wider wavelength range on such a surface. Although the antireflection film will be described in detail later, the antireflection film according to each example has a multilayer structure including seven layers, and the seventh layer of the outermost surface layer is formed by using a wet process and is refracted with respect to the d line. The rate is 1.26 (see Table 6 below).

(Second embodiment)
The converter lens CL according to the second example will be described with reference to FIGS. 4 and 5 and Table 2. FIG. FIG. 4 is a diagram illustrating a configuration in which the converter lens CL according to the second example is mounted on the master lens ML. As shown in FIG. 4, the converter lens CL according to the second example includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power arranged in order from the object side. .

  The first lens group G1 includes a biconvex positive lens L1 (first lens) and a biconcave negative lens L2 (second lens) arranged in order from the object side.

  The second lens group G2 includes a cemented positive lens of a biconvex positive lens L3, a biconcave negative lens L4, and a biconvex positive lens L5 arranged in order from the object side, and a concave surface facing the object side. The positive meniscus lens L6 and the negative meniscus lens L7 having a concave surface facing the object side. The lens surface on the object side of the positive meniscus lens L6 is aspheric.

  Table 2 below lists specifications of the master lens ML and the converter lens CL according to the second example attached to the image side of the master lens ML. The surface numbers 1 to 37 in Table 2 correspond to the surfaces 1 to 37 shown in FIG. Surface numbers 1 to 25 indicate the master lens ML, and surface numbers 26 and after indicate the converter lens CL.

(Table 2)
[Surface data]
Surface number r d nd νd
Object ∞ ∞
1 ∞ 4.00 1.51680 64.10
2 ∞ 0.60
3 173.866 12.00 1.49782 82.52
4 -978.065 0.20
5 133.636 15.00 1.49782 82.52
6 -464.694 5.00 1.80411 46.54
7 332.918 46.30
8 99.554 3.50 1.74400 45.00
9 55.631 15.90 1.49782 82.52
10 -1371.060 29.55
11 -169.969 2.70 1.51680 64.10
12 67.285 4.51
13 -192.927 7.00 1.80384 33.89
14 -43.081 2.80 1.58913 61.09
15 83.887 19.21
16 ∞ 1.70 (Aperture)
17 194.039 5.80 1.51860 69.98
18 -90.958 3.10
19 -43.595 3.50 1.79504 28.56
20 -64.790 7.60
21 -175.804 6.70 1.48749 70.41
22 -53.035 14.50
23 ∞ 3.63
24 ∞ 2.00 1.51680 64.10
25 ∞ 38.62
26 41.365 5.00 1.62004 36.26
27 -169.892 0.80
28 -618.114 1.50 1.80400 46.58
29 22.751 5.40
30 43.584 9.00 1.62004 36.30
31 -19.386 2.00 1.88300 40.76
32 35.157 8.20 1.57501 41.49
33 -35.157 2.90
34 * -58.619 6.40 1.58913 61.16
35 -28.567 0.50
36 -34.421 2.50 1.88300 40.76
37 -121.391 (Bf)
Image plane ∞

[Aspherical data]
34th surface κ = 1.0000
A4 = 1.05550E-05
A6 = 7.82650E-09
A8 = 0.00000E + 00
A10 = 0.00000E + 00

[Various data]
f (ML) = 294.001
FNO (ML) = 2.89
f (ML + CL) = 581.9
R = ∞
S = 38.7
f1 = -64.8
f2 = 444.6
FNO = 5.7
2ω = 4.3
Y = 21.6
Bf = 52.5
D = 5.40
TL = 44.20
fc = 108.07
fn = -44.54
Np1 = 1.62004
Nn = 1.88300
Np2 = 1.57501

[Conditional expression values]
(1) D / TL = 0.122
(2) (-fn) / fc = 0.412
(3) Np1 / Nn = 0.860
(4) Np2 / Nn = 0.836
(5) β = 1.97

  FIG. 5 is a diagram showing various aberrations (spherical aberration, astigmatism, distortion aberration, coma aberration, and lateral chromatic aberration) when the converter lens CL according to Example 2 is focused at infinity. As is apparent from each aberration diagram, it can be seen that the converter lens CL according to Example 2 has various aberrations corrected well and has excellent imaging performance.

(Third embodiment)
The converter lens CL according to the third example will be described with reference to FIGS. FIG. 6 is a diagram illustrating a configuration in which the converter lens CL according to the third example is mounted on the master lens ML. As shown in FIG. 6, the converter lens CL according to the third example includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side. .

  The first lens group G1 includes a biconvex positive lens L1 (first lens) and a biconcave negative lens L2 (second lens) arranged in order from the object side.

  The second lens group G2 includes a cemented positive lens of a biconvex positive lens L3, a biconcave negative lens L4, and a biconvex positive lens L5 arranged in order from the object side, and a concave surface facing the object side. The positive meniscus lens L6 and the negative meniscus lens L7 having a concave surface facing the object side. The lens surface on the object side of the positive meniscus lens L6 is aspheric.

  Table 3 below lists specifications of the master lens ML and the converter lens CL according to the third example attached to the image side of the master lens ML. The surface numbers 1 to 37 in Table 3 correspond to the surfaces 1 to 37 shown in FIG. Surface numbers 1 to 25 indicate the master lens ML, and surface numbers 26 and after indicate the converter lens CL.

(Table 3)
[Surface data]
Surface number r d nd νd
Object ∞ ∞
1 ∞ 4.00 1.51680 64.10
2 ∞ 0.60
3 173.866 12.00 1.49782 82.52
4 -978.065 0.20
5 133.636 15.00 1.49782 82.52
6 -464.694 5.00 1.80411 46.54
7 332.918 46.30
8 99.554 3.50 1.74400 45.00
9 55.631 15.90 1.49782 82.52
10 -1371.060 29.55
11 -169.969 2.70 1.51680 64.10
12 67.285 4.51
13 -192.927 7.00 1.80384 33.89
14 -43.081 2.80 1.58913 61.09
15 83.887 19.21
16 ∞ 1.70 (Aperture)
17 194.039 5.80 1.51860 69.98
18 -90.958 3.10
19 -43.595 3.50 1.79504 28.56
20 -64.790 7.60
21 -175.804 6.70 1.48749 70.41
22 -53.035 14.50
23 ∞ 3.63
24 ∞ 2.00 1.51680 64.10
25 ∞ 38.62
26 43.495 5.00 1.62004 36.26
27 -176.601 1.63
28 -901.179 1.50 1.81600 46.62
29 23.156 2.49
30 40.689 8.24 1.62588 35.65
31 -20.747 2.00 1.88300 40.76
32 24.572 8.11 1.56732 42.70
33 -50.264 4.61
34 * -77.902 7.00 1.58913 61.16
35 -31.925 0.10
36 -38.235 2.50 1.88300 40.76
37 -80.004 (Bf)
Image plane ∞

[Aspherical data]
34th surface κ = 1.0000
A4 = 1.32520E-05
A6 = 1.02370E-08
A8 = 0.00000E + 00
A10 = 0.00000E + 00

[Various data]
f (ML) = 294.001
FNO (ML) = 2.89
f (ML + CL) = 582.0
R = ∞
S = 38.7
f1 = -64.9
f2 = 467.5
FNO = 5.7
2ω = 4.3
Y = 21.6
Bf = 53.2
D = 2.49
TL = 43.17
fc = 335.50
fn = -61.68
Np1 = 1.62588
Nn = 1.88300
Np2 = 1.56732

[Conditional expression values]
(1) D / TL = 0.058
(2) (-fn) / fc = 0.184
(3) Np1 / Nn = 0.863
(4) Np2 / Nn = 0.832
(5) β = 1.97

  FIG. 7 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion aberration, coma aberration, and lateral chromatic aberration) when the converter lens CL according to Example 3 is focused at infinity. As can be seen from the respective aberration diagrams, the converter lens CL according to the third example has various aberrations corrected satisfactorily and has excellent imaging performance.

(Fourth embodiment)
A converter lens CL according to a fourth example will be described with reference to FIGS. 8 and 9 and Table 4. FIG. FIG. 8 is a diagram showing a configuration in which the converter lens CL according to the fourth example is mounted on the master lens ML. As shown in FIG. 8, the converter lens CL according to the fourth example includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, which are arranged in order from the object side. .

  The first lens group G1 includes a biconvex positive lens L1 (first lens), a biconcave negative lens L2 (second lens), and a biconvex positive lens L3 arranged in order from the object side. Consists of

  The second lens group G2 includes a cemented positive lens of a biconvex positive lens L4, a biconcave negative lens L5, and a biconvex positive lens L6 arranged in order from the object side, and a concave surface facing the object side. The positive meniscus lens L7 and the negative meniscus lens L8 having a concave surface facing the object side. The lens surface on the image side of the positive meniscus lens L7 is an aspherical surface.

  Table 4 below lists specifications of the master lens ML and the converter lens CL according to the fourth example attached to the image side of the master lens ML. The surface numbers 1 to 39 in Table 4 correspond to the surfaces 1 to 39 shown in FIG. Surface numbers 1 to 25 indicate the master lens ML, and surface numbers 26 and after indicate the converter lens CL.

(Table 4)
[Surface data]
Surface number r d nd νd
Object ∞ ∞
1 ∞ 4.00 1.51680 64.10
2 ∞ 0.60
3 173.866 12.00 1.49782 82.52
4 -978.065 0.20
5 133.636 15.00 1.49782 82.52
6 -464.694 5.00 1.80411 46.54
7 332.918 46.30
8 99.554 3.50 1.74400 45.00
9 55.631 15.90 1.49782 82.52
10 -1371.060 29.55
11 -169.969 2.70 1.51680 64.10
12 67.285 4.51
13 -192.927 7.00 1.80384 33.89
14 -43.081 2.80 1.58913 61.09
15 83.887 19.21
16 ∞ 1.70 (Aperture)
17 194.039 5.80 1.51860 69.98
18 -90.958 3.10
19 -43.595 3.50 1.79504 28.56
20 -64.790 7.60
21 -175.804 6.70 1.48749 70.41
22 -53.035 14.50
23 ∞ 3.63
24 ∞ 2.00 1.51680 64.10
25 ∞ 38.62
26 49.516 5.00 1.62004 36.26
27 -73.947 0.27
28 -82.701 1.50 1.81600 46.62
29 26.746 3.21
30 139.929 4.18 1.67270 32.11
31 -111.051 3.00
32 120.000 6.91 1.72342 37.95
33 -22.968 2.00 1.88300 40.76
34 27.016 8.42 1.56732 42.70
35 -46.582 6.39
36 -59.851 5.84 1.58913 61.16
37 * -28.452 0.10
38 -34.892 2.50 1.88300 40.76
39 -115.137 (Bf)
Image plane ∞

[Aspherical data]
37th surface κ = 1.0000
A4 = 1.22110E-05
A6 = 5.14870E-09
A8 = 0.00000E + 00
A10 = 0.00000E + 00

[Various data]
f (ML) = 294.001
FNO (ML) = 2.89
f (ML + CL) = 582.0
R = ∞
S = 38.7
f1 = -150.8
f2 = -160.5
FNO = 5.7
2ω = 4.3
Y = 21.6
Bf = 50.0
D = 3.00
TL = 49.32
fc = 1897.08
fn = -83.73
Np1 = 1.72342
Nn = 1.88300
Np2 = 1.56732

[Conditional expression values]
(1) D / TL = 0.061
(2) (-fn) / fc = 0.044
(3) Np1 / Nn = 0.915
(4) Np2 / Nn = 0.832
(5) β = 1.96

  FIG. 9 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion aberration, coma aberration, and lateral chromatic aberration) when the converter lens CL according to Example 4 is in focus at infinity. As can be seen from the respective aberration diagrams, the converter lens CL according to the fourth example has various aberrations corrected well and has excellent imaging performance.

(5th Example)
A converter lens CL according to a fifth example will be described with reference to FIGS. 10 and 11 and Table 5. FIG. FIG. 10 is a diagram illustrating a configuration in which the converter lens CL according to the fifth example is mounted on the master lens ML. As shown in FIG. 10, the converter lens CL according to the fifth example includes a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power, which are arranged in order from the object side. .

  The first lens group G1 includes a biconvex positive lens L1 (first lens) and a biconcave negative lens L2 (second lens) arranged in order from the object side.

  The second lens group G2 includes a cemented positive lens of a biconvex positive lens L3, a biconcave negative lens L4, and a biconvex positive lens L5 arranged in order from the object side, and a concave surface facing the object side. The positive meniscus lens L6 and a negative biconcave lens L7.

  Table 5 below lists specifications of the master lens ML and the converter lens CL according to the fifth example attached to the image side of the master lens ML. The surface numbers 1 to 37 in Table 5 correspond to the surfaces 1 to 37 shown in FIG. Surface numbers 1 to 25 indicate the master lens ML, and surface numbers 26 and after indicate the converter lens CL.

(Table 5)
[Surface data]
Surface number r d nd νd
Object ∞ ∞
1 ∞ 4.00 1.51680 64.10
2 ∞ 0.60
3 173.866 12.00 1.49782 82.52
4 -978.065 0.20
5 133.636 15.00 1.49782 82.52
6 -464.694 5.00 1.80411 46.54
7 332.918 46.30
8 99.554 3.50 1.74400 45.00
9 55.631 15.90 1.49782 82.52
10 -1371.060 29.55
11 -169.969 2.70 1.51680 64.10
12 67.285 4.51
13 -192.927 7.00 1.80384 33.89
14 -43.081 2.80 1.58913 61.09
15 83.887 19.21
16 ∞ 1.70 (Aperture)
17 194.039 5.80 1.51860 69.98
18 -90.958 3.10
19 -43.595 3.50 1.79504 28.56
20 -64.790 7.60
21 -175.804 6.70 1.48749 70.41
22 -53.035 14.50
23 ∞ 3.63
24 ∞ 2.00 1.51680 64.10
25 ∞ 38.62
26 82.235 5.00 1.62004 36.26
27 -146.695 2.68
28 -726.932 1.50 1.81600 46.62
29 21.704 2.68
30 27.564 11.00 1.63980 34.56
31 -17.932 2.00 1.88300 40.76
32 47.494 9.25 1.51742 52.31
33 -25.996 4.14
34 -35.907 5.26 1.58913 61.16
35 -23.885 0.10
36 -45.558 2.50 1.88300 v40.76
37 433.303 (Bf)
Image plane ∞

[Various data]
f (ML) = 294.001
FNO (ML) = 2.89
f (ML + CL) = 581.4
R = ∞
S = 38.7
f1 = -40.6
f2 = 84.1
FNO = 5.7
2ω = 4.2
Y = 21.6
Bf = 49.3
D = 2.68
TL = 46.10
fc = 47.03
fn = -71.01
Np1 = 1.63980
Nn = 1.88300
Np2 = 1.51742

[Conditional expression values]
(1) D / TL = 0.058
(2) (-fn) / fc = 1.510
(3) Np1 / Nn = 0.871
(4) Np2 / Nn = 0.806
(5) β = 1.95

  FIG. 11 is a diagram illustrating various aberrations (spherical aberration, astigmatism, distortion, coma aberration, and lateral chromatic aberration) when the converter lens CL according to Example 5 is focused at infinity. As is apparent from each aberration diagram, it can be seen that the converter lens CL according to Example 5 has various aberrations corrected satisfactorily and has excellent imaging performance.

  FIG. 12 is a diagram showing various aberrations of the master lens ML used in each example when focusing on infinity. As described above, the same master lens ML is used in each embodiment. However, this master lens ML is merely an example, and the configuration of the master lens ML is not limited thereto.

  Next, a camera (optical device) on which the master lens ML and the converter lens CL according to the first example are mounted will be described. Here, the case where the converter lens CL according to the first embodiment is mounted will be described, but the same applies to the case where the converter lens of another embodiment is used.

  FIG. 13 is a diagram illustrating a configuration of a camera including the converter lens CL according to the first example. In FIG. 13, the camera 1 is a digital single-lens reflex camera provided with a master lens ML and a converter lens CL according to the first embodiment attached to the master lens ML as a photographing lens 2. In the camera 1, light from an object (subject) (not shown) is collected by the taking lens 2 and is focused on the focusing screen 4 via the quick return mirror 3. The light imaged on the focusing screen 4 is reflected in the pentaprism 5 a plurality of times and guided to the eyepiece lens 6. Thereby, the photographer can observe the subject image as an erect image through the eyepiece 6.

  When the release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted out of the optical path, and light from the subject (not shown) reaches the image sensor 7. As a result, light from the subject is picked up by the image sensor 7 and recorded as a subject image in a memory (not shown). In this way, the photographer can shoot the subject with the camera 1.

  As described above, in this embodiment, the camera 1 has high performance by mounting the master lens ML as the photographing lens 2 and the converter lens CL according to the first example attached to the master lens ML. A camera can be realized.

  Here, the antireflection film used in the converter lenses of the first to fifth embodiments will be described. As shown in FIG. 14, the antireflection film 101 according to the present embodiment includes seven layers (first layer 101a to seventh layer 101g), and is formed on the optical surface of the optical member 102 of the converter lens.

  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. In this way, the antireflection film 101 of this embodiment is formed.

  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. The optical member 102 is completed by heat treatment at 160 ° C. for 1 hour in the air after the seventh layer 101g is formed. 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 spectral characteristics shown in FIG. FIG. 15 shows the spectral characteristics when the light ray is vertically incident when the antireflection film 101 is designed under the conditions shown in Table 6 below when the reference wavelength λ is 550 nm. Table 6 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 a 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 6)
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. 15, 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 converter lens of the first example, the refractive index of the positive lens L3 of the third lens component is 1.62004, and the refractive index of the substrate is 1 on the object-side lens surface of the positive lens L3 of the third lens component. .62 can be used. Further, since the refractive index of the negative lens L7 is 1.88300, it is possible to use an antireflection film corresponding to the refractive index of the substrate of 1.85 on the object-side lens surface of the negative lens L7.

  In the converter lens of the second example, the refractive index of the positive lens L3 of the third lens component is 1.62004, and the refractive index of the substrate is 1 on the object-side lens surface of the positive lens L3 of the third lens component. .62 can be used. Further, since the refractive index of the negative lens L7 is 1.88300, it is possible to use an antireflection film corresponding to the refractive index of the substrate of 1.85 on the object-side lens surface of the negative lens L7.

  In the converter lens of the third example, the refractive index of the positive lens L3 of the third lens component is 1.62588, and the refractive index of the substrate is 1 on the object-side lens surface of the positive lens L3 of the third lens component. .62 can be used. Further, since the refractive index of the negative lens L7 is 1.88300, it is possible to use an antireflection film corresponding to the refractive index of the substrate of 1.85 on the object-side lens surface of the negative lens L7.

  In the converter lens of the fourth example, the refractive index of the fourth lens component positive lens L4 is 1.72342, and the refractive index of the substrate is 1 on the object-side lens surface of the positive lens L4 of the fourth lens component. .74 can be used. Further, since the negative lens L8 has a refractive index of 1.88300, an antireflection film corresponding to a refractive index of the substrate of 1.85 can be used on the object-side lens surface of the negative lens L8.

  In the converter lens of the fifth example, the refractive index of the positive lens L3 as the third lens component is 1.63980, and the refractive index of the substrate is 1 on the object-side lens surface of the positive lens L3 as the third lens component. .62 can be used. Further, since the refractive index of the negative lens L7 is 1.88300, it is possible to use an antireflection film corresponding to the refractive index of the substrate of 1.85 on the object-side lens surface of the negative lens L7.

  As described above, by applying the antireflection film 101 of the present embodiment to the converter lenses of the first to fifth examples, respectively, a converter lens having a good optical performance in which ghost and flare are further reduced, and this 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 7 below. Note that the sol-gel method described above is used to form the fifth layer. Table 7 shows design values when the reference wavelength λ is 550 nm and the refractive index of the substrate is 1.52.

(Table 7)
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. 16 shows spectral characteristics when light is vertically incident on the antireflection film of the modification. FIG. 16 shows that the reflectance is suppressed to 0.2% or less over the entire wavelength range of 420 nm to 720 nm. FIG. 17 shows the spectral characteristics when the incident angles are 30, 45, and 60 degrees.

  For comparison, FIG. 18 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 8 below. FIG. 19 shows spectral characteristics when the incident angles are 30, 45, and 60 degrees.

(Table 8)
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. 16 and 17 are compared with the spectral characteristics of the conventional example shown in FIGS. 18 and 19, the low reflectance of the antireflection film according to the modification can be clearly seen.

  According to each of the above embodiments, it is possible to provide a converter lens that can achieve good optical performance with reduced ghosts and flares.

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

  In the present embodiment, the two-group configuration is shown, but the present invention can also be applied to other group configurations such as a three-group configuration. 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.

  Further, in the present embodiment, as a focusing lens group that performs focusing from an object at infinity to a short-distance object by moving the single lens group or a plurality of lens groups, or the partial lens group or the entire converter lens in the optical axis direction. Also good. The focusing lens group can be applied to autofocus, and is also suitable for driving a motor for autofocus (using an ultrasonic motor or the like).

  In the present embodiment, the lens group or the partial lens group is moved so as to have a component in a direction perpendicular to the optical axis, or is rotated (swinged) in the in-plane direction including the optical axis, thereby An anti-vibration lens group that corrects image blur caused by blur may be used. In particular, it is preferable that at least a part of the second lens group is an anti-vibration lens group.

  In the present embodiment, the lens surface may be formed as a spherical surface, a flat surface, or an aspheric surface.

  In the present embodiment, it is preferable that the lens surface is a spherical surface or a flat surface because lens processing and assembly adjustment are facilitated, and deterioration of optical performance due to errors in processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance.

  In this embodiment, 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, and an aspheric surface made of resin on the glass surface. Any aspherical surface of the composite 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.

  In the present embodiment, the magnification is about 1.4 to 2.5.

  In addition, in order to explain the invention according to the present embodiment in an easy-to-understand manner, the configuration requirements of the above-described embodiment have been described, but the present invention is not limited to this.

ML master lens CL converter lens G1 first lens group G2 second lens group L1 first lens (positive lens constituting the first lens group)
L2 Second lens (negative lens constituting the first lens group)
S Aperture stop I Image plane
1 Camera (optical device)
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 (12)

A detachable converter lens used on the image side of the master lens,
At least one of the optical surfaces constituting the converter lens has a layer formed by using a wet process, which includes a cemented lens having a positive refractive power including at least a positive lens, a negative lens, and a positive lens. A converter lens comprising an antireflection film including at least one layer. The antireflection film is a multilayer film,
The converter lens according to claim 1, wherein an outermost surface layer of the multilayer film is a layer formed by using the wet process. When the refractive index at the d-line of the layer formed using the wet process is nd, the following formula nd ≦ 1.30
The converter lens according to claim 1, wherein the following condition is satisfied.   The converter lens according to claim 1, further comprising a first lens having a positive refractive power and a second lens having a negative refractive power, which are arranged in order from the most object side. Having a first lens group and a second lens group arranged in order from the object side;
The distance from the most image side surface of the first lens group to the most object side surface of the second lens group is D, and the light from the most object side lens surface of the converter lens to the most image side lens surface When the distance on the axis is TL, the following formula 0.01 <D / TL <0.25
The converter lens according to claim 1, wherein the following condition is satisfied. When the combined focal length of the cemented lens is fc and the focal length of the negative lens constituting the cemented lens is fn, the following expression 0.02 <(− fn) / fc <2.00
The converter lens according to claim 1, wherein the following condition is satisfied. When the refractive index of the d-line of the negative lens constituting the cemented lens is Nn, and the refractive index Np1 of the d-line of the positive lens on the object side joined to the negative lens constituting the cemented lens is Formula 0.75 <Np1 / Nn <0.95
The converter lens according to claim 1, wherein the following condition is satisfied. When the refractive index of the d-line of the negative lens constituting the cemented lens is Nn and the refractive index of the d-line of the positive lens on the image side cemented to the negative lens constituting the cemented lens is Np2, The following formula 0.70 <Np2 / Nn <0.95
The converter lens according to claim 1, wherein the following condition is satisfied. When the magnification of the converter lens is β, the following formula 1.40 ≦ β
The converter lens according to claim 1, wherein the following condition is satisfied.   The converter lens according to claim 1, wherein the converter lens has an aspherical surface. The converter lens according to claim 10 , wherein the aspheric surface is disposed on the image side of the cemented lens.   An optical device comprising the converter lens according to claim 1.

Images