JP2003241086A - Front tele converter lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easily assembled front tele converter lens having a simple constitution in terms of lens. <P>SOLUTION: The lens is constituted of a 1st lens group G1 having a positive refractive power and a 2nd lens group G2 having a negative refractive power in this order from an object side, the 1st lens group G1 is constituted of a doublet of a negative meniscus lens L11 whose convex side faces the object and a biconvex positive lens L12 in this order from the object side, the 2nd lens group G2 is constituted of a doublet of a positive meniscus lens L21 whose concave side faces the object and a biconcave negative lens L22 in this order from the object side. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front teleconverter lens which is attached to the object side of a taking lens to extend the focal length of the entire system.

[0002]

2. Description of the Related Art Conventionally, a front teleconverter lens, which is attached to the object side of a taking lens and extends the focal length of the entire system by about 1.5 times, has been disclosed in JP-A-55-320.
No. 46, Japanese Patent Laid-Open No. 3-59508, and the like.

[0003]

However, the front teleconverter lens disclosed in Japanese Patent Application Laid-Open No. 55-32046 has a lens configuration of 2 elements in 2 groups, and the number of lenses is as small as 2. Therefore, chromatic aberration and the like are caused. However, it is difficult to correct various aberrations, and it is difficult to obtain good imaging performance. Further, the front teleconverter lens disclosed in JP-A-3-59508 is
Since the lens configuration is four in three groups and the number of lens groups is as large as three, there is a disadvantage that the lens barrel structure becomes complicated and the number of parts in the lens barrel portion increases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a front teleconverter lens having a simple lens structure and easy to assemble.

[0005]

In order to solve the above problems, a front converter lens of the present invention is mounted on the object side of a taking lens and is used for extending the focal length of the taking lens. In addition, in order from the object side, it is composed of a first lens group having a positive refractive power and a second lens group having a negative refractive power, and the first lens group has, in order from the object side, a negative lens having a convex surface facing the object side. The second lens group comprises, in order from the object side, a positive meniscus lens having a concave surface facing the object side and a double-concave negative lens. Therefore, the following conditional expressions (1) to (4) are satisfied. (1) 0.40 <(R3 + R1) / (R3-R1) <0.90 (2) -0.25 <(R6 + R4) / (R6-R4) <0.90 (3) 40 <ν2-ν1 ( 4) 15 <ν4-ν3 where R1 is the radius of curvature of the first lens group closest to the object side, and R3 is the radius of curvature of the first lens group closest to the image side.
R4 is a radius of curvature of the most object side surface of the second lens group, R4
6 is the radius of curvature of the most image-side surface of the second lens group, ν1 is the Abbe number of the negative meniscus lens of the first lens group, ν2 is the Abbe number of the biconvex positive lens of the first lens group, ν3 is the Abbe number of the positive meniscus lens of the second lens group, and ν4 is the Abbe number of the biconcave positive lens of the second lens group.

The front teleconverter lens of the present invention, which is composed of a first lens group having a positive refractive power and a second lens group having a negative refractive power in order from the object side, satisfactorily corrects various aberrations such as chromatic aberration. Therefore, it is desirable that each of the first lens group and the second lens group be composed of a positive lens and a negative lens.

Further, in the front teleconverter lens of the present invention, in order to simplify the lens barrel structure and facilitate the assembly, each of the first lens group and the second lens group is used as a cemented lens of a positive lens and a negative lens. It is desirable to have a group of four.

Further, in the front teleconverter lens according to the present invention, the first lens group includes, in order from the object side,
A cemented lens of a negative meniscus lens having a convex surface facing the object side and a biconvex positive lens is preferable for aberration correction.

In the front teleconverter lens of the present invention, the second lens group is a cemented lens of a positive meniscus lens having a concave surface facing the object side and a biconcave negative lens in order from the object side. It is preferable for correction.

Conditional expression (1) relates to the shape of the first lens group and is a conditional expression for favorably correcting spherical aberration and coma of the front teleconverter lens of the present invention. If either the upper limit value or the lower limit value of the conditional expression (1) is exceeded, it becomes difficult to satisfactorily correct spherical aberration and coma.

Conditional expression (2) relates to the shape of the second lens group, and is a conditional expression for favorably correcting spherical aberration, coma aberration, and field curvature aberration of the front teleconverter lens of the present invention. If either the upper limit value or the lower limit value of the conditional expression (2) is exceeded, it becomes difficult to satisfactorily correct spherical aberration, coma aberration, and field curvature aberration.

Conditional expression (3) relates to the Abbe number of the lens of the first lens group, and is a conditional expression for favorably correcting the chromatic aberration of the front teleconverter lens of the present invention. If the lower limit of conditional expression (3) is exceeded, it will be difficult to satisfactorily correct chromatic aberration.

Conditional expression (4) relates to the Abbe number of the lens of the second lens group, and is a conditional expression for favorably correcting the chromatic aberration of the front teleconverter lens of the present invention. If the lower limit of conditional expression (4) is exceeded, it will be difficult to satisfactorily correct chromatic aberration.

Further, in order to satisfactorily correct the chromatic aberration, in the front teleconverter lens of the present invention, the Abbe number ν2 of the biconvex positive lens of the first lens group must satisfy the following conditional expression (5). Is desirable. (5) 75 <ν2 By satisfying the conditional expression (5), it is possible to further correct chromatic aberration.

In the front teleconverter lens of the present invention, any surface of the first lens group and the second lens group may be an aspherical surface or a diffractive surface. Further, any lens of the first lens group to the second lens group may be a gradient index lens (GRIN lens) or a plastic lens. Further, by moving any one of the first lens group to the second lens group in the direction orthogonal to the optical axis,
It is also possible to use a front teleconverter lens for camera shake correction.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a front teleconverter lens according to the present invention will be described with reference to the drawings.

FIG. 1 is a lens sectional view when a front teleconverter lens C according to a first embodiment of the present invention is mounted on a master lens M. The front teleconverter lens C according to the first embodiment is composed of, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power, and the first lens group G1 is It is composed of a cemented lens of a negative meniscus lens L11 having a convex surface facing the object side and a positive lens L12 having a biconvex shape in order from the object side, and the second lens group G2 has a concave surface facing the object side in order from the object side. The positive meniscus lens L21 and the biconcave negative lens L22 are cemented together.

Table 1 shows specifications and numerical values corresponding to the conditional expressions of the front teleconverter lens C according to the present embodiment as Example 1. In the table, f is the combined focal length of the front teleconverter lens C and the master lens M, Ri is the radius of curvature of the i-th lens surface in order from the object side, di is the i-th lens thickness in order from the object side, and The air spacing between the lens surfaces, ni and νi, are i-th order from the object side, respectively.
The refractive index and Abbe number of the medium with respect to the d-line (λ = 587.6 nm) of the th lens, and the refractive index of 1.0000000 of air is omitted. Further, d6 is an air gap between the most image-side lens surface of the front teleconverter lens C and the most object-side lens surface of the master lens M.

The unit of the focal length, radius of curvature, surface spacing and other lengths in the table is generally "mm", but the same optical performance can be obtained even if the optical system is enlarged or reduced proportionally. So it is not limited to this.

The same applies to other embodiments.

[0021]

[Table 1] [Example 1] (Specifications) f = 103.52 R1 = 64.6545 d1 = 2.5000 n1 = 1.80100 ν1 = 34.96 R2 = 47.0020 d2 = 12.3000 n2 = 1.49782 ν2 = 82.52 R3 = -251.6046 d3 = 33.3000 R4 = -103.5345 d4 = 4.0000 n3 = 1.80518 ν3 = 25.43 R5 = -50.0830 d5 = 2.0000 n4 = 1.73400 ν4 = 51.47 R6 = 131.0049 d6 = 3.9000 (Value corresponding to conditional expression) (1) (R3 + R1) / (R3-R1) = 0 .591 (2) (R6 + R4) / (R6-R4) = 0.117 (3) ν2-ν1 = 47.56 (4) ν4-ν3 = 26.04 (5) ν2 = 82.52 FIG. FIG. 11 is a lens cross-sectional view when a front teleconverter lens C according to a second embodiment of the invention is attached to a master lens M. The front teleconverter lens C according to the second embodiment comprises, in order from the object side, a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power, and the first lens group G1 is an object. The cemented lens is composed of, in order from the side, a negative meniscus lens L11 having a convex surface facing the object side and a biconvex positive lens L12.
The lens group G2 includes, in order from the object side, a positive meniscus lens L21 having a concave surface facing the object side and a biconcave negative lens L2.
It consists of a cemented lens with 2.

Table 2 shows the specifications and numerical values corresponding to the conditional expressions of the front teleconverter lens C according to the present embodiment as Example 2.

[0023]

[Table 2] [Example 2] (Specifications) f = 103.50 R1 = 66.2754 d1 = 2.5000 n1 = 1.80100 ν1 = 34.96 R2 = 48.7355 d2 = 11.9898 n2 = 1.49700 ν2 = 81.61 R3 = -281.3518 d3 = 34.0237 R4 = -131.8334 d4 = 3.7673 n3 = 1.80518 ν3 = 25.43 R5 = -52.1516 d5 = 2.0000 n4 = 1.80400 ν4 = 46.58 R6 = 152.7603 d6 = 3.7193 (Values corresponding to conditional expressions) (1) (R3 + R1) / (R3-R1) = 0 .619 (2) (R6 + R4) / (R6-R4) = 0.0735 (3) ν2-ν1 = 46.65 (4) ν4-ν3 = 21.15 (5) ν2 = 81.61 In Table 3, A master lens M to which the front teleconverter lens C according to the first or second embodiment is attached
The specifications of In Table 3, fm is the focal length of the master lens, FNO is the F number, 2A is the maximum value of the shooting angle of view, and other symbols are the same as in the previous table.

[0024]

[Table 3] [Master lens] (Specifications) fm = 69.07 FNO = 4.44 2A = 9.32 ° R7 = 112.4351 d7 = 1.3000 n5 = 1.84666 ν5 = 23.78 R8 = 46.6040 d8 = 4.1000 n6 = 1.78800 ν6 = 47.38 R9 =- 1133.2893 d9 = 0.1000 R10 = 33.8557 d10 = 3.1500 n7 = 1.49782 ν7 = 82.52 R11 = 95.7487 d11 = 30.9447 R12 = 108.3076 d12 = 1.2000 n8 = 1.80400 ν8 = 46.58 R13 = 10.0068 d13 = 4.3000 R14 = -29.0221 d14 = 0.9000 n9 = ν9 = 54.66 R15 = 21.5697 d15 = 1.7000 n10 = 1.84666 ν10 = 23.78 R16 = 36.0418 d16 = 0.7000 R17 = 22.2130 d17 = 2.1000 n11 = 1.84666 ν11 = 23.78 R18 = 133.9390 d18 = 2.5720 R19 = ∞ d19 = 0.5000 R20 = 19.0286 d20 = 3.0500 n12 = 1.49782 ν12 = 82.52 R21 = -26.3022 d21 = 0.2000 R22 = 14.4696 d22 = 4.9000 n13 = 1.75700 ν13 = 47.82 R23 = 43.2842 d23 = 0.7500 R24 = -27.1397 d24 = 0.9000 n14 = 1.68893 ν14 = 31.09 R25 = 15.2385 d25 = 1.4085 R26 = 28.7363 d26 = 0.9000 n15 = 1.83481 ν15 = 42.72 R27 = 10.1303 d27 = 3.8500 n16 = 1.51823 ν16 = 58.96 R28 = -21.2189 d28 = 24.4561 R29 = 27.6733 d29 = 3.0000 n17 = 1.80400 ν17 = 46 .58 R30 = -78.3460 d30 = 1.0000 n18 = 1.84666 ν18 = 23.78 R31 = 103.6796 d31 = 5.5636 R32 = ∞ d32 = 2.7600 n19 = 1.51633 ν19 = 64.22 R33 = ∞ d33 = 2.4700 R34 = ∞ d34 = 0.5000 n20 = 1.51633 ν20 = 64.22 R35 = ∞ d35 = 1.0328 FIG. 3 shows various aberration diagrams when the front teleconverter lens C of the first embodiment is mounted on the master lens M, and FIG. 4 shows the front teleconverter lens C of the second embodiment as a master. FIG. 5 is a diagram showing various aberrations when mounted on the lens M, and FIG. 5 is a diagram showing various aberrations of the master lens M alone.

In each aberration diagram, FNO is the F number (the value corresponding to the maximum aperture in the spherical aberration diagram), and A is the half field angle (the astigmatism diagram and the distortion aberration diagram, the maximum value thereof is the coma aberration). In the figure, for each half angle of view, d is the d line (λ = 587.6n)
m) and g indicate the g line (λ = 435.6 nm), respectively. In the astigmatism diagram, the solid line shows the sagittal image plane, and the broken line shows the meridional image plane.

From each aberration diagram, it is apparent that the front teleconverter lens according to each embodiment of the present invention has various aberrations well corrected and has excellent image forming performance.

[0027]

As described above, according to the present invention, the focal length of the entire system can be extended by about 1.5 times, the lens configuration is simple with 4 elements in 2 groups, the assembling is easy, and the chromatic aberration, etc. It is possible to provide a front teleconverter lens in which various aberrations described above are less likely to occur.

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which a front teleconverter lens according to a first embodiment of the present invention is mounted on a master lens.

FIG. 2 is a diagram showing a state in which a front teleconverter lens according to a second embodiment of the present invention is mounted on a master lens.

FIG. 3 is a diagram showing various types of aberration when the front teleconverter lens according to the first embodiment of the present invention is mounted on a master lens.

FIG. 4 is a diagram showing various types of aberration when a front teleconverter lens according to a second embodiment of the present invention is mounted on a master lens.

FIG. 5 is a diagram showing various aberrations of a single master lens.

[Explanation of symbols]

C: Front teleconverter lens M: Master lens G1 ... First lens group G2: Second lens group S: Aperture of master lens M

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H087 LA30 PA02 PA12 PA16 PA19                       PB04 PB17 QA02 QA06 QA17                       QA21 QA25 QA39 QA41 QA45                       SA87

Claims (2)

[Claims] 1. A front teleconverter lens which is attached to the object side of a taking lens and extends the focal length of the taking lens, comprising: a first lens unit having a positive refractive power and a negative refractive power in order from the object side. The second lens group, wherein the first lens group comprises, in order from the object side, a cemented lens of a negative meniscus lens having a convex surface facing the object side and a biconvex positive lens, Is a cemented lens composed of, in order from the object side, a positive meniscus lens having a concave surface facing the object side and a biconcave negative lens, and satisfies the following conditional expression. 0.40 <(R3 + R1) / (R3-R1) <0.90-0.25 <(R6 + R4) / (R6-R4) <0.9
0 40 <ν2-ν1 15 <ν4-ν3 where R1 is the radius of curvature of the most object side surface of the first lens group, R3 is the radius of curvature of the most image side surface of the first lens group, and R4 is the second lens group , R6 is the radius of curvature of the most image-side surface of the second lens group, ν1 is the Abbe number of the negative meniscus lens of the first lens group, and ν2 is the biconvex shape of the first lens group Abbe number of the positive lens of the shape, ν3 is the Abbe number of the positive meniscus lens of the second lens group, and ν4 is the Abbe number of the biconcave negative lens of the second lens group. 2. The front teleconverter lens according to claim 1, wherein the Abbe number ν2 of the biconvex positive lens of the first lens group satisfies the condition of 75 <ν2.