JP4645112B2 - Zoom lens - Google Patents

Description

  The present invention relates to a high-performance zoom lens mainly used in a small-sized imaging device using an image sensor such as a CCD (charged coupled device) such as a digital still camera.

In recent years, various zoom lenses have been announced for use in imaging devices of digital still cameras. For example, by effectively arranging an aspheric lens made of a resin material, there is a zoom lens that has a high resolution, a small distortion, a compact size, and a small number of components (see Patent Document 1).
JP 2003-057542 A

  This has a problem that when used in an imaging device of an ultra-thin digital still camera, the total length during use or storage is too long.

  In view of the circumstances described above, the present invention is to provide a zoom lens that is high resolution, has low distortion, and is compact and inexpensive even when used and retracted, by effectively arranging an aspheric lens. Objective.

The zoom lens according to the present invention includes, in order from the object side, a first lens group and a second lens group. The first lens group has negative refractive power, and the enlargement side has a convex meniscus shape and has negative refractive power. A second lens group including a first lens that is a lens (hereinafter, negative lens) and a second lens that is a convex meniscus lens having a positive refractive power (hereinafter, positive lens). Is a positive lens having a positive refracting power and having a small radius of curvature on the enlargement side, a fourth lens being a positive lens, and being used in a joined state with the fourth lens. A zoom that is configured by disposing a fifth lens of a negative lens as a material and a sixth lens having a small power, and changing the position by moving the positions of the first lens group and the second lens group. In the lens, Characterized in that it satisfies the following conditional expression (1) and (2) with respect to the optical axis direction dimension of's entire system. (Claim 1)
(1) TL / f _W <1.9
(2) 0.6 <f _W / f _II <0.77
However,
TL: Total length of the first lens group and the second lens group f _W : Total focal length of the entire lens system at the wide angle end f _II : Total focal length of the second lens group

  Conditional expression (1) defines the total lens length when retracted. When the upper limit is exceeded, it is difficult to sufficiently reduce the size. Conditional expression (2) defines the power distribution of each group that can achieve both miniaturization and performance with appropriate power. If the upper limit is exceeded, power will be excessive and performance will be reduced. If the lower limit is exceeded, the size will increase.

Further, in the zoom lens according to claim 1, the following conditional expression (3) is satisfied with respect to the power of the first lens constituting the first lens group, and the condition regarding the material of the first lens and the second lens is satisfied. It is preferable that the expressions (4) and (5) are satisfied and the following conditional expression (6) is satisfied with respect to the shape of the reduction-side surface of the first lens. (Claim 2)
(3) −1.1 <f _W / f ₁ <−0.8
(4) 10 <ν ₁ −ν ₂
(5) 1.66 <n ₂
(6) 1.16 <f _W / R ₂ <1.51
However,
f ₁ : Focal length of the first lens ν ₁ : Abbe number of the first lens ν ₂ : Abbe number of the second lens n ₂ : Refractive index at the d-line of the second lens R ₂ : Surface on the reduction side of the first lens Radius of curvature

  Conditional expression (3) relates to appropriate distribution of power to the first lens group having negative refractive power. This is a balance of conditions for appropriately correcting the size of the entire optical system and various aberrations. If the lower limit is exceeded, the negative power of the first lens group becomes large, and accordingly, the positive power of the second lens group must be strengthened, and it becomes difficult to balance various aberrations, and the performance deteriorates. . On the other hand, if the upper limit is exceeded, the air gap from the second group must be increased, and the overall size of the optical system increases, making it unsuitable for use as a compact digital still camera.

  Conditional expression (4) relates to chromatic aberration correction. If the lower limit is exceeded, chromatic aberration due to the first lens cannot be corrected, and correction within the first group becomes difficult. Conditional expression (5) relates to field curvature correction. If the lower limit is exceeded, the Petzval sum becomes large, and the field curvature cannot be corrected.

  Conditional expression (6) is a conditional expression regarding the shape of the reduction side surface of the first lens, which is a concave surface having a large curvature. By providing a curvature within the range of conditional expression (6), the occurrence of various aberrations is basically reduced by forming a concentric shape with respect to the entrance pupil. When the upper limit is exceeded, the radius of curvature of the reduction side surface of the first lens becomes small and processing becomes difficult, and the negative power becomes excessively large, and the Petzval sum becomes excessively small. Conversely, when the lower limit is exceeded, it is advantageous in processing, but concentricity is deteriorated, and it becomes difficult to correct distortion and curvature of field.

  In the zoom lens according to any one of the first and second aspects, it is preferable that the shape of the reduction-side surface of the first lens is an aspherical surface. (Claim 3)

In the zoom lens according to claim 1, the following conditional expressions (7) and (8) are satisfied with respect to the material of the third lens constituting the second lens group, and the following conditional expression (9) with respect to power is satisfied. And the following conditional expression (10) is satisfied with respect to the shape, and the following conditional expression (11) is satisfied with respect to the shapes of the third lens and the fifth lens, and 2 of the lens surfaces constituting the second lens group. The shape above the surface is preferably an aspherical surface. (Claim 4)
(7) 29.7 <(ν ₃ + ν ₄ ) / 2−ν ₅
(8) 1.45 <(n ₃ + n ₄ ) / 2 <1.78
(9) 0.5 <f _W / f ₃ <0.85
(10) 0.8 <f _W / R ₅ <1.45
(11) 0.75 <R ₅ / R ₉ <1.45
However,
ν ₃ : Abbe number of the third lens ν ₄ : Abbe number of the fourth lens n ₃ : Refractive index at the d-line of the third lens n ₄ : Refractive index at the d-line of the fourth lens f ₃ : Focal point of the third lens Distance R ₅ : radius of curvature of the enlargement side surface of the third lens R ₉ : radius of curvature of the reduction side surface of the fifth lens

  Conditional expression (7) is a conditional expression for maintaining good chromatic aberration correction. Exceeding this condition makes it difficult to correct chromatic aberration. Conditional expression (8) relates to field curvature correction. If the upper limit or lower limit is exceeded, the Petzval sum becomes inappropriate and the field curvature cannot be corrected. Conditional expression (9) relates to an appropriate distribution of power to the third lens having a positive refractive power. This is a balance of conditions for appropriately correcting the size of the entire optical system and various aberrations. If the condition deviates from this condition, the positive power of the third lens becomes large, and accordingly, the negative power of the first lens group has to be increased, and it becomes difficult to balance various aberrations, and the performance deteriorates.

  Conditional expression (10) is a condition for correcting the under spherical aberration caused by the third lens having a strong positive power and reducing the size by the positive and negative teletype configuration as the second group. If the upper limit is exceeded, it is advantageous for downsizing, but the performance is lowered. Conditional expression (11) is a requirement for correcting spherical aberration and coma aberration. Since a thick on-axis and off-axis light beam enters the second group, a concentric surface is required for the incident light beam. If deviating from this condition, spherical aberration and coma cannot be corrected satisfactorily.

  In the zoom lens according to claim 4, it is preferable that the shape of two or more lens surfaces constituting the second lens group is an aspherical surface. (Claim 5)

  In the zoom lens according to any one of the first and second aspects, the center thickness of the five lenses can be reduced by using a translucent ceramic having high strength. Unless the thickness is 0.45 mm or less, it is not possible to reduce the adverse effects of coloring that are characteristic of high refractive index lens materials. (Claim 6)

  According to the present invention, by effectively arranging an aspheric lens and a composite aspheric lens, it is possible to provide a zoom lens that has high resolution and low distortion, and is compact even when used and retracted. .

  Hereinafter, the present invention will be described with respect to specific numerical examples. In Examples 1 to 5 below, the lens unit includes a first lens group LG1 and a second lens group LG2, and the first lens group LG1 is a lens having a negative meniscus shape having a convex surface on the enlargement side (hereinafter referred to as a lens having a negative refractive power). A first lens L1 that is a negative lens) and a second lens L2 that is a convex meniscus lens having a positive refractive power (hereinafter, positive lens), and the second lens group LG2 Translucent ceramics that are used in a joined state with the third lens L3, which is a positive lens having a positive refractive power and whose enlargement side has a small radius of curvature, the fourth lens L4, which is a positive lens, and the fourth lens L4 The negative lens is made of a fifth lens L5 and a sixth lens L6 with a small power.

  In addition, a single or a plurality of parallel plane glasses LP are disposed between the second lens group LG2 and the reduction-side object image plane IP with an air gap. The parallel plane glass LP is composed of a plurality of or a single product such as a CCD cover glass, a crystal filter, and an infrared absorption filter in detail. However, since there is no optical problem, it is equal to the total thickness of these. It is expressed by a single plane-parallel glass.

As is well known, the aspherical surface used in each embodiment has an aspherical formula when taking the Z axis in the optical axis direction and the Y axis in the direction orthogonal to the optical axis:
Z = (Y ² / r) [1 + √ {1- (1 + K) (Y / r) ² }] + A ₄ · Y ⁴ + A ₆ · Y ⁶
+ A ₈・ Y ⁸ + A ₁₀・ Y ¹⁰
Is a curved surface obtained by rotating the curve given by around the optical axis, giving paraxial radius of curvature: r, conic constant: K, higher order aspherical coefficients: A ₄ , A ₆ , A ₈ , A ₁₀ Define the shape. In the notation of the conic constant and the higher-order aspheric coefficient in the table, “E and the number following it” represent “power of 10”. For example, “E-4” means 10 ⁻⁴ , and this numerical value may be multiplied by the immediately preceding numerical value.

Example 1
Table 1 shows numerical examples of the first embodiment of the zoom lens according to the present invention. FIG. 1 is a lens configuration diagram, and FIG.

In the tables and drawings, f represents the focal length of the entire lens system, F _No represents the F number, 2ω represents the total angle of view of the lens, and b _f represents the back focus. The back focus b _f is an air-converted distance of the distance from the sixth lens reduction side surface constituting the second lens group to the reduction side object image surface. Further, R is a radius of curvature, D is a lens thickness or a lens interval, n _d is a refractive index of d line, and ν _d is an Abbe number of d line. C, d, and g in the various aberration diagrams are aberration curves at the respective wavelengths. S represents sagittal and M represents meridional.

(Example 2)
Numerical examples of the second embodiment are shown in Table 2. FIG. 3 is a diagram showing the lens configuration, and FIG. 4 is a diagram showing various aberrations thereof.

(Example 3)
Numerical examples of the third embodiment are shown in Table 3. FIG. 5 is a lens configuration diagram, and FIG.

Example 4
Numerical examples are shown in Table 4 for the fourth embodiment. FIG. 7 is a lens configuration diagram, and FIG.

  Next, Table 5 collectively shows values corresponding to the conditional expressions (1) to (11) regarding the first to fourth embodiments.

  As is clear from Table 5, the numerical values related to the examples of Examples 1 to 4 satisfy the conditional expressions (1) to (11), and are also apparent from the aberration diagrams in the examples. Each aberration is corrected well.

  In addition, by using a high-strength translucent ceramic for the five lenses of Examples 1 to 4, it becomes possible to reduce the center thickness, thereby reducing the coloring effect that is characteristic of the high refractive index lens material. I was able to.

1 is a lens configuration diagram of a first embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the first example The lens block diagram of 2nd Example of the zoom lens by this invention. Various aberration diagrams of the lens of the second example 3 is a lens configuration diagram of a third embodiment of a zoom lens according to the present invention. FIG. Various aberration diagrams of the lens of the third example 4 is a lens configuration diagram of a fourth embodiment of a zoom lens according to the present invention. FIG. Various aberration diagrams of the lens of the fourth example

Claims (6)

In order from the object side, the lens unit includes a first lens group and a second lens group. The first lens group has a negative refractive power, and a lens having a negative meniscus shape having a convex surface on the enlargement side (hereinafter, a negative lens). ) And a second lens which is a convex meniscus lens having a positive refractive power (hereinafter, positive lens), and the second lens group has a positive refractive power. The third lens, which is a positive lens having a small curvature radius on the enlargement side, the fourth lens, which is a positive lens, and a negative lens which is used in a joined state with the fourth lens and is made of translucent ceramics. In a zoom lens that is configured by arranging 5 lenses and a sixth lens having a small power, and performing zooming by moving the positions of the first lens group and the second lens group, To the dimension in the optical axis direction And the following conditional expressions (1) and a zoom lens, characterized in that satisfies the (2).
(1) TL / f _W <1.9
(2) 0.6 <f _W / f _II <0.77
However,
TL: Total length of the first lens group and the second lens group f _W : Total focal length of the entire lens system at the wide angle end f _II : Total focal length of the second lens group The following conditional expression (3) is satisfied with respect to the power of the first lens constituting the first lens group, and conditional expressions (4) and (5) are satisfied with respect to the materials of the first lens and the second lens. 2. The zoom lens according to claim 1, wherein the following conditional expression (6) is satisfied with respect to the shape of the reduction side surface of one lens.
(3) −1.1 <f _W / f ₁ <−0.8
(4) 10 <ν ₁ −ν ₂
(5) 1.66 <n ₂
(6) 1.16 <f _W / R ₂ <1.51
However,
f ₁ : Focal length of the first lens ν ₁ : Abbe number of the first lens ν ₂ : Abbe number of the second lens n ₂ : Refractive index at the d-line of the second lens R ₂ : Surface on the reduction side of the first lens Radius of curvature   3. The zoom lens according to claim 1, wherein a shape of the reduction side surface of the first lens is an aspherical surface. 4. Regarding the material of the third lens constituting the second lens group, the following conditional expressions (7) and (8) are satisfied, the following conditional expression (9) is satisfied regarding power, and the following conditional expression (10) is satisfied regarding shape. Further, the following conditional expression (11) is satisfied with respect to the shapes of the third lens and the fifth lens, and the shape of two or more lens surfaces constituting the second lens group is an aspherical surface. The zoom lens according to claim 1.
(7) 29.7 <(ν ₃ + ν ₄ ) / 2−ν ₅
(8) 1.45 <(n ₃ + n ₄ ) / 2 <1.78
(9) 0.5 <f _W / f ₃ <0.85
(10) 0.8 <f _W / R ₅ <1.45
(11) 0.75 <R ₅ / R ₉ <1.45
However,
ν ₃ : Abbe number of the third lens ν ₄ : Abbe number of the fourth lens n ₃ : Refractive index at the d-line of the third lens n ₄ : Refractive index at the d-line of the fourth lens f ₃ : Focal point of the third lens Distance R ₅ : radius of curvature of the enlargement side surface of the third lens R ₉ : radius of curvature of the reduction side surface of the fifth lens   5. The zoom lens according to claim 4, wherein the shape of two or more lens surfaces constituting the second lens group is an aspherical surface.   In the zoom lens according to any one of claims 1 and 2, the center thickness of the fifth lens is 0.45 mm or less.

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