KR20060047157A - Zoom lens - Google Patents

Abstract

An object of the present invention is to provide a zoom lens having a wide angle of view, a low cost, a high zoom ratio, and a smaller (thin) lens.

The zoom lens according to the present invention includes the first lens group G1, the second lens group G2, and the third lens group G3 in this order from the object side. The 1st lens group G1 is equipped with the 1st lens 1 which has negative power, and the prism 2 which is located in the rear end of the 1st lens 1, refracts an optical path, and has positive power. In addition, the Abbe's number of the first lens 1 is larger than the Abbe number of the prism 2.

Description

Zoom lens {ZOOM LENS}

1 is a diagram illustrating a configuration of a zoom lens according to the first embodiment;

2 is a diagram illustrating a configuration of a zoom lens according to the first embodiment;

3 is a view showing the state of each aberration at the wide-angle end of the zoom lens according to the first embodiment;

4 is a view showing the state of each aberration in the middle of the zoom lens according to the first embodiment;

5 is a diagram showing the state of each aberration in the telephoto end of the zoom lens according to the first embodiment;

6 is a diagram illustrating a configuration of a zoom lens according to the second embodiment;

7 is a diagram illustrating a configuration of a zoom lens according to the second embodiment;

8 is a view showing the state of each aberration at the wide-angle end of the zoom lens according to the second embodiment;

9 is a diagram showing the state of each aberration in the middle of the zoom lens according to the second embodiment;

Fig. 10 is a diagram showing the state of each aberration in the telephoto end of the zoom lens according to the first embodiment.

Explanation of symbols for the main parts of drawings

1: first lens 2: prism

3: second lens 4: third lens

5: lens 10: fourth lens

G1: first lens group G2: second lens group

G3: third lens group S1: aperture

F1: infrared cut filter P1: optical upper surface

The present invention relates to a zoom lens, and can be applied to, for example, a mobile phone with a camera.

As a technique regarding a small zoom lens mounted on a cellular phone, a digital camera, or the like, there are patent documents 1 to 3, for example.

In the zoom lenses disclosed in Patent Documents 1 to 3, the optical path is refracted by the first lens group. This makes it possible to reduce the thickness of mobile phones and the like.

[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-70235

[Patent Document 2] Japanese Patent Application Laid-Open No. 2004-53993

[Patent Document 3] Japanese Unexamined Patent Application Publication No. 2000-131610

By the way, in the case of a cellular phone with a camera or the like, the photographer himself may photograph himself, so the angle of view is required to be about 2 to 75 degrees (that is, a wide angle of view is required).

However, in the invention according to Patent Document 1, the angle of view is as small as 68 ° at 2ω. In addition, in the invention according to Patent Document 2, the angle of view is as small as 61 ° at 2ω.

In addition, in the invention according to Patent Document 1 and the invention according to Patent Document 3, since some glass members are used, the cost is increased by that amount.

In addition, in the invention according to Patent Document 2, the zoom ratio is reduced to about 2 times. Further, in the invention according to Patent Document 3, since the number of lenses is nine, the size of the entire zoom lens is also increased.

Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide a zoom lens having a wide angle of view, a low cost, a high zoom ratio, and a smaller (thin) lens.

In order to achieve the above object, the zoom lens according to claim 1 of the present invention comprises a first lens group having a negative power of position fixing at variable displacement, and a position variable fixed at variable displacement. The second lens group having a positive power and the third lens group having a positive power having a variable position in shifting are provided in this order from the object side, and the shifting is performed by varying the interval of each lens group. A zoom lens for performing the above, wherein the first lens group includes a first lens having negative power, a rear end of the first lens, a function of refracting an optical path, and a prism having a positive power, Abbe's number of the first lens is larger than that of the prism.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated concretely based on the drawing which shows embodiment.

(Embodiment 1)

The zoom lens according to the present embodiment is a zoom lens having a three-group configuration.

1 is a diagram illustrating a configuration of a zoom lens according to the present embodiment. 2 is a block diagram showing linearly the optical path of the zoom lens shown in FIG. In addition, the prism which has an internal reflecting surface is shown by the parallel flat plate in FIG. 1 and 2, the object side is the front end side, and the upper surface side is the rear end side.

In Figs. 1 and 2, ri (i = 1, 2, 3, ...) is the i-th surface counting from the object side, and the number increases as it approaches the upper surface side. In addition, di (i = 1, 2, 3, ...) is an i-axis space | interval space | interval counting from an object side, and a number becomes large as it approaches an upper surface side.

As shown to FIG. 1, 2, the 1st lens group G1, the 2nd lens group G2, and the 3rd lens group G3 are arrange | positioned in the said order from the object side to the image surface side. Here, the second lens group G2 is a variator having a variable function. In addition, the third lens group G3 is a compensator for performing correction of a shop.

In the zoom lenses shown in Figs. 1 and 2, shifting is performed by changing the intervals of the lens groups G1, G2, and G3.

Specifically, shifting is performed by moving the lens groups G1 to G3 in the directions M and N of the arrows shown in FIG. 2. As shown in FIG. 2, the position of the 1st lens group G1 does not fluctuate by shift. In addition, when the second lens group G2 moves in the shear direction along the optical axis in the variable speed (especially zooming from the wide-angle end W to the telephoto end T), the third lens group G3 is moved. Moves to the front end after moving to the rear end once along the optical axis (see FIG. 2).

The position of the first lens group G1 does not change due to shift, and has negative power. The position of the second lens group G2 varies with variation, and has a positive power. The position of the third lens group G3 varies with variation, and has a positive power.

In addition, the diaphragm S1 is arrange | positioned at the front end of 2nd lens group G2. In addition, an infrared cut filter F1 made of a parallel plate is disposed at the rear end of the third lens group G3, and an optical image surface P1 is disposed at the rear end of the infrared cut filter F1. This is arranged.

The optical upper surface P1 is, for example, a solid-state imaging device such as a CCD (Charge Coupled Device) or a CMOS (Complementary MOS) sensor. By the imaging device, the optical image formed by the zoom lens is converted into an electrical signal. In addition, instead of the infrared cut filter F1, you may use the optical low pass filter and cover glass which consist of parallel flat plates.

Next, the specific structure of each lens group G1-G3 is demonstrated.

The 1st lens group G1 is comprised from the 1st lens 1 and the prism 2, as shown to FIG.

The first lens 1 is disposed most on the object side and has negative power. The prism 2 is located at the rear end of the first lens 1 and has a positive power.

The object side surface r1 and the image surface side surface r2 of the first lens 1 have a concave curved surface shape, and at least one surface has an aspherical surface shape. By this curved shape, the first lens 1 has negative power as a whole.

In addition, the prism 2 bends the optical axis Z1 (optical path) 90 degrees on the reflection surface r4. As described above, the optical path is refracted by the prism 2, thereby making the length of the incident optical axis direction (that is, the depth direction (up and down direction in FIG. 1)) of the zoom lens system short and constant. Here, for example, aluminum or the like is deposited on the reflecting surface r4 of the prism 2. This minimizes the amount of light loss.

The bending angle of the optical axis Z1 (optical path) on the reflection surface r4 may be an angle other than 90 °, and the angle may be set as necessary. In addition, the reflection surface r4 may have power, and the optical axis Z1 (optical path) may be bent using a refractive surface or a diffraction surface instead of the reflection surface.

In addition, the object side surface r3 of the prism 2 is a convex curved surface shape, and the upper surface side surface r5 of the prism 2 is a concave curved surface shape. By the curved shape, the prism 2 has a positive power as a whole.

The Abbe number of the first lens 1 is larger than the Abbe number of the prism 2.

By the way, the distribution of Abbe's numbers, such as a plastic lens, is distributed in the range of 27-34, and the range of 49-58. Therefore, when the first lens 1 and the prism 2 are made of plastic, a material having an Abbe number of 49 or more is employed as the first lens 1, and a material having an Abbe number of less than 35 is used as the prism 2. can do.

Next, a specific configuration of the second lens group G2 will be described.

The 2nd lens group G2 is comprised from the 2nd lens 3 and the 3rd lens 4, as shown to FIG.

The second lens 3 is arranged at the rear end of the first lens group G1 and has a positive power. The third lens 4 is located at the rear end of the second lens 3 and has negative power.

The object-side surface r6 and the image-side surface r7 of the second lens 3 have a convex curved surface shape, and at least one surface has an aspherical surface shape. By the curved shape, the second lens 3 has a positive power as a whole.

In addition, the object-side surface r8 and the image-side surface r9 of the third lens 4 are concave curved surfaces, and the third lens 4 has negative power as a whole by the curved surface.

In addition, the Abbe number of the second lens 3 is larger than the Abbe number of the third lens 4. For example, when the plastic 2nd lens 3 and the 3rd lens 4 are employ | adopted, as a 2nd lens 3, Abbe's number employs a material 49 or more, and also as the 3rd lens 4, A material having an Abbe number of less than 35 can be employed.

In addition, the 3rd lens group G3 is comprised only by the lens 5, as shown to FIG.

The lens 5 is arrange | positioned at the rear end of the 2nd lens group G2, and has positive power. The object side surface r10 of the lens 5 has a convex curved surface shape, and the image side surface r11 of the lens 5 has a concave curved surface shape. By the curved shape, the lens 5 has a positive power as a whole.

In addition, the zoom lens according to the present embodiment is designed to satisfy the following equations (1) and (2).

Here, f1 is a focal length of the first lens group G1. fW is the focal length of the entire zoom lens system at the wide-angle end. f2 is a focal length of the second lens group G2.

Since the zoom lens which concerns on this embodiment is comprised as mentioned above, it has the effect shown below.

In the zoom lens according to the present embodiment, a prism 2 having a positive power is provided, and the Abbe number of the first lens 1 is larger than the Abbe number of the prism 2.

Therefore, the magnification chromatic aberration generated when the negative power of the first lens 1 is increased can be corrected by the prism 2 having the positive power. Since the correction is possible, in the zoom lens according to the present embodiment, the negative power of the first lens group G1 can be designed to be larger.

In this way, by increasing the negative power of the first lens group G1, the wide angle of view of the first lens group G1 is enabled. In addition, since light from a wide angle is also incident on the first lens group G1, the aperture of the first lens group G1 can be made smaller. In addition, the back focus can be shortened by increasing the negative power of the first lens group G1 (shortening of the optical full length). Therefore, the whole zoom lens system can be made more compact.

In addition, in the zoom lens according to the present embodiment, since the magnification chromatic aberration correction is effectively performed in the first lens group G1, the magnification ratio (zoom ratio) can be increased.

In addition, it is assumed that the difference between the Abbe number of the first lens 1 and the Abbe number of the prism 2 is made larger. In this case, even if the difference between the negative power of the first lens 1 and the positive power of the prism 2 is not large, the magnification chromatic aberration generated in the first lens 1 can be corrected by the prism 2. .

In other words, the smaller the Abbe number of the prism 2 is, the larger the Abbe number of the first lens 1 is, the smaller the positive power of the prism 2 is, and the negative power of the first lens 1 is obtained. Can be set large.

As described above, when the positive power of the prism 2 decreases, the curvature of the prism 2 can be made smaller. Thereby, manufacture of the prism 2 becomes easy. Moreover, when the positive power of the prism 2 is small, it also has the effect that the structure of the whole zoom lens system can be performed easily.

In addition, Abbe numbers, such as a lens, differ according to the material which comprises the said lens. In the case of employing a plastic lens or the like, the first lens 1 may be a material having an Abbe number of 49 to 58 (49 or more), and the prism 2 as an Abbe number of 27 to 34 (less than 35). What is necessary is just to employ | adopt the material of.

In general, the smaller the Abbe number, the larger the refractive index. Therefore, if the Abbe number of the prism 2 is made small as mentioned above, the refractive index of the prism 2 will become large. In this way, when the refractive index of the prism 2 becomes large, the inclination angle in the prism 2 of the chief ray can be made small at the wide-angle end. Therefore, the first lens group G1 can be miniaturized.

By the way, it is assumed that the first lens 1 made of plastic having a lower refractive index than the glass material is adopted. In this case, since the first lens 1 has a relatively small refractive index, when the negative power is increased, large negative distortion aberration occurs at the wide-angle end of the first lens 1.

Therefore, in the zoom lens according to the present embodiment, at least one surface of the first lens 1 is aspheric. This corrects the negative distortion aberration. Therefore, the negative power of the first lens group G1 can be made larger.

In addition, it is assumed that the second lens 3 is made of a material having a small refractive index (for example, plastic). In this case, since the refractive index of the second lens 3 is small, negative spherical aberration occurs according to the second lens 3 having positive power.

Therefore, in the zoom lens according to the present embodiment, at least one surface of the second lens 3 having positive power is aspheric. This corrects the spherical aberration.

As is well known in the above formula (1), when (-f1 / fW) is 1.5 or less, it is impossible to increase the ratio and the magnification decreases. In addition, when (-f1 / fW) becomes 4.0 or more, the back focus becomes long and the length of the entire zoom lens system becomes long. Therefore, by satisfying the above expression (1), it is possible to make both the ratio and the miniaturization of the zoom lens system compatible.

In the second lens group G2 of the zoom lens according to the present embodiment, the third lens 4 having negative power is disposed at the rear end of the second lens 3 having positive power. In addition, the Abbe number of the second lens 3 is made larger than the Abbe number of the third lens 4.

Therefore, the axial chromatic aberration generated in the second lens 3 having the positive power can be corrected by the third lens 4.

By the way, as the number of curved surfaces in the zoom lens system increases, the correction of each aberration can be more effectively executed.

Therefore, in the zoom lens according to the present embodiment, the two surfaces r3 and r5 of the prism 2 are curved. Therefore, magnification chromatic aberration generated in the first lens 1 can be more surely corrected by the prism 2.

In the zoom lens according to the present embodiment, all the lenses and prisms may be made of lightweight and inexpensive plastic.

Thereby, cost reduction of the whole zoom lens system can be aimed at. In addition, even if the device on which the zoom lens system is mounted is accidentally dropped on the ground, the impact force applied to the zoom lens system can be minimized. That is, the zoom lens system excellent in impact resistance can be provided.

When (-f2 / f1) becomes 1.0 or less in Equation 2, negative top curvature occurs. This is based on the following reasons.

The absolute value of the negative power of the first lens group G1 needs to be equal to the sum of the absolute value of the positive power of the second lens group G2 and the absolute value of the positive power of the third lens group G3. have. However, when (-f2 / f1) is 1.0 or less, the absolute value (| 1 / f2 |) of the positive power of the second lens group G2 is equal to the absolute value (|) of the negative power of the first lens group G1. It exceeds 1 / f1 |). In this case, negative top curvature occurs as a result.

The negative image curvature generated in this way is difficult to correct even if the aspherical surface is extensively used in the zoom lens system.

When (-f2 / f1) is 2.0 or more, the second lens group G2 and the third lens group G3 collide with each other when changing. Further, when (-f2 / f1) becomes 2.0 or more, the aperture of the first lens group G1 becomes so large that it cannot be mounted in a mobile phone or the like, and it becomes impractical, so that the wide angle of view becomes impossible or zooms. The compactness of the lens system also becomes impossible.

However, in the zoom lens according to the present embodiment, since the above expression (2) is satisfied, the above problems can be solved. In addition, the upper limit "2.0" is determined by the rule of thumb.

In addition, in the zoom lens of the type in which the optical axis Z1 is not bent by the prism 2, in order to shorten the overall length of the zoom lens system in the object-side direction, the lens part is stored in the apparatus when the camera is not in use (sink). Instrument).

It is said that the zoom lens of the immersion mechanism was used for the mobile telephone. In this case, if the mobile phone is dropped on the ground during shooting (the state in which the barrel protrudes from the device), the protruding barrel may collide directly with the ground surface and the lens may be damaged. Brings about.

However, the zoom lens according to the present embodiment employs a mechanism that vertically bends the optical axis Z1 (optical path) by using the prism 2, not the oscillation mechanism. Thereby, even when the depth of the apparatus (mobile phone etc.) which mounts a zoom lens system is narrow, it is not necessary to protrude the barrel part from an apparatus. Therefore, even if the apparatus is dropped, the barrel can also be prevented from directly colliding with the ground plane.

When the zoom lens of the mechanism that bends the optical axis Z1 (optical path) is mounted on a cellular phone or the like that is subjected to violent handling, the above effects are more exhibited.

(Example 1)

Simulation results of the zoom lens according to Embodiment 1 shown in FIGS. 1 and 2 are shown below. Table 1 shows the specific configuration data of Example 1. Table 2 is a table showing aspherical surface coefficients of the respective lenses.

In Table 1, ri is the radius of curvature (axis curvature radius in the aspherical surface) of the surface of the lens (or prism, filter) present in the i-th from the object side. In addition, the infinite radius of curvature indicates that the surface is planar.

In Table 1, di is the distance from the surface of the lens (or prism, filter) present in the i-th to the surface of the lens (or prism, filter) in the i + 1th. In the case where the distance di changes in the variation, the di is displayed in the order of the wide-angle end (short focal length end, W) to middle (middle focal length state, M) to telephoto end (long focal length end, T). It is.

In Table 1, ni is the refractive index at the d (yellow) line (wavelength: 587.56 nm) of the lens (or prism, filter) present at the i-th from the object side. Further, ν i is the Abbe's number of the lens (or prism or filter) existing in the i-th from the object side.

In Table 2, ri is the surface number of the curved surface of the lens (or prism) present at the i-th from the object side.

In addition, the aspherical surface coefficient shown in Table 2 has shown each coefficient shown by following formula.

In the above formula, "z" is the depth from a tangent plane with respect to a vertex. "C" is paraxial curvature of a surface. "H" is the height from the optical axis. "K" is a cone multiplier. "A" is a fourth-order aspherical surface coefficient. "B" is a 6th-order aspherical surface coefficient. "C" is an eighth-order aspherical surface coefficient. "D" is an aspherical coefficient of tenth order.

In Example 1, Xeonex® E48R is employed as the first lens 1, the second lens 3, and the lens 5. In addition, PC (polycarbonate) is adopted as the prism 2 and the third lens 4. That is, the zoom lens according to the first embodiment is composed of five plastic lenses (including a prism). In addition, all refractive surfaces are made aspherical.

As a result of the simulation of the zoom lens according to Example 1 of the above configuration, the electric field focal length f (mm) is 3.03 (W) to 5.25 (M) to each focal length state (W, M, T). 9.09 (T). The F number FNO is 3.2 (W) to 4.6 (M) to 5.9 (T) for each focal length state (W, M, T). The angle of view 2ω is 75.0 ° (W) to 47.8 ° (M) to 28.7 ° (T) for each focal length state (W, M, T).

Moreover, as a result of the simulation of the zoom lens which concerns on Example 1 of the said structure, the focal length f1 of the 1st lens group G1 is -8.12 mm. The focal length f2 of the second lens group G2 is 8.18 mm. The focal length fW of the entire zoom lens system at the wide-angle end is 3.03 mm as described above.

From the simulation results, it can be seen that the value of (-f1 / fW) is 2.68. This value satisfies the relationship of the equation (1). In addition, it turns out that the value of (-f2 / f1) is 1.01. This value satisfies the relationship of equation (2).

In addition, the angle of view 2ω at the wide-angle end is 75 °, the angle of view is wide, and the zoom ratio (9.09 / 3.03) also secures about three times.

3, 4, and 5 show aberration diagrams of the zoom lens according to the first embodiment. 3 is an aberration diagram at the wide-angle end W. FIG. 4 is an aberration diagram in the middle M. FIG. 5 is an aberration diagram in the telephoto end T. FIG. 3, 4 and 5 show spherical aberration, astigmatism, and distortion aberration from the left. In addition, "FNO" has shown the F number value, and "Y" has shown the maximum height (mm).

In each spherical aberration diagram, the solid line d shows the spherical aberration (mm) with respect to the d (yellow) line (wavelength: 587.56 nm). Moreover, the broken line g has shown the spherical aberration (mm) with respect to the g (blue-purple) line (wavelength: 435.84 nm). In addition, the dashed-dotted line c shows the spherical aberration with respect to the c (red) line (wavelength: 656.27 nm).

In the astigmatism diagram, the solid line S represents the astigmatism (mm) with respect to the d (yellow) line in the sagittal plane. In addition, the broken line M has shown the astigmatism (mm) with respect to the d (yellow) line in a meridional plane.

In the distortion aberration diagram, the solid line represents the distortion (%) with respect to the d (yellow) line.

3, 4, and 5, each data line is almost zero. From this, it is understood that each aberration is sufficiently corrected in the zoom lens according to the first embodiment. In addition, in the spherical aberration diagram of FIG. 5, the aberration at the g line has a slightly larger aberration near zero. However, since the value of the aberration in the vicinity of the incident height near 0 is less than 0.2 mm, it can be said that it can be sufficiently corrected.

(Embodiment 2)

The zoom lens according to the present embodiment is also a zoom lens having a three-group configuration.

6 is a diagram illustrating a configuration of a zoom lens according to the present embodiment. 7 is a block diagram showing linearly the optical path of the zoom lens shown in FIG. In addition, the prism which has an internal reflecting surface is shown by the parallel flat plate in FIG. 6 and 7, the object side is the front end side, and the upper surface side is the rear end side.

6 and 7, ri (i = 1, 2, 3, ...) is the i-th surface counting from the object side, and the number increases as it approaches the upper surface side. In addition, di (i = 1, 2, 3, ...) is the i-axis upper surface spacing counting from the object side, and the number increases as it approaches the upper surface side.

In addition, in the zoom lens shown in FIGS. 6 and 7, shifting is performed by changing the interval of each lens group G1, G2, G3.

Specifically, shifting is performed by moving the lens groups G1 to G3 in the directions M and N of the arrows shown in FIG. 7. As shown in FIG. 7, the position of the 1st lens group G1 does not fluctuate by shift. In addition, when the second lens group G2 is moved in the shear direction along the optical axis in the variable magnification (particularly, the zooming from the wide-angle end W to the telephoto end T), the third lens group G3 is the optical axis. Thus, once it moves to the rear end side and then to the front end side (see FIG. 7).

The zoom lens according to the present embodiment has a configuration substantially the same as that of the zoom lens according to the first embodiment, but differs in the following points. Hereinafter, only the difference is mentioned. In addition, since the other structure is the same as that of the zoom lens which concerns on Embodiment 1, description here is abbreviate | omitted.

In the zoom lens according to the present embodiment, as shown in FIGS. 6 and 7, the first lens group G1 having negative power is newly provided with the fourth lens 10. The fourth lens 10 has negative power and is disposed at the rear end of the prism 2.

The object side surface r6 of the fourth lens 10 has a concave curved surface shape, and the image side surface r7 of the fourth lens 10 has a convex curved surface shape (in addition, the convex shape is near the center of the lens). The curvature becomes smoother toward the end of the lens and becomes positive curvature (concave shape) near the end of the lens). By the curved shape, the fourth lens 10 has negative power as a whole. In addition, the Abbe number of the fourth lens 10 is larger than the Abbe number of the prism 2.

By the way, the distribution of Abbe's numbers, such as a plastic lens, is distributed in the range of 27-34, and the range of 49-58. Therefore, when the fourth lens 10 and the prism 2 are made of plastic, a material having an Abbe number of 49 or more is employed as the fourth lens 10 and a material having an Abbe number of less than 35 is used as the prism 2. can do.

In addition, in this embodiment, the object side surface r1 of the 1st lens 1 is a convex curved surface shape.

In addition, in this embodiment, the object side surface r3 of the prism 2 is planar, and the upper surface side surface r5 of the prism 2 is convex curved shape.

Contrary to the above, the object-side surface r3 of the prism 2 may be a convex curved surface shape, and the upper surface side surface r5 of the prism 2 may be flat. That is, any one of the object side surface r3 and the upper surface side surface r5 of the prism 2 should just be flat, and the other surface should just be made into the shape in which the prism 2 has the positive power as a whole.

The zoom lens according to the present embodiment is also designed to satisfy the above expressions (1) and (2).

Since the zoom lens which concerns on this embodiment is comprised as mentioned above, it has the effect shown below in addition to the effect demonstrated by Embodiment 1. As shown in FIG.

In the zoom lens according to the present embodiment, a fourth lens 10 having negative power that has an Abbe number larger than the Abbe number of the prism 2 is newly provided. Therefore, the negative power of the first lens group G1 can be managed by the first lens 1 and the fourth lens 10. Thereby, the lens thickness of the 1st lens 1 can be made thinner, and as a result, the thickness of the depth direction (up-down direction of FIG. 6) of a zoom lens can be made thinner.

In addition, the distortion of the distortion aberration can be easily performed by the fourth lens 10.

 In the zoom lens according to the present embodiment, either one of the object side surface r3 and the image side surface r5 of the prism 2 is a plane. Therefore, the core shift | offset | difference between the object side surface r3 and the upper surface side surface r5 of the prism 2 can be prevented. Thereby, the prism 2 excellent in performance can be manufactured easily, and manufacturing cost can also be reduced.

Moreover, in Embodiment 1, 2, you may employ | adopt the structure which each lens and prism has an aspherical surface. Thereby, since each aberration correction can be performed with each lens, the zoom lens can be constituted by a smaller number of lenses.

Each lens group constituting the zoom lens according to the first and second embodiments is only a refractive lens that deflects incident light rays by refraction (that is, a lens of a type in which deflection is performed at an interface between media having different refractive indices). Consists of. However, it is not limited to this.

For example, a diffractive lens for deflecting incident light by diffraction, a refraction / diffractive hybrid lens deflecting incident light by a combination of diffraction and refraction actions, and a refractive index distribution for deflecting the incident light beam according to the refractive index distribution in the medium Each lens group may be constituted by a lens or the like.

(Example 2)

Simulation results of the zoom lens according to Embodiment 2 shown in FIGS. 6 and 7 are shown below. Table 3 shows specific configuration data of Example 2. In addition, Table 4 is a table | surface which shows the aspherical surface coefficient of each lens.

Definitions of ri, di, ni, υi and the like in Tables 3 and 4 are the same as in Example 1.

In Example 2, Xeonex® E48R is employed as the first lens 1, the second lens 3, the fourth lens 10, and the lens 5. In addition, PC (polycarbonate) is adopted as the prism 2 and the third lens 4. That is, the zoom lens according to the second embodiment is composed of six plastic lenses (including a prism). In addition, all refractive surfaces except surface r3 are aspherical.

As a result of the simulation of the zoom lens according to the second embodiment of the above configuration, the electric field focal length f (mm) is 3.03 (W) to 5.56 (M) to 9.09 (T) for each focal length state (W, M, T). to be. The F number FNO is 32 (W) to 4.6 (M) to 5.7 (T) for each focal length state (W, M, T). The angle of view 2ω is 75.0 ° (W) to 45.3 ° (M) to 28.7 ° (T) for each focal length state (W, M, T).

Moreover, as a result of the simulation of the zoom lens which concerns on Example 2 of the said structure, the focal length f1 of the 1st lens group G1 is -6.44 mm. The focal length f2 of the second lens group G2 is 7.37 mm. The focal length fW of the entire zoom lens system at the wide-angle end is 3.03 mm as described above.

From the simulation results, it can be seen that the value of (-f1 / fW) is 2.13. This value satisfies the relationship of the equation (1). In addition, it turns out that the value of (-f2 / f1) is 1.14. This value satisfies the relationship of equation (2).

In addition, the angle of view 2ω at the wide-angle end is 75 °, the angle of view is wide, and the zoom ratio (9.09 / 3.03) also secures about three times.

8, 9, and 10 show aberration diagrams of the zoom lens according to the second embodiment. 8 is an aberration diagram at the wide-angle end W. FIG. 9 is aberration diagrams in the middle M. FIG. 10 is an aberration diagram in the telephoto end T. FIG. 8, 9, and 10 show spherical aberration, astigmatism, and distortion aberration from the left. In addition, "FNO" has shown the F number value, and "Y" has shown the maximum image height (mm).

In each aberration diagram, display of each data (each solid line, each broken line, etc.) is the same as that described in Example 1. FIG.

In Figs. 8, 9 and 10, each data line is almost zero. From this, it is understood that each aberration is sufficiently corrected in the zoom lens according to the second embodiment.

The zoom lens according to claim 1 of the present invention has a first lens group having negative power of position fixing at variable speed, a second lens group having positive power of variable position at variable speed, and a positive power of variable position at variable speed. A zoom lens for carrying out the above-mentioned shifting by providing a third lens group in this order from the object side and changing the interval of each lens group, wherein the first lens group includes a first lens having negative power and And a prism positioned at a rear end of the first lens and having a function of refracting an optical path and having a positive power, and the Abbe number of the first lens is greater than the Abbe number of the prism, Magnification chromatic aberration generated when the negative power is increased can be corrected by a prism having a positive power. Since the correction is possible, the negative lens of the first lens group can be designed larger in the zoom lens according to claim 1. In this way, the negative angle of the first lens group can be widened by increasing the negative power of the first lens group. Further, since light from a wide angle is also incident on the first lens group, the aperture of the first lens group can be made smaller. In addition, by increasing the negative power of the first lens group, the back focus can be shortened (shortening the optical overall length). Therefore, the whole zoom lens system can be made more compact. Further, since the magnification chromatic aberration correction can be effectively performed in the first lens group, the variation ratio (zoom ratio) can be increased.

Claims (14)

A first lens group having negative power in positional variation in displacement, and A second lens group having a positive power in positional variation in variation; Third lens group having positive power in positional variation in variation From the object side in this order, As a zoom lens for performing the above shift by changing the interval of each lens group, The first lens group, A first lens having negative power, A prism positioned at a rear end of the first lens, having a function of refracting an optical path, and having a positive power Equipped with Abbe's number of the first lens is larger than Abbe's number of the prism A zoom lens characterized in that. The method of claim 1, At least one surface of the first lens is an aspherical surface. The method of claim 1, The second lens group includes a second lens having a positive power, At least one side of the second lens is an aspherical surface A zoom lens characterized in that. The method of claim 1, A zoom lens, which satisfies the following conditional expression 1.5 <-f1 / fW <4.0 (where f1 is the focal length of the first lens group and fW is the focal length of the entire zoom lens system at the wide-angle end). . The method of claim 1, The second lens group, A second lens having positive power, A third lens positioned at a rear end of the second lens and having a negative power; Equipped with Abbe number of the second lens is larger than Abbe number of the third lens A zoom lens characterized in that. The method of claim 1, A zoom lens, wherein the object side and the image side of the prism are curved surfaces. The method of claim 1, Any one of the object side and the image side surface of the prism is a flat lens. The method of claim 1, The first lens group further includes a fourth lens positioned at a rear end of the prism and having a negative power. Abbe number of the fourth lens is larger than Abbe number of the prism A zoom lens characterized in that. The method of claim 1, A zoom lens, wherein each lens constituting the lens group and the prism are made of plastic. The method of claim 1, The first lens and the prism are made of plastic, Abbe number of the first lens is 49 or more, Abbe number of the prism is less than 35 A zoom lens characterized in that. The method of claim 5, wherein The second lens and the third lens are made of plastic, Abbe number of the second lens is 49 or more, Abbe number of the third lens is less than 35 A zoom lens characterized in that. The method of claim 8, The fourth lens is made of plastic, Abbe number of the fourth lens is 49 or more A zoom lens characterized in that. The method of claim 1, A zoom lens, characterized in that each lens and prism provided in each lens group has an aspherical surface, respectively. The method of claim 1, A zoom lens satisfying the following conditional expression 1.0 <-f2 / f1 <2.0 (where f1: focal length of the first lens group and f2: focal length of the second lens group).

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