JP2006119324A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which has a wide viewing angle, a low cost and a high zoom ratio, and is made small-sized (thin). <P>SOLUTION: The zoom lens is provided with a first lens group G1, a second lens group G2 and a third lens group G3 in the order from the object side. The first lens group G1 is provided with a first lens 1 having negative power and a prism 2 which is positioned on the post step of the first lens 1, deflects an optical path and has positive power. Further, Abbe number of the first lens 1 is larger than the Abbe number of the prism 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  For example, Patent Documents 1 to 3 are related to a small zoom lens mounted on a mobile phone, a digital camera, or the like.

  In the zoom lenses disclosed in Patent Documents 1 to 3, the optical path is bent in the first lens group. This makes it possible to reduce the thickness of a mobile phone or the like.

JP 2004-70235 A JP 2004-53993 A JP 2000-131610 A

  By the way, in the case of a camera-equipped mobile phone or the like, since the photographer himself may photograph himself, the angle of view needs to be about 75 ° at 2ω (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. Also in the invention according to Patent Document 2, the angle of view is as small as 61 ° at 2ω.

  Furthermore, in the invention according to Patent Document 1 and the invention according to Patent Document 3, since a glass member is used in part, the cost increases accordingly.

  In the invention according to Patent Document 2, the zoom ratio is as small as about twice. Furthermore, in the invention according to Patent Document 3, since the number of lenses is nine, the overall size of the zoom lens is also increased.

  Accordingly, the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a zoom lens that has a wide angle of view, is inexpensive, has a high zoom ratio, and is smaller (thin).

  In order to achieve the above object, a zoom lens according to claim 1 of the present invention includes a first lens group having a negative power that is fixed in position at zooming, and a positive lens that is variable in position at zooming. A second lens group having the following power, a third lens group having a positive power that is variable in magnification, and an object side in this order, and by changing the interval between the lens groups, The zoom lens for performing zooming, wherein the first lens group has a first lens having a negative power and a function of bending the optical path, located at the rear stage of the first lens. And the first lens has an Abbe number greater than the Abbe number of the prism.

  The zoom lens according to claim 1 of the present invention includes a first lens group having a negative power that is fixed in position at zooming, and a second lens group having a positive power that is variable in position at zooming. A zoom lens that is provided with a third lens group having a positive power that is variable in zooming, and in this order from the object side, and that performs zooming by changing the interval between the lens groups. The first lens group includes a first lens having a negative power, and a prism having a function of bending an optical path and positioned at the rear stage of the first lens and having a positive power. Since the Abbe number of the first lens is larger than the Abbe number of the prism, the lateral chromatic aberration generated when the negative power of the first lens is increased is corrected by the prism having a positive power. CanSince this correction is possible, in the zoom lens according to claim 1, the negative power of the first lens group can be designed to be larger. Thus, by increasing the negative power of the first lens group, it is possible to widen the angle of view of the first lens group. In addition, since light from a wider angle is also incident on the first lens group, the aperture of the first lens group can be made smaller. Furthermore, by increasing the negative power of the first lens group, the back focus can be shortened (shortening of the optical total length). Therefore, the entire zoom lens system can be made more compact. In addition, since the chromatic aberration of magnification is effectively corrected in the first lens group, the zoom ratio can be increased.

  Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.

<Embodiment 1>
The zoom lens according to the present embodiment is a three-group zoom lens.

  FIG. 1 is a diagram illustrating a configuration of a zoom lens according to the present embodiment. FIG. 2 is a configuration diagram linearly showing the optical path of the zoom lens shown in FIG. In addition, the prism which has an internal reflective surface is represented by the parallel plate in FIG. In each of FIGS. 1 and 2, the object side is the front side, and the image plane side is the back side.

  In FIGS. 1 and 2, ri (i = 1, 2, 3,...) Is the i-th surface counted from the object side, and the number increases as it approaches the image surface side. In addition, di (i = 1, 2, 3,...) Is the i-th axis upper surface interval counted from the object side, and the number increases as it approaches the image surface side.

  As shown in FIGS. 1 and 2, the first lens group G1, the second lens group G2, and the third lens group G3 are arranged in this order from the object side to the image plane side. Here, the second lens group G2 is a variator having a zooming function. The third lens group G3 is a compensator that corrects an image point.

  In the zoom lens shown in FIGS. 1 and 2, zooming is performed by changing the distance between the lens groups G1, G2, and G3.

  Specifically, zooming is performed by moving the lens groups G1 to G3 in the directions of arrows M and N shown in FIG. As shown in FIG. 2, the position of the first lens group G1 does not vary during zooming. When the second lens group G2 moves in the front direction along the optical axis at zooming (particularly zooming from the wide-angle end (W) to the telephoto end (T)), the third lens group G3 After moving to the rear side once along the axis, the head moves to the front side (see FIG. 2).

  The first lens group G1 does not change its position during zooming and has negative power. The position of the second lens group G2 varies during zooming and has a positive power. The position of the third lens group G3 varies during zooming and has positive power.

  A diaphragm S1 is disposed in front of the second lens group G2. In addition, an infrared cut filter F1 made of a parallel plate is disposed downstream of the third lens group G3, and an optical image plane P1 is disposed downstream of the infrared cut filter F1. .

  Here, the optical image plane P1 is a solid-state image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary MOS) sensor composed of a plurality of pixels. The image sensor converts the optical image formed by the zoom lens into an electrical signal. Further, instead of the infrared cut filter F1, an optical low-pass filter made of a parallel plate or a cover glass may be used.

  Next, a specific configuration of each of the lens groups G1 to G3 will be described.

  The first lens group G1 includes a first lens 1 and a prism 2, as shown in FIGS.

  The first lens 1 is disposed closest to the object side and has negative power. The prism 2 is located after 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 are concave curved surfaces, and at least one of the surfaces has an aspherical shape. Due to the curved shape, the first lens 1 has a negative power as a whole.

  Further, the prism 2 has the optical axis Z1 (optical path) bent 90 degrees on the reflection surface r4. In this way, by bending the optical path by the prism 2, the length of the zoom lens system in the incident optical axis direction (that is, the depth direction (vertical direction in FIG. 1)) is made short and constant. Here, for example, aluminum or the like is deposited on the reflection surface r4 of the prism 2. This minimizes light loss.

  The bending angle of the optical axis Z1 (optical path) on the reflecting surface r4 may be an angle other than 90 °, and the angle may be set as necessary. Further, the reflecting surface r4 may be given power, or the optical axis Z1 (optical path) may be bent using a refracting surface or a diffractive surface instead of the reflecting surface.

  The object side surface r3 of the prism 2 has a convex curved surface shape, and the image surface side surface r5 of the prism 2 has a concave curved surface shape. Due to the curved surface shape, the prism 2 as a whole has a positive power.

  Further, 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 numbers of plastic lenses or the like is distributed in the range of 27 to 34 and in the range of 49 to 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 adopted as the first lens 1 and a material having an Abbe number smaller than 35 is adopted as the prism 2. can do.

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

  The second lens group G2 includes a second lens 3 and a third lens 4, as shown in FIGS.

  The second lens 3 is disposed downstream of the first lens group G1 and has a positive power. The third lens 4 is located after the second lens 3 and has negative power.

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

  Further, the object side surface r8 and the image surface side surface r9 of the third lens 4 are concave curved surfaces, and the third lens 4 as a whole has negative power due to the curved surface shape.

  Further, the Abbe number of the second lens 3 is larger than the Abbe number of the third lens 4. For example, when the plastic second lens 3 and the third lens 4 are employed, a material having an Abbe number of 49 or more is employed as the second lens 3, and the Abbe number is employed as the third lens 4. A material having a number smaller than 35 can be employed.

  The third lens group G3 includes only the lens 5 as shown in FIGS.

  The lens 5 is disposed downstream of the second lens group G2 and has a positive power. The object side surface r10 of the lens 5 has a convex curved surface shape, and the image surface side surface r11 of the lens 5 has a concave curved surface shape. Due to the curved surface shape, the lens 5 as a whole has a positive power.

  Note that the zoom lens according to the present embodiment is designed to satisfy the following expressions (1) and (2).

1.5 <−f1 / fW <4.0 (1)
1.0 <−f2 / f1 <2.0 (2)
Here, f1 is the 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 the focal length of the second lens group G2.

  Since the zoom lens according to the present embodiment is configured as described above, the zoom lens has the following effects.

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

  Therefore, the lateral chromatic aberration generated when the negative power of the first lens 1 is increased can be corrected by the prism 2 having a positive power. Since this 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 can be increased. In addition, since light from a wider angle is also incident on the first lens group G1, the aperture of the first lens group G1 can be further reduced. Furthermore, by increasing the negative power of the first lens group G1, the back focus can be shortened (shortening of the total optical length). Therefore, the entire zoom lens system can be made more compact.

  Moreover, in the zoom lens according to the present embodiment, the chromatic aberration of magnification is effectively corrected in the first lens group G1, so that the zoom ratio (zoom ratio) can be increased.

  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 lateral chromatic aberration generated in the first lens 1 can be corrected in the prism 2. .

  That is, the smaller the Abbe number of the prism 2 and the larger the Abbe number of the first lens 1, the smaller the positive power of the prism 2 and the negative power of the first lens 1. Can be set larger.

  As described above, if the positive power of the prism 2 is small, the curvature of the prism 2 can be further reduced. Thereby, manufacture of the prism 2 becomes easy. Further, if the positive power of the prism 2 is small, there is also an effect that the entire zoom lens system can be easily configured.

  In addition, the Abbe number of a lens etc. changes with the materials which comprise the said lens etc. When a plastic lens or the like is used, a material having an Abbe number of 49 to 58 (49 or more) may be used as the first lens 1, and an Abbe number of 27 to 34 ( The material of less than 35) may be used.

  In general, the smaller the Abbe number, the greater the refractive index. Therefore, if the Abbe number of the prism 2 is reduced as described above, the refractive index of the prism 2 increases. Thus, if the refractive index of the prism 2 increases, the tilt angle of the principal ray within the prism 2 at the wide angle end can be reduced. Therefore, the first lens group G1 can be reduced in size.

  By the way, it is assumed that the first lens 1 made of plastic having a lower refractive index than the glass material is employed. In this case, since the first lens 1 has a relatively low refractive index, if the negative power is increased, a large negative distortion 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 an aspherical surface. As a result, the negative distortion is corrected. Therefore, the negative power of the first lens group G1 can be further increased.

  Further, 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 is generated by the second lens 3 having a 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 an aspherical surface. Thereby, the spherical aberration is corrected.

  In the above formula (1), as is well known, when (−f1 / fW) is 1.5 or less, the zoom ratio cannot be increased, and the magnification is reduced. On the other hand, when (−f1 / fW) is 4.0 or more, the back focus becomes longer and the entire length of the zoom lens system becomes longer. Therefore, satisfying the above expression (1) makes it possible to achieve both a zoom ratio and a compact zoom lens system.

  Further, in the second lens group G2 of the zoom lens according to the present embodiment, the third lens 4 having negative power is arranged at the rear stage of the second lens 3 having positive power. Further, the Abbe number of the second lens 3 is made larger than the Abbe number of the third lens 4.

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

  By the way, normally, the larger the number of curved surfaces in the zoom lens system, the more effectively each aberration can be corrected.

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

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

  As a result, the cost of the entire zoom lens system can be reduced. Further, even if an apparatus equipped with the zoom lens system is accidentally dropped on the ground, it is lightweight, so that the impact force applied to the zoom lens system can be minimized. That is, it is possible to provide a zoom lens system having excellent impact resistance.

  In the above equation (2), when (−f2 / f1) is 1.0 or less, negative field curvature occurs. This is due to the following reason.

  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. There is. 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 the negative power of the first lens group G1. Exceeds the absolute value of (| 1 / f1 |). In this case, as a result, negative field curvature occurs.

  The negative curvature of field generated in this way is difficult to correct even if a large number of aspheric surfaces are used in the zoom lens system.

  If (−f2 / f1) is 2.0 or more, the second lens group G2 and the third lens group G3 collide during zooming. Further, when (−f2 / f1) is 2.0 or more, the aperture of the first lens group G1 becomes so large that it cannot be mounted on a mobile phone or the like, and becomes impractical. It is also impossible to make the zoom lens system more compact.

  However, since the zoom lens according to the present embodiment satisfies the above expression (2), the above problems can be solved. The upper limit “2.0” is determined based on empirical rules.

  Further, in a zoom lens in which the optical axis Z1 is not bent by the prism 2, in order to shorten the entire length of the zoom lens system in the object side direction, the lens unit is stored in the apparatus when the camera is not used (collapse mechanism). ).

  Assume that the zoom lens of the retractable mechanism is used for a mobile phone. In this case, if the mobile phone is dropped on the ground during shooting (the lens barrel protrudes from the device), the protruding lens barrel may directly collide with the ground. Cause damage.

  However, the zoom lens according to the present embodiment adopts a mechanism that uses the prism 2 to bend the optical axis Z1 (optical path) vertically instead of the retracting mechanism. Thereby, even when the depth of a device (such as a mobile phone) equipped with a zoom lens system is narrow, there is no need to project the lens barrel portion from the device. Therefore, even if the apparatus is dropped, the lens barrel can be prevented from directly colliding with the ground.

  The zoom lens having a mechanism that bends the optical axis Z1 (optical path) exhibits the above-described effect when mounted on a mobile phone or the like that is assumed to be handled roughly.

<Example 1>
The simulation results of the zoom lens according to Embodiment 1 shown in FIGS. Table 1 shows specific configuration data of the first embodiment. Table 2 shows the aspheric coefficient of each lens.

  In Table 1, ri is the radius of curvature of the surface of the i th lens (or prism, filter) from the object side (on the aspherical surface, the radius of curvature on the axis). The infinite radius of curvature indicates that the surface is a plane.

  In Table 1, di is the distance from the surface of the i th lens (or prism, filter) to the surface of the i + 1 th lens (or prism, filter) from the object side. When the distance di changes during zooming, the di is from the wide-angle end (short focal length end, W) to the middle (intermediate focal length state, M) to the telephoto end (long focal length end, T). They are shown in order.

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

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

  The aspheric coefficients shown in Table 2 indicate the coefficients shown in the following formula.

z = ch ² / [1+ {1 · (1 + K) c ² h ² } ^1/2 ] + Ah ⁴ + Bh ⁶ + Ch ⁸ + Dh ¹⁰
In the above equation, “z” is the depth from the tangent plane with respect to the surface vertex. “C” is the paraxial curvature of the surface. “H” is the height from the optical axis. “K” is a cone multiplier. “A” is a fourth-order aspheric coefficient. “B” is a sixth-order aspheric coefficient. “C” is an 8th-order aspheric coefficient. “D” is a 10th-order aspheric coefficient.

  In Example 1, ZEONEX (registered trademark) E48R is employed as the first lens 1, the second lens 3, and the lens 5. Further, PC (polycarbonate) is adopted as the prism 2 and the third lens 4. In other words, the zoom lens according to Example 1 includes five plastic lenses (including a prism). All refractive surfaces are aspherical.

  As a result of the simulation of the zoom lens according to Example 1 having the above-described configuration, the total focal length f (mm) is 3.03 (W) to 5.25 (for each focal length state (W, M, T)). M) to 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 field angle 2ω is 75.0 ° (W) to 47.8 ° (M) to 28.7 ° (T) for each focal length state (W, M, T).

  Furthermore, as a result of the simulation of the zoom lens according to Example 1 having the above-described configuration, the focal length f1 of the first 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 Expression (1). It can also be seen that the value of (−f2 / f1) is 1.01. This value satisfies the relationship of Expression (2).

  In addition, the angle of view 2ω at the wide angle end is as wide as 75 °, and the zoom ratio (9.09 / 3.03) is secured about 3 times.

  Aberration diagrams of the zoom lens according to Example 1 are shown in FIGS. Here, FIG. 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 at the telephoto end (T). 3, 4 and 5, from the left, a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram are shown. “FNO” indicates an F-number value, and “Y” indicates a maximum image height (mm).

  In each spherical aberration diagram, a solid line (d) indicates spherical aberration (mm) with respect to a d (yellow) line (wavelength: 587.56 nm). A broken line (g) indicates spherical aberration (mm) with respect to g (blue purple) line (wavelength: 435.84 nm). The alternate long and short dash line (c) indicates spherical aberration with respect to the c (red) line (wavelength: 656.27 nm).

  In the astigmatism diagram, a solid line (S) indicates astigmatism (mm) with respect to the d (yellow) line on the sagittal surface. A broken line (M) indicates astigmatism (mm) with respect to the d (yellow) line on the meridional surface.

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

  3, 4, and 5, each data line converges to almost zero. From this, it can be seen that in the zoom lens according to Example 1, each aberration is sufficiently corrected. In the spherical aberration diagram of FIG. 5, the g-line has a slightly larger aberration when the incident height is near zero. However, since the value of the aberration near the incident height of 0 is less than 0.2 mm, it can be said that it has been sufficiently corrected.

<Embodiment 2>
The zoom lens according to the present embodiment is also a three-group zoom lens.

  FIG. 6 is a diagram showing a configuration of the zoom lens according to the present embodiment. FIG. 7 is a configuration diagram linearly showing the optical path of the zoom lens shown in FIG. In addition, the prism which has an internal reflective surface is represented by the parallel plate in FIG. 6 and 7, the object side is the front side and the image plane side is the rear side.

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

  In the zoom lens shown in FIGS. 6 and 7, zooming is performed by changing the distance between the lens groups G1, G2, and G3.

  Specifically, zooming is performed by moving the lens groups G1 to G3 in the directions of arrows M and N shown in FIG. As shown in FIG. 7, the position of the first lens group G1 does not vary during zooming. When the second lens group G2 moves along the optical axis in the preceding stage at zooming (particularly zooming from the wide-angle end (W) to the telephoto end (T)), the third lens group G3 After moving to the rear side once along the axis, the head moves to the front side (see FIG. 7).

  The zoom lens according to the present embodiment has substantially the same configuration as the zoom lens according to Embodiment 1, but they are different in the following points. Only the differences will be mentioned below. Since the other configuration is the same as that of the zoom lens according to Embodiment 1, the description thereof is omitted here.

  In the zoom lens according to the present embodiment, as shown in FIGS. 6 and 7, the first lens group G <b> 1 having a negative power newly includes a fourth lens 10. The fourth lens 10 has a negative power and is disposed at the rear stage 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. The curvature becomes gentler toward the part, and a positive curvature (concave) is formed near the end of the lens). Due to the curved surface shape, the fourth lens 10 has a negative power as a whole. Further, 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 numbers of plastic lenses or the like is distributed in the range of 27 to 34 and in the range of 49 to 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 used as the fourth lens 10, and a material with an Abbe number smaller than 35 is used as the prism 2. can do.

  In the present embodiment, the object side surface r1 of the first lens 1 has a convex curved shape.

  In the present embodiment, the object side surface r3 of the prism 2 is a flat surface, and the image surface side surface r5 of the prism 2 is a convex curved surface.

  Contrary to the above, the object side surface r3 of the prism 2 may be a convex curved surface shape, and the image surface side surface r5 of the prism 2 may be a flat surface. That is, one of the object side surface r3 and the image side surface r5 of the prism 2 only needs to be a flat surface, and the other surface may have a shape in which the prism 2 has a positive power as a whole.

  It should be noted that the zoom lens according to the present embodiment is also designed so as to satisfy the above formulas (1) and (2).

  Since the zoom lens according to the present embodiment is configured as described above, it has the following effects in addition to the effects described in the first embodiment.

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

  In addition, the fourth lens 10 can easily correct distortion.

  In the zoom lens according to the present embodiment, one of the object side surface r3 and the image side surface r5 of the prism 2 is a flat surface. Therefore, misalignment between the object side surface r3 and the image side surface r5 of the prism 2 can be prevented. Thereby, the high-performance prism 2 can be easily manufactured, and the manufacturing cost can be reduced.

  In the first and second embodiments, a configuration in which each lens and prism has an aspherical surface may be adopted. As a result, each aberration can be corrected by each lens or the like, so that a zoom lens can be configured with a smaller number of lenses.

  Each lens group constituting the zoom lens according to Embodiments 1 and 2 includes a refractive lens that deflects incident light by refraction (that is, a lens that is deflected at an interface between media having different refractive indexes). ) Only. However, it is not limited to this.

  For example, a diffractive lens that deflects incident light by diffraction, a refractive / diffractive hybrid lens that deflects incident light by a combination of diffraction and refraction, and a refractive index distribution that deflects incident light by a refractive index distribution in the medium Each lens group may be constituted by a lens or the like.

<Example 2>
The simulation results of the zoom lens according to Embodiment 2 shown in FIGS. Table 3 shows specific configuration data of the second embodiment. Table 4 is a table showing the aspheric coefficients of the respective lenses.

  The definitions of ri, di, ni, νi, etc. in Tables 3 and 4 are the same as in the first embodiment.

  In Example 2, ZEONEX (registered trademark) E48R is adopted as the first lens 1, the second lens 3, the fourth lens 10, and the lens 5. Further, PC (polycarbonate) is adopted as the prism 2 and the third lens 4. That is, the zoom lens according to Example 2 is configured by six plastic lenses (including a prism). All the refractive surfaces except the surface r3 are aspherical.

  As a result of the simulation of the zoom lens according to Example 2 configured as described above, the total focal length f (mm) is 3.03 (W) to 5.56 (for each focal length state (W, M, T). M) to 9.09 (T). The F number FNO is 3.2 (W) to 4.6 (M) to 5.7 (T) for each focal length state (W, M, T). The field angle 2ω is 75.0 ° (W) to 45.3 ° (M) to 28.7 ° (T) for each focal length state (W, M, T).

  Further, as a result of the simulation of the zoom lens according to Example 2 having the above-described configuration, the focal length f1 of the first 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 Expression (1). Also, it can be seen that the value of (−f2 / f1) is 1.14. This value satisfies the relationship of Expression (2).

  In addition, the angle of view 2ω at the wide angle end is as wide as 75 °, and the zoom ratio (9.09 / 3.03) is secured about 3 times.

  Aberration diagrams of the zoom lens according to Example 2 are shown in FIGS. Here, FIG. 8 is an aberration diagram at the wide-angle end (W). FIG. 9 is an aberration diagram in the middle (M). FIG. 10 is an aberration diagram at the telephoto end (T). 8, 9, and 10, from the left, a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram are shown. “FNO” indicates an F-number value, and “Y” indicates a maximum image height (mm).

  Each data display (each solid line, each broken line, etc.) in each aberration diagram is the same as that described in the first embodiment.

  In FIGS. 8, 9, and 10, each data line converges to almost zero. From this, it can be seen that in the zoom lens according to Example 2, each aberration is sufficiently corrected.

1 is a diagram illustrating a configuration of a zoom lens according to Embodiment 1. FIG. 1 is a diagram illustrating a configuration of a zoom lens according to Embodiment 1. FIG. FIG. 6 is a diagram illustrating a state of each aberration at the wide angle end of the zoom lens according to Example 1; FIG. 6 is a diagram illustrating various aberrations in the middle of the zoom lens according to Example 1; FIG. 6 is a diagram illustrating a state of each aberration at the telephoto end of the zoom lens according to Example 1; 6 is a diagram illustrating a configuration of a zoom lens according to Embodiment 2. FIG. 6 is a diagram illustrating a configuration of a zoom lens according to Embodiment 2. FIG. FIG. 10 is a diagram illustrating a state of each aberration at the wide angle end of the zoom lens according to Example 2; FIG. 10 is a diagram illustrating a state of each aberration in the middle of the zoom lens according to Example 2; FIG. 6 is a diagram illustrating a state of each aberration at the telephoto end of the zoom lens according to Example 1;

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st lens, 2 prism, 3 2nd lens, 4 3rd lens, 5 lens, 10 4th lens, G1 1st lens group, G2 2nd lens group, G3 3rd lens group , S1 stop, F1 infrared cut filter, P1 optical image plane.

Claims (14)

A first lens group having a negative power and fixed in position at zooming;
A second lens group having a positive power and variable position at zooming;
A third lens group having a positive power, variable in position at zooming, and in this order from the object side,
A zoom lens that performs the zooming by changing the interval of each lens group,
The first lens group includes:
A first lens having negative power;
A prism located at the rear stage of the first lens, having a function of bending the optical path, and having a positive power;
The Abbe number of the first lens is greater than the Abbe number of the prism;
A zoom lens characterized by that. At least one surface of the first lens is an aspheric surface,
The zoom lens according to claim 1. The second lens group includes:
A second lens having positive power,
At least one surface of the second lens is an aspheric surface.
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The zoom lens according to any one of claims 1 to 3, wherein the following conditional expression is satisfied:
1.5 <−f1 / fW <4.0 (1)
However,
f1: focal length of the first lens group,
fW: focal length of the entire zoom lens system at the wide-angle end,
It is. The second lens group includes:
A second lens having positive power;
A third lens located at the rear stage of the second lens and having a negative power,
The Abbe number of the second lens is larger than the Abbe number of the third lens,
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The object side surface and the image surface side surface of the prism are curved surfaces.
The zoom lens according to any one of claims 1 to 5, wherein: Either one of the object side surface and the image surface side surface of the prism is a plane.
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The first lens group includes:
A fourth lens located at the rear stage of the prism and having a negative power;
The Abbe number of the fourth lens is larger than the Abbe number of the prism;
The zoom lens according to any one of claims 1 to 5, or the zoom lens according to claim 7. Each lens constituting each lens group, and the prism,
Made of plastic,
9. The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The first lens and the prism are made of plastic,
The Abbe number of the first lens is 49 or more,
The prism Abbe number is less than 35;
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The second lens and the third lens are made of plastic,
The Abbe number of the second lens is 49 or more,
The Abbe number of the third lens is less than 35;
The zoom lens according to claim 5. The fourth lens is made of plastic;
The Abbe number of the fourth lens is 49 or more.
The zoom lens according to claim 8. Each lens and prism included in each lens group each have an aspherical surface,
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The zoom lens according to claim 1, wherein the following conditional expression is satisfied:
1.0 <−f2 / f1 <2.0 (2)
However,
f1: focal length of the first lens group,
f2: focal length of the second lens group,
It is.

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