JPH10253882A - Two-group zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the variable power ratio of about two times, and obtain excellent image forming performance with the small, inexpensive and simple constitution by providing a first lens group of negative meniscus, biconcave and positive lenses and a second lens group of positive, positive, biconcave and positive lenses from the object side, changing an air interval between the first and the second lens groups at power variable time, and satisfying a specific condition about a focal distance or the like. SOLUTION: A first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power are arranged in order from the object side. G1 has a negative meniscus lens L1, a biconcave lens L2 and a positive lens L3 in order from the object side, and G2 has positive lenses L4, 5, a biconcave lens L6 and a positive lens L7 in order from the object side, and an interval between G1 and G2 changes at power variable time, and expressions II to III are satisfied. Here, a focal distance of L4 and 5 is denoted by fL4 and 5, and a focal distance of G2 is denoted by f2, and a radius of curvature on the image side of L1 is denoted by r2, and a radius of curvature on the object side of L2 is denoted by r3, and a focal distance of G1 is denoted by f1, and a focal distance on the wide angle side and the telescopic side of the whole lens system is denoted by fw and ft.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact two-unit zoom lens having a glass structure of seven groups and seven elements, and more particularly to a zoom lens for a single-lens reflex camera or an electronic still camera.

[0002]

2. Description of the Related Art In recent years, an interchangeable lens for a 35 mm still camera includes, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power.
Among the group-structured zoom lenses, a so-called standard zoom lens including a standard angle of view of about 47 ° and a zoom ratio of about 2 times replaces a lens which is a conventional standard lens with a focal length of 50 mm. It is becoming standard equipment. Therefore, such a standard zoom lens is used as a regular lens, and is frequently carried while being attached to a camera body.

Therefore, the standard zoom lens needs to be compact and inexpensive while ensuring sufficient imaging performance. The two-unit zoom lens is optimal for realizing such a zoom lens, and various proposals have been made so far.

For example, Japanese Patent Laid-Open Publication No. Hei 8-5919 and Japanese Patent Publication No. Sho 61-46809 disclose a two-group zoom lens having a seven-group, seven-element structure. JP-A-59-142515
Japanese Patent Application Publication No. JP-A-2002-115122 discloses a two-group zoom lens having a seven-group, seven-element structure and a variable aperture stop mechanism provided on the object side of the second lens group, that is, between the first lens group and the second lens group. It has been disclosed.

[0005]

However, the zoom lenses disclosed in JP-A-8-5919 and JP-B-61-46809 have a problem that the distance between the first lens group and the second lens group at the telephoto end is small. First too short
It is difficult to provide a variable aperture stop mechanism in the space between the lens group and the second lens group. Therefore, a variable aperture stop mechanism must be provided in the second lens group, which causes problems such as an increase in the number of components of the lens barrel and an increase in cost.

The zoom lens disclosed in Japanese Patent Application Laid-Open No. Sho 59-142515 has a seven-group, seven-element structure, and is sandwiched between the first lens group and the second lens group on the object side of the second lens group. It is characterized in that a variable aperture stop mechanism is provided in a closed space. However, aberration correction is insufficient.
Further, since the first and second lenses from the object side have a negative meniscus configuration, it is effective for widening the angle of view. Therefore, since the lenses pass through more distant positions, the diameters of the first and second lenses are relatively large, and there is a disadvantage that compactness cannot be achieved.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a zoom lens having a zoom ratio of about 2 times, a small size, an inexpensive structure, a simple structure, and excellent imaging performance. The purpose is to:

[0008]

In order to solve the above problems, the present invention provides, in order from the object side, a first lens group G1 having a negative refractive power as a whole and a second lens group G as a whole having a positive refractive power. G2, wherein the first lens group G1 is a negative meniscus lens L having a convex surface facing the object side in order from the object side.
1, a biconcave lens L2, and a positive lens L3. The second lens group G2 includes, in order from the object side, a positive lens L4, a positive lens L5, a biconcave lens L6, and a positive lens L7. At the time of magnification, the distance between the first lens group G1 and the second lens group G2 changes, the focal length of the positive lens L4 of the second lens group G2 is fL4, the focal length of the positive lens L5 is fL5, Let the focal length of the two lens group G2 be f
2. The negative meniscus lens L of the first lens group G1
1, the radius of curvature on the image side of the first lens group G1 is r2, the radius of curvature of the biconcave lens L2 of the first lens group G1 on the object side is r3,
When the focal length of the lens group G1 is f1, the focal length at the wide-angle end in the entire lens system is fw, and the focal length at the telephoto end in the entire lens system is ft, the following conditions are satisfied: Is satisfied.

With this configuration, for the following reasons,
A compact zoom lens with a relatively small overall length change due to zooming has been realized.

As shown in FIG. 17, the second lens group G2 is divided into a lens group G21 having a positive refractive power and a lens group G22 having a negative refractive power in order from the object side. The focal length is f2, the focal length f21 of the positive lens group G21, the focal length of the lens group G22 having a negative refractive power is f22, and the image-side principal point H of the lens group G21 having a positive refractive power.
21 and the object side principal point H of the lens group G22 having a negative refractive power.
22, when the principal point intervals H21 and H22 are dh, the following equation (a) is obtained. To establish.

[0011] The first lens system is made compact while the lens system is made compact.
In order to obtain a necessary distance between the lens G1 and the second lens group G2, the refractive power of the lens group G21 is increased, that is, the value of the focal length f21 is reduced, and the focal length f2 of the lens group G2 is reduced.
It is necessary to optimize the distance d between the principal points and the focal length f22 of the lens group G22 so that is constant.

Generally, in order from the object side, in a two-unit zoom lens including a first lens group G1 having a negative refractive power as a whole and a second lens group G2 having a positive refractive power as a whole, the first lens group Let the focal length of G1 be f1,
The imaging magnification of the second lens group G2 at the wide angle end is β2w, and the imaging magnification of the second lens group G2 at the telephoto end is β2.
Let t be the focal length f of the entire lens system at the wide-angle end.
w and the focal length ft of the entire lens system at the telephoto end satisfy the following expressions (b1) and (b2), and fw = f1.beta.2w (b1) ft = f1.beta.2t (b2).

Here, it is assumed that the conjugate lengths of the second lens unit G2 at the wide-angle end and the telephoto end are equal, and β2t = 1 /
Assuming β2w, the above equations (b1) and (b2) are given by the following equation (c) Can be rewritten as When the condition of Expression (c) is satisfied, the total length at the wide-angle end is equal to the total length at the telephoto end, and a change in the total length of the lens due to zooming can be minimized.

Therefore, it is not preferable to set the focal length f1 of the first lens group G1 so as to largely deviate from the condition shown in the equation (c), since the change in the entire length of the lens due to zooming becomes too large. In order to reduce the size of the zoom lens, the magnification β2t at the telephoto end of the second lens group G2 needs to be used at a magnification exceeding 1: 1.

Further, in order to satisfy the conditions of the above equations (a) and (c) while favorably correcting aberrations with a compact lens system, the first lens group G1 and the second lens group G
It is necessary that 2 has a relatively strong refractive power. Therefore, in the conventional zoom lens, each lens group tends to be configured with a large number of lenses, and each lens group has a large thickness, and the effect of miniaturization has been reduced.

In the zoom lens according to the present invention, unlike the conventional lens, the refractive power arrangement suitable for miniaturization is set by considering the relationship of the above equations (a) and (c), and the negative power is set. Lens group G1 having a refractive power of
, A negative / negative / positive three-lens configuration having two negative lenses L1, L2 and a positive lens L3, and a second lens group G2 having a positive refractive power is connected to two positive lenses L4, L5 and a negative lens L6, The positive lens L7 has four positive, positive, negative, and positive lenses. According to the present invention, this configuration achieves a zoom lens that is small and has a relatively small change in the overall length due to zooming.

Next, the conditional expressions (1) to (3) of the present invention will be described. It is desirable that the zoom lens of the present invention satisfies the following conditional expressions (1), (2) and (3). Here, each symbol indicates the following. fL4: focal length of the positive lens L4 in the second lens group G2 fL5: focal length of the positive lens L5 in the second lens group G2 f2: focal length of the second lens group G2 r2: negative focal length of the first lens group G1 The radius of curvature of the lens L1 on the image side r3: The radius of curvature of the negative lens L2 in the first lens group G1 on the object side f1: The focal length of the first lens group G1 fw: The focal length at the wide-angle end of all lens systems ft: All Focal length at the telephoto end of the lens system Conditional expression (1) is an expression that determines an appropriate distance between the first lens group G1 and the second lens group G2. As described above, the position of the principal point of the second lens group G2 is optimized by changing the refractive power of the positive lens L4 and the positive lens L5 in the second lens group G2 within a range satisfying conditional expression (1). As a result, the distance between the first lens group G1 and the second lens group G2 can be maintained.

When the value exceeds the upper limit of conditional expression (1), the refractive power of the positive lens L4 and the positive lens L5 in the second lens group G2 increases. In such a case, in order to properly correct the aberration, the absolute value of the radius of curvature of each lens must be reduced, the thickness of the lens must be increased, or the number of lenses must be increased. As a result, the cost is increased and the overall length is undesirably increased. vice versa,
If the lower limit of conditional expression (1) is exceeded, the distance between the first lens group G1 and the second lens group G2 becomes narrow, so that an aperture stop mechanism is arranged between the first lens group G1 and the second lens group G2. It becomes difficult to do. Therefore, when the distance between the first lens group G1 and the second lens group G2 is small, for example,
An aperture stop mechanism is provided between the positive lens L5 and the negative lens L6 in the lens group G2. For this reason, when the aperture stop mechanism is arranged on the object side of the second lens group, the lens barrel member which has been completed at one point is divided into two points, which leads to an increase in cost, which is a problem. Further, dividing the lens barrel into two parts is not preferable because it causes eccentricity of the lens due to a manufacturing error of the barrel, which leads to deterioration of the imaging performance.

Conditional expression (2) defines an appropriate shape of the air lens formed between the first lens L1 from the object side of the first lens group G1 and the second lens L2 from the object side. The air lens shape at the lower limit is a biconvex lens shape in which the absolute value of the object-side radius of curvature is smaller than the absolute value of the image-side radius of curvature, and the air lens shape at the upper limit is a plano-convex lens in which the image-side radius of curvature is a plane. Shape. An air lens shape satisfying conditional expression (2) is defined between the biconvex lens and the plano-convex lens.

When the lower limit of conditional expression (2) is not reached, the air lens shape is changed from a biconvex lens shape in which the absolute value of the object side radius of curvature is smaller than the absolute value of the image side radius of curvature to the object side radius of curvature. The shape changes to a biconvex lens shape in which the absolute value of the image-side radius of curvature is equal, and further to a biconvex lens shape in which the absolute value of the image-side radius of curvature is smaller than the absolute value of the object-side radius of curvature.
In this case, it is difficult to correct the downward coma aberration and the chromatic aberration of magnification at the wide angle end. In addition, the fluctuation of the lower coma due to the magnification change becomes large, which is not preferable.

When the value exceeds the upper limit of conditional expression (2), the air lens shape becomes a meniscus shape with the convex surface facing the object side. In such a case, the meniscus shape is advantageous for correcting the downward coma aberration and the like. However, in order to reduce the size and cost as in the present invention, the incident height of oblique rays at the wide-angle end is reduced. Since the lens passes through a position farther from the optical axis, the diameter of the front lens increases, and the weight also increases. Furthermore, it is not preferable that a zoom lens having a large zoom ratio or a large-aperture zoom lens be disadvantageous in correcting spherical aberration at the telephoto end.

Conditional expression (3) is a conditional expression for keeping the total length change in the above-mentioned variable power range within an appropriate range. If the upper limit of conditional expression (3) is exceeded, the overall length at the wide-angle end becomes unnecessarily long. In this case, the diameter of the front lens becomes large, which leads to an increase in weight and cost, which is not preferable. Also, forcibly reducing the diameter of the front lens in a situation where the overall length is long is not preferable because the peripheral light amount is reduced.

On the other hand, if the lower limit of conditional expression (3) is not reached, the total length at the telephoto end is unnecessarily long, and the distance between the first lens group G1 and the second lens group G2 is required. Since the length is shorter than the above, it is difficult to provide the above-described aperture stop mechanism, which is not preferable. Further, it is difficult to correct downward coma aberration at the wide-angle end, spherical aberration and field curvature at the telephoto end, which is not preferable.

In the present invention, the following conditional expressions (4) to (6): n1 <1.75 (4) 1.73 <n7 (a) in order to realize cost reduction and good imaging performance. 5) It is preferable to satisfy ν4, ν5 <65 (6). Here, each symbol indicates the following. n1: refractive index at the d-line of the negative meniscus lens L1 in the first lens G1 n7: refractive index at the d-line of the positive lens L7 in the second lens group G2 ν4: refractive index of the positive lens L4 in the second lens group G2 Abbe number ν5: Abbe number of the positive lens L5 in the second lens group G2 Conditional expressions (4) and (5) are satisfied by the first lens group G1.
Appropriate refractive indices of the negative meniscus lens L1 in the middle and the positive lens L7 in the second lens group G2 are determined.

When n1 exceeds the upper limit value of the conditional expression (4), the curvature of the field becomes large, so that it is difficult to correct the peripheral best image plane. In addition, the astigmatism also increases, which deteriorates the imaging performance, which is not preferable.

Further, when n7 is below the lower limit of conditional expression (5), similarly to conditional expression (4), the Petzval sum becomes too small, the field curvature becomes large, and the astigmatism also increases. Therefore, the imaging performance deteriorates, which is not preferable.

Conditional expression (6) defines an appropriate range of the Abbe number of the positive lenses L4 and L5 in the second lens group G2.
If ν4 and ν5 exceed the upper limit of conditional expression (6), axial chromatic aberration is undesirably corrected excessively. Further, since a glass material having an Abbe number of 65 or more is relatively expensive, it is inconvenient to realize cost reduction.

[0028]

Embodiments of the present invention will be described below.

The zoom lens according to each embodiment of the present invention includes, in order from the object side, a first lens group G1 having a negative refractive power as a whole and a second lens group G2 having a positive refractive power as a whole. The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave lens L2, and a positive lens L3.
2 is a positive lens L4 and a positive lens L5 in order from the object side.
, A biconcave lens L6, and a positive lens L7. Zooming is performed by changing the distance between the first lens group G1 and the second lens group G2. In each example,
An aperture stop mechanism is provided between the first lens group G1 and the second lens group G2.

(First Embodiment) FIGS. 1A to 1C show
FIG. 3 is a diagram illustrating a lens configuration of the zoom lens according to the first example of the present invention and a moving state of each lens group during zooming. The zoom lens of FIG. 1 has, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave lens L2 having a smaller absolute value of the radius of curvature on the image side than on the object side, and a positive lens having a convex surface facing the object side. A first lens group G1 composed of a meniscus lens L3, a biconvex lens L4 having a larger absolute value of the radius of curvature on the image side than on the object side, a positive meniscus lens L5 having a convex surface facing the object side, A biconcave lens L6 having a smaller absolute value of the radius of curvature, and a biconvex lens L having a smaller absolute value of the radius of curvature on the image side than on the object side.
The second lens group G2 includes a second lens group G2.

Table 1 below shows data values of the first embodiment.
In the table, f is the focal length, Fno is the F number,
2ω represents the angle of view. Further, the surface number indicates the order of the lens from the object side, and the refractive index and Abbe number indicate the d-line (λ = 587.
6 nm).

[0032]

[Table 1] 2 to 4 are graphs showing various aberrations of the first embodiment. In each aberration diagram, FNO represents the F number, Y represents the image height, and d represents d.
Line (λ = 587.6 nm) and g is the g line (λ = 435.
8 nm). In the aberration diagram showing astigmatism,
The solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. Further, in the aberration diagram showing spherical aberration, a broken line indicates a sine condition. Hereinafter, the reference numerals in the aberration diagrams in each embodiment are the same as those in the first embodiment.

FIG. 2 is a diagram illustrating various aberrations at the wide-angle end, FIG. 3 is a diagram illustrating various aberrations at the intermediate focal length, and FIG. 4 is a diagram illustrating various aberrations at the telephoto end. As is clear from the aberration diagrams, in the present embodiment, various aberrations at each focal length are satisfactorily corrected.

(Second Embodiment) FIGS. 5A to 5C show
FIG. 8 is a diagram illustrating a lens configuration of a zoom lens according to a second embodiment of the present invention and movement of each lens group during zooming. The zoom lens in FIG. 5 has, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave lens L2 having a smaller absolute value of the radius of curvature on the image side than on the object side, and a positive lens having a convex surface facing the object side. A first lens group G1 composed of a meniscus lens L3, a biconvex lens L4 having a larger absolute value of the radius of curvature on the image side than on the object side, a positive meniscus lens L5 having a convex surface facing the object side, A biconcave lens L6 having a smaller absolute value of the radius of curvature, and a biconvex lens L having a smaller absolute value of the radius of curvature on the image side than on the object side.
And a second lens group G2.

Table 2 below summarizes data values of the second embodiment of the present invention. Each symbol in the table is the same as in the first embodiment.

[0036]

[Table 2] f = 36-68mm Fno = 3.59-5.15 2ω = 63.94-34.99 ° Surface number Curvature radius Surface spacing Abbe number Refractive index 1) 49.650 1.8 48.04 1.71700 L1 2) 18.827 7.5 1.00000 3) -132.266 1.6 48.04 1.71700 L2 4) 66.618 0.5 1.00000 5) 31.668 3.8 31.08 1.68893 L3 6) 284.133 (d6 = variable) 1.00000 8) 38.764 2.8 60.14 1.62041 L4 9) -86.219 0.2 1.00000 10) 21.785 4.3 58.54 1.61272 L5 11) 56.053 3.2 1.00000 12) -72.708 5.0 25.35 1.80518 L6 13) 21.889 2.2 1.00000 14) 399.589 2.8 35.19 1.74950 L7 15) -28.897 (d15 = variable) 1.00000 (variable interval value in scaling) f 36 51.6 68 d6 39.708 23.017 13.728 d15 62.972 74.009 85.613

6 to 8 show various aberration diagrams of the second embodiment. 6 is a diagram illustrating various aberrations at the wide-angle end, FIG. 7 is a diagram illustrating various aberrations at the intermediate focal length, and FIG. 8 is a diagram illustrating various aberrations at the telephoto end. As is clear from the aberration diagrams, in the present embodiment, various aberrations at each focal length are satisfactorily corrected.

(Third Embodiment) FIGS. 9A to 9C show
FIG. 8 is a diagram illustrating a lens configuration of a zoom lens according to a second embodiment of the present invention and movement of each lens group during zooming. The zoom lens shown in FIG. 9 has, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave lens L2 having a smaller absolute value of the radius of curvature on the image side than on the object side, and a positive lens having a convex surface facing the object side. A first lens group G1 composed of a meniscus lens L3, a biconvex lens L4 having a larger absolute value of the radius of curvature on the image side than on the object side, a positive meniscus lens L5 having a convex surface facing the object side, A biconcave lens L6 having a smaller absolute value of the radius of curvature, and a biconvex lens L having a smaller absolute value of the radius of curvature on the image side than on the object side.
And a second lens group G2.

Table 3 below summarizes the data values of the third embodiment of the present invention. Each symbol in the table is the same as in the first embodiment.

[0040]

[Table 3] f = 36〜68mm Fno = 3.67〜5.43 2ω = 64.55〜35.25 ° Surface number Curvature radius Surface spacing Abbe number Refractive index 1) 45.347 1.8 47.1 1.62374 L1 2) 19.000 6.5 1.00000 3) -289.248 2.2 58.5 1.65160 L2 4) 41.929 3.0 1.00000 5) 30.913 3.5 29.46 1.71736 L3 6) 85.110 (d6 = variable) 1.00000 8) 31.627 2.9 60.14 1.62041 L4 9) -197.500 0.2 1.00000 10) 29.475 4.3 50.84 1.65844 L5 11) 123.048 2.2 1.00000 12) -61.539 8.0 25.8 1.78472 L6 13) 22.958 1.6 1.00000 14) 88.008 2.8 37.9 1.72342 L7 15) -32.533 (d15 = variable) 1.00000 (value of variable interval in scaling) f 36 51.6 68 d6 24.759 9.328 0.740 d15 49.633 61.572 74.123

FIGS. 10 to 12 show various aberrations of the third embodiment. FIG. 10 is a diagram showing various aberrations at the wide-angle end, and FIG.
Are aberration diagrams at the intermediate focal length, and FIG. 12 is an aberration diagram at the telephoto end. As is clear from the aberration diagrams, in the present embodiment, various aberrations at each focal length are satisfactorily corrected.

(Fourth Embodiment) FIGS. 13A to 13C
FIG. 9 is a diagram illustrating a lens configuration of a zoom lens according to a second embodiment of the present invention and movement of each lens group during zooming. 13 is a negative meniscus lens L1 having a convex surface facing the object side in order from the object side, and a biconcave lens L having a smaller absolute value of the radius of curvature on the image side than on the object side.
2. A first lens group G1 including a positive meniscus lens L3 having a convex surface facing the object side, a biconvex lens L4 having a larger absolute value of the radius of curvature on the image side than on the object side, and a positive meniscus having a convex surface facing the object side. The second lens group G2 includes a lens L5, a biconcave lens L6 having a smaller absolute value of the radius of curvature on the image side than on the object side, and a positive meniscus lens L7 having a convex surface facing the image side.

Table 4 below summarizes data values of the fourth embodiment of the present invention. Each symbol in the table is the same as in the first embodiment.

[0044]

[Table 4] f = 36〜68mm Fno = 3.63〜4.93 2ω = 64.41〜35.01 ° Surface number Curvature radius Surface spacing Abbe number Refractive index 1) 57.512 1.8 41.96 1.66755 L1 2) 19.661 6.5 1.00000 3) -368.609 2.2 58.5 1.65160 L2 4) 65.584 1.3 1.00000 5) 30.533 3.5 27.61 1.75520 L3 6) 75.154 (d6 = variable) 1.00000 8) 42.886 2.9 58.54 1.61272 L4 9) -89.795 0.2 1.00000 10) 22.882 4.3 60.03 1.64000 L5 11) 72.332 2.4 1.00000 12) -80.724 6.3 25.8 1.78472 L6 13) 22.402 1.6 1.00000 14) -833.924 2.8 35.19 1.74950 L7 15) -29.230 (d15 = variable) 1.00000 (variable interval value in scaling) f 36 51.6 68 d6 30.390 12.285 2.207 d15 47.627 58.352 69.627

FIGS. 14 to 16 show various aberration diagrams of the fourth embodiment. FIG. 14 is a diagram showing various aberrations at the wide-angle end, and FIG.
5 is a diagram showing various aberrations at the intermediate focal length, and FIG. 16 is a diagram showing various aberrations at the telephoto end. As is clear from the aberration diagrams, in the present embodiment, various aberrations at each focal length are satisfactorily corrected.

Table 5 below shows conditions corresponding to the above embodiments.

[0047]

[Table 5]

[0048]

According to the present invention, a two-unit zoom having a zoom ratio of about 1.9 times, a small size over the entire zoom range, a simple configuration, and excellent imaging performance. A lens can be realized.

[Brief description of the drawings]

FIGS. 1A to 1C are diagrams showing a lens configuration of a zoom lens according to a first embodiment of the present invention and movement of each lens group during zooming.

FIG. 2 is a diagram illustrating various aberrations of the first embodiment at a wide-angle end.

FIG. 3 is a diagram illustrating various aberrations of the first example at an intermediate focal length.

FIG. 4 is a diagram illustrating various aberrations of the first example at a telephoto end.

FIGS. 5A to 5C are diagrams illustrating a lens configuration of a zoom lens according to a second embodiment of the present invention and a movement of each lens group during zooming.

FIG. 6 is a diagram illustrating various aberrations of the second embodiment at a wide-angle end.

FIG. 7 is a diagram illustrating various aberrations of the second example at an intermediate focal length.

FIG. 8 is a diagram illustrating various aberrations of the second embodiment at a telephoto end.

FIGS. 9A to 9C are diagrams illustrating a lens configuration of a zoom lens according to a third embodiment of the present invention and movement of each lens group during zooming.

FIG. 10 is a diagram illustrating various aberrations of the third embodiment at a wide-angle end.

FIG. 11 is a diagram illustrating various aberrations of the third example at an intermediate focal length.

FIG. 12 is a diagram illustrating various aberrations of the third example at a telephoto end.

FIGS. 13A to 13C are diagrams showing a lens configuration of a zoom lens according to a fourth embodiment of the present invention and movement of each lens group during zooming.

FIG. 14 is a diagram illustrating various aberrations of the fourth example at the wide-angle end.

FIG. 15 is a diagram illustrating various aberrations of the fourth example at an intermediate focal length.

FIG. 16 is a diagram illustrating various aberrations at the telephoto end of the fourth example.

FIG. 17 is a conceptual diagram when the second lens group G2 is divided into a positive lens group G21 and a negative lens group G22.

[Explanation of symbols]

 G1 First lens group G2 Second lens group L1 Negative meniscus lens L2 Biconvex lens L3, L4, L5, L7 Positive lens L6 Biconvex lens G21 Positive lens component of second lens group G22 Negative lens component dh G21 of second lens group Principal point interval with G22

Claims (2)

[Claims] 1. An optical system comprising a first lens group G1 having a negative refractive power as a whole and a second lens group G2 having a positive refractive power as a whole, in order from the object side. Negative meniscus lens L1 having a convex surface facing the object side in order from the side, and a biconcave lens L2
And a positive lens L3. The second lens group G2 is a positive lens L4 in order from the object side.
, A positive lens L5, a biconcave lens L6, and a positive lens L7
The first lens group G1 and the second lens group G during zooming.
2, the focal length of the positive lens L4 of the second lens group G2 is fL4, the focal length of the positive lens L5 is fL5, the focal length of the second lens group G2 is f2, and the first The radius of curvature of the image side of the negative meniscus lens L1 of the lens group G1 is r2, the radius of curvature of the biconcave lens L2 of the first lens group G1 on the object side is r3, the focal length of the first lens group G1 is f1, A two-unit zoom lens, wherein the following condition is satisfied when the focal length at the wide-angle end in the entire lens system is fw and the focal length at the telephoto end in the entire lens system is ft. 2. The positive lens L of the second lens group G2.
4, the Abbe number of the positive lens L5 of the second lens group G2 is v5, and the refractive index of the negative meniscus lens L1 of the first lens group G1 with respect to d-line is n.
2. The two-unit zoom lens according to claim 1, wherein the following condition is satisfied when the refractive index n7 of the second lens group G2 with respect to the d-line of the positive lens L7 is satisfied. n1 <1.75 (4) 1.73 <n7 (5) ν4, ν5 <65 (6)