JP2001166207A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens of two-group constitution which is lower in cost, smaller in size and lighter in weight. SOLUTION: This zoom lens comprises, successively from an object side, a first lens group having positive refracting power and a second lens group having negative refracting power and varies the power by changing the spacing between both. The first lens group consists, successively from an object side, of three lens elements; the first lens, the second lens and the third lens and their image side diaphragm. The first lens is a plastic lens, the second lens has negative refracting power and the third lens has positive refracting power and the second lens group consists of two lens elements and is a fourth lens and a fifth lens having negative refracting power toward the image plane side. The zoom lens satisfies the following conditions: 1.50<=n3<=1.90, 1.50<=n5<=1.90, where n3: the refractive index of the third lens counted from the object side, n5: the refractive index of the fifth lens counted from the object side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly, to a low-cost and compact two-group zoom lens suitable for a lens shutter type camera and the like having a limited back focus.

[0002]

2. Description of the Related Art Conventionally, as one type of zoom lens, there is a two-group zoom lens. The two-group zoom lens has a first lens group having a positive refractive power and a negative refractive lens in order from the object side. And a second lens group for power. In addition, the two-group zoom lens has a relatively simple structure,
Since the entire length of the lens is short and easy to unite, it is widely used in lens shutter type cameras and the like.

The two-unit zoom lens further includes:
The first lens is classified into a negative lens advance type and a positive lens advance type depending on whether the first lens is positive or negative. Among them, the positive-lens-preceding type easily reduces the telephoto ratio, and is suitable for the focal length range of the telephoto system.

[0004]

However, in recent years,
There is a strong demand for smaller and lighter zoom lenses with lower cost. Conventional positive lens type 2
A zoom lens having a group configuration has a problem in that the number of constituent lenses is relatively large and the use of plastic lenses is small.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a zoom lens having a two-group configuration, which is lower in cost, more compact and lightweight, and in which aberration is well corrected. is there.

[0006]

The above object can be achieved by any of the following means.

(1) A zoom lens system comprising, in order from the object side, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power. Comprises, in order from the object side, a first lens, a second lens, and a third lens, and a diaphragm on the image side thereof. The first lens is a plastic lens, and the second lens is negatively refracted. The third lens has a positive refractive power, the second lens group includes two lens elements, and a fourth lens toward the image plane side, a fifth lens having a negative refractive power And a zoom lens satisfying the following conditions.

[0008] 1.50 ≦ n ₃ ≦ 1.90 ········ formula _{[1] 1.50 ≦ n 5 ≦} 1.90 ········ formula [2] where, n _3: refractive index of the third lens, counted from the object side n _5: according to the refractive index of the fifth lens counted from the object side (2) said that the third lens is characterized in that it is a glass lens (1) Zoom lens.

(3) The zoom lens according to (1) or (2), wherein at least one surface of the fourth lens uses an aspheric surface and satisfies the following conditions.

0.64 ≦ f _W /D≦1.0 Expression [3] 0.50 ≦ | f _RC | / f _W ≦ 1.00 Expression [4] f _W : focal length at the wide-angle end D: screen diagonal length f _RC : focal length of the second lens group (4) The first lens is a plastic lens having a positive refractive power and at least one surface is an aspheric surface; The fourth
The lens is a plastic lens and has at least one aspherical surface, and satisfies the following conditions (1) to (3).
The zoom lens according to any one of the above items.

−5 ≦ (φ _P + φ ₄ ) · f _T ² / F _T ≦ 5 Expression (5) where φ _P : the sum of the power of the plastic lenses in the first lens group φ ₄ : the fourth Lens power f _T : focal length at telephoto end F _T : F-number at telephoto end (5) In order from the object side, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power are arranged. In the zoom lens that performs zooming by changing the power, the first lens group includes, in order from the object side, a first lens, a second lens, and a third lens.
The first lens element and the image-side stop.
The lens and the second lens are plastic lenses;
The third lens has a positive refractive power, the second lens group includes two lens elements, a fourth lens toward the image plane side, and a fifth lens having a negative refractive power. A zoom lens, wherein at least four aspheric surfaces are used, and the following conditions are satisfied.

1.50 ≦ n ₅ ≦ 1.90 ( ₅ ) where n _{5 is} the refractive index of the fifth lens counted from the object side. (6) The third lens is glass The zoom lens according to (5), wherein the zoom lens is a lens.

(7) The zoom lens according to (5) or (6), wherein at least one surface of the fourth lens uses an aspherical surface and satisfies the following condition.

0.64 ≦ f _W /D≦1.0 Expression [7] 0.50 ≦ | f _RC | / f _W ≦ 1.00 Expression [8] where f _W : Focal length at wide-angle end D: Screen diagonal length f _RC : Focal length of second lens group (8) The first lens has a positive refractive power, the second lens has a negative refractive power, and the The zoom lens according to any one of (5) to (7), wherein the four lenses are plastic lenses and satisfy the following conditions.

−5 ≦ (φ ₁ + φ ₂ + φ ₄ ) · f _T ² / F _T ≦ 5 Expression (9) where φ _{i is} the power of the ith lens (i = 1, 2, 4) f _T : Focal length at telephoto end F _T : F-number at telephoto end (9) Consisting, in order from the object side, of a first lens unit having a positive refractive power and a second lens unit having a negative refractive power. In the zoom lens that performs the above, the first lens group includes, in order from the object side, a first lens, a second lens, and a third lens.
The first lens element and the image-side stop.
The lens and the second lens are plastic lenses;
The third lens has a positive refractive power, the second lens group includes two lens elements, and includes a fourth lens toward the image plane side and a fifth lens having a negative refractive power. A zoom lens that satisfies the conditions.

[0016] 1.50 ≦ n ₃ ≦ 1.90 ········ formula _{[10] 1.50 ≦ n 5 ≦} 1.90 ········ formula [11] where, n ₃ : Refractive index of the third lens counted from the object side n ₅ : Refractive index of the fifth lens counted from the object side (10) The third lens is a glass lens Zoom lens.

(11) The zoom lens according to (9) or (10), wherein at least one surface of the fourth lens uses an aspheric surface and satisfies the following conditions.

0.64 ≦ f _W /D≦1.0 Expression [12] 0.50 ≦ | f _RC | / f _W ≦ 1.00 Expression [13] f _W : focal length at the wide-angle end D: screen diagonal length f _RC : focal length of the second lens group (12) The first lens has a positive refractive power, and at least one surface uses an aspheric surface. The second lens has a negative refractive power, at least one surface uses an aspheric surface, and the fourth lens is a plastic lens, and satisfies the following conditions. The zoom lens according to claim 1.

−5 ≦ (φ ₁ + φ ₂ + φ ₄ ) · f _T ² / F _T ≦ 5 Expression (14) where φ _i : power of the i-th lens (i = 1, 2, 4) f _T : Focal length at the telephoto end F _T : F-number at the telephoto end (13) Consisting of, in order from the object side, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power. Wherein the first lens group comprises three lens elements of a first lens, a second lens and a third lens, and the second lens group comprises two lenses of a fourth lens and a fifth lens The first lens is a plastic lens having a positive refractive power, the second lens is a plastic lens, and the third lens is a meniscus glass having a positive refractive power with a concave surface facing the object side. A lens having a negative refractive power. A zoom lens characterized by being a stick lens.

(14) The zoom lens according to (13), wherein the third lens satisfies the following condition.

[0021] _{0.10 ≦ (r a -r b)} / (r a + r b) ≦ 0.95 ·· formula [15] However, r _a: radius of curvature of the object side surface of the third lens radius (r _a <0 ) R _b : radius of curvature of the image side surface of the third lens (r _b <0) (15) The zoom lens according to (13) or (14), wherein the following condition is satisfied.

0.64 ≦ f _W /D≦1.0 (16) 0.50 ≦ | f _RC | / f _W ≦ 1.00 Formula [17] where, f _W : focal length at the wide-angle end D: screen diagonal length f _RC : focal length of the second lens group (16) The second lens has a negative refractive power and satisfies the following condition: The zoom lens according to any one of (13), (14), and (15), wherein:

−5 ≦ {φ ₁ + φ ₂ + (φ _PRC / m _T )} · f _T ² / F _T ≦ 5 Expression [18] where m _T = f _T / f _FC φ _i : Power of i lens (i = 1, 2) φ _PRC : Sum of power of plastic lens of second lens group f _T : Focal length at telephoto end F _T : F number at telephoto end f _FC : Focus of first lens group Distance Here, each of the above items will be described.

According to the invention described in the above (1), the first lens group having a positive refractive power and the second lens group having a negative refractive power are provided.
In a zoom lens having a group structure, the first lens is made of plastic, the third lens has an appropriate refractive index range with a positive refractive power, and the fifth lens has an appropriate refractive index range with a negative refractive power. By using a plastic lens, cost can be reduced and the coma aberration and the field curvature aberration are well corrected, and the distortion on the wide-angle side is particularly well corrected even with a small lens configuration.

According to the invention described in the above (2), since the third lens is a glass lens, the positive refractive power is sufficiently arranged on the third lens without increasing the focal position fluctuation due to the temperature change. can do. As a result, the first
The rear principal point of the lens group approaches the second lens group, so that the zoom ratio can be easily obtained, and the positive distortion at the wide-angle end can be reduced. In addition, since the refractive power of the third lens is generally concentrated, the deviation of the optical axis of the lens greatly affects the imaging performance. However, if the lens is a camera lens, it is not necessary to consider expansion due to temperature rise, and the lens is incorporated. In this case, the clearance can be reduced. For this reason, the optical position relationship between the third lens and the diaphragm mechanism or the lens shutter mechanism incorporated in the vicinity is easily formed, and the influence of internal distortion or the like is reduced.

According to the invention described in the above (3), at least one surface of the fourth lens uses an aspherical surface, and the relationship between the focal length f _W at the wide-angle end and the screen diagonal length D is expressed by the equation [3]. By setting the relationship between the focal length f _W at the wide-angle end and the focal length f _RC of the second lens group in the appropriate range shown in Expression [4], it is possible to prevent an increase in the diameter of the rear lens and to reduce the overall length. In addition, even if the second lens group is composed of two lenses, the lens aberration is less deteriorated, the workability of the lens is good, the zoom movement amount is not increased, and the overall length is compact.

According to the invention described in the above (4), the first lens is a plastic lens having a positive refractive power, at least one surface of which is an aspherical surface, and the fourth lens is at least one surface of an aspherical surface. The sum of the powers of the plastic lenses in the first lens group φ _P , the power of the fourth lens φ ₄ ,
By setting the relationship of the focal length f _T at the telephoto end in the range shown in Expression [5], the cost and weight can be reduced by using a plastic lens, and furthermore, at the telephoto end where the focal position greatly fluctuates with respect to temperature changes, the reasons to be described later. Thereby, the fluctuation of the focal position can be reduced.

According to the invention described in the above (5), the first lens group having a positive refractive power and the second lens group having a negative refractive power are provided.
In the group-structure zoom lens, the first lens and the second lens are made of plastic, the third lens has a positive refractive power, and the fifth lens has a negative refractive power and has an appropriate refractive index.
By using an aspheric surface for at least four surfaces in the whole system,
Plastic lenses can reduce cost and weight,
Despite having a small lens configuration, the use of an aspherical surface makes it possible to correct each aberration well, and particularly corrects distortion on the wide-angle side.

According to the invention described in the above (6), the third lens is a glass lens, so that the positive refractive power can be sufficiently arranged on the third lens without increasing the focal position fluctuation due to the temperature change. can do. As a result, the first
The rear principal point of the lens group approaches the second lens group, so that the zoom ratio can be easily obtained, and the positive distortion at the wide-angle end can be reduced. In addition, since the refractive power of the third lens is generally concentrated, the deviation of the optical axis of the lens greatly affects the imaging performance. However, if the lens is a camera lens, it is not necessary to consider expansion due to temperature rise, and the lens is incorporated. In this case, the clearance can be reduced. For this reason, the optical position relationship between the third lens and the diaphragm mechanism or the lens shutter mechanism incorporated in the vicinity is easily formed, and the influence of internal distortion or the like is reduced.

According to the invention described in the above (7), at least one surface of the fourth lens uses an aspherical surface, and the relationship between the focal length f _W at the wide-angle end and the screen diagonal length D is expressed by the equation [3]. By setting the relationship between the focal length f _W at the wide-angle end and the focal length f _RC of the second lens group in the appropriate range shown in Expression [4], it is possible to prevent an increase in the diameter of the rear lens and to reduce the overall length. In addition, even if the second lens group is composed of two lenses, the deterioration of lens aberration is small, the workability of the lens is good, the zoom movement amount is not increased, and the overall length is compact.

According to the invention described in the above (8), the first level
Lens has a positive refractive power, the second lens has a negative refractive power,
The first, by making the lens a plastic lens,
Power of 2 and 4 lenses φ₁, Φ_Two, Φ_Four, Focal length at telephoto end
Separation f_T, F-number F at the telephoto end _TIs shown in equation [9].
By setting the appropriate range, the plastic lens
Low cost, light weight, and focus position against temperature change
At the telephoto end, where the fluctuation of
Point position fluctuations can be kept small.

According to the invention described in the item (9), the first lens group having a positive refractive power and the second lens group having a negative refractive power are provided.
In the zoom lens having a group structure, the first lens and the second lens are made of plastic, the third lens has a positive refractive power and an appropriate refractive index range, and the fifth lens has a negative refractive power and an appropriate refractive index. By setting the range, the coma aberration and the field curvature aberration are well corrected, and the distortion on the wide-angle side is particularly well corrected, even though the cost and weight are reduced by the plastic lens and the lens configuration is further reduced.

According to the invention described in the above (10), the third aspect
By using a glass lens as the lens, the third lens can be provided with a sufficient positive refractive power without increasing the focal position fluctuation due to a temperature change. As a result, the rear principal point of the first lens group approaches the second lens group, so that a variable power ratio can be easily obtained, and positive distortion at the wide-angle end can be reduced. In addition, since the refractive power of the third lens is generally concentrated, the deviation of the optical axis of the lens greatly affects the imaging performance. However, if the lens is a camera lens, it is not necessary to consider expansion due to temperature rise, and the lens is incorporated. In this case, the clearance can be reduced. For this reason, the optical position relationship between the third lens and the diaphragm mechanism or the lens shutter mechanism incorporated in the vicinity is easily formed, and the influence of internal distortion or the like is reduced.

According to the invention described in the above (11), the fourth aspect
At least one surface of the lens uses an aspherical surface, and the relationship between the focal length f _W at the wide-angle end and the screen diagonal length D is expressed by Equation [1].
2], and the relationship between the focal length f _W at the wide-angle end and the focal length f _RC of the second lens group is set to an appropriate range shown in Expression [13], so that an increase in the rear lens diameter direction can be prevented. Prevent,
The overall length can be reduced, and even if the second lens group is composed of two lenses, the deterioration of lens aberration is small, the workability of the lens is good, the zoom movement amount is not large, and the overall length is compact. .

According to the invention described in the above (12), the first
The lens has a positive refractive power, at least one surface has an aspherical surface, the second lens has a negative refractive power, at least one surface has an aspherical surface, the fourth lens has a plastic lens, and the first, second, and third lenses have a positive refractive power. By setting the relationship among the powers φ ₁ , φ ₂ , φ _{4 of} the four lenses, the focal length f _{T at} the telephoto end, and the F-number F _T at the telephoto end in an appropriate range shown in Expression [14], low cost by using plastic is achieved. Further, at the telephoto end where the focal position greatly fluctuates with respect to temperature changes, it is possible to suppress the focal position fluctuation to be small.

According to the invention described in the above (13), in the zoom lens having a two-group structure including the first lens group having a positive refractive power and the second lens group having a negative refractive power, the first lens has a positive refractive power. By using a plastic lens as the second lens, a plastic lens as the second lens, a third lens as a meniscus glass lens having a concave surface facing the object side with a positive refractive power, and a fifth lens as a plastic lens with a negative refractive power, By using the plastic material described above, and particularly by using a plastic lens as the fifth lens having the largest lens outer diameter, cost reduction and weight reduction can be achieved. Further, for example, if the refractive power of the fifth lens is reduced and the refractive power of the first lens is increased while the number of lenses is small, the temperature change in the entire system can be suppressed to be small. Further, for example, the distortion on the wide-angle side, which is increased by increasing the refractive power of the first lens, can be corrected by using a meniscus glass lens having a positive refractive power with the concave surface facing the object side.

According to the invention described in the above (14), the third
Lens object side surface curvature r _a and the image side surface of curvature r _b equation [15]
For example, if the refractive power of the fifth lens is reduced and the positive refractive power of the first lens is increased by setting the appropriate range shown in (1), the temperature change in the entire system can be suppressed to be narrow, and The distortion at the wide-angle end, which is increased by increasing the refractive power of the lens, can be corrected.

According to the invention described in the above (15), the relationship between the focal length f _W at the wide angle end and the screen diagonal length D is expressed by the formula [16].
And the focal length f _W at the wide-angle end.
And the focal length f _RC of the second lens group within the appropriate range shown in Expression [17], it is possible to prevent the rear lens from increasing in the radial direction and shorten the overall length.
Even if it is constituted by a single lens, the deterioration of the lens aberration is small, the workability of the lens is good, the zoom movement amount is not large, and the overall length is compact.

According to the invention described in the above (16), the second
The lens has a negative refractive power, the powers φ ₁ and φ _{2 of} the first and second lenses, the sum φ _PRC of the powers of the plastic lenses of the second lens group, the focal length f _{T at} the telephoto end, and the F-number F at the telephoto end. The relationship between _T and the focal length f _FC of the first lens group is expressed by Equation [1].
8], the focal position fluctuation can be suppressed to a small value at the telephoto end where the focal position varies greatly with respect to the temperature change.

Here, each conditional expression will be described. Conditional expressions [1] and [10] determine an appropriate range of the refractive index of the third lens. If the lower limit is exceeded, coma tends to deteriorate. Conversely, if the value exceeds the upper limit, the Petzval sum becomes negative and large, and it becomes difficult to obtain a good image surface. The range of the conditional expression is 1.50 ≦ n ₃ ≦ 1.90, and preferably 1.50 ≦ n ₃ ≦ 1.90.
50 ≦ n ₃ ≦ 1.75.

Conditional expressions [2], [6], and [11] define an appropriate range of the refractive index of the fifth lens. If the lower limit is exceeded, distortion on the wide-angle side tends to deteriorate. Conversely, if the value exceeds the upper limit, the use of glass optical material in which chromatic aberration easily occurs or the use of expensive glass material leads to an increase in cost, so that the range of the conditional expression is 1.50 ≦ n ₅ ≦ 1.
90, and preferably 1.50 ≦ n ₅ ≦ 1.75.

Conditional expressions [3], [7], [12] and [16] determine the focal length at the wide-angle end suitable for the zoom lens of the present invention. is there. If the lower limit is exceeded, the peripheral light amount is likely to be insufficient due to the positive lens leading type, and the diameter of the rear lens increases due to the shortened back focus, thereby impairing the radial compactness. Conversely, exceeding the upper limit increases the overall length,
The advantages of the positive lens type can not be used. Range of the conditional expression is 0.64 ≦ f _W /D≦1.0, preferably 0.70 ≦ f _W /D≦1.0.

The conditional expressions [4], [8], [13], and [17] determine an appropriate range of the focal length of the second lens unit. If the absolute value of the focal length of the second lens group becomes smaller than the lower limit, when the second lens group is composed of two lenses, the aberration is deteriorated and the radius of curvature of the specific concave surface is reduced, so that the glass polishing processing is performed. Not suitable for Conversely, if the upper limit is exceeded, the amount of zoom movement of the second lens group becomes large, and the compactness of the zoom lens barrel is impaired. The range of the conditional expression is 0.50 ≦ | f
_RC | / f _W ≦ 1.00, preferably 0.60 ≦ |
f _RC | / f _W ≦ 1.00.

Conditional expression [5], conditional expression [9], conditional expression [14], and conditional expression [18] are conditions for suppressing a change in the focal position with respect to a temperature change. When the sum of the power of the plastic lens and the sum of the power of the plastic lenses in the second lens group satisfy this condition, the focal position fluctuation is suppressed to a small value at the telephoto end where the focal position fluctuation is large with respect to the temperature change. be able to.

[0045] Here, explaining why a [nu value of the temperature of the plastic lens is _{{(n d -1) / Δn} } a uniformly [nu _T, at the telephoto end, the axial ray ray height of each Assuming that the plastic lens has substantially the same value, the variation value δ _S at the focal position is approximately expressed by Expression [19].

[0046] _{δ S = - (φ P +} φ PRC / m T) · f T 2 / ν T ······· formula [19] However, phi _P: Power of plastic lens in the first lens group Sum φ _PRC : Sum of the power of the plastic lenses of the second lens group m _T : f _T / f _FC f _T : Focal length at the telephoto end f _FC : Focal length of the first lens group ν _T : Temperature ν value, (n _d- 1) / Δn Δn: change in refractive index with respect to temperature change ΔT n _d : Abbe number at d-line of the lens material Here, the permissible circle of confusion is 0.05 mm, and the depth is ±
If 0.05 mm, the temperature “ν _T ” with respect to a temperature change of 30 ° C. is approximately −100. Therefore, as a conditional expression, the variation value “δ _S ” of the focal position at this time falls within a predetermined depth. There is equation [18]. The range of the conditional expression is −5 ≦
{Φ ₁ + φ ₂ + (φ _PRC / m _T )} · f _T ² / F _T ≦ 5.

When only the fourth lens in the second lens group is a plastic lens and the sum of the powers of the plastic lenses in the second lens group, “φ _PRC ”, is small, the above equation [19] is approximated. Equation [20] is obtained.

Δ _S = − (φ _P + φ _P4 ) · f _T ² / ν _T (20) Here, the permissible circle of confusion is 0.05 mm, and the depth is ±
If 0.05 mm, the temperature “ν _T ” with respect to a temperature change of 30 ° C. is approximately −100. Therefore, as a conditional expression, the variation value “δ _S ” of the focal position at this time falls within a predetermined depth. There are equations [5], [9] and [14].
The range of the conditional expression is −5 ≦ (φ _P + φ ₄ ) · f _T ² / F _T ≦ 5, and -5 ≦ (φ ₁ + φ ₂ + φ ₄ ) · f _T ² / F _T ≦ 5. .

Further, conditional expression [15] is a condition for obtaining good aberration. If the lower limit of the condition is exceeded, distortion at the wide-angle end becomes large. Conversely, if the value exceeds the upper limit, spherical aberration and coma occurring on the image side surface of the third lens become undesirably large. The condition range is 0.10 ≦ (r _a −r _b )
/ (R _a + r _b ) ≦ 0.95, preferably 0.3
_{0 ≦ (r a -r b)} / (r a + r b) it is ≦ 0.75.

[0050]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the zoom lens according to the present invention will be described below, but the present invention is not limited thereto. Here, the symbols used in each embodiment are as follows.

F: F number ω: Half angle of view r: Curvature radius of refraction surface _d : Distance between refraction surfaces n _d : Refraction index at d-line of lens material ν _d : Abbe number of lens material f: Focal length f _b : Back focus In each embodiment, the shape of the aspheric surface is such that the X axis is taken in the optical axis direction, the height is h in the direction perpendicular to the optical axis, and K, A ₄ , A ₆ , A
₈ , A ₁₀ and A ₁₂ are represented by “Equation 1” as aspherical coefficients.

[0052]

(Equation 1)

(Embodiment 1) Embodiment 1 is an embodiment included in claims 1 to 4. FIG. 1 is a lens cross-sectional view of Example 1, and Tables 1 and 2 show lens data.

[0054]

[Table 1]

[0055]

[Table 2]

The first lens group LG1 includes a first plastic lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power. The second lens group LG2 includes a fourth plastic lens having a negative refractive power and a fifth lens having a negative refractive power. FIG. 2 shows (A) of Example 1, the short focal length end,
It is a lens aberration figure in (B) middle and (C) long focal end.

(Embodiment 2) Embodiment 2 is an embodiment included in claims 1 to 4. FIG. 3 is a lens cross-sectional view of Example 2, and Tables 3 and 4 show lens data.

[0058]

[Table 3]

[0059]

[Table 4]

The first lens group LG1 is composed of a plastic first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power. Also, the second lens group LG2
Is composed of a plastic fourth lens having a weak positive refractive power and a fifth lens having a negative refractive power. FIG. 4 is a lens aberration diagram of the second embodiment at (A) the short focal length end, (B) at the middle focal length, and (C) at the long focal length end.

(Embodiment 3) Embodiment 3 is an embodiment included in claims 1 to 4. FIG. 5 is a lens cross-sectional view of Example 3, and Tables 5 and 6 show lens data.

[0062]

[Table 5]

[0063]

[Table 6]

The first lens group LG1 includes a first lens of plastic having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power. Also, the second lens group LG2
Is a plastic fourth lens with little power,
The fifth lens has a negative refractive power. FIG. 6 is a lens aberration diagram of the third embodiment at (A) the short focal length end, (B) at the middle focal length, and (C) at the long focal length end.

(Embodiment 4) Embodiment 4 is an embodiment included in claims 5 to 8. FIG. 7 is a lens sectional view of the fourth embodiment. Tables 7 and 8 show lens data.

[0066]

[Table 7]

[0067]

[Table 8]

The first lens group LG1 includes a first lens made of a plastic having a positive refractive power, a second lens made of a plastic having a negative refractive power, and a third lens having a positive refractive power. The second lens group LG2 includes a fourth lens made of plastic having almost no power and a fifth lens made of negative refractive power. FIG. 8 is a lens aberration diagram of the fourth embodiment at (A) the short focal length end, (B) at the middle focal length, and (C) at the long focal length end.

(Embodiment 5) Embodiment 5 is an embodiment included in claims 5 to 8. FIG. 9 is a lens cross-sectional view of Example 5, and Tables 9 and 10 show lens data.

[0070]

[Table 9]

[0071]

[Table 10]

The first lens group LG1 includes a first lens made of a plastic having a positive refractive power, a second lens made of a plastic having a negative refractive power, and a third lens having a positive refractive power. The first lens and the second lens are Joined. Also, the second lens group LG
Reference numeral 2 includes a plastic fourth lens having almost no power and a fifth lens having negative refractive power. FIG. 10 is a lens aberration diagram at (A) the short focal length end, (B) the middle focal length, and (C) the long focal length end of the fifth embodiment.

(Embodiment 6) Embodiment 6 is an embodiment included in claims 5 to 12. FIG. 11 is a lens cross-sectional view of Example 6, and Tables 11 and 12 show lens data.

[0074]

[Table 11]

[0075]

[Table 12]

The first lens group LG1 includes a first lens made of a plastic having a positive refractive power, a second lens made of a plastic having a negative refractive power, and a third lens having a positive refractive power. The second lens group LG2 includes a fourth lens made of plastic having almost no power and a fifth lens made of negative refractive power. FIG. 12 shows (A) the short focal length end, (B) the middle, and (C) of the sixth embodiment.
It is a lens aberration figure at the long focal end.

(Embodiment 7) Embodiment 7 is an embodiment included in claims 5 to 12. FIG. 13 is a lens cross-sectional view of Example 7, and Tables 13 and 14 show lens data.

[0078]

[Table 13]

[0079]

[Table 14]

The first lens group LG1 includes a first lens made of a plastic having a positive refractive power, a second lens made of a plastic having a negative refractive power, and a third lens having a positive refractive power. The first lens and the second lens are formed. Are joined. The second lens unit L
G2 is composed of a plastic fourth lens having almost no power and a fifth lens having negative refractive power. FIG. 14 shows a seventh embodiment.
3A is a lens aberration diagram at the short focal length end, (B) at the middle focal length, and (C) at the long focal length end.

(Embodiment 8) Embodiment 8 is an embodiment included in claims 5 to 12. FIG. 15 is a lens cross-sectional view of Example 8, and Tables 15 and 16 show lens data.

[0082]

[Table 15]

[0083]

[Table 16]

The first lens group LG1 includes a first lens made of a plastic having a positive refractive power, a second lens made of a plastic having a negative refractive power, and a third lens having a positive refractive power. The second lens group LG2 includes a fourth lens made of plastic having almost no power and a fifth lens made of negative refractive power. FIG. 16 shows (A) the short focal length end, (B) the middle, and (C) of the eighth embodiment.
It is a lens aberration figure at the long focal end.

(Embodiment 9) Embodiment 9 is an embodiment included in claims 5 to 12. FIG. 17 is a lens sectional view of Example 9, and Tables 17 and 18 show lens data 18.

[0086]

[Table 17]

[0087]

[Table 18]

The first lens group LG1 includes a first lens made of a plastic having a positive refractive power, a second lens made of a plastic having a negative refractive power, and a third lens having a positive refractive power. The first lens and the second lens are joined. Is done. Also, the second lens group LG2
Is a plastic fourth lens with almost no power,
The fifth lens has a negative refractive power. FIG. 18 is a lens aberration diagram of the ninth embodiment at (A) the short focal length end, (B) the middle focal length, and (C) the long focal length end.

(Embodiment 10) Embodiment 10 is directed to claims 1 to
Examples included in 3, 5 to 7, 9 to 11, and 13 to 16. FIG. 19 is a lens cross-sectional view of Example 10, and Tables 19 and 20 show lens data.

[0090]

[Table 19]

[0091]

[Table 20]

The first lens group LG1 includes a first lens made of a plastic having a positive refractive power, a second lens made of a plastic having a negative refractive power, and a third lens having a positive refractive power. The second lens group LG2 includes a fourth plastic lens having almost no power and a fifth plastic lens having negative refractive power. FIG. 20 is a lens aberration diagram at (A) the short focal length end, (B) the middle focal length, and (C) the long focal length end of the tenth embodiment.

(Embodiment 11) Embodiment 11 relates to claims 1 to
Examples included in 3, 5 to 7, 9 to 11, and 13 to 16. FIG. 21 is a lens cross-sectional view of Example 11, and Tables 21 and 22 show lens data.

[0094]

[Table 21]

[0095]

[Table 22]

The first lens group LG1 includes a first lens made of a plastic having a positive refractive power, a second lens made of a plastic having a negative refractive power, and a third lens having a positive refractive power. The second lens group LG2 is made of a plastic fourth material having almost no power.
The lens comprises a fifth lens made of plastic having a negative refractive power. FIG. 22 is a lens aberration diagram of Example 11 at the (A) short focal length end, (B) the middle focal length, and (C) the long focal length end.

(Twelfth Embodiment) A twelfth embodiment will be described below.
16 is an embodiment included in FIG. FIG. 23 is a lens cross-sectional view of Example 12, and Tables 23 and 24 show lens data.

[0098]

[Table 23]

[0099]

[Table 24]

The first lens group LG1 includes a first lens made of plastic having a positive refractive power, a second lens made of plastic having a negative refractive power, and a third lens having a positive refractive power. The second lens group LG2 includes a fourth plastic lens having almost no power and a fifth plastic lens having a negative refractive power. FIG. 24 shows (A) the short focal length end of the twelfth embodiment, and (B)
It is a lens aberration figure in an intermediate | middle and (C) long focal end.

Here, the values of the conditional expressions in each embodiment are shown in Tables 25, 26 and 27.

[0102]

[Table 25]

[0103]

[Table 26]

[0104]

[Table 27]

As shown in Tables 25, 26, and 27, the conditional expressions of the present invention are satisfied.

[0106]

Since the zoom lens according to the present invention is constructed as described above, the following effects can be obtained. It is possible to provide a two-unit zoom lens which is lower in cost, more compact and lightweight, is suitable for a lens shutter type camera and the like, and has various aberrations well corrected.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a first embodiment.

FIGS. 2A and 2B are lens aberration diagrams of Example 1 at (A) a short focal end, (B) an intermediate position, and (C) a long focal end.

FIG. 3 is a sectional view of a lens according to a second embodiment.

4A and 4B are lens aberration diagrams at the short focal length end, (B) an intermediate position, and (C) a long focal length end according to the second embodiment.

FIG. 5 is a sectional view of a lens according to a third embodiment.

FIGS. 6A and 6B are lens aberration diagrams at a short focal length end, (B) an intermediate position, and (C) a long focal length end according to a third embodiment.

FIG. 7 is a sectional view of a lens according to a fourth embodiment.

FIG. 8 is a diagram illustrating lens aberrations of the fourth embodiment at (A) the short focal length end, (B) at the middle focal length, and (C) at the long focal length end.

FIG. 9 is a sectional view of a lens according to a fifth embodiment.

10A and 10B are lens aberration diagrams at a short focal length end, (B) an intermediate position, and (C) a long focal length end in Example 5.

FIG. 11 is a sectional view of a lens according to a sixth embodiment.

12A and 12B are lens aberration diagrams at a short focal length end, (B) an intermediate position, and (C) a long focal length end in Example 6.

FIG. 13 is a sectional view of a lens according to a seventh embodiment.

14A and 14B are lens aberration diagrams at a short focal length end, (B) an intermediate position, and (C) a long focal length end in Example 7.

FIG. 15 is a sectional view of a lens according to an eighth embodiment.

16A and 16B are lens aberration diagrams at a short focal length end, (B) an intermediate position, and (C) a long focal length end in Example 8.

FIG. 17 is a sectional view of a lens according to a ninth embodiment.

18A and 18B are lens aberration diagrams at a short focal length end, (B) an intermediate position, and (C) a long focal length end according to a ninth embodiment.

FIG. 19 is a lens sectional view of a tenth embodiment.

20A is a short focal length end of Example 10, (B) an intermediate position,
(C) is a lens aberration diagram at the long focal length end.

FIG. 21 is a sectional view of a lens according to an eleventh embodiment.

FIG. 22 (A) Short focal length end, (B) Middle,
(C) is a lens aberration diagram at the long focal length end.

FIG. 23 is a sectional view of a lens according to a twelfth embodiment.

FIGS. 24A and 24B are (A) short focal length end, (B) middle,
(C) is a lens aberration diagram at the long focal length end.

[Explanation of symbols]

 LG1 first lens group LG2 second lens group 1 first surface 2 second surface 3 third surface 4 fourth surface 5 fifth surface 6 sixth surface 7 seventh surface 8 eighth surface 9 ninth surface 10 tenth surface

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA01 PA04 PA05 PA17 PA18 PB05 QA02 QA07 QA12 QA14 QA22 QA25 QA37 QA41 QA42 QA45 RA05 RA12 RA13 RA36 SA06 SA10 SA62 SA63 SB04 SB13

Claims (16)

[Claims] 1. A zoom lens which comprises a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side and changes the distance between the first and second lens units. In order from the object side, there are three lens elements of a first lens, a second lens, and a third lens, and an aperture on the image side thereof.
The first lens is a plastic lens, and the second lens is
The lens has a negative refractive power, the third lens has a positive refractive power, and the second lens group includes two lens elements. The fourth lens has a negative refractive power toward the image plane. A zoom lens comprising: a fifth lens having the following condition: _{1.50 ≦ n 3 ≦ 1.90 1.50 ≦} n 5 ≦ 1.90 where, n _3: refractive index of the third lens, counted from the object side n _5: refractive index of the fifth lens counted from the object side 2. The zoom lens according to claim 1, wherein the third lens is a glass lens. 3. The zoom lens according to claim 1, wherein at least one surface of the fourth lens uses an aspheric surface and satisfies the following condition. 0.64 ≦ f _W /D≦1.0 0.50 ≦ | f _RC | / f _W ≦ 1.00 where f _W : focal length at wide-angle end D: screen diagonal line length f _RC : second lens group Focal length 4. The first lens is a plastic lens having a positive refractive power, and at least one surface is an aspheric surface.
The zoom lens according to any one of claims 1 to 3, wherein the fourth lens is a plastic lens and at least one surface uses an aspherical surface, and satisfies the following conditions. −5 ≦ (φ _P + φ ₄ ) · f _T ² / F _T ≦ 5 where φ _{P is} the sum of the power of the plastic lenses in the first lens group φ ₄ : the power of the fourth lens f _T : the focal point at the telephoto end Distance F _T : F-number at telephoto end 5. A zoom lens which comprises a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side and performs zooming by changing the distance between the first lens unit and the second lens unit. In order from the object side, there are three lens elements of a first lens, a second lens, and a third lens, and an aperture on the image side thereof.
The first lens and the second lens are plastic lenses, the third lens has a positive refracting power, the second lens group is composed of two lens elements, and a fourth lens is disposed on the image surface side. A zoom lens comprising a fifth lens having a negative refractive power, using at least four aspheric surfaces in the entire system, and satisfying the following conditions. 1.50 ≦ n ₅ ≦ 1.90 where n _{5 is} the refractive index of the fifth lens counted from the object side 6. The zoom lens according to claim 5, wherein the third lens is a glass lens. 7. The zoom lens according to claim 5, wherein at least one surface of the fourth lens uses an aspheric surface and satisfies the following condition. 0.64 ≦ f _W /D≦1.0 0.50 ≦ | f _RC | / f _W ≦ 1.00 where f _W : focal length at wide-angle end D: screen diagonal line length f _RC : second lens group Focal length 8. The first lens has a positive refractive power, the second lens has a negative refractive power, and the fourth lens is a plastic lens, and satisfies the following conditions. The zoom lens according to any one of claims 5 to 7. −5 ≦ (φ ₁ + φ ₂ + φ ₄ ) · f _T ² / F _T ≦ 5, where φ _i : power of the i-th lens (i = 1, 2, 4) f _T : focal length at the telephoto end F _T : F-number at telephoto end 9. A zoom lens, which includes a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side and performs zooming by changing the distance between the first lens unit and the first lens unit. In order from the object side, there are three lens elements of a first lens, a second lens, and a third lens, and an aperture on the image side thereof.
The first lens and the second lens are plastic lenses, the third lens has a positive refracting power, the second lens group is composed of two lens elements, and a fourth lens is formed on the image surface side. And a fifth lens having a negative refractive power and satisfying the following condition. _{1.50 ≦ n 3 ≦ 1.90 1.50 ≦} n 5 ≦ 1.90 where, n _3: refractive index of the third lens, counted from the object side n _5: refractive index of the fifth lens counted from the object side 10. The zoom lens according to claim 9, wherein the third lens is a glass lens. 11. The zoom lens according to claim 9, wherein at least one surface of the fourth lens uses an aspheric surface and satisfies the following condition. 0.64 ≦ f _W /D≦1.0 0.50 ≦ | f _RC | / f _W ≦ 1.00 where f _W : focal length at wide-angle end D: screen diagonal line length f _RC : second lens group Focal length 12. The first lens has a positive refractive power, at least one surface uses an aspherical surface, the second lens has a negative refractive power, and at least one surface uses an aspherical surface, The zoom lens according to any one of claims 9 to 11, wherein the fourth lens is a plastic lens and satisfies the following condition. −5 ≦ (φ ₁ + φ ₂ + φ ₄ ) · f _T ² / F _T ≦ 5, where φ _i : power of the i-th lens (i = 1, 2, 4) f _T : focal length at the telephoto end F _T : F-number at telephoto end 13. A zoom lens which comprises a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side and changes the distance between the first and second lens units. The second lens group includes two lens elements of a fourth lens and a fifth lens, and the first lens has positive refraction. The second lens is a plastic lens, the third lens is a meniscus glass lens having a positive refractive power with a concave surface facing the object side, and the fifth lens is a negative refractive lens. A zoom lens characterized by being a plastic lens having power. 14. The zoom lens according to claim 13, wherein the third lens satisfies the following condition. _{0.10 ≦ (r a -r b)} / (r a + r b) ≦ 0.95 where, r _a: radius of curvature of the object side surface of the third lens radius _{(r a <0) r b} : the image of the third lens Radius of curvature of side surface (r _b <0) 15. The zoom lens according to claim 13, wherein the following condition is satisfied. 0.64 ≦ f _W /D≦1.0 0.50 ≦ | f _RC | / f _W ≦ 1.00 where f _W : focal length at wide-angle end D: screen diagonal line length f _RC : second lens group Focal length 16. The apparatus according to claim 13, wherein the second lens has a negative refractive power and satisfies the following condition.
Or the zoom lens according to claim 15. −5 ≦ {φ ₁ + φ ₂ + (φ _PRC / m _T )} · f _T ² / F _T ≦ 5, where m _T = f _T / f _FC φ _i : power of the i-th lens (i = 1, 2 ) Φ _PRC : Sum of the power of the plastic lens of the second lens group f _T : Focal length at the telephoto end F _T : F-number at the telephoto end f _FC : Focal length of the first lens group