JP2000221392A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a zoom lens which is constituted of six or less lenses including a plastic lens, at which various aberrations are excellently corrected and that is made compact and is suitable for an inexpensive lens shutter type camera or the like. SOLUTION: At the zoom lens orderly consisting of the first lens group of positive refracting power and the second lens group of negative refracting power from the side of an object and executing variable power by changing the interval of both groups, the first lens group is orderly constituted of four lens components of a first lens, a second lens, a third lens and a fourth lens from the side of the object and a diaphragm on the side of an image, and the first lens possesses the positive refracting power, and at least one lens out of the first lens, the second lens and the third lens is the plastic lens, and the fourth lens is a glass lens having the positive refracting power and the second lens group is constituted of one or two lens components.

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 small two-lens zoom lens suitable for a lens shutter type camera and the like, which has a limited back focus.

[0002]

2. Description of the Related Art Conventionally, as a type of zoom lens, there is a two-unit zoom lens. The two-unit zoom lens 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. , The structure is simple and the total lens length is short. Therefore, it is widely used in cameras such as lens shutter type cameras.

[0003] The two-unit zoom 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. The positive lens leading type is easy to reduce the telephoto ratio, and is suitable for a telephoto focal length range.

[0004]

However, the two-group zoom lens of the positive lens leading type has a large number of lens components and a large number of glass lens components, so that it is a compact zoom lens taking cost into consideration. It was difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens which is suitable for a compact, low-cost lens shutter type camera and the like having a good image forming performance, in which various aberrations are satisfactorily corrected.

[0006]

The above object is achieved by one of the following constitutions.

[0007] 1. In a zoom lens that 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 changes the distance between the first and second lens units, the first lens group includes a first lens unit in order from the object side. The lens comprises four lens elements, one lens, a second lens, a third lens, and a fourth lens, and a diaphragm on the image side thereof. The first lens has a positive refractive power, and the first lens, the second lens, At least one of the lens and the third lens is a plastic lens, the fourth lens is a glass lens having a positive refractive power, and the second lens group is composed of one or two lens elements. A featured zoom lens.

[0008] 2. 2. The zoom lens according to 1, wherein the following condition is satisfied.

0.64 ≦ f _W /D≦1.0 (1) 0.50 ≦ | f _RC | / f _W ≦ 0.80 (2) 1.50 ≦ n ₄ ≦ 1.90 (3) 0 ≦ ν ₁ −ν ₄ ≦ 40 (4) where f _W : focal length at the wide-angle end D: screen diagonal line length f _Rc : focal length of the second lens group n ₄ : refractive index of the fourth lens counted from the object side ν ₁ , ν ₄ : _first and _fourth lenses, respectively Abbe number of The second lens group includes, in order from the object side, a fifth lens element and a sixth lens element. The fifth lens element is a plastic lens, and the sixth lens element is a glass lens. 1 characterized by satisfaction
A zoom lens according to claim 1.

−5 ≦ | φ _p + φ ₅ | · f _T ² / F _T ≦ 5 (5) where φ _{p is} the sum of the power of the plastic lenses in the first lens group φ ₅ : 3. Power of 5 lenses f _T : focal length at telephoto end F _T : F-number at telephoto end 4. The zoom lens according to 3, wherein the following condition is satisfied.

0 ≦ φ _p · f _T ≦ 2.0 (6) −2.0 ≦ φ ₅ · f _T ≦ 0 ... (7) where φ _p : the sum of the powers of the plastic lenses in the first lens group φ ₅ : the power of the fifth lens f _T : the focal length at the telephoto end In a zoom lens that 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 changes the distance between the first and second lens units, the first lens group includes a first lens unit in order from the object side. It is composed of four lens elements, one lens, a second lens, a third lens, and a fourth lens, and a diaphragm on the image side thereof.
The first lens has a positive refractive power, and at least one of the first lens, the second lens, the third lens, and the fourth lens is a plastic lens, and the second lens
A zoom lens, wherein the lens group includes one or two lens elements and satisfies the following conditions.

1.50 ≦ n ₄ ≦ 1.90 (3) where n _{4 is} the refractive index of the fourth lens counted from the object side. 6. The zoom lens according to 5, wherein the following condition is satisfied.

0.64 ≦ f _W /D≦1.0 (1) 0.50 ≦ | f _RC | / f _W ≦ 0.80 (2) 0 ≦ ν ₁ −ν ₄ ≦ 40 (4) where f _W : focal length at the wide-angle end D: screen diagonal length f _Rc : focal length of the second lens group ν ₁ , ν ₄ : Abbe numbers of the first lens and the fourth lens, respectively. The second lens group includes, in order from the object side, a fifth lens element and a sixth lens element. The fifth lens element is a plastic lens, and the sixth lens element is a glass lens. 5 characterized by satisfaction
A zoom lens according to claim 1.

−5 ≦ | φ _p + φ ₅ | · f _T ² / F _T ≦ 5 (5) where φ _{p is} the sum of the power of the plastic lenses in the first lens group φ ₅ : 7. Power of fifth lens f _T : focal length at telephoto end F _T : F-number at telephoto end 8. The zoom lens according to 7, wherein the following condition is satisfied.

0 ≦ φ _p · f _T ≦ 2.0 (6) −2.0 ≦ φ ₅ · f _T ≦ 0 ... (7) where φ _p : sum of the power of the plastic lenses in the first lens group φ ₅ : power of the fifth lens f _T : focal length at the telephoto end A zoom lens having 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 performing zooming by changing the distance between the first lens unit and the zoom lens having a zoom ratio of 1.6 or more. One lens group includes a first lens,
The first lens has a positive refracting power, and includes the first lens, the second lens, the third lens, and the fourth lens.
A zoom lens, wherein at least one of the lenses is a plastic lens, and the second lens group includes one or two lens elements.

10. 10. The zoom lens according to 9, wherein the following condition is satisfied.

0.64 ≦ f _W /D≦1.0 (1) 0.50 ≦ | f _RC | / f _W ≦ 0.80 (2) 0 ≦ ν ₁ −ν ₄ ≦ 40 (4) where f _W : focal length at the wide-angle end D: screen diagonal length f _Rc : focal length of the second lens group ν ₁ , ν ₄ : Abbe numbers of the first lens and the fourth lens, respectively. The second lens group includes, in order from the object side, a fifth lens element and a sixth lens element. The fifth lens element is a plastic lens, and the sixth lens element is a glass lens. 10. The zoom lens according to 9, wherein the zoom lens is satisfied.

−5 ≦ | φ _p + φ ₅ | · f _T ² / F _T ≦ 5 (5) where φ _{p is} the sum of the power of the plastic lenses in the first lens group φ ₅ : 11. Power of 5 lenses f _T : focal length at telephoto end F _T : F-number at telephoto end 10. The zoom lens according to 9, wherein the following condition is satisfied.

0 ≦ φ _p · f _T ≦ 2.0 (6) −2.0 ≦ φ ₅ · f _T ≦ 0 ... (7) where φ _p : the sum of the powers of the plastic lenses in the first lens group φ ₅ : the power of the fifth lens f _T : the focal length at the telephoto end Here, the conditional expressions will be described. Conditional expression (1) is
The focal length at the wide-angle end suitable for the zoom lens of the present invention is determined. If the lower limit is exceeded, the peripheral light quantity for the positive lens leading type tends to be insufficient, and the back focus is shortened, and the rear lens system is increased, which impairs the radial compactness. Exceeding the upper limit lengthens the overall length, making it impossible to take advantage of the positive lens advance type.

Conditional expression (2) defines an appropriate range of the focal length of the second lens group. 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 made up of two or less lenses, aberrations are deteriorated, and the radius of curvature of the specific concave surface is reduced, and glass polishing is performed. It is not suitable for processing. 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.

Conditional expression (3) defines an appropriate range of the refractive index of the fourth lens. If the lower limit is exceeded, the frame tends to deteriorate. If the value exceeds the upper limit, the Petzval sum becomes negative and large, and it becomes difficult to obtain a good image surface.

Conditional expression (4) is a condition relating to correction of chromatic aberration. If the lower limit is exceeded, the magnification color deteriorates in the direction in which the image height of the short wavelength becomes larger, and if the upper limit is exceeded, the axial color deteriorates to the under side.

Conditional expression (5) is a condition for suppressing the change of the focal position with respect to the temperature change, and the power of the plastic lens in the first lens group and the power of the plastic lens in the second lens group satisfy this condition. Accordingly, at the telephoto end where the focal position changes greatly with respect to the temperature change, the focal position fluctuation can be suppressed within the depth. Assuming that the temperature ν of the plastic lens is uniformly ν _T and that the heights of the axial rays at the telephoto end are substantially equal for each plastic lens, the focal position variation δS is approximately expressed by the following equation.

ΔS = −f _T ² (φ _p + φ ₅ ) / ν _T Allowable circle of confusion is 0.05 mm and depth is ± 0.05 m
mF _T (where F _T is the F-number at the telephoto end) is 30
Since ν _T with respect to a temperature change of ° C. is approximately −100, there is an expression (5) as a conditional expression in which δS at this time falls within the depth.

Conditional expressions (6) and (7) are also conditions relating to the change of the focal position with respect to the temperature change. The second lens group is 2
In the case of a single-lens configuration, by giving negative or zero power to the plastic lens in the second lens group, the negative power of another lens in the second lens group does not become extremely strong, which is advantageous for aberration correction. . At this time, by giving positive or zero power to the plastic lens in the first lens group, it is possible to cancel a focus change due to a temperature change. However, when the value exceeds the upper limit of the expression (6) or the lower limit of the expression (7), it is difficult to suppress the focus variation due to the temperature variation regardless of zooming.

Next, the preferred ranges of the conditional expressions are as follows.

0.70 ≦ f _W /D≦0.95 0.68 ≦ | f _RC | / f _W ≦ 0.80 1.50 ≦ ν ₄ ≦ 1.65 13 ≦ ν 1 −ν ₄ ≦ 40 -3 ≦ | φ _p + φ ₅ | · f _T ² / F _T ≦ 3

[0028]

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: radius of curvature of refraction surface _d : interval 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
The _8, A ₁₀ as aspherical coefficients are represented by "Equation 1".

[0030]

(Equation 1)

(Embodiment 1) FIG. 1 is a lens sectional view of Embodiment 1. Tables 1 and 2 show lens data.

[0032]

[Table 1]

[0033]

[Table 2]

The first lens group includes a first lens having a positive refractive power,
Plastic second lens with positive refractive power, third lens with negative refractive power
The second lens group includes a fifth lens made of plastic having a negative refractive power and a sixth lens having a negative refractive power.

FIG. 2 shows (A) the short focal length end and (B) of the first embodiment.
It is a lens aberration figure in an intermediate | middle, (C) long focal point.

FIG. 3 is a sectional view of a lens according to a second embodiment. Tables 3 and 4 show lens data.

[0037]

[Table 3]

[0038]

[Table 4]

The first lens group includes a first lens having a positive refractive power,
2nd lens with positive refractive power, 3rd plastic with positive refractive power
The second lens group includes a fifth lens made of plastic having a negative refractive power and a sixth lens having a negative refractive power.

FIG. 4 shows (A) the short focal length end and (B) of the second embodiment.
It is a lens aberration figure in an intermediate | middle, (C) long focal point.

(Embodiment 3) FIG. 5 is a lens sectional view of Embodiment 3. Tables 5 and 6 show lens data.

[0042]

[Table 5]

[0043]

[Table 6]

The first lens group includes a first lens having a positive refractive power,
2nd lens with negative refractive power, 3rd plastic with positive refractive power
The second lens group includes a fifth lens made of plastic having no refractive power and a sixth lens having negative refractive power.

FIG. 6 shows (A) the short focal length end and (B) the third embodiment.
It is a lens aberration figure in an intermediate | middle, (C) long focal point.

(Embodiment 4) FIG. 7 is a lens sectional view of Embodiment 4. Tables 7 and 8 show lens data.

[0047]

[Table 7]

[0048]

[Table 8]

The first lens group includes a first lens having a positive refractive power,
2nd lens with negative refractive power, 3rd plastic with positive refractive power
The second lens group includes a fifth lens made of plastic having no refractive power and a sixth lens having negative refractive power.

FIG. 8 shows (A) the short focal length end and (B) of the fourth embodiment.
It is a lens aberration figure in an intermediate | middle, (C) long focal point.

Table 9 shows the values of the conditional expressions in each embodiment.

[0052]

[Table 9]

As shown in Table 9, the condition of the present invention is satisfied.

[0054]

The zoom lens according to the present invention has the following advantages because it is constructed as described above. The zoom lens is composed of six or less lenses including a plastic lens, and has various aberrations corrected satisfactorily. The zoom lens is suitable for a compact, low-cost lens shutter type camera and the like.

[Brief description of the drawings]

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

FIG. 2 shows (A) a short focal length end, (B) an intermediate position,
FIG. 3C is a lens aberration diagram at the long focal end.

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

FIG. 4 shows (A) a short focal length end, (B) an intermediate position,
FIG. 3C is a lens aberration diagram at the long focal end.

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

FIG. 6 shows (A) a short focal length end, (B) an intermediate position,
FIG. 3C is a lens aberration diagram at the long focal end.

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

FIG. 8 shows (A) a short focal length end, (B) an intermediate position,
FIG. 3C is a lens aberration diagram at the long focal end.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st surface 2 2nd surface 3 3rd surface 4 4th surface 5 5th surface 6 6th surface 7 7th surface 8 8th surface 9 9th surface 10 10th surface 11 11th surface 12 12th surface

Claims (12)

[Claims] 1. A zoom lens system comprising 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, wherein the distance between the first and second lens units is changed. The first lens has a positive refractive power, and the first lens has a positive refractive power. The first lens has four lens elements of a first lens, a second lens, a third lens, and a fourth lens in this order from the side.
At least one of the lens, the second lens, and the third lens is a plastic lens, the fourth lens is a glass lens having a positive refractive power, and the second lens group is one or two lenses. A zoom lens comprising elements. 2. The zoom lens according to claim 1, wherein the following condition is satisfied. 0.64 ≦ f _W /D≦1.0 0.50 ≦ | f _RC | / f _W ≦ 0.80 1.50 ≦ n ₄ ≦ 1.90 ≦ ν ₁ −ν ₄ ≦ 40 where f _W : Focal length at wide-angle end D: Screen diagonal line length f _Rc : Focal length of second lens group n ₄ : Refractive index of fourth lens counted from object side ν ₁ , ν ₄ : First lens and fourth lens respectively Abbe number 3. The second lens group is a fifth lens unit in order from an object side.
The lens according to claim 1, wherein the fifth lens is a plastic lens, and the sixth lens is a glass lens, and satisfies the following condition. Zoom lens. −5 ≦ | φ _p + φ ₅ | · 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 ₅ : power of the fifth lens f _T : focal point at the telephoto end Distance F _T : F-number at telephoto end 4. The zoom lens according to claim 3, wherein the following condition is satisfied. 0 ≦ φ _p · f _T ≦ 2.0 −2.0 ≦ φ ₅ · f _T ≦ 0, where φ _{p is} the sum of the power of the plastic lenses in the first lens group φ ₅ : the power f _{T of} the fifth lens : Focal length at telephoto end 5. A zoom lens system comprising 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, wherein the distance between the first and second lens units is changed. The first lens has a positive refractive power, and the first lens has a positive refractive power. The first lens has four lens elements of a first lens, a second lens, a third lens, and a fourth lens in this order from the side.
At least one of the lens, the second lens, the third lens, and the fourth lens is a plastic lens, and the second lens group includes one or two lens elements and satisfies the following conditions. A zoom lens characterized in that: 1.50 ≦ n ₄ ≦ 1.90 where n _{4 is} the refractive index of the fourth lens counted from the object side 6. The zoom lens according to claim 5, wherein the following condition is satisfied. 0.64 ≦ f _W /D≦1.0 0.50 ≦ | f _RC | / f _W ≦ 0.80 0 ≦ ν ₁ −ν ₄ ≦ 40 where f _W : focal length at the wide-angle end D: screen diagonal Length f _Rc : focal length of the second lens group ν ₁ , ν ₄ : Abbe numbers of the first lens and the fourth lens, respectively 7. The fifth lens group includes a fifth lens unit in order from an object side.
The lens according to claim 5, comprising two lens elements, a lens and a sixth lens, wherein the fifth lens is a plastic lens, and the sixth lens is a glass lens, and satisfies the following conditions. Zoom lens. −5 ≦ | φ _p + φ ₅ | · 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 ₅ : power of the fifth lens f _T : focal point at the telephoto end Distance F _T : F-number at telephoto end 8. The zoom lens according to claim 7, wherein the following condition is satisfied. 0 ≦ φ _p · f _T ≦ 2.0 −2.0 ≦ φ ₅ · f _T ≦ 0, where φ _{p is} the sum of the power of the plastic lenses in the first lens group φ ₅ : the power f _{T of} the fifth lens : Focal length at telephoto end 9. A zoom system comprising 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 changing the distance between the two to perform zooming and having a zoom ratio of 1.6 or more. In the lens, the first lens group includes, in order from the object side, a first lens, a second lens, a third lens, and a fourth lens element, wherein the first lens has a positive refractive power; At least one of the first lens, the second lens, the third lens, and the fourth lens is a plastic lens, and the second lens group includes one or two lens elements. Zoom lens. 10. The zoom lens according to claim 9, wherein the following condition is satisfied. 0.64 ≦ f _W /D≦1.0 0.50 ≦ | f _RC | / f _W ≦ 0.80 0 ≦ ν ₁ −ν ₄ ≦ 40 where f _W : focal length at the wide-angle end D: screen diagonal Length f _Rc : focal length of the second lens group ν ₁ , ν ₄ : Abbe numbers of the first lens and the fourth lens, respectively 11. The second lens group includes, in order from the object side, a fifth lens element and a sixth lens element,
The zoom lens according to claim 9, wherein the fifth lens is a plastic lens, and the sixth lens is a glass lens, and satisfies the following condition. −5 ≦ | φ _p + φ ₅ | · 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 ₅ : power of the fifth lens f _T : focal point at the telephoto end Distance F _T : F-number at telephoto end 12. The zoom lens according to claim 9, wherein the following condition is satisfied. 0 ≦ φ _p · f _T ≦ 2.0 −2.0 ≦ φ ₅ · f _T ≦ 0, where φ _{p is} the sum of the power of the plastic lenses in the first lens group φ ₅ : the power f _{T of} the fifth lens : Focal length at telephoto end