JP2003222796A - Two-group zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-group zoom lens having 5 five-groups of a low cost and a good yield in a mass production. <P>SOLUTION: The two-group zoom lens comprises a first group having a positive refractive power and a second group having a negative refractive power from an object side. In this zoom lens, the first group has a negative first lens, a negative second lens and a positive third lens from the object side, and the second group has a positive fourth lens, and a negative fifth lens from the object side. Further, the first lens and the second lens have one or more aspherical surfaces and satisfy a formula (1): 0.26<|√(ϕW×ϕT)/(B×ϕ2)| and a formula (2): r4/D<4.5, wherein ϕW is a power (a reverse number of a focal length) of a wide end, ϕT is a power (a reverse number of a focal length) of a telescopic end, B is a zoom ratio, r4 is a curvature of an image side face of a second lens of the first group, and D is a distance from the image side face of the second lens to the diaphragm. <P>COPYRIGHT: (C)2003,JPO

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 zoom lens for a lens shutter camera.

[0002]

2. Description of the Related Art A conventional 38-90 mm two-group zoom lens has six
There are many configurations with more than one sheet, and cost is high. In order to improve the performance even with a structure of 6 or less, it is dealt with by using a lens with tight tolerances, a double-sided aspherical lens that is difficult to adjust, or a plastic lens with high birefringence such as PC (polycarbonate).

[0003]

However, although these conventional lenses have good design data, the performance of actual mass-produced products is lower than the design data, resulting in poor yield and resulting in high cost in many cases. .

In view of the above, it is an object of the present invention to provide a two-group zoom lens composed of five-group, five-lens structure which is inexpensive and has a high yield in mass production.

[0005]

In order to achieve the above-mentioned object, the present invention according to claim 1 provides, in order from the object side, a first group having a positive refractive power and a negative refractive power. There is a second
In an optical system that is composed of a group and changes the angle of view by changing between the first group and the second group, the first group includes a negative first lens, a negative second lens, and a positive third lens from the object side. The second group is composed of a fourth lens positive from the object side and a fifth lens negative, and the first lens and the fourth lens are
It is characterized by having one or more aspherical surfaces and satisfying the following conditional expressions. 0.26 <| √ (φW × φT) / (B × φ2) | (1) r4 / D <4.5 (2) where φW: power at wide end (reciprocal of focal length) φT: power at tele end (Inverse of focal length) B: Zoom ratio r4: Curvature of the image side surface of the first lens unit second lens D: Distance from the image side surface of the second lens to the diaphragm. In the group zoom lens, one surface of each of the first lens and the fourth lens is an aspherical lens, and the following conditional expression is satisfied. -0.18 <FW / F1 <-0.16 (3) where FW: focal length at wide end F1: focal length of first lens The invention according to claim 3 is the two-group zoom lens according to claim 1 or 2. The first lens is a negative meniscus lens having a convex surface directed toward the object side, the second lens is a negative lens, and the third lens is a biconvex lens.
The lens and the fourth lens are plastic lenses.

Here, the conditional expression (1) is an expression for defining the power of the second lens group, and by satisfying this expression, performance deterioration during zooming can be suppressed. If the value is out of the range of this expression, performance deterioration such as astigmatism is observed during zooming. The conditional expression (2) is an expression that regulates the curvature of r4 and suppresses the negative action. By observing this expression, the eccentricity tolerance of r4 can be loosened. Conditional expression (3) is an expression that regulates the power of the first lens, and by keeping this range, the eccentricity tolerance of the first lens and the performance can be balanced.

The above condition is satisfied, and the first lens group is composed of a negative meniscus lens having a convex surface facing the object side, a negative lens, and a biconvex lens, and the first lens and the fourth lens are zoom lenses which are plastic lenses. If the above condition is satisfied, it is possible to obtain a lens with a higher yield.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Next, specific embodiments of the two-group zoom lens according to the present invention will be described. As shown in FIG. 1, the radius of curvature of the i-th surface from the object side is ri, the surface distance di, the refractive index ni of the glass material, and the Abbe number are νi.
The surface marked with * represents an aspherical surface and is formed according to the following formula. Z = ch ² /

[1+ {1- (1 + K) c ² h} ^1/2 ] + Ah ⁴ + Bh ⁶ + Ch
⁸ + Dh ¹⁰ Here, c = 1 / r.

[0009]

[Table 1]

[0010]

[Table 2]

[0011]

[Table 3]

It should be noted that FIGS. 1 to 3 are described in the case of wide, standard and tele with the enlargement ratio being changed in order from the top.

[0013]

As described above, the claims of the present invention
According to the invention described in item 1, it is possible to obtain a 2-group zoom lens which is inexpensive and has a high yield in mass production with a 5-group 5-element configuration.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram and an optical path diagram of Example 1 of the present invention.

FIG. 2 is a lens configuration diagram and an optical path diagram of Example 2 of the present invention.

FIG. 3 is a lens configuration diagram and an optical path diagram of Example 3 of the present invention.

FIG. 4 is an aberration diagram for a wide range according to Example 1 of the present invention.

FIG. 5 is an aberration diagram in the case of the standard of Example 1 of the present invention.

FIG. 6 is an aberration diagram in the case of tele according to the first embodiment of the present invention.

FIG. 7 is an aberration diagram for a wide range according to Example 2 of the present invention.

FIG. 8 is an aberration diagram for a standard according to Example 2 of the present invention.

FIG. 9 is an aberration diagram for telephoto according to example 2 of the present invention.

FIG. 10 is an aberration diagram in the case of Example 3 wide of the present invention.

FIG. 11 is an aberration diagram in the case of the standard of Example 3 of the present invention.

FIG. 12 is an aberration diagram for telephoto according to Example 3 of the present invention.

[Explanation of symbols]

1st lens 2 second lens 3rd lens 4th lens 5th lens

Claims (3)

[Claims] 1. A first group consisting of a first group having a positive refractive power and a second group having a negative refractive power in order from the object side.
In the optical system for changing the angle of view by changing between the groups, the first group includes a negative first lens, a negative second lens from the object side,
It is composed of a positive third lens, the second group is composed of a positive fourth lens and a negative fifth lens from the object side, and the first lens and the fourth lens have one or more aspherical surfaces. A two-group zoom lens, which satisfies the following conditional expression. 0.26 <| √ (φW × φT) / (B × φ2) | (1) r4 / D <4.5 (2) where φW: power at wide end (reciprocal of focal length) φT: power at tele end (Reciprocal of focal length) B: Zoom ratio r4: Curvature of the image side surface of the second lens in the first group D: Distance from the image side surface of the second lens to the diaphragm 2. The two-group zoom lens according to claim 1, wherein each of the first lens and the fourth lens is an aspherical lens, and the following conditional expression is satisfied. lens. -0.18 <FW / F1 <-0.16 (3) where FW: focal length at wide end F1: focal length of first lens 3. The two-group zoom lens according to claim 1, wherein the first lens is a negative meniscus lens having a convex surface directed toward the object side, the second lens is a negative lens, and the third lens is a third lens.
The lens is composed of a biconvex lens, and includes the first lens and the fourth lens.
2 characterized in that the lens is a plastic lens
Group zoom lens.