JP2001215407A - Wide-angle zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-group type wide-angle zoom lens constituted of the small number of lenses, excellently compensating aberration, having a zoom ratio being about 2 and realizing high performance and low production cost by the appropriate constitution of two groups and the effective use of aspherical surfaces. SOLUTION: A 1st group I is constituted of a meniscus negative lens whose convex surface faces the object side and whose front surface is aspherical and a meniscus positive lens whose convex surface faces the object side arranged in this order from the object side, and a 2nd group II is constituted of elements having positive, negative and positive power in this order from the object side. By making the surface r9 of the positive power element aspherical and making the distance between the negative and positive lenses in the 1st group I and the distance between the head positive lens and the following negative lens in the 2nd group II satisfy a fixed condition, the appropriate lens constitution of two groups having the negative and positive power is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is mainly used as a wide-angle zoom lens of an interchangeable lens for a 35 mm single-lens reflex camera.

[0002]

2. Description of the Related Art A wide-angle zoom lens for a single-lens reflex needs a retrofocus type structure composed of two negative and positive groups in order to obtain a long back focus at a wide end. However, since the retrofocus type configuration of the two-group system wide-angle zoom lens having negative and positive powers has no symmetry in power arrangement, it is generally difficult to correct aberration fluctuation due to zooming even in a system having a zoom ratio of about 2. is there. Therefore, good aberration correction has been realized by increasing the number of elements constituting the system. For example, the focal length is 35-70 mm, and the F number is 3.5-4.
Many wide-angle zoom lenses having a long back focus and a large degree have a system in which the first group includes at least three lenses and the second group includes four or more lenses.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a two-group wide-angle zoom lens having a small number of lenses and a low manufacturing cost.

[0004]

SUMMARY OF THE INVENTION The present invention is directed to an appropriate lens configuration of two groups of negative and positive power, that is, the first group is a meniscus negative lens having a convex surface facing the object side in order from the object side and an aspheric front surface. And a meniscus positive lens having a convex surface facing the object side. The second group is composed of elements having positive, negative, and positive power in order from the object side, and one surface of any of the positive power elements is an aspheric surface, and The following conditions

(1) 0.4 | f1 |>Df> 0.2 | f1 | (2) 0.4f2>Db> 0.2f2 where f1: focal length of the first group f2: focal point of the second group Distance Df: Air gap between negative and positive lenses in the first group Db: Satisfies the air gap between the first lens and the second lens in the second group, thereby greatly reducing the number of components compared to the conventional lens and equal to or more than that Performance was achieved.

A major problem in aberration correction of the two-unit zoom method is correction of negative distortion generated by the strongly divergent first lens unit unique to the retrofocus type. For this correction, a method of introducing a positive lens into the divergent first lens group is well known. However, adding positive power to the first group of negative power as a whole is a contradiction in which the power of the negative component must be increased, and is not preferable for aberration correction. In order to reduce this inconsistency, the present invention introduces an aspheric surface into the front negative lens to correct distortion, and further arranges a positive lens with a large air gap from the first lens, and shifts its shape to the object side. By forming a meniscus shape with the convex surface facing, it is possible to correct aberrations in which strong positive power is generated with weak positive power.

The second lens unit has a minimum configuration capable of satisfactorily correcting various aberrations, that is, a triplet, that is, a single lens of positive, negative, positive, and one surface of the front or rear positive lens near the stop. Is made aspherical to increase the potential for aberration correction.

By defining the size of the air gap in each lens group so as to enhance the effect of aberration correction together with the effective operation of the aspherical surface, a high-performance wide-angle zoom lens can be obtained with a small number of components. I was able to.

[0009]

Function 1 defines the distance between the negative and positive lenses in the first group. When the interval is smaller than the lower limit, the compactness and the correction of distortion can be easily performed, but it is not preferable for the correction of spherical aberration. Conversely, if the value is increased beyond the upper limit, it becomes easier to correct the aperture aberration, but it is not desirable because the system becomes larger.

Condition 2 is a condition relating to the air gap between the first lens in the second lens unit and the negative lens disposed next to the first lens. If this interval exceeds the upper limit and becomes large, the back focus becomes insufficient, and negative distortion increases. When it is smaller than the lower limit, it is not preferable for correcting astigmatism.

The two quantitative specifications given in the conditions 1 and 2 are features not found in the same type of zoom lens.

Also, as is well known, aspherical surface near the stop is extremely effective for correcting the aperture aberration. However, in the present invention, the first group first surface for correcting the distortion is used. In addition to the aspherical surface, one surface of the positive lens closer to the stop of the second group was made aspherical, so that good correction of aperture aberration could be realized.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Numerical embodiments 1 and 2 of the wide-angle zoom lens according to the present invention will be described below.

FIG. 1 is a lens configuration diagram of a numerical example 1, and FIG.
4 is a lens configuration diagram of Numerical Example 2. FIG. 1 and 2
Reference numeral I denotes a first lens unit having a negative refractive power, and II denotes a second lens unit having a positive refractive power. 3 is an aberration diagram at the wide-angle end of Numerical Embodiment 1 of the present invention, FIG. 4 is an aberration diagram at a telephoto end of Numerical Embodiment 1 of the present invention, and FIG. 5 is an aberration diagram at the wide-angle end of Numerical Embodiment 2 of the present invention. 6 is an aberration diagram at the telephoto end of Numerical Example 2 of the present invention.

In Numerical Examples 1 and 2, f is the focal length, Fno is the F number, ω is the half angle of view, ri is the radius of curvature of the i-th lens surface in order from the object side, and di is The i-th lens thickness and air gap in order from the object side, and ni and vi are the i-th lens refractive index and Abbe number in order from the object side. The aspherical shape is represented by the following equation when the x axis is in the optical axis direction and the y axis is in the direction perpendicular to the optical axis.

X = (y ² / r) / [1+ ｛1-A (y ²
/ R ² )｝ ^1/2 ] + A4y ⁴ + A6y ⁶ + A8y ⁸ +
A10y ¹⁰

R is the paraxial radius of curvature, A4, A6, A8, A
10 is an aspherical coefficient, and A is a conical coefficient.

Numerical Example 1 f = 36.02 to 68.10 Fno = 3.79 to 3.81 ω = 31.7 ° to 17.7 °

Ridinini vi 1 100.6600 3.9300 1.77250 49.7 2 23.9300 14.8000 3 30.8600 3.8600 1.84666 23.9 4 36.770 Variable 528.7800 4 .8200 1.69680 55.6 6 -367.6100 9.5300 7 -27.9500 1.1700 1.696995 30.1 8 74.8900 0.8900 9 274.0500 7.0200 1.556384 60.8 10-20.7900 1.2300 11 Aperture stop 18.0000 12 Fixed stop

Focal length 36.02 50.04 68.10 d4 36.1000 15.7496 1.8776

R1 A 1.00 A4 0.166969E-05 A6.48239800E-09 A8 0.599779E-12

R9 A 1.00 A4 -0.2223900E-04 A6 -0.24679600E-08

Conditional expression (1) 0.4 | f1 | = 22.8 0.2 | f1 | = 11.4 (2) 0.4f2 = 18.3 0.2f2 = 9.18

Numerical Example 2 f = 35.99 to 68.00 Fno = 3.88 to 3.91 ω = 31.8 ° to 17.7 °

Ridinini vi 1 156.5900 3.6600 1.665455.5 2 23.3000 17.3500 3 29.6500 2.2700 1.84666 23.9 4 33.8100 Variable 5 33.99005 0.0100 1.56907 69.7 6-89.4900 12.8600 7-165.4600 3.1100 1.68955 30.18 355.2200 1.2500 9 135.5500 4.4500 1.61800 63.0 10-32.5700 1.5900 11 Aperture stop 15.0000 12 Fixed stop

Focal length 35.99 50.04 68.00 d4 36.1000 15.7496 1.8776

R1 A 0.2497500E + 02 A4 0.146713E-05 A6 -0.1067993E-08 A8 0.3717379E-11 A10 -0.34912755E-14

R5 A−0.68690000E + 00 A4−0.110111838E−05 A6−0.95462017E−08 A8 0.4729595E−10 A10−0.125227224E−12

Conditional expression (1) 0.4 | f1 | = 22.6 0.2 | f1 | = 11.3 (2) 0.4f2 = 18.6 0.2f2 = 9.30

[0030]

As described above, in the present invention, by using an aspherical surface, it is possible to realize a wide-angle zoom lens having a zoom ratio of about 2 with good aberration correction and a small number of components, and an appropriate two groups. Through the effective use of the configuration and the aspherical surface, the number of components as small as five as a whole can be realized, and further, the manufacturing cost can be significantly reduced, and a high-performance and compact wide-angle zoom system can be realized.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of Numerical Example 1 of the present invention.

FIG. 2 is a lens configuration diagram of Numerical Example 2 of the present invention.

FIG. 3 is an aberration diagram at a wide-angle end according to Numerical Example 1 of the present invention.

FIG. 4 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention.

FIG. 5 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 6 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

[Explanation of symbols]

 I First lens unit II Second lens unit ri The ith radius of curvature di The ith lens thickness and lens spacing

Claims (1)

[Claims] 1. A zoom system comprising a first group having a negative refractive power and a second group having a positive refractive power in order from the object side, and changing a focal length by changing an air gap between the first group and the second group. In the lens, the first group includes a meniscus negative lens having a convex surface facing the object side in order from the object side and a meniscus negative lens having a front surface facing the aspheric surface, and the second group includes a positive, negative, positive lens in order from the object side. A wide-angle zoom lens comprising a power element, wherein one surface of any of the positive power elements is aspherical, and satisfies the following conditions. (1) 0.4 | f1 |>Df> 0.2 | f1 | (2) 0.4f2>Db> 0.2f2 where f1: focal length of the first group f2: focal length of the second group Df: Db: Air gap between the first lens of the second group and the second lens.