JPH02203314A - Zoom lens - Google Patents

Abstract

PURPOSE:To increase the telephoto-side focal length while realizing compact constitution by composing the zoom lens of 1st-3rd lens groups and satisfying specific conditions. CONSTITUTION:The 1st lens group consists of a lens 11 which has negative refracting power and a meniscus lens 12 which has positive refracting power, an aspherical surface, and a convex surface on the object lens. The 2nd lens group consists of lenses 21 and 22 which have positive refracting power, a biconcave lens 23, and a biconvex lens 24, and the 3rd lens group has a meniscus lens 31 which has a concave surface on the image side and inequalities I-IV hold. In the inequalities I-IV, r2, r3, r9 and r10 are the radii of curvature on the image side of the lens 11, on the object sides of the lenses 12 and 23, and on the image side of the lens 23, f1 the focal length of the 1st lens group, fy the focal length of the whole system on the telephoto end, and n5 the refractive index of the Fraunhofer d-line of the lens 23. Consequently, the zoom lens is reduced in size and increased in focal length.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a zoom lens, and is particularly suitable for a photographic lens that requires a relatively long back focus, such as an optical reflex camera or a still video camera. This invention relates to a zoom lens in which lens groups are arranged.

<Prior Art> Conventionally, in a negative-eye reflex camera, a rotary reflector is provided behind the photographic lens to reflect the light flux from the photographic lens and guide it to the finder system.

For this reason, the photographic lens used in the eye reflex camera is required to be a zoom lens that can easily obtain a long back focus that is equivalent to arranging the above-mentioned reflector, and that also has a high zoom ratio while maintaining high optical performance. has been done.

Furthermore, as camera bodies become smaller, it is desired that the photographing lens itself be made smaller and lighter.

As a zoom lens that is relatively compact and suitable for single-lens reflex cameras, it has negative refractive power in order from the object side.
For example, a two-group zoom lens with positive refractive power is
Including JP-A No. 49-2545, JP-A-52
This method has been proposed in Japanese Patent Application Laid-Open No. 59-64811, etc.

Furthermore, a zoom lens with a fixed negative lens arranged on the image side as an advanced version of the above-mentioned two-group zoom lens to further promote miniaturization is disclosed in Japanese Patent Laid-Open No. 58-111013 or Japanese Patent Laid-Open No. 61-183613. This method has been proposed in Japanese Patent Application Laid-open No. 112115/1983. This Japanese Patent Application Publication No. 61-183613, Japanese Patent Application Publication No. 62-11211
No. 5 discloses a zoom lens that uses aspheric surfaces in some lens groups to achieve miniaturization.

Problems to be Solved by the Present Invention The above zoom lens is basically a reverse telephoto type wide-angle lens, and is suitable for a zoom lens that covers a focal length on the wide-angle side.

By the way, the products are generally 35 mm to 70 mm.
Widely used as a standard zoom. On the other hand, recently there has been a desire to extend the focal length of such a standard zoom toward the telephoto side, and for example, Japanese Patent Application Laid-open No. 75108/1983 discloses
A zoom lens with a high magnification of 35 mm to 85 mm and 35 mm to 140 mm has been proposed in Japanese Patent Publication No. 55-14403, etc., but it requires a large number of lenses (and a large number of moving lens groups). (This results in a complicated lens barrel structure, which is expensive, and also increases the overall length of the lens, making it insufficient as a standard zoom for regular use.)

It is an object of the present invention to provide a zoom lens that further achieves the above-mentioned two problems of standard zooms, namely compactness and low cost, while maintaining optical performance, and has an expanded focal length on the telephoto side.

<Means and configuration for solving the problem> In order from the object side, the first lens group has negative refractive power and moves along the optical axis during zooming, the first lens group has positive refractive power and moves along the optical axis during zooming, and the first lens group has negative refractive power and moves along the optical axis during zooming. The first lens group consists of 11 lenses each having a negative refractive power and a strong concave surface on the image side. , has 12 meniscus-shaped lenses having a positive refractive power, an aspherical surface, and a convex surface facing the object side, and the second lens group has 2 lenses having a positive refractive power, 2 lenses having a positive refractive power, The third lens group has 31 lenses having a meniscus shape with the concave surface facing the image side, and satisfies the following conditions. be.

That is, (1) -0,65<f, /f, < -0,4
5(2) 0.43 < r 2 / r 3 < 0.
63(3)re/r+. <-15 (4) n 5 >1.8.

However, r 2 ; r 3 ; r 9 ; rto; , the radius of curvature of the 23 lenses on the image side, the focal length of the first lens group, the focal length of the entire system at the telephoto end, and the refractive index of the 23 lenses at the Franhofer d-line.

<Example> FIG. 2, FIG. 4, FIG. 6, and FIG. 8 are cross-sectional views of lenses of Numerical Examples 1.2.3.4 related to the present invention.

■ is a first lens group that has negative refractive power and moves along the trajectory shown by the arrow when zooming from the telephoto end to the wide-angle end;
2 is a second lens group that has a positive refractive power and moves along a trajectory shown by an arrow during zooming, and 2 is a third lens group that has a negative refractive power and is fixed during zooming. Note that focusing is performed by moving the first lens group along the optical axis.

By the way, in order to increase the zoom ratio, it is common to increase the amount of movement of the first and second lens groups, but the distance between the first and second lens groups at the wide-angle end Also, the distance from the second lens group to the image plane at the telephoto end becomes large, and the total length of the lens becomes long.

On the other hand, in order to obtain the desired zoom ratio while keeping the overall length of the lens relatively short, it is necessary to strengthen the refractive power of each lens group, but in the case of a two-group configuration, the solution is almost uniquely determined, resulting in This results in disadvantages in that the overall length of the lens on the wide-angle side is long, and the amount of focusing movement increases. Therefore, it is advisable to adopt a zoom type lens having a three-group structure, as described in the above-mentioned Japanese Patent Laid-Open No. 58-111013.

In the present invention, the above-mentioned object is achieved by making further improvements and determining the refractive power arrangement and lens shape of each lens group as described above.

Next, the significance of the numerical range of each conditional expression will be explained.

If the refractive power of the first lens group is weakened by exceeding the lower limit of conditional expression (1), the total length of the lens on the wide-angle side will increase, and the amount of focusing will increase, increasing the total length of the lens barrel. The outer diameter of the lens is large to ensure sufficient peripheral light,
Undesirable. If the refractive power is increased beyond the upper limit, distortion and astigmatism will occur particularly on the wide-angle side, and even if an aspherical surface is used, the correction limit will be exceeded.

Conditional expression (2) is a condition for satisfactorily correcting spherical aberration and coma aberration caused by increasing the refractive power of the first lens group. Table 1 shown for reference shows the Seidel aberration values of each surface of Numerical Example 1.

As can be seen from the table, the spherical aberrations generated at r2 and r3 increase significantly at the telephoto end, and the amount of increase becomes significant as the focal length at the telephoto end is increased. On the other hand, coma aberration has a change in sign that is reversed between the wide-angle side and the telephoto side, and it becomes impossible to correct spherical aberration and coma aberration simultaneously even if the upper limit or lower limit of conditional expression (2) is exceeded.

Conditional expression (3) is an expression regarding the sharing of refractive power between both surfaces of the 23 lenses. When increasing the refractive power of the first lens group according to conditional expression (1), the total length of the lens is shortened by simultaneously increasing the refractive power of the second lens group, but in order to correct the intragroup aberration of strong positive refractive power, A negative lens surface is required, and in order to realize it with a small number of lenses, a single biconcave lens with an appropriate shape is required. When the r, side is strengthened, higher-order aberrations occur, r,. If the side is strengthened, the off-axis aberration worsens, but conditional expression (4
), a high refractive index glass material is used, and the conditional expression (3
), a stronger curvature is given to the r to side, and the 31st lens of the third lens group is a negative meniscus lens having a strong concave surface on the image side, thereby making it possible to perform good aberration correction. As can be seen from Table 1, the 31 lens has the effect of over-correcting astigmatism on the wide-angle side and under-correcting astigmatism on the telephoto side.

More preferably, the image side surface of the 12 lenses is made aspherical,
Good aberration correction is possible by giving the shape such that the curvature becomes weaker toward the periphery, that is, the negative refractive power becomes weaker toward the periphery.In general, wide-angle zoom lenses have astigmatism. If we focus on correcting distortion, there is no big difference in effectiveness no matter which surface of the first lens group is made aspheric, but as explained in conditional expression (2), the zoom range is expanded toward the telephoto side. In this case, the situation is different, and in addition to the condition of formula (2), it is preferable to make the image side of the 12 lenses aspherical.Furthermore, according to conditional formula (2), the refractive power of the first lens group is strengthened, and the first lens group The surface closest to the aperture in the lens group, that is, the surface with the lowest number 5 in aberration theory, has a large amount of aspherical surface, and its shape is such that the local radius of curvature is reversed at the periphery. It is necessary to give it so that it is positive at the center and negative at the periphery. Fig. 1 is a deformed representation of an aspherical shape, and the shape is convex at the periphery.

In the present invention, it is more preferable to use a low-dispersion glass material having an Abbe number greater than 50 (ν>5o) for the 31 lens. The minimum configuration is a single lens, and if the refractive power is strengthened to shorten the overall length, zoom fluctuations in lateral chromatic aberration, color coma, and astigmatism will occur at the telephoto end, so it is necessary to reduce dispersion.

Further, as mentioned above, the 31 lens corrects zoom fluctuations due to astigmatism, but there is a limit in a spherical system, and making it an aspheric lens is effective in improving astigmatism on the wide-angle side.

By the way, it is advantageous in catalogs to express the total lens length of a zoom lens by the shortest total length when stored, such as the wide-angle end or the telephoto end, or if the first lens group moves back and forth, the intermediate zoom position. Dew. However, it has the disadvantage of being weak against shock. For example, I've heard stories of people boarding a sightseeing bus with a camera slung over their shoulder and accidentally hitting the tip of the lens against a steel pipe on the handrail, breaking it. In order to create a structure that is resistant to such careless mistakes, it is sufficient to provide a fixed lens barrel that is stronger toward the object side than the longest part during zooming and which moves toward the object side when focusing.

In order to ensure sufficient compactness under such disadvantageous conditions in terms of the overall lens length, it is preferable to share the refractive power as described above so that the overall lens lengths at the wide-angle end and the telephoto end are approximately equal.

Next, numerical examples of the present invention will be shown. In numerical examples R
4 is the radius of curvature of the i-th lens surface in order from the object side, D
i is the i-th lens thickness and air distance from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side.

Note that the aspherical shape has an X axis in the optical axis direction and an H axis in the perpendicular direction to the optical axis.
axis, the traveling direction of light is positive, R is the paraxial radius of curvature, A,
B, C, D, E, ..., A'B'C'
When p l,... are each aspherical coefficients, 10FH12
+ GH14+ HH"+ A'H'10B'H'+ C
It is expressed by the formula 'H' + D'H' ten...

Front angle end M ^S T S 0.457476 0.126369 0.081929 1.558912 Telephoto end S A M S T S -0,004122 -0,001433 -0,002698 -0,115931 -0,185630 -0 ,032142 0,081929 -0,206285 A Spherical aberration S Distortion [Effect of the invention] As explained above, by adopting the configuration of the present invention, it is possible to extend the zoom range of a standard zoom lens in the 35-70 mm class to the telephoto side. Despite the enlargement, it has the effect of shortening the overall lens length, especially at the longest zoom position.

Furthermore, by effectively using aspherical surfaces, the number of lenses and lens barrel structure can be simplified, making it possible to provide the lens at low cost. Currently, the technology for molding glass that has been softened under high temperatures using an aspherical mold has been perfected, and aspherical lenses are no longer as expensive elements as they used to be.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the state of an aspherical surface related to the present invention. FIG. 2, FIG. 4, FIG. 6, and FIG. 8 each show numerical example 1 of the present invention. 2.3.4 lens sectional view. 3, 5, 7, and 9 show numerical examples 1 and 2 of the present invention, respectively.
3. 4 various aberration diagrams. ■ ■ ■ ■ ■ ■ FNO/f, otw=ts' IJ-15゜1J=15” ENG■ ■ 工■ ■ FNO/3.q 1go 316 buttocks=31@W.YopiFNO/3.q W Mi 31''W=31''d=31'F:NO/<t5 U-23,40 Low?3.40 -・23゜1m

Claims (1)

[Claims] (1) In order from the object side, a first lens group that has negative refractive power and moves along the optical axis during zooming, a first lens group that has positive refractive power and moves along the optical axis during zooming; a second lens group,
The third lens group has a negative refractive power and is fixed during zooming. It has 12 meniscus-shaped lenses with spherical surfaces and convex surfaces facing the object side, and the second lens group includes, in order, 21 lenses with positive refractive power, 22 lenses with positive refractive power, and 23 lenses with biconcave surfaces. , a zoom lens having 24 biconvex lenses, the third lens group having 31 meniscus lenses with a concave surface facing the image side, and satisfying the following conditions. (1) -0.65<f_1/f_T<-0.45(2)
0.43<r_2/r_3<0.63(3)r_9/R
_1_0<-15 (4)n_5>1.8 However, r_2: radius of curvature on the image side of the 11 lenses, r_3: radius of curvature on the object side of the 12 lenses, r_9: radius of curvature on the object side of the 23 lenses, r_1_0: radius of curvature of the 23 lenses on the image side, f_1: focal length of the first lens group, f_T: focal length of the entire system at the telephoto end, n_5: refraction of the Franhofer d-line of the 23 lenses rate. (2) The zoom lens according to claim 1, wherein the twelve lenses have an aspherical surface on the lens surface on the image side, and the aspherical surface has a radius of curvature that increases toward the periphery. (3) The local radius of curvature of the aspherical surface of the 12 lenses is:
3. The zoom lens according to claim 2, wherein the zoom lens is positive at the center of the lens and negative at the periphery. (4) When the Atsube number of the 31 lenses is ν_3, ν
The zoom lens according to claim 1, wherein the zoom lens satisfies the following conditional expression: _3>50. (5) The zoom lens according to claim 1, wherein the 31 lens is an aspherical lens. (6) The zoom lens according to claim 1, wherein the total lens length at the wide-angle end and the telephoto end is approximately equal.