JPS6057813A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a telephoto zoom lens system of compact constitution which has high variable power, i.e. almost within a photographic view angle variation range of about 35-12 deg. while excellent aberration compensation is performed and flare is small over the entire focal length range by using a glass material with abnormal divergency effectively. CONSTITUTION:The zoom lens consists of the 1st lens group having positive refracting power, the 2nd lens group having negative refracting power, the 3rd lens group having positive refracting power, and the 4th lens group having positive refracting power successively from an object side. Then, the gap between the 1st and the 2nd lens groups and the gap between the 2nd and the 3rd lens groups are varied and the 3rd lens group is moved to hold the image forming position constant. The compensation of the secondary chromatic aberration at the zoom position of the telephoto end is performed excellently by using glass having abnormal divergency as the positive lens of the 1st lens group. In this case, glass satisfying an inequality as to the relation with the Abbe number of the glass of the negative lens is used to compensate the on-axis chromatic aberration and the spherical aberration of the 1st lens group.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens, and in particular to a telephoto zoom lens in which the range of change in the shooting angle of view is approximately 35 degrees to 12 degrees. However, a zoom lens with a short overall length and good portability is disclosed in Japanese Patent Application Laid-Open No. 53-97451. This method has been proposed in Japanese Patent Application Laid-Open No. 56-42208. However, the zoom lenses proposed above generally have a large amount of secondary chromatic aberration remaining on the telephoto side, and flare is not sufficiently removed over the entire focal length range. Secondary chromatic aberration is mainly caused by the wavelength characteristics of the glass material, and flare is mainly caused by increasing the refractive power of each element of the lens in order to shorten the overall length of the lens.

It is generally known that it is effective to use anomalous dispersion glass such as fluorite to correct secondary chromatic aberration. However, since the refractive precipitation of anomalous dispersion glass is low, in order to obtain the desired refractive power, the four cardinal radii of the lens surfaces must be made small, and as a result, flare occurs from these lens surfaces. There were drawbacks. Therefore, even with the use of anomalous dispersion glass, it has been difficult to achieve a zoom lens f that has a high magnification potential, is concise, yet corrects secondary chromatic aberration well, and sufficiently eliminates flare. In view of the above-mentioned drawbacks, the present invention provides a compact and high-power zoom lens that effectively uses a glass material with anomalous dispersion and achieves good aberration correction with little flare over the entire focal length range. The main features of the lens configuration for achieving the object of the present invention are, in order from the object side, an i lens group having a positive refractive power, a second lens group having no negative refractive power, and a positive lens group having a positive refractive power. A third lens group having a refractive power of 3 and a 4th lens group having a refractive power of 3. , and in which the image forming position is kept constant by moving the third lens group, the third lens group is composed of a negative lens, a positive lens, and a positive lens in order from the object side, and the second lens group is composed of a negative lens, a positive lens, and a positive lens in order from the object side. The group consists of a negative lens and a cemented lens of a negative and positive lens in order from the object side, the third lens group consists of a cemented lens of a positive and negative lens in order from the object side, and the fourth lens group consists of a cemented lens of a negative and negative lens in order from the object side. N1-j and N1-4
are the Atsbe number and refraction coefficient of the glass of the j-th lens of the i-th lens group, respectively. Let be the radius of curvature of the j-th lens surface of the i-th lens group, let Stone be the average refraction of the glass of the lens in the second lens group, and let fW be the focal length at the zoom position at the wide-angle end, then sil-2- Sie 1〉45.0・Mountain・・Song・Song・・
...Mountain... (1)n, > 1.72...
・・・・Bright・・・・・・・・・・Old・Song・・Side・
(2) -0,30<03-1-n3. <-0,1
5. times-・-(3)-〇, 33〈n4-2 ”4-3
< −0,16−・−・−Song−(4) o, sf, ,,
< l r2-41 < o, 6ztw-=------
-------(5) is to be satisfied.

In the present invention, by using the above-mentioned zoom type, the overall length of the lens is shortened, and the above-mentioned conditions are further satisfied to achieve good aberration correction. In other words, in order to satisfactorily correct secondary chromatic aberration at the telephoto end zoom position, it is most effective to use anomalous dispersion glass for the positive lens of the lens group. At this time, longitudinal chromatic aberration and spherical aberration occurring in the lens group are favorably corrected by using a glass whose relationship with the Abbe number of the negative lens is the equation (1) plus /1illII.

If Conditional Expression (1) is not satisfied, the secondary chromatic aberration at the telephoto end zoom position will not be sufficiently corrected, which is not suitable. The second lens group is a lens group that mainly performs magnification change, and by suppressing the aberrations of this partial system to a small level, aberration fluctuations during zooming are reduced. In the present invention, the radius of curvature of each lens surface is made looser by increasing the average refraction name of each lens so as to satisfy the condition of equation (2), thereby creating a high T surface!勺尤Y1guILυ≠haaka-i1+or nailshi/1iτ
If Conditional Expression (2) is not satisfied, the radius of curvature of each lens surface must be made small, which is undesirable because aberration fluctuations due to zooming become large.

Equations (3) and (6) are conditional expressions that determine how to select the glass material for the third lens group and the appropriate value of the radius of curvature of the cemented lens surface.
If the upper limit of equation (3) is exceeded, the spherical aberration will be under-corrected, and if the lower limit is exceeded, the spherical aberration will be over-corrected. However, zooming increases fluctuations in astigmatism, which is not desirable. If the upper limit of equation (6) is exceeded, it becomes difficult to properly correct spherical aberration and Hosochromatic aberration at the same time.
If the expansion value is exceeded, it becomes difficult to correct variations in off-axis chromatic aberration due to zooming, and the off-axis chromatic aberration varies greatly for each angle of view, which is undesirable. This is a conditional expression for appropriately determining the refractive wheel difference between the second lens and the third lens.If the upper limit value is exceeded, the image plane at the intermediate focal length will be overextended, spherical aberration will be undercorrected, and other If you make further corrections in certain areas, flare will occur. Moreover, if the lower limit is exceeded, the image plane on the telephoto side becomes undersized, which is not preferable.

Equation (5), together with conditional expression (2), relates to the second V lens group. Conditional expression (2) maintains the average refractive index of the second lens group appropriately, and also This is to make the spherical aberrations of different wavelengths the same by appropriately determining the cemented lens surface of the cemented lens of the lens. If the lower limit of equation (5) is exceeded, short wavelength spherical aberration will be over-corrected on the wide-angle side and under-corrected on the telephoto side.

If the upper limit is exceeded, the spherical aberration will be overcorrected in the partial system of the second lens group, and flare will occur over the entire focal length, which is not preferable.

The zoom lens of the present invention is achieved by satisfying the above conditions, but in order to achieve better aberration correction, it is preferable to satisfy the following conditions. That is, if the refractive powers of the two positive lenses constituting the lens group are respectively ψ, -2, and ψ1-2 in order from the object side, then 071〈ψ1-3/ψ+-z (1, 51...
......(7) is to satisfy the condition.

Conditional expression (7) is an appropriate refractive power distribution in order to effectively use the anomalous dispersion glass in the Luns group,
If the upper limit value is exceeded, the effect of correcting secondary chromatic aberration will be reduced, and if the lower limit value is exceeded, it will become difficult to correct Hosochi chromatic aberration, spherical aberration, and aberration fluctuations due to focusing.

In the zoom lens according to the present invention, if anomalous dispersion glass is used in the lens group, it is most effective in correcting secondary chromatic aberration at the telephoto end zoom position, but if it is used in a lens near the aperture, it can be used in a wide-angle lens group. Secondary chromatic aberration can be well corrected at the side zoom position.

In the embodiment of the zoom lens of the present invention, high image quality is achieved by using the positive lens of the third lens group or the positive lens of the second lens of the fourth lens group. If the idea is to use it for a lens in a position near the aperture where a large axial light beam passes through, it would be possible to achieve the same effect even if it is used for other types of zoom lenses; In a zoom lens, the third lens of the fourth lens group
It is preferable to provide a member that blocks toxic light and glands at an intermediate angle of view at an appropriate position between the lens and the fourth lens, since the optical performance can be further improved.

The idea behind the zoom lens according to the present invention is that it is a type of zoom lens in which the distance between the first lens group and the second lens group, and the distance between the second lens group and the third lens group changes with zooming. It can also be applied to any type of zoom lens. The second. Type in which the third lens group moves, first and second
．． It is not only applicable to the type in which the third lens group moves; for example, the first lens group. The present invention is also applicable to a type of zoom lens in which the third lens group moves.

In addition, in the present invention, focusing is performed by moving the 4th lens group, which reduces aberration fluctuations, but if focusing is performed by moving part or all of the 4th lens group, the amount of movement can be reduced. preferable.

Next, numerical examples of the present invention will be shown. In numerical examples R
i 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 gap in order from the object side,
N1 and νi are the refraction coefficient and Abbe number of the glass of the first lens, respectively, in order from the object side.

1st example F=71.5~205.13 F/l6=l:4.1
2ω=33.7~12,0f3=90.529 f4
=119.880 Second Example F=71.0-203.69 FA=t:4. t2ω
=33.9~12.1f3=90.529 f4=l1
9.047 Third Example F=rx, o~203.69 F'ma=1:4.14
2ω=33.9°~12.1'f3=90.529 f
4=l17.941 4th example R24=-83,54 t1=106.08 n=-3z, 78i3=90
．． 35 r4=txs, 29 Fifth Example F'=71.5~191.097 FA6=t:
4.1 2ω=33.7~12.9fl=105.35
6 f2=-32,000f3-90.529f4-1
05.552 As explained above, according to the present invention, it is possible to achieve a zoom lens with a telephoto ratio of about 0.9, which is a compact zoom lens, but has very good aberration correction throughout the entire focal length. be able to. In particular, the width of secondary chromatic aberration at the telephoto end zoom position can be suppressed to about one-third of that when conventional general glass materials are used. Further, if a zoom type lens is adopted in which the lens group is moved during zooming, as in the fifth embodiment, the overall length of the lens can be further shortened.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a lens structure according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of a lens structure according to a fifth embodiment. 3 to 7 are diagrams of various aberrations of Examples 1 to 5 of the present invention. In Figures 3 to 7, (a), (b), (
C) is at the wide-angle end and middle, respectively. Diagram of various aberrations at the telephoto end zoom position. In the figure, d is the spherical aberration of the d-line, the spherical aberration of the grt-g line, and S
, C represents the sine condition, M represents the meridional component, and S represents the image plane of the sagittal component. The diaphragm 15 in FIG. 1 and the i-mo 14 in FIG. 2 represent a diaphragm and are a diaphragm for preventing SFD flare in the 0th and 4th lens groups.

Claims (1)

[Claims] (1) In order from the object side, a lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a lens group having a positive refractive power. a fourth lens group, the distance between the lens group and the second lens group and the distance between the second lens group and the third lens group are changed, and the third lens group is moved. A zoom lens configured to keep an image position constant, wherein the first lens group is made up of a negative lens, a positive lens, and a positive lens in order from the object side, and the second lens group is made up of a negative lens in order from the object side. The third lens group is composed of a cemented lens of a negative and a positive lens in order from the object side, and the fourth lens group is composed of a cemented lens of a positive lens and a negative lens in order from the object side. −/ 工 １ノ り −／ 】−１イ A １
+ -ノ +/ 1 Sun haze resistance - Consisting of a negative lens and a positive lens separated by distance, shimmy 4 and N1-j are respectively the Atsube number of the glass of the j-th lens of the fifth lens group and the refraction book, 几i
−j is the clay radius of the Fjth lens surface of the fifth lens group,
'z is the average refractive group 1 of the glass of the lens of the m2 lens group,
When fw is the focal length at the zoom position at the wide-angle end, shoe 2-shi'1-t ) 45.0 n, ) 1.72 -0.30 < n3. -n3. (-0,15-0,
33< n4-2-n4-1(-0,160,5f,,
<l r2.1< 0.62fwO, 32fw<Ir
A zoom lens that satisfies the following conditions: 3-21<o, 52fw. (2) If the refractive powers of the two positive lenses constituting the lens group are respectively ψ, -2, and ψ1-3 in order from the object side, then 0.71<91-8/ψ, -2<1.51 Sotosunesha 7. The zoom lens described in item 1 above.