JPS58224322A - Small-sized three-group zoom lens - Google Patents

Abstract

PURPOSE:To obtain a zoom lens which eliminates the need for a long focus and is suitable to a lens shutter type camera. CONSTITUTION:The lens system consists of the 1st - the 3rd groups which have positive, positive, and negative refracting powers successively from an object side; the 1st lens group includes at least >=2 positive lenses and at least one negative lens, the 2nd lens group includes at least one positive lens, and the 3rd lens group includes at least one negative lens. As the composite focal length of the whole system is varied from the shortest length to the longest length, the interval between the 1st and the 2nd lens groups is decreased monotonously and the interval between the 2nd and the 3rd lens groups is increased monotonously.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compact three-group zoom lens suitable for cameras that do not require a long back focus, particularly for lens-shutter cameras.

Recently, the portability, economy, and ease of operation of lens-shutter cameras have been reaffirmed, but at the same time, there is also a strong demand for their ability to function, and lenses with variable magnification [1? Lens-shutter cameras are in demand.

However, most conventional zoom lenses for still cameras are those developed for single-lens reflex cameras, and are designed to have the back focus necessary for quick return mirror operation, so even at the shortest focus position, It has a considerable size as a lens body, and is suitable for lens-shutter cameras.
If it is used in history, it will damage the mobile music.

Zoom lenses that do not have a long puncture focus are also known, such as the one described in Japanese Patent Laid-Open No. 56-128911. This zoom lens is composed of a lens group having a positive Jte refractive power and a second lens group having a negative refractive power, and the distance between the 02 and 0 lens groups is changed to perform a change. At the wide-angle end, the total length of the lens plus the back focus is about the same as the total system υ composite fishpoint distance at the wide-angle end, which is even better than on a portable camera.

17 or 1. / % In the above two-group zoom, there is no group that can completely cancel out the aberration fluctuations that occur in the second lens group due to zooming, that is, the strong positive distortion that occurs on the wide-angle side and the negative spherical aberration that occurs on the telephoto side. Therefore, by forming the second lens group with a thick structure consisting of a positive '7) L lens and a negative lens group arranged at a constant air interval in order from the object side, the second lens group can be Therefore, it was a good idea to try to correct the aberrations that occur. Increasing the air gap between the positive v single lens and the negative lens group in the second lens group is advantageous in suppressing negative spherical aberration that occurs on the telephoto side, but
Since it is disadvantageous in correcting positive distortion that occurs on the wide-angle side, the zoom ratio cannot be set very high, and the performance is unsatisfactory. FIG. 1 shows the refractive power arrangement of this type υ zoom lens and the movement path of each lens group O.

The present invention Vi is composed of three lens groups, in order from the object side: a lens group with a positive refractive power, a second lens group with a positive O refractive power, and a third lens group with a negative υ refractive power. As the combined focal length of the system is changed from the shortest to the longest, the distance between the first lens group and the second lens group υ is dramatically reduced, and the distance between the second and third lens groups is monotonically increased. An attempt is made to obtain a compact zoom lens system that does not have the above-mentioned drawbacks by creating a three-group zoom lens system as described above.

According to such a configuration, at the wide-angle end, the second positive lens group is close to the third negative lens group, producing the effect of correcting strong positive υ distortion and multiplier chromatic aberration generated by the third negative lens group. At the telephoto end, the second positive lens group and the third negative lens group are separated, so that the height of the paraxial ray in the second positive lens group is higher than the height in the third negative lens group, and the third negative lens group f )F It produces the effect of correcting the strong negative spherical aberration that occurs, and it is possible to maintain good power while having a sufficient zoom ratio. This relationship is shown in FIG. 2, a movement path diagram of the lens 11η. In order to obtain a zoom lens that has the above-mentioned basic structure and has good aberration O correction, the lens group must have at least two positive lenses and at least one negative lens. The second lens group needs to be made up of at least one positive lens, and the third lens group needs to be made up of at least one negative lens.

In the zoom lens of the present invention as in 7) above, both the second and third lens groups are located near one quadrant at the wide-angle end, and the paraxial ray height in these υ lens groups is In the Luns group, the paraxial 1 of / is considerably lower than the upper ray height.

For this reason, the effect of correcting spherical aberration and comatic aberration, which are the main aberrations, becomes small, so it is necessary that the first lens group '7) corrects these υ main aberrations. KoO
Therefore, in order to have a lens configuration such as a triplet that can independently correct aberrations well, the first lens group must be composed of at least two υ positive lenses and at least one negative lens.

Fourth, the zoom lens system of the present invention preferably satisfies the following conditions: 0 0, 5 fw < f+ < fw
...(1) 0.5/f1<l'/2+'Asl
<t5/f1. = (2) U < d2s(T)
-d23(w) (021f31...(3) However, fi: Composite focal length of the second lens group fw: Whole system '7) Shortest value of composite distance fT: Equivalent length value (123r
w) : Distance t from the 1st elephant side principal point of the 2nd lens group to the 3rd lens ti '7) vIJ body side principal point at fw
123(1・) - ``second limit of the condition (1) in the same < fr? If it exceeds the lens group, a negative lens group consisting of the second lens group and the third lens group with a paraxial lateral magnification greater than 1 cannot be placed behind the lens group.1.The basic configuration of the zoom lens system of the present invention It becomes impossible to meet the requirements. Also, if the lower limit is exceeded, the refractive power of the lens group becomes too strong, and sieve-order aberrations tend to occur on the telephoto side, making it difficult to achieve sufficient magnification. I can't take it anymore.

Condition (2) is related to the variable power ratio, and by continuing to arrange the second lens group and the third lens fJTi relatively close to each other over the entire %2 range, the refractive power of the synthetic thread can be increased. 66tl ('/f2-F'/'3' can be approximated by ,!
Negative V ball lJ generated at l0111! + Aberrations exceed the curvature of the meridian quadrant t? 11i I can't get it right.

If the lower limit is exceeded, the second half will have an advantage, but f medium 1
．． Having a sufficient variable power ratio of 5 or more is 44 clear.

Condition (3) is the change in the distance between the second and third lens groups, the negative spherical (3) aberration that occurs at the telephoto end and the wide-angle end, and +F-
v This is a condition for effectively using the distortion aberration υ correction, and when the upper limit is exceeded, the second lens and the third lens are closed at the telephoto end.
The paraxial axial light @ sieve υ difference becomes too large, and it becomes difficult to correct the spherical aberration and the axial chromatic aberration.

Hereinafter, examples of the zoom lens of the present invention will be shown.
The second and third rows show examples of bifocal lenses that use both the telephoto end and the wide-angle end. can also be υ.

First example focal length f=39. U7~fi 8. L) U
F 3.5~45 strokes 2W=56.4~3
5.3 (or later) fl=31.008 f2=68295
f3=-227313 Second actual example focal length f=42. :U(l-65,53F 3.5
-4.5 square 2W = 52.5 ~ 36.6 (
1&')fl=31.872 f2=Q2.068 f
3 = -27,967 Example 3 Focal length f = 42.30-65.118 F"3.
5-=1.51 angle 2W=52.5~3
6.6(K)fl=32.857 f2=74.074
f3=-26,835

[Brief explanation of the drawing]

Fig. 1 is a movement path diagram of a conventional zoom lens with a short back focus υ, and Fig. 2 is a movement path diagram of the zoom lens of the present invention υ゛.
Figures 3, 4, and 5 are the first one.
1. $2, 3rd
It is an aberration diagram of an example. 1 person, 1 person, 1 person, 1 person, 1 person, 1 person, 4 shares
Masu [41st person Fumi Sato (and 1 other person)]
name) w1 Figure 2 Figure ': 3 Figure 4 Figure 5 Spherical aberration JP, 4A aberration Distortion number X
゛Figure 6 71ヅ1 fl: 1fll convergence;', I: 1 ton aberration A・curve convergence, 7th spherical aberration J1 point sourness X O,:2 0.2 −0.2 F4.5 18 I・Difference in number of songs: 2° 18.2

Claims (1)

[Claims] In order from the object side, a lens group having a positive υ refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power.
Lens group: Consists of three lens groups, and as the combined focal length of the entire system is varied from the shortest to the longest, the distance between the 2nd lens group and the 2nd lens group υ decreases, and the distance between the 2nd lens group and the 3rd lens group increases. This is a three-group zoom lens system in which the zero distance between lens groups is increased to a certain extent, and the first lens group has at least two zero lenses.
A compact 3 lens comprising a positive lens and at least one negative lens, a second lens group comprising at least one υ positive lens, and a third lens group comprising at least one negative lens. group zoom lens