JPS6031110A - Zoom lens - Google Patents

Abstract

PURPOSE:To make a titled zoom lens compact, and also to convert a photographing view angle at a zoom position of a wide angle end, to a wide angle, by moving independently the first lens group - the third lens group, in case of zooming. CONSTITUTION:The fourth lens group of a positive refractive power which is fixed in the course of zooming is place. Accordingly, the first lens group through the third lens group have a positive refractive power, therefore, its refractive power becomes weaker than a positive refractive power of the whole system. Also, when the refractive power of the third lens group is made the same as a conventional one, the refractive power of the first lens group and the second lens group can be made weaker than a conventional one, and an aberration variation due to zooming is reduced. Also, when zooming to a telephoto end from a wide angle end, the second lens group moves to the direction of an object side, and in this case, the third lens group is moved to the direction of the same object side as the second lens group. It is executed easily to make it compatible to make a zoom lens compact and have a high performance, by controlling a ratio of a moving extent of the third lens group against this second lens group.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens, in particular a zoom magnification starting from the focal length of a standard lens for a TTL 35 mm single-lens reflex camera or a shorter focal length, preceded by a lens group of negative refractive power. This relates to a zoom lens with a diameter of about 2 to 3.

Conventionally, it is composed of three lens groups, in order from the object side: the first lens group with negative refractive power, the second lens group with positive refractive power, and the third lens group with negative refractive power, and these lens groups are independent. British patent 39830 allows you to zoom by moving to
7. JP-A-54-26754, JP-A-57-502
3, proposed in Japanese Patent Publication No. 57-13850, etc. These zoom types have two types: negative refractive power and positive refractive power.
Compared to a zoom lens composed of two lens groups, it can achieve higher magnification, and can also be made more compact or higher in performance to some extent. However, when trying to make a zoom lens more compact or widening the angle of view at the wide-angle end zoom position, the refractive power of each lens group must be strengthened, and zooming and focusing (the first lens When focusing is performed in groups), variations in various aberrations become large, making it extremely difficult to achieve high performance and large apertures. In particular, as the refractive power of the second lens group increases, aberration fluctuations due to focusing and zooming tend to increase, and as the refractive power of the second lens group increases, aberration fluctuations due to zooming tend to increase.

Another conventional example is from the object side.

It is composed of three lens groups: the first lens group with negative refractive power, the second lens group with positive refractive power, and the third lens group with positive refractive power, and these lens groups move independently to perform zooming. has been proposed, for example, in Japanese Patent Laid-Open No. 56-158316. This is because the second and third lens groups are close to each other at the wide-angle end zoom position, and although the shooting angle of view at the wide-angle end is relatively wide, F/4 is bright and the aberration correction is good. It has certain characteristics. However, if zoom lenses are made more compact, or if the angle of view is widened at the wide-angle end zoom position, the refractive power of each lens group must be strengthened, as in the conventional example, so zooming Alternatively, there was a tendency for fluctuations in various aberrations due to focusing to become large.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compact, wide-angle zoom lens that achieves wide-angle imaging at a zoom position at the wide-angle end.

The main features of the lens configuration for achieving the purpose of the present invention are, in order from the object side, the first lens group with negative refractive power, the second lens group with positive refractive power, and the third lens group with positive refractive power. It has four lens groups, including a fourth lens group with positive refractive power, and the fourth lens group, second lens group, and third lens group are moved independently during zooming.

More preferably, the lens configuration is such that the lens group and the second lens group are closest to each other at a telephoto end zoom position, and the third lens group is closest to the fourth lens group at a wide-angle end zoom position. That's true.

A feature of the present invention is that, compared to the conventional example, a fourth lens group having a positive refractive power that is fixed during bezooming is provided. Therefore, since the lens group from the lens group to the third lens group has positive refractive power, the refractive power is weaker than the positive refractive power of the lens group from the lens group to the fourth lens group (the entire system). This allows the refractive power from the first lens group to the third lens group to be weaker than that of conventional zoom lenses, and as a result, higher performance is possible. Furthermore, when the refractive power of the third lens group is made the same as the conventional one (the latter example), the refractive power of the third lens group and the second lens group can be made weaker than the conventional one, and focusing,
and aberration fluctuations due to zooming are further reduced,
It becomes easier to realize higher performance and larger diameter. Furthermore, in order to make the zoom lens more compact, the arrangement of each lens group at the wide-angle end and the telephoto end is configured as described above. That is, when zooming from the wide-angle end to the telephoto end, the second lens group moves in the object side direction, and at this time, the third lens group moves in the same direction as the second lens group. By controlling the ratio of the amount of movement of the third lens group to the second lens group, it becomes easy to make the zoom lens both compact and high-performance.

As the ratio of the amount of movement is decreased, aberration fluctuations due to zooming tend to decrease, but the total lens length (distance from the first surface to the film surface) at the telephoto end becomes longer, and if the ratio is further increased, the aberration fluctuations due to zooming tend to decrease. It becomes longer than the total length of the lens. Furthermore, increasing the ratio of the moving amounts causes a tendency opposite to the above, which is not preferable. Here, the ratio of the amount of movement of the third lens group to the second lens group is desirably larger than 0.4 and smaller than 1.5, and furthermore, it is close to this embodiment, i.e., larger than 0.7 and smaller than 1.3. This makes it extremely easy to achieve both compactness and high performance. In other words, it is preferable to achieve high performance within a range where the total length of the lens at the telephoto end is not longer than the total length of the lens at the wide-angle end (the limit of compactness). At this time, it is the second lens group that obtains the most magnification through movement, so in order to maintain compactness, it is necessary to move the second lens group efficiently, at least at the telephoto end. It is preferable that the lens group and the second lens group are placed closest to each other. In addition, the 3rd and 4th lens groups do not have very strong refractive power, so in order to shorten the overall lens length and secure the necessary amount of back focus at the wide-angle end, the 3rd and 4th lens groups are closest to each other at the wide-angle end. The lens configuration is good.

Although the objective of the present invention is achieved with the above lens configuration, in order to achieve even better aberration correction and to achieve a compact zoom lens, it is preferable to satisfy the following conditions.

Said 1st. Second. When the focal lengths of the third and fourth lens groups are respectively f, , f, , f, and f, and the focal length of the entire system at the telephoto end zoom position is fT, (1) i<ra/fT< 5 (2) 0.5 < lfl l/fT < 1.2 (3
) 't < I fr l <.

Conditions (1), (2), and (2) limit the refractive power of each lens group, and are especially necessary to achieve both compactness and high performance when realizing a zoom lens for a TTL 35 mm reflex camera. Below the lower limit of condition (2), it becomes difficult to form the fourth lens group into a simple lens structure, resulting in an increase in the size of the zoom lens. Above the upper limit, the refractive power of the fourth lens group becomes too weak, and the effects of compactness and high performance are diminished. Below the lower limit of condition (2), the total lens length tends to be longer at the telephoto end than at the wide-angle end, and furthermore, it becomes difficult to increase the aperture or to satisfactorily correct spherical aberration at the telephoto end. If the value exceeds the upper limit, the overall length of the lens at the wide-angle end will not be shortened enough. In addition, the second lens group has the function of increasing magnification, so it needs to have the strongest refractive power, and the second lens group is the next lens group to refract because it controls the front lens diameter or the amount of focusing. It is necessary to make the power stronger, and the third lens group uses the third lens group and the second lens group to eliminate aberration fluctuations due to magnification and zooming.
It is preferable that the refractive power is weaker than that of the lens group. On the other hand, the fourth
The first lens group is mainly used to eliminate aberration fluctuations caused by zooming. It is preferable that the refractive power is weaker than that of the second lens group.

Next, the aberrational effect of the fourth lens group having positive refractive power, which is a feature of the present invention, will be described. Table 1 shows the third-order aberration coefficients of a numerical example of the present invention, and since the fourth lens group is fixed during zooming, the spherical aberration (Sum) is constant. However, there are some aberrations that are not constant during zooming, and coma aberration (CM) causes extroverted coma most often at the wide-angle end. In general, if you use a zoom type lens that has negative refractive power and the wide-angle end has a large angle of view and is compact, there is a tendency for inward coma to appear near the principal ray of the off-axis beam near the wide-angle end. The fourth lens group is effective in canceling out this introverted coma. Also, on the telephoto side, the value is small and there is little negative effect. As a result, in the present invention, the aberration of the AC component generated from the first to third lens groups by the fourth lens group (an amount that varies depending on zooming)
can be effectively canceled out, making it easy to improve performance. Therefore, a so-called rear attachment lens (which alone eliminates aberrations) is attached between the conventional zoom lens consisting of three lens groups (aberrations are eliminated in the entire system) and the image plane. The effects of the fourth lens group of the present invention are completely different from those of the above lens system.

In the zoom lens according to the present invention, focusing is normally performed for different object distances by extending the first lens group. 4
It is also possible to perform lens group focusing, and such a configuration is preferable because it is mechanically simple.

Next, numerical examples of the present invention will be shown. In the numerical example, the radius of curvature of the first lens surface, Di
are the fifth lens thickness and air spacing in order from the object side, N
i and νi are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

Numerical Example 1 F=100-195 FA=1:4.2-4.7 2ω
=34~63.4R1=490.01 DI=1
2.67 N l=1.72916 ν1= 54.7
82=-3024,79D 2=0.43R3=・
−261,89D 3= 7.19 N 2=1.80
610 C2=40.9B, 6=-190,22D
6= 10.17R7= -155,72D 7= 4
．． 39 N 4=1.80610 ν4=40.988
= 166.54 D 8 = 8.13 R9 = 98.
48 1) 9=11.08 N 5=1.8466
6 ν5= 23.9R1O= 157.00 D10
= Variable PLlt= 111.23 D11= 9.4
7 N 6=l, 72916 Shiro=54.7R12=
3040.15 DI2= 0.29R13= 94
．． 23 D13=10.26 N7=1.6204
1 Schiff=60.3R14=557.28 D14=
2.23R15= Aperture D15= 5.76 R16= -198,81D16= 12.66 N8
=1.64769 ν8= 33.8R17= 69.
61 D17= 10.04R18= 780.47
D18= 11.11 N 9=1.60729 ν9
=49.2R19= -102,76D19= Variable R
20= 170.66 D20= 11.76 N10
=1.71300 ν10=53.8B21=-92
,94D21=5.82 N11=1.59551
ν11= 39.2R22= 171.64 D22=
Variable fu3 = 216.84 D23 = 12.33
N12=1.48749 ν12=70.1R24
= 409.60 Numerical Example 2 F=100.0~204.9 F=l:4~4.52
ω=40.6°-74,3°R1= 311.49 D
I=8.05 N1=1.72000 Si1=43.
7R,2= 88,65 D 2= 23.54R3=
-680,58D 3= 13.30 N 2=1.
61293 Shi2=37.0R4=-159,47D
4=1.47R5=-385,75D 5=6.
58 N3=1.77250 C3=49.6R8=
131.36 D8= 14.01 N5=1.64
769 ν5= 33.8R9= 838.07 D9
= variable 1 (10 = 185.27 DIO = 10.50 N
6=1.69350 Shiro=53.2all=-122
8,02D11= 5.60R12= Aperture DI2=
1.75 Rta= 86.16 D13= 8.50 N 7=
1.60729 Schiff=49.2R1'4=214.
69 D14= 3.54115= 102.55 D
15=19.49 N8=1.61484 C8=5
1.2R16= 235.12 D16= 2°87R
17=-1196,75D17=15.78 N 9
=l, 84666 ν9=23.9R18=65.5
0 D18= 5.11819= -340,73D1
9=5.97 N10=1.63636 plO=3
5.4B, 20=-98,55D20= variable R21
= 371.07 D21. = 7.00 N11=1
．． 62588 Shi11=35.7R22=509.0
8 D22= 7.00 N12=1.53113 C12=62.4R23= 3500.11 D23=
Variable R25=-260,79

[Brief explanation of drawings]

FIGS. 1 and 2 show numerical example 1 of the present invention. 2, FIG. 3, and FIG. 4 are various aberration diagrams of Numerical Example 1.2 of the present invention. In the figure, arrows indicate movement states due to zooming. M is a meridional image surface, and S is a sagittal image surface. I, 1
．． III and IV are respectively No. 1. 2nd゜3rd. This is the fourth lens group. F, -15y, 24- CH=/6 crime

Claims (1)

[Claims] (1) In order from the object side, the first lens group has a negative refractive power, the second lens group has a positive refractive power, the third lens group has a positive refractive power, and the fourth lens group has a positive refractive power. It has four lens groups,
A zoom lens characterized in that the first lens group, the second lens group, and the third lens group are each independently moved during zooming. (2) The lens group and the second lens group are closest to each other at a telephoto end zoom position, and the third lens group is closest to the fourth lens group at a wide-angle end zoom position. A zoom lens according to claim 1. (3) Above 1. Second. Let the focal lengths of the third and fourth lens groups be fIsfts and f4, respectively, and let the focal length of the entire system at the telephoto end zoom position be fth, then 1 <f+/'T< 8 0.5 <1'+1 /fT < 1.2ft <
A zoom lens according to claim 1 or 2, characterized in that the zoom lens satisfies the following condition: 1fll<ts.