JPS59164517A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a front-group movable type zoom lens with high performance by providing four lens groups with positive, negative, positive, and positive refracting power from a subject side, and allowing them to meet specific requirements. CONSTITUTION:This zoom lens consists of four groups, and the 4th lens group includes >=1 positive lens, a negative single lens having a large radius of curvature on the subject side, a positive lens group including >=1 positive lens, a negative single lens having a large radius of curvature on the image side, >=2 positive lenses, and a negative single lens having a large radius of curvature on the subject side; and inequalities I -IV hold. In the inequalities, Fw is the shortest focal length of the whole system, F1 is the focal length of the 1st lens group, and nIV is the means refractive index of the d-line of lens elements constituting the 4th lens group; and fBW, fBT, and fBM are the shortest, the longest, and the longest back focuses of the whole system with focal length of 0.78 power, and nIVn is the mean refractive index of the d-line of three negative single lenses in the 4th lens group. Consequently, the lens system which has highly variable magnification and a wide angle of view is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high variable power zoom lens including wide-angle to telephoto lenses mainly for use in 35mm-eye reflex cameras.

With the progress and development of zoom lens design technology, the popularity of zoom lenses as interchangeable lenses for 35-eye reflex cameras has been remarkable.

Wide-angle zoom, standard zoom, telephoto zoom, etc. are currently in extremely wide use, and zoom lenses from wide-angle to semi-telephoto and zoom lenses from semi-wide-angle to telephoto have also become popular in recent years in response to user requests. be. However, there are very few compact zoom lenses that are high-performance, portable, and include a wide-angle lens with a comprehensive angle of about 77 degrees to a telephoto lens with a comprehensive angle of about 18 degrees. There are a few well-known zoom lenses for eye reflex cameras that are compact and relatively high-performance and have a high variable magnification range from wide-angle to telephoto, but such zoom lenses have a front lens diameter that is small by focusing with the normal front lens group. Focusing is performed by extending the entire lens to prevent the lens from becoming large, and a complex mechanical mechanism is used to move the focus due to zooming, which occurs when focusing with a varifocal lens or an optical system other than the front group for close objects. This creates manufacturing difficulties such as corrections.

The present invention relates to a zoom lens that achieves high performance and compactness while enabling focusing by moving the front group like conventional zoom lenses.

The present invention will be explained in detail below.

The present invention provides a first lens group having positive refractive power from the object side,
The first lens group has a negative refractive power, and the second lens group has a positive refractive power.
A zoom lens consisting of a lens group and a 2nd lens group having positive refractive power, each lens group moves independently in the optical axis direction as the focal length changes, and the 2nd lens group is A single negative lens with a tight radius of curvature facing the object side, a positive lens group containing one or more positive lenses, a single negative lens with a tight radius of curvature facing the image side, 2
Consists of at least one positive lens, a negative single lens with a tight radius of curvature facing the object, and (1) 0.25Fw < Fl < 0.45FW (2
) 1.65 < n engineering (3) 1.2f13w<f[3□<0.95fBM(4
) 1.8 < nTgfi However, the shortest focal length Fl of the entire F2 system: Focal length nV of the ■th lens group: d- of the lens elements constituting the ■th lens group
1ine average refractive index fBW "Back focus at the shortest focal length of the entire system fB□: Back focus at the longest focal length of the entire system f, 1., l: Focal point 0.78 times the longest focal length of the entire system Back focus ny7q at distance: d- of the three negative single lenses in the ■th lens group
This is a zoom lens with a high zoom ratio and a wide angle of view that satisfies each condition of the average refractive index of 1ine.

Condition (1) is a condition corresponding to focusing by extending the front lens group (first lens group) in the present invention, and when F□ becomes larger than the upper limit, the amount of extension of the focusing lens increases to ensure a sufficient shortest distance. This leads to an increase in the diameter of the front lens. On the other hand, if Fl is smaller than the lower limit, it is advantageous for making the optical system more compact, but the spherical aberration increases on the telephoto side, and within the range of existing glass materials, the chromatic aberration generated in the lens group on the telephoto side increases. Correction becomes difficult.

Condition (2) is a condition regarding the average value of the refractive index of the lens group (2) constituting the present invention. In order to ensure a high zoom ratio including a wide angle as in the present invention, the width of the light beam that passes through the ① lens group and converges near the center of the screen becomes wider from medium telephoto to telephoto, and It is extremely difficult to reduce the spherical aberration that occurs. Therefore, conventionally,
Among high-power zoom lenses, there were many that kept the brightness of the lens low from mid-telephoto to telephoto. The present invention is a zoom lens that ensures sufficient brightness even in medium to telephoto settings, and for this purpose, it is important to minimize the spherical aberration occurring in the 1st lens group. In other words, when - becomes smaller than the lower limit in condition (2), the radius of curvature of the lens group (2) becomes tighter on average, and the occurrence of spherical aberration increases. It becomes difficult to design.

Condition (3) is such that when a high variable power zoom lens including a wide angle lens is implemented with an optical system of a 4-group independently movable type as in this configuration, the state of movement of each lens group as it changes magnification is arbitrary. However, it defines the conditions for movement of the 2nd lens group in order to achieve good aberration correction. In other words, unless the lens group ■ moves so that f and □ become larger than the lower limit from wide-angle to telephoto, it is necessary to increase the power of the lens group ■ to ensure a high zoom ratio that satisfies this specification. There is an increase in the number of configuration sheets.

An increase in the number of lenses in the second lens group becomes an extremely disadvantageous factor in reducing the diameter of the front lens, and also increases costs.

Furthermore, unless the Ⅰth lens group moves so that f6□ becomes smaller than the upper limit from mid-telephoto to telephoto, the screen to the ① lens group must be moved to ensure the brightness of the embodiment of the present invention on the telephoto side. The beam of light that converges near the center of the lens becomes too wide, making it difficult to correct spherical aberration.

Condition (4) is d of the three negative single lenses in the ■th lens group.
-1ine average refractive index, and if nWn is smaller than the lower limit, the radius of curvature in these negative single lenses becomes tight, leading to worsening of astigmatism in the entire zoom range and worsening of spherical aberration on the telephoto side. Therefore, unless this condition (4) is satisfied, sufficient brightness cannot be ensured on the telephoto side as in the embodiments of the present invention.

Next, data of an example of the zoom lens of the present invention will be shown. Here, F is the focal length and r is the radius of curvature of the lens.

d is lens thickness or lens spacing, n is lens d-1in
The refractive index of e is the Abbe number for d-1ine of the lens.

[Example 1] F=28.806 to 132.342
No, r d n
ν1 505.700 2.00
1.80ri18 25.42 69.1
20 1.883 71.400 9.
84 1.72916 54.74 -4
44.818 0.155 66.300
5.69 1.88300 40.86
175.741 Variable interval 7 1B4.399 1.20 1.8
8300 40.88 18.240
5.709 -119.280 1.30
1.81600 46.610 57
．． 091 0.1011 28.002
7.41 1.75520 27.512 -
28.002 1.20 1.81600 46
．． 613. 75.000 variable interval 14
26.470 2.00 '1.75520
27.515 22.339 2.001
6 33.299 3.30 1.7725
0 49.717, 154.400 Variable interval 1B 31.120 4.50 1.61
800 63.419 -206.849
2.2220 -32.889 1.20
1.80518 25.421 -181
．． 168 0.2022 32.889
9.39 1.62041 60.323
-52.500 0.3024
260.000 1.30 1.834B1
42.725 24.157 2.
3026 35.862 4.84
1.48749 70.127 -61.4
11 0.2028 104.599
5.06 1.66680 33.029
-36.800 3.2130 -1
9.380 1.30 1.88300
40.831 -88.200 FE =0.31FWII]V=1.702fB, =
0.91 fBM= 1.54 fBy,, nWn=
+, 941 [Example 2] F = 28.801
〜132.316Nα r
d n ν1
270.359 2.00 1.8
0518 25.42 66.762
1.403 68.597 9.
39 1.72916 54.74 -1
277.450. 0.155 66.
300 6.00 1.81600 46
．． 66 218.700 Variable interval 7 242.19g 1.20
1.88300 40.88 1B,
768 5.709 -117.780
1.30 1.83481 42.710
．． 50.845 0.1011
28.598 7,41 1.8051
8 25.412 -28.598
1.20 1.88300 40.813
79.199 Variable interval 14 27.
300 2.00 1.80518 25
．． 415 23.370 2.001
6 35.000 3.30 1.
77250 49.717 349.704
Variable interval 18 29.989 4.5
0 1.61800 63.419
6450.000 2.6920, -31
．． 514 1.20 1.80518 2
5.421 -226.050 0.202
2 34.871 8. ．． 80 1
．． 56873 63.223 -54.3
00 0.3024 118.902
1.30 1.83481 42.725
25.97J) 2.3026
39.900 4.88 1.4874
9 70.127 -59.800
0.2028 136.110 5.06
1.67270 32.129 -
37.200 4.4230 -19.60
0 1.30 1.88300 40.8
31 -65.243 F1= 0.32 FW n, = 1.69
6f8. =0.89f, 1.1=1.58f13w
ny, = r, 84r [Example 33 F = 28.
820~132.448No, r
d n ya1 377.370 2.00 1.
80518 25.42 69.147
1.203 70.160 9.
77 1.72916 54.74 -
533.185 0.155 69.1
20 5.39 1.88300 40.
86 178.352 Variable interval 7 183.798 1.20 1.
88300 4σ, 88 1B, 372
5.709 -116.421 1.
30 1.83481 42.710
57.600 0.1011 27.
9L5 1.00 1.80440 39
．． 612' 21.000 6.61
1.75520 27.513 -29
．． 210 1.00 1.81554 4
4.414 76.700 Variable interval 15
26.946 2.00 1.75520
27.516 22.606 2.0
017 33.306 3.30 1.7
7250 49.618 173.952 Variable interval 19 31.800 4.50 1
．． 61800 63.420 -2139.3
38 2.3621 -32.000 1
．． 20 1.8[)518 25.422
-195.000 0.2023 34.
040 7.12 1.67000 57.42
4 -30.134 2.00 1.568
73 63.125 -96.900 0
．． 3026 165.100 1.30 1
．． 88300 40.827 25.06
4 2.3028 37.980 5.
08 1.48749 70.129 -5
1.300 0.2030 193.485
' 5.06 1.66680 33.031
-36.395 4.3232 -
19.080 1.30 1.88300 40
．． 833 -56.405 F ni = 0, 30 Fw ni = 1,
883fB7 =0.94 fBM=1.59 fB
W n1yn ” '=”7

[Brief explanation of the drawing]

FIG. 1 is a lens configuration diagram of Example 1 of the present invention, and
The figure is an aberration diagram of Example 1, and Figure 2 shows the time at the shortest focal length.
FIG. 3 shows the first intermediate focal length, FIG. 4 the second intermediate focal length, and FIG. 5 the longest focal length. Figure 6 is a lens configuration diagram of Example 2 of the present invention, Figures 7 to 1O are aberration diagrams of Example 2, Figure 7 is at the shortest focal length, and Figure 8 is at the first intermediate focal length. , FIG. 9 shows the state at the second intermediate focal length, and FIG. 10 shows the state at the maximum focal length. Fig. 11 is a lens configuration diagram of Example 3 of the present invention, Figs. 12 to 15 are aberration diagrams of Example 3, Fig. 12 at the shortest focal length, and Fig. 13 at the first intermediate focal length. , FIG. 14 shows the state at the second intermediate focal length, and FIG. 15 shows the state at the maximum focal length. Fig. 1 Fig. 2 Sine condition Fig. 3 Sine strip Fig. 4 Sine condition 8 Fig. 9 Sine condition Fig. 10 Fig. 11 Fig. 12 Sine condition Fig. 13 Fig. 14 Sine condition Spherical aberration Chromatic aberration I Point guard sine condition

Claims (1)

[Scope of Claims] 1. From the object side: a first lens group having a positive refractive power, a ■ lens group having a negative refracting power, a ■ lens group having a positive refractive power, and a ■ lens group having a positive refractive power. This is a zoom lens in which each lens group moves independently in the optical axis direction as the focal length changes, and the first lens group has one or more positive lenses and a tight radius of curvature on the object side. Positive lens group containing one or more positive lenses, Negative single lens with a tight radius of curvature facing the image side, Positive lens with two or more positive lenses, Negative single lens with a tight radius of curvature facing the object side (1) 0.25FW<F engineering<0.45FW (2)
1.65 < n (3) 1.2 fBW < fI3-1 < 0.95
f, M(4) 1.8 < nV. However, Fw: Shortest focal length of the entire system Fe: Focal length of the first lens group n1v" d of the lens element constituting the th lens group
-1ine average refractive index few: Back focus fB at the shortest focal length of the whole system: Back focus fB at the longest focal length of the whole system, 1: When the focal length is 0.78 times the longest focal length of the whole system Back focus n[)q: d- of the three negative single lenses in the ■th lens group
A zoom lens with a high zoom ratio and a wide angle of view that satisfies each condition of the average refractive index of 1ine.