JPS60126618A - Zoom lens - Google Patents

Abstract

PURPOSE:To reduce the number of lenses, and to reduce deterioration of a performance caused by a temperature variation by forming a plastic lens, whose one surface has a non-spherical shape, and a relay lens system constituted by containing said lens, so that a specified condition is satisfied. CONSTITUTION:A relay lens system having an image forming function is constituted of lenses L8-L12, and as for the lens L9 among them, the sixteenth surface of an image side is a plastic lens of a non-spherical shape, and a focal distance satisfies an expression I . Unless this condition is satisfied, a moving extent of an image forming surface by a temperature variation becomes larger than a depth of focus within a working temperature range of a zoom lens for a video camera, and its lens is not used practically. Also, with respect to a small number of lenses and a large aperture ratio, the non-spherical aberration can be corrected by leading in a non-spherical shape. Moreover, when the relay lens system satisfies expressions II-V, the aberration correction can be further advanced. In this way, the number of lenses is reduced, and deterioration of a performance caused by a temperature variation can be reduced.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to a zoom lens for a video camera, and in particular, a zoom lens for a video camera that reduces the number of lenses by utilizing an aspherical plastic lens, thereby realizing a compact and lightweight zoom lens. It concerns aperture and high-performance zoom lenses.

Conventional configurations and their problems Recently, operability and mobility have been emphasized in video cameras, and in response to this demand, image pickup tubes are becoming smaller and lighter.

There is a strong demand for high-performance zoom lenses with large aperture ratios and large zoom ratios. Furthermore, there is a strong desire to reduce costs, and there is a strong need to realize a zoom lens that reduces the number of lenses while maintaining high performance.

On the other hand, the F number is about 1.4. Conventional large-diameter, high-performance zoom lenses with a zoom ratio of approximately 6 times have the disadvantage of having a large number of lenses (14 to 15 lenses) and having a long overall lens length.

In conventional zoom lenses, each group that makes up the variable power section is often configured with three lenses from the first lens group, three lenses from the second lens group, and one lens from the third lens group, but the reduction in the number of lenses is achieved by using a relay lens system. I'm confused about the structure. There are limitations to this relay lens system, such as the exit pupil position needing to be at least a certain distance from the image plane to prevent color shading, and the need for a long back focus because the crystal is placed in front of the image plane. ,
There is a strong demand for the creation of an appropriate relay lens system with good aberration performance and a small number of lenses.

In order to reduce the number of lens components while maintaining the imaging performance of the lens system, it is effective to use a lens having an aspherical shape. However, a glass lens having an aspherical shape has a drawback in that it is difficult to mass-produce it and is also expensive. On the other hand, aspherical plastic lenses are excellent in terms of mass production, cost, and weight reduction, but have drawbacks such as curvature and very large changes in optical performance due to temperature changes.

purpose of invention The purpose of the present invention is to reduce the number of lenses and increase the aperture.

To provide a zoom lens for a video camera that exhibits extremely little performance deterioration due to temperature changes despite using an aspherical plastic lens in order to achieve a large zoom ratio and high performance.

Structure of the Invention The zoom lens of the present invention includes, in order from the object side, a lens group with a positive refractive power, a second lens group with a negative refractive power, a third lens group with a negative refractive power, and a lens group with a positive refractive power. A relay lens system with refractive power is arranged.The first lens group has a focusing function, the second lens group controls magnification, and the third lens group controls the image point for magnification changing. The relay lens system has a role of correcting fluctuations, and has an imaging function, and further has a weak refractive power that satisfies the condition (1) 1o, ofH<1fpl, and at least one surface has an aspherical shape. It is constructed to include a glass lens with a large aperture.

This has resulted in a high-performance zoom lens that has a large zoom ratio, reduces the number of lenses, and exhibits extremely little performance deterioration due to temperature changes. Here, fR is the focal length of the IJ relay lens system, and fP is the focal length of the plastic lens.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration diagram of a zoom lens according to an embodiment of the present invention. In FIG. 1, Ll, L2.・
... is the lens number counted sequentially from the object side.

r, t r 2 t... are the radius of curvature of the refractive surface, dl, d2. . . . indicates the surface spacing. In FIG. 1, the flat plate placed near the focal plane is a crystal plate that serves as a low-frequency optical filter and has no lens effect. Lens L1. L2. L3 is Sb2 L6? L6 represents the second lens group, L7 represents the third lens group, L8 . L9. Ll. , Lll, and L12 constitute the relay lens system. The lens Le is made of a glass material, and the 16th surface on the image side is aspherical.
Furthermore, the focal length of the lens L9 satisfies condition (1).

The zoom lens of this embodiment configured as described above will be explained. Plastic materials that can be used for lenses include:
It exhibits an order of magnitude larger coefficient of thermal expansion and temperature change in refractive index than optical glass. Therefore, if a plastic lens that does not satisfy condition (1) is used, the amount of movement of the imaging plane due to temperature changes will be greater than the depth of focus within the operating temperature range of the video camera zoom lens ±40°C. Therefore, it is impossible to create a practical zoom lens. Furthermore, if an attempt is made to achieve a large aperture using only a small number of lenses and lenses having a spherical shape, aberration performance deteriorates, and in particular, correction of spherical aberration becomes extremely difficult. However, it has been found that by introducing an aspherical shape to at least one surface, a high-performance zoom lens with well-corrected spherical aberration can be realized. Furthermore, by using a lens made of plastic material, an aspherical lens with excellent mass productivity can be realized. Furthermore, condition (1)
A plastic lens that satisfies the above requirements has a weak refractive power, has a small difference in wall thickness between the center and the periphery, and is extremely easy to work with, so it has great practical significance.

Furthermore, the relay lens system includes a fourth lens group consisting of a positive biconvex lens L8 and the glass lens L9,
A meniscus cemented lens L with a concave surface facing the object side with a relatively large air distance d16 from the fourth lens group.
,. , Lll and a positive single lens L12, and further satisfies the following conditions, thereby providing a zoom lens with even better aberration correction.

(gon 1, 1 f, H<f4< 1, 6 fR(
−41, 1fR<f6<1. f5fR(43,6f5<
f6 (ee oa 4 f R<d16<0.6 f H
However, f4. f6 is the focal length of the fourth lens group and the fifth lens group, f6 is the focal length of the meniscus cemented lens in the sixth lens group, and d16 is the air distance between the fourth and sixth lens groups ○ Conditions (Gun is a condition regarding the refractive power of the fourth lens group in the relay lens system. If the lower limit is exceeded, the back focus will become shorter and the focal length f5 of the fifth lens group will increase. Therefore, the exit pupil position is necessary. cannot be secured.f4
When exceeds the upper limit, the light beam exiting the fourth lens group becomes a diverging light beam, which increases the refractive power and light rays of the sixth lens group, making it difficult to correct spherical aberration, and increasing the lens diameter of the sixth lens group. This becomes large and is a practical problem.

One major feature of the embodiment of the present invention is that the fourth lens group is composed of a positive biconvex lens and an aspherical plastic lens.
These are two characteristics. The diaphragm is placed immediately after or in front of the fourth lens group. Therefore, the fourth lens group is the position where the light beam becomes the thickest in the relay lens system, and correction of spherical aberration by introducing an aspherical shape is most effective. In addition, configuring the positive convex lens, which shares almost all of the refractive power of the fourth lens group, which has a large refractive power, in a biconvex shape, reduces the occurrence of spherical aberration while minimizing the occurrence of spherical aberration. The curve also leads to a radius, which facilitates lens processing and is beneficial in manufacturing.

Condition (4 is related to the refractive power of the 6th lens group,
If the upper limit is exceeded, the exit pupil position will be close to the image pickup tube, which is not desirable as a video camera lens.

Furthermore, when f5 exceeds the lower limit, the refractive power of the sixth lens group becomes too strong, resulting in overcorrection of spherical aberration.

One of the features of the present invention is that the sixth lens group is composed of a meniscus cemented lens with a concave surface facing the object side and a positive single lens. Therefore, the principal point of the sixth lens group is on the image plane side, which is advantageous in ensuring bank focus and the exit pupil position, and is also advantageous in correcting off-axis aberrations and chromatic aberrations. Condition (4) relates to the refractive power of the meniscus cemented lens, and if this condition is not satisfied, the above-mentioned effect is not sufficient.

Condition (The condition relates to the air distance between the fourth and fifth lens groups, and is a condition to maintain a good balance between axial and off-axis aberrations. In particular, if the lower limit is exceeded, outward coma will occur, When the upper limit is exceeded, both distortion and astigmatism tend to be negative, making it difficult to correct them.

Next, a specific example that satisfies these conditions will be shown. In the table, "1?"2+... is the radius of curvature of each lens surface counted in order from the object side, dl, d2. ...... is the wall thickness between lens surfaces''!, air gap, nl, n2...
... is the refractive index for the d-line of the material forming each lens, vl.

V 2 t... is the Abbe number for the d-line. Further, a surface having an aspherical shape (indicated by an arrow) is defined by the following formula.

where Z: Distance from the tangent plane of the aspherical vertex of a point on the aspherical surface with height y from the optical axis y: Height from the optical axis r: Radius of curvature at the aspherical vertex: Conic constant E, F, G: Aspheric coefficient (Example 1) f=9.300-52,810 F=1:1,45r1
=55.460d1:1,43n1=1.80518
V1=25.5z2=3j, 470 d2=8.34
n2=1.62041 V2=60.3r3=clOd
3-o, 2°r4=47.614d4=4.0On3=1.62o4
1v3=60.3r5=207.967 d6 (variable) r6=63.278 d6=0.96 n4==1.7
1300 V4=53.9r7==13. sea d7
=4+s.

r8=17.176 a8=o, 96 n6=1.6
0311 V6=6α7r9=15.675 d9=3
．． 19 n6=1.80518 V6=25.5r1゜=105.664d1o (variable) r 11=-21,4
69d11=0.98 n7=1.60311 V-r
-60,7r 12=-71,660ci12 (variable)
r13=31.911 d13=s, so n8=1.
65844 v8=50.8r 14=-28,280
d14=0.12r16=-26,052d16=1
．． 0On9=1.49180 V9=57.2■ r 16=-26,269d16=10.45r17=
-48,539d17=1. oo nl. =1.80
518 v1o=25.5r18=22.510 d1
8=5.70 n11=1.57250 V11=57
．． 6r 19=-18,842d19=0.20r2d
=36.251d2d=3.45n12-1.6031
1v12-60.7r21=-50,005d21=5
．． o.

r22=force d22-6.40n13-1.61633v
13-64°1r23:c'O Diaphragm surface; position 1.5o behind the 116th surface The aspheric coefficient of the 16th surface marked with an arrow is the following constant.

16th surface K -1,34117X10" D -2,19238X 10 E 4.87871X10"-7 F -3,65817X10-10 G -1,15676X10-" Also, the air spacing that can be changed by zooming is as follows. .

fd5d1od12 9,. 300 1.5B2 28.835 2.806
24.760 19.043 7.638 6.542
52.810 27.130 4.455 1.838
Further, various quantities related to conditions (1) to (@ are as follows.

fR/fp””614 * f4/fR=1.172f
6/fR=-302yf6/f5=ts, 77°d1
6/j'H=o, s2° (Example 2) f=9.296~52.788 F=1:1.45r1
=55+460 d, =1.43 n1=1.8051
8 V1=25.5r2==31.470 d2==8
．． 34 n2=1.62041v2-60.3r3-■
d3 town, 2 r4=47-614 d4=4.0On3==1.62
Q41 V3=60.3r6=207.967 d5(
variable) z6=53.278 d6=o, 96 n4=1.7
1300 V4=53.9r8=-17,176d8=
0.96 n6=1.60311 V6=60.7r9
==15.675 d9=3.19 n6=1.805
18 V6=25.5r1o-106,664d1o(
variable) r11=-21,469dll:0.96n,
=1.60311 v7s0.7r 1°=-71,6
60d12 (variable) r13=33.244d13-3+
6on8-1.65844v8-50.8r 14--
35.024 d14=0.20r16-28.827
d15-1.0On9=1.4918ov9=67.2
Bitter r16=30.021 d16=9.45r 1. Knee 49.709 d17=1. oo n1d-1,80
518Vlo:26. tsr18=26+169d1
8=5.70n11-1.67260v11-67.6
r 19=-19,663d190.20r2o-32
,065d2o=3.45 n12=1.60311
V12=60.7r21=-48,665d21=5.
00r22-oOd22-6.40n13-1+516
33v13=64+1r23:■ Aperture surface; rear of surface 116 2.26 The aspherical coefficient of surface 16 with a position arrow attached is as follows.

16th surface K 4.72042 D ' 4.73450X 10-" E -1,99151X10""7 F 3,60247X10"-' G -1,97086X10"-" Also, the air spacing that can be changed by zooming is as follows. It is.

fd5d10d12 9.296 1.582 28.835 2.8062
4.740 19.043 7. e! 38 6.542
52.788 27.130 4.455 1.638
Further, the various quantities related to conditions (1) to (1119) are as follows: 0゛fR/fp=58 t f4/fR=1.287.

f6/fR=1-247? f6/f5=6. ol
.

d 16/f H=o, 475 FIGS. 2, 3, and 4 show the aberration performance of Example 1 at the wide-angle, standard, and telephoto ends, respectively. Furthermore, the aberration performance of Example 2 at the wide-angle, standard, and telephoto ends is shown in Fig. 6, Fig. 8, and Fig. m7, respectively.

As is clear from the figure, it can be seen that the zoom lens of the present invention has good performance even though the number of lenses is as small as 12.

In the above-mentioned examples, the glass lenses are all made of polymethyl methacrylate resin, but the material for forming the plastic lenses is not limited to polymethyl methacrylate resin. Any transparent material may be used as long as it is an optical plastic. For example, polycarbonate or polystyrene resin can be used.

In the above-mentioned embodiments, both surfaces having an aspherical shape are provided on the image plane side of the plastic lens, but even if the aspherical shape is placed on the object side, it is also possible that both surfaces are aspherical. Substantially the same effect can be obtained even with a spherical shape. Effects of the Invention As is clear from the above explanation, based on the present invention ~ under the lens configuration and various conditions, the F number is approximately 1.4. ．． A high-performance zoom lens for a video camera having a zoom ratio of about 6 times, a small number of lenses, and extremely little deterioration of optical performance due to temperature changes can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an aspherical zoom lens according to an embodiment of the present invention, FIGS. 2, 3, and 4 are diagrams showing various aberrations in Example 1 of the present invention, and FIG. FIG. e and FIG. 7 are diagrams showing various aberrations in Example 2. However, in the diagram of spherical aberration, the solid line shows the spherical aberration for the d-line, and the dotted line shows the spherical aberration for the q-line. In the diagram of astigmatism, the solid line shows the sagittal curvature of field, and the dotted line shows the meridional curvature of field. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure r3 14 15 L41S16 L7 L8L'l LIOLIILI2
Fig. 2 1%) Fig. 3 0 (Bird) Fig. 4 Spherical aberration Non-Kujoka Distortion 1h Kai ('A) No. 5 Hedron surface aberration Soji, aberration Distortion aberration (%) Fig. 6 Spherical aberration Non-focal aberration Vine Distortion (%) Figure 7

Claims (1)

[Claims] (1) In order from the object side, the lens group has a positive refractive power, the second lens group has a negative refractive power, and the third lens group has a negative refractive power.
A zoom lens is composed of a lens group and a relay lens system with positive refractive power, in which the first lens group has a focusing function, the second lens group controls magnification, and the third lens group has a focusing function.
The lens group plays the role of correcting fluctuations in the image point due to zooming,
A zoom lens characterized in that the relay lens system has an imaging function, and further includes a plastic lens having a weak refractive power that satisfies the following conditions and having at least one surface an aspherical shape. 1o, ofH<Ifp, where fR represents the focal length of the relay lens system, and fP represents the focal length of the plastic lens. ('4 The relay lens system includes a fourth lens group consisting of a positive biconvex lens and the plastic lens, and the fourth lens group.
It is composed of a sixth lens group consisting of a meniscus cemented lens with a concave surface facing the object side and a positive single lens with a relatively large air distance from the lens group, and is further characterized by satisfying the following conditions. A zoom lens according to claim 1. 1, 1 f R< f 4 < 1, 5 f R1,
1f R< f 5< 1.5 f R3, 5f5<f
6 0-4 Z R< d 1e< O-6f R However,
f4t'f5 is the focal length of the fourth lens group and the fifth lens group, f6° is the focal length of the meniscus cemented lens in the fifth lens group, and d16 is the air distance between the fourth and fifth lens groups. show.