JPH026917A - Small-sized variable focal length lens - Google Patents

Abstract

PURPOSE:To obtain the variable focal length lens of a simple constitution which have an off-axis aberration compensated sufficiently by including a lens group which has two positive lenses arranged while having their low-curvature surfaces opposite each other cross a diaphragm in a 1st lens group. CONSTITUTION:The lenses are arranged symmetrically across the stop and then an aberration is generates so that off-axis luminous flux cancel luminous flux around a main light beam before and behind the diaphragm thereby reducing aberrations generated by the whole front group. Specially, the generation of the distortion aberration is reduced and the outward coma of the comatic aberration which is generated by a front positive lens as to upper luminous flux, for example, before the diaphragm is canceled with the inward coma generated by the positive lens behind the diaphragm. Specially, when the luminous flux is thin, a flare generated at the peripheral part of the luminous flux is eliminated and sufficient compensation effect is obtained. Consequently, the lens system which has its various aberrations compensated with good balance is obtained although the constitution is simplified.

Description

Detailed Description of the Invention (Industrial Application Field) This invention is a compact variable focal length lens, particularly suitable for lens shirts, tar cameras, etc.
The present invention relates to a variable focal length lens including a wide angle lens of about 1000 yen.

(Prior technology) In recent years, compact cameras have built-in converter lenses.
Lenses that can easily change the focal length and those that are equipped with a zoom lens have become popular, and the demand for these variable magnification lenses is also increasing.

The one with a built-in converter lens is JP-A-56.
-95210, etc. are known.

This has a built-in rear converter and is attached after the main lens when using long focal lengths. For zoom lenses, JP-A-57
-201213, Japanese Unexamined Patent Publication No. 60-48009, etc. are known.

(Problems to be Solved by the Invention) However, these variable power lenses are not suitable as simple variable power lenses required for compact cameras and the like.

The number of lens components is too large. For example, the above-mentioned JP-A-56-
The rear converter method disclosed in Japanese Patent Publication No. 95210 requires six lenses including the main lens and converter lens, and the zoom lens disclosed in Japanese Patent Application Laid-Open No. 57-201213 is composed of five to eight lenses. . Furthermore, even the zoom lens disclosed in Japanese Patent Application Laid-Open No. 60-48009, which has a relatively small number of lenses, is composed of four lenses. In addition, in this embodiment of the zoom lens, the focal length on the short focal length side is 40m5, which is slightly longer than the wide angle, and in order to widen this to about 35nyn, it is necessary to properly correct off-axis aberrations.
It would be difficult to compose it with only 4 men's pieces, which would be 7.

The present invention aims to provide a compact L-nons system with an extremely small number of lens components, which has a variable focal length of 41 mm and can be widened to about 35 m on the short focal length side.

(Failure to solve the problem) One nons configuration for achieving the purpose of the present invention is as follows.

As an example is shown in FIG. 1, a so-called telefka 1-type lens having a positive 11th lens group and a negative 2nd lens group is constructed. In a variable focal length lens such as a zoom lens that moves forward while narrowing the distance between the 1121st group and the second lens group, or a multifocal lens that is used for several focal lengths at both ends and in the middle, the 1121st group It is characterized by including a lens group in which two positive lenses are arranged so that their surfaces with weak curvature face each other across an aperture.

(Function) Lenses are arranged symmetrically across the aperture. :by and
Regarding off-axis rays, 1,1 aberration occurs due to mutual (9:') cancellation in front of the aperture with respect to the rays around the principal ray, and it is possible to reduce aberrations generated in the four elements in the front group.In particular, distortion The occurrence of aberrations is small, and with regard to (2) ma aberration, for example, in the case of an upward beam in front of the aperture, the extroverted coma that occurs in the front positive lens cancels out the introverted coma that occurs in the positive lens that is gradually moving toward the aperture. Especially when the light beam is narrow, there is no flare that occurs at the periphery of the light beam, and a sufficient correction effect can be obtained.For this reason, for example, a simple variable focal length lens with an F number of 5.6 degrees can be used with this type of lens. By using a simple configuration, off-axis aberrations can be sufficiently corrected with the minimum number of components.
Become. In addition, there are many lens surfaces arranged concentrically, and astigmatism is less likely to occur.

As described above, according to the present invention, it is possible to provide a variable focal length lens that sufficiently suppresses the occurrence of off-axis aberrations with a very simple configuration. It is desirable to satisfy the following conditions.

f, /fW <-0゜5(1) 0.7< l f,/f, l<1.6
(3) In order to perform even better aberration correction, it is desirable to satisfy the following conditions.

1) r/f w > 0.04 f/fB
(4) Here, fl and f are the first
121st group, focal length of second lens group, f+, +, fB”
are the focal length and back focus at the short focus end, respectively, and are the sum of the axial thicknesses of the lenses behind the aperture in the 11th non-lens group.

When the -1- limit of condition (1) is exceeded, the back focus at the short focal length end becomes short and the rear lens diameter becomes large.

Condition (2) is for shortening the total lens length at the short focal length end. Generally at the short focus end! If the total length of the lens, that is, the distance from the tip of the lens to the imaging plane, is 1 or 2, then L
w can be expressed by the following formula, Lw = f'z (
2m, ) + f-(5) where m2 is the imaging magnification of the second lens group, which can be expressed by the following formula.

m2=　f　w/　f　1 (5) Substituting into equation I-w=f2 (2-fw/f, -f/fw)+f.

When f2 is constant, this formula is minimized in the f-factor that satisfies the following conditions.

f1/f□== c L-Z,,! f H-)-/
'f2/fw-1 Therefore, if f□ and f are determined so as to satisfy condition (2), 1.1. becomes smaller. In other words, the total length at the short focal length end is shortened, and the entire camera equipped with this lens can be made more compact.

Condition (3) is a condition regarding the amount of movement of the 21st men's group during zooming. Generally, in a variable focus lens such as the one of the present invention, the rear lens has a large lens diameter, and the second lens group including the rear lens moves largely forward to change the magnification. Therefore, reducing the amount of movement of the second lens group is another method for compactness.If the upper limit of condition (3) is exceeded, the amount of movement of the second lens group becomes too large, and conversely, If the lower limit of (3) is exceeded, the amount of movement of the second lens group will become smaller, but the overall lens length will tend to become longer, and the back focus will also become shorter, leading to an increase in the rear lens diameter.

Condition (4) is a condition regarding aberration correction, particularly correction of distortion aberration. In a variable focus lens such as the one of the present invention, when the back focus becomes short, positive distortion tends to occur.

To correct this, it is effective to make the lens behind the aperture thicker, and if the axial thickness is determined as in condition (4), distortion can be improved.

(Example) Examples of the present invention that satisfy each of the above conditions will be shown below.

First Embodiment In the first embodiment, as shown in the cross section in Fig. 1, the first lens group consists of only two positive meniscus lenses arranged with their concave surfaces facing each other across an aperture. , a variable focal length lens is realized with the minimum configuration of one negative lens in the negative second lens group.
It is desirable to select the glass for each lens so that it satisfies the following conditions:

(Sh, ◆ν2)/2>50 (6) Here, Sh1. C2 is the Abbe number of the first and second lenses, and when it falls below the lower limit of this condition, the chromatic aberration becomes under.

Further, the second lens group plays the role of flattening the image plane in addition to correcting aberrations, and it is desirable that the following conditions be satisfied in order to reduce the Petzval sum.

n a < 1.7 (7) where n
, is the refractive index of the negative lens of the second lens group. Furthermore, in order to offset the positive distortion generated by this negative lens, the axial thickness of the positive meniscus lens behind the aperture is increased.

Furthermore, by bending the negative lens in the rear group, the astigmatism coefficient can be controlled. If the meniscus shape is convex toward the image side, the image surface will be over, and conversely, if the meniscus shape is convex toward the object side, the image surface will be under. 1st
In the embodiment, in order to correct the slight residual curvature of field in the front group, a biconcave lens whose image-side lens surface is nearly flat is used to effectively correct the excess curvature of field. In other words, in this embodiment, it is desirable that the following conditions be satisfied60.
5〈Red LSI (8) rG-r.

Here, r6 and r are respectively the object side of the rear group negative lens,
This is the radius of curvature of the image side.

Furthermore, in this embodiment, by making the surfaces on both sides of the aperture aspherical, high-order spherical aberration and coma flare are effectively corrected.

The surfaces marked with "*" in the data table below are aspherical, and the aspherical shape has the X-axis in the optical axis direction, the direction of light travel as positive, and the Y-axis in the direction perpendicular to the X-axis. Then, the aspheric coefficient is A, A2, A1, A, P, P,, P,, P4.
It is expressed by the following formula using .

Here R is the paraxial radius of curvature.

f=36.1~49. OFNo=5.6~7.6ω=
30.9'~23.8°Nα RD N
-ν -121,605 cars 2.07
1.48749 66.02 24.
813 4.003 -26.033 *
8.00 1.49700 81.64 -10
．． 468 * Variable 5 -24.429 *
1.00 1.58700 30.06 64
1.890 f D4 36.1 22.3 49.0 13.8 Aspheric coefficient on the second surface = 4.26392 A,: 5.08966X10-' A, = 2.57852X10-@ P1= P2= 4. 0 6.0 A3= A4 On the 3rd side - A, = A, = A, = On the 4th side - A, = A2 = A, = A4 = On the 5th side - A, = A, = A, = A, = 3.76242x10-" P, = 8.0 4.75883X10-" P, = 10.0 1.65485 X 10 -7.22522X 10-'3.01457X10-" 3.20262X No-" 1. 03666X10-" P, = P, = P4 = 4.0 G.0 8.0 10°O 2°37790X 10-" 1°71857X 1O-S -1,15170x 10-" -6,13432x 1o-12 - 209790 15293X10-" P1=P,=P,=P,=4゜0 6゜0 8゜0 10゜0 In the second embodiment, in order to further improve chromatic aberration, the cross-sectional view is shown in Fig. 3. , a negative meniscus lens with a convex surface facing the object is placed closest to the object side of the front group. This improves the symmetry of the entire system before and after the aperture, and the distortion becomes extremely small.

Furthermore, by using a negative lens, the Petzval sum is further reduced, and field curvature is well corrected.

The angle of incidence of the off-axis light beam on the second lens is also small, and the occurrence of coma aberration is extremely small.

In this example, a plastic lens is used, but the refractive index of a plastic lens changes greatly with temperature changes.
Therefore, back focus, that is, a change in the imaging point becomes a problem. Although this can be corrected mechanically, it is desirable that it be corrected by the lens itself. Generally, in a two-group variable focal length lens like the present invention, the back focus changes as shown in the following equation due to changes in the focal length and principal point position of each group.

ΔfB= (f/f, )"Δf-+(f', 3/f-
)”Δf.

−(f/f,)2ΔD−8P, (9) Here, Δfe is the change in back focus 2Δf1, Δf
, are the changes in the focal length of the 11th lens group and the 2nd lens group, ΔD is the change in the distance between the rear principal point of the 1st lens group and the front principal point of the 2nd lens group, and ΔP is the change in the focal length of the 11th lens group and the 2nd lens group, respectively. This is a change in the rear principal point position of the lens group. Furthermore, f and fa are the focal length and back focus of the entire system, respectively.

In the variable focus lens of the present invention, the back focus f9 is extremely short compared to the focal pressure device f, and (f
/f,)2 is much larger than CfP/f,')'. Furthermore, Δl] and ΔP2 due to changes in the position of the principal point are small, so it is difficult to correct changes in focal length caused by temperature changes in the first lens group by changes in the focal length of the second lens group. In other words, it is necessary to correct the influence of temperature changes in each group. In this way, in this example, the change in back focus when changed by +30° from the standard use is - at the short focal length end. 0,0
6. It was possible to achieve a very small value of -0.1 at the long focal length end. Additionally, three out of the four lenses are made of plastic, which helps reduce the weight of the camera.

f=36.0-49. OFNo=5.6~7.62ω
=31.0'~23.4'RDN.

86°825 0.80 1°58700
30.013.855 * 0.50 10.423 * 2゜50 1.49200
57.023.505 * 4.00 -56.928 5,50 1.71300
53.9-13.458 Variable 24.339 1.00 1.67270
32.1323.360 36.0 21.5 49.0 14.8 Aspheric coefficient on the second surface = A, = A, = A, = A, = on the third surface = A□ = A, = A, = A, = on the 4th side = A1 = A, = A, = A, = 3.69373 1.56640X10-'-54I988X10-'5.35799X10""1.16529X10-" P□ = P, = P, = P4= 4.0 6.0 8.0 10.0 2.01413 -1.90739X10-'3.03073X10-" -2,45431X10-14 -4.57696xtO-" P1= P2; P, = P4= 4.0 6.0 8.0 10.0 1.98782X 10 2.33857X10-'-4,16131X10-"-1,80062X10-"1.09292X10""Pl; 6.0 8.0 10.0 Third Embodiment In the third embodiment, the first lens of the first embodiment is made by laminating a negative meniscus lens and a positive meniscus lens. As in the second embodiment, chromatic aberration was well corrected, and the first and second lenses were
The eccentricity of the lens is eliminated, making it an easy-to-manufacture lens.

f=36.0~49. OFNo=5.6~7.6ω=
31.0°～23.8°Nct RD
N−ν.

1 56.224 0.80 1.5927
0 35.32 11.092 3.00
1.69680 55.53 45.274
4.004 -20.267
Car 8,00 1.49200
57.05 -9.702 *
Variable 6 -24.308 1.00 1.58
700 30.07 268.253 f Ds 36.0 22.1 49.0 14.1 Aspheric coefficient on the 4th surface = A, = A, = A3 = A4 = 5th surface 1.20973X 10 -1.12389X10 -'7.42209X10-" 1.25441
1.85240X10-' P1=4.0
A2= 1.99205X10-' P2=
6. OA, = 2.88111X10-”
P, = LO Fourth Embodiment In the fourth embodiment, as the cross section is shown in FIG. 7, a negative meniscus lens with a concave surface facing the object side is placed immediately after the positive meniscus lens behind the aperture. This suppresses the occurrence of chromatic aberration in the first lens group, and also satisfactorily corrects other aberrations.In this embodiment, it is further desirable to arrange the glass materials so as to satisfy the following conditions.

('11.+C2) /2>50 (
10) Ya, < 40
(11) Ya, > 50
(12) Here, ν□, v2, ν1, and ν are the Abbe numbers of the first, second, third, and fourth lenses, respectively, of the fourth embodiment. When the lower limit of (10) and the upper limit of (11) are exceeded, the longitudinal chromatic aberration becomes undervalued, and when the lower limit of (12) is exceeded, the variation in chromatic aberration due to zooming increases.

f=36.0~49. OFNo=5.6~7.62ω=
31.0''~23.8'' Nα RD Nd 1 12.45] 2.00 1.696
80 55.52 17.182 4.15
3 -14.590 * 2.66 1.49
200 57.04 -5.457 * 0
．． 205 -6.442 4.80 1,5
8700 30.06 -12.094 *
Variable 7-17.698 pieces 1,001.4920057.
08 -82.605 * f D.

36.1 49.0 20.0 9.74 Aspheric coefficient on the third surface = 6°95955 X 10-'A, = -
1゜92999 x 10-'P, = 4゜0A
2=2゜42767 x 10-' P, =
6.0 4th surface K = -4,24130X 10-”A, = 1
．． 91680X10-'P, = 4゜0A2=
1.41469X10-' p2=6゜O
A, = 4.70122X10-' P3 = 8
．． 0 6th surface K = -4,18723X 1.0-1A Yu =
-1,95957X 10-' P1= 4゜0
A2=-2,47628X10”1IP2=6.0
Co to the 7th side -9゜44908 x 10'''A, = -4
゜97890 x 10-'P, = 4.0A
2-3゜19130 x 10-' P, =
6.0 8th surface K = 1.09452 X IP”A, = 2
．． 99062xlO-'P, = 4. OA-
5゜76995 X No"" P, = 6.
0 Fifth Embodiment In the fifth embodiment, as shown in cross section 4 in FIG. 9, chromatic aberration is corrected by using a positive lens behind the aperture as a combination of a positive meniscus lens and a negative meniscus lens.

In particular, by laminating, lateral chromatic aberration can be corrected very well.
There is also little change in chromatic aberration due to zooming. In addition, since the lens is laminated structurally, it is only necessary to hold the rear negative meniscus portion when the lens is assembled, which creates more space for the diaphragm and shutter mechanism.

f=36.0~49. OFNo=5.6~7.62ω
=31゜0'～23゜8゜Na RD Nyo1 15゜707 2.00 1.7725
0 49°62 20.597 2.163
-21.814 5.99 1.603
42 38°04 -5.320 2.8
6 1.80518 25.45 -10.2
49 Variable 6 -28.974 1.00 1.56
883 56.37 125.970 D 36.0 24.0 49.0 14.88 Focusing in the present invention is performed in the first. This can be achieved by moving the lens group forward or by moving the second lens group backward, and the change in aberration is also small. As you can see, although it has an extremely simple lens configuration of about 4 lenses, it is compact, includes a wide angle of about 30' in half angle of view, and each aberration is well corrected by 1 degree. It is particularly suitable for

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a first embodiment of the present invention. At the same time, the method of changing the focal length according to the present invention is shown. Figures 2-A and 2-B are aberration diagrams at the short focus end and long focal length of the first embodiment, respectively, and Figures 3, 4-A, and 4-B are aberration diagrams of the second embodiment. FIGS. 5, 6-A, and 6-B are the sectional views and aberration diagrams of the third embodiment, and FIGS. 7, 8-A, and 8-B. The figures are a sectional view and aberration diagram of the fourth embodiment, Figures 9 and 10-A, and Figures 10-
Figure B is a cross-sectional view and an aberration diagram of the fifth embodiment. In the aberration diagrams below, rdJ is the spherical aberration for the d-line, rgJ is the spherical aberration for the g-line, rsc, 1 is the sine condition, "ΔS" is the sagittal image surface, and "ΔM" is the meridional image surface.

Claims (1)

[Claims] It has a positive first lens group and a negative second lens group, and when changing magnification from the short focal length end to the long focal length end, the first lens group and the second lens group move forward together while closing the gap. A variable focal length lens with a two-group configuration, characterized in that the first lens group includes a lens group in which two positive lenses are arranged with a diaphragm in between so that their surfaces with weak curvature face each other. A small variable focal length lens.