JPS6144288B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention has a focal length at the wide-angle end that is shorter than the diagonal length of the image size, and
Regarding wide-angle zoom lenses of the 4-group type with a zoom ratio greater than 2.5 and a convergent lens group in front, it is particularly important that various aberrations on the wide-angle side are well corrected, and aberration fluctuations due to zooming are also well corrected. This is a compact system. Conventionally, in order to realize a wide-angle zoom lens of the above specification with a four-group type preceded by a convergent lens group, it was necessary to make the focal length of each group of the zoom section extremely small to prevent an increase in the diameter of the front lens. However, when the focal length of each group in the zoom section is made small, aberration fluctuations due to zooming, especially fluctuations in distortion, astigmatism, and spherical aberration, become extremely noticeable, making it no longer possible to realize a wide-angle zoom lens with good performance. Ta.
Also, the so-called 2-group zoom type, which has a diverging lens group in front, is generally more advantageous in correcting aberrations on the wide-angle side and reducing the diameter of the front lens than the 4-group zoom type, which has a convergent lens group in front, but the zoom magnification is lower. At higher magnifications, such as 2.5x or higher, it is extremely difficult to maintain good telephoto performance and to increase the aperture. The present invention improves the wide-angle side performance of a wide-angle zoom lens with a zoom ratio greater than 2.5, which has been considered extremely difficult in the past, especially distortion and astigmatism. The purpose is to correct. And in the example
It has a zoom ratio of about 2.8x, maintains good telephoto performance, and has an FNo. of 1:3.5 over the entire zoom range.
Furthermore, it has realized a wide-angle zoom lens with a compact lens system. The features of the wide-angle zoom lens of the present invention will be described below. First, the configuration of the wide-angle zoom lens of the present invention consists of a convergent first lens group that is fixed during zooming and moves along the optical axis for focusing, and a convergent lens group that moves along the optical axis during zooming. A diverging second lens group for magnification, a third lens group that moves to keep the image plane constant when the second lens group moves, and a fourth lens group that is fixed during zooming behind it. Consists of. This convergent first lens is composed of four elements in three groups, consisting of a bonded lens and two positive lenses in order from the object side.These three groups have a meniscus shape convex toward the object side, and the bonded lens faces the object side. It is an almost afocal lens group with a convex diverging bonding surface. The second diverging lens group is composed of four lenses, in order from the object side, two meniscus negative lenses convex toward the object side, a biconcave negative lens, and a positive lens group, with an air gap formed between the negative lens and the positive lens. has an astringent effect. First, by configuring the convergent first lens group as described above, the diameter of the front lens can be further reduced, making it possible to easily correct aberrations. Furthermore, the entire first lens group has a convex meniscus shape on the object side, and the power (reciprocal of the focal length) of the bonded lens with the largest outer diameter, which is located closest to the object side, is -0.06/fw and 0.03/fw.
(fw: overall focal length at the wide-angle end of the entire system), in other words, by making it almost afocal, the light beam at the maximum angle of view on the wide-angle side is hardly refracted when passing through this afocal lens, and then Since the lens is refracted by the subsequent positive lens with a relatively small outer diameter, an increase in the diameter of the front lens can be prevented, and aberrations (especially distortion and astigmatism) can be corrected without causing extreme high-order aberrations (especially distortion and astigmatism).
In addition, the above afocal lenses are laminated together,
In order to remove spherical aberration and chromatic aberration generated from the first lens group with this bonded surface having a diverging effect,
Other positive lenses do not need to be laminated, so
The thin wall thickness is good and the overall lens length can be shortened. In addition, since the object side bonded lens is afocal, the thickness around the lens does not change much compared to the thickness on the optical axis, so the curvature of the bonded surface can be strengthened without increasing the wall thickness that much. In particular, spherical aberration and chromatic aberration on the telephoto side generated from the first lens group can be removed extremely well, and aberration fluctuations due to focusing can also be well corrected. At this time, if the power 1/f ₁ (f ₁ : focal length of the bonded lens) of the bonded lens is smaller than -0.06/fw, the first lens group has positive power, so the other two positive lenses Because the power of the lens becomes too strong and the outer diameter becomes large, high-order aberrations occur from these two positive lenses on the wide-angle side, making it impossible to correct aberrations and further increasing the overall length of the lens. vice versa,
If it is larger than 0.03/fw, higher-order aberrations will occur from this bonded lens on the wide-angle side, and the diameter of the front lens will further increase. Furthermore, all the lenses in the first lens group must have a meniscus shape convex toward the object side. This is to prevent the luminous flux at the maximum angle of view on the wide-angle side from being sharply refracted on the image side of each lens, causing higher-order aberrations.In particular, the radius of curvature on the image side of a laminated lens with a large outer diameter is It is desirable that R ₃ be between 3fw and 5fw. At this time, if R ₃ is smaller than 3fw, the curvature of this surface will become too strong, and the fluctuation of spherical aberration due to focusing on the telephoto side will become large.
On the other hand, if it is larger than 5fw, higher-order aberrations will occur from this surface on the wide-angle side, making it impossible to correct aberrations easily. Next, the diverging second lens group is configured as above,
By placing a positive lens behind the three negative lenses, the front principal point of the second lens group comes out near the first surface of the second lens group, so the first and second lens groups collide at the wide-angle end. The distance between these principal points can be reduced without any problems, and this is extremely effective in reducing the diameter of the front lens. In addition, by making the two negative lenses on the object side into a meniscus shape that is convex on the object side,
The light emitted from the convergent first lens group at a large angle,
Since the angle of the light beam at the maximum angle of view on the wide-angle side is gradually loosened by these two negative lenses, high-order aberrations do not occur as much from this part, and distortion and astigmatism, especially on the wide-angle side, can be easily eliminated. It can be corrected. Furthermore, by providing three negative lenses, the overcorrected spherical aberration on the telephoto side generated from the second lens group is shared by each lens and minimized, and
By making the air lens between the third negative lens and the next positive lens convergent, the overcorrected spherical aberration can be corrected very well.
Together with the correction effect of the first lens group, it is possible to satisfactorily correct aberration fluctuations due to zooming. In the past, there have been examples in which the second lens group is composed of three negative lenses and one positive lens, and the last negative lens and positive lens are cemented together from the object side, but the features of the present invention are as follows. This lens is fundamentally different from the lens of the example. A zoom lens described in Japanese Patent Publication No. 45-8840 as one of the conventional examples,
A table comparing the results with the first embodiment of the present invention listed later is shown below.

[Table] However, f ₂ : Focal length of the second lens group, f ₂₁ , f ₂₂ , f ₂₃ : Focal length of each negative lens from the object side of the second lens group, O ₁ : Focal length of the second lens group As shown in the table, the distance of the front principal point from the first plane, O ₁ , is much smaller in Example 1. With the conventional value, it is no longer the first value.
Will the lens group and the second lens group collide?
Or the front lens diameter becomes extremely large. The reason for this is that in Example 1, |1/f ₂₁ |
＞｜1/f ₂₂ ｜＞｜1/f ₂₃ ｜, but in the conventional example, ｜1/f ₂₁ ｜＜｜1/f ₂₂ ｜＜｜1/f ₂₃ ｜
They have a completely opposite relationship. Therefore, at least |1/f ₂₁ | needs to be larger than |1/f ₂₂ | and |1/f ₂₃ |. This is a condition for setting the front principal point position near the first surface of the second lens group. And even more ideally, |1/f ₂₁ |>|1/f ₂₂ |>|
It is desirable to satisfy the condition of 1/f ₂₃ |. This is because, in addition to the condition of the front principal point position, the luminous flux at the maximum angle of view on the wide-angle side is gradually refracted by the negative lens of the second lens group, and the occurrence of higher-order aberrations can be extremely well prevented. f ₂ , f ₂₁ , f ₂₂ , f ₂₃ , and O ₁ in the second and third embodiments are as follows.

[Table] In addition, by using a converging air lens between the third negative lens and the positive lens of the second lens group,
Spherical aberration on the telephoto side can be corrected extremely well. This is extremely noticeable compared to the case where this part is joined. Furthermore, in order to completely correct chromatic aberration, the negative lens in the first lens group and the positive lens in the second lens group are made of high dispersion glass, and the positive lens in the first lens group and the negative lens in the second lens group are made of high dispersion glass. It is even better to use a low dispersion glass type. Since the power of the diverging third lens group is not so strong, it can be composed of a single negative lens or a combination of negative lenses, and its shape should be concave toward the object side so that overcorrected spherical aberration does not occur as much as possible. Let it be the meniscus of Furthermore, it is better to have a smaller thickness of the third lens group by bringing the aperture closer to the first surface. The above is the configuration of the zoom section.Next, the relay lens section (fourth convergent lens group) is connected to the zoom section.
Since a fairly strong axially divergent light beam is incident, the back focus tends to be long. Therefore, it is necessary to arrange a positive lens with strong power in front of the fourth lens group. However, since this positive lens generates a lot of spherical aberration that is insufficiently corrected, we next place a bonded positive lens with a concave diverging bonded surface on the object side to partially correct the spherical aberration.
The Petzval sum is improved by increasing the difference in the refractive index of this bonded lens. Next, leave an air gap within the range where the rear ball diameter does not become extremely large,
Negative, positive, and positive lenses are arranged to completely correct the undercorrected spherical aberration, and further correct distortion, astigmatism, and coma in a well-balanced manner throughout the zoom range. In a 4-group type zoom lens with a convergent lens group in front, when the oblique light beam at the maximum angle of view passes through the first surface, the zoom position where this position is farthest from the optical axis is at the wide-angle end or from the wide-angle end. It can be said that it has been zoomed in somewhat. Therefore, if the diaphragm, which is generally located on the front surface of the relay lens, can be moved closer to the first surface near the wide-angle end, the distance from the optical axis through which the oblique light flux passes through the first surface can be reduced, and the diameter of the front lens can be reduced. It is extremely effective. Therefore, the wide-angle zoom lens according to the embodiment of the present invention moves the aperture. In this way, the configuration of the wide-angle zoom lens according to the embodiment of the present invention is such that the air gap between the third lens group and the fourth lens group is kept large at the wide-angle end, and the aperture is moved together with the third lens group. The above effects have been achieved. Also,
If the aperture is brought closer to the first surface, the diameter of the rear lens increases, contrary to the reduction of the diameter of the front lens, but in the wide-angle zoom lens of the present invention, the back focus becomes longer because the diverging light beam enters the fourth lens group. Since this is a zoom configuration in which the diameter of the rear lens can be made small, if the amount of movement of the diaphragm toward the first surface becomes extremely large, performance will not deteriorate due to an increase in the diameter of the rear lens. Therefore, the air gap between the third lens group and the fourth lens group does not become extremely large at the wide-angle end, and at least f ₁ >e−2f ₂ (f ₁ ,
f ₂ is the focal length of the first and second lens groups, e
It is desirable to have a power arrangement that satisfies the condition of (the distance between the principal points of the first lens group and the second lens group at the wide-angle end). Furthermore, since the outer diameter and aperture diameter of the third lens group are extremely small compared to the diameter of the front lens, even if the aperture moves together with the third lens group, the aperture mechanism and the third lens group can be integrated into the cam of the third lens group. It can be mounted on a mechanism, and while the internal structure is slightly more complicated than the conventional method, it does not affect the increase in the outer diameter of the lens barrel. By using the configuration described above, the angle of view at the wide-angle end is 61.7 degrees and the focal length is 36.2 mm to 102 mm, or 36.2 mm, as shown in this example.
We were able to create a compact wide-angle zoom lens with an F number of 1:3.5 at 83mm and excellent performance.

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【table】 [Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a lens corresponding to Example 1.
Fig. 2 is a diagram of various aberrations at infinity, Fig. 3 is a sectional view of a lens corresponding to Example 2, Fig. 4 is a diagram of various aberrations at infinity, and Fig. 5 is a lens corresponding to Example 3. It is a sectional view, and FIG. 6 is a diagram of various aberrations at infinity. In the figure, R is the lens surface number and radius of curvature, D is the lens thickness or interval, or their number, m is the meridional focal line, and S is the sagittal focal line.

Claims (1)

[Claims] 1. In order from the object side, a convergent first lens group that is fixed during zooming and moves along the optical axis for focusing, and a variable power lens group that moves along the optical axis during zooming. A wide-angle zoom lens that has a diverging second lens group for the purpose of zooming, a third lens group that moves to keep the image plane at a constant position when the second lens group moves, and a fourth lens group that is fixed during zooming behind it. In the above, the convergent first lens group includes, in order from the object side, a bonded lens,
It is composed of four lenses in three groups of two positive lenses, and these three groups have a meniscus shape convex to the object side, and the bonded lens is a substantially afocal lens having a diverging bonded surface convex to the object side, The second diverging lens group consists of four convex meniscus negative lenses, a biconcave negative lens, and a positive lens in order from the object side.
The air gap created by the biconcave negative lens and the positive lens has a convergent effect, and in the convergent first lens group, the focal length of the composite lens is f ₁₁ The radius of curvature of the side surface of the image plane R ₃ is the total focal length at the wide-angle end of the wide-angle zoom lens, fw is the total focal length at the wide-angle end of the wide-angle zoom lens, and in the second divergent lens group, the focal lengths of the three negative lenses from the object side are f ₂₁ , f ₂₂ , and f ₂₃ , respectively. -0.06/fw＜1/f ₁₁ ＜0.03/fw……(1) 3fw＜R ₃ ＜5fw……(2) ｜1/f ₂₁ ｜＞｜1/f ₂₂ ｜, ｜1/ A wide-angle zoom lens that satisfies the following conditions: f ₂₁ ｜＞｜1/f ₂₃ ｜……(3).