JPS6042451B2 - wide angle zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wide-angle zoom lens suitable for cameras, particularly cameras using Brownie film.

A wide-angle zoom lens with an angle of view of 600 or more at the shortest focal length and a zoom ratio of around 2x is composed of a front group with negative refractive power and a rear group with positive refractive power. By changing the air spacing, the focal position is kept constant while changing the magnification.
So-called two-group zoom lenses have been significantly developed, mainly for 357WL size single-lens reflex cameras.

The total focal length f of the two-group zoom lens is expressed as f : flβ2, where the focal length f of the front group and the lateral magnification (hereinafter simply referred to as magnification) β2 of the rear group are expressed as f : flβ2. By changing the magnification, the magnification is changed.

The amount of change Δ5 in the air distance between the front and rear groups is the focal length of the rear group f. , if the magnification of the rear group at the shortest focal length and longest focal length are β2ω and β2t, respectively, then lβ
As 2tI increases, ΔS1 decreases, and 1
f11 also becomes smaller.

Therefore, if the aperture moves integrally with the rear group, ! β
As 2tI increases, the position of the entrance pupil approaches the front lens,
The filter diameter can be made smaller. However, performance is generally better when the rear group is used at reduced magnification. Further, the movement amount ΔS2 of the rear group is as follows, and the smaller lβ2t1 is, the more ΔS
2 becomes smaller, and it is considered that the change in aberration also becomes smaller.

In other words, the two-group zoom lens has the disadvantage that reducing the filter diameter and correcting aberrations contradict each other. The above-mentioned drawbacks are not a big problem with a 35 ugly format camera, and it can be designed to have sufficient performance and a reasonable size for practical use, but the 35
If a two-group zoom lens for 7WL format is designed by enlarging it as is, the above-mentioned drawbacks will become a problem, and it will not be possible to reduce the filter diameter and improve performance at the same time, even if the brightness is sacrificed to some extent.

In the present invention, the filter diameter is small and aberrations can be corrected well.

The purpose of the present invention is to provide a wide-angle zoom lens suitable for cameras that mainly use prony film. Therefore,
The wide-angle zoom lens according to the present invention has negative refractive power as a whole, and in order from the object side, the first lens is a convex lens, the second lens is a concave lens with a convex surface facing the object side, and the concave meniscus lens has a convex surface facing the object side. and a first group consisting of a fourth lens which is a convex meniscus lens with a convex surface facing the object side, and has a positive refractive power as a whole, and at least:
The second lens consists of three convex lens components and one concave lens component.
group, a concave lens component and a convex lens component in order from the object side.
The second group moves on the optical axis to change the magnification, the first group works in conjunction with the second group to keep the focal length constant, and the second group moves on the optical axis to change the focal length. The third group is a zoom lens configured as a relay lens system that expands the focal length of the variable power system composed of the first group and the second group. (1) 0.
85 × β2t × 1.15 (2) 1.1 × β3 × 1.3 However, β2t: Lateral multiplication of the second group at the longest focal length
Ratio β3: Satisfies each condition for the lateral magnification of the third group.

To describe the theoretical basis of the present invention in detail, the focal length f of the entire system is: the focal length f1 of the first group, the magnification β2 of the second group, and the
The group magnification β3 is expressed as follows, and the magnification is changed by changing β2.

The amount of change ΔS1 in the air gap between the first group and the second group is
If the focal length of the group is F2, and the magnifications of the second group at the shortest and longest focal lengths are β2ω and β2t, respectively,
becomes.

Further, the movement amount ΔS2 of the rear group is as follows.

Regarding ΔS1 and ΔS2, the results are exactly the same as with the two-group zoom lens; the larger lβ2tI is, the smaller ΔS1 is, and the smaller 1f1J is, which has the effect of reducing the filter diameter. Conversely, the smaller lβ2tI is, the smaller ΔS2 is.
becomes small, and aberration correction becomes advantageous. The present invention prioritizes aberration correction and reduces 1β2t1. In order to reduce the filter diameter, the focal length of the variable power system is shortened by providing the third group with an appropriate magnification. As the focal length of the variable magnification system becomes shorter, F2 becomes smaller, ΔS1 becomes smaller, and 1f11 also becomes smaller.
The position of the entrance pupil moves closer to the front lens, making it possible to reduce the filter diameter. In addition, with a two-group zoom lens, naturally, aberrations in the entire zoom range had to be corrected simultaneously using only the front and rear groups, but with the addition of a relay lens system in the present invention, the zoom system is Even if aberrations themselves remain, it is enough as long as the fluctuations in the aberrations can be corrected, and the aberrations that remain in the variable magnification system can be canceled out by the relay lens system, which means that the degree of freedom in correcting aberrations has increased. .

This is also a major feature of the present invention. The focal length F3 of the third group is expressed as follows, where e(f) is the distance from the rear principal point of the variable magnification system to the front principal point of the third group. It can take either value or negative value.

Here, the minimum size of Prony film is 4.5 x 6.
35wr with the same size and angle of view! Comparing n-size lenses, the difference is 1. in terms of residual amount of various aberrations and lens size.
There are huge differences.

That is, the residual amount of various aberrations and the size of the lens, which were hardly a problem with a 35Tr$L-format two-group zoom lens, become extremely serious problems with a Prony-format lens.

In the present invention, as a means of solving this problem, a third group is added, and various aberrations are favorably corrected under the above conditions (1) and (2), and the filter diameter is minimized. was completed.

Next, each of the above conditions will be explained in detail.

Condition (1) is to maintain a balance between aberration correction and filter diameter; if the upper limit is exceeded, aberration correction becomes difficult, similar to a two-group zoom lens, and if the lower limit is exceeded, the filter diameter becomes large. If the purpose of the present invention cannot be achieved,
Alternatively, if β3 is increased in order to reduce the filter diameter, brightness must be sacrificed as will be described later.

Condition (2) is intended to maintain a balance between filter diameter and brightness. The F number FN of the entire system is determined by the F number FNZ of the variable power system.

For example, when β3 becomes 1.4, F is one step brighter for variable magnification systems.
Since this requires a number and makes it difficult to correct aberrations, it is appropriate to limit the number to 1.3. Furthermore, if β3 is less than 1.1, the refractive power arrangement of the variable power system becomes close to that of a two-group zoom lens, and the object of the present invention, which is to solve the drawbacks of a two-group zoom lens, cannot be achieved. Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram of Embodiment 1 of the present invention, which has a minimum focal length of 65 degrees and a zoom ratio of about 1. The brightness is F4.5. The third group is characterized by consisting of a concave lens and a convex lens in order from the object side. The radius of curvature of the image side surface of the concave lens is m1 The radius of curvature of the object side surface of the convex lens is Rp
Then, it is appropriate to satisfy the following condition: 0.6rp<Rn×1.05rp.

When aberration fluctuations are corrected using a variable magnification system, distortion is well corrected using only the variable magnification system, but a large amount of astigmatism remains. In order to counteract this, the relay lens system needs to correct astigmatism without causing distortion. If the upper limit of the above conditions is exceeded, it becomes difficult to correct astigmatism, and if the lower limit is exceeded, pincushion-shaped distortion occurs from the third group, making correction difficult at the longest focal length. Next, numerical examples of Example 1 will be shown.

Embodiment 1 The effective diameter of one ball is φ, the image circle is D), and the filter thread diameter is approximately 1.1D. The angle is 65mm, the zoom ratio is approximately 1.9x, and the brightness is 4.5x.

The third group consists of a concave lens component and a convex lens in order from the object side, and is a cemented lens of the concave lens component and the concave lens, and is characterized by satisfying the following conditions. ,R
la: refractive index of the convex lens of the cemented lens m'': refractive index of the concave lens of the cemented lens The two conditions are 4 corrections for spherical aberration and Petzval sum.

When aberration fluctuations are corrected in a variable magnification system, depending on the structure of the group, there may be cases where spherical aberration is insufficiently corrected and the Petzval sum becomes too small. ) It is difficult to correct. Astigmatism and distortion are real U
1 configuration can correct astigmatism and distortion? In order to correct spherical aberration and Petztur sum without significantly affecting . i
Example 2 A short focal length with an angle of view of 76°, a zoom ratio of approximately 1.7 times, and a brightness of F4.6.

The third group is composed of a three-piece cemented lens consisting of a convex lens, a concave lens, and a convex lens in order from the object side, and is characterized by satisfying the following conditions. Oil<Oil′ Surface〃<Oil′ However, Nb: Refractive index of the convex lens on the object side of the third group Oil′:
Refractive index of the concave lens of the third group Oil'': Refractive index of the image-side convex lens of the third group The above conditions relate to correction of spherical aberration, astigmatism, and Petzval sum remaining in the variable power system.

As the angle of view becomes wider, it becomes more sensitive to eccentricity of each lens, so the third group was constructed from one lens group rather than two lens groups as in Examples 1 and 2. Generally speaking, it is less susceptible to eccentricity and has a better manufacturing fit. When aberration fluctuations are corrected with a variable magnification system, especially with a zoom lens with a wide angle of view, the spherical aberration tends to be insufficiently corrected with only a variable magnification system, the curvature of field tends toward the lens side, and the Petzval sum becomes too small. There is. As Nb<oil', a cemented surface with negative refractive power is arranged with the concave surface facing the aperture to correct spherical aberration and Petzval's sum, and as Nb"<oil', the convex surface faces the aperture. By arranging a cemented surface with negative refractive power and correcting astigmatism, it is possible to cancel the aberration of the variable magnification system with one lens group.Example 3 f=1.000~1.192~ 1.691F4.6rd
ndvd10.39250.086 71.7215129.2 -10.3925 0.0043 4.1717 0.05421.8040046.60.69550. 16011. 37980. 04341.8040046.60. 85480. 12760. 79720. 09321.7215129.21.51200. 8186~0.5438~0.1222 1.1168 0.07591.7200050.2 -10.4795 0.0043 0.7088 0.18171.6935053.2 -0.7088 0.05421.7440044.73.78580. 06082. 40170. 04341.7552027.5 0.5793 0.0770 25.0836 0.05641.7725049.6 - 0.8320 0.0156 ~ 0.1303 ~ 0.4277 - 2.11
700.0867nb1.6223053.2-0.6
173 0.0325nb'1.8040046.61.180
60.1344nb″1.7015441.2-1.1
806 bf=1.241β2ω=-0.592 f1=-1.496β2t=-1.000f2=1.0
08β3 = 1.13 f3 = -24.958φ = 0.86D In order to solve the drawbacks of the two-group zoom lens, the present invention
Although a zoom lens system consisting of groups has been provided, considering the structure of the mirror body, a fixed lens group is simply added after the two-group zoom lens, and the conventional technology can be used as is for the structure of the mirror body.

That is, the present invention simultaneously achieves miniaturization and improved performance, which were impossible with a two-group zoom lens, without making the structure of the mirror body more complicated than in a two-group zoom lens.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are block diagrams of Example 1, Example 2, and Example 3, respectively, and FIGS. 4, 5, and 6 are configuration diagrams of Example 1, Example 2, and Example 3, respectively. FIG. 7 is an aberration curve diagram of spherical aberration, non-5k aberration, and distortion aberration at each focal length in Example 3.

Claims (1)

[Claims] 1. Having negative refractive power as a whole, in order from the object side, a first lens is a convex lens, a second lens is a concave lens with a convex surface facing the object side, and a concave meniscus lens with a convex surface facing the object side. A first group consisting of a third lens, a fourth lens which is a convex meniscus lens with a convex surface facing the object side, and a first group having positive refractive power as a whole and consisting of at least three convex lens components and one concave lens component. It consists of a second lens group and a third lens group consisting of two lens groups, a concave lens component and a convex lens component, in order from the object side.The second group moves on the optical axis to change the magnification, and the first lens group
A zoom lens configured as a relay lens system in which the group works in conjunction with the second group to keep the focal length constant, and the third group expands the focal length of the variable power system made up of the first and second groups. A wide-angle zoom lens that satisfies the following conditions. (1) 0.85<β_2t<1.15 (2) 1.1<β_3<1.3 However, β_2t: Lateral magnification of the second group at the longest focal length β_3: Lateral magnification of the third group 2 Third group The wide-angle zoom lens according to claim 1, wherein the ninth lens is a cemented concave lens consisting of a convex lens and a concave lens, and satisfies the following conditions. na<na' where, na: refractive index of the convex lens of the cemented lens na': refractive index of the concave lens of the cemented lens 3 The third group is composed of a three-piece cemented lens consisting of a convex lens, a concave lens, and a convex lens in order from the object side, A wide-angle zoom lens according to claim 1, which satisfies each of the following conditions. nb<nb'nb''<nb' where nb: refractive index nb' of the object-side convex lens of the third group
:Refractive index of the concave lens in the 3rd group nb″:Refractive index of the convex lens on the image side of the 3rd group