JPH0470609B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a compact zoom lens suitable for cameras with no restrictions on backfocus, such as lens shutter cameras. Conventionally, as a photographic zoom lens that includes a standard region, a negative-leading two-component zoom lens is known, which is composed of two components, negative and positive, in order from the object side. On the other hand, with the recent increase in the magnification of zoom lenses, various so-called multi-component movable zoom lenses of the front leading type have been proposed. However, most of these zoom lenses were mainly developed for single-lens reflex cameras, and due to backfocus constraints, the total length of the lens system (the length from the front surface of the lens closest to the object to the film surface) ) is becoming a big thing. Also, as zoom lenses for cameras with no restrictions on back focus, JP-A-128911 and JP-A-57
A positive-leading type two-component zoom is known, such as -201213, which is composed of two components, positive and negative, in order from the object side. However, in this type of zoom lens, the amount of movement of the lens group that moves for zooming is generally large, and even if the lens system is compact, the total length of the lens system becomes large when the lens barrel is included. In addition, in the above-mentioned zoom type, the aperture moves during zooming, which is not preferable in, for example, a lens shutter camera, as this causes the camera body to become larger and more complicated. That is, in a lens shutter camera, not only the aperture diaphragm but also the shutter blades and their driving unit must be arranged at the aperture position and these must be moved, so the above point can be said to be a very serious drawback.
In addition, since the F number changes greatly with zooming, if the camera's metering method is external light, an aperture correction mechanism is required to ensure exposure, which makes the configuration even more difficult. It gets complicated. SUMMARY OF THE INVENTION An object of the present invention is to provide a compact and high-performance zoom lens system suitable for cameras with no restrictions on backfocus. A further object of the present invention is to provide a compact and high-performance zoom lens system that takes into account the miniaturization and simplification of the camera body. The zoom lens system of the present invention is composed of, in order from the object side, a first positive lens group, a second negative lens group, a third positive lens group, and a fourth negative lens group, and has a longest focal length from the shortest focal length end (S end). When zooming to the end (L end), the first positive lens group and the fourth
The negative lens group moves from the image side to the object side, and at least the second negative lens group or the third positive lens group moves during zooming. Based on the above-described configuration, the zoom lens system of the present invention uses the first positive lens group and the second positive lens group during zooming from the S end to the L end.
By increasing the air distance between the negative lens group and decreasing the air distance between the third positive lens group and the fourth negative lens group, the zooming effect can be shared, so the amount of movement of each moving group can be reduced. It is possible to do so. Furthermore, the zoom lens system of the present invention has the above-described configuration and has a relatively strong negative lens group closest to the image side, so that the back focus at the S end is reduced to 1/2 of the diagonal length of the screen. The following extremely
It constitutes a compact lens system with a short overall length. According to an embodiment of the present invention, as shown in FIGS. 1 to 4, the zoom lens system fixes the lens group including the diaphragm during zooming, so that it can be used for compact cameras such as lens shutter cameras. As a zoom lens for cameras, it has greatly contributed to the miniaturization and simplification of the camera body. The zoom lens system of the present invention is further characterized in that it satisfies the following conditional expression based on the above basic configuration. 0.7＜fs／｜f ₄ ｜＜2.0 (1) fs: Focal length of the entire system at the S end f ₄ : Focal length of the fourth lens group Conditional expression (1) defines the refractive power of the fourth lens group If the lower limit is exceeded under these conditions, the back focus at the S end becomes long, making it impossible to construct a compact zoom lens system. On the other hand, if the upper limit is exceeded, it becomes difficult to correct the fluctuations in astigmatism and spherical aberration in a well-balanced manner when the aberrations fluctuate during zooming. Furthermore, it is desirable for the zoom lens system of the present invention to satisfy the following conditions. 0.5＜fs ₁₂₃ /｜f ₄ ｜＜1.8 (2) 1.15＜β _L4 /βs4＜2.0 (3) 0.1＜Δd ₃₄ /fs＜1.0 (4) However, fs ₁₂₃ is the first positive lens group at the S end to the third
The combined focal length to the positive lens group, β _L4 and βs ₄ are the lateral magnifications of the fourth negative lens group at the L end and S end, respectively, and Δd ₃₄ are the 3rd and 4th lenses in zooming from the S end to the L end. Amount of axial air spacing reduction between groups. Conditional expression (2) is a condition for specifying that the lens system is a telephoto type at the S end in order to shorten the back focus.If the upper limit is exceeded, the telephoto type becomes extreme and positive distortion cannot be corrected. On the other hand, if the lower limit is exceeded, compactness cannot be achieved and the magnification effect of the fourth lens group also decreases. Conditional expression (3)
Conditional expression (4) and Conditional expression (4) both define the magnification change effect of the fourth group. The amount of movement of the group increases, making it difficult to realize the fourth group with a relatively simple configuration, and making it difficult to correct the balance of field curvature during zooming. On the other hand, if the lower limit is exceeded, the burden of zooming on units other than the fourth group becomes too strong, and the compact zoom lens system that is the object of the present invention cannot be realized. On the other hand, in conditional expression (4), if the upper limit is exceeded, the axial air gap between the third and fourth groups at the S end becomes large, making it difficult to ensure image plane illuminance at the S end, and conditional expression Similar to the upper limit of (3), it becomes difficult to have a relatively simple configuration of the fourth group and to correct the balance of field curvature during zooming. When the lower limit of condition (4) is exceeded, the variable power effect of the fourth lens group becomes virtually meaningless. Further, as a specific configuration of the zoom lens system of the present invention, the following is preferable. That is, the first
The lens group includes at least a negative lens with a convex surface facing the object side, and a positive lens with a concave surface facing closest to the image side. The above configuration reduces fluctuations in various aberrations, especially astigmatism, when focusing on a nearby object with the first lens group. Further, the second lens group includes at least one negative lens and one positive lens and corrects chromatic aberration during zooming, particularly the balance of lateral chromatic aberration. The third lens group is a positive/negative/positive triplet type or a modified type thereof, which is most preferable for correcting spherical aberration and coma aberration. Furthermore, the fourth lens group includes at least one negative meniscus lens closest to the image side, making the entire system compact.
This contributes to correction of the image plane near the S end. Specific examples of the present invention will be described below. 1 to 4 are cross-sectional views of lenses at the S end and L end of Examples 1 to 4 of the zoom lens system of the present invention, respectively. Further, in the following example, ri is the radius of curvature of the i-th curve from the object side, di is the i-th axial distance from the object side, and Ni and νi are the curvature radius of the i-th lens from the object side, respectively. These are the refractive index and the Atpe number. As is clear from each embodiment, the change in the F number is small when the aperture diameter is fixed, and it is also possible to omit the aperture diameter correction mechanism. 5 to 8 are aberration diagrams of Examples 1 to 4 when the object distance is infinite, respectively. In addition, in Examples 1 to 4, the second
All lens groups are fixed during zooming, but instead of this, a diaphragm may be provided in the third lens group and this may be fixed. Furthermore, if mechanical circumstances permit, it is optically easy to move both the second and third lens groups, and as long as it achieves the effect of constructing a compact zoom lens system, there is no deviation from the requirements of the present invention. isn't it. Example 1

【table】

【table】 Example 2

【table】 Example 3

【table】 Example 4

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【table】 [Brief explanation of the drawing]

1 to 4 show examples 1 to 4 of the present invention.
FIG. 3 shows lens cross-sectional views at each S end and L end of the zoom lens system. FIG. 5 to FIG. 8 show the above-mentioned Example 1.
4 shows various aberrations at each focal length of the zoom lens system when the object distance is infinite. I...first positive lens group,...second negative lens group,
...Third positive lens group, ...Fourth negative lens group, S...Aperture.

Claims (1)

[Claims] 1 Consisting of, in order from the object side, a first positive lens group, a second negative lens group, a third positive lens group, and a fourth negative lens group, from the shortest focal length end (S end) to the longest focal length end. When zooming to the distance end (L end), the first positive lens group and the fourth negative lens group move from the image side to the object side, and at least the second negative lens group or the third positive lens group moves during zooming. As a result, when zooming from the S end to the L end, the air gap between the first and second lens groups increases, and the air gap between the third and fourth lens groups decreases, and the air gap at the S end increases. A compact zoom lens system characterized by a back focus of 1/2 or less of the screen diagonal length and satisfying the following conditions: 0.5 < f _S123 / | f ₄ | < 1.8 However, f _S123 : At the S end composite focal length from the first positive lens group to the third positive lens group, f ₄ : focal length of the fourth negative lens group. 2. The zoom lens system according to claim 1, wherein the second negative lens group includes an aperture. 3. The zoom lens system according to claim 1, which further satisfies the following conditions: 0.7<f _S / | f ₄ | <2.0, where f _S is the focal point of the entire system at the S end. distance. 4. The zoom lens system according to claim 1, further satisfying the following conditions: 1.15<β _L4 /β _S4 <2.0 0.1<Δd ₃₄ /f _S <1.0 However, β _L4 , β _S4 : Lateral magnification of the fourth negative lens group at the L end and S end, respectively. Δd ₃₄ : Amount of decrease in the axial air distance between the third and fourth lens groups during zooming from the S end to the L end. 5. The zoom lens system according to claim 2, wherein the second negative lens group is fixed during zooming. 6. The zoom lens system according to claim 1, wherein the third positive lens group includes an aperture. 7. The zoom lens system according to claim 6, wherein the third positive lens group is fixed during zooming. 8. The zoom lens system according to claim 1, wherein both the second negative lens group and the third positive lens group move during zooming.