JPH03200907A - Zoom lens - Google Patents

Abstract

PURPOSE:To reduce the size and cost of the whole zoom lens and simplify the zoom lens by providing a 1st moving means which moves lens groups of the optical axis without varying their mutual interval, and a 2nd moving means which moves only one lens group on the 1st moving means. CONSTITUTION:A cam cylinder 2 is rotated by a motor for focal length variation to move the 2nd lens group L2 to an optional zoom position. At this time, the 1st lens group L2 and 2nd lens group L2 move in one body unless the motor 5 is driven, and their group interval is not variable, so the rotation of the cam cylinder 2 is used as the 1st moving means. Then the motor 5 is driven to move the 1st lens group L1 to a specific position. Simultaneously the focal length of the whole lens system is varied, the lens groups are put in focus; and the 2nd lens group L2 is stationary and the motor 5, a gear, and a screw correspond to the 2nd moving means. Thus, the two driving means which have different characteristics are used. Consequently, various restrictions required to hold an image plane position are removed and the zoom lens can be reduced in size and cost and simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zoom lens, and particularly to a driving method for a lens group in a zoom lens, including focusing.

(Prior art) Conventionally, in the lens group movement system of zoom lenses used in still cameras, video cameras, etc., the movement of each group for zooming is provided by a cam, and the movement of each group for zooming is provided separately from zooming. Generally, the focusing group was moved by means such as a focusing motor. For the sake of simplicity, a two-group zoom will be explained as an example.

FIG. 2 is a conceptual diagram of a cross section of a lens barrel of a two-group zoom lens that is often used in lens-shutter cameras and is composed of two positive and negative lens groups. In the figure, reference numeral 1 denotes a fixed cylinder, and a straight rail is provided. 2 is a cam cylinder provided with a cam groove, and by rotating this cam cylinder, each lens group L1. The sliding frame 3.4 of L2 moves, and the lens group moves. After moving to a predetermined zoom position, the focusing motor 5 fixed to the frame 3 is driven to advance the lens group through the gear 6 and screw 7 to perform focusing.

However, such a lens barrel configuration requires different cams and sliding frames for the number of independently movable lens groups, which inevitably increases costs due to the complexity of the mechanism and the large number of parts. Furthermore, if there is even one lens group that moves a large amount, the diameter of the cam barrel becomes large, leading to an increase in the size of the entire camera.

Furthermore, in order to keep the image plane position constant, in many cases,
A curved cam groove is required, making it difficult to maintain accuracy. On the other hand, Japanese Patent Laid-Open No. 1-191821 proposes a method in which all cam grooves are made linear and the resulting focus deviation is corrected by focusing. However, even in this case, when there is a group that moves a large amount, an increase in the cam cylinder diameter is unavoidable.

Separately, with conventionally called varifocal lenses, the focus position shifts during zooming, but the focus position must remain unchanged, at least for objects at infinity, so there are no restrictions. It remained.

(Problems to be solved by this invention) The purpose of this invention is to propose a new driving method for zoom lenses, alleviate the above-mentioned constraints necessary to keep the image plane position constant, and The entire zoom lens including the miniaturization, simplification,
The aim is to achieve cost reduction.

(Means for Solving the Problem) In order to achieve the above object, the zoom lens of the present invention has a plurality of lens groups that move on the optical axis during zooming, while changing the intervals between the lens groups. a first moving means that carries at least two moving lens groups and provides movement on the optical axis without changing the distance therebetween; and a first moving means that moves only the one lens group on the first moving means. It is characterized by having a second moving means.

Note that zooming here refers to changing the focal length of the lens system while keeping the imaging position of the entire lens system for an object at infinity within the depth of focus relative to a predetermined position where the film or image sensor is placed. It means to change.

Further, the first moving means and the second moving means are electrically linked, and for operational reasons or the like, the lens group on the first moving means is moved by the second means while the first moving means is moving. It goes without saying that you may move the .

(Examples) Hereinafter, the present invention will be explained in detail with reference to Examples. 1st
The figure is a schematic cross-sectional view of the lens barrel when the present invention is implemented with a zoom lens having the same lens group configuration as in FIG.
Identical members are given the same reference numerals. In this example,
A motor 5 and a second lens group L2 are fixed to the sliding frame 8. All movement of the second lens group □ with respect to the second lens group L2 is provided by this motor.

Zooming is performed as follows. The cam barrel 2 is rotated manually or by a motor for changing the focal length (not shown), and the second lens group L2 is moved to an arbitrary zoom position. At this time, if the motor 5 is not driven, the lens group holder moves together with the second lens group L2, and the distance between the first lens groups remains unchanged. This rotation of the cam cylinder 2 is the first rotation in the present invention.
It becomes a means of transportation. Next, the motor 5 is driven to move the first lens group L to a predetermined position, thereby changing the focal length of the entire lens system and focusing.

At this time, the second lens group L2 is stationary, and the motor 5, gear 6, and screw 7 serve as the second moving means in the present invention. Here, the cam cylinder, motor, and gears are used as the first and second moving means, respectively, but it goes without saying that other opening means may be used as long as they provide the same effect.

In the above-mentioned embodiment, the configuration that conventionally required two sliding frames can now be replaced with one sliding frame. In addition, with this configuration, the movement of the cam barrel 2 only needs to be restricted to the position of the second lens group, regardless of the position of the first lens group, so it is difficult to maintain high precision with the curved cam. The use of is no longer necessary.

In the above embodiment, the second lens group on the object side of the second zoom group is moved away by the second moving means, but the second lens group on the image side may be moved open. A schematic diagram of the lens barrel configuration at this time is shown in FIG. 3 as Example 2. In the first embodiment, the cam barrel was left in place for comparison with the conventional example, but if the present invention is implemented in the second group zoom, there is no need to use a cam, and the third
As shown in the figure, a linear rail parallel to the optical axis may be provided on the copying cylinder 11, and the sliding frame 12 to which one lens group is fixed may be moved along the rail. In the case of a two-group zoom, the amount of movement of the rear group was large, leading to an increase in the diameter of the cam barrel.
With such a configuration, there is no need for a cam for the movement of the rear group, making it possible to downsize the lens barrel.

The movement by the second moving means in the zoom lens of the present invention includes a focusing operation, but the amount of focusing and the resulting change in performance are large, and it may be inappropriate to use the moving lens group as a focusing group. . In such a case, the focusing problem can be solved by increasing the F number a little and adopting a fixed focus method.

Furthermore, in a zoom lens having three or more lens groups, focusing may be performed by groups other than the lens groups moved by the first and second moving means.

A schematic diagram of the lens barrel configuration at this time is shown in FIG. 4 as Example 3. In this example, the second and third lens groups L2 and L3 are two lens groups mounted on the first moving means referred to in the present invention. The lens groups L0, L2, L,
After moving to an arbitrary zoom position, focusing is performed by moving the lens group L1, which is moved by a moving means different from the first and second moving means, such as the focusing motor 13. Of course, at this time, the third lens group L3 can also be used as an auxiliary focusing lens group. By driving the third lens group L3, which has the largest amount of movement, with the second moving means, a cam for the third lens group L3 becomes unnecessary, and as in Example 2, this greatly contributes to the miniaturization of the lens barrel. .

In the embodiment shown in FIG. 3 as well, the positive front group L of the second zoom group can be used as the focusing group. Third
The figure shows the state of focus at infinity at a certain focal length,
Assume that it is necessary to extend the front lens group L1 by an amount of X during close-range photography. For this purpose, first move the sliding frame 12 forward by X. At this time, the rear group also moves forward by X, but if the motor M is rotated at the same time to move the rear group X backward relative to the front group, the rear group appears to remain stationary at the reference position, and the front lens becomes the focus. Of course, the rear group does not need to be fixed at the reference position; it goes without saying that it may be moved from the reference position as an auxiliary focusing group, and in special cases, it may be possible to extend the entire rear group, but in this case, focusing The rotation of the motor M for this purpose becomes unnecessary.

In this way, when focusing, the first moving means and the second
By simultaneously using the moving means, the position of the lens group moved by the second means can be arbitrarily set.

Focusing can be performed not only in two-group zoom but also in cases where the lens group moved by the second moving means is inappropriate as a focusing group.

In the present invention, if the second moving means is used for focusing and the lens group moved by this means is made into an independent focusing group, the range of application and effects will be further expanded.

The explanation will be returned to the embodiment shown in FIG. In the figure, 9 is a focal length detection device, and 10 is an object distance measurement device, and the amount of movement of the first group (position relative to the second group) required for focusing can be determined from these pieces of information. The focal length of the entire corresponding lens system is determined from the rotation angle of the cam barrel 2 or the position of the sliding frame 8, and the amount of extension of the front group L1 at that focal length with respect to the object distance from the object distance measuring device 10 is determined. , the front Wcr-x may be moved by the motor 5 to a position corresponding to its focal length and extension amount.

FIG. 5 is a schematic diagram of the lens barrel structure of Example 4, and shows the corrective work and
This is an example in which the negative second group is used as a focal length changing and focusing group in a three-group zoom of negative L2 and positive L3. 1st and 3rd
The lens groups L1 and L are fixed to one sliding frame 16 (first moving means) together with the second lens group swinging motor M (second moving means), and are moved as a unit.

The arrows in the figure indicate the movements of each lens group during zooming.

In this example, 11. An imaging state detection device 15 is disposed at a position equivalent to the imaging plane, and information from the imaging state detection device 15 is used to detect the second lens group L.
2 is driven by motor M and focused. In this case, as in the third embodiment, the cam is unnecessary.

FIG. 6 is a schematic diagram of the lens barrel configuration of Example 5, in which a negative lens group is arranged behind the lens system of FIG. 5 to form a four-group zoom. That is, the movement of the sliding frame 17 for the first and third lens groups and the sliding frame 18 for the fourth lens group is controlled by the cam cylinder 19 (first moving means), and the first
- Relative movement of the second lens group with respect to the three lens groups is provided by a motor M (second moving means). Although peripheral devices for focusing are not shown in the figure,
Either method shown in the figure may be used. As shown in FIGS. 5 and 6, by moving the groups on both sides of the focusing group as a whole, the 1st group zoom can be achieved with the same lens barrel configuration as the (i-2) group zoom. Downsizing, simplification,
This can greatly contribute to cost reduction.

The focusing method shown in Figures 5 and 6 is called the inner focus type, which has the advantage of being smaller in diameter than the front focusing lens, but has the disadvantage that the amount of focusing for the same object distance varies depending on zooming. There is. However, by using the focusing method as in the above embodiment, the above drawbacks can be easily overcome and the effects of the inner focusing method can be maximized.

In particular, it is effective to use a focal length detection device and a distance measuring device as shown in FIG. In reality, it stores the position of the focusing group corresponding to each focal length and object distance, or the position of the focusing group for a specific focal length, and the conversion coefficients used to calculate the position at other focal points NJl. It has a storage device, and focuses by moving the focusing group to a position stored therein or to a position calculated using a conversion coefficient. In other words, even if the focusing amount differs depending on the focal length due to the inner focus method, it is only necessary to store the position data or the conversion coefficients necessary for calculation, which are calculated in advance on the premise of inner focus, in the storage device mentioned above. It is about.

The first aspect of the present invention. There may be a plurality of sets of second moving means. FIG. 7 is a cross-sectional view of the sixth embodiment, which has two first moving means, and by integrally moving the lens groups on both sides of the lens group moved by the respective second means, the 6
The group zoom is achieved with the same lens barrel configuration as the second group zoom.

When the present invention is used, the number of focusing groups does not need to be one, and as already mentioned in the description of the embodiment shown in FIG. 4, there may be a plurality of focusing groups. In this case, if the group moved by the second moving means of the present invention is one of the focusing groups, the above-mentioned effects can be expected as is. In actual use, focusing may be performed with multiple lenses only for close-up photography, or multiple lenses may be used for all subject distances.

Furthermore, it is said that a zoom lens is one in which the image plane position does not change even when the focal length is changed, and a varifocal lens is one in which the image plane position changes over the range of the depth of focus. ing. However, in the present invention, at least two means are used to change the focal length, and these means are also used for focusing at the same time, so it is difficult to clearly distinguish them according to conventional definitions. Therefore, in the present invention, for objects at infinity, there is a device that has a means for changing the focal length while keeping fluctuations in the image plane position within the depth of focus, and also a device that has a means for changing the focal length while keeping fluctuations in the image plane position within the depth of focus. It also falls under the category of zoom lenses.

(Effects of the Invention) As described above, the zoom lens of the present invention uses two moving means with different properties for a plurality of lens groups that move on the optical axis while changing the distance between them, so that the zoom lens of the present invention This eliminates the various constraints that were necessary to maintain the surface position, opening up the possibility of miniaturization, simplicity, and cost reduction.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the lens barrel configuration of an embodiment of the zoom lens of the present invention, and Fig. 2 is a schematic diagram of the lens barrel configuration of a conventional two-group zoom lens.
One example schematic diagram, FIG. 3.4.5.6.7, is a schematic diagram of the lens barrel configuration of Example 2.3.4.5.6, respectively. 1: Fixed cylinder 2.19: Cam cylinder 3.4:
Sliding frame 5.13.14: Rotating motor 6: Gear 7: Screw 8.12.16.17.18: Sliding frame 9: Focal length detection device 10: Object distance measurement device 11: Fixed barrel 15: Imaging state detection device

Claims (7)

[Claims] (1) In a zoom lens having a plurality of groups that move on the optical axis during zooming, at least two lens groups that move while changing the distance between them are installed so that the optical axis can be moved without changing the distance between them. A zoom lens comprising: a first moving means for moving above; and a second moving means for moving only one lens group on the first moving means. (2) In claim 1, the zoom lens uses a fixed focus method that focuses at a hyperfocal distance. (3) The zoom lens according to claim 1, wherein the focusing group is controlled based on distance measurement information and focal length information. (4) The zoom lens according to claim 1, which detects the imaging state and further controls the focusing group based on focal length information as necessary. (5) A zoom lens according to claim 3 or 4, characterized in that it has a plurality of focusing groups. (6) The zoom lens according to claim 3 or 4, characterized in that a lens group other than the lens group closest to the object side is a focusing group. (7) A zoom lens according to claim 6, characterized in that lens groups on both sides of the focusing group move together.