JPH02266312A - Zoom lens system - Google Patents

Abstract

PURPOSE:To control a focusing system at high speed with high accuracy by providing a focus position arithmetic means and calculating the position of the focusing system corresponding to an optical object distance from the position information on a focusing system. CONSTITUTION:When the object is focused by manual focusing or automatic focusing before zooming operation, a zoom encoder 8 detects the position of a variator 6, a focus encoder 9 detects the position of the focusing system 7, and respective pieces of information on them are outputted to a focus position arithmetic means 10. At this time, the focus position arithmetic means 10 calculates the position of the focusing system corresponding to the optional object distance from respective pieces of position information on the focusing system corresponding to >=3 object distances. Consequently, fast, high-accuracy arithmetic operation is performed, so the zooming operation is carried out while a focusing state is maintained at the optional object distance.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a zoom lens system used in video cameras, still cameras, and the like.

Various focusing methods for conventional cameras have been proposed, and many proposals have also been made for focusing using lens groups other than the front-most blade group closest to the subject, that is, so-called rear focus lens systems.

Although this rear focus method has the advantage of being able to focus up to close range without increasing the size of the lens system, and because the moving lens group is light, the load on the drive system is lightened. There is a drawback that when the focal length is changed relative to the subject distance, the imaging position changes unless the focusing system is moved.Means for solving this drawback have conventionally been proposed, for example, in Japanese Patent Laid-Open No. 52-66445.
JP-A-52-114321, JP-A-55-40447, and the like.

In Japanese Patent Application Laid-Open No. 52-66445, a relational expression between the focal length and the position of the focusing system recognized from the subject distance and the position of the zooming system is used, and the image forming position is corrected by a mechanical method using the above relational expression as a cam shape. One example realizes the correction of the focusing system position, and the other realizes the correction of the imaging position by an electrical method using arithmetic means.
Store the desired focusing system position in M as a table and ROM it.
It has been shown that the image forming position is corrected by reading out the image from the image data, and Japanese Patent Application Laid-Open No. 55-40447 discloses that an autofocus device is used to correct the change in the image forming position.

Problems to be Solved by the Invention The mechanical control method disclosed in JP-A-52-66445 requires a highly accurate and complicated cam mechanism, resulting in an expensive and large system. When using the complex calculation formula described in JP-A-52-114321, it is difficult to perform high-speed calculations and the speed of zooming that can be tracked by the focusing system becomes slow, making it impractical. In this case, the memory becomes expensive, and the ROM becomes expensive and requires a large mounting area. Furthermore, considering manufacturing errors in the mechanism, it is disadvantageous to store all focusing system position information in ROM because it lacks flexibility. The means disclosed in Japanese Unexamined Patent Publication No. 55-40447 requires time for the autofocus device to determine and process the in-focus state, making it difficult to follow a high-speed focusing system.

In addition, when calculating the movement amount of the focusing system using a certain arithmetic expression, the movement amount of the focusing system is Δ, the subject distance is u2, the focal length of the focusing system is f, then the following functional formula is used: Δ−f 2 / u It is known that approximation is possible. Since the second function has a simple form, it is easy to perform high-speed calculations on a microcomputer, etc. However, the accuracy of the movement amount determined becomes worse as the subject distance becomes shorter, resulting in image blurring. There is.

The present invention solves the above-mentioned problems, and makes it possible to perform high-accuracy and high-speed calculations by appropriately calculating the movement of the focusing system that corrects changes in the imaging position due to changes in zooming and subject distance. The objective is to provide a compact and lightweight zoom lens system.

Means for Solving the Problems A zoom lens system according to the present invention uses a lens group other than the lens group closest to the subject among a plurality of lens groups constituting the zoom lens system, or a part thereof as a focusing means, A zoom encoder that has a manual or automatic zooming function and detects the position of the zoom system, which is a lens group used for zooming, and a focus encoder, which detects the position of the focusing system, which is a lens group or image pickup device used for focusing. and a focus position calculation means for calculating the position of the focusing system based on the outputs of the zoom encoder and the focus encoder so as to maintain a focused state during zooming, and the focus position calculation means includes at least three or more It has position information of the focusing system at the subject distance, and is configured to calculate the position of the focusing system at an arbitrary subject distance from the position information of the focusing system at the at least three subject distances.

Effect of the Invention The present invention can provide a zoom lens system that can perform zooming without maintaining focus at any object distance because high-speed and high-precision calculations can be performed with the above-described configuration.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

Figure 1 shows a lens arrangement diagram of an embodiment of the zoom lens of the present invention.The zoom lens of this embodiment has a fixed lens group 1 with positive power and a variable lens group 1 with negative power from the subject side. It consists of a movable lens group 2 as a variator with a multiplier effect, a fixed lens group 3 with positive power, and a movable lens group 4 as a focusing lens group with a positive power waiting and focusing effect. When moving from the short focus side to the long focus side, the variator moves in the direction of the arrow in FIG. The focusing lens group moves as indicated by the arrow in FIG. 1 as the variator moves. FIG. 2 is a graph showing the relationship between the object distance and the movement of the focusing system due to the movement of the variator. In FIG. 2, the vertical axis is the position of the focusing system, and the horizontal axis is the position of the variator. Ll is the locus (tracking curve) of the movement of the focusing system during zooming at an infinite subject distance, and L2. La... indicates a tracking curve of a shorter distance. These tracking curves are for an open lens system, and in the case of FIG. 2, they are for a zoom lens with a zoom ratio of 6 times and an F number of approximately 1.4.

As shown in Figure 2, the amount of movement of the focusing system during zooming is not constant, and the tracking curve does not change linearly as the subject distance changes.It is possible to follow the trajectory of such a tracking curve. A diagram explaining the principle of the present invention is shown in FIG.
is a tracking curve of the object distance stored in the ROM in the calculation microcomputer. The areas surrounded by each tracking curve are designated as Area and Area2, respectively, and when the position of the second group is X, the position of the focusing system in each tracking curve can be calculated from the contents of the ROM.
b, Xc. If the focusing system is now at point P and in focus, it can be seen that point P is located in Area 2 by comparing the magnitudes of P, Xa, Xb, and Xc. Furthermore, if R is the ratio of the distance between P and xb and the distance between xb and Xc, then R
-(P-Xb)/(Xc-Xb) When the position of the second group changes from X to X', Xb and Xc corresponding to X' are determined and the position P' of the focusing system is moved to maintain the in-focus state. is P' -RX (X
c-Xb). By performing this operation in response to changes in subject distance and zoom position, it is possible to perform the zoom operation while maintaining the in-focus state.

FIG. 4 shows a system block diagram of the present invention.

As already shown in FIG. 1, the zoom lens 5 is composed of a variator 6, a focusing system 7, and other lenses.

Before starting zooming, when focusing on a subject using manual focus or autofocus, the position of the variator 6 is detected by the zoom encoder 8, the position of the focusing system 7 is detected by the focus encoder 9, and each position information is used to set the focus. It is output to the position calculation means 10. At this time, the focus position calculating means 10 calculates the ratio R described above from the two input signals. When zooming starts, the position of the variator 6 changes, the output of the zoom encoder 8 changes, and enters the focus position calculation means IO. The position of the focusing system 7 that is in focus at the changed zoom position is calculated by the above calculation. The calculated position of the focusing system is transmitted to the focus driving section 11, and the focusing system 7 is driven by the motor 12.

Note that the zoom lens system of the present invention can be applied to a so-called inner focus type zoom lens other than the birch configuration shown in FIG.

Further, it is sufficient that the focusing position information at the subject distance to be stored in the ROM should be at least two types, i.e., infinite distance and close distance, but if high accuracy is required, three or more types are desirable.

As described in detail, the zoom lens system of the present invention can control the focusing system at high speed and with high precision by executing the above calculations, so it can maintain focus at any subject distance. Compact and capable of high-speed zooming
Since it is possible to provide a lightweight zoom lens system, it has an effect of extremely high practical value.

[Brief explanation of drawings]

FIG. 1 is a layout diagram of a zoom lens system according to an embodiment of the present invention, FIG. 2 is a graph showing the relationship between the object distance and the movement of the focusing system due to the movement of the variator, and FIG. 3 is a diagram explaining the principle of the present invention. FIG. 4 is a system block diagram of the present invention. l...Fixed lens group, 2...Variator, 3...Fixed lens group, 4...Focusing system, 5...Z, -Mullens, 6...
... Variator, 7 ... Focusing system, 8 ... Zoom encoder, 9 ... Focus encoder, 10 ... Subject distance calculation means, 11. ...Focus position calculation means, 12
...Focus drive unit", 13...motor. Agent's name: Patent attorney Shigetaka Awano.

Claims (1)

[Claims] A zooming function that is performed manually or automatically in a zoom lens system that uses a lens group other than the lens group closest to the subject, or a part thereof, as a means of focusing among the multiple lens groups that make up the zoom lens system. a zoom encoder that detects the position of a zoom system that is a lens group used for zooming, a focus encoder that detects the position of a focusing system that is a lens group or an image sensor used for focusing, and the zoom encoder and the focus encoder. The focus position calculating means calculates the position of the focusing system based on the output of the focusing system so as to maintain the focused state during zooming, and the focus position calculating means calculates position information of the focusing system at at least two or more subject distances. What is claimed is: 1. A zoom lens system comprising: a zoom lens system, wherein the position of the focusing system at an arbitrary subject distance is calculated from the position information of the focusing system at the at least three subject distances.