JPH0365911A - Automatic focusing controller - Google Patents

Abstract

PURPOSE:To make an error extremely small by using sensitivity when the error is larger than a mean value by inputting the sensitivity value at specific intervals from the start to the end of sensor storage, finding the mean value, and calculating a lens driving quantity by using the sensitivity value at the start of the storage. CONSTITUTION:When the absolute value of a defocusing quantity (d) is larger than a specific value, a lens system is driven by V to detect the sensitivity repeatedly throughout the storage. Thus, the sensitivity value is detected repeatedly throughout the storing operation and mean values S0 - S3 of the detected sensitivity value are used to find the lens driving quantity V. Consequently, the lens driving quantity V is accurately found. Further, when the frequency of sensitivity detection is low, the sensitivity is used instead of the mean values S0 - S3, so trouble in a state wherein the error in the mean value becomes large can be eliminated by the system which uses the mean values S0 - S3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focus adjustment device used for photography and videography.

[Conventional technology]

BACKGROUND ART Today, cameras equipped with an automatic focus adjustment (hereinafter referred to as AF) function have become mainstream as cameras for photographing and the like. In this AF camera, images are accumulated in the AF sensor, and the accumulated sensor output signals are used to perform correlation calculations, etc. to calculate the amount of defocus up to the in-focus position. A relational expression between the defocus amount and the driving amount of the focusing lens is obtained to calculate the lens driving amount, and the lens is driven and controlled so as to be in focus.

Here, the lens relational expression is a calculation formula for calculating the amount of lens drive from the amount of defocus, and includes a coefficient called sensitivity, which is determined by the focal length of the lens and the characteristics of the drive control system. The focus amount and sensitivity have the following relationship.

■ = Lens drive amount d: Defocus amount So: 0th-order sensitivity Sl: 1st-order sensitivity S2: 2nd-order sensitivity S3: 3rd-order sensitivity The lens system attached to the camera is a zoom lens. If , the sensitivity changes depending on the zoom position, so the sensitivity is obtained when calculating the drive amount.In the following explanation, unless otherwise specified, the relational expression refers to the sensitivity. shall be ignored.

[Problem that the invention is trying to solve]

As a focus adjustment method for recent lens systems, an inner focus method (inner focus method), in which the lens portion to be driven is small and lightweight, is increasingly being used.

In this internal focusing method, as mentioned above, the lens part used for focus adjustment can be made small and lightweight, so the load on the driving actuator can be reduced, and there are advantages in making the actuator itself smaller and speeding up the driving. It also has the advantage that the shortest photographing distance can be made smaller compared to the front lens extension method. However, the sensitivity of internal focusing lens systems generally varies greatly depending on the position of the focusing lens, so if you perform AF processing while driving the focusing lens system, the lens position at the time of sensor accumulation may change. Since the lens position when calculating the lens drive amount during AF calculation processing is different, the sensitivity obtained when calculating the lens drive amount and the sensitivity during sensor accumulation are different, and the calculated lens drive amount also differs from the actual lens. There is a drawback that the amount of drive is different.

Next, the above drawbacks will be explained with reference to FIG. Figure 3 is a graph of sensitivity changes depending on the position of the focusing lens (position of the distance ring) at the telephoto end of a zoom lens with a focal length of 35 to 135 mm. It is an internal focusing lens. As is clear from the figure, the internal focusing type lens has a larger change in sensitivity than the front lens extension type lens. (In Figure 3, the sensitivity at infinite position is normalized to 1.0.) For example, the distance ring changes from 2 m to 1.3 during sensor accumulation.
When driven up to m, the sensitivity changes only from 0.95 to 0293 in the front lens system (dotted line), but changes significantly from 0.62 to 0.5 in the internal focus system (solid line).

Further, when the defocus calculation is completed and the sensitivity is acquired, the sensitivity should have changed further, and it will be thicker (different) from the average sensitivity during sensor accumulation.

In this way, in the case of the front lens method, the change was negligible, but in the case of the internal focus method, the change was large, making it impossible to accurately calculate the amount of lens drive.

A method to solve the above problem is to detect the sensitivity at the start and end of sensor accumulation or at an intermediate point in sensor accumulation, find the average value of the sensitivity, and use this average value to calculate the lens drive amount. For example, Japanese Patent Application Laid-Open No. 63-30
It is known as Publication No. 4233. However, as shown in Figure 3, the sensitivity is linear with respect to the lens position.
Therefore, even if the average value of the sensitivity at the start and end of sensor accumulation is used, it is not possible to obtain an accurate sensitivity value.

[Means to solve the problem]

The present invention has been developed in view of the above-mentioned problems.The present invention repeatedly captures sensitivity values at predetermined time intervals from the start of sensor accumulation to the end of accumulation, and calculates the average value. It is an object of the present invention to provide an automatic focus adjustment device that calculates a lens drive amount using a sensitivity value at the start of accumulation instead of an average value. With this configuration, it is possible to obtain an accurate average value of the sensitivity during the accumulation time, and when the number of times the sensitivity is acquired is small and the error with respect to the above average value is large, it is possible to obtain an accurate average value of the sensitivity during the accumulation time. This makes it possible to determine the lens drive amount using the sensitivity up to and minimize the above-mentioned error.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of a camera having an automatic focus adjustment device according to the present invention.

In the figure, 2 indicates a lens device, and 2d in the lens device 2 indicates a focusing lens system. 2f is a driving coupler connected to the shaft of a motor circuit 1f including a motor on the camera side, which will be described later; 2a is a coupling system having a gear train connected to the coupler and driving the lens system 2d;
2b is an encoder as a lens position detection circuit that detects the position of the lens system 2d and outputs a position signal according to the lens position, and 2c is an in-lens microcomputer (hereinafter referred to as microcomputer) that communicates with the camera's in-camera microcomputer, which will be described later. Communication takes place via line 3. The microcomputer 2C also has the above-mentioned sensitivity S for each lens position. +Sl+S2+S3
is built in, and sensitivity (So, Sll S2, S3) is stored in the ROM as a set for each address, with the lens position as an address. The address of the ROM is designated by the lens position signal from the encoder 26, and the sensitivity of the designated address is communicated to the camera via line 3 as described below.

1 is a camera body, and inside the camera body there is a main mirror I.
D. A distance measuring sub-mirror 1e is provided. 1a is a sensor device having the mirror system 1d, a pair of sensor arrays for distance measurement that receives the subject image via le, and a monitor sensor for controlling storage time; 1g is a microcomputer that receives image signals from the array of the sensor devices; A monitor signal from a monitor sensor is inputted via lines lb and lc, and accumulation start and end signals are transmitted to the sensor device 1a via line ld. Further, the microcomputer 1g has a built-in program to be described later, and performs lens drive amount calculation based on the defocus amount and data communication with the microcomputer 2.

Next, the operation of the embodiment shown in FIG. 1 will be explained using the flowchart shown in FIG.

Step 1 is started by pressing a release button (not shown), and in step 2, counter n in 74171g is set to O. Also, the sensor device 1a is connected via the line 1d.
An accumulation start signal is transmitted to the sensor device 1a, and the array of sensor device 1a starts accumulating image signals.

In step 3, the value of the counter n is incremented by 1, and communication with the microcomputer 2c is performed via line 3. The microcomputer 2C outputs a sensitivity value from an address corresponding to the position signal from the encoder 2b corresponding to the lens position at that time, and this sensitivity value is input to address n(1) of the memory in the microcomputer 1g. In step 4, it is determined whether or not the storage by the sensor device has been completed, and steps 3 and 4 described above are repeatedly executed until the storage is completed. On the other hand, the microcomputer Ig inputs the monitor signal from the monitor sensor via the line 1c, and when the accumulated value of the monitor signal reaches a predetermined value, the microcomputer Ig inputs the monitor signal from the monitor sensor to the sensor device 1a via the line 1d.
The storage end signal is sent to the storage end signal to end the storage. When the completion of the accumulation is detected in step 4, the process proceeds to step 5, where it is determined whether the count value of the counter n incremented during the accumulation time is n≧3. Now, if it is determined that n≧3, the process proceeds to step 6, and each time the counter n is incremented, the total value of the sensitivity for each method read into the memory is divided by the value of the counter n. Find the average value for each sensitivity of each method. In step 8, the defocus amount d is determined based on the image signal from the storage-controlled array, and the lens driving amount is determined using the following equation (1) using the average value of the sensitivity of each of the methods described above.

■-... (1) go +a's, +d''g2 +d''S3 ■= Lens drive amount, d = nib focus, 5o = average value of O-order sensitivity, S, = 1st-order sensitivity Average value, 52==average value of second-order sensitivity, 53=average value of third-order sensitivity.

In step 9, it is determined that the focus is in focus when the absolute value of the defocus amount obtained in step 8 is within a predetermined value, and step 11. Proceed to step 12. On the other hand, when it is determined that the valve is in focus, the process proceeds to step 10, where the lens driving amount V is transmitted to the motor circuit 1f, and the lens system 2a is driven by the amount of V via the coupler 2f and the coupling system 2a. Also, step 10
At the same time that lens driving is started, step 2 returns to step 2, the above-mentioned steps are executed, and the image signal accumulation operation and the like in the lens driving state are repeatedly executed. If it is determined that the lens is in focus in step 9 while repeating the above steps, lens driving by the motor circuit if is stopped in step 11, and the AF operation is ended in step 12. As described above, sensitivity is repeatedly detected during accumulation, and the average value is used as the sensitivity used for calculation, so accurate calculation processing can be performed even if the lens moves during accumulation operation. .

Also, in step 5 above, the count value of counter n is n
If it is determined that <3, step 7 is executed instead of step 6.
is executed. In step 7, the sensitivity value of each method read into the memory when the value of the counter n is i, that is, at the start of the storage operation, is used as the sensitivity of each method used in equation (1). This eliminates the inconvenience caused when the accumulation time is short and the error when calculating the average value becomes large.

Note that when step 7 is executed, the accumulation time is short and the amount of lens movement during this time is also small.
There is no practical problem in using a single point sensitivity value instead of the average value.

Furthermore, in the embodiment, the sensitivity used at step 7 is the one at the start of accumulation, but a sensitivity value at the end of accumulation or during accumulation may be used.

〔effect〕

As described above, in the present invention, the sensitivity value is repeatedly detected during the accumulation operation, and the average value of the detected sensitivity values is used to determine the lens drive amount, so it is possible to determine the accurate lens drive amount. , and when the number of detections of the above sensitivity is small, one sensitivity is used instead of the above average value. Therefore, in the method using the above average value, there are no inconveniences in situations where the error in the average value is large. It is preventable.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of an automatic focus adjustment device according to the present invention, Fig. 2 is an explanatory diagram showing a program flow for explaining the operation of the embodiment shown in Fig. 1, and Fig. 3 is a sensitivity diagram. FIG. 3 is an explanatory diagram showing the relationship between lens position and lens position. 2d... Lens system 2c, Ig... Microcomputer 1a... Sensor device Tsuta 2

Claims (2)

[Claims] (1) A focus detection circuit that detects a focus state based on an accumulated signal from a signal accumulation type sensor device and outputs a focus signal, and a relational expression showing the relationship between the focus signal amount and the driving amount of the focus adjustment lens. a relational expression generation circuit having a relational expression generation circuit; a lens drive amount calculation circuit that calculates a lens drive amount based on the relational expression from the relational expression generation circuit and a focus signal from the focus detection circuit; and a lens calculated by the calculation circuit. In an automatic focusing device having a lens drive circuit that drives the lens according to a driving amount, an average value calculation circuit is provided for calculating an average value of changes in the relational expression during an accumulation time of an image signal by the sensor device, The lens drive amount calculation circuit calculates the lens drive amount based on the above average value, and when the image signal accumulation time is short, the lens drive amount is calculated at any point in time between the image signal accumulation time and the end, instead of the above average value. An automatic focus adjustment device characterized in that a lens drive amount is determined using a relational expression from a relational expression generation circuit. (2) A focus detection circuit that detects a focus state based on an accumulated signal from a signal accumulation type sensor device and outputs a focus signal, and a relational expression that indicates the relationship between the focus signal amount and the driving amount of the focus adjustment lens. a relational expression generation circuit having a relational expression generation circuit; a lens drive amount calculation circuit that calculates a lens drive amount based on the relational expression from the relational expression generation circuit and a focus signal from the focus detection circuit; and a lens calculated by the calculation circuit. In an automatic focusing device having a lens drive circuit that drives the lens according to a drive amount, the relational expression from the generation circuit is repeatedly detected during the accumulation time of the image signal by the sensor device, and the relational expression of the relational expression is detected. An average value calculation circuit for calculating an average value is provided, and the lens drive amount by the lens drive amount calculation circuit is calculated based on the average value, and when the number of times the relational expression is detected during the accumulation of the image signal is less than a predetermined value. An automatic focusing device characterized in that a lens driving amount is determined using one of the detected relational expressions instead of the average value.