JPS63279232A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To raise a focusing rate and also to shorten the time from the measurement of distance to photographing by computing a focal position based on the distance measured result of plural points in a screen and moving a lens unit to a specified position. CONSTITUTION:A microprocessor unit MPU 6 gives a light emission starting signal to a light emission control circuit 2 through an interface circuit 5. The circuit 2 sequentially lights light projecting elements 1a, 1b and 1c in a specified timing and a reflected light from an object is inputted in a light receiving element 3, then a distance measuring circuit 4 computes a distance to the object. The distance measured information is inputted in the MPU 6 and the order relation of a central object to other objects is decided so as to compute the distance difference among the central object, the front side and the decided object. And the lens unit 8 is moved by the mean value of the difference, setting a distance value nearer to the front side than the central object as a focal position. Thus, the focusing rate can be raised and also the time from the measurement of distance to photographing can be shortened.

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention relates to an automatic focusing device used in still cameras, video cameras, etc. The present invention relates to an automatic focusing device that determines a focus based on a plurality of distance measurement results.

(Background of the Invention) The drawback of the conventional single-point distance measuring autofocus device is that in scenes where two people are lined up or where the person is biased toward the edge, Subject (person)
In order to solve this problem, a so-called wide-field distance measuring method was proposed that measures multiple points within the screen. has been done.

Examples of conventionally known autofocus devices that use such wide-field distance measurement include: (1) one that focuses on the closest distance measurement result among multiple distance measurement results (for example, General & Mechanical
ECHANICAL) 4582424, JP-A-1981-
(No. 88211, Japanese Unexamined Patent Publication No. 81-55FI18) (2) Closest distance measurement value - Focus on the closest point from the distance measurement point, or within a certain range with respect to the intermediate value of multiple distance measurement results. There are methods that select whether to focus on a value obtained using, for example, an average value.

However, the above method (1) has the problem that if there is an obstacle in front of the main subject or a foreground, the focus will be on it and the main subject will not be in focus.

In addition, the above-mentioned method (2) judges whether or not there is an obstacle based on the distance measurement value and the distance measurement point, and if it is an obstacle, it ignores the closest one, and if it is within a certain range with respect to the intermediate value. By focusing on the average value, etc., and focusing on the closest object if it is not an obstacle, it prevents the focus from being focused on nearby obstacles, but the center where the main subject is most likely to be Since the distance measurement information of the central part is treated equally to the distance measurement information of the peripheral part except for the determination of obstacles, there is a problem that the central part becomes less focused.

Since the algorithm is complex, it takes time from the start of distance measurement until the shutter is actually released, and it also requires a large amount of memory space, which increases costs.

(Object of the Invention) The present invention has been made from the above-mentioned viewpoints, and its purpose is to provide an automatic focusing device that performs wide-field distance measurement to find a focus, and uses distance measurement results for multiple points within a screen. Autofocus focuses on distance measurement information in the center, where the main subject is most likely to be present, and prevents focusing on the nearest peripheral subject, as well as preventing the center from becoming out of focus. The purpose is to provide a device.

(Summary of the Invention) The gist for achieving the object of the present invention is to shift the focal point to a position nearer to the center object by the average distance difference between the center object and objects nearer than the center object. In other words, the focus rate of the main subject is increased by weighting the distance value of the central subject and averaging it with other subjects.

(Embodiments of the Invention) The present invention will be described in detail below based on embodiments shown in the drawings. .

Embodiment 1 FIG. 1 is a diagram showing the principle of active distance measurement applicable to the present invention, and this method utilizes the triangulation method used in, for example, lens-shutter cameras.

In FIG. 1, the output light of the light emitting element 22 is
The spot light is focused as a narrow beam onto the subject 25, and the spot light reflected by the subject 25 is caused to form a real image on the surface of the light receiving element 24 by the light receiving lens 23. The deviation d of the spotlight from the center position shown in Fig. 1 is inversely proportional to the distance to the subject, and the closer it gets, the larger d becomes.
This relationship is expressed as f/L=d/S (where f is the focal length of the light receiving lens 23,
S is the baseline length).

Note that the number of points within the screen to be measured in the wide-field distance measurement method is determined as appropriate depending on the purpose of the camera using the autofocus device, cost, etc., but in the following example, for convenience, the method shown in Fig. 3 is used. An example will be explained in which the distance is measured from a total of three points, one point at the center of the screen and two points at the periphery of the screen shown in FIG.

FIG. 2 is a block diagram showing the configuration of the automatic focusing device according to the first embodiment of the present invention, and in this figure, la, lb
, lc designate a block of a light projecting element and a light projecting lens for performing distance measurement corresponding to the three points on the screen, and the light emission is controlled by the light emission control circuit 2. Reference numeral 3 indicates a block of a light receiving element and a light receiving lens, and an output terminal from the light receiving element is connected to a distance measuring circuit 4 that calculates the distance to the subject. Reference numeral 5 denotes an interface circuit having an A/D conversion function, which connects a microprocessor unit (hereinafter referred to as MPU) 6 and various circuits. 7
is the photographic lens unit 8 based on the control signal from the MPU.
A moving circuit for moving the lens to the in-focus position is shown.

The operation of the automatic focusing device in this example configured as described above begins with turning on the main switch (not shown).
A light emission start signal is given from the PU to the light emission control circuit 2 via the interface circuit 5. Thereby, the light emission control circuit 2 sequentially lights up the light emitting elements 1a, lb, and lc at timings given by various constants preset in the circuit.

The output light from the light emitting element is reflected by the subject and passes through the light receiving element 3.
A real image is formed on the surface of the object, and the distance to the subject corresponding to each distance measurement point shown in FIG. be done.

The distance measurement information calculated in the distance measurement circuit 4 is read into the MPU 6 via the interface circuit 5, and the focus position is calculated in the MPU 6 as described below.
Based on the calculation result, the driving circuit 7 moves the photographing lens unit 8 to a predetermined position.

The drive circuit 7 has two types: a stepless drive method that drives the lens unit 8 steplessly according to the focal position, and a stepwise drive method that drives the lens unit 8 stepwise in consideration of the amount of blur, depth of field, etc. In this stepped drive system, the focusing stages are called 1 @, 2 teeth, 3 teeth, etc. in order from the far side to the near side, and the MPU
This number of teeth is calculated from the distance information obtained in step 6.

The feature of the autofocus device of the first embodiment having the above configuration and operation is that the photographing lens unit 8 is moved based on the distance measurement result information (distance measurement value) for the three points mentioned above from the distance measurement circuit 4. The operation procedure of the MPU 6 for calculating, calculating and outputting the control signal is performed according to the flowchart shown in FIG.

The procedure will be explained in detail below.

The MPU 6 reads the distance measurement results for three points on the screen, and compares the distance measurement results at the periphery of the screen, t, (1), L (3), with the distance measurement results at the center of the screen, 2). Shi,t,
If (t), L(3) is closer to L(2), calculate the difference (XI + xm) between t, (t), t, (3) and L(2), respectively. The difference is 172
The lens unit is driven with a value obtained by subtracting L(2) from L(2), that is, a value that is closer to the center distance value by the difference of 172, as the focal position. Note that L(1), L(
2) , L(3) is the number of teeth.

However, if t, (2) > L (1), then
! If OlL (2) > L (3), then x, xO
shall be.

Since L(1), L(2), and L(3) are the number of teeth, the in-focus position must also be the number of teeth, so they are converted into integers using an int function.

Therefore, the focusing rate of the central subject, where there is a high probability that the main subject exists, is increased, and peripheral subjects, where there is a high probability that an obstacle or the like exists, are prevented from being brought into focus.

Embodiment 2 FIG. 5 shows a flowchart of Embodiment 2, and this embodiment uses the same distance measuring device as Embodiment 1.

In this embodiment, as in the first embodiment, the MPU 6 reads the distance measurement results at three points on the screen and calculates the focal position, and the drive circuit 7 controls the photographing lens unit 8 based on the calculation results.

MPtJ6 reads the distance measurement results of the three points and calculates the distance measurement results L (1), L (3) for the peripheral area and the distance measurement result L (
2), L (1) and L (3) are L (2)
If it is closer, L (1), L (3)
To calculate the difference between L(2) and L(2), let this be X I * x2), and calculate the value closer to the proximal side by 172 of the difference. However, L (1) and L (3) are L
(2) If it is on the far side, set Xl and x2 to zero. Furthermore, compare L with L (1) and L (3), and if this difference is large due to a constant determined from the focal length of the photographing lens, the open F value, etc., the distance measurement value L (
2) will also be the closest distance value 1) or L(3)
There is a high possibility that none of the images will be in focus, so
In this case, the distance measurement value at the center of ° is taken as the focal position. In other cases, L is the focal position.

Further, the flowchart of the second embodiment can be rewritten as shown in FIG. In this case, the distance values at the periphery are both closer to the distance value at the center, and the distance values at the periphery are similar values (L (1) 2L (3)). If this is the case, the distance measurement value at the periphery is used as the focus position, and otherwise the distance measurement value at the center is used as the focus position. The determination of L (1), L (3) is made based on whether the absolute value of (L (1), L (3)) is large or small with respect to the constant k, which is determined from the focal length of the photographic lens, the aperture F value, etc. . In other words, I L(1) -L(3) If l <k, determine L(1)2L(3), and L(1) and L(3)
The focal position is the average of

Embodiment 3 FIG. 6 shows a flowchart of Embodiment 3, in which the same distance measuring device as in Embodiment 1 is used.

In this embodiment, as in the first embodiment, the MPU 6 reads the distance measurement results at three points on the screen, calculates the focal position, and the drive circuit controls the photographing lens unit based on the calculation results. M
The PU 6 averages the read distance measurement results of the three points according to the following formula to obtain a focal ratio of 1iL.

Note that L(1), L(2), and L(3) indicate distance, and a is a constant number of about 2 to 5, which is determined by the focal length of the lens, photographing conditions, etc. This method achieves the same effect as the first and second embodiments by weighting and averaging the distance measurement results of three points using center weight and near point.

Example 4 In Example 3, the MPU calculates the weighted average of the distance measurement values at three points, but in this example, an optical system is used to optically calculate the weighted average on the light receiving element surface. .

That is, as shown in FIG. 7, the light emission control circuit 2 receives a light emission start signal from an MPU (not shown) and controls the light emission amount of the three light projecting elements 1a, lb, and lc to be 1:a:1. Each light emitting element is controlled and turned on simultaneously. The output light from each light projecting element reflected by the object forms a real image on the surface of the light receiving element 24 by the light receiving lens 23, and the amount of each reflected light reaches the surface of the light receiving element approximately in inverse proportion to the square of the distance. Therefore, it is possible to optically take a weighted average on the surface of the light receiving element 24. 26 indicates a reflecting mirror.

Further, as shown in FIG. 8, instead of controlling the amount of light emitted by the light emission control circuit 2 shown in FIG. 7, the light emitting element 1a,
Insert an ND filter 27 in front of the LB and LC to increase the ratio of the amount of emitted light to 1:a:! When a light emission start signal is given from the MPU, if the light emitting elements 1a, lb, and tc are turned on at the same time, a weighted average can be obtained optically on the surface of the light receiving element 24. Note that the insertion position of the ND filter 27 is the 8th
It does not have to be on the light emitting side as shown in the figure, and may be inserted on the light receiving side.

In each of the above embodiments, the first Uf! Although the active distance measuring device shown in J is used, the algorithms of the first, second and third embodiments of the present invention can be applied to cases where other distance measuring devices are used. For example, the distance measuring device is SS
Possible examples include a Padge-Eve type distance measuring device called T, and a Padge-Eve type distance measuring device using a small recombination lens group, which is mainly used in the AF of single-lens reflex cameras.

(Effects of the Invention) As explained above, the present invention focuses on the nearest subject where there is a high probability of an obstacle being present by emphasizing distance measurement information in the central area where there is a high probability that the main subject exists. In addition to preventing this, it also prevents the central area from becoming loosely focused, which results in a higher focusing rate compared to conventional single-point distance measurement or wide-field distance measurement.
This has the effect of simplifying the algorithm for determining the focal position.

Furthermore, by simplifying the algorithm, the time from distance measurement to actual photographing can be shortened, and the required memory area can also be reduced.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of active distance measurement applicable to the present invention, Fig. 2 is a block diagram showing an embodiment of an automatic focusing device according to the present invention, and Fig. 3 is a diagram showing a light projecting element within the screen. Figures 4, 5, 6, and 9 showing the light projection positions of
The figure is a flowchart, FIG. 7 is a diagram for explaining an example of weighting based on the amount of light from a light emitting element, and FIG. 8 is an ND
FIG. 3 is a diagram for explaining an example in which weighting is performed using a filter. 1 a, 1 b, 1 c, 22 - light emitting element 2... light emission control circuit 3.24... light receiving element 4... distance measuring circuit 5... interface circuit 6... microprocessor - Unit (MPU) 7・
...Drive circuit 8...Lens unit 21...
- Light projecting lens 23... Light receiving lens 25... Subject 26... Reflecting mirror 27... ND filter Figure 1 Figure 2 Figure 3 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. Distance measuring means for detecting the distance to the subject at least two points including one point approximately in the center of the screen;
a focus position means for determining a focus position for focusing on a main subject based on a plurality of distance measurement information from the distance measurement means, and a photographing lens unit that is moved to match the focus position given by the focus position determination means. The focus position determining means determines the front-back relationship of other subjects with respect to the central subject, calculates a distance difference between the central subject and the subject determined to be in front, and calculates an average value of the differences. An automatic focusing device using a wide-field distance measuring method, characterized in that it is configured to set a focus position at a distance value that is closer to the central subject by the amount of time. 2. A distance measuring means for detecting the distance to the subject at least two points including one point approximately in the center of the screen;
a focus position means for determining a focus position for focusing on a main subject based on a plurality of distance measurement information from the distance measurement means, and a photographing lens unit that is moved to match the focus position given by the focus position determination means. the focus position determining means is configured to weight the measured distance value of the central subject and average it with other subjects to determine the focal position. A distance-based autofocus device. 3. Distance measuring means for detecting the distance to the subject at least two points including one point approximately in the center of the screen;
a focus position means that averages and determines a focus position to focus on the main subject based on a plurality of distance measurement information from the distance measurement means;
and a lens driving means for moving the photographing lens unit to match the focal position given by the focal position determining means, and the distance measuring means is configured to weight distance measurement information of the central subject. A wide-field distance measuring automatic focusing device.