JPS61186917A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To detect correctly a focus even in case when a contrast of an object is low by constituting a titled device so that focusing can be executed based on an average value of distance detecting information of plural times from a object distance detecting device. CONSTITUTION:A surface F corresponds to a focal plane of a photographic lens 1. That is to say, when a video camera is supposed, an image pickup sur face position of an image pickup tube becomes F. Accordingly, when the lens 1 changes a position by moving back and forth on an optical axis, a distance of an object for forming an image correctly on the surface F is different, and outputs an, bn of each picture element An, Bn, become an=bn and an-1=bn-1, respectively, but in case an image of an object which is not in a focused dis tance is caught said outputs become an=bm and anot equal to m. In order to calculate a shifting quantity and a direction of an an curve and a bn curve, a CPU executes a prescribed processing. The shifting quantity against the distance of the object is brought to a distance measuring operation repeatedly by pre scribed number of times, and its output is impressed to an averaging circuit 118. This circuit 118 operates an arithmetic average value of plural pieces of shifting quantity, and the lens is adjusted to a focused state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focus adjustment device suitable for photographing devices such as video cameras and still cameras.

[Conventional technology]

Conventionally, the distance to the subject was detected using a distance detection device,
Various automatic focus adjustment devices have been proposed that automatically adjust the focus of an objective lens of a photographing device. Broadly speaking, these conventional methods detect distance information by projecting a light projection pattern onto a subject and detecting the reflected light. It can be divided into the so-called active method and the so-called passive method (for example, U.S. Pat. No. 4,185,191), which blurs the subject or forms two images of the subject through different optical paths and detects the amount of deviation between the two to detect distance information. .

However, the former and latter methods have advantages and disadvantages.
It! For example, in the latter passive method, the beauty point adjustment operation often becomes unstable in the following cases.

(1) When the detection sensor cannot extract the contrast of the subject under low brightness.

(2) When the object itself has low contrast and the detection sensor cannot extract its features.

Under the above conditions, the detection sensor cannot accurately output a distance signal, resulting in a decrease in the accuracy of beauty point adjustment and, for example, in devices that require continuous operation such as a video camera. Since the photographing lens is adjusted in response to an inaccurate detection signal, it also causes a decrease in operational stability. Here are some methods that have been proposed in the past to eliminate the drawbacks in such cases.

a. Only when the previous judgment result and the current judgment result match, perform the actual intention adjustment operation.

b1 Two effective profit ranges (so-called dead band widths) (a wide range where stability is maintained and a narrow range where beauty point adjustment accuracy is ensured)
Set it and switch it at an appropriate timing.

There are other methods. That is, in the former case a, the distance signals before and after the phase are detected, and if they are not the same or almost the same, they are determined to be true subject distance signals, and based on this signal, the automatic focus adjustment operation is performed. If the two signals are different, they are treated as false signals and canceled, thereby allowing automatic fish collection adjustment operation to be performed based only on the true signal.

In addition, the latter method uses the contrast of the subject itself or
If a sufficient contrast signal cannot be obtained, the dead band width can be alternately selected to select a wide dead band width to avoid outputting unnecessary false signals, and then a narrow dead band width to ensure accurate beauty point adjustment accuracy. This is what I did.

All of the above-mentioned methods were designed to achieve both operational stability and beauty point adjustment accuracy, but passive automatic focusing devices cannot accommodate all conditions of the subject. .

However, in the above case, even though the contrast is said to be low, it is assumed that the distance measurement operation is barely possible or impossible, but depending on the case, the contrast of the subject itself or the surrounding brightness may change. This also applies to cases where the temperature changes from outside the area to a wide area.

On the other hand, if correct results cannot be expected even after performing distance measurement operations, the lens may be moved to infinity or flash photography may be used as necessary, as disclosed in Japanese Patent Application Laid-Open No. 57-198418. etc. must be taken into consideration.

[Problems to be Solved by the Invention] The purpose of the present invention is to eliminate one or more of the drawbacks of the conventional example, and it is possible to perform approximately correct actual point detection even when the contrast of the subject is low. It is an object of the present invention to provide an automatic focus adjustment device that allows the automatic focus adjustment to be performed.

[Structure of the invention]

By detecting the contrast of the subject, the present invention
The present invention is characterized in that it provides an automatic focus adjustment device configured to perform focus adjustment based on the average value of distance detection information from a subject distance detection device in accordance with the contrast.

The contrast of the subject is not only the contrast of the subject itself, but also the contrast of the subject as mentioned above,
In other words, it is used to include cases where a sufficient contrast signal cannot be obtained under low luminance even if the contrast is sufficient.

According to the configuration described above, when a sufficient contrast signal cannot be obtained, focus adjustment is performed by averaging the results of multiple distance measurements. Adjustments will be made. Furthermore, if the contrast signal is above a predetermined value, the m! i is performed, and a focusing operation with good responsiveness is performed.

Therefore, if the contrast is low due to the contrast signal itself, sensitivity will deteriorate due to repeated distance measurements, but stability is emphasized and automatic adjustment based on false signals will not be performed inadvertently. On the other hand, if the contrast exceeds a predetermined value, the focus will be adjusted by each distance measurement operation, and the response will be good, and the automatic adjustment will be performed smoothly, so that the image will always look the same depending on the subject. This enables a good automatic fish gathering adjustment operation.

Furthermore, the above-mentioned subject distance detection device has a detection section such as a so-called T sensor in which a COD sensor measures image light passing through a photographing lens.
TL type and so-called non-TTL that does not measure the passing light
In the former method, the amount of deviation between the focal position of the photographing lens and the current position is obtained as the output of the distance detection device, while in the latter method, absolute distance information of the subject is output.

Although the object distance detection device according to the present invention can be applied to either type, the former type is particularly referred to in the following embodiments. Of course, it goes without saying that the present invention can be applied to the latter method.

〔Example〕

Specific embodiments of the present invention will be described below in Figures 1 to 6.
This will be explained with reference to the figures.

FIG. 1 shows a principle diagram of the optical system configuration of an automatic focusing device suitable for carrying out the present invention.
is a lens element, and 2 is a group of small lenses for re-forming the image of the pupil plane of the lens element. Although it is depicted as consisting of two small lenses in the s1 diagram, it actually consists of more than 20 lenses. is used. 3 to 6 indicate each pixel element of a light receiving element made of a COD element, for example, pixel elements 3 and 4 correspond to the small lens 2-1, and pixel elements 5 and 6 correspond to the small lens 2-2. , the pixel element 3 looks at the aperture 8 portion through the small lens 2-1, and the pixel element 4 looks at the aperture portion through the small lens 2-1. Similarly, the pixel element 5 looks at the aperture 8 portion through the small lens 2-2, and the pixel element 6 looks at the aperture portion through the small lens 2-2.

As mentioned above, there are more than 20 rows of small lenses and sensors, and let us assume that 2-1 is the n-th row and 2-2 is the n-th row.
Assuming that it is the 1llth small lens, for the sake of explanation, n
The pixel element that looks at the aperture 8 through the th lens is An, and the pixel element that looks at the aperture A is Bn.
Let the pixel element An-1 look at the aperture 8 through the n-1th lens, and the pixel element Bn-1 look at the seventh aperture 7.

The F plane corresponds to the beauty surface of the photographing lens l. In other words, assuming a video camera, the imaging plane position (equivalent position) of the image pickup tube is F.
becomes. Therefore, the lens l moves back and forth on the optical axis (in the drawing,
The object distance at which an image is correctly formed on the F plane differs by changing the position in the horizontal direction (left and right), and when the image of an object at a distance is captured as the output of the light receiving element array, the output an of each pixel element An, Bn , bH is husband #an=bn
, an-1=bn-1, whereas when an image of an object that is not within the distance is captured, al=bm and n≠m.

In FIG. 1, if distance R1 is the focal distance of lens 1, the images of 9 points enter pixel elements 3 and 4 indicated by An*Bn, and the images of 10 points enter An-1 and Bn-1. It enters pixel elements 5 and 6 indicated by . Looking at it in the opposite way, rays 11 and 12 intersect at point 10, and rays 13 and 14 intersect at point 9.

FIG. 2 is a graph in which the output of the light-receiving element array explained in FIG. 1 is plotted on the vertical axis, and the position of the light-receiving element array is plotted on the horizontal axis.

This figure shows a case where the An element output afi and the Bn citrus output bn are shifted by the number of pixel elements of the light receiving element, and the amount of defocus can be detected by detecting the shift between &fi and bn. .

FIG. 3 shows an overall configuration diagram for implementing the present invention by applying the optical system shown in FIG. 1 to an automatic focus adjustment device of an actual video camera. The lens group 15 is an adjustment system called a ball, and the lens group 15 is a variable power correction system, and the lens group is for making the beauty point distance of the photographic lens variable.The lens group 16 is a half prism.17
is a total reflection mirror, 18 is an AF system lens group, and 19 is a first
A sensor unit including a small lens array and a light receiving element array shown in the figure, 20 is an aperture meter, 21 is an aperture blade, 22 is an imaging system lens, and 23 is a solid-state image sensor that forms a video signal as an image sensor. board, 24 is an A/D converter that converts the signal obtained from the sensor into a digital signal; 25 is an A/D converter that converts the signal obtained from the sensor into a digital signal;
A CPU that determines non-collection and calculates the amount of defocus,
26 is a motor drive circuit, 27 is an AF mode for making the position of lens group 10 variable, and 28 is lens group 1.
An encoder 29 is for detecting the position information of 0, and an encoder 29 is for detecting the beauty point distance information of the photographing lens.

The CPU 25 includes a calculation circuit that calculates an odor-containing signal as distance information from the output of the A/D converter 24.
-1&n+1-bnl) is calculated,
It is determined that odor is present when Hf is almost zero.

Here, in order to calculate the amount and direction of deviation between the afi curve and the bn curve in FIG. 2 (that is, the degree of defocus and the distinction between front focus and rear focus), the CPU further performs a second calculation process, Hpf=Σ (Ian+-bn+1l-1an+x+1
-bnl), HPf is calculated as variable from =-c to C. Here, the value of C is determined by the number of small lenses mentioned above. Figure 4 shows the calculation result when k is plotted on the horizontal axis and HPf is plotted on the vertical axis. Here, the curve 31 becomes Hpf=O when = 0, and therefore the current state of the photographing lens. It can be considered that the image is in focus. On the other hand, songs! ! In curve 30, k is negative, and in curve 32, k is positive and HPf is zero.The degree of blur is calculated from the sign of k at this time, and the absolute value of the front focus and rear focus * an It depends on how +bn is taken, but if k is negative, it is the rear bin, then the result of curve 30 is the rear bin, and the result of 1 curve 32 is the front bin.

FIG. 5 shows only the electric circuit corresponding to the specific embodiment of the present invention extracted from the A/D converter 24 and cpU circuit shown in FIG. After the analog electrical signal is converted into a digital data group by the A/D converter 24, the contrast signal of the subject is calculated, and the AF momo drive speed is switched between normal speed and low speed based on this signal. It is composed of Note that these circuits are actually processed by software using a microcomputer, which has become common these days, and in this embodiment, this functional part is also configured by a microcomputer, but its function is For the sake of explanation, FIG. 5 shows the circuit section broken down into functional block circuits. In FIG. 5, 104 is an arithmetic processing unit, and as mentioned above, HPf=Σ(lan+ -bn+tl-1an+x+t
-bnl) to find the value at the point where Hpf=O.

The polarity of ko obtained from this indicates the focus shift direction, and its absolute value indicates the focus shift amount.

On the other hand, there are several ways to obtain the evaluation value indicating the contrast of the subject, but in this embodiment, it is obtained in the process of calculating the HPf described above. This is the differential coefficient, or slope, at the zero-crossing point of the S-shaped characteristic curve. In digital processing within a microcomputer, this value is determined as follows. Adding to the explanation of the conventional example,
kO is determined by interpolating the point where the value of HPf changes from positive to negative with k variable from -C to C, but m≦kO
< m + 1 HPf(m)・Hp f (m+
The value of the difference in 1) becomes this contrast evaluation amount. In this way, the calculation unit 104 outputs 112 contrast evaluation amounts.

Reference numeral 113 denotes a contrast determination unit, in which the contrast evaluation amount signal 112 from the calculation unit 104 is compared with a predetermined threshold value. As a result, when the contrast is low, a low contrast signal 114 is output. Reference numeral 115 indicates a control signal generation circuit in the CPU, and a low contrast signal 114
In response to this, the digital switch 116 is switched from the b side to the a side. The control signal generation circuit 115 is also responsive to the low contrast signal 114 for repeatedly applying ranging command signals to each circuit.

The A/D conversion unit 24 and the deviation amount calculation unit 104 repeat the deviation amount from the subject distance an appropriate number of times, perform a distance measurement operation, and apply the output to the averaging circuit 118. Same circuit 118
calculates the arithmetic average value of multiple deviation amounts, and the result is stored in the memory in the same circuit. The stored value of the circuit is compared with the current value 28 signal of the lens 10 and its output 121
A control signal 122 for the motor drive circuit 26 is formed by this. The lens 10 is driven by the same motor, and the lens corresponding to the deviation between the average deviation value and the current value of the lens is adjusted, and the lens is adjusted to a focused state. Specifically, when the motor is stopped and the lens is in focus, the control signal generation circuit 115 supplies a heliset signal to each circuit,
Each circuit is set to an initial state. Of course, the number of distance measurement operations for the contrast evaluation amount in the contrast determination section 113 may be made variable so that the lower the contrast, the greater the number of distance measurement operations.

With the above configuration, when the contrast of the subject is low, the contrast determination unit 113 uses the contrast evaluation amount signal 112 from the calculation unit 104 to drive the AF motor 27 based on the average value of the distance measurement results multiple times. On the other hand, if the contrast is not low, focus adjustment is performed according to the amount of deviation from the calculation unit 104. As a result, the fifth
The stability of the illustration processing system is increased, and since error components are averaged for objects with low contrast that are likely to include false signals, fewer practical adjustments are made for each pix. On the other hand, as the contrast increases, the contrast determination unit 113 uses a control signal to perform a normal distance measurement operation, and the switch 116 is switched to the b side. Repeat the money collection action.

FIG. 6 shows a flowchart of this embodiment.

As described above (in Stapl, 2, Hpf and contrast evaluation amount are executed in the calculation unit 104, 5tep3
In step 4, the determination unit 113 executes low contrast (low contrast determination), and if the contrast is not low based on the result, the shift direction and amount are calculated in step 4. If the contrast is not low, the above-mentioned as,
The distance measuring operation is repeated, and in step 5, calculation is performed to obtain the average value.In step 6, the deviation from the current value of the lens 26 is determined based on any of the signals (the amount of deviation or the average value of the amount of deviation), and the deviation is determined. At 5 step 7 for the amount corresponding to the amount,
It drives the motor. These steps are repeated until a focused state is obtained, and when the focused state is detected, the motor is stopped (Step 8).

In the above-mentioned embodiments, an example has been described in which the focusing means is moved with the photographic lens to create a focusing state, but for example, the refractive power is varied. The motor 2 is used to adjust the focal position without moving the lens along the optical axis using a fluid-filled or liquid-filled lens.
Of course, it may be adjusted by 7.

〔Effect of the invention〕

As mentioned above, in the present invention, by evaluating the amount of contrast of the subject, the focusing operation is adjusted accordingly.
Since the distance measurement information or the average value of multiple distance measurement results is used, the sensitivity is slightly impaired in the case of low contrast, but the error component is averaged, and the focus adjustment is not performed using an incorrect signal. As a result, approximately proper focusing operation can be performed. On the other hand, if the contrast is greater than a predetermined value, a matching operation with excellent responsiveness will be performed.
Therefore, it is necessary to aim without harmonizing stability and sensitivity, and it is possible to perform the optimal collection operation each time. 2. It is possible to perform stable automatic tJR movement for various subjects, and the effect is extremely remarkable. It is.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing the principle of an optical system of an automatic beauty adjustment device to which the present invention is applied. FIG. 2 is an explanatory diagram of the operation of the device shown in the first diagram; FIG. 3 is a diagram of the overall configuration of the automatic concentration adjustment device to which the present invention is applied; FIG. 4 is a diagram explanatory of the operation of the device shown in the third diagram. FIG. 5 is an electric circuit diagram showing an embodiment of the present invention, FIG. 6 is an operation flowchart of the apparatus shown in FIG. A circuit 116 for calculating and storing the average value of distance measurement information: a digital switch that is switched according to the amount of contrast.

Claims (1)

[Scope of Claims] A detection device that detects the contrast of a subject and a distance detection device that detects a distance to the subject, and corresponding to the output of the contrast detection device,
An automatic focus adjustment device characterized in that focus adjustment is performed based on an average value of distance detection information from a plurality of times from the distance detection device.