JPS6315860Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention uses a method that utilizes the principle of so-called image matching, in which the subject image is divided into two parts and the two subject images match when they are in focus, and an automatic focus detection method that utilizes the principle that the contrast of the subject images is maximized when the subject images are in focus. The present invention relates to a focus detection device for a camera, which is suitable for use in a camera, and is capable of detecting focus over a wide range of subject brightness. BACKGROUND ART Many automatic focus detection devices that apply the principle of image matching using a plurality of photoelectric conversion elements or changes in the contrast of a subject have been considered, and some of them are beginning to be put into practical use. In addition, photoelectric conversion elements have changed from CdS etc. to photodiodes, etc., and recently there are fewer output terminals, the light-receiving surface can be made smaller, many photoelectric conversion elements can be configured on the same substrate, and processing circuits can also be integrated. Highly advantageous self-scanning
A group of photoelectric conversion elements that apply CCD and BBD principles,
MOS type photoelectric conversion elements using MOS shift registers are beginning to be used. However, this self-scanning photoelectric conversion element group
Because it utilizes the discharge phenomenon of the element, output can only be obtained in a narrow brightness range for a fixed discharge time.In order to obtain output in a wide brightness range, that is, a wide range of subject brightness, it is necessary to Variable discharge time according to subject brightness, that is, variable drive frequency or one scanning period (this variable operation will be referred to as brightness modulation from now on)
Action is required. Therefore, the photoelectric conversion elements necessary to measure the subject brightness, that is, the photoelectric conversion elements for brightness modulation, and the photoelectric conversion elements (the above-mentioned self-scanning photoelectric conversion element group is shown) that obtain the information necessary for automatic focus detection. This operation is called brightness detection.), and to obtain the same subject image on both elements, an optical system or an optical member such as a half mirror is required. In addition, if a photoelectric conversion element for brightness modulation is installed near a group of photoelectric conversion elements for brightness detection, there is no need for an optical member such as a half mirror. In this case, brightness modulation that does not occur will be applied to the brightness detection photoelectric conversion element group, making it impossible to obtain a desirable output. In view of the above background, the present invention uses a self-scanning photoelectric conversion element for both brightness detection and brightness modulation, and also devises its output form so that the output for brightness modulation can be obtained instantaneously after charge accumulation. Another object of the present invention is to provide a focus detection device for a camera that is capable of detecting focus in a wide range of subject brightnesses, includes a processing circuit, and can be miniaturized. Embodiments of the present invention will be described below with reference to the drawings. Figure 1 shows an example of a self-scanning photoelectric conversion element group using a MOS shift register.
Reference numeral 1 denotes a scanning circuit having a shift register, which is driven by a clock φ and a start pulse ST, and turns on semiconductor address switches S ₁ , S ₂ ...S _o through output terminals G ₁ , G ₂ ...G _o of the sequential scanning circuit 1. Make it. Next, focusing on photodiode _d2 , the operating principle will be briefly explained. The scanning pulse from the scanning circuit 1 causes the address switch S ₂ to be connected to the address switch S _{2 through the output terminal G 2} .
When ON, the photodiode _d2 is reverse biased through the external power supply voltage E and the load resistance R, and the capacitor of the photodiode _d2 is charged until it is saturated, and the address switch is output through the output terminal _G2 .
When S ₂ is OFF, the photodiode is turned off for one scanning period.
d ₂ is reverse biased. At this time, when light enters the photodiode _d2 , a discharge current flows in the photodiode _d2 , and the charge stored in the photodiode _d2 decreases in proportion to the amount of incident light, and the decrease is then transferred to S. ₂ is turned on, and the charging current becomes the video output Vout. Also, if the interval of one scanning period, that is, the interval of start pulses ST, is increased,
It is also sensitive to light in the low-illuminance range, increasing the apparent sensitivity and enabling focus detection in the low-illuminance range. Fig. 2 is a diagram showing the temporal change in the video output Vout in _{Fig .}
. . . When S _o is turned ON in this order, the video output Vout is outputted in the order of V ₁ , V ₂ , . . . V _o .
Note that each waveform is naturally a charging waveform. FIG. 3 shows an example in which a general focus detection device is added to a single-lens reflex camera. Basically, the configuration is such that a group of self-scanning photoelectric conversion elements is used to detect the contrast of a subject and perform focus detection. In the figure, light from the subject passes through a photographic lens 2, is reflected by a total reflection mirror 3, and forms an image on the lower part of a condenser lens 4.
At the same time when viewing with the eye 7 through the eyepiece 6, a half mirror 3' and a full-length self-scanning photoelectric conversion element group 10 (hereinafter referred to as a detection element) for brightness detection are placed at a position optically equivalent to the film surface 11. It is projected via the reflection mirror 9. As mentioned above, since the detection element 10 must determine one scanning period depending on the brightness of the object, the object projected onto the detection element 10 through the half mirror 4' in the center of the condenser lens 4 is The light corresponding to the image is transmitted to a photoelectric conversion element 8 for brightness modulation.
(hereinafter referred to as a modulation element), and is used to control the detection element 10 through a processing circuit 12. Next, the focus detection operation will be explained. First, simultaneously with focus detection, the processing circuit 12 receives the output of the modulation element 8, converts the value of the output into a frequency, and provides a preferable scanning period to the detection element 10, that is, after determining the interval of the start pulse ST, The photographic lens 2 starts moving in one direction from the near point or the ∞ point by the photographic lens drive circuit 13. Next, each output of the detection element 10 shown in FIG.
When calculating ε= _o-1 〓 ⁱ⁼¹ |V _i −V _i+1 | using V ₁ , V ₂ . . . V _o , this value becomes maximum when the focus is met.
In other words, the fact that the contrast is maximum when in focus is utilized. These arithmetic operations are carried out by the processing circuit 12.
When the output ε reaches the maximum, if the photographing lens is stopped via the photographing lens drive circuit 13, focusing is achieved. FIG. 4 shows the change in the focus detection output ε with respect to the amount of extension of the photographing lens. Focus position a ₀
It is shown that the focus detection output ε attains the maximum value ε ₀ when . FIG. 5 shows an example of the focus detection device of the present invention, which applies the principle of the focus detection device shown in FIG.
Compared to FIG. 3, this embodiment does not have the modulating element 8 shown in FIG. 3, so there is no half mirror 4' in the condenser lens 4, and the mechanism is very simple.
The photoelectric conversion element is a self-scanning photoelectric conversion element group 10' for both brightness detection and modulation (hereinafter referred to as a detection and modulation shared element), and the processing circuit is slightly different from the processing circuit 1.
4, but optically the configuration is exactly the same as that shown in FIG. 3. That is, the present invention can be applied to any focus detection method based on any principle using a self-scanning photoelectric conversion element group. The detection/modulation shared element 10' and processing circuit 14 of the present invention will be explained with reference to FIGS. 6 and 7.
Incidentally, the boundary between the detection/modulation common element 10' and the processing circuit 14 is not made clear because they may be configured together. The explanation will be based on the automatic focus detection procedure. First, the automatic focus detection mechanism turns on the automatic focus detection start switch 15.
When the operation starts, the brightness detection/modulation switching circuit 16 sends an H signal for a certain period _of time as shown by to the semiconductor switch B 1 through the semiconductor switch B ₂ and the inverter I ₁ . This semiconductor switch is
As shown in the diagram on the right, when terminal 3 is H, the period between 1 and 2 is ON,

[Formula] It is configured so that it is in the OFF state when it is L. Therefore, the semiconductor switch _B2 is turned on and the semiconductor switch _B1 is turned off. Also, the output of AND circuit A ₁ , A ₂ ...A _o is the output terminal of scanning circuit 1
Since G ₁ , G ₂ ... is L regardless of the state of G _o , the semiconductor address switches S ₁ , S ₂ ... S _o are ON, but the semiconductor switch S ₀ is OFF due to the action of the inverter I ₀ ( Furthermore, semiconductor address switches S ₁ , S ₂ ……
Assume that S _o and S ₀ are turned ON at L. ), so
_No reverse bias is _applied to each photodiode _{d 1 ,} d _{2 .} A corresponding current flows, and the input indicated by is obtained through the semiconductor switch _B2 to the brightness modulation circuit 17 (this type of operation will be referred to as static type from now on). Frequency conversion is performed in this circuit 17,
A clock φ and a start pulse ST corresponding to the subject brightness are input to the scanning circuit 1 in the form shown by . At the same time, brightness detection and modulation switching circuit 1
The output of 6 becomes L, so the semiconductor switch
B ₂ is OFF, B ₁ is ON, S ₀ is also ON, and AND
The outputs of the circuits A ₁ , A ₂ ...A _o are in the same state as the output terminals G ₁ , G ₂ ...G _o of the scanning circuit 1, and the outputs of the circuits A 1 , A 2 ...A _o are the same as those of the output terminals G ₁ , G ₂ ... Outputs are sequentially input to the focus detection circuit 18 through a video line in proportion to the amount of light. At the same time, the photographing lens driving device 13 starts moving the photographing lens 2 shown in FIG. 5 in one direction from the near point or the ∞ point. The focus detection device 18 provides video outputs V ₁ , V ₂ . . . at each time point.
...calculates ε= _o-1 〓 ⁱ⁼¹ |V _i −V _i+1 | by VS o, detects the maximum value ε ₀ of the focus detection output ε, and gives that information to the photographic lens driving device 13 _, Focus matching is achieved by stopping the photographing lens 2. In addition, the state of integral calculation within the focus detection circuit 18 is shown. FIG. 8 illustrates an example of a brightness modulation method. This corresponds to the subject brightness (in the embodiment of the present invention, it corresponds to the average value of the subject projected onto the detection modulation element 10', and weighting may be added to the average value, in short, the detection modulation element 11' Any method may be used as long as an output is obtained during the detection operation.) The frequency of the clock φ, that is, one scanning period, is changed in a stepwise manner, but of course, a linear change may also be used. Also, brightness modulation can be detected if it does not affect the focus detection output.
Any combination that modulates once for every 10 times may be used. As described above, by using the focus detection device according to the present invention, not only the two photoelectric conversion elements for detection and modulation functions are combined into one, but also there is no need for an optical system or optical member for the modulation element. , enables focus detection in a wide brightness range, especially in low light areas,
It is possible to obtain a camera focus detection device that can be applied to any focus detection device using a self-scanning photoelectric conversion element, and the effects are extremely large, such as the ability to obtain an output for brightness modulation instantly after charge accumulation. .

[Brief explanation of the drawing]

Figure 1 shows the MOS in the self-scanning photoelectric conversion element group.
This is an example using a shift register. FIG. 2 shows the change in Vout over time in FIG. 1.
FIG. 3 is an example of a single-lens reflex camera with a general automatic focus detection device added thereto. FIG. 4 shows a general focus detection output. FIG. 5 is an example of a focus detection device showing an embodiment of the present invention. FIG. 6 is an example of an electric circuit of a focus detection device according to the present invention. 7th
The figure shows temporal changes in the output at each point in FIG. FIG. 8 is an example of brightness modulation according to the present invention. 1: Scanning circuit, 2: Photographic lens, 3: Total reflection mirror, 3': Half mirror, 4: Condenser lens, 4': Half mirror, 5: Pentaprism,
6: Eyepiece, 7: Eye, 8: Photoelectric conversion element for brightness modulation, 9: Total reflection mirror, 10: Group of photoelectric conversion elements for self-scanning brightness detection, 10': Photoelectric conversion element for brightness detection and modulation using the present invention Conversion element, 11: Film surface, 12: Processing circuit, 13: Photographic lens drive device, 14: Processing circuit according to the present invention, 15: Automatic focus detection start switch, 16: Brightness detection, modulation switching circuit, 17: For brightness modulation Circuit, 18: Focus detection circuit, G ₁ , G ₂ ...G _o : Output terminal of scanning circuit 1, S ₁ , S ₂ ... S _o : Semiconductor address switch,
d ₁ , d ₂ ... d _o : Photodiode, R: Load resistance, E: External power supply, φ: Clock, ST: Start pulse, Vout: Video output, V ₁ , V ₂ ... V _o :
Video output of each photodiode d ₁ , d ₂ ...dn, T: time, A ₁ , A ₂ ...A _o : AND circuit, S ₀ ,
B ₁ , B ₂ : Semiconductor switch, I ₀ , I ₁ : Inverter, ~: Indicates each position, ε: Focus detection output,
a ₀ : Focus position, ε ₀ : Maximum focus detection output.

Claims (1)

[Scope of utility model registration request] In an electrical focus detection device having a self-scanning photoelectric conversion element, each clock from each output terminal in a scanning circuit that sequentially scans each photoelectric conversion unit of the self-scanning photoelectric conversion element is applied to each photoelectric conversion unit. A gate control signal for controlling opening/closing of the gate circuit is commonly input to one input terminal of each of the corresponding gate circuits, and a gate control signal for controlling opening/closing of the gate circuit is commonly input to each input terminal of the other gate circuit. each switch for turning on and off the respective parts is turned on when each of the gate circuits is closed,
A brightness modulation circuit according to the parallel composite output of each of the photoelectric conversion units obtained during brightness modulation in which each of the gate circuits is closed by the gate control signal and all of the switches are turned on regardless of the presence or absence of the clock. to form a driving frequency of the self-scanning photoelectric conversion element, and each clock signal from each output terminal of the scanning circuit based on the driving frequency is set at the time of brightness detection in which each gate circuit is opened by the gate control signal. The respective switches are sequentially turned on and off via the respective gate circuits to obtain discrete detection signals in time series from the respective photoelectric conversion units, and the driving circuit of the photographing lens is controlled based on the detection signals. A focus detection device for a camera, characterized in that focus detection is performed by