JPS59201009A - Auto focus detecting device - Google Patents

Abstract

PURPOSE:To make a spatial adjustment of a lens photodetector and a stroboscope device unnecessary, and to raise the productivity by deriving an output ratio of two photodetecting means, and detecting a distance of an object to be photographed. CONSTITUTION:A stroboscope flashgun ST illuminates an object to be photographed under a prescribed view angle, and a reflected luminous flux corresponding to a distance of the object to be photographed is made incident to photodetectors PD1, PD2. A light quantity ratio of the photodetector PD1 and PD2 is large in a short distance side and draws near ''1'' as the object goes toward a long distance. A photodetecting output is inputted to sample holding circuits 52, 55 through photocurrent amplifiers 50, 53 and differentiating circuits 51, 54, the light quantity ratio of the photodetectors PD1, PD2 is calculated by an operating circuit 56, and a distance information of the object to be photographed is derived.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an autofocus detection device, and more particularly to an autofocus detection device configured to measure the distance of a subject to which contrast is added using a light emitting device using a distance meter method.

Conventionally, active and passive methods have been known as autofocus detection devices, but each method has advantages and disadvantages in terms of subject conditions such as difficult-to-detect objects and manufacturing conditions that require assembly precision. Currently, various types of cameras use different autofocus methods.

In particular, in the active method, it is difficult to determine which part of the light receiver placed at a predetermined distance the light beam from the light emitter will be reflected, in other words, a triangular distance measurement method is adopted, so the above-mentioned subject conditions are Although this is advantageous, it has the disadvantage that it requires very high precision in the relative position of the light emitting body and the light receiving body, which increases the manufacturing cost for precision control.

In addition, in the Nonotsive method, some systems are known that are equipped with a light emitter that illuminates the subject in order to improve focus detection accuracy when the subject is dark, but in principle, focus detection is performed to detect deviations in the subject image. For example, the light-receiving element for illumination of the subject becomes expensive, and the light emitter for illuminating the subject requires a lot of power, and the power supply voltage decreases during focus detection, which has a negative impact on other shared circuits, especially in the case of a shared power supply. There are drawbacks.

Therefore, in view of the above circumstances, it is an object of the present invention to provide an autofocus detection device that has the superiority of the subject conditions of the active method and the superiority of the manufacturing conditions of the passive method, and this purpose is to provide contrast to the subject. two lens means arranged at a predetermined baseline distance apart and forming an image of a subject; two light receiving means arranged on the imaging plane of these lens means;
This is achieved by including a calculation means for calculating the total output ratio of the two light receiving means outputted by the light emission of the light emitting means, and by configuring the object distance to be detected based on the calculation output.

Hereinafter, the present invention will be explained based on one embodiment of the accompanying drawings.

FIG. 1 shows a principle diagram of the autofocus detection device of the present invention, in which PDl is a light receiving element placed at a position where a subject image within a predetermined angle of view of the photographed subject is formed by lens system L1, and PD2 is a lens system. L2 is a light receiving element placed at a position where a subject image within a predetermined angle of view of the subject to be photographed is formed, and these two sets of detectors (L1, PDI and L2, PD2) have the same configuration. The only difference is that they are arranged at a predetermined baseline distance. Therefore, as a matter of course, a /4 lux is generated between these light receiving elements PDI and PD2, and this lux is used for focus detection.

In addition, these light receiving elements PDI and PD2 are arranged so that the dystro is sensitive only to the light from the light emitter ST using the method described later, and the detection object is located between the two light receiving elements and at the center so that there is a difference in the output between the light receiving elements. A strobe placed at a slightly biased position (FIG. 1) or outside both light receiving elements (not shown) is illuminated by the light emitter ST and lens system L3 at a predetermined illumination angle within the field of view of the subject to be photographed. It is assumed that

Here, if there is a photographic subject at position d1, the subject image irradiated by the flashlight by the light emitter ST will be transferred to the light receiving element PD2.
Although almost no image is formed on the light receiving element PDI, most of the image is formed on the light receiving element PDI. However, when the photographic subject distance moves away from d2 and d3, the light receiving element PD
I Stroyj for the object image formed on it? The rate of increase in the proportion of the subject image irradiated by the light emitter ST is smaller than the rate of increase in the proportion of the subject image irradiated by the strobe emitter ST to the subject image formed on the photodetector PDZ. .

Therefore, the light amount ratio (
PDI/PD2) is large on the short distance side and approaches 1 as the distance increases, and it is understood that focused focus detection can be performed by calculating this light amount ratio. These characteristic diagrams are shown in FIG. 2, where the horizontal axis represents the distance, and the vertical axis represents the light intensity ratio (P D 1 / p D 2 ) of the light-receiving muntons PDI and PD2, respectively. ing.

Here, d1 to d3 correspond to the distances d1 to d3 shown in FIG.

The above is a focus detection principle that is recognized under conditions that ignore the brightness of the outside world, so in order to incorporate it into an actual camera, a detection method that can approximately satisfy this condition (
For example, it goes without saying that it is necessary to adopt a configuration in which the outputs of the light receiving elements PDI and PD2 are sensitive only to the strobe light emitter.

Figure 3 is a front view of a camera that employs the focus horizontal tilting device based on the above principle, Figure 4 is a cross-sectional view of the focus detection device shown in Figure 3, and Figure 5 is a circuit diagram of the focus horizontal tilting device shown in Figure 3. The same symbols refer to the same objects.

Referring to FIGS. 3 and 4, an autofocus unit 10 is attached to the upper part of the camera body 1, and this unit 10 includes a lens system L1 that focuses a subject image within a predetermined angle of view onto a light receiving element PDI; A lens system L2 that forms an image of the subject within a predetermined angle of view onto the light receiving element PD2, and a lens that diffuses the luminous flux of the light emitter 8T within the predetermined angle of view within the photographic angle of view so as to add contrast to the photographed subject. System L3,
It is composed of many parts.

The light receiving outputs of these light receiving elements PDI and PD2 are used to calculate a p light amount ratio by a processing circuit which will be described later and adjust the focus of the photographing lens 3 of the lens barrel 2, or are calculated based on the light amount ratio in the viewfinder 4. Distance information will be displayed and focus will be adjusted semi-automatically.

It goes without saying that these focus control mechanisms can be designed in any manner.

FIG. 5 shows the processing circuit of the focus unit.
The signal is amplified by 0.53, and is input to a sample-and-hold circuit 52.55 via a differentiation circuit 51.54 that allows only the change in the received light output to pass through. At this point in time when the sample and hold circuit 52.550 is held, the strobe power supply circuit 5T and the light receiver IST are ν′1°21
(7))+J″-!″″cxF) The luminous flux from the light emitter ST passes through the subject to the light receiving elements PDI, P.
It is set to hold the change in the received light output during the time between returning to and returning to D2. The hold circuits 52 and 55 may integrate and hold only the reflected light from the above, or may integrate and hold only the reflected light from T, or may integrate and hold only the reflected light from the It goes without saying that the output itself may be held. Also, holding the output of this change when the light emitter ST is almost emitting light is to reduce the influence of external brightness on the light receiving elements PDI and PD2, and based on this focus detection principle, it is necessary to perform the necessary processing. Marriage is the same as mentioned above. However, this hold action may be configured to be performed after processing by the arithmetic circuit 56, which will be described later.

(In this case, only one sample and hold circuit is required, but
(The above-mentioned integration effect becomes difficult.) These held outputs are divided by the arithmetic circuit 56, that is, the change output of the light receiving element PDI is divided by the output of the light receiving element PD2.
The value divided by the change in output is calculated.

As shown in Figure 2, this calculated value has a value that corresponds to the subject distance, so if you correct it for a subject at a predetermined distance, you can easily see the correspondence with subject distances from close range to far distance. Desired.

The operation of the above configuration will be explained below with reference to FIGS. 31 to 5.

When the release of the camera 1 presses the button 5, power is supplied to the 7-focus unit and the main capacitor (not shown) of the power supply circuit 5T is rapidly charged (this amount of charge for focus detection is not enough for normal shooting). This is possible because the amount of charge required for the strobe is small, but it may be configured to charge constantly), and the trigger signal is given after this charging. In response to this trigger signal, the cystologo emitter ST emits light and illuminates the subject under a predetermined angle of view. Since this predetermined angle of view is for adding contrast to the subject, the angle of view for photographing is also set to be smaller. Therefore, according to the principle shown in FIG. 1, the light flux from the arc tube ST that passes through the subject is incident on the light receiving elements PDI, PD2 at different rates depending on the distance to the subject.

The differential circuit 51.54 extracts only the amount of change in the amount of incident light, that is, the amount of light emitted from the light emitter ST by the sample and hold circuit 52.5.
It is held at 5. These hold outputs are calculated by the arithmetic circuit 56 as the light amount ratio of the light receiving elements PDI and PD2, and object distance information is obtained.

This object distance information is transmitted to a focus control mechanism (not shown), such as a sensor. The signal is used as a drive signal for the photographing lens 3 by a drive mechanism or a lens drive mechanism such as a spring to automatically adjust the focus, or is displayed in the finder 4 as object distance information.

In the above explanation, the electric processing circuit is used to make the light receiving elements PDI and PD2 sense the luminous flux of only the strobe light emitter ST, but another method is to use an infrared light emitting strobe for the light emitter and a red flash for the light receiving element. An external light receiving element or an infrared light transmitting filter may be arranged in front of the light receiving element.

It is also possible for the flash to function as a light emitter and the flash for photography to also function as a device. In this case, two main capacitors are provided for the light emitter, one for focus detection and one for photography, and the light emission is controlled in chronological order. However, the light emission distribution of the light emitter needs to include the visible light region.

As explained above, according to the autofocus detection device of the present invention, the correspondence between the light intensity ratio of the light receiving element and the subject distance can be electrically corrected, so there is no need for spatial adjustment of the lens, the light receiving element, and the 4M device. Productivity improves dramatically.

Furthermore, since a light emitter is used, the problem of reduced focus detection ability when photographing a dark subject in the arm-to-shoulder method is solved, and the positional accuracy of the arc tube in the active method is not required because it is based on the light amount ratio of both light-receiving elements.

Furthermore, when a light emitting tube is used as a light emitting tube, the light-receiving element has a large output, which reduces malfunctions caused by a drop in output, and since the light does not consume current when emitting light, it also prevents noise from entering between each circuit. come.

As described above, according to the device of the present invention, it is possible to provide an autofocus detection device with a very simple configuration but with high practicality. Equipment can be provided.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the principle of the device of the present invention, Figure 2 is a diagram showing the relationship between subject distance and light amount ratio based on this principle, and Figure 3 is a diagram showing the relationship between subject distance and light amount ratio.
The figure shows a front view of a camera incorporating the device of the invention, FIG. 4 shows a cross-sectional view of the device of the invention, and FIG. 5 shows a processing circuit connection diagram of the device of the invention. Ll, L2, L3... Lens system PDI, PD2... Light receiving element ST... Stroke is arc tube 1... Camera 2... Lens barrel 3... Taking lens 4... Finder 5 ...Release button 50.53...Photoelectric amplifier 51.54...Differential circuit 52.55...Sample and hold circuit 56...Arithmetic circuit Applicant: Fuji Photo Hikane Co., Ltd./Fig. 3 diagram

Claims (1)

[Scope of Claims] l) A light emitting means arranged to give a contrast to a subject, two lens means arranged at a predetermined baseline distance apart and forming an image of the subject, and an image forming method of these lens means. Two light-receiving means arranged on a surface, and a calculating means for calculating the output ratio of the two light-receiving means output by light emission from the light-emitting means. An autofocus detection device characterized by being configured to detect. 2) The autofocus detection device according to claim 1, characterized in that a strobe device is used as the light emitting means. 3) The autofocus detection device according to claim 1, characterized in that an infrared light emitting device is used as the light emitting means. 4) The autofocus detection device according to claim 1, wherein an element sensitive only to infrared light is used as the light receiving means. 5) An autofocus detection device according to claim 1, characterized in that the light emitting means also serves as a strobe device for photographing.