JPH0478967B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention enables focus detection with a simple configuration by projecting light onto the subject and detecting the reflected light using a plurality of photoelectric elements having apertures for transmission. and a focus position setting device that compares and detects the output levels of the plurality of photoelectric elements and moves a photographic lens back and forth to set the focus position.

In general, in optical observation devices and optical photographing devices such as endoscopes, cameras, and television cameras, the image forming position of the photographing optical system of the device is A focus detecting means is provided for detecting whether or not the object is located at the position of the image forming plane of the film or the like. In some cases, a device (hereinafter referred to as a focus position setting device) that can automatically move and set the imaging device of the photographic optical system to a focus position is attached.

Conventional focus detection devices do not work well when the subject is dark or when a dark photographic optical system is used.
Generally, the detection output by the photoelectric element becomes small, making focus detection almost impossible.

For this reason, as disclosed in Japanese Patent Publication No. 49-19810, there is a method for irradiating a beam of a certain shape toward the subject, but the irradiation section is made using an optical system independent of the photographing lens system. Therefore, it cannot be applied to endoscopes, etc., which require imaging using a single optical path.

Furthermore, as disclosed in JP-A-56-128923, the method using a split prism requires at least two or more minute photoelectric elements each on the upper and lower sides, and when a certain level of accuracy or higher is required. In addition to arranging a large number of photoelectric elements, the circuit system for comparing their output signals and detecting whether or not they are in focus is complicated, which results in high costs, especially for products that are manufactured in small quantities. It was hot.

Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 56-125713, by flashing a light source and projecting light onto the subject, and subtracting the output signal in the off section from the output signal in the on section, external light other than the above light source can be detected. There is a focus detection device that can reduce the influence of the camera and detect whether or not it is in focus even when the subject is dark or when the photographic optical system is dark, but because the configuration is complicated, this focus detection device and this device are There has been a problem in that an optical device equipped with a focus position setting device that sets the photographing optical system to a focus position using the above method becomes expensive.

This invention was made in view of these circumstances, and it is possible to detect with a simple configuration whether or not the subject is in the focal position, and if it is not in the focal position, in which direction it is shifted. It can be used even with a subject or a dark photographic optical system, and it can also be used with an endoscope or other equipment where there is no space to install it side by side other than a single photographic optical system, and it can also be used with multiple photoelectric elements. Based on the output level detected by the sensor, it is possible to determine in which direction the photographic lens should be moved to bring it into focus, and by arranging a large number of photoelectric elements, it is possible to control the amount of deviation from the focus position. It is an object of the present invention to provide a focus detection device and a focus position setting device that are capable of detecting a focus position.

In order to achieve the above object, the focus detection device according to the invention is an optical device that focuses an image of a subject through a photographic lens on a predetermined position where a film surface or the like is placed. a plurality of photoelectric elements disposed at least before and behind a position conjugate to the predetermined position on the axis; an aperture provided approximately at the center of the photoelectric element; and a light source that projects an image of the opening onto the subject.

On the other hand, a focusing position setting device is an optical device that focuses an image of a subject at a predetermined position where a film surface or the like is placed through a photographing lens that can move back and forth, and is located at a position equivalent to the position on the photographing optical axis behind the photographing lens. a plurality of photoelectric elements disposed at least before and after a position where the optical path is conjugate with the predetermined position on the axis; an aperture provided approximately at the center of the photoelectric element; and a plurality of photoelectric elements disposed near the rear of the aperture; The camera includes a light source that projects an image of the aperture onto a subject through a photographic lens, and means for moving the photographic lens back and forth in accordance with the detection output level of the plurality of photoelectric elements.

Hereinafter, the present invention will be specifically explained with reference to the drawings.

1 to 7 relate to a first embodiment of the present invention, and FIG. 1 shows an optical system of a focus position setting device using the focus detection device of the present invention in a camera adapter of an endoscope. , FIG. 2 shows the shape of the photoelectric element used in the first embodiment, FIG. 3 is a diagram explaining the principle of focus detection, and FIG. 4 shows the photoelectric element with respect to the position of the subject in FIG. 3. FIG. 5 shows an enlarged view of the main parts of the projection light source and light detection optical system in FIG. 1, and FIGS. 6 and 7 show the photographing optical system (photographing lens). Fig. 8 shows the output level of the photoelectric element when is not in the in-focus position.
A focus position setting device for moving and setting a photographing lens to a focus position using a focus detection device is shown in an electric circuit block diagram.

In FIG. 1, there is shown an elongated insertion section 1 housing an objective optical system on the distal end side, the distal end side connected to the proximal end of the insertion section 1, and a light guide base section 2 on the side thereof. , an eyepiece section 3 of an endoscope 4, which includes an eyepiece section 3 in which an eyepiece optical system is housed.
A camera adapter 5 is detachably attached to the rear end side. A camera 6 or a television camera can be detachably attached to the rear end side of the camera adapter 5.

The camera adapter 5 houses an embodiment of a focus position setting device that can automatically move and set the photographing lens to a focus position using the first embodiment of the focus detection device of the present invention. .

That is, on the optical axis 7 when the endoscope 4 is attached, there is a movable back and forth (on the optical axis 7) at a rear position facing the eyepiece system of the endoscope 4 as shown by the arrow. A photographic lens 8 is disposed, and a focusing lens 9 formed of a semi-transparent mirror is disposed on the optical axis 7 behind the photographic lens 8 and is inclined (for example, at a 45 degree inclination) to the optical axis 7. has been done.

A re-imaging lens 10 is disposed on the reflected optical axis 7' (in the upper position in FIG. 1) where the light incident along the optical axis 7 is reflected by the focusing mirror 9, and further behind the reflected optical axis 7'. On both sides close to the optical axis 7', photoelectric elements 12A and 12 are installed before and after a position 11 that is conjugate with a predetermined imaging plane (corresponding to a film surface, etc.), respectively.
Further, focusing light sources 14A and 14B are arranged behind pinholes 13A and 13B provided in each photoelectric element 12A and 12B.

On the reflective optical axis 7' on the back side of the focusing mirror 9 (lower position in FIG. 1), there is a lamp lens 15, and a focus indicator lamp 16 for indicating focus.
are arranged in sequence.

The photoelectric element 12A (or 12B) has a pinhole (shaped opening) 1 in the center as shown in FIG.
It has the shape of a disk (of course, it can be a square, rectangle, or other shape) provided with 3A, and the front surface of this disk is a photosensitive element, such as a photodiode,
The photocathode 17 is formed of an element whose current characteristics change depending on light, such as a phototransistor, an element that generates photovoltaic force, such as a solar cell, or an element whose resistance value changes, such as a CDS. A light shielding surface 18A is formed on the back side, and the pinhole 1
The photoelectric element 12A is configured so as not to be directly exposed to light from a focusing light source 14A, which is a projecting light source for detecting focus at a position behind (in FIG. 1, above) 3A. (The same applies to the photoelectric element 12B).

On the other hand, in the camera 6 attached from the rear of the camera adapter 5, a return mirror 21 is arranged on the optical axis 7 behind the focusing mirror 9 and is inclined with respect to the optical axis 7 (for example, a 45-degree inclined surface). Further, a photographic film 22 is disposed behind it.

A pentaprism 23 is disposed on the reflection optical axis of the return mirror 21 (in the upper direction in the figure), and the pentaprism 23 is horizontally inverted and returned to an erect image.
A finder lens 24 is disposed at the rear on the optical axis after passing through the lens.
It is constructed so that it is possible to observe an optical image equivalent to that formed by The return mirror 21 is
The structure is such that during photographing, the ejected light is focused on the surface of the film 22.

Each photocathode 17 of the photoelectric elements 12A and 12B
The position approximately midway between A and 17B is the above (film 2).
2) The position 11 is optically conjugate with the position of the imaging plane.

That is, the light emitted from each light source 14A, 14B and passed through the photographic lens 8 is reflected by the subject 25,
The optical path length when the image is formed on the rear film 22 surface, and the light is reflected by the focusing mirror 9, passes through the re-imaging lens 10, and travels to each photocathode 17A, 17B of each photoelectric element 12A, 12B. In this case, the optical path lengths formed at the intermediate position 11 are set to be equal to each other.

In the optical system arranged in this way, the principle of focus detection in the camera adapter 5 that houses the focus position setting device that moves and sets the photographic lens 8 to the focus position will first be simplified to a linear optical system. This will be explained with reference to FIG.

In FIG. 3, only one set of light sources 14A, 14B and photoelectric elements 12A, 12B are shown. In the figure, when the subject 25 is at the position indicated by symbol b, the light reflected at that position is
Pinhole 1 of photoelectric element 12 via photographic lens 8
The light condensing point (also referred to as an imaging point or focal point in a broad sense) converges at the position 3, and the positions when the subject 25 is too close or too far from the position indicated by the symbol b are indicated by symbols a and c, respectively. Indicated by

Subject 25 from light source 14 through pinhole 13
The output level of the photoelectric element 12 due to the light projected and reflected in the above case will be explained below.

First, in the case of symbol b, the reflected light converges at the position of the pinhole 13, so that it hardly reaches the photocathode 17, and the output level Pb of this photoelectric element 12 becomes almost zero. On the other hand, in the case of symbol a,
Since the focal point is at the rear position of the photoelectric element 12,
The reflected light considerably reaches the photocathode 17 and the photoelectric element 12
is the output level Pa corresponding to the light reached,
Naturally, it is larger than Pb.

Similarly, in the case indicated by the symbol c, the photoelectric element 12
Since it becomes a focal point already at the front position of , and then expands, a considerable amount of light reaches the photocathode 17 as in the case of symbol a above. Therefore, the output level Pc of the photoelectric element 12 in this case also becomes greater than Pb. In other words, when the pinhole 13 of the photoelectric element 12 is located at the imaging point or focal point, the output level of the photoelectric element 12 becomes minimum.

In the above description, only the case where light from the light source 14 is incident is considered, but in reality, not only the above-mentioned light but also external light such as illumination light passing through a light guide is incident on the endoscope 4. Therefore, the output signal of the photoelectric element 12 is increased by the output level due to the above-mentioned external light, as shown in FIG. 4. Here, the horizontal axis indicates the position of the subject 25,
The vertical axis indicates the detection output level of the photoelectric element 12.

That is, the output level is minimum when the photoelectric element 12 provided with the pinhole 13 is at the focused position, and increases as the photoelectric element 12 moves forward and backward from this position. In other words, by moving the photographic lens 8 back and forth so that the output level of the photoelectric element 12 becomes the minimum value with respect to the subject 25 at an arbitrary distance, the photographing optical system can be set to the in-focus position.
If you take a photo at this position, you will be able to take a clear photo.

Although the above description has been made regarding a single light emitting means and light reception detecting means constituted by the light source 14 and the photoelectric element 12 shown in FIG. 3, the same applies to the case of two sets shown in FIG. 5.

Also in this case, the light source 14A and the photoelectric element 12A and the other light source 14B and the photoelectric element 12B
The above is applicable to each set of .
In this case, the intermediate position between the photocathode 17A, 17B is set in advance as a position 11 which is conjugate with the surface of the film 22 serving as the imaging plane. The output levels of 12B (denoted as P _A and P _B , respectively) are set to be equal. Therefore, when the photographic lens 8 is in the focused position with respect to the subject 25 at an arbitrary (or specific) distance, the output levels P _A and P _B of both photoelectric elements 12A and 12B are equal (the positions of both at this time are A', B' and output level P are shown in Figure 6).
When the photographing lens 8 is in focus on a distance far away or a short distance from the subject 25, the output levels P _A and P _B of both photoelectric elements 12A and 12B are different, respectively. In other words, in the former case, the photoelectric element 12 is placed behind the position 11 that is conjugate with the surface of the film 22.
As shown in FIG. 6, the output level P _B of the photoelectric element 12A becomes lower than the output level P _A of the other photoelectric element 12A (because it is close to in-focus), and in this case, the photographic lens 8 is moved forward (as shown in FIG. 3 or 5). By moving the lens to the left (in the figure), it can be brought closer to the in-focus position. In the latter case, the relationship between the output levels P _A and P _B is reversed as shown in Fig. 7, and in this case, by moving the photographing lens 8 backward, the photographing lens 8 can be set to the in-focus position. be able to.

In this way, it is possible to detect whether the surface of the film 22 is in the in-focus position depending on whether or not the output levels P _A and P _B detected by both photoelectric elements 12A and 12B are equal.
Alternatively, the focus detection device of the present invention is configured, which can detect whether or not the photographing lens 8 is at the in-focus position. If the two output levels P _A and P _B do not match, that is, the case corresponds to Fig. 6, the photographing lens 8 is moved forward, and the case corresponding to Fig. 7, the photographing lens 8 is moved backward. When the output levels P _A and P _B match, the photographing lens 8 is set to the focus position, which constitutes the focus position setting device of the present invention.

FIG. 8 shows a focus position setting device for moving and setting the photographing lens 8 to a focus position using the above-mentioned focus detection device, as well as an automatic exposure device using electric circuit blocks.

That is, this focusing position setting device 31 includes a light emitting circuit 33 that causes a focusing lamp (corresponding to the focusing light sources 14A and 14B) 32 to emit light onto the subject.
, the reflected light from the subject is passed through pinholes 13A, 1
A focus detection circuit 34 that amplifies the signal output detected by the photoelectric elements 12A and 12B provided with 3B to detect whether or not the focus is on, and an indicator (on the focus indicator lamp 16) that displays when the focus is on. (corresponding) 35, and a (taking lens) drive device 36 that moves the taking lens 8 in order to set the taking lens 8 to the in-focus position.

The light emitting circuit 33 is, for example, a release button 3
By pressing the button 7, the switch SW ₁ is turned on from off (during which the switch SW ₂ is also kept on), and a focusing lamp 32 such as an LED is turned on. The focus detection circuit 34 is
It consists of an amplifier 39 that differentially amplifies the output signals of the photoelectric elements 12A and 12B, and a comparison detection circuit 40, and the comparison detection circuit 40 is configured such that, for example, the driving device 36 moves the photographing lens 8 back and forth at a constant speed. If the detection signal (amplified by the amplifier 39) is input continuously or at appropriate minute intervals, the output level P _A of the photoelectric element 12A is higher than the output level P _B of the other photoelectric element 12B. At times, the photographing lens 8 is moved forward, and when vice versa, the photographing lens 8 is moved backward, and when both output levels match, the movement of the photographic lens 8 is stopped, and the display 35
It is configured to light up.

On the other hand, when the relay button 37 is further pressed, the third switch SW ₃ is turned on from off (the second switch SW ₂ is turned off, and the focus position setting device 31 is not operated), and the automatic focusing position setting device 31 described below is turned on. An exposure (EE) device 41 is configured to operate.

That is, this EE device 41 includes an amplifier 44 that is supplied with power from a power source 42 when the switch SW ₃ is turned on and amplifies the detection signal of the photoelectric element 43 for photometry, and an EE shutter 45 that uses this amplified signal. and an EE control circuit 47 that controls a light amount control circuit 46 that controls the shutter speed of the camera and the light amount of a light source for photographing (in the case of an endoscope, an illumination light source for photographing), and an operation of turning on the switch SW ₃ . As a result, the EE control circuit 47 operates to adjust the shutter speed and light amount to an appropriate level.

Focusing position setting device 31 configured as described above
The photographing lens 8 is moved by the operation described below.
Move and set to the focus position.

That is, when the release button 37 is pressed with a finger or the like and the switch SW ₁ is turned on, the light emitting circuit 33 turns on the focusing lamp 32 and focuses the pinholes 13A, 1.
3B, further passes through the re-imaging lens 10, is reflected by the focusing mirror 9, passes through the photographing lens 8, and is projected onto the subject. The light reflected by the subject passes through the photographic lens 8 again and is reflected by the focusing mirror 9.
The light advances to photoelectric elements 12A and 12B provided with pinholes 13A and 13B, respectively. When the photographic lens 8 is in a focused position with respect to the subject, the output levels of both photoelectric elements 12A and 12B become equal.
Therefore, the differentially amplified signal output becomes 0, and in this case, the operation of the driving device 36 to move the photographing lens 8 back and forth is stopped, and the display 35 lights up.

On the other hand, if the photographic lens 8 is out of focus, the output of the differentially amplified signal will be positive or negative, so the photographic lens 8 is moved forward or backward depending on the direction of the signal. If so, the differential amplification output becomes zero, and the photographing lens 8 can be set at the in-focus position as described above.

When the photographic lens 8 is set at the in-focus position in this way, the display 35 such as the focus display lamp 16 displays an image, so the observer visually confirms this and then presses the release button 37 more firmly. Then,
The EE device 41 operates and clear photographs can be taken. In this case, the EE devices 41 can be operated simultaneously or in succession. Further, the display 35 may operate a buzzer or the like instead of lighting a lamp.

In the above description, the position where the output levels P _A and P _B of both photoelectric elements 12A and 12B are equal is set to be in focus, but the relationship is not limited to this.

FIG. 9 shows three sets of photoelectric elements 51A, 51B, 5
1C and light sources 52A, 52B, and 52C (in a focus detection device and a focus position setting device that uses this focus detection device to set a focus position)
A second example is shown.

In this embodiment, a photoelectric element 51B having a pinhole 53B is placed on the optical axis 7' of the film 22.
Photoelectric elements 51A, 51B are set at positions conjugate with the plane, and have pinholes 53A, 53C on both sides of the front and rear sides, respectively.
A, 52B, 52C are arranged, and light sources 52A, 5
In addition to correcting variations between 2B and 52C and distance differences during light projection, each photoelectric element 51A and 51
Variable resistance resistor 5 that can adjust the detection characteristics of B, 51C
It is connected to the battery 55 via 4A, 54B, and 54C, respectively.

Photoelectric elements 51 arranged at the front and rear positions in this embodiment
Position 1 where A, 51C is conjugate with the 22nd surface of the film
1, when the output level P _B detected by the photoelectric element 51B is smaller than the output levels P _A and P _C of the photoelectric elements 51A and 51C disposed at the front and rear positions, the photographing lens 8 is determined to be in focus, and in other cases, that is, P _A <
In each case of P _B or P _C <P _B , the photoelectric element 51B can perform a focus detection function that indicates that it is not in the focus position, and in these cases, by moving the photographic lens 8 backward and forward, respectively, it will be in the focus position. Can be set.

In the case of the above embodiment, two sets of differential amplifiers are used,
If the amplified output is detected by a combination of logic circuits or a multiplexer and the photographing lens 8 is moved back and forth and stopped, a focus position setting device can be formed.

The third embodiment shown in FIG. 10 is based on the light source 5 of FIG.
2A, 52B, 52C are used as one light source 52, right angle prisms 56A, 56C are arranged on both sides instead of the light sources 52A, 52C arranged in front and behind on both sides, and the light from the light source 52 is a cover arranged in front of it. glass 5
7 and the pinhole 53 of the photoelectric element 51B in front
This light source 52
The light of
The light is projected forward through each of 3A and 53C.

The effects in this case are similar to those of the second embodiment. In addition, the photoelectric elements 51A, 51B, 51 in the embodiment using these prisms 56A, 56C
The transmittance of the prisms 56A, 56C may be selected and used as a means for adjusting the light amount and correcting variations in (the detection surface of) C, or each photoelectric element 51A,
It may be provided on the detection circuit side of 51B and 51C.

Figure 10 shows pinholes 61, 61,..., 61
A large number (7 in the figure) of photoelectric elements 62, 62, . 4 Examples are shown below.

The photoelectric elements 62, 6 arranged in large numbers in the form of an inclined plane
A filter 63 is bonded in the form of a thin plate to the back side of the light shielding plate attached to the back side of 2,..., 62, and an elongated prism 6 is further attached to the back side of this filter 63.
4 is joined, and by a light source 65 close to one end of this prism 64, the projecting light is multiple-reflected on the inner surface of the prism 64, passes through the filter 64, and passes through the pinholes 61, 61, . . . 61 and is configured to be emitted forward. In this embodiment, if the characteristics of the photoelectric elements 62, 62, . . . , 62 vary depending on the projection distance and the detection level differs, if the filter 63 is arranged to change the transmission characteristics, The characteristics at the time of detection can be made close to optimal.

In this embodiment, a number of photoelectric elements 62,
Since the photoelectric elements 62, . . . , 62 are arranged, the distance between adjacent photoelectric elements 62, 62 in the front-rear direction along the optical axis 7' can be made sufficiently small, and these photoelectric elements 62, 62, . By comparing the output levels detected at 62, it is possible to detect which position is the focus position. In other words, since the position of the photoelectric element 62 that has the minimum output level becomes the focal point, it is possible to detect deviations from the position 11 that is conjugate with the surface of the film 22. You can know when you are in a state of focus.

Note that if infrared light is used as the light source in the above, the influence of illumination light and other external light can be reduced. In other words, in this case, the photoelectric element 1 shown in FIG.
The output characteristics of No. 2 are as shown in FIG. 12, and the signal-to-noise ratio can be increased and detection accuracy can be improved.

Moreover, the photoelectric element 12A in each of the above-mentioned embodiments,
12B, 51A, 51B, 51C, 62,..., 6
The opening provided in 2 is the pinhole 1 shown in FIG.
The opening is not limited to the 3A shape, but may be a slit-like opening as shown in FIG. 13, or may have another shape. Therefore, for example, it is of course possible to arrange two photoelectric elements with a slight spacing between them.

In each of the embodiments described above, a focus position setting device using a focus detection device is provided in the camera adapter 5 (for a camera or a television camera) attached to the endoscope 4. Of course, the present invention is not limited to this embodiment, and can be applied not only to endoscope cameras but also to optical instruments or devices in which it is important whether or not the camera is in focus, such as ordinary cameras. In this case, the photographic lens refers to a part or all of the lens used for imaging in an optical device (or device), and may be moved back and forth along the optical axis.

As explained above, according to the present invention, with a simple configuration, it is possible to accurately detect whether or not the subject is in the focused position, and if it is not in the focused position, in which direction it is shifted. It can be used even in dark photographic optical systems, and can also be used with endoscopes and other devices that do not have space to install side by side other than a single photographic optical system, and can be detected using multiple photoelectric elements. Based on the output level, it is possible to determine in which direction the photographing lens should be moved to bring it into focus, and by arranging a large number of photoelectric elements, it is also possible to detect the amount from the focus position. It has the following effect.

[Brief explanation of drawings]

1 to 8 relate to a first embodiment of the present invention, and FIG. 1 shows the present invention housed in a camera adapter that is inserted when a camera is attached to an endoscope. An explanatory diagram showing an optical system of a focus position setting device using a focus detection device in , FIG. 2 is a front view showing a photoelectric element provided with a pinhole,
Figure 3 is a schematic explanatory diagram showing the focus detection operation of the optical system in Figure 1 converted to a linear optical system, and Figure 4 is a diagram showing the focus detection operation of the optical system in Figure 3 when the position of the subject is changed. Characteristic diagram showing the output characteristics of the photoelectric element, No. 5
The figure is an enlarged explanatory diagram showing the main parts of the optical system for light projection and light reception detection in Figure 1, and Figures 6 and 7 show that the photographing optical system (photographing lens) is not in focus. Indicates the output level of the photoelectric element in the case of
Fig. 6 is an explanatory diagram showing the output level in a state shifted backward, Fig. 7 is an explanatory diagram showing the output level in a state shifted forward, and Fig. 8 is an explanatory diagram showing the output level in a state shifted forward. FIGS. 9 to 11 are explanatory diagrams showing the configurations of a focus position setting device and an automatic exposure device that move and set the camera to a focusing position, and FIGS. FIG. 10 is an explanatory diagram showing the second embodiment, FIG. 11 is an explanatory diagram showing the fourth embodiment, and FIG. 12 is an explanatory diagram showing a light source that emits infrared light. Characteristic diagram showing the output characteristics of the photoelectric element when used, 1st
FIG. 3 is a front view showing another embodiment in which the opening of the photoelectric element is shaped like a slit. 4...Endoscope, 5...Camera, 7, 7'...Optical axis, 8...Photographing lens, 9...Focusing mirror, 1
2A, 12B, 51A, 51B, 51C, 62...
...Photoelectric element, 13A, 13B, 53A, 53B,
53C, 61...pinhole, 14A, 14B,
52A, 52B, 52C, 52, 65... light source,
17A, 17B...Photocathode, 18A, 18B...
Light shielding surface, 22...Film, 31...Focus position setting device, 32...Focusing lamp, 33...Light emitting circuit, 34...Focus detection circuit, 35...Display device, 3
6... Drive device, 37... Release button, 38
...Battery, 41...Automatic exposure device, 54A,
54B, 54C...variable resistance, 56A, 56C,
64...Prism.

Claims (1)

[Scope of Claims] 1. In an optical device that images a subject through a photographing lens at a predetermined position on which a film surface or the like is arranged, the predetermined position is formed on an axis equivalent to the photographing optical axis behind the imaging lens. a plurality of flat photoelectric elements having light-receiving surfaces located at least before and after a position conjugate with the photoelectric element; a narrow opening provided through the photoelectric element approximately in the center; A focus detection device comprising: a light source that projects an image of the aperture onto a subject through a photographic lens. 2. In an optical device that images a subject at a predetermined position on which a film surface or the like is arranged through a photographing lens that can move back and forth, an axis that is conjugate with the predetermined position on an axis equivalent to the photographing optical axis behind the photographic lens. a plurality of flat photoelectric elements having light-receiving surfaces located at least before and after the position where the image is taken; a narrow opening provided through the photoelectric element approximately in the center; A focusing position setting device comprising: a light source that projects an image of the aperture onto a subject through a lens; and means for moving a photographing lens back and forth in accordance with detection output levels of the plurality of photoelectric elements. .