JPH0353609B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves forming a through hole in a part of a photoelectric element having a photoelectric conversion surface, passing through the through hole from the back side, and then passing an imaging lens system through the through hole to an object (examination). A means for detecting whether or not the imaging lens system is in focus, or measuring the distance to the object, by projecting light, forming a reflected image from the object on the photoelectric conversion surface, and measuring the amount of light. The present invention relates to a photoelectric device suitable for use in a means.

Generally, when observing or photographing a subject or subject optically clearly using an optical device such as a camera, television camera, or endoscope, the imaging (photographing) lens system is adjusted and set to the focal position. There are often things that need to be done. In this case, a photoelectric element with a photoelectric conversion function is widely used as a means for detecting whether the imaging lens system is in the focused position, that is, whether the subject is clearly imaged on the imaging plane. There is.

For example, the method using a split prism as disclosed in Japanese Patent Application Laid-Open No. 56-128923 requires at least two or more minute photoelectric elements on the upper and lower sides, and requires a certain level of accuracy or higher. In this case, in addition to arranging a large number of photoelectric elements, the circuit system for comparing their output signals and detecting whether or not the focus is in focus becomes complicated, which can be expensive, especially for products that are produced in small numbers. There is a problem with becoming.

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 effects of this and detect whether or not the subject is in focus even when the subject is dark or the photographic optical system is dark, but the configuration is complicated, so it is difficult to The problem is that it is expensive.

For this reason, the present applicant first provided a through hole such as a pinhole in the photoelectric element, and focused the reflected projection image projected onto the subject through this through hole on the photoelectric element, and the amount of light in that case By detecting
We submitted a photoelectric device that can detect

To simply provide pinholes, slits, or other through-holes in the above-mentioned photoelectric element, an optical semiconductor formed by forming or bonding a thin P-type semiconductor to an N-type semiconductor layer is used, and its surface is chemically treated. A known method is to form through holes by etching (erosion), as shown in FIG.

As shown in the figure, in a photoelectric element 2 having a through hole 1 formed by ordinary etching,
The thin P (type semiconductor) layer that becomes the photoelectric (conversion) surface 2a is used as the etching surface, and the diameter (or width) 1a of the through hole 1 on the P layer side is the same as the diameter (or width) 1a of the through hole 1 on the N (type semiconductor) layer 3 side on the base side. Diameter (or width) of hole 1
It becomes larger than b. In this case, the difference between the diameter (width) 1a and 1b of the through hole 1 on the front and back surfaces may reach about 0.2 [mm], although it depends on the thickness. In such a case, inconveniences will occur when used for in-focus point detection as shown in FIG. 2, which will be explained below.

FIG. 2 shows the principle of detecting a focused point using the photoelectric element 2 described above.

In the figure, light lit by a lamp 5 is condensed by a condenser lens 6 and irradiated onto one end face of an illumination fiber (of course, a single fiber may be used) 7, and the other end face is located at the photoelectric The optical axis 8 passes through the through hole 1 of the element 2 and further in front of it.
Light is projected onto a subject 10 through an imaging lens (system) 9 disposed above.

A battery 11 is installed on the PN junction surface of the photoelectric element 2.
and a resistor 12 are connected in series, and when light is incident on the photocathode 2a, the resistance value of the PN junction surface changes depending on the amount of light, and the current change according to the change in resistance value is reflected at the output terminals of both ends of the resistor 12. It is configured so that it can be detected as a voltage change from

The back side of the photoelectric element 2 is fixed to a light shielding plate 13 by adhesion or the like, and the fiber 7 is further fixed to this light shielding plate 13 with a sealing member 14 or the like.

In the optical system arranged as above, now,
Suppose that the subject 10 is in focus at the position indicated by b, but the positions if it is too close or too far away are indicated by a and c, respectively.

In the above case, the light reflected at the position b passes through the imaging lens 9 and the position of the through hole 1 on the photocathode 2a becomes the convergence point (imaging point), Since the light does not reach the photocathode 2a,
In this case, since almost no current flows, the voltage on both sides of the resistor 12 becomes approximately zero.

On the other hand, the light reflected at the position a has a convergence point at the rear position of the through hole 1, so as shown in the figure, the light reaches the photocathode 2a on the outer periphery of the through hole 1 and is irradiated with this light. A current flows through the PN junction surface, and a detection voltage is output across the resistor 12. Similarly, the light reflected at the position c already becomes a convergence point at the front position of the through hole 1 and then spreads out, so that the light reaches the photocathode 2a and a voltage is output from both ends of the resistor 12.
It can be seen that the focal point is when the voltage at the output terminals across the resistor 12 becomes minimum.

However, in the photoelectric element 2 having the above-mentioned shape, when the subject 10 is at a position slightly rearwardly shifted from the in-focus position b, that is, at a position indicated by the symbol b', the image formation position is closer to the photocathode 2a. Although it is slightly expanded at the front position of the photocathode 2a, since the through hole 1 is expanded forward, the photocathode 2a is slightly expanded.
I can't reach a. In other words, it may be detected as a focused point. This also applies when the subject 10 is slightly shifted forward from the in-focus position b.

As mentioned above, the conventional etching process has the disadvantage that the function of detecting the point of light convergence is degraded. The above-mentioned problem is also inconvenient when measuring distance with the imaging lens set at a focused point.

The present invention has been made in view of the above-mentioned points, and it is possible to detect the in-focus point and measure the distance of the subject with high precision, and also to avoid the direct flow of photocurrent when the illumination light passes through. It is an object of the present invention to provide a photoelectric element that can accurately measure the amount of light reflected from a subject without causing any interference.

In order to achieve the above object, the photoelectric element according to the present invention is provided by forming a through hole in the photoelectric element provided on one side of the photoelectric conversion surface, and projecting light onto a subject through the through hole and an imaging lens system. A photoelectric element used for means for measuring the focal position of an imaging lens system with respect to the subject or the distance to the subject by measuring the amount of light by forming a counter-projected image of the subject on the photoelectric conversion surface, The through hole is formed in a shape in which the diameter or width on the photoelectric conversion surface side is smaller or equal to that on the back side, and a layer that does not cause photoelectric change is formed on the inner wall of the through hole as a layer that is homogeneous with the semiconductor layer that will become the back layer. It is set up.

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 3 shows a light amount measuring means for detecting a focused point when a photoelectric element is used in the first embodiment of the present invention.

Compared to FIG. 2, the diameter (or width) 22a of the photoelectric element 21 in FIG.
It is characterized by being smaller than 2b. That is, in this case, the surface to be etched is not the photocathode 23 side but the N layer 24 side on the back side. The other parts have substantially the same configuration as in FIG. 2.

The diameter (or width) 22a of the through hole 22 on the photocathode 23 side is formed to be approximately equal to the diameter (or width) of the other output end of the illumination fiber 7. In the photoelectric element 21 in which the through hole 22 is formed, the peripheral wall surface at the front end of the through hole 22 is thinly covered with an N layer 24 so that illumination light does not directly reach (the P layer forming the) photocathode 23. ing.

Incidentally, reference numeral 25 is a light shielding plate for preventing unnecessary reflected light from entering.

It will be explained below that the light amount measuring means for detecting a focused point using the photoelectric element 21 in the first embodiment configured as described above can detect a focused point with high accuracy.

Similarly to the above, it is assumed that the imaging lens 9 is in focus when the subject 10 is at the position indicated by the symbol b, and when the subject 10 is located slightly behind the position indicated by the symbol b.
The position of is indicated by the symbol b'. The position where the light reflected from the position indicated by the symbol b (indicated by the thin solid line) is imaged is on the optical axis 8, as described above, on the photocathode 2.
Since the point is flush with 3, the light does not reach the photocathode 23 in this case.

However, the light reflected at the position indicated by the symbol b' (indicated by the dashed line) already forms an image point in front of the photocathode 23;
Expanding light is incident on the side.

In the case described above, the light could not reach the photocathode 2a because the through hole 1 was expanded toward the photocathode 2a side (that is, expanded toward the front side), but according to this embodiment, the light could not reach the photocathode 2a. Since the hole 22 is formed to expand toward the back side, light reaches the photocathode 23. In other words, it is possible to detect that the subject 10, which is slightly shifted from the in-focus point with respect to the imaging lens 9, is not in the in-focus point.

Note that the above-described through hole 22 can be formed not only by etching but also by drilling from the back side with a drill having a tapered blade.

On the other hand, it is also possible to form a photoelectric element 33 by machining, as shown in the second embodiment of FIG. 4, by providing through holes 32 of the same shape on both the photocathode 31 side and the back side.

Even in this case, if the front edge of the through hole 32 is directly adjacent to the photocathode 31, a direct photocurrent will flow when the illumination light passes through, making it difficult to accurately measure the amount of light from the reflected light from the subject 10. Therefore, the peripheral wall surface of the through hole 32 is not the photocathode 31 (for example) N
Covered with layer 34. In this case, a means for shielding the photocathode exposed in the through hole 32 from light, such as by fitting a coating material or a thin pipe, may be provided.

In the above description, each photocathode 23, 31 of the photoelectric elements 21, 33 is set as the P layer side in the PN junction, but if the polarity of the applied voltage is changed, the N layer side can also be set as the photocathode 23, 31. can.

Further, as the optical semiconductor that can be used in the above-mentioned photoelectric element, in addition to photodiodes and phototransistors using silicon, germanium, etc., solar batteries, CdS, CdSe, etc. can be used.

Note that solar cells do not require a battery.

Furthermore, although the phototransistor has a three-layer structure, it has approximately the same shape when providing through holes.

As described above, according to the present invention, even if the projected image reflected by the subject and formed is slightly shifted from the focused point, the amount of light can be detected in the light amount plane, and as a result, the focused point can be detected. Moreover, it is possible to measure the distance to the object with high precision, and there is no direct photocurrent flowing when the illumination light passes through, making it possible to accurately measure the amount of light from the reflected light from the object. .

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing the shape of a photoelectric element formed by conventional etching, and Fig. 2 is an explanation showing a light amount measuring means for detecting a focused point in a previous application using the photoelectric element of Fig. 1. Figures, Figures 3 to 4
The figures relate to the present invention; FIG. 3 is an explanatory diagram showing a light amount measuring means for detecting a focused point using a photoelectric element in the first embodiment; and FIG. 4 is a sectional view showing the second embodiment. be. 5... Lamp, 7... Fiber, 9... Imaging lens, 10... Subject, 21, 33... Photoelectric element, 22, 32... Through hole, 23, 31... Photocathode, 24, 34... ...N layer.

Claims (1)

[Claims] 1 A through hole is formed in the photoelectric element provided on one side of the photoelectric conversion surface, and light is projected onto the subject through the through hole and the imaging lens system, and a reversely projected image by the subject is focused on the photoelectric conversion surface. In a photoelectric element used as a means for measuring the amount of light by imaging and measuring the focal position of an imaging lens system with respect to a subject or the distance to the subject, the through hole has a diameter or a width on the photoelectric conversion surface side. A photoelectric element formed in a shape smaller than or equal to the shape on the back side thereof, and provided with a layer on the inner wall of the through hole that does not cause a photoelectric change as a layer homogeneous with the semiconductor layer serving as the back side layer.