JPH0522220B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an automatic focus detection device for a camera that detects the image formation state of a light emission pattern by a distance measuring optical system, that is, so-called blur, and detects the distance to a subject. Conventionally, many automatic focus detection devices have been proposed, including those based on triangulation and those based on contrast detection. The triangulation method uses a light emitter equipped with a light emitting element such as an infrared light emitting diode (hereinafter referred to as IRD) with a certain baseline length, and a silicon photodiode (hereinafter referred to as IRD) that detects the light emitted onto the subject.
If the light receiver is equipped with a light emitting element such as SPD (described as SPD), and the light receiver includes one light receiving element, what is the angle formed by the optical axis of the optical system of the light emitter and the light receiver? In addition, if the light emitter and receiver are fixed, the light receiving element of the receiver must be divided into multiple units.
In the method of sweeping the angle formed by the optical axis, reliability is reduced due to the intervening mechanical movement, and in the method of dividing the light receiving element into multiple parts, the distance measurement zone is affected by the configuration of the light receiving optical system. Since the baseline length is fixed, it is not very versatile. In addition, there is a triangulation method that measures distance by matching images from two optical systems with different base line lengths, but this method requires a large number of light-receiving elements and is expensive. Moreover, it has the disadvantage that it is easily influenced by the pattern of the subject. In any case, in addition to the above-mentioned drawbacks, the triangulation method also has a drawback in terms of camera design, in that it requires a baseline length. On the other hand, the method using contrast detection can detect the image formed by the photographic lens and is independent of the focal length of the photographic lens. In order to detect the focused position, it is necessary to move the lens and change the focal position for detection, which results in poor quick-shooting performance and is not suitable for cameras with lens shutters for snapshots. The purpose of the present invention is to take into consideration the drawbacks of the above-mentioned conventional examples,
To provide an automatic focusing device for a camera that is inexpensive and highly reliable regardless of the baseline length. Hereinafter, the present invention will be explained based on embodiments shown in the drawings. FIG. 1 is an external view showing one embodiment of the basic configuration of the focus adjustment device of the present invention, in which 1 is the main body of the device, 2 is an aspherical lens for light emission, and 3 is an aspherical lens for light reception. FIG. 2 is a partial external view of another embodiment, in which a finder block (finder objective lens 4) is arranged between a light emitting block 2 and a light receiving block 3. It will be described later that even when a baseline length exists, the ranging system of the present invention can respond immediately. FIG. 3 is a perspective view showing an embodiment of the ranging block, where 20 is an IRD, 21 is an IRD chip, and 22 is an IRD chip.
The IRD electrode 26 is a parallel plane plate, and is arranged to be rotatable around two mutually orthogonal axes that are perpendicular to the optical axis. 30 is a light receiving circuit block, 31 is a circular SPD, and 32 is arranged around the SPD 31.
It is SPD. The light receiving circuit block 30 is arranged so as to be movable in the optical axis direction. Figure 4 is a central horizontal sectional view corresponding to Figure 1.
FIG. 5 is a perspective view of the parallel plane plate 26 block. The IRD 20 enclosed in the IRD chip 21 is arranged to be slightly movable in the optical axis direction due to the relationship between the spring washer 41 and the support plate 42. The parallel plane plate 26 basically has an axis (X axis) 26a placed perpendicular to the optical axis, is rotatably supported on the holding frame 27 by the axis 26a, and has an arm 26b. is forming. Also,
The holding frame 27 has an axis (Y axis) 27a that is basically perpendicular to the optical axis and orthogonal to the axis 26a, and is rotatably supported on the main body 1 by the axis 27a. At the same time, a window 27b and an arm 27c are formed through which the arm 26b of the parallel plane plate 26 passes. Further, as shown in FIG. 1, the arms 26b and 27c pass through windows 1a and 1b formed in the main body 1 and protrude to the outside of the main body 1. The holding frame 27 is rotated about the shaft 27a by operating the lower part of the frame by adjusting the screw 28 screwed into and supported by the back cover 5 of the main body 1, and the parallel plane plate 26 is rotated about the shaft 27a. is the holding frame 27
The arm 26b is operated and rotated about the shaft 26a on the holding frame 27 by adjusting the screw 29 screwed into and supported by the arm 27c.
Therefore, the plane-parallel plate 26 is adjusted in a complex manner in the X-axis and Y-axis directions perpendicular to the optical axis. 33 is a printed circuit board, 34 is a shield plate for preventing electromagnetic disturbance, and 35 is an IR filter that blocks visible light and transmits only infrared rays. It is supported on a base plate 36 which is arranged so as to be movable in the direction. Then, the base plate 36 is moved in the optical axis direction by adjusting the screw 37 screwed and supported by the back cover 5 into and out, thereby adjusting the positions of the SPDs 31 and 32 in the optical axis direction. Note that the following movement of the parallel plane plate 26, the holding frame 27, and the base plate 36 with respect to the return (exit) direction of the screws 28, 29, and 37 is controlled by a spring (not shown). Figure 6 [a is front view, b is bottom view] is IRD20
In the detailed diagram, it is IRD chip 2 that emits infrared light.
The one-sided, circular IRD electrode 22 has a light-shielding property, and no light is emitted from the electrode 22 portion. Figure 7 [a is front view, b is bottom view] is SPD3
1 and 32, the divided SPD 31 and the surrounding SPD 32 are separated so as not to interfere with each other. Here, the diameter of the SPD 31 is such that the infrared light from the surface of the IRD chip 21 is projected by the light emitting aspherical lens 2, and the inner diameter of the projected light corresponds to the outer diameter of the circular IRD electrode 22. Therefore, it can be assumed that the electrode 22 forms an image on the object, and the IRD profile on the imaged object is imaged on the SPDs 31 and 32 by the light-receiving aspherical lens 3.
IRD electrode 22 on IRD chip 21 imaged on 2
The image is set so that it matches the image of SPD31. That is, the diameter of the IRD electrode 22 on the IRD chip 21 is φD, the diameter of the SPD 31 is φd, and the aspherical lens 2 for light emission is
When the focal length of the light receiving aspherical lens 3 is F, and the focal length of the light-receiving aspherical lens 3 is f, then d=f/F·D (1) is set. Further, the SPD 32 may be large enough to form an image of the infrared light from the IRD chip 21 surface. Next, the principle of the present invention will be explained based on FIG. In order to simplify the explanation, the optical axes of the light-emitting aspherical lens 2 and the light-receiving aspherical lens 3 are made to coincide, and therefore, the base line length is zero. 91 is a splitter for separating the optical axes of the IRD chip 21 and the SPDs 31 and 32, and is arranged so as to match the logic shown in FIG. 9a. Now, in part a of Fig. 9, IRD chip 2
1. The IRD electrode 22 and the SPDs 31 and 32 are optically equidistant from each other from the lenses 2 and 3, and the lenses 2 and 3 are arranged in a circular shape on the IRD chip 21.
The arrangement is such that the real image of the IRD electrode 22 is formed at a position 5 m from the lenses 2 and 3. Therefore,
The real images of the SPDs 31 and 32 are similarly formed at a position 5 m from the lenses 2 and 3. In other words, a subject located at a distance of 5 m is formed as a real image on the SPDs 31 and 32. In this case, since lenses 2 and 3 are common, from equation (1) above, the diameter of electrode 22 and
The diameters of the SPDs 31 are set to be equal. Then, when pulse electricity is applied to the electrode 22,
The surface of the chip 21 emits pulsed light, and when the light emission intensity is plotted in the radial direction of the electrode 22, a light emission pattern as shown in section b is obtained. In section b, the horizontal axis D represents the entire radial line segment of the IRD 20 passing through the center (optical axis) of the electrode 22, and the vertical axis P represents the light intensity. The reason why the light intensity of the light emission pattern drops sharply at a point corresponding to the diameter D ₀ of the circular electrode 22 with the optical axis as the center is because the electrode 22 has a light-shielding property. The smooth drop in intensity on both sides of the far side corresponds to the end face of the chip 21, and the light intensity increases again as it moves away from the optical axis, but this is due to the fact that the light intensity decreases smoothly on both sides. Parabola (see number 23 in Figure 3)
This is due to Light-emitting aspherical lens 2 and light-receiving aspherical lens 3
If the diffraction phenomenon is not considered ideally, a pattern similar to that shown in section b should be imaged on the object at a distance of 5 m. The size of the image is large because the light emitting optical system is a magnifying system, and the distance to the subject is L, and the focal length of lenses 2 and 3 is f.
Then, the image of the electrode 22 at that 5m distance is
D _A becomes D _A =L/f・D ₀ (2). Therefore, if f = 20 mm and L = 5 m, D _A = 5 × 10 ³ /2 × 10 ・D ₀ = 2.5 × 10 ² × D ₀ , which is a magnification of 250 times, and the 5 m The light amount P _A per unit area of the image formed at a distance of is
It is determined by the light emission profile (not the light emission pattern) of the IRD 20, the aperture diameter, f, L, and subject reflectance R of the lens 2, but since the light emission optical system is fixed, the electrode 22 at each distance position is determined. Image diameter D _i and light intensity per unit area of the image of the light emitting pattern P _i
is the relational expression D _i 〓L, P _i ∝R・L ^-2 (3) (where, i=A, B, C (A, B, C indicate each distance). Object at a distance of 5 m In the above light emission pattern, as shown in part e, the image of the arrow electrode 22 is formed with a high contrast.However, when the subject approaches the lenses 2 and 3 from 5 m, the light emission optical system becomes unstable. 21. Since the image of the electrode 22 is set to be formed at a distance of 5 m, the light emitting pattern is no longer imaged, resulting in a so-called out-of-focus state.
For example, on a subject at a distance of 2.3 m, the distance
When photographing a subject at a distance of 1.4m, there is blur as shown in section c.
The contrast of the image of the electrode 22 on the chip 21 gradually decreases. On the other hand, the light emission pattern is imaged on these subjects on the SPDs 31 and 32, but if the subject is at a distance of 5 m, the light emission pattern on the subject is completely imaged on the SPDs 31 and 32. be done.
That is, the light emission pattern of the chip 21 and the electrode 22 is directly imaged onto the SPDs 31 and 32. However, as the subject approaches the lenses 2 and 3, the image of the subject shifts from the surface of the SPDs 31 and 32, resulting in what is called an out-of-focus image. In other words, as the distance from the lens to the subject becomes shorter, the light emission pattern on the subject becomes blurred, and the electrode 22
The contrast of
The light emitting pattern imaged on the top becomes more blurry and the electrode 2
The contrast of No. 2 is further reduced due to the synergistic effect of the blur caused by the light emitting optical system and the blur caused by the light receiving optical system. The size of the light emission pattern imaged on the SPDs 31 and 32 depends only on the focal length of the lenses 2 and 3 as described above, since the distance L between the light emission optical system and the light reception optical system is common. It doesn't change even if you change the distance. Further, the amount of light per unit area of the light emitting pattern imaged on the SPDs 31 and 32 is inversely proportional to the square of the distance L. Therefore, the average diameter D _S of the electrode 22 imaged onto the SPDs 31 and 32 is D _S =D ₀ (4) (when the focal lengths of the lenses 2 and 3 are equal). In addition, the light intensity P _S per unit area of the light emitting pattern imaged on the SPDs 31 and 32 is P _S 〓R・L ^-2 (5) if there is no blur, and the blur element is included in it. It will look like section f. However, in order to be able to compare the degree of blur at each subject distance, the P axis of the f section is (5/1・4) ² times when L = 5 m, and (2.3/1.4) when L = 2.3 m.
The scale is ^twice as large as the one with L = 1.4m. The light emitting pattern of the chip 21 and the electrode 22 formed in this way is detected by the SPDs 31 and 32. Since the diameter d of the SPD 31 is made equal to the diameter D _S of the image formation of the electrode 22, the SPD 31 detects the light emission pattern of the chip 21 and the electrode 22. ,
Further, the SPD 32 detects the amount of imaged light from the light emitting section of the chip 21. The image of the IRD electrode 22 is ideally dark,
Therefore, SPD31 has only dark current and noise.
Although it is constant regardless of the object distance L, in reality, the image of the electrode 22 does not become dark due to the aberration of the optical system, internal reflection, reflection from the surface of the electrode 22, etc., and the image formed on the electrode 22 does not become dark. Some photoelectric power is produced. Here, if the image formation of the electrode 22 and the light emitting pattern does not become blurred due to a change in the subject distance L, then
According to the above equation (5), the photovoltaic currents I (Ia, Ib) generated in the SPDs 31 and 32 have different proportional coefficients, but the following relational expression holds true: I=R·L ⁻² +C (6). C is a dark current and noise component, which can be ignored if the S/N ratio is sufficiently large.
The photovoltaic current I generated in the SPD32 can be written as I〓R・L ^-2 (7). Now, considering the case where burnout occurs due to a change in the subject distance L, as shown in section f, when the subject is closer than 5 m, the contrast of the image of the electrode 22 decreases and the edges of the image become gentle. As the area gets older, light from the periphery of the area of SPD 31 enters, and the increase in the amount of light due to this blur increases monotonically as a function of R・L ^-2 , while the amount of light in the area of SPD 32 decreases. death,
It is a monotonically decreasing function of R・L ^-2 . Therefore, the monotonically increasing function for L<5m can be expressed as g
(L), and if the monotonically decreasing function is expressed by h(L), then
The photovoltaic currents Ia and Ib generated in SPDs 31 and 32 are Ia〓R・L ^-2・g(5−L)+C (8) Ib〓R・L ⁻²・f(5−L) (9) expressed. Now, in the case explained with reference to FIG. 9, the base line length is zero, but in reality, as shown in FIGS. 1 and 2, there may be quite a few base line lengths. In that case, as the subject gets closer than 5m,
The image of the IRD electrode 22 on the IRD chip 21 becomes blurred and at the same time shifts laterally from the SPD 31.
31, it is expected that the amount of light will increase more than that due to blurring. This increase in light amount monotonically increases as the subject distance L approaches from 5 m due to a function of R L ^-2 , and decreases again when the distance is below a certain distance.
The distance at which the distance starts to decrease is outside the distance measurement range using the commonly considered baseline length, and the light emitting pattern can be expanded using the parabola of IRD20. In other words, in the practical ranging range, even if there is a baseline length and triangulation elements are included, the SPD31 photovoltaic current Ia
If is a monotonically increasing function of R.L ^-2 , then the photovoltaic current I _a can be reduced to the above equation (8). Similarly, the photovoltaic current Ib can be reduced to the above equation (9). Figure 10 shows the photovoltaic current I in equation (7) above, which does not take into account the effects of blur and triangulation, and the photovoltaic currents Ia and Ib in equations (8) and (9) above, as a function of object distance L. FIG. 2 is a characteristic diagram of changes in photoelectromotive current versus subject distance expressed logarithmically. However, it is standardized so that the same value is obtained when L=5m. Now, the photovoltaic current (output) Ia of SPD31 and
The photovoltaic current (output) Ib of the SPD 32 monotonically increases and decreases as a function of R·L ⁻² depending on the distance L, but as it is, it depends on the subject reflectance R and distance measurement is not possible. Therefore, when calculating Ia/Ib using a circuit, Ia/Ib=K _A・R・L ^-2・g(5−L)+C/K _B・R・L ^-2
・h(5-L)=Kg(5-L)/h(5-L)+C/
K _B・R・L ^-2・h(5−L)(10) Here, g(5-L) is zero when L=5m, and h(5-L) takes a maximum when L=5m, and the second on the right side of equation (10) This term cannot be ignored compared to the first term, but since C is originally a dark current and a noise component, the second term has a very small value. Therefore, when the subject distance L approaches from 5 m, g(5
-L) increases and h(5-L) decreases, so
Immediately, the second term becomes negligible. In other words, in the area where Ia/Ib can actually be detected by distance measurement, the second term on the right side of equation (10) can be ignored,
Equation (10) can be written as Ia/Ib=Kg(5-L)/h(5-L) (11) (K is constant). As mentioned above, as the distance L approaches, g(5-L) monotonically increases and h(5-L) monotonically decreases in the distance measurement range, so Ia/Ib is the reflectance R of the subject.
It monotonically increases as the subject approaches, regardless of the [For distance L, g(L): monotonically decreasing;
Since h(L): monotonically increases, Ia/Ib monotonically decreases from L: 0 → 5] Now, until now, the imaging position of the light emitting optical system and the light receiving optical system was set at 5 m, but in reality Even if the optical configuration is set to create an infinite or negative distance, that is, a virtual image, the same conclusion (the distance measurement range extends to 5 m or more) can be drawn. Figure 11 shows the cases where a is imaged at a distance L = 5 m and b is imaged at a position of ∞, respectively.
Ia/Ib is shown in the graph. Figure 11 shows the case corresponding to three-point zone focus. For example, the boundary distances of the three zones are
Assuming that the distances are 1.8m and 3.2m, if you set the corresponding Ia/Ib values r ₁ and r ₂ in the graph, (Ia/Ib)>r ₁
When r ₁ ≧ (Ia/Ib) ≧ r ₂ , it is medium distance.
When (Ia/Ib) < r ₂ , it is sufficient to use long distance. however,
When the imaging position of the light-emitting optical system and the light-receiving optical system is set to 5 m, there is a point where Ia/Ib becomes r ₁ and r ₂ when the distance L is 5 m or more, but the subject position at that time is 1.8 m or more.
Since it is quite far compared to 3.2m, the output Ib of SPD32 is very small from Ib∝L ^-2 . Therefore, in this case, when Ib becomes less than the set value, it is sufficient to set the distance to a long distance. Further, no matter how the light emitting/light receiving optical system is set, when the subject distance becomes a certain distance, the output of the SPD 31 and SPD 32 decreases or disappears, making it impossible to calculate Ia/Ib. Therefore,
It is necessary to monitor the output Ib of the SPD32 and recognize that it is a long distance when the output Ib falls below the set value. Figure 12 shows a graph corresponding to Figure 11 in the case of two-point zone focus, where the zone boundary distance is 2.05 m and the corresponding Ia/Ib
The principle is the same. Next, the imaging positions of the light emitting optical system and the light receiving optical system are
Considering the short distance side of the ranging range, for example, when the distance L = 1m, Ia, Ib are Ia∝R・L ^-2・g(L)+C (12) g(L): L≧1m Monotonically increases at Ib∝R・L ^-2・h(L) (13) h(L): Monotonically decreases when L≧1m. Therefore, Ia/Ib becomes (Ia/Ib)=R[g(L)/h(L)] (14), and Ia/Ib monotonically increases as the distance L moves away from 1 m. That is, the photovoltaic current I in the above equation (7) and the photovoltaic currents Ia and Ib in the above equations (12) and (13)
FIG. 2 is a characteristic diagram showing the change in photoelectromotive current versus subject distance expressed logarithmically in relation to subject distance L. 1st
Based on Figure 3, Ia/Ib imaged at distance L = 1m
In the example of Fig. 14, which is a three-point zone focus graph, when (Ia/Ib) < r ₁ , it is short distance, and when r ₁ ≦ (Ia/
Ib) ≦ r ₂ means medium distance, r ₂ < (Ia/Ib) or Ib ≒ 0
In this case, it is better to use long distance. Also, if the subject distance L is closer than 1 m, Ib
Since Ib becomes a considerably large value, an extremely short distance warning may be issued when Ib becomes larger than a certain set value. Although examples of three-point and two-point zone focuses have been shown so far, it is obvious that the number of zone focuses can be increased in the same way. Now, although the principle of distance measurement has been explained above, various adjustments are required in order to actually measure distance. Therefore, since the focus adjustment method of the light emitting optical system and the light receiving optical system has already been described, here we will explain the position adjustment on the plane perpendicular to the optical axis (superimposing the image of the IRD electrode 22 on the IRD chip 21 on the SPD 31). I will explain about it. As explained in FIGS. 3 to 5, the position adjustment in the present invention is performed by tilting the plane parallel plate 26, which is located perpendicular to the optical axis, and shifting the optical axis. The adjustment will be explained in detail with reference to FIG. Assuming that the thickness of the parallel plane plate 26 is t, the refractive index is n, and the angle between the perpendicular to the plane of the plate 26 and the optical axis is θ,
The optical axis deviation Δx at that time is expressed as Δx=t/CosΨSin(θ−Ψ) (15) where Ψ=Sin ⁻¹ Sinθ/n (16). On the other hand, the deviation of the focal point position in the optical axis direction Δf
is Δf=t(1-1/n) {Cos(θ-Ψ)/CosΨ-1
)}(17). For example, when t=1 mm, the relationship between θ, Δx, and Δf is as shown in Table 1, where Δf (focal position movement) is smaller than Δx (optical axis shift) by more than one digit.
Therefore, by tilting the parallel plane plate 26, the optical axis can be adjusted without changing the imaging state.

[Table] As described above, the automatic focus adjustment device of the present invention has no mechanically movable parts and does not select the base line length, so it is inexpensive and highly reliable, so it is suitable for use in cameras. It is valid.

[Brief explanation of the drawing]

Fig. 1 is an external view showing one embodiment of the basic configuration of the device of the present invention, Fig. 2 is a partial external view of another embodiment, Fig. 3 is a perspective view of the ranging block, and Fig. 4 is a A central horizontal sectional view corresponding to Figure 1, Figure 5 is a perspective view of the parallel plane plate block, Figure 6 is a detailed view of the IRD,
Figure 7 is a detailed view of the SPD, Figure 8 is an illustration of the position adjustment of the parallel plane plate, Figure 9 is an illustration of the distance measurement principle of the present invention, and Figure 10 is a focus set at the subject distance L = 5 m. Fig. 11 shows the photovoltaic current ratio of the two SPDs based on the change characteristic diagram in Fig. 10 for the case of three-point zone focus. Figure 12 is an explanatory diagram showing the ratio of photovoltaic currents of two SPDs in response to the case of two-point zone focus based on the change characteristic diagram of Figure 10.
The figure shows the change characteristics of SPD subject distance vs. photovoltaic current when focusing at subject distance L = 1 m, and Figure 14 shows the ratio of the photovoltaic currents of two SPDs based on the change characteristic diagram of Figure 13. FIG. 3 is an explanatory diagram showing the case of three-point zone focus. 1...Main body, 2...Aspherical lens for light emission, 3...
...Aspherical lens for light reception, 4...Finder objective lens, 5...Back cover, 20...IRD, 21...
IRD chip, 22... IRD electrode, 23... Parabola, 26... Parallel plane plate, 27... Holding frame, 2
8, 29...Screw, 31, 32...SPD, 33
...Printed circuit board, 34...Shield plate, 35...
...IR filter, 36...base plate, 37...screw,
91...Splitter.

Claims (1)

[Scope of Claims] 1. A light-emitting block having a light-emitting optical system, a light-emitting element, and a light-shielding member formed on the light-emitting element to block part of the light emitted from the light-emitting optical system, and a light-receiving optical system and functionally a plurality of light-receiving elements. a light-receiving block having: a subject distance at which an image of the light-blocking member is formed on the subject by the light-emitting optical system; and a subject distance at which the image of the light-blocking member is formed on the light-receiving element by the light-receiving optical system are approximately When the image of the light-shielding member is set to be equal and is formed on the subject by the light-emitting optical system and is again imaged on the light-receiving element by the light-receiving optical system, the image forming position is at least one What is claimed is: 1. An automatic focus adjustment device for a camera, which is set to substantially overlap a photosensitive area of a light-receiving element, and is configured to calculate a photovoltaic current of each light-receiving element to generate a distance measurement output. 2. A light-emitting block having a light-emitting optical system, a light-emitting element, and a light-shielding member formed on the light-emitting element and blocking a portion of the light emitted; a light-receiving block having a light-receiving optical system and functionally a plurality of light-receiving elements; The shape of the light-shielding member and the shape of the photosensitive area of at least one of the light-receiving elements are substantially similar, and the size ratio is such that the image of the light-shielding member is projected onto the subject by the light-emitting optical system. The image of the light-shielding member is set to be equal to the ratio of the subject distance imaged on the light receiving element and the subject distance imaged on the light receiving element by the light receiving optical system, and the image of the light shielding member is imaged on the subject by the light emitting optical system. When the image is again formed on the light-receiving element by the light-receiving optical system, the image-forming position is set to substantially overlap the photosensitive area of at least one light-receiving element, and the light of each light-receiving element is An automatic focus adjustment device for a camera, characterized in that it generates a distance measurement output by calculating an electromotive current.