JPS61137117A - Focus detecting device - Google Patents

Abstract

PURPOSE:To reduce malfunction against an object with large contrast difference and to perform focus detection wherein crosstalk effect is attained by arranging an optical member which compensates the convergence of incident light in front of two areas of a photodetector. CONSTITUTION:When pieces of reflected luminous flux a1-a4 of reflected light of a spot image from the object are incident on an optical member 12 at the right-hand side of its center line 24 and pieces b1-b4 are incident at the right- hand side, only the pieces of luminous flux a1-a3 are refracted by triangular grooves 25a-25c as shown in a figure and the pieces of luminous flux a1, a2, and a3 are incident on points B3, B2, and B1 in the area 21B respectively; and other pieces of luminous flux a4 and b1-b4 are incident on the areas 21A and 21B of the photodetecting element 21 because of a parallel plane glass part. A convergence state is varied according to the shape of the optical member installed in the front and only luminous flux incident on the boundary parts of the areas 21A and 21B which has certain width is weighted, distributed, and refracted to obtain the same function with such constitution that the areas 21A and 21B are entangled with each other, thereby attaining the crosstalk effect.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is a focus detection device, in particular, a focus detection device that projects infrared light onto a subject and receives the reflected light with a differential sensor to perform automatic focus adjustment. The present invention relates to a focus detection device used in an active automatic focus adjustment device. - <Prior art> This type of conventional automatic focus detection device (hereinafter referred to as rAF device)
) will be explained based on FIGS. 6 to 12.

FIG. 6 schematically shows the overall configuration of an example of the AF device, in which the lens group 1 involved in the focusing operation in the photographic lens
In conjunction with the movement of 2 areas 8A through filter 7
, 8B divided into PIN photodiodes or charge-coupled devices, etc., and at this time, the light receiving element 8 also moves in conjunction with the movement of the lens group 1, and its output signal is used. The automatic focus detection circuit (hereinafter referred to as "AF circuit") 10 detects the distance to the subject 5, controls the driving of the focusing lens group driving motor 9, and sets the lens group 1 to the focusing position. Then, a photographic lens system including a lens group 1 forms a sharp object image on an imaging plane 2 of an imaging tube (an imaging plane of a solid-state image sensor or a film depending on the camera).

Note that in the case of this AF device, the light receiving element 8 is arranged such that the region 8A is on the side closer to the light projecting element 3, and the region 8B is also on the far side.

Therefore, regarding the distance measurement function of the AF device shown in Fig. 6,
When the subject 5 is at a distance of 12 from the image plane 2, the reflected light of the projected spot image S is reflected by the light receiving element 8'' as shown in FIG. Suppose that the light is received at In this case, in the light receiving element 8, the difference -vB between the integral value VA obtained by integrating the output from the region 8A over time and the integral value VB obtained by integrating the output from the region 8B over time becomes approximately zero. In terms of optical path,
The light emitted from the light emitting element 3 passes through the optical path b2, hits the subject 5, is diffusely reflected, and further passes through the optical path b2, forming an image on the light emitting element 8'-. Therefore, if it is assumed that the lens group 1 is at the focus position at this time and the subject 5 moves forward to a distance of 11, the focus position of the lens group 1 will naturally shift to the rear, resulting in a rear bin state. On the other hand, if the light projecting element 3 and the light receiving element 8 are at the intersection, the light path hits the subject 5 and is diffusely reflected, passing through the light path b2' and forming an image on the light receiving element 8. , as shown in FIG. 7(b), the imaging position is shifted toward the dog listening area 8B, and the VA-
VB does not become zero.

On the other hand, the AF circuit 10 rotates the motor 9 forward or reverse according to the sign of the signal ①A-VB to retract or extend the lens group 1. When vA-vB is negative as described above, lens group 1 is extended. In Figure 6, lens group 1
It is assumed that when the object 5 is extended to a position 1', an image of the subject 5, which has moved a distance 11, is sharply formed on the imaging plane 2. At this time, a cam or the like (not shown) moves the light emitting element 3. The light receiving element 8 moves in conjunction with the lens group 1 to positions 3' and 8', respectively. Then, the projected optical path is aI + the reflected optical path is C
2, and as a result, as shown in FIG.
At this time, VA-VB becomes almost zero, and the motor 9 stops. On the other hand, when the subject 5 moves to the position 63, the lens group 1 and the like move in the opposite direction to the above, and perform a focusing operation so that the angle becomes ①A-VB20.

In this case, the projection optical path is indicated by CI and the reflected optical path is indicated by C2.

8 to 11 show other conventional AF devices that perform distance measurement based on the same principle as the device shown in FIG. 6, and are different from the device shown in FIG.

The shape of the light receiving system is different. However, the same parts as in the apparatus shown in FIG. 6 are given the same reference numerals.

The apparatus shown in FIG. 8 projects a light spot from a light projecting element 3 through a projecting lens 4 and a prism 11 having a reflective surface 11a consisting of a cold mirror disposed in the photographing optical path. It is a so-called half-TTL distance measuring type in which the reflected light is transmitted through the group 1 onto the subject 5, and the reflected light is received by the light receiving element 8 provided outside the camera through the light receiving lens 6 and the visible light cant filter 7. is the imaging plane 2
It is placed at a position conjugate to the photoluminescence. The movement of the focusing lens group 1 is mechanically interlocked with the light receiving element 8 to move the AF circuit 1.
This is done by a motor 9 controlled by 0.

The reflected light passes through the focusing lens group 1 through the reflecting surface 11a of the prism 11 onto the subject 5, and the reflected light is transmitted again through the focusing lens group 1 and the reflecting surface 11b of the prism 11 to the light receiving lens 6 and the visible light. It is a so-called TTL ranging type in which light is received by a light receiving element 8 through a light cut filter 7, and both the light emitting element 3 and the light receiving element 8 are arranged at a position optically conjugate with the imaging plane 2, and each projection The light beam and the received light beam are configured to pass through positions near the outer periphery of the pupil of the lens group 1 and separated from each other.

Note that the light projecting element 3 and the light receiving element 8 are fixedly installed, and there is no need for mechanical interlocking with the photographic lens.

The device shown in FIG. 10 is a modification of the device shown in FIG. 9, and the reflecting surface of the prism 11 is
The device is the same as the device shown in FIG. 9 except that 1a is formed.

The device shown in FIG. 11 uses the same device as the device shown in FIG. 9 for the light projection system, and uses an image sensor 14 provided on the focal plane as a light receiving element for focus adjustment and imaging. The image signal received by the image sensor 14 is sent to the distribution circuit 1.
2 into an AF circuit 10 and an imaging circuit 13.

FIG. 12 shows the photosensitive surface of the image sensor 14 in the apparatus shown in FIG. However, it is necessary to pass infrared light onto the image sensor 14 during distance measurement and remove the infrared light during imaging.

<Problems to be Solved by the Invention> By the way, among the conventional examples described above, the type shown in FIG. 6 has a projection lens 4. Since the light-receiving lens 6 is located outside the photographing lens group 1, the light-emitting lens 4. It is possible to increase the size of the light receiving lens 6, which is advantageous in terms of reach distance, but
On the other hand, it has the disadvantage that the whole structure is not compact. On the other hand, the type shown in FIG. 9 has advantages and disadvantages opposite to those of the type shown in FIG. Also, the photographic lens group 1 and the thrower.

It also has the advantage of a simple structure because it does not require precise mechanical interlocking with the light receiving system, and the type shown in Fig. 8 is intermediate between the type shown in Fig. 6 and the type shown in Fig. 9. have a property.

The type shown in Figure 10 is more effective in throwing, compared to the type in Figure 9.
The baseline length of the light receiving system is shortened, which is disadvantageous in terms of distance measurement accuracy, but
Along with the type shown in FIG. 8, this has the advantage that the projected light beam remains at the center of the finder even when out of focus. Incidentally, in all of the above-mentioned types, the light spot image formed on the subject 5 by the light projecting element 3 is formed on the optical axis of the photographing lens when in focus. That is, in each of the above devices, the distance measurement zone is located at the center of the finder, and the AF devices are parallax-free.

Furthermore, in the device shown in FIG. 11, the light-receiving area of the image sensor 14 as the AF light-receiving element is equal to the light-receiving area of the photographic lens, so the light-receiving area is much larger than that of other types of devices. This is advantageous in terms of reach distance. In addition, in the device shown in FIG. 11, the signal from the image sensor 14 is distributed to the AF circuit 10 and the image pickup circuit 13, but since it is practical to distribute this in a time-sharing manner, this type of device is not suitable for photographing. This is suitable for systems such as methyl video cameras that complete distance measurement in advance. However, because the conventional device was configured as described above, it could focus correctly on a subject with uniform reflectance for infrared light, but it would have a distance measurement error ( This method had the disadvantage of causing "contrast blur" (hereinafter referred to as "contrast blur").

Here, this contrast blur will be explained based on FIGS. 13 and 14.

In FIG. 13(a), S is an infrared spot image on the light receiving element 8, and its radius is set to 1.

The left side hatched part of the spot image S is the part reflected from the subject with infrared reflectance l, and the right part is the part reflected from the subject with infrared reflectance k (k is 1 to 1).
It shall take a value between ~. ) is the part reflected from the subject. -1, Figure 13 (a), (b)
The horizontal axis l indicates the position of the reflectance boundary with the geometric center 0 of the spot image S as the origin. In state (a),
G is the center of the signal intensity of the spot image S, and the signals on the left side and the signals on the right side of G are balanced. O.G.
The relationship diagram in (b) shows E with the reflectance boundary position as the horizontal axis, and here shows the case of =8. In other words, when the reflectance boundary position l is approximately (16), OG or E takes the maximum value of approximately 07.Of course, when l knee 1 or l-1, the spot is projected onto an object with uniform reflectance. It is E-0.

E is an amount corresponding to contrast blur, which will be further explained with reference to FIG. 14.

FIG. 14(a) corresponds to FIG. 4, in which the light receiving element 8 of an infrared spot projected onto a subject with uniform reflectance.
The image S on the surface is (1) → (U) → (III) and the light receiving element 8
When the top is moved relatively from area 8A to area 8B, the 14th
This is represented by the characteristic diagram shown by the solid line in Figure (b). That is,
The geometric center 0 of the spot image S is the area 8A of the light receiving element 8
, 8B, the AF multiplied signal becomes zero, which tends to cause contrast blurring.

Next, as shown in FIG. 14(a), l:0.6. ni = 8
The spot image S consisting of the contrast pattern is (I)
→ (■) → (III) When the AF multiplied signal is plotted when relative movement is made on the light receiving element, it is expressed as a broken line in FIG. 14(b), and the zero cross position is shifted by ΔX. The spot image S at this zero crossing is shown in Figure 14 (a
), and the signal intensity center G is on the boundary line between regions 8A and 8B of the light receiving element 8. Therefore,
E in FIG. 13 corresponds to ΔX in FIG. 14(b), and the AF multiplied signal becomes zero at a position where the spot image S is shifted by ΔX on the light receiving element.

Determine the base line length of the triangulation distance measurement, and set the focal length of the light receiving lens to f8.
When the focal length of the photographic lens is f and the amount of defocus on the focal plane is Δb, contrast blurring is produced in proportion to ΔX.

When the contrast ratio k becomes extremely high, the maximum value in FIG. 13(b) moves to the upper right, and ΔX in FIG.
The contrast bokeh also looks like a dog.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the conventional example described above and to provide a focus detection device with less contrast blur for objects having different reflectances.

A last resort to solve the problem The present invention will be explained based on the drawings.

First, the meaning of the crosstalk zone C, which is provided by centering the boundary between the two areas A and B of the light receiving element, which is the basic principle of the present invention, will be explained with reference to FIG.

FIGS. 5(a) and 5(b) show the 14th case in the conventional example.
Figure (a).

It is a figure corresponding to (b). In FIG. 5(a), the width of the crosstalk zone C is defined as U, and the ratio of the diameter of the pot image S to the diameter of the spot on the light receiving element is defined as J.

−ri In FIG. 5(c), the light shines on two areas A and B of the light receiving element.

The characteristic of the solid line α is that when the bright spot is within the crosstalk zone C, the signal from the bright spot is distributed equally to area A and area B.
This is a case where the amount is distributed in increments of 0%.

When illustrated, it becomes as shown in FIG. 5(b). However, j
-05.

In FIG. 5(b), the solid line is for a spot image with uniform contrast, and the broken line ■ is the same as in FIG. 14(b).
In the case of a spot image consisting of a contrast pattern with an output of 0.6 and a contrast pattern of 8, because there is a crosstalk zone, ΔX in this case is about half of that when there is no crosstalk zone. If the absolute value of the X coordinate at which j starts to thicken is large, then j=1. That is, A.F.
sensitivity decreases.

ε in FIG. 5(b) indicates the permissible dead zone of the AF system, and at least the slope of the zero cross must be approximately equal to that in the case where there is no crosstalk zone within the range of ε. That is, there is a maximum allowable value of j.

= 12 - Next, as k becomes larger, the characteristics will become as shown by the broken line ■ in Figure 5 (bl).Therefore, if the dead zone ε is zero, there will be no problem, but if the stability at the focused point is to be ensured, ε has a predetermined size, and in this case, when the spot image moves from one side of X, a larger AF error will occur than in the case where there is no crosstalk zone.
This effect is called the "expansion effect." ) Since this error increases as j increases, there is also a maximum value of j from this perspective.

Next, there is also a concept of changing the pattern for allocating signals to areas A and B of the light receiving element within the crosstalk zone.

The broken line β in FIG. 5(c) is when VA=V
B = 100 (%): 0 (%), when X20, VA:
vB = 50 (%): 50 (%) Toshi, x = T t7
), when vA:vB=.

(%): Averaged to 100 (%). That is, α is a uniform crosstalk type, and β is a constant crosstalk change rate type. The broken line γ shows the case where the crosstalk change rate is further changed. By changing the crosstalk characteristics in the β and γ directions in this way, it is possible to reduce the distance measurement error when k is large. However, in this case, the degree of improvement in ΔX relative to a normal contrast ratio of about k=8 is also slightly reduced, so it is necessary to make 3 thicker to compensate for this.

Therefore, the crosstalk pattern (types of α, β, γ, etc.) must be determined in consideration of the dead zone ε and k at which the enlargement effect occurs (hereinafter referred to as k).

For example, ε20.15. Assuming that the distribution is 50, in the case of the crosstalk pattern α, it becomes J-05, and in the case of the cross-talk pattern β, it becomes J-07.

Therefore, the present invention will be explained with reference to FIGS. 1 to 4.Based on the above-mentioned principles, in order to achieve the above object, a light spot is projected onto the subject from a light projecting element, and the reflected light is divided into two In a focus detection device that receives light with a light receiving element 21 consisting of a region and determines that the focus is in focus when the output signals from the two regions 21A and 21B of the light receiving element 21 become approximately equal, A flat glass optical member 23 having a light-receiving area equal to or larger than that of the light-receiving element 21 is installed in front of the light-receiving element 21, and the areas 21A and 21 are formed on the surface of the optical member 23.
The line 2 is formed into a sawtooth-shaped part whose center line is the line 24 corresponding to the boundary line 22 of B, that is, a triangular part 25 and 26 whose bases are the lines 24 formed alternately across the line 24.
A plurality of small triangular grooves 25a whose cross section is perpendicular to 4.
, 25b, 25c and 26a, 26b,
26c, and correct the incident state of only the incident light incident on the boundary line 22 of the areas 21A and 21B of the light receiving element 21.

For Kusaku Next, its operation will be explained with reference to FIGS. 3 and 4.

3 is an enlarged sectional view taken along the line II in FIG. 1, and FIG. 4 is an enlarged sectional view taken along the line ■-■ in FIG.

In FIG. 1, among the reflected light of the spot image from the subject on both sides of the center line 240 of the optical member 23, on the left side there are reflected light beams a, + a2 + a3 + a4, and on the right side there are reflected light beams a, b2. b3. When the light beam b4 enters the optical member 23, the light beam a1.
a2. Only a3 has a triangular groove 25a in its triangular portion 25,
25b.

25c as shown in the figure, and the luminous flux a1 is similarly refracted at 33 points on the area 21B of the light receiving element 21.
2 is incident on the point B2, and the light beam a3 is incident on the point B1, and the other light beams a4, s, and b4 are incident on the parallel plane glass portion, and are incident as they are on the regions 21A and 21B of the light receiving element 21, respectively. become. Therefore, among the luminous fluxes a1 to a4, the luminous flux a that enters the triangular part 25,
~a, only is refracted and incident on the region 21B of the light receiving element 21.

On the other hand, in the part shown in FIG. 4, the luminous flux bl + b2 r
b3 Luminous flux out of rb4, b2. Only b3 is the triangular grooves 26a, 26b, 26 of the triangular portion 26.
c as shown in the figure, and the light beam b1 is refracted at point A3 on the area 21A of the light receiving element 21, and the light beam b2 is similarly refracted by the light beam b2.
is at point A2, and the luminous flux b3 is at point A.

The other luminous fluxes b4 and a1~
a4 is the area 21 of the light receiving element 21 as in FIG.
The light will be incident on B and 21A, respectively.

Therefore, out of the luminous flux ~b4, the triangular part 26
Only the incident light beam S, -b, is refracted and passes through the light receiving element 2.
The light is incident on the area 21A of No. 1.

As described above, even if the boundaries between the areas 21A and 21B of the light receiving element 21 are straight, the light condensing state of the optical member 23 placed in front of the area can be changed depending on the shape of the optical member 23, so that the areas 21A and 21B have a certain width. Only the light flux incident on the boundary portion having 21 is weighted and refracted, and as a result, it is possible to have the same function as a configuration in which the boundary lines of the areas 21A and 21B of the light receiving element 21 are made to intersect with each other,
A crosstalk effect can be achieved.

<Effects of the Invention> As explained above, the present invention reduces malfunctions for subjects with large contrast differences by arranging optical members in front of the three areas of the light receiving element to compensate for the convergence of the incident light. It has the effect of being able to be used as a focus detection device.

[Brief explanation of drawings]

1 and 2 are main part configuration diagrams of the focus detection device according to the present invention, and FIGS. 3 and 4 are operation explanatory diagrams taken along the I-I line and ■-■ line cross section in FIG. 1, respectively. Figure 5 (a) (b
) (c) is an explanatory diagram of the principle of crosstalk effect,
6 to 12 are schematic configuration diagrams of various conventional focus detection devices, and FIGS. 13(a), (b), and 14(a).
(b) is an explanatory diagram of the operation of the light receiving section of the conventional example. 21... Light receiving element, 21A, 2B - Divided area, 22... Boundary line, 23... Optical member, 24
Center line, 25.26-Triangle part, 25a, 2
5b, 25c. 26a, 26b, 26c - triangular grooves. =19--r 1--area ku■, O procedural amendment March 7, 1986

Claims (1)

[Claims] 1. A light spot is projected onto the subject from a light projecting element, and the reflected light is received by two adjacent light receiving elements each consisting of at least one pixel, and when the output signals of the two light receiving elements become approximately equal, the in-focus state is established. In a focus detection device that determines that A focus detection device characterized by changing a condensing state.