JPH01133015A - Focus detector and its production - Google Patents

Abstract

PURPOSE:To improve the accuracy of focus detection by disposing a filter having such a density distribution as to negate the nonuniformity in the light quantity distribution in the diametral direction centering at the optical axis, which nonuniformity is generated in an optical system of a pupil splitting system, on the optical axis forward of the intersected point excluding a conjugate position. CONSTITUTION:The filter 7 which has the density changing gradually in accordance with the distances from the optical axis X and in which the change of the density changes symmetrically with the optical axis is disposed on the optical axis X except the conjugate position R of the apertures of imaging lens 4a, 4b nearer on a subject side than the point S where the split luminous fluxes 6a, 6b respectively split from the luminous flux from the subject in the different parts of the pupil of a photographing lens 1 and passed through said parts intersect with the optical axis X. The nonuniform light quantity distribution generated by the optical system is thereby approximately uniformly corrected. The light quantity of the image on a photodetecting element array is, therefore, uniformized with inexpensive and simple constitution. The accuracy of the focus detection is thereby improved.

Description

Detailed Description of the Invention (a) Technical Field The present invention relates to a focus detection device and a method for manufacturing the same, and more specifically, the present invention relates to a focus detection device and a method for manufacturing the same. A condenser lens is placed on the same axis, two imaging lenses are placed at symmetrical positions with respect to the optical axis, and a photodetector array is placed at a position where the two images re-formed by the imaging lenses can be electrically detected. The present invention relates to a focus detection device for a camera that detects the focus of the photographing lens by comparing the two images, and a method for manufacturing the same.

(b) Prior Art In the past, various methods have been proposed as means for detecting the focus of a camera, one of which is a method called a pupil division method.

FIG. 11 shows the configuration of an optical system of a focus detection device using this pupil division method.

In FIG. 11, 50 is an optical axis, 51 is a photographic lens disposed on this optical axis, 52 is an imaging plane of this photographic lens,
53 is a condenser lens; 54 is an imaging lens section consisting of two imaging lenses 54a and 54b arranged symmetrically about the optical axis 50; 55 is a light receiving section consisting of a row of light receiving elements 55a and 55b; and 54b. Furthermore, this optical system is
It is configured symmetrically with respect to the optical axis 50. Further, the left side of the photographing lens 51 in the figure is the subject side. condenser lens 5
3, the imaging lens 54 simultaneously changes the direction of the incident light.
conjugate point (conjugate position 1) R of each aperture of a, 54b
It plays a major role in pupil division by creating the image on the photographing lens 51 side. That is, the three points ALL, BL1, and CLI on the imaging plane 52 of the photographing lens 51 are changed to the three points AL2, BL1, and CLI on the light receiving element array 55a by the imaging lens 54a. BL2 and CL
2 to form an imaging relationship. In addition, points AUI, BU1, and CUI are the same points as the above three points ALL, BLI, and CLI, but due to the imaging lens 54b, the light receiving element array 55b
Upper point AU2. An imaging relationship is formed between BU2 and CO2. Also, the aperture PL2 of the imaging lens. QL2 and PU2
．． QU2 has PLI, QLI, PUI, and QUI on the photographing lens 51 side through the condenser lens 53.
form an imaging relationship.

Now, as described above, since the optical system is symmetrical with respect to the optical axis 50, the light amount distribution on the light receiving section 55 is not uniform as shown in FIGS. 12 and 13. In other words, on the light receiving element array 55a side, the point CL in the periphery far from the optical axis 50
2 decreases, and on the light-receiving element array 55b side, the light amount at the peripheral point AU2 also decreases, and points AL2 and AU2, points BL2 and BU2, and point CL, which should theoretically have the same light amount, decrease.
2 and CO2 have different amounts of light, which causes a significant deterioration in distance measurement accuracy.

Conventionally, in order to solve this problem, for example, one divided light beam 56 was used.
The opening angle between a and 56b is narrowed, that is, the points ALL and BL
There is a proposal to reduce the influence of uneven light intensity distribution in the diametrical direction centered on the optical axis 50 by configuring an optical system such that the distance between the points CLI and BLl is narrower, and the distance between the points CLI and BLl is narrower. When configured in this way, a new problem arises in terms of space constraints.

Furthermore, as shown in Japanese Patent Application Laid-open No. 62-115407, for example, there is a device that electrically processes the output from a photoelectric conversion element array that is a light receiving section to correct the above-mentioned non-uniformity.
This had the disadvantage of causing a significant increase in cost.

(C) Purpose The present invention was made in view of the above-mentioned circumstances, and its purpose is to equalize the light amount of the image on the light receiving element array and improve the accuracy of focus detection with a simple and inexpensive structure. An object of the present invention is to provide an improved focus detection device and a method for manufacturing the same.

(d) Structure In order to achieve the above-mentioned object, the present invention includes a condenser lens arranged coaxially with the optical axis of the photographic lens, behind the focal plane of the photographic lens, in order from the photographic lens side, and symmetrical to the optical axis. Two imaging lenses are placed at the same positions, and a light receiving element array is placed at a position where the two images re-formed by the imaging lenses can be electrically detected, respectively, and the two images are compared with each other. In the focus detection device for a camera that detects the focus of the photographic lens, a first invention (the invention set forth in claim 1) is characterized in that the light flux from the subject is divided into different parts of the pupil of the photographic lens. On the optical axis excluding the conjugate position of the aperture of the imaging lens on the object side from the point where the divided light flux passing through the optical axis intersects with the optical axis, the density thereof gradually changes in accordance with the distance from this taper. However, the present invention is characterized in that a filter is disposed in which the density changes symmetrically with respect to the optical axis, so that the uneven light amount distribution caused by the optical system is corrected to be substantially uniform. A second invention (the invention set forth in claim 2) is characterized in that on the optical axis between the imaging lens and the light-receiving element array, the concentration is adjusted according to the distance from the optical axis. It is characterized by a structure in which a filter whose density changes gradually and whose density changes symmetrically with respect to the optical axis is arranged so that uneven light intensity distribution caused by the optical system is corrected to be substantially uniform. The third invention (the invention described in claim 3) is
Behind the focal plane of the photographic lens, in order from the photographic lens side,
a condenser lens coaxially with the optical axis of the photographing lens, two imaging lenses at positions symmetrical to the optical axis, and positions where the two images re-formed by the imaging lenses can be electrically detected. In the method for manufacturing a focus detection device for a camera, the imaging lens and the light receiving element array on the optical axis are arranged on the optical axis, and the imaging lens and the light receiving element array are arranged on the optical axis, respectively, and the focus of the photographing lens is detected by comparing the two images with each other. A negative film is placed at a predetermined position between the photographic lens, a light beam from a predetermined light source placed in front of the photographic lens is made to enter the photographic lens, and the device is adjusted to a focused state, and the light beam is brought into the By exposing a negative film to light and developing the exposed negative film, the degree changes gradually in accordance with the distance from the optical axis, and this change in density is symmetrical with respect to the optical axis. The present invention is characterized in that a filter that changes in shape is manufactured and this filter is disposed at the predetermined position.

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

1 and 2 are side views showing the configurations of a first embodiment and a second embodiment of a focus detection device according to the first invention, respectively. Incidentally, the only difference between FIG. 1 and FIG. 2 is that the positions of the filters are different, so the same numbers are given to everything other than the filters.

1 and 2, 1 is a photographing lens, 2 is an image plane of the photographic lens 1 formed behind the photographic lens 1, and 3 is the image forming surface of the photographic lens 1 on the optical axis X. A condenser lens 4 disposed behind the image plane 2 is disposed symmetrically with respect to the optical axis .

4b is an imaging lens section, and 5 is a light receiving section consisting of a pair of light receiving element arrays 5a and 5b disposed at a position where the pair of re-imaged images can be electrically detected. It is configured to perform focus detection by comparing the electrical outputs corresponding to each other.

Note that all of the above optical systems are configured symmetrically with respect to the optical axis X (hereinafter, this will be referred to as "optical axis symmetry"). Although not shown, it is assumed that there is a subject in front of the photographic lens 1 (to the left in the figure).

Reference numeral 6 indicates the above-mentioned split light flux 6a and 6b, etc., in which the light flux from the subject is divided at different pupil portions of the photographing lens 1 and passes through them, and S indicates that the divided light flux 6 is on the optical axis The intersecting points 7 and 8 are both filters disposed perpendicular to the optical axis On the contrary, the filter 8 of the first embodiment is configured such that the density gradually decreases as the light increases, and this decrease is distributed symmetrically about the optical axis. The filter of the second embodiment is configured such that the density gradually increases as the distance from the axis X increases, and this gradual increase is distributed symmetrically with respect to the optical axis X. Further, in the above optical system, the photographing lens 1
The three points ALL, BLI and CLI on the imaging plane of
2 and CL2, and the points AUI, BUI, and CUI are configured to have an imaging relationship with the above three points ALL,
Point AU2. which is the same point as BLI and CLI, but on the light receiving element array 5b by the imaging lens 4b. BU2 and Cu2
The imaging lens unit 4 is configured to have an imaging relationship with each aperture PL2 . QL2 and PU2. QU
2 is configured to have an imaging relationship of PLI, QLI, PUl, and QUI on the photographing lens 1 side by a condenser lens 3, respectively.

1 and 2 excluding filters 7 and 8.
It is assumed that the optical system shown in the figure has a characteristic that, like the optical system shown in FIG. 11, the light quantity distribution is non-uniform in the diametrical direction centered on the optical axis X on the light receiving section 5.

3 and 4 are graphs showing the light amount distribution on the light receiving section S of the above embodiment, FIG. 3 is the light amount distribution on the light receiving element row 5a, and FIG. 4 is the light amount distribution on the light receiving element row 5b. It shows. In FIGS. 3 and 4, the horizontal axis represents the position on the light receiving section 5, and the vertical axis represents the amount of light. Note that DS indicates the distance from the optical axis (in this figure, the direction away from the optical axis).

5 and 6 are graphs showing the concentration distribution of the filter 7 of the first embodiment and the filter 8 of the second embodiment, respectively. In the figure, the horizontal axis shows the distance MDS from the optical axis with O as the position of the optical axis X, and the vertical axis shows the density.

FIG. 7 is a side view showing the configuration of an embodiment (hereinafter referred to as a third embodiment) of a focus detection device according to the second invention. Note that the same parts as in FIGS. 1 and 2 are given the same reference numerals and redundant explanations will be omitted.

In FIG. 7, reference numeral 9 denotes a filter made of developed negative film and disposed just before the light receiving section 5. As shown in FIG.

FIGS. 8 and 9 are graphs showing the light amount distribution in which the position on the light receiving section 5 and the light amount thereof are plotted on the horizontal and vertical axes, respectively, in the third embodiment shown in FIG. 7. Note that DS indicates the distance from the optical axis X (in this figure, the direction away from the optical axis).

Figure 10 shows the distance DS from the optical axis, assuming the position of the optical axis is 0.
7 is a graph showing a concentration distribution, with the horizontal axis representing the concentration of the filter 9 of the third embodiment shown in FIG. 7 and the vertical axis representing the concentration of the filter 9 of the third embodiment shown in FIG.

Next, the operation of this embodiment configured as described above will be explained. First, in the first embodiment, the arrangement position of the filter is behind the photographing lens 1 as described above, but more specifically, the aperture P of each of the imaging lenses 4a and 4b is
L2. QL2 and PU2. Since it is behind the conjugate position R of QU2 and in front of the intersection S where the divided light beams 6a and 6b do not overlap with each other, the filter 7 fully exhibits its effect. Incidentally, when the filter 7 is disposed at the conjugate position R, the aperture PL2. QL2 and PU2. Although the light amount distribution on QU2 can be changed, the light amount distribution on light receiving section 5 cannot be changed.

Now, as shown in FIG. 5, the concentration of the filter in the first embodiment is highest at position 0 of the optical axis Therefore, the filter 7 splits the divided light beam 6 with respect to the light receiving element array 5a.
Among b, the light quantity of the light flux L2 passing through the point AL1 is relatively reduced compared to the light flux L1 passing through the point CLI on the imaging plane 2. On the other hand, in the optical system without the filter 7, since the light amount at the point CL2 on the light receiving element 5a is smaller (decreased) than the light amount at the point AL2, the light amount at the point AL2 is relatively 3, as shown in Figure 3.
Point CL2. BL2. The light amount of AL2 is made approximately uniform. still,
The same concept holds true for the divided luminous flux 6a, and as shown in FIG. 4, each point CU2 . BU2.
The light amount of the AU2 is also made substantially uniform by the filter 7. Although it is desirable that the uniformized (corrected) light amount distribution be a straight line, the graph will be a slight curve as shown in FIGS. 3 and 4. However, since focus detection is performed by comparing two images on the light receiving section 5, if their characteristics are the same as shown in Figures 3 and 4, there will be no negative impact on the detection accuracy. do not have.

Next, in the second embodiment shown in FIG. 2, the filter 8 is disposed in front of the photographic lens 1, more specifically, in front of the conjugate position R, so that the filter 8 can fully exhibit its effect. . Then, the light beams L1 and L2 switch inside and outside with the conjugate position [R as the boundary. In other words, from the conjugate position R to the intersection S
Until then, the light beam L1 is on the outside with respect to the optical axis X than L2, and at the conjugate position [in front of the IR (on the subject side), the light beam L2 is on the outside with respect to the optical axis X than L1.

Therefore, as shown in FIG. 6, the filter 8 has a density distribution such that the density is the lowest (lightest) at position 0 of the optical axis
As a result, the light quantity of the light beam L2 is reduced (decreased), so that the light quantity distribution on the light-receiving element array 5a is made substantially uniform as in the first embodiment, that is, as shown in FIG. 3. In addition, the light receiving element array 5
A similar concept holds true for the light amount distribution on b, and the light amount distribution is made approximately uniform as shown in FIG.

Next, before describing the operation of the third embodiment, a method for manufacturing a focus detection device according to the third invention (hereinafter referred to as the fourth embodiment) will be explained.

First, a white light source is placed in front of the photographing lens 1 (on the subject side) in FIG. 7, and a white signal is made to enter the optical system. Then, a negative film whose γ characteristic is optimally selected is placed at the planned position where the filter 9 will be placed, and the negative film is exposed after the optical system is adjusted to a focused state. Since the optical system has a characteristic that the amount of light decreases as it moves away from the optical axis
And the exposure amount of the part corresponding to AU2 is small, and the point AL
2 and Cu2 have the highest exposure amount. Therefore, when the negative film exposed in this manner is developed, the areas corresponding to the points CL2 and AU2 become the darkest (black), and the areas corresponding to the points AL2 and Cu2 become the brightest (white). In other words, as shown in FIG. 10, the developed negative film has a density distribution that cancels out and corrects (uniforms) the uneven light amount distribution of the optical system. Therefore, by disposing the developed negative film as the filter 9 at the predetermined position, the focus detection device of the third embodiment can be manufactured.

Next, the operation of the third embodiment shown in FIG. 7 will be briefly explained. The idea is the same as in the first and second embodiments described above, and the filter 9 having the density distribution shown in FIG. 10 cancels out the uneven light amount distribution of the optical system and makes it uniform. As shown in FIG. 9, the light quantity distribution in the diametrical direction centered on the optical axis X on the light receiving section 5 is made uniform. The difference between FIG. 3 and FIG. 4 is that the graph is a straight line. In other words, since the filter 9 is fabricated by directly utilizing the non-uniform light intensity distribution characteristics of the optical system, the accuracy of uniformization (correction) is increased.

As described above, according to this embodiment, the non-uniformity of the light quantity distribution in the diametrical direction centered on the optical axis In the embodiment and the second embodiment, filters 7 and 8 having density distributions that cancel out the above-mentioned non-uniformity are disposed on the optical axis in front of the intersection S excluding the conjugate position R. There is an advantage that the light amount distribution on the lens 5 is made substantially uniform, and the accuracy of focus detection can be improved.

In addition, as a manufacturing method of the fourth embodiment, the non-uniform light intensity distribution on the light receiving part 5 (strictly speaking, the scheduled position immediately before it) of the optical system having the above-mentioned non-uniform light intensity distribution is directly exposed to a negative film. Since the filter 9 was fabricated using the above-mentioned method and arranged in the above-mentioned predetermined position to have the same configuration as in the third embodiment, there is an advantage that the filter 9 can be fabricated extremely easily, and furthermore, the light intensity distribution characteristics of the optical system can be improved. This has the advantage of being able to correct (uniform) with higher precision.

Note that the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the spirit of the invention.

For example, in the first invention, the filters 7 and 8 are not limited to being composed of members independent of the photographic lens 1, but may be formed as thin films having a predetermined concentration distribution on the lens surface of the photographic lens 1. Further, the photographing lens 1 may be constructed using a material that has a density distribution itself, and may also serve as the filter 7.8.

Each of the filters in the first to third embodiments may be configured to be movable between a predetermined optical path and outside the optical path, and may be configured to be retracted outside the optical path during photographing.

(e) Effects As detailed above, condenser lenses are arranged on the optical axis in order behind the focal plane of the photographic lens, and two imaging lenses and two light receiving element arrays are arranged symmetrically about the optical axis. established,
According to the first aspect of the invention, in a focus detection device using an optical system having a non-uniform light quantity distribution in the diametrical direction centered on the optical axis, the focus detection device uses a focus detection device that uses an optical system having a non-uniform light quantity distribution in a diametrical direction centered on the optical axis. A filter whose density gradually changes in accordance with the distance is arranged on the optical axis except for a conjugate position of the aperture of the imaging lens, which is closer to the object than the point where the divided light beam intersects with the optical axis. Therefore, the first effect is that the light intensity of the image on the light receiving element array can be made uniform with a simple and inexpensive configuration, and therefore, the accuracy of focus detection can be improved, and the second invention According to the above, at a predetermined position on the optical axis between the imaging lens and the light-receiving element array, the density thereof gradually changes in accordance with the distance from the optical axis so as to cancel out the uneven light intensity distribution. According to the third aspect of the present invention, the imaging lens and the light receiving element on the optical axis are arranged so that the same effect as the first effect can be achieved. A negative film is placed at a predetermined position between the photographic lens and the photographic lens, and a beam of light from a predetermined light source placed in front of the photographing lens is made to enter the optical system, and the optical system is brought into focus, and then the negative film is placed. Since the focus detection device is manufactured by exposing and developing the film and disposing it as a filter at the predetermined position, the second effect is that the uniformity can be made more suitable for the optical system. It is possible to provide a focus detection device capable of more accurate focus detection than the first effect, and as a third effect, the focus detection device according to the second invention can be manufactured easily and at low cost. can do.

[Brief explanation of the drawing]

1 and 2 are side views showing the configurations of optical systems of a first embodiment and a second embodiment of the focus detection device according to the first invention, respectively, and FIGS. 3 and 4 are respectively A graph showing the light amount distribution on the light receiving element row 5a and the light receiving element row 5b of the first example and the second example, respectively;
5 and 6 are graphs showing the density distribution of the filter of the first embodiment and the filter of the second embodiment, respectively, and FIG. 7 is an embodiment of the focus detection device according to the second invention. A side view showing the configuration of the optical system of (third example),
8 and 9 are graphs showing the light intensity distribution on the light receiving element rows 5a and 5b of the third embodiment shown in FIG. 7, respectively, and FIG. 10 is a υ3 degree distribution of the filter of the third embodiment, respectively. 11 is a side view showing a conventional pupil division optical system, and FIGS. 12 and 13 are graphs showing light receiving element rows 55a and 55 of the conventional example shown in FIG. 11, respectively.
It is a graph which shows the light quantity distribution on b. 1... Photography lens, 2...
Image plane. 3...Condenser lens, 4...Imaging lens section. 4a, 4b...imaging lenses. 5... Light receiving section, 5a, 5b... Light receiving element array, 6.6a, 6
b...Divided light flux, 7.8.9...Filter, Ll, L2...Light flux, X...Optical axis, S...Intersection , R...
- Conjugate position.

Claims (3)

[Claims] (1) At the back of the focal plane of the photographic lens, in order from the photographic lens side, place a condenser lens coaxially with the optical axis of the photographic lens,
Two imaging lenses are disposed at positions symmetrical to the optical axis, and light-receiving element arrays are disposed at positions where the two images re-formed by the imaging lenses can be electrically detected, respectively.
In a camera focus detection device that detects the focus of the photographic lens by comparing two images with each other, the light beam from the subject is divided into different parts of the pupil of the photographic lens, and the divided light beams that pass through are aligned with the optical axis. On the optical axis excluding the conjugate position of the aperture of the imaging lens on the object side from the intersection point, the density changes gradually in accordance with the distance from the optical axis, and this change in density causes the light to change. What is claimed is: 1. A focus detection device characterized in that a filter that changes symmetrically with respect to an axis is disposed so as to substantially uniformly correct an uneven light amount distribution caused by an optical system. (2) Behind the focal plane of the photographing lens, in order from the photographing lens side, a condenser lens is placed coaxially with the optical axis of the photographing lens, and two imaging lenses are installed at positions symmetrical to the optical axis of the imaging lens. In a focus detection device for a camera, light receiving element arrays are arranged at positions where two images re-formed by can be electrically detected respectively, and the two images are compared with each other to detect the focus of the photographing lens. , on the optical axis between the imaging lens and the light-receiving element array, the density changes gradually according to the distance from the optical axis, and the change in density is symmetrical with respect to the optical axis. What is claimed is: 1. A focus detection device characterized in that the focus detection device is configured to include a filter that changes depending on the direction of the focus, so as to substantially uniformly correct the non-uniform light amount distribution caused by the optical system. (3) Behind the focal plane of the photographing lens, in order from the photographing lens side, a condenser lens is placed coaxially with the optical axis of the photographing lens, and two imaging lenses are installed at positions symmetrical to the optical axis of the imaging lens. A focus detection device for a camera that detects the focus of the photographing lens by disposing a light receiving element array at a position where two images re-formed by can be electrically detected respectively, and comparing the two images with each other. In the manufacturing method, a negative film is placed at a predetermined position between the imaging lens and the light receiving element array on the optical axis, and a light beam from a predetermined light source placed in front of the taking lens is directed to the taking lens. After adjusting the device to a focused state, the negative film is exposed to the light flux, and the exposed negative film is developed, so that its density gradually increases in accordance with the distance from the optical axis. 1. A method for manufacturing a focus detection device, comprising: manufacturing a filter whose density changes and whose density change is symmetrical with respect to the optical axis, and arranging this filter at the predetermined position.