JPH02910A - Focus detection optical device - Google Patents

Abstract

PURPOSE:To enlarge a space between a position where luminous flux is deflected and a light receiving means and to set the deflection angle of the luminous flux out of an optical axis to an optical axis side to be small by arranging a light deflection means near an image-formation surface by a photographic lens. CONSTITUTION:A prism block 13 functioning as the light deflection means is provided close to a visual field mask 6, that is, near the primary image- formation surface of an object by the photographic lens, between the visual field mask 6 and an AF (autofocusing) module 30. Separator lenses 8a-8f are integrally formed on one lens substrate 8 and CCD line sensors (photodetectors) 9-11 are provided on one substrate 12. Even in the case that the optical path of an out-of-optical axis focus detection optical system is deflected in order to miniaturize the substrate where the photodetectors are placed, the deflection angle can be made small and the adjusting precision in the optical axis direction of the photodetector may be lower than the conventional one.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a focus detection optical device that detects the focus of an optical system such as a camera, and in particular, the present invention relates to a focus detection optical device that detects the focus of an optical system such as a camera, and in particular detects focus at multiple points on the optical axis and off the optical axis. The present invention relates to a focus detection optical device for multiple distance measurement.

(Prior art) In a multi-distance focus detection optical device, if the focus detection zones are formed at a distance so that the light beams of each focus detection system do not interfere with each other, the position of the image re-formed for focus detection also changes. Because they are spaced apart from each other, the light receiving elements (e.g. CCD line sensor)
cannot be formed close to each other.

Therefore, if the sensor is installed on one chip, the board becomes large, and if it is installed on an independent board, adjustments such as optical axis alignment must be made for each board. It takes up more space and AP
(Auto Focus) The module as a whole becomes larger and the cost becomes higher.

(Problems to be Solved by the Invention) Therefore, as shown in FIG. Prism 4.5 behind .3
proposed a configuration in which the re-imaging position is brought closer to the optical axis 9 by providing a
issue).

The light flux incident from the photographing lens is divided into three areas (range-finding zones) by a field mask 6 provided in alignment with the imaging plane.
limited to condenser lenses 1, 2, 3, prism 4
, 5, CC via aperture mask 7 and separator lens 8
A pair of subject images is formed again on each of the D line sensors 9, 10, and 11.

According to this configuration, the light flux from the ranging zone outside the optical axis 9 of the photographing lens is bent toward the optical axis 9 side due to the action of the prism 4.5 and the prism action due to the eccentricity of the condenser lens 1.3. Ru. Therefore, the re-imaging positions can be brought close to each other, and the CCD line sensors 9, 10.1
It is possible to reduce the size of the substrate 12 on which one is set and the entire AF module surrounded by the broken line.

However, in this configuration, since the deflection angle of the optical path of the focus detection optical system located outside the optical axis 9 of the photographic lens is relatively large, when adjusting the position of the substrate 12 in the optical axis direction, the CCD line sensor 9 .10.11 deviates from the position covering the set ranging zone.

In addition, in order to make the thickness of the prism 4 smaller than a predetermined value, the deflection angle cannot be generated only by the action of the prism 4, and the prism action due to the eccentricity of the condenser lens 1 as described above must also be used. ing.

Therefore, as shown in FIG. 9, the light beam passage area PZ is the peripheral part of the condenser lens 1, so the outer diameter and center thickness of the lens must be increased to secure this area, which may also cause aberrations. big.

Furthermore, since the distance between the imaging plane and the prism 4 is large, there is also the problem of large lateral chromatic aberration.

(Means for Solving the Problems) In order to achieve the above object, the present invention arranges a portion near the optical axis of a primary image formed through a photographing lens in a line shape using a divided re-imaging lens system. An on-axis focus detection optical system that re-images a pair of images on the light-receiving element array and detects the in-focus state near the optical axis, and a re-imaging lens system that detects the off-axis portion of the primary image. The optical axis focus detection optical system detects the in-focus state off the optical axis by re-forming the image on the light-receiving element array, and the optical axis focus detection optical system It is characterized by comprising a light deflecting means for deflecting the light beam toward the optical axis.

(Example) Below, an example of the focus detection optical device according to the present invention will be described based on the drawings.

1 to 3 show an embodiment in which the focus detection optical device of the present invention is applied to an automatic focusing device of a camera.

FIG. 2 is a schematic diagram showing the overall configuration of the camera.
is a photographic lens detachably attached to the camera body 21;
22 is a main mirror for guiding the photographing light beam to the finder 23; 24 is a submirror for guiding the photographing light beam that has passed through the main mirror 22 to the AP module 30;

F is a film surface, 41 is a light shielding plate, and 42 is an opening provided in the light shielding plate 41.

FIG. 3 conceptually shows the optical system of the AF module 30 described above.

This device includes an on-axis focus detection optical system A that detects the in-focus state near the optical axis 9 of the photographic lens 20, and an on-axis focus detection optical system A that is provided on both sides of the on-axis focus detection optical system an optical axis focus detection optical system B that detects the in-focus state outside of 9;
It is equipped with C. Each focus detection optical system consists of a divided re-imaging lens system consisting of a condenser lens (see Figure 1) and separator lenses 88 to 8f, and a CCD line sensor (
It is composed of light receiving elements) 9, 10, and 11.

In addition, in FIG. 3, the central optical axis of the on-axis focus detection optical system A coincides with the optical axis 2 of the photographic lens 20. 91 is the central axis of the optical axis focus detection optical system B, I12 is the central axis of the optical axis focus detection optical system C, and the optical axis 9 of the photographing lens and the central axis g1.92 (B y lens 20 They intersect at the center 0 of the exit pupil EP.

The light flux incident from the photographing lens 20 forms a primary image of the subject on the field mask 6 arranged at a position optically conjugate with the film plane F. The subject image on the field mask 6 is formed in focus when the photographing lens 20 is in focus.

Note that the exit pupil EP of the photographic lens 20 seen from the central distance measurement zone 6a is approximately circular as shown by the solid line, whereas the exit pupil EP- seen from the peripheral distance measurement zones 6b and 6c is approximately circular. Due to the influence of vignetting, it becomes approximately elliptical as shown by the broken line.

Each of the separator lenses 8a to 8f is in an optically conjugate positional relationship with the photographic lens 20 via a condenser lens.

And the separator lens 8 of the on-axis focus detection optical system A
a, 8b are arranged in the horizontal direction in the figure, and are located through the central distance measurement zone 6a to the virtual aperture area EP1. Looking at EP2. The separator lenses 8a and 8b capture the light beams that have passed through the aperture areas EPI and EP2, and a pair of images is re-formed on the CCD line sensor lo.

Off-axis hot spot detection optics iB, C separator lens 8c,
8d, 8e, and 8f are respectively arranged in the vertical direction in FIG.
P vertical opening area EP3. Looking at EP4.

The separator lenses 8c, &I, 8e, 8f have opening areas EP3. The luminous flux that passed through EP4 is captured and c
A pair of images is respectively re-formed on the cD line sensor 9°11. The reason why the separator lenses of the optical axis focus detection optical systems B and C are arranged vertically is as follows.
This is to avoid the influence of vignetting and ensure a sufficient baseline length between lenses.

FIG. 1 is a detailed diagram of the above AP module 3o.

The AF module 3o is constructed by integrally housing members surrounded by broken lines in a case.

A prism block 13 as a light deflecting means is provided between the field mask 6 and the AF module 3o, close to the field mask 6, that is, near the primary imaging plane of the subject by the photographing lens 2o.

This prism block 13 includes prism portions 13 provided corresponding to the peripheral ranging zones Bb and 6c of the visual field mask 6.
a, 13b, and a parallel plane portion 13c provided corresponding to the central distance measurement zone 6a.

Note that the thickness of the parallel plane portion 13c is the same as that of the prism portion 13a,
The thickness is set to be equal to the thickness of the central portion of the optical axis 13b, and the difference in optical path length between the light beam at the optical axis 9 portion and the light beam outside the optical axis 9 due to the provision of the prism is reduced.

The separator lenses 8a to 8f described above are integrally formed on the negative lens substrates 8. Also, three COD
The line sensors 9, 10, 11 are provided on the − number of substrates 12.

An infrared cut filter 14 is provided between the condenser lens and the separator lens.

Further, an auxiliary lens 15 is bonded to the light incident side of the separator lens substrate 8 in order to make the light intensity distribution uniform and reduce distortion. Mask 7 is sandwiched. Note that the reference numeral 16 is a cover glass of the line sensor.

The on-axis focus detection optical system A uses a condenser lens 1 and separator lenses 8a and 8b to form a pair of images on the COD line sensor 1o by using a condenser lens 1 and separator lenses 8a and 8b to form a light beam near the optical axis 9 that has passed through the central distance measurement zone 8a of the field mask 6. Split and reimage.

The image interval on the CCD line sensor 10 is approximately proportional to the amount of defocus of the photographing lens 20. Therefore, by calculating this image interval, it is possible to determine the defocus state of the photographing lens 2o with respect to the subject in the 9yI region corresponding to the central distance measurement zone 66.

The two optical axis focus detection optical systems deflect the light beams outside the optical axis 9 that have passed through the peripheral distance measurement zones 6b and 6c of the field mask 6 toward the optical axis 9 side by prism parts 13a and 13b, respectively, and convert them into condenser lenses. 2.3 and a pair of separator lenses 8c, &1. 8e and 8f, the images are divided and re-imaged onto the CCD line sensors 9 and 11 as a pair of images.

The defocus state of the photographic lens 20 with respect to the subject in the area corresponding to the peripheral distance measurement zones 6b and 6c is as follows:
It can be detected based on the output of the CCD line sensor 9.11.

The photographer selects a distance measurement zone that covers the subject to be focused on. The automatic focusing device drives the photographing lens 20 to a focusing position based on the defocus direction and defocus amount corresponding to the selected distance measurement zone.

By arranging the prism near the imaging plane of the photographing lens as described above, the position where the light beam is deflected and C
The distance from the CD line sensor can be increased compared to the conventional one, and the deflection angle of the off-axis light beam toward the optical axis 9 side can be set small.

The following effects occur due to this reduction in the deflection angle.

(1) The accuracy of position adjustment along the optical axis of the CCD line sensor can be lower than in the past.

That is, since the deflection angle is small, even if the CCD line sensor is moved in the direction of the optical axis, it will not easily deviate from the area of the light beam incident from the predetermined distance measurement zone.

(2) The apex angle of the prism can be made small.

Therefore, the thickness of the prism can be reduced.

(3) According to (2) above, even if the thickness of the prism is kept to the same level as in the conventional case, there is no need to add a prism effect due to eccentricity of the condenser lens.

Therefore, as shown in FIG. 4, the light beam transmission region PZ can be set near the optical axis of the condenser lens, and the effective diameter of the condenser lens can be secured without increasing the center thickness of the lens. Furthermore, it is possible to suppress the occurrence of aberrations due to the use of the peripheral portion of the lens.

On the other hand, by placing the prism near the imaging plane,
Lateral chromatic aberration can be reduced.

As shown in FIG. 5, the light beam from one point on the imaging plane has a predetermined spread angle as shown by the solid line and the broken line due to the difference in the refractive index of the prism depending on the wavelength.

This is lateral chromatic aberration.

When the image plane is separated from the prism 13a as shown by Fl, the apparent image of point P1 on the image plane as seen from the CCD line sensor side! 1 has a relatively large spread.

On the other hand, when the image forming plane is placed close to the prism 13a as shown by F2 in FIG. 5 as in the embodiment shown in FIG. The apparent image (2) of point P2 has only a relatively small extent.

This suggests that the smaller the distance M between the imaging plane and the prism, the more chromatic aberration can be reduced.

FIG. 6 shows a reference example in which the arrangement of prisms is different from the embodiment shown in FIG. 1, and the same reference numerals are used for the same members as in the above embodiment. In the configuration shown in FIG. 6, the distance between the imaging plane and the prism is larger than that in the configuration shown in FIG. 1, and the other configurations are the same.

Figure 7 shows the lateral chromatic aberration on the sensor between the configuration in Figure 6 and the configuration in Figure 1, where the solid line in the graph is the reference example of Figure 6, and the broken line is the implementation of Figure 1. An example is shown. From FIG. 7, it can be seen that by changing the arrangement of the prisms, the lateral chromatic aberration can be reduced to about half.

Note that this lateral chromatic aberration appears in a direction perpendicular to the element arrangement direction of the CCD sensor lO, so it is not a problem.However, in order to prevent unknown problems from occurring, it is better to have less aberration. preferable.

(Effects of the Invention) As described above, the focus detection optical device of the present invention can also be used when deflecting the optical path of the optical axis focus detection optical system for the purpose of downsizing the substrate on which the light receiving element is mounted. , the deflection angle can be made smaller than before.

Therefore, it is sufficient that the adjustment precision of the light-receiving element in the optical axis direction is lower than that of the conventional art.

Moreover, the apex angle of the prism can be made small, and its thickness can be suppressed.

Furthermore, if the thickness of the prism is approximately the same as that of the conventional prism, the deflection angle can be obtained without adding a prism effect due to eccentricity of the condenser lens. Therefore, the vicinity of the optical axis of the condenser lens can be used as a transmission area for the light beam, and the effective diameter can be ensured without increasing the center thickness, and aberrations can be reduced.

On the other hand, since the light deflecting means is provided near the imaging plane of the subject by the photographic lens, it is possible to suppress the occurrence of chromatic aberration on the light receiving element.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an optical system showing an embodiment of the focus detection optical device according to the present invention, FIG. 2 is an explanatory diagram of a camera in which the above device is installed, and FIG. 3 is an illustration of the arrangement of the focus detection optical system. FIG. 4 is an explanatory diagram showing the relationship between the condenser lens and the light beam transmission area in the optical system shown in FIG. 1, and FIG. 5 is a schematic perspective view showing the relationship between the position of the imaging plane and the occurrence of chromatic aberration. FIG. 6 is an explanatory diagram showing the relationship, FIG. 6 is an explanatory diagram showing a reference example of a focus detection optical device that differs only in the arrangement position of the prism, and FIG. 7 is a graph showing the occurrence of chromatic aberration depending on wavelength. FIG. 8 is an explanatory diagram showing an optical system of a focus detection device in which a prism is provided behind a condenser lens, and FIG. 9 is an explanatory diagram showing the relationship between the condenser lens and a light beam transmission area in this optical system. 1.2.3... Condenser lens 6... Field mask 8a to 8f... Separator lens 9.10.11... COD line sensor (light receiving element) 13... Prism block (light deflection means) FIG.
2 FIG, l FIG. FIG.

Claims (4)

[Claims] (1) A portion of the primary image formed through the photographic lens near the optical axis is re-imaged as a pair of images on a line of light-receiving elements arranged in a line by a split re-imaging lens system, and the portion near the optical axis is an on-axis focus detection optical system for detecting the in-focus state at the optical axis; an off-axis focus detection optical system that detects a focus state; and a light deflection means that is provided near an imaging plane on which the primary image is formed and deflects the off-axis light beam toward the optical axis. A focus detection optical device characterized by: (2) The focus detection optical device according to claim 1, wherein two systems of the off-axis focus detection optical system are provided on both sides of the on-axis focus detection optical system. (3) The light deflecting means is an integrated block including a prism portion that deflects a light beam outside the optical axis and a parallel plane portion that transmits a light beam near the optical axis. Or the focus detection optical device according to 2. (4) The focus detection optical device according to claim 3, wherein the center thickness of the prism portion and the thickness of the parallel plane portion are approximately equal.