JPH08262320A - Focus detector - Google Patents

Abstract

PURPOSE: To prevent the deterioration of performance due to the asymmetry of a secondary image forming system in a device having the expance of visual field parallel with the sides of a screen around a position obliquely apart from the center of the screen by relaxing the optical path difference of a light beam transmitted through each lens by a secondary image forming lens and comprising a member for relaxing the change of angle due to the refraction of a light ray. CONSTITUTION: In a focus detecting device, a visual field mask 31' having a range finding visual field having the expanse in the direction parallel with the sides of a screen around a position obliquely apart from the center of the screen is provided in the vicinity of planned image forming plane. A pair of secondary image forming lenses to which light beams passing through range finding visual fields 41-44 are provided with an optical member removing the optical path lengths of light beams transmitted through the respective lenses and the angular change due to the refraction of light rays incident on or transmitted from the respective lenses. Consequently, the difference of image characteristics of two light quantity distributions is removed or relaxed and a small and accurate device is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device for optical equipment. More specifically, the present invention relates to improvement of an optical system that constitutes a focus detection device.

[0002]

2. Description of the Related Art Various focus detecting devices for detecting the focus adjustment state of an objective lens of a camera or the like have been proposed, one of which is shown in FIG. In FIG. 8, 1 is an objective lens, 2 is a field mask arranged in the vicinity of the planned focal plane of the objective lens 1, 3 is a field lens, and 4 is symmetrically arranged with respect to the optical axis of the objective lens 1. The secondary imaging lens 5 composed of two positive lenses 4-1 and 4-2 is the two lenses 4-1 and 4-2.
Corresponding to the two sensor rows 5 arranged behind it.
A sensor composed of 1, 5-2, and 6 are diaphragms having two openings 6-1 and 6-2 arranged corresponding to the two lenses 4-1 and 4-2. 7 is divided into 2
Objective Lens 1 Composed of Two Regions 7-1 and 7-2
Showing the exit pupil of each. In the field lens 3, the openings 6-1 and 6-2 are formed in the area 7 of the exit pupil of the objective lens 1.
-1, 7-2 has an effect of forming an image in the vicinity of the sensor array 5 and the object light flux transmitted through each of the regions 7-1, 7-2
The light amount distributions are respectively formed on -1, 5-2.

In the focus detecting apparatus shown in FIG. 8, when the image forming point of the objective lens 1 is on the front side of the planned focal plane, the light quantity distributions formed on the two sensor rows 5-1 and 5-2 are mutually different. When the state is approaching and the image forming point of the objective lens 1 is on the rear side of the planned focal plane, the two sensor rows 5-
The light amount distributions formed on 1 and 5-2 are separated from each other. Moreover, since the deviation amount of the light amount distribution formed on each of the two sensor rows 5-1 and 5-2 has a certain functional relationship with the deviation amount of the focus of the objective lens 1, if the deviation amount is calculated by an appropriate calculation means. It is well known that the direction and amount of defocus of the objective lens 1 can be detected.

The focus detection apparatus shown in FIG. 8 can measure the distance only to an object existing in the center of the range photographed by the objective lens 1 or observed by the finder. On the other hand, a focus detection device having a distance measuring visual field other than the center of the imaged or observed range is disclosed by the applicant in Japanese Patent Application No. 62-279835. FIG. 9 is a perspective view showing the optical system. 8 is a field mask, 9 is a field lens, 10 is a diaphragm having two apertures 10-1 and 10-2, and 11 is two positive lenses 11-1 and 11. -2
A secondary image forming lens, and 12 are sensors. Although the objective lens 1 shown in FIG. 8 is omitted,
It is located on the left in the figure. What is different from the focus detection apparatus shown in FIG. 8 is that the field mask 8 has a plurality of openings 13 to 17 corresponding to a plurality of fields to be distance-measured, and the light flux regulated by the field mask 8. Of the plurality of pairs of sensor arrays 18-1 and 18-2, 19-1 and 19-2, 20 so as to receive a plurality of pairs of light amount distributions formed by the secondary imaging system 11.
-1 and 20-2, 21-1 and 21-2, 22-1 and 22
-2 is provided as the sensor 12. The principle of distance measurement is the same as that of the focus detection apparatus of FIG. 8, and the amount of deviation of the light amount distribution formed on each sensor pair is calculated to perform focus detection for each visual field. According to this focus detection device, the central part of the range to be photographed or observed and both sides 4
The distance can be measured at a total of 5 places. The number of distance measuring fields is not limited to this, but is determined by the number of openings in the field mask and the number of sensor pairs.

The focus detecting apparatus shown in FIG. 9 is an improvement over the drawback of the focus detecting apparatus shown in FIG. 8 in that the distance can be measured only for an object existing in the center of the range photographed or observed by the objective lens. . However, in the focus detection device shown in FIG. 9, the direction in which the two light amount distributions on the sensor relatively move depending on the focus state of the objective lens is the up and down direction, so that the light amount distribution changes substantially in this direction. It is possible to measure the distance only to the object, and the distance is measured to the object whose light intensity distribution changes only in the direction perpendicular to this, such as a black and white edge pattern with the vertical line as the boundary. Was difficult.

The present applicant has proposed a focus detection device that solves this problem. FIG. 10 is a diagram showing the configuration of the optical system.

In the figure, 31 is a visual field mask, which has a cross-shaped opening 31-1 in the center and vertically long openings 31- in the peripheral portions on both sides.
It has 2, 31-3. Reference numeral 32 denotes a field lens, which has three openings 31-1, 31-2, 3 of the field mask.
Corresponding to 1-3, three parts 32-1, 32-2, 3
It consists of 2-3. Reference numeral 33 denotes a diaphragm, and a pair of apertures 33-1a and 33-1 are provided at the center, one pair vertically and horizontally.
b, 33-1c, 33-1d, and one to two openings 33-2a, 33-2b and 33-3 in the left and right peripheral portions.
a and 33-3b are provided respectively. Regions 31-1, 31-2, 31-3 of the field lens 32
Respectively these aperture pairs 33-1, 33-2, 33-
3 has an action of forming an image near the exit pupil of the objective lens (not shown). 34 is a four-pair total of eight positive lenses 34-1a,
34-1b, 34-1c, 34-1d, 34-2a, 3
It is a secondary optical member in which a secondary imaging lens made up of 4-2b, 34-3a, and 34-3b is integrated, and is arranged behind the aperture 33 corresponding to each aperture. Reference numeral 35 is a four-pair total of eight sensor rows 35-1a, 35-1b, and 35-1.
c, 35-1d, 35-2a, 35-2b, 35-3
The sensor is composed of a and 35-3b, and is arranged so as to receive the image corresponding to each secondary imaging lens. FIG. 11 shows an image area formed on the sensor 35. 36-1a, 36-1b, 36-1c, 36-
1d shows that after the light flux transmitted through the central aperture 31-1 of the field mask and the central portion 32-1 of the field lens is regulated by the apertures 33-1a, 33-1b, 33-1c, 33-1d of the diaphragm, The secondary image forming lenses 34-1a and 3
Image areas formed on the sensor surface by 4-1b, 34-1c, and 34-1d are shown, respectively. 36-2a,
Reference numeral 36-2b shows that after the light flux transmitted through the opening 31-2 around the field mask and the peripheral portion 32-2 of the field lens is regulated by the openings 33-2a and 33-2b of the diaphragm,
The image area formed on the sensor by the secondary image forming lenses 34-2a and 34-2b located behind is shown. Similarly,
36-3a and 36-3b are openings 31 around the field mask.
-3 and the peripheral portion 32-3 of the field lens are regulated by the apertures 33-3a and 33-3b of the diaphragm, and then the lens 34-3 of the secondary image forming system behind them.
Image areas formed on the sensor surface by a and 34-3b are shown respectively.

The distance measuring principle of the focus detection device shown in FIG. 11 is to detect the relative position of the image of the pair of sensors in the column direction as in the conventional case, but the structure described above is adopted. As a result, near the center of the range photographed or observed by an unillustrated objective lens, it is possible to perform good distance measurement even for an object whose light amount distribution changes only in one direction, up and down or left and right, Further, it is possible to measure the distance to an object located at a position other than the center and corresponding to the openings 31-2 and 31-3 around the field mask.

[0009]

In the focus detection device shown in FIGS. 9 and 10, not only in the center of the range (screen) photographed or observed by the objective lens, but also in the peripheral portion of the screen separated from the center to the left and right. Distance measurement (detection) is now possible. To develop this further and enable distance measurement in the peripheral part vertically separated from the center, although there are problems such as how to guide the luminous flux for distance measurement, arrangement, and space,
It is possible in principle.

For example, if the peripheral visual field of the focus detection apparatus of FIG. 10 is rotated by 90 ° around the optical axis passing through the center of the system and arranged so as not to interfere with the system before rotation, as shown in FIG. A focus detection device having a wide range-finding field can be configured.
Further, if the angle of rotation at that time is an angle other than 90 °, for example ± 45 °, a focus detection device having a distance measuring (detecting) visual field inclined at a position obliquely separated from the center as shown in FIG. Can be realized relatively easily.

However, focusing as shown in FIG. 13 with a range-finding field that is obliquely inclined with respect to a rectangular screen lacks a sense of stability, and is very difficult for the user to use. I will end up. Considering that most general subjects are composed of vertical lines and horizontal lines, even if there is a distance measuring field at a position diagonally separated from the center of the screen, the direction of the field of view is measured as shown in FIGS. 14 and 15. It is desirable to be parallel to each side of the screen to show the distance field.

As described above, such a focus detecting device cannot be constructed by simply rotating the optical system, and the concept of the conventional focus detecting system cannot be used as it is.

An object of the present invention is to provide a focus detecting device as shown in FIGS. 14 and 15, which has a field of view spread in parallel to each side of the screen centered on a position obliquely separated from the screen center. That is. It is more desirable to eliminate or mitigate the difference in performance between the two images due to the asymmetry of the two secondary imaging systems forming a pair, and to provide a compact and highly accurate focus detection system.

[0014]

In order to achieve the above-mentioned object, the invention according to the present application is directed to a field mask arranged near the planned image plane of the objective lens for regulating the field of view, and also a planned objective lens. A pair of secondary imaging lenses for re-imaging the image formed by the field lens and the objective lens disposed near the imaging surface, and the secondary imaging lens disposed in front of or behind the secondary imaging lens. A stop having a pair of apertures for restricting light passing through the lens, and a secondary imaging system including a sensor array for detecting a light amount distribution formed by the secondary imaging lens, which is off the optical axis of the objective lens. In a focus detection system capable of detecting a focus in a field area having a spread in a certain direction, the direction of the field area spread is not orthogonal to a virtual plane including the optical axis of the objective lens and passing through the center of the field area. Light flux passing through the field of view The pair of receiving secondary imaging lenses has a member that alleviates a difference in optical path length of a light flux that passes through each lens and alleviates an angular change due to refraction of a light beam that enters or exits each lens. .

More preferably, the member is a prism member provided on one of the entrance surface and the exit surface of the pair of secondary imaging lenses, and the prism member is provided in the direction of expansion of the field of view and in the field of view. It consists of a plane determined by a normal vector that also has a component in the spread and vertical direction, and
It is characterized in that the regions corresponding to the pair of secondary imaging lenses have a step difference from each other and are not on the same plane.

[0016]

FIG. 1 is a diagram showing an embodiment of the present invention, in which the field mask, field lens, diaphragm, secondary imaging lens, and sensor have the same basic configuration as the focus detection system shown in FIG. , The following points are different.

That is, in the visual field mask 31 ', four openings 41, 42, 43, 44 having a horizontal spread are newly provided at positions obliquely separated from the center,
Correspondingly, the field lens 32 'has four regions 51, 52, 53, 54, and the diaphragm 33' has four pairs of apertures 61-a and 61-b, 62-a and 62-b. 6
3-a and 63-b, 64-a and 64-b, four lens pairs 71-a and 71-b, 72 on the secondary optical member 34 '.
-A and 72-b, 73-a and 73-b, 74-a and 74
-B, and the sensor 35 'has four sensor pairs 81-
a and 81-b, 82-a and 82-b, 83-a and 83-
b, 84-a and 84-b are added. In addition, diaphragm 3
3'may be in front of or behind the secondary imaging lens, and a pair of sensors may use one sensor row divided into two.

In such a structure, each region 51 of the field lens 32 ', as described in the description of FIG. 10,
52, 53 and 54 are aperture pairs 61-of the diaphragm 33 ', respectively.
a and 61-b, 62-a and 62-b, 63-a and 63-
b, 64-a and 64-b are objective lenses not shown (in the figure,
(Located to the left) has the effect of forming an image near the exit pupil,
In addition, the light transmitted through the pair of diaphragm apertures respectively receives the lens pair 7
1-a and 71-b, 72-a and 72-b, 73-a and 7
3-b, 74-a and 74-b allow sensor pairs 81-a and 81-b, 82-a and 82-b, 83-a and 83-b,
A light amount distribution regarding the secondary image of the object is formed on 84-a and 84-b.

Therefore, in comparison with the conventional focus detecting device, it is inferred that focus can be detected in principle in the distance measuring fields 41, 42, 43 and 44 which are diagonally separated from the center. However, the range of the distance measuring fields (horizontal direction in this embodiment) includes the optical axis of the objective lens (not shown), and the centers 45, 46, 47, 4 of the respective distance measuring fields.
It is different from the conventional distance measuring fields 31-1, 31-2, 31-3 shown in FIG. 103 in that it is not perpendicular to the plane passing through 8.

Due to such differences, it is desirable in view of optical characteristics that each component of the focus detection system has a structure different from the conventional one.

FIG. 2 shows only the secondary optical member 34 'in which the secondary imaging lens of FIG. 1 is incorporated, and FIG. 3 is a plan view thereof. The same parts as those in FIG. 1 or 10 are designated by the same reference numerals. As is clear from these figures, the lens pair 34-1 related to the conventional focus detection system
a and 34-1b, 34-1c and 34-1d, 34-2a
And 34-2b, 34-3a and 34-3b are symmetrical with respect to a straight line or a plane perpendicular to the straight line connecting the vertices of the respective lenses, but the lens pairs 71-a and 72- according to the present embodiment. b, 72-a and 72-b, 73-a
And 73-b and 74-a and 74-b, there is no line of symmetry or plane of symmetry for such shapes. That is, in FIG. 3, lens pairs 71-a and 72-b, 72-a and 7-
Originally, 2-b, 73-a and 73-b, and 74-a and 74-b are center lines whose boundary lines lie in a plane that bisects the line segment connecting the vertices of each lens vertically. 75, 76, 7
It is considered that the most common structure is the same as 7, 78. However, in the present embodiment, the positions 75 ', 76', 77 ', 7 shifted away from the center in the left-right direction, respectively.
8'is set as the boundary line between each lens pair, and as a result, it has an asymmetric shape.

On the other hand, FIG. 4 is a perspective view of the secondary optical member 34 'shown in FIGS. 1 to 3 as viewed from the light emitting side. In the figure, four lens pairs 71-a, 71-b, 72
-A and 72-b, 73-a and 73-b, 74-a and 74
4 pairs of prism members 101-a and 101-b, 102-a and 1 on the exit side of the secondary optical member 34 'corresponding to -b.
02-b, 103-a and 103-b, 104-a and 10
4-b is provided. These prism members are
The prism member is composed of a surface inclined with respect to the flat surface portion 34 ″ of the next optical member 34 ′, and the pair of prism members have steps.

The lens pair 34-2a and 34-2b, 34-3a and 34-3b on the exit side of the secondary optical member 34 '.
A prism member 105 having an inclination in a portion corresponding to
106 also includes lens pairs 34-1a, 34-1b, 34-
In the portion corresponding to 1c and 34-1d, the protruding member 107
Is provided. In order to clearly show the shape and arrangement, these prism members or projecting members are not shown in FIG.
Although they are illustrated as being provided so as to be isolated from each other on the next optical member 34 ′, such a configuration is not necessarily required. Rather, when molding the secondary optical member 34 'with a material such as plastic, it is generally preferable to make these members in contact with each other so that the undulations of the surface of the secondary optical member are as small as possible. It is easy to obtain a good molded product.

FIG. 5 shows the prism member 101-a of FIG.
Only the same -b is shown in an enlarged manner. As described above, the surfaces 108-a and 108- that form each prism member.
b is a plane inclined with respect to the plane portion 34 "of the secondary optical member 34 ', but as is clear from FIG. 5, these planes are the lens pairs 71-a and 71-b and the prism pair 1.
01-a and 101-b have inclinations in two directions, that is, the direction of the field of view (41 in FIG. 1) or the sensor array (81-a and 81-b in FIG. 1) and the direction orthogonal thereto. . That is, the surfaces 108- that form the prism members 101-a and 101-b.
The normal vectors for a and 108-b are 109
Assuming −a and 109-b, these vectors have components in both the viewing direction 110 and the direction 111 perpendicular thereto.

Further, the prism members 101-a, 101-
The flat portions 108-a and 108-b of b are not on the same plane and have a step along the boundary line between them. Of course, the flat portions 108-a and 108-b of each prism member are connected to each other with a smooth curved surface without providing a step as shown in FIG. May be.

The prism members 101-a and 10 shown in FIG.
Other than 1-b, the prism members 102-a and 10 shown in FIG.
2-b, 103-a, 103-b, 104-a, 104
-B is also composed of a plane having a similar inclination.

The effect of providing such a prism member will be described below with reference to FIGS. 6 and 7.

FIG. 6 is a view when the portion related to the openings 41, 43 or 42, 44 of the field mask of FIG. 1 showing the focus detection system according to the present embodiment is projected on a horizontal plane, and is the same as FIG. The same reference numerals are attached to the. 45 ', 46',
47 'and 48' are the openings 41 and 4 of the visual field mask 31 '.
It represents the center of the distance measuring field controlled by 2, 43, 44, and 55-a and 55-b, 56-a and 56-, respectively.
b, 57-a and 57-b, 58-a and 58-b pass through the centers 45 ′, 46 ′, 47 ′ and 48 ′ of the distance measuring fields and form four light amount distributions on the sensor 35 ′. Shows the luminous flux of. The field lens 32 'has two parts 51 and 53.
Alternatively, the optical axes 52 and 54 are displaced with respect to the optical axis of the objective lens (not shown) in the plane of the paper of FIG. 6 and in the direction perpendicular to the plane of the paper. Most commonly, the optical axes of the two lens surfaces that make up each region of the field lens do not necessarily have to coincide, and need not be parallel to the optical axis of the objective lens. In addition, it is effective to make at least some of the surfaces forming the field lens aspherical surfaces in order to maintain good optical characteristics.

The focus detection system as shown in FIG. 6 is required in terms of form in order to reduce the total length of the system from the viewpoint of incorporating it in a camera while keeping the distance measuring field of view as far away from the center as possible. Is. Further, in terms of manufacturing cost, the ratio of the sensor is very high, and reducing the area of the sensor is particularly effective for cost reduction.

In order to satisfy the above requirements and realize an optimum focus detection system, the diaphragm 33 'or 2 in FIG.
55-a, 55-b, 57- with respect to the next optical member 34 '
It is desirable that the light beams such as a and 57-b are incident at a large angle and the light beams are converged toward the sensor. However, as the angle of incidence of each light beam on the secondary optical member 34 ′ increases, the angle of the light beam with respect to the secondary optical member when exiting also increases, and the exit surface is a surface perpendicular to the optical axis 112. Receives a large angle change due to refraction. As a result, various aberrations such as astigmatism, coma and chromatic aberration that deteriorate image forming performance become large, and it becomes difficult to obtain image information for good focus detection.

Regarding this point, in this embodiment, FIG.
101-a, 101-b, 102-a, 102-b,
As shown in 103-a, 103-b, 104-a, and 104-b, by making the exit surface of the secondary optical member 34 'a tilted prism surface, the occurrence of aberration is suppressed and good image information is obtained. It is possible to detect.

Further, if the paired prism surfaces are made to be the same plane, the difference in the optical path lengths of the paired light beams in the secondary optical member 34 'becomes large, and an image of equivalent performance is formed on the same sensor surface. Becomes difficult. Therefore, in this embodiment, as shown in FIG. 6, a step is provided between the paired prisms to change the thickness, thereby eliminating or relaxing the optical path length difference.

On the other hand, FIG. 7 is a view in which a portion relating to the visual fields 41, 42 or 43, 44 of FIG. 1 is projected on a vertical plane,
The same components are designated by the same reference numerals. That is, FIG. 7 corresponds to a view seen from below or above FIG.

Also in the projection view of FIG. 7, the light beams 55-a, 55-b, 57-a, 57-b or 56-a, 56-b, 58-a, 58- are used as in the case of FIG. b is 2
When the light is obliquely incident on the next optical member 34 'and the exit surface of the same is a surface perpendicular to the optical axis 112, the above-mentioned various aberrations occur. Therefore, also in FIG. 7, the exit surface is a tilted prism surface. As a result, the prism member provided on the exit side of the secondary optical member 34 'has a direction 111 perpendicular to the field of view in the field of view 110 as described in FIG.
Will have a normal vector with components.

The pair of prism members may have the same normal vector for the sake of simplicity, but as is clear from the purpose and effect of the prism member of the present invention, it is not always necessary. Instead, the optimum inclination is set individually.

Further, although the prism member is provided on the exit surface side of the secondary optical system in the above embodiments, the present invention is not limited to this, and the entrance surface of the secondary optical system is not limited to this. The object can also be achieved by a structure in which a prism member is provided on the side and a lens surface having an image forming action is provided on the exit surface side. Further, the prism member does not have to be integrally formed, and the separate lens and the prism member may be brought into contact with each other.

[0037]

As described above, according to the present invention, at the time of constructing a focus detection device having a field of view parallel to each side of the screen at a position obliquely separated from the center of the screen, It is possible to eliminate or mitigate the difference between the image characteristics of the two light amount distributions formed on the sensor, and it is possible to realize a compact and highly accurate focus detection device.

[Brief description of drawings]

FIG. 1 is a perspective view showing a focus detection system of the present invention.

FIG. 2 is a perspective view showing an optical member according to the present invention.

FIG. 3 is a plan view showing an optical member according to the present invention.

FIG. 4 is a perspective view showing an optical member according to the present invention.

FIG. 5 is a partially enlarged view of FIG.

FIG. 6 is a projection view onto a horizontal plane showing an optical path of a focus detection system of the present invention.

FIG. 7 is a projection view onto a vertical plane showing an optical path of the focus detection system of the present invention.

FIG. 8 is a diagram illustrating a conventional example.

FIG. 9 is a diagram illustrating a conventional example.

FIG. 10 is a diagram illustrating a conventional example.

FIG. 11 is a diagram illustrating a conventional example.

FIG. 12 is a diagram illustrating a problem of the invention.

FIG. 13 is a diagram for explaining the problems of the invention.

FIG. 14 is a diagram illustrating a problem of the invention.

FIG. 15 is a diagram illustrating a problem of the invention.

[Explanation of symbols]

 1 Objective Lens 2,8,31,31 'Field Mask 3,9,32,32' Field Lens 4,11 Secondary Optical System 5,12,35,35 'Sensor 6,10,33,33' Aperture 7 Objective Exit pupil of lens 13 to 17, 41 to 44 Field of view mask opening 18 to 22, 81 to 84 Sensor array 34, 34 'Optical member 36 Image area on sensor 45 to 48, 45' to 48 'Field of view 55 to 55 58 luminous flux 71-74 lens 75-78 center line of lens pair 75'-78 'boundary line of lens pair 101-103 prism member 107 projecting member 108 prism member surface 109 normal vector 110 arrow 111 indicating the viewing direction 111 perpendicular to the viewing field Arrow indicating the right direction 112 Optical axis

Claims (3)

[Claims] 1. An image formed by a field mask, which is arranged near the planned image forming surface of the objective lens and regulates a visual field region, a field lens which is also arranged near the planned image forming surface of the objective lens, and an objective lens. A secondary imaging lens for reimaging
A diaphragm having a pair of apertures for restricting light passing through the secondary imaging lens, a secondary imaging system including a sensor array for detecting a light amount distribution formed by the secondary imaging lens, and an objective lens In a focus detection system capable of performing focus detection on a field area having a spread in a certain direction outside the optical axis of, the direction of expansion of the field area is a virtual line passing through the center of the field area including the optical axis of the objective lens. The pair of secondary imaging lenses, which are not orthogonal to the plane, alleviate the difference in the optical path length of the light flux passing through each lens and alleviate the angle change due to the refraction of the light rays entering or exiting each lens. A focus detection device having an optical member. 2. The optical member is a prism member provided on one of an entrance surface and an exit surface of a pair of secondary imaging lenses, and the prism member extends in the direction of expansion of the visual field region. And a plane determined by a normal vector having a component also in the vertical direction, and regions corresponding to the pair of secondary imaging lenses have steps and are not on the same plane. The focus detection device according to 1. 3. The pair of secondary imaging lenses have an asymmetrical shape when viewed from the front.
The focus detection device described in.