JP2012133246A - Focus detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus detector capable of removing stray light by a simple structure and enhancing focus detection accuracy.SOLUTION: A focus detector 100 of phase difference system has level differences A to D between lens parts 121, 126 of a center section and lens parts 122, 123, 127, 128 of a peripheral section on the incident side and the emission side of a field lens 120. In a cross section including the optical axis L' of the focus detector and parallel to a direction P in which three openings 111 to 113 of a field mask 110 are aligned, a distance Mbetween a light-shielding mask and an end part 129aof the level difference C on the emission side of the field lens in the optical axis direction of the focus detector is larger than a distance Mbetween the field mask and an end part 124aof the level difference A on the incident side of the field lens in the optical axis direction of the focus detector. At the level difference C of the field lens, the lens part 126 of the center section is projected over the lens part 127 of the peripheral section.

Description

  The present invention relates to a focus detection apparatus.

  In Patent Document 1, a separator extending in parallel to the optical axis is attached to the exit side of a field lens composed of three lens portions to prevent the light beam that has passed through the peripheral lens portion from entering the focus detection sensor in the central portion as stray light. A phase difference type focus detection apparatus is disclosed. However, the separator is difficult and expensive to assemble. Therefore, Patent Document 2 discloses a phase difference type focus detection device in which a light-shielding mask is disposed at a position away from the field lens on the exit side of the field lens in the description of the prior art in order to prevent stray light without using a separator. Is disclosed. There exists patent document 3 as another prior art.

JP 2006-3472 A JP-A-64-49012 Japanese Patent No. 3371500

  However, as described in the prior art of Patent Document 2, this alone is not sufficient for removing stray light. In addition, Patent Document 2 chamfers the end surfaces of the steps of adjacent lens portions as a means for solving the problem so as not to be parallel to the optical axis, but stray light when the focus detection areas are densely arranged. The prevention effect is reduced.

  Accordingly, an object of the present invention is to provide a focus detection apparatus that can remove stray light with a simple structure and increase focus detection accuracy.

  The focus detection apparatus of the present invention is a focus detection apparatus that performs focus detection of a photographic lens with respect to three areas of a photographic screen by a phase difference method, and is disposed in the vicinity of the imaging surface of the photographic lens and corresponds to the area A field mask having three openings and a light-shielding portion, and three lens portions corresponding to the region are respectively provided on the incident side and the exit side, and each of the three lens portions on the entrance side and the exit side is provided. There is a step between a central lens portion and a peripheral lens portion, a field lens for condensing light that has passed through the field mask, three openings corresponding to the region, and the focus detection device A light-shielding mask that extends perpendicularly to the optical axis and shields part of the light that has passed through the field lens, and includes three optical apertures of the field mask including the optical axis of the focus detection device One where parts line up The exit of the light shielding mask and the field lens is greater than the distance in the optical axis direction of the focus detection device between the field mask and the end of the step on the incident side of the field lens closest to the field mask in a cross section parallel to the field mask. The distance in the optical axis direction of the focus detection device to the end of the side step closest to the light-shielding mask is greater in the optical axis direction of the focus detection device, and the center of the step on the exit side of the field lens than the peripheral lens portion The lens part of the part protrudes.

  ADVANTAGE OF THE INVENTION According to this invention, the focus detection apparatus which can remove a stray light with a simple structure and can raise a focus detection precision can be provided.

It is a schematic sectional drawing of the imaging device of this embodiment. It is an expanded partial sectional view of the focus detection apparatus shown in FIG. FIG. 3 is a plan view of the field mask shown in FIG. 2. FIG. 3 is a perspective view of the field lens shown in FIG. 2. FIG. 3 is a plan view of the light shielding mask shown in FIG. 2. It is an enlarged partial sectional view of a field lens for explaining the effect of this embodiment. It is a top view of the aperture_diaphragm | restriction shown in FIG. FIG. 3 is a plan view of the secondary imaging lens shown in FIG. 2. FIG. 3 is a plan view of the focus detection sensor shown in FIG. 2.

  FIG. 1 is a central cross-sectional view of a single-lens reflex digital camera (imaging device) incorporating a focus detection device 100 of the present embodiment. Note that an imaging apparatus to which the focus detection apparatus of this embodiment can be applied is not limited to a digital camera such as a video camera or a silver salt camera.

  In FIG. 1, reference numeral 200 denotes a single-lens reflex camera body, 201 denotes a photographing lens, and L denotes an optical axis of the photographing lens 201. An imaging element unit 204 including an optical low-pass filter, an infrared cut filter, and an imaging element is disposed in the vicinity of the planned imaging plane of the photographing lens 201. The photographing lens 201 and the image sensor unit 204 are provided with a main mirror 202 and a sub mirror 203 that are retracted out of the photographing light beam during photographing by a known quick return mechanism. The main mirror 202 is a half mirror, and the photographing light beam is separated into reflected light guided to the upper viewfinder optical system and transmitted light incident on the sub mirror 203. The reflected light forms an image on the mat surface of the focusing plate 205 having the mat surface and the Fresnel surface, and is guided to the eyes of the observer through the pentaprism 206 and the eyepiece lens group 207. On the other hand, the transmitted light changes its optical path downward by the sub mirror 203 and is guided to the focus detection apparatus 100. L ′ is the optical axis of the focus detection apparatus 100 corresponding to the optical axis L.

  FIG. 2 is a cross-sectional view taken along a plane that includes the optical axis L ′ of the focus detection apparatus 100 and is orthogonal to FIG. 1. That is, FIG. 2 shows an enlarged portion of the focus detection device 100 in a cross section including the optical axis L ′ of the focus detection device 100 and parallel to a direction P in which three openings 111, 112, and 113 of the field mask 110 described later are arranged. It is sectional drawing. The focus detection apparatus 100 is a phase difference type focus detection apparatus that performs focus detection by detecting a phase difference between image signals of two subject images obtained from a pair of pupil regions of the photographic lens 201, and performs automatic focus adjustment ( AF). In the present embodiment, the focus detection apparatus 100 detects the focus of the photographic lens 201 by using a phase difference method for three regions of the photographic screen.

  As shown in FIG. 2, the focus detection apparatus 100 includes a field mask 110, a field lens (condenser lens) 120, a light shielding mask 130, an infrared cut filter 140, an aperture 150, and a secondary connection in order from the incident side along the optical path. An image lens 160 and a focus detection sensor 170 are included.

  FIG. 3 is a plan view of the field mask 110 viewed from the sub mirror 203 side. The field mask 110 is disposed in the vicinity of the planned imaging surface of the photographing lens 201 and is disposed on the incident side of the field lens 120. The field mask 110 includes three openings 111, 112, and 113 and a light shielding portion 114 that extends perpendicular to the optical axis L ′ and shields part of incident light.

  Since the field mask 110 is disposed in the vicinity of the planned imaging plane of the photographic lens 201, the internal areas of the three openings 112, 113, and 114 become focus detection areas in the photographic screen of the camera 200. That is, the opening 111 functions as a focus detection area corresponding to the center of the shooting screen, and the openings 112 and 113 function as focus detection areas corresponding to the peripheral part. Note that the actual focus detection region is a region that is slightly smaller than the opening in consideration of vignetting due to errors in the field mask 110 and the light shielding mask 130, displacement of the field mask 110 from the intended imaging plane, and the like.

  4A and 4B are perspective views of the field lens 120 that collects the luminous flux. FIG. 4A shows the incident surface side on the field mask 110 side, and FIG. 4B shows the exit surface side on the light shielding mask 130 side. Show.

  As shown in FIGS. 2 and 4A, the field lens 120 is divided into three lens portions 121, 122, and 123 corresponding to the three openings 111, 112, and 113 of the field mask 110 on the incident side. Yes. The opening 111 corresponds to the lens part 121, the opening 112 corresponds to the lens part 122, and the opening 113 corresponds to the lens part 123. The direction in which the three lens portions 121, 122, and 123 are aligned is parallel to the direction P.

  There is a step A between the central lens portion 121 and the peripheral lens portion 122, and there is a step B between the central lens portion 121 and the peripheral lens portion 123. The step A has an end surface 124a, and the step B has an end surface 124b. The peripheral lens portions 122 and 123 protrude toward the field mask 110 side (incident side) rather than the central lens portion 121. The direction in which the three lens portions 126, 127, and 128 are aligned is parallel to the direction P.

  On the other hand, as shown in FIGS. 2 and 4B, the field lens 120 is divided into three lens portions 126, 127, and 128 corresponding to the lens portions 121, 122, and 123 on the exit side. There is a step C between the central lens portion 126 and the peripheral lens portion 127, and there is a step D between the central lens portion 126 and the peripheral lens portion 128. The step C has an end surface 129a, and the step B has an end surface 129b. Then, the central lens portion 126 protrudes toward the light shielding mask 130 (emission side) from the peripheral lens portions 127 and 128.

  Since the end surfaces 124a and 124b of the step A and the step B and the end surfaces 129a and 129b of the step C and the step D of the present embodiment are parallel or substantially parallel to the optical axis direction, when viewed from the focus detection sensor 170, the stray light source Is smaller than that of Patent Document 2.

  In FIG. 2, the length of the step A along the optical axis L ′ is larger than the length of the step C along the optical axis L ′, and the length of the step B along the optical axis L ′ is the optical axis of the step D. It is larger than the length along L ′. In other words, the step amount of the field lens 120 is configured such that the exit surface side is smaller than the entrance surface side. Since the steps C and D on the exit surface side of the field lens 120 are small, the area that becomes a stray light source is small.

  As described above, the field lens 120 is divided into the three lens portions of the central portion and the peripheral portions on both sides, and these lens portions are integrally formed.

  In FIG. 2, steps A and B are formed symmetrically with respect to the optical axis L ′, and steps C and D are also formed symmetrically with respect to the optical axis L ′. Therefore, the lengths of the steps A and B along the optical axis L ′ are equal, and the lengths of the steps C and D along the optical axis L ′ are equal.

  The field lens 120 is arranged so as to have an optical power for projecting the aperture 150 in the vicinity of the exit pupil of the photographing lens 201, and a phase difference type focus detection is realized by using a pair of focus detection light beams.

  FIG. 5 is a plan view of the light shielding mask 130 viewed from the field lens 120 side. The light-shielding mask 130 is disposed on the exit side of the field lens 120, and has three openings 131, 132, 133 corresponding to the three lens portions of the field lens 120, and light that passes through the field lens and extends perpendicularly to the optical axis L ′. It is comprised from the light-shielding part 134 which light-shields one part. The opening 131 corresponds to the lens portion 126, the opening 132 corresponds to the lens portion 127, and the opening 133 corresponds to the lens portion 128.

The light shielding mask 130 and the end portion of the step C (or step D) closest to the light shielding mask 130 than the distance in the optical axis direction between the field mask 110 and the end portion of the step A (or step B) closest to the field mask 110. The distance in the optical axis direction is greater. Here, the “distance in the optical axis direction between the field mask 110 and the end portion of the step A closest to the field mask 110” is equal to the surface 114 a on the emission side of the light shielding portion 114 of the field mask 110, as shown in FIG. the distance _{M a} between the end portion 124a ₁ of the end face 124a of the step a. The “distance in the optical axis direction between the light shielding mask 130 and the end portion of the step C closest to the light shielding mask 130” is the incident side of the light shielding portion 134 of the light shielding mask 130 as shown in FIG. and the surface 134a of the distance _{M C} between the ends 129a ₁ of the end face 129a of the step C. In the present embodiment, M _A <M _C is set.

  In this embodiment, stray light is prevented without using a separator that is a partition wall (partition plate) extending in the optical axis direction. The stray light can be divided into a light beam that passes through the lens portion in the peripheral portion and travels toward the center portion, and a light beam that exits from the step.

  In the present embodiment, the light shielding mask 130 is disposed away from the field lens 120 toward the focus detection sensor 217, so that light directed toward the center from the peripheral lens portion of the field lens 120 is caused by the light shielding portion 134 of the light shielding mask 130. Shaded.

  Since the lens portions 121 and 126 at the center of the field lens 120 and the lens portions 122, 123, 127 and 128 at the peripheral portion are formed of different optical surfaces, steps A to D are generated. In general, the field mask 110 and the light-shielding mask 130 are brought close to the field lens 120 so that only the region corresponding to the lens portion is prevented from being exposed to the light beam at the step. A means for opening is used. Conventionally, the light passing through the peripheral lens portion by the separator is prevented from stray light toward the central portion.

  In the present embodiment, the field mask 110 is disposed close to the field lens 120, but the light shielding mask 130 is disposed at a certain distance from the field lens 120 as described above, and therefore stray light caused by a step. A means for shielding or reducing the light is required. In particular, the end (edge) E of the step C is rounded by a sag such as molding to scatter light and become a stray light source. Hereinafter, the step C will be described, but this description also applies to the step D.

  In the present embodiment, in order to prevent stray light, on the side where the focus detection sensor 217 is present, the lens portion 126 at the center of the field lens 120 is closer to the side where the focus detection sensor 217 is located than the peripheral lens portions 127 and 128. It is protruding.

  6A, 6B, and 6C are cross-sectional views for explaining stray light in the edge portion EA, and correspond to enlarged cross-sectional views of the step C in FIG.

  FIG. 6A is an enlarged cross-sectional view in the case where the peripheral lens portion 127A protrudes from the central lens portion 126A and the light-shielding mask is disposed close to the field lens. Light rays are scattered from the end EA serving as a stray light source as indicated by an arrow, and light rays indicated by a solid line can become stray light. However, the stray light is shielded by bringing the light shielding portion 134A of the light shielding mask close.

  FIG. 6B is a cross-sectional view showing a state in which the light shielding mask is separated from the field lens as in this embodiment in FIG. In this case, it can be seen that two of the three stray lights indicated by the solid line arrows are not shielded by the shading part 134 of the shading mask.

  FIG. 6C is an enlarged cross-sectional view of the step C in FIG. As shown in FIG. 6C, when the central lens portion 126 protrudes from the peripheral lens portion 127, the light scattered at the end E does not go to the vicinity of the center of the stop 150 and therefore does not become stray light. .

  Further, in the present embodiment, an area that can be a stray light source is reduced by setting the step amount of the steps C and D to be smaller (than the step amount of the steps A and B).

  The infrared cut filter 140 is a parallel plate glass that cuts infrared light unnecessary for focus detection.

  FIG. 7 is a plan view of the diaphragm 150 having a plurality of openings as viewed from the light shielding mask 130 side. The diaphragm 150 includes four openings 151 a to 151 d corresponding to the opening 131 of the light shielding mask 130, two openings 152 a and b corresponding to the opening 132, and two openings 153 a and b corresponding to the opening 133. The light shielding portion 154 has. The openings 151 a and 151 c are a pair, the openings 151 b and 151 d are a pair, and each pair corresponds to a pair of pupil regions of the photographing lens 201.

  FIG. 8 is a plan view of the secondary imaging lens 160 as viewed from the focus detection sensor 217 side. The secondary imaging lens 160 has four lens portions 161 a to 161 d, two lens portions 162 a and b, and two lens portions 162 a and b corresponding to the aperture of the diaphragm 150. The lens portions 161 a and 161 c are a pair, the lens portions 161 b and 161 d are a pair, and each pair corresponds to a pair of pupil regions of the photographing lens 201.

  FIG. 8 is a view of the exit surface side unlike the case of the diaphragm 150 of FIG. 7, and therefore the lens portion at a position that is vertically inverted with respect to the opening of the diaphragm 150 corresponds. FIG. 8 shows a lens portion on the exit side of the secondary imaging lens, but a lens portion is also formed on the incident side in the same manner as the field lens 120.

  FIG. 9 is a plan view of the focus detection sensor 170 as seen from the secondary imaging lens 160 side. The focus detection sensor 170 includes a photoelectric conversion element unit that photoelectrically converts a subject image formed by the secondary imaging lens 160, and is sealed with a cover glass and a resin layer. The focus detection sensor 170 includes four photoelectric conversion element units 171a to 171d corresponding to the four lens units of the secondary imaging lens 160, two photoelectric conversion element units 172a and 172b corresponding to the two lens units, and two lenses. Two photoelectric conversion element portions 173a and 173b corresponding to the portions are provided. The photoelectric conversion element portions 171a and 171c are a pair, the photoelectric conversion element portions 171b and 171d are a pair, and each pair corresponds to a pair of pupil regions of the photographing lens 201.

  The light fluxes that have passed through the opening 111 of the field mask 110 are the lens portions 121 and 126 of the field lens 120, the opening 131 of the light-shielding stop 130, the infrared cut filter 140, and the openings 151a to 151d of the stop 150, and secondary imaging. It passes through the lens portions 161a to 161d of the lens 160. Then, optical images are formed on the photoelectric conversion units 171a to 171d of the focus detection sensor 170. Thereafter, a processing circuit (not shown) calculates the focus state of the subject image of the focus detection sensor 170, performs focus detection on the three focus detection areas, and outputs an AF signal.

  Unlike Patent Document 1, the focus detection apparatus 100 is configured by a straight optical system that does not have a reflection mirror (reflection member) that turns the optical path between the field lens 120 and the secondary imaging lens 160. That is, the optical axis L ′ is not linearly deflected. Since the straight optical system does not require a reflecting member, the number of parts is reduced, contributing to downsizing and cost reduction and improving focus detection accuracy.

  Further, when there is a reflection mirror, it is easy to mechanically interfere with the reflection mirror and the secondary imaging lens when the light shielding mask 130 is separated from the field lens 120. However, in this embodiment, since there is no reflection mirror, the degree of freedom in arrangement is increased. Has increased. Specifically, it is easy to separate the light shielding mask 130 from the field lens 120 toward the secondary imaging lens 160 so that the steps C and D are not visible from the openings 151a to 151d of the diaphragm 150.

  When the position of the light shielding mask 130 is determined, the angle of the stray light beam that passes through the openings 132 and 133 in the peripheral portion of the light shielding mask 130 and enters the openings 151a to 151d of the stop 150 is roughly determined. The main mirror 202 and the sub mirror 203 are provided with a light shielding member (not shown) that transmits and reflects only an effective light beam necessary for focus detection, and cuts stray light rays.

  As described above, it is possible to provide a focus detection device that prevents stray light and has high focus detection accuracy without using an expensive and difficult-to-assemble separator. The field lens may be divided into three or more.

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist thereof.

  The focus detection apparatus of this embodiment can be applied to an imaging apparatus such as a digital camera.

100 lens unit 124a _1, 129a ₁ end 130 blocking mask 200 imaging device A~D step L 'focal point of the lens portion 122,123,127,128 periphery of the detection device 110 field mask 120 a field lens 121 and 126 central Optical axis of detection device

Claims (4)

A focus detection device that performs focus detection of a photographic lens using a phase difference method for three areas of a photographic screen,
A field mask disposed in the vicinity of the imaging surface of the photographing lens and having three openings and a light-shielding portion corresponding to the region;
Three lens portions corresponding to the region are provided on the incident side and the emission side, respectively, and the center lens portion and the peripheral lens portion of the three lens portions on the incident side and the emission side, respectively. A field lens that collects the light that has passed through the field mask,
A light-shielding mask having three openings corresponding to the region and a light-shielding portion that extends perpendicularly to the optical axis of the focus detection device and shields part of the light that has passed through the field lens;
Have
In the cross section including the optical axis of the focus detection device and parallel to the direction in which the three openings of the field mask are arranged, the field mask and an end of the step on the incident side of the field lens closest to the field mask The distance in the optical axis direction of the focus detection apparatus is greater than the distance in the optical axis direction of the focus detection apparatus and the end portion closest to the light shielding mask of the step on the exit side of the field lens.
The focus detection apparatus, wherein the central lens portion projects from the peripheral lens portion at the step on the exit side of the field lens.   The focus detection apparatus according to claim 1, wherein the optical system including the field lens is a straight optical system.   3. The focus detection apparatus according to claim 1, wherein in the cross section, a step amount of the step on the exit side of the field lens is smaller than a step amount of the step on the incident side of the field lens.   An imaging apparatus comprising the focus detection apparatus according to claim 1.