JP2012242416A - Focus detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus detection device which achieves miniaturization while reducing an influence of stray light resulted from reflection of light on a light receiving element on a focus detection result.SOLUTION: A focus detection device divides light flux having passed through an image lens and detects a focus state in accordance with relative position relations among a plurality of optical images formed by the divided light flux. The focus detection device comprises: a photoelectric conversion element which receives the light flux and converts the same into an electric signal; a high reflectivity section which is arranged on a surface of the photoelectric conversion element, has a first reflectivity and receives the light flux; a low reflectivity section which is arranged in a region of the optical images on the surface of the photoelectric conversion element and has a second reflectivity lower than the first reflectivity; and an optical member which transmits the light flux and is not in parallel with the photoelectric conversion element. At least a portion of stray light reflected at the low reflectivity section reaches the high reflectivity section after being reflected by the optical member.

Description

  The present invention relates to a focus detection apparatus.

  With the widespread use of imaging devices represented by digital cameras and video cameras, higher quality and smaller size are increasingly required for imaging devices. In particular, high accuracy and downsizing of a focus detection device that detects the focus state of an imaging lens (imaging optical system) of the imaging device are desired. In recent years, a TTL phase difference method has been used in which the pupil of the imaging lens is divided into a plurality of regions, and the focus state of the imaging lens is detected from the relative positional relationship of a plurality of optical images formed by the light flux that has passed through each region. Focus detection devices are becoming mainstream.

  For example, Patent Document 1 discloses a countermeasure method for stray light generated in a focus detection device for the purpose of improving the accuracy of the focus detection device. In Patent Document 1, stray light in the target focus detection apparatus is reflected again on a parallel plate arranged before the light receiving element, and is reflected again as stray light on the light receiving portion of the light receiving element. To reach. By arranging the stray light generated in this manner with the parallel plate inclined, the optical path when the stray light is reflected by the parallel plate is controlled so that the stray light does not reach the light receiving element.

Japanese Examined Patent Publication No. 7-104478

  However, the conventional technique disclosed in Patent Document 1 has the following problems.

  In recent years, the focus detection apparatus has expanded the focus detection range within the photographing range as the functions thereof have increased. In Patent Document 1, a parallel plate having an infrared cut function is generally arranged on the imaging surface of the photographing lens. However, when the same arrangement is performed in a recent focus detection device, the focus detection range is expanded. The parallel plate also needs to be enlarged. For this reason, in recent focus detection devices, a parallel plate having an infrared cut function is disposed in the vicinity of the aperture opening of the focus detection device, thereby realizing a reduction in size of the parallel plate. When the technique described in Patent Document 1 is applied with such an arrangement of parallel plates, the distance between the light receiving element that is the source of stray light and the parallel plates is narrow. Therefore, in order to avoid stray light from reaching the light receiving element again, it is necessary to tilt the parallel plate more greatly than when the parallel plate is arranged on the imaging surface of the photographing lens, and the focus detection device is enlarged. Leads to.

  On the other hand, due to the expansion of the focus detection range, the range of the light receiving portion on the light receiving element tends to be expanded. For this reason, the thickness of the light beam reaching the light receiving element is also increased, and more stray light is generated. In such a situation, when the technique described in Patent Document 1 is applied, in order to cause the stray light beam to reach a stray light beam outside the light receiving range of a wider range of light receiving elements, the parallel plate is inclined more greatly. This leads to an increase in the size of the focus detection device.

  Some recent focus detection apparatuses have a cross-type focus detection region. This has two pairs of optical systems in directions substantially orthogonal to each other, and performs focus detection corresponding to the contrast of the subject in the vertical and horizontal directions. In a focus detection apparatus having a cross-type focus detection region, when the technique described in Patent Document 1 is applied, reflected light from a parallel plate is detected by a light receiving element against stray light generated in each of two pairs of optical systems. The inclination of the parallel plate must be set so as not to reach. This also makes it necessary to tilt the parallel plate more greatly, leading to an increase in the size of the focus detection device.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a focus detection device that achieves downsizing while reducing the influence of stray light generated by reflection of light on a light receiving element on a focus detection result.

  In order to achieve the above object, the present invention divides a light beam that has passed through an imaging lens, and detects a focus state according to the relative positional relationship of a plurality of optical images formed by the divided light beam. A detection device, the photoelectric conversion element that receives the light beam and converts it into an electrical signal, and a high reflectance part that has a first reflectance on the surface of the photoelectric conversion element and receives the light beam; A low reflectance part having a second reflectance lower than the first reflectance, disposed in a region of the optical image on the surface of the photoelectric conversion element; and transmitting the light flux; and the photoelectric conversion element; And at least a part of the stray light reflected by the low reflectance part reaches the high reflectance part after being reflected by the optical member.

  According to the present invention, it is possible to reduce the size of the focus detection device while enabling highly accurate focus detection without being affected by stray light generated in the focus detection device.

Central sectional view of a single-lens reflex camera incorporating the focus detection device of the present invention The perspective view of the focus detection apparatus of this invention A plan view of the diaphragm 213 viewed from the field mask 210 side The top view which looked at the entrance plane side and the exit plane side of the secondary imaging lens unit 214 The top view which looked at the light receiving element 216 from the view mask 210 side The back projection of each light receiving element row of the light receiving element 216 on the field mask 210 The figure which shows the example of the optical path of the stray light generated with the light receiving element 216 of this invention The figure which shows the positional relationship of a light receiving element row | line | column and a stray light area | region on the light receiving element 216.

[Example 1]
Hereinafter, an example in which the focus detection device of the present invention according to the first embodiment of the present invention is applied to a single-lens reflex type digital camera with interchangeable lenses will be described.

  FIG. 1 is a central sectional view of a single-lens reflex camera incorporating a focus detection device of the present invention.

  In the figure, 200 is a single-lens reflex camera body, 201 is a photographing lens, and L is an optical axis of the photographing lens 201. An image sensor unit 204 including an optical low-pass filter, an infrared cut filter, and an image sensor is disposed in the vicinity of the planned imaging plane of the photographic lens 201. The photographic 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 photographic 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. Further, part of the light diffused by the focus plate 203 passes through the photometric lens 220 and reaches the photometric sensor 221. On the other hand, the transmitted light changes its optical path downward by the sub mirror 203 and is guided to the focus detection device 208.

  Next, the focus detection apparatus included in the camera described in FIG. 1 will be described. FIG. 2 is a perspective view of the focus detection apparatus 208 of the present invention, and uses phase difference focus detection as a distance measurement principle. Although the actual focus detection apparatus is made compact by folding the optical path with a reflecting mirror or the like, the figure is developed straight to eliminate the complexity of the figure.

  Reference numeral 210 denotes a field mask, which has a rectangular opening 210a at the center. The field mask 210 is disposed in the vicinity of a position equivalent to the planned imaging plane of the photographing lens 201 and the imaging plane of the imaging element unit 204. A field lens 211 is disposed behind the field mask 210. The field lens 211 includes a lens portion 211a having an optical action, and the lens portion has the same lens optical axis as the optical axis L of the photographing lens. The lens portion 211 a corresponds to the opening 210 a of the field mask 210.

  An infrared cut filter 212 removes an infrared wavelength component unnecessary for focus detection. The infrared cut filter 212 corresponds to the optical member in the claims. Reference numeral 213 denotes a stop having a plurality of openings, and reference numeral 214 denotes a secondary image forming lens unit (image forming lens unit) including lens portions corresponding to the plurality of openings of the stop 213. The secondary imaging lens unit 214 re-images the object image on the planned imaging surface imaged by the objective lens 201 on the light receiving element array of the light receiving elements 216 arranged behind the object image. The light receiving element 216 corresponds to the photoelectric conversion element in the claims. The light beam that enters the focus detection device and reaches the light receiving element is the thinnest in the vicinity of the stop 213. Therefore, by arranging the infrared cut filter 212 in the vicinity of the stop, the required area can be minimized, and downsizing and cost reduction can be realized.

  3 to 5 are plan views of each member in the perspective view of FIG. 2, FIG. 3 is a plan view of the diaphragm 213 viewed from the field mask 210 side, and FIG. 4A is the secondary imaging lens unit 214. FIG. 4B is a plan view of the optically effective portion of the secondary imaging lens unit 214 viewed from the exit surface side, and FIG. 5 is a field mask of the light receiving element 216. A plan view seen from the 210 side is shown.

  In FIG. 3, the diaphragm 213 has two pairs of openings 213a-1 and 213a-2, 213a-3 and 213a-4 at the center.

  In FIG. 4A, a prism portion corresponding to the aperture of FIG. 3 is formed on the incident surface side of the secondary imaging lens unit 214. Accordingly, like the diaphragm 213, two pairs of prism portions 214a-1 and 214a-2 and 214a-3 and 214a-4 are formed in the center portion.

  In FIG. 4B, a spherical lens portion is formed on the exit surface side of the secondary imaging lens unit 213 corresponding to the prism portion of FIG. Similarly, two pairs of lens portions 215a-1 and 215a-2, 215a-3 and 215a-4 are formed in the central portion.

  In FIG. 5, a light receiving element array corresponding to the lens portion in FIG. 4B is formed on the light receiving element 216. Two pairs of light receiving element array groups 216av1 and 216av2, 216ah1 and 216ah2 are formed in the central portion. The light receiving element array group 216a is a generalization of the light receiving element array groups 216av1, 216av2, 216ah1, 216ah2. In FIG. 5A, 217 av 1, 217 av 2, 217 ah 1, and 217 ah 2 are optical images formed by the opening 210 a of the field mask 210. Optical images 217av1 and 217av2 are formed by the openings 213a-1 and 213a-2 of the stop 213, and optical images 217ah1 and 217ah2 are formed by the openings 213a-3 and 213a-4. The optical image 217a summarizes the optical images 217av1, 217av2, 217ah1, 217ah2.

  At least a part of the light receiving element array groups 216av1 and 216av2 is arranged inside the optical images 217av1 and 217av2, and at least a part of the light receiving element array groups 216ah1 and 216ah2 is arranged inside the optical images 217ah1 and 217ah2. . The light receiving element array groups 216av1 and 216av2 are composed of three pairs of light receiving element arrays, and the light receiving element array groups 216ah1 and 216ah2 are also composed of three pairs of light receiving element arrays. Details of these light receiving element array groups are shown in FIG. In FIG. 5B, for easy understanding, the light receiving element array is schematically deformed. The light receiving element array group 216av1 includes light receiving element arrays 216av1-1 to 216av1-3, and the light receiving element array group 216av2 includes light receiving element arrays 216av2-1 to 216av2-3. Similarly, the light receiving element array group 216ah1 includes light receiving element arrays 216ah1-1 to 216ah1-3, and the light receiving element array group 216ah2 includes light receiving element arrays 216ah2-1 to 216ah2-3. Each light receiving element array is composed of a plurality of pixels, and an optical image can be extracted as an electrical signal by extracting the output of each pixel as a signal.

  In addition, on the surface of the light receiving element 216, a range other than the light receiving element array is provided with a color filter in order to suppress light reflection. The color filter portion 218 is represented by a hatched portion in FIG. Since the optical image 217a is formed on both the light receiving element array group 216a and the color filter section 218, stray light is generated at the light receiving element array group and the color filter section so that the reflected light affects the focus detection result. Become. In this embodiment, compared with the light receiving element array 216a, the color filter portion 217a is configured with a low reflectance in a wavelength region in which the light receiving element array 216a has sensitivity. The light receiving element array group 216a corresponds to the high reflectance part in the claims. The color filter portion 218 corresponds to the low reflectance portion in the claims.

  In the focus detection apparatus having the above-described configuration, the pair of optical images move toward or away from each other with the defocusing of the photographing lens 201 with respect to the planned imaging plane.

  For example, the optical images inside the pair of optical images 217av1 and 217av2 move in the vertical direction, and this movement is detected by arranging the light receiving element rows in the vertical direction as shown in FIG. That is, the light amount distribution relating to this optical image is detected based on the outputs of the light receiving element array groups 216av1 and 216av2, and is calculated using a well-known correlation calculating means, thereby focusing the pair of optical image intervals associated with the photographing lens 201. Find the amount of change over time.

  If the change amount of the pair of optical image intervals can be known, the relationship between the change amount and the defocus amount of the photographing lens 201 is approximated in advance by a polynomial having the change amount as a variable. The focus amount can be predicted, and the focus of the photographic lens 201 can be detected. In the case of the light receiving element array groups 216ah1 and 216ah2, the basic operation is the same except that the vertical direction described above is changed to the horizontal direction.

  When stray light is generated in the focus detection apparatus and the stray light reaches the light receiving element array, a change occurs in the signal of the paired optical image detected by the light receiving element. In general, stray light is not necessarily generated at the same position with respect to a pair of optical images, but is generated at different locations and at different intensities in each of the pair of optical images. Therefore, a mismatch occurs in the signals of the pair of optical images, and an error occurs when calculating the above-described optical image interval. The error is a cause of stray light affecting the focus detection result.

  The pair of light receiving element array groups 216av1 and 216av2 are suitable for focus detection of a subject having a contrast component in the vertical direction because the light receiving elements are arranged in the vertical direction, while the light receiving element array groups 216ah1 and 216ah2 have the light receiving elements in the horizontal direction. Since they are arranged side by side, they are suitable for focus detection of a subject having a contrast component in the left-right direction. When both are combined, so-called cross-type focus detection is performed that is not affected by the direction of the contrast component of the subject.

  FIG. 6 is a diagram in which each light receiving element row of the light receiving element 216 is back-projected on the field mask 210. Since the field mask is disposed in the vicinity of the planned imaging plane of the photographic lens 201, there is no problem even if FIG. 6 is considered as the planned imaging plane. In the figure, a rectangle 300 indicated by a dotted line that is slightly larger than the field mask 210 is a photographing range by the photographing lens 201, and in the field mask opening 210a, back-projected images 301av1, 301av2, 301ah1, light receiving element rows indicated by crosses, 301ah2 is formed. Since the pair of light receiving element arrays coincide on the planned imaging plane, they are displayed in an overlapping manner. Since the back-projected images 301av1, 301av2, 301ah1, and 301ah2 are light receiving element arrays, the light amount distribution of the subject can be detected in this region. That is, these back-projected images become a so-called cross-type focus detection region. In the present embodiment, as shown in FIG. 6, the focus detection area is arranged so as to have a total of nine points of intersection of three points vertically and three points horizontally within the imaging range 300. By using these intersections as ranging positions used by the photographer, a focus detection device having nine cross-type focus detection areas can be obtained, and the focus detection of the subject in the focus detection areas can be performed. The cross-type focus detection area has two directions in which the spreading directions are orthogonal to each other, so that focus detection can be performed on most subjects regardless of the contrast component direction of the subject.

  Next, a configuration for reducing the influence of stray light on the focus detection result of the focus detection apparatus of the present invention will be described with reference to FIG.

  FIG. 7 is a side view of the focus detection apparatus 208 of the present invention, and shows from the infrared cut filter 212 to the light receiving element 216 when observed from the X-axis direction of FIG. The same components as those in FIG. 2 are shown with the same subscripts.

  As shown in FIG. 7, in the present invention, the infrared cut filter 212 is inclined with respect to the light receiving element 216 with respect to the X axis and the Y axis. The effect obtained by tilting the infrared cut filter 212 will be described. An arrow 401 is a light beam that has passed through the opening 210a of the field mask and is used for focus detection, and represents a typical light beam of the light beam that forms the optical image 217av2, together with the traveling direction of the light. A light beam indicated by an arrow 401 indicates a path of a light beam that reaches substantially the center of the optical image 217av2, and when a vector component is expressed with the coordinate axes in FIG. 7, it does not have an X-axis component. As described above, a certain amount of light is reflected on the surface of the light receiving element group 216av2 on the light receiving element 216 and proceeds in the direction of the arrow 402. Since the normal vector on the surface of the light receiving element 216 also has no X-axis component, the vector component of the arrow 402 also has no X-axis component.

  The light beam again passes through the secondary imaging lens unit 214 and the diaphragm 213, and a part of the light beam is reflected by the surface of the infrared cut filter 212. Since the surface of the infrared cut filter 212 is rotated about the Y axis with respect to the light receiving element 216, the reflected light of the surface of the infrared cut filter 212 has a vector component in the X axis direction along the coordinate axis in FIG. Have. An arrow 403 indicates the direction of the reflected light on the surface of the infrared cut filter 212 and indicates that the light reaches the light receiving element 216 again as stray light. The arrival position of the light beam indicated by the arrow 403 reaches a position that is shifted in both the X-axis direction and the Y-axis direction with respect to the arrival position of the light beam indicated by the arrow 401. The amount of deviation of the arrival position of stray light on the light receiving element 216 in the arrow 403 in the X-axis direction can be controlled by the inclination angle of the infrared cut filter. In the present invention, stray light that is reflected on the surface of the light receiving element group 216 a having a relatively high reflectance on the light receiving element 216 is reflected by the infrared cut filter 212 by tilting the infrared cut filter 212 about two axes. Then, when the light reaches the light receiving element again, it reaches a place other than the light receiving element group. Thereby, the influence of the stray light on the focus detection result is reduced.

  FIG. 8 shows a position where stray light generated by reflection of the light receiving element group reaches the light receiving element again. FIG. 8 is overlaid on FIG. 5B, and the same suffix is used for the same configuration.

  The stray light regions 404av1-1, 404av1-2, and 404av1-3 are reflected by the infrared cut filter 212 when stray light generated by reflection on the surfaces of the light receiving element arrays 216av1-1, 216av1-2, and 216av1-3, respectively. The range reaching the light receiving element 216 again is shown. As described above, since the infrared cut filter 212 is tilted in two axes, the arrival position of stray light is shifted with respect to the light receiving element array position in the X axis positive direction and the Y axis negative direction in FIG. . The stray light generated in the light receiving element arrays 216av1-1 and 216av1-2 reaches the range of the stray light regions 404av1-1 and 404av1-2. At the same time, stray light generated in the color filter unit 218 between the light receiving element arrays 216av1-1 and 216av1-2 reaches between the stray light areas 404av1-1 and 404av1-2, that is, in the vicinity of the light receiving element array 216av1-2. It means to do. As described with reference to FIG. 5B, the surface of the light receiving element 216 of the present invention is color-filtered in a region other than the light receiving element group, and has a lower reflectance than the surface of the light receiving element group. Yes. Therefore, stray light generated in the light receiving element array having a high reflectance as described above does not reach the light receiving element, but stray light generated in the color filter unit 218 having a low reflectance reaches the light receiving element array. By configuring, the influence of stray light on focus detection can be reduced. The same applies to the stray light generated in the light receiving element group 216av2.

  Similarly, for the pair of optical element rows 216ah1 and 216ah2, the infrared cut filter 212 is set such that the stray light regions 404ah1-1 to 404ah1-3 and 404ah2-1 to 404ah2-3 are outside the range of the light receiving element rows. By tilting to the X axis center, the influence of stray light on focus detection can be reduced.

  As described above, a color filter is applied to a region other than the light receiving element array group so as to have a low reflectivity characteristic, and by setting the inclination of the infrared cut filter 212, the light receiving element array having a relatively high reflectivity is set. It is possible to prevent the generated stray light from reaching the light receiving element again. Thereby, focus detection errors due to stray light can be reduced, and highly accurate focus detection can be realized.

  Further, in the present embodiment, by tilting the infrared cut filter 212 about two axes, stray light generated in the pair of light receiving element array groups 216av1 and 216av2 in the vertical direction also becomes a pair of light receiving element array groups 216ah1 and 216ah2 in the horizontal direction. The stray light generated in can also be reduced at the same time.

  Conventionally, a method for preventing stray light reflected and generated on a light receiving element by tilting the infrared cut filter 212 has been disclosed. However, since the entire stray light region (for example, 404av1-1 to 404av) is configured to reach outside the range of the light receiving element array group (for example, 216av1), the infrared cut filter 212 needs to be greatly inclined. It was. In addition, in the focus detection apparatus having both vertical and horizontal focus detection areas as in the present embodiment, the inclination of the infrared cut filter 212 is set so that the stray light area is greatly deviated from the area of the light receiving element array. As a result, the stray light region may overlap another light receiving element array. For example, when stray light generated in the light receiving element array group 216av1 largely deviates in the X-axis direction in FIG. 8 and reaches the light receiving element 216 again, it reaches the light receiving element array group 216ah1 and detects the focus in the horizontal direction. This will affect the focus detection result of the area. In the present invention, since the high reflectance portion and the low reflectance portion are provided on the light receiving element 216, the influence of stray light can be avoided by arranging the infrared cut filter 212 at a smaller inclination angle.

  Further, in this embodiment, for example, stray light generated in the light receiving element array 216av1-1 is configured to reach between the light receiving element array 216av1-1 and the light receiving element array 216av1-2. In this way, by making the light receiving element array region and the arrival region of the stray light generated there substantially adjacent, the inclination angle of the infrared cut filter 212 can be minimized, and a large space is required in the focus detection device. The infrared cut filter 212 can be arranged without need.

  In the above description, stray light reflected and generated by the light receiving element 216 controls the range of the light beam that reaches the light receiving element 216 again by the inclination of the infrared cut filter 212, but the present invention is not limited to this. Other optical components including the secondary imaging lens unit 213 can obtain the same effect by setting the tilt in the same manner.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

200 SLR camera body 208 Focus detection device 212 Infrared cut filter 216 Light receiving element 216av1, 216av2, 216ah1, 216ah2 Light receiving element row group 218 Color filter unit

Claims (3)

A focus detection device that divides a light beam that has passed through an imaging lens and detects a focus state according to a relative positional relationship between a plurality of optical images formed by the divided light beam,
On the surface of the photoelectric conversion element that receives the luminous flux and converts it into an electrical signal, and on the surface of the photoelectric conversion element, has a first reflectance, and on the surface of the photoelectric conversion element that has the first reflectance and receives the luminous flux A low reflectance part having a second reflectance lower than the first reflectance, and an optical member that transmits the light flux and is disposed non-parallel to the photoelectric conversion element; Have
At least a part of the stray light reflected by the low reflectance part is reflected by the optical member and then reaches the high reflectance part. The beam splitting is performed on the photoelectric conversion element in first and second directions orthogonal to each other, and the optical member rotates in both the first direction and the second direction. The focus detection apparatus according to claim 1. The focus detection apparatus according to claim 1, wherein the high reflectivity part and the low reflectivity part are arranged adjacent to each other in a direction orthogonal to the light beam splitting direction.

Images