JP2020079957A - Focus detection device - Google Patents

Abstract

To obtain a compact focus detection device while ensuring a wide focus detection area.SOLUTION: A focus detection device has, in an optical path order from a photographic lens side, a first mirror, a second mirror, and a third mirror that sequentially reflect a light beam transmitting through the photographic lens, and an AF sensor on which the light beam reflected on the third mirror is incident, wherein the second mirror is located on a subsequent stage of a scheduled imaging surface of the photographic lens located on a reflection optical axis of the first mirror, and a reflection surface of the second mirror is arranged in an inside space of virtual roof surfaces made by a virtual plane including a reflection surface of the first mirror and a virtual plane including a reflection surface of the third mirror.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a focus detection device used for a single-lens reflex camera or the like.

  Conventionally, as a focus detection device mounted on a camera such as a single-lens reflex camera, a device using a so-called phase difference detection method is generally often used (Patent Documents 1 and 2). In a camera equipped with this type of focus detection device, the light flux that has passed through the taking lens is split into two by a main mirror. Specifically, the main mirror reflects part of the light flux (reflected light flux) that has passed through the shooting lens toward the finder optical system, and the rest (transmitted light flux) toward the sub-mirror arranged behind the main mirror. To Penetrate. Then, the transmitted light flux is reflected downward by the sub-mirror and guided to the focus detection optical system (focus detection device) below the mirror box. The focus detection device includes a re-imaging optical system and a focus detection sensor, and the re-imaging optical system includes a condenser lens, a reflecting member, a separator mask, and a separator lens. The phase difference detection method calculates the relative position (phase difference) of a pair of images re-formed on the pair of line sensors of the focus detection sensor, and detects the calculation result as a position shift (defocus amount). This is the method for performing focus detection.

  In recent years, the size of image sensors has increased, and along with this, a wider focus detection area has been desired. If an attempt is made to widen the focus detection area, the image area on the focus detection sensor also becomes large. Therefore, it is indispensable to set a large interval between paired images. For this reason, it is necessary to set the slit spacing of the pair of separator masks or the lens spacing of the separator lens to be large, and as a result, the distance from the condenser lens to the separator mask (or separator lens) along the optical axis is set longer. I have no choice but to do it. This is a factor that leads to an increase in size of the focus detection device.

  In Patent Documents 1 and 2, two (or three) reflecting surfaces are arranged between a condenser lens and a separator lens, and the optical axis is folded back twice (or three times) to downsize the focus detection device. An example is shown.

JP 08-122625 A JP-A-2009-300607

  In order to secure a wide focus detection area, the width of the reflected light flux reflected by the sub-mirror becomes larger, so that the sub-mirror also needs to be made larger. However, since the space from the sub mirror to the image pickup surface (image sensor) is narrow and the shutter and the like are arranged, the size of the sub mirror is limited by these conditions.

  In Patent Document 1, since the light flux transmitted through the main mirror is reflected downward at an angle of 90° with respect to the incident light flux, when the sub-mirror is enlarged in order to secure a wide focus detection area, the sub-mirror interferes with a shutter or the like. There is a problem that it ends up.

  Further, in Patent Document 2, it cannot be said that the constituent members of the focus detection device can be arranged with high space efficiency, and there is a problem that the focus detection device cannot be sufficiently miniaturized.

  The present invention has been made on the basis of the above awareness of the problems, and an object of the present invention is to obtain a compact focus detection device while ensuring a wide focus detection area.

  In one aspect thereof, the focus detection device of the present invention includes a first mirror, a second mirror, and a third mirror that sequentially reflect the light flux that has passed through the photographing lens in the order of the optical path from the photographing lens side, and the light is reflected by the third mirror. A focus detection device including an AF sensor to which the reflected light flux is incident, wherein the second mirror is located at a stage subsequent to a planned image formation plane of the photographing lens located on the reflection optical axis of the first mirror. And the reflecting surface of the second mirror is arranged in an inner space of a virtual roof surface formed by a virtual plane including the reflecting surface of the first mirror and a virtual plane including the reflecting surface of the third mirror. It is characterized by

  A virtual plane including the reflecting surface of the third mirror may intersect with the reflecting surface of the first mirror.

  In another aspect, the focus detection device of the present invention includes a first mirror, a second mirror, and a third mirror that sequentially reflect the light flux that has passed through the photographing lens in the optical path order from the photographing lens side, and the light is reflected by the third mirror. A focus detection device having an AF sensor on which the reflected light flux is incident, wherein the second mirror is located at a stage subsequent to a planned image formation plane of the photographing lens located on the reflection optical axis of the first mirror. That the first mirror is provided so that the optical axis reflected by the first mirror intersects the optical axis of the taking lens at an acute angle, and the second mirror and the third mirror are It is characterized in that the reflection optical axis of the first mirror and the reflection optical axis of the third mirror intersect each other.

  The angle formed by the optical axis incident on the first mirror and the reflected optical axis is α, and the angle formed by the optical axis reflected by the first mirror and the optical axis reflected by the third mirror is θ. At this time, the angle θ may be larger than the angle α.

The angle α and the angle θ may satisfy the following condition (1).
1.1 α<θ<85° (1)

  According to the present invention, it is possible to obtain a compact focus detection device while ensuring a wide focus detection area.

It is a figure which shows a part of optical structure of the camera of one Embodiment. It is a figure which shows the structure of the focus detection unit (focus detection apparatus) of one embodiment. It is a 1st figure with which explanation is given for the relation between angle α, angle θ, and stray light. FIG. 6 is a second diagram for explaining the relationship between the angle α, the angle θ, and stray light. It is a 3rd figure with which explanation of the relation between angle alpha, angle theta, and stray light is offered. It is a figure which shows the state which expanded the mirror of a focus detection unit (focus detection apparatus).

  An embodiment of the focus detection device of the present invention will be described in detail below with reference to the drawings. The focus detection device of the present invention is not limited to this embodiment. The directions (front-back direction, up-down direction) in the following description are based on the respective directions of the arrow lines shown in the drawings.

  FIG. 1 is a diagram showing a part of an optical configuration of a camera of an embodiment. In FIG. 1, a camera (imaging device) 1 has a finder optical system 10, a main mirror (quick return mirror) 20, and a focus detection unit (focus detection device) 30.

  The main mirror 20 is retracted from the mirror-down position (the position shown in FIG. 1) located on the optical axis P1 of the taking lens (not shown) and the optical axis P1 by a rotation drive mechanism (not shown). It is rotationally driven between a mirror-up position (not shown in FIG. 1). The main mirror 20 is positioned on the optical axis P1 immediately after the main mirror 20 when the main mirror 20 is in the mirror-down position, and when the main mirror 20 is in the mirror-up position, A sub-mirror 31 that is retracted from the optical axis P1 is attached together.

  When the main mirror 20 is in the mirror-up position, the light flux of the subject incident from the photographing lens forms an image of the subject on the light receiving surface of the image sensor (not shown). This subject image is converted into electric pixel signals by a large number of pixels arranged in a matrix, and is output to a camera CPU (not shown) as image data. The camera CPU subjects the image data from the image sensor to predetermined image processing, displays this on an LCD (not shown), and stores it in an image memory (not shown).

  When the main mirror 20 is at the mirror-down position, the light flux from the subject that has entered through the taking lens reaches the main mirror 20 along the optical axis P1 of the taking lens. The main mirror 20 is arranged in a state of being inclined by about 45° with respect to the optical axis P1, and a part of the light flux reaching the main mirror 20 is reflected upward by the main mirror 20 and is along the optical axis P2. And advances to enter the finder optical system 10.

  The finder optical system 10 includes a finder screen (focus plate) 11, a pentaprism 13, an eyepiece lens group (loupe optical system) 15, and a cover glass 17. The finder screen 11 forms the light flux of the subject reflected by the reflecting surface of the main mirror 20 as a subject image. The image plane of the finder screen 11 is optically equivalent to the image plane of the image sensor. The pentaprism 13 converts the subject image formed by the finder screen 11 into an upright image (makes it upright). The subject image in the light flux emitted from the pentaprism 13 is magnified by the eyepiece lens group 15, passes through the cover glass 17, and can be observed through a finder window (not shown).

  On the other hand, of the light flux from the subject that has entered through the taking lens, a part of the light flux other than the light reflected upward by the main mirror 20 passes through the main mirror 20 and passes through the optical axis P3 (optical axis P1). Is extended to the rear of the main mirror 20) and is incident on the focus detection unit (focus detection device) 30.

  As shown in FIG. 1, the focus detection unit (focus detection device) 30 includes a sub mirror 31 (first mirror), a housing 32, a condenser lens 33, mirrors 34 and 35 (second mirror, third mirror). It has a separator mask 36, a separator lens 37, and an autofocus (AF) sensor 38. The housing 32 includes a fixed frame 32A for fixedly supporting the condenser lens 33, a fixed frame 32B for fixedly supporting the mirror 34, a fixed frame 32C for fixedly supporting the mirror 35, and a fixed frame 32D for fixedly supporting the separator mask 36. It has a fixed frame 32E for fixedly supporting the separator lens 37.

  The light transmitted through the main mirror 20 and traveling along the optical axis P3 reaches the sub mirror 31. Then, the light flux that has reached the sub-mirror 31 is reflected obliquely downward and forward by the sub-mirror 31 and travels along the optical axis P4.

  The light reflected by the sub-mirror 31 forms an image on the planned image forming surface (primary image forming surface) PL1, and then reaches the condenser lens 33 located on the optical path later than the planned image forming surface PL1. The light that has reached the condenser lens 33 enters from the incident surface 33A, travels inside the condenser lens 33, and is emitted from the emission surface 33B.

  The light emitted from the emission surface 33B of the condenser lens 33 is reflected obliquely upward and forward by the reflection surface 34A of the mirror 34 arranged so as to intersect with the optical axis P4, and travels along the optical axis P5.

  The light reflected by the mirror 34 is reflected by the reflection surface 35A of the mirror 35 arranged so as to intersect with the optical axis P5 toward the diagonally lower rear side and travels along the optical axis P6.

  The optical axes P1, P3, P4, P5 and P6 form a reference optical axis (single optical axis) located in the same reference plane.

  The light reflected by the mirror 35 travels along the optical axis P6 and reaches the separator mask 36. The light that has reached the separator mask 36 passes through a slit (not shown) of the separator mask 36 and then passes through a pair of lenses 37A of the separator lens 37, reaches the AF sensor 38, and forms an image plane of the AF sensor 38. An image is formed on PL2 (secondary image plane).

  The angle α of the angle AG1 formed by the optical axis P3 (P1) and the optical axis P4 is larger than 45° and smaller than 90°. That is, the sub mirror 31 is arranged so that the reflected optical axis P4 of the sub mirror 31 makes an acute angle with the optical axis P1 (P3) of the taking lens. From another point of view, the sub mirror 31 is arranged such that the angle β of the angle AG2 formed with the main mirror 20 is larger than 45° and smaller than 90°. Therefore, the sub mirror 31 is arranged so that the angle γ of the angle AG3 formed with the vertical direction is larger than 0° and smaller than 45°, and the occupied width of the sub mirror 31 in the front-rear direction is small. Therefore, even if the sub-mirror 31 must be enlarged in order to secure a wide focus detection area as the size of the image sensor increases, the shutter or the image sensor immediately after the sub-mirror 31 may interfere with the sub-mirror 31. Can be prevented.

  As shown in FIG. 1, the mirror (second mirror) 34 and the mirror (third mirror) 35 have a reflection optical axis P4 by the sub-mirror (first mirror) 31 and a reflection optical axis P6 by the mirror (third mirror) 35. It is arranged to intersect. The mirror 34, the mirror 35, and the separator mask 36 face the intersection of the optical axis P6 and the optical axis P4, respectively, and are arranged so as to surround the intersection. As a result, the mirror 34, the mirror 35, and the separator mask 36 can be arranged with high space efficiency.

  Further, the angle θ of the angle AG4 formed by the optical axis P4 and the optical axis P6 shown in FIG. 1 is larger than the angle α. As a result, the mirror 34, the mirror 35, the separator mask 36, and the separator lens 37 can be efficiently arranged in the space below the condenser lens 33. Therefore, even when the sub-mirror 31 that reflects at an acute angle is used, The detection unit 30 can be downsized (compact).

  From another perspective, as shown in FIG. 2, the reflecting surface 34A of the mirror 34 is formed by a virtual plane PL3 including the reflecting surface 31A of the sub mirror 31 and a virtual plane PL4 including the reflecting surface 35A of the mirror 35. It is arranged in the inner space of the virtual roof surface PL5. Thereby, the sub mirror 31, the mirror 34, and the mirror 35 can be arranged with high space efficiency.

  Further, in FIG. 2, the virtual plane PL4 including the reflection surface 35A of the mirror 35 intersects with the reflection surface 31A of the sub mirror 31. Thereby, the sub mirror 31, the mirror 34, and the mirror 35 can be arranged with higher space efficiency.

  As described above, the compact focus detection device 30 can be obtained while ensuring a wide focus detection area.

  Here, the relationship between the angle α, the angle θ, and the stray light will be described with reference to FIGS. 3 to 5. FIG. 3 shows a focus detection unit (focus detection device) arranged at an angle α=65° and an angle θ=78°. Further, FIG. 4 illustrates a focus detection unit (focus detection device) arranged at an angle α=angle θ=65°. Further, FIG. 5 shows a focus detection unit (focus detection device) arranged at an angle α=65° and an angle θ=90°. That is, FIGS. 3 and 5 show a state in which the angle θ is larger than the angle α, and FIG. 4 shows a state in which the angle θ is equal to the angle α. Here, in FIGS. 3 to 5, the broken line indicates the effective luminous flux range of the cross section including the light ray passing through the center of the condenser lens 33. Further, in the state where the mirror 34 and the mirror 35 are expanded (FIG. 6), the effective luminous flux ranges are the same in FIGS. 3 to 5.

  The light flux that has passed through the condenser lens 33 also exists outside this effective light flux range. A part of the light outside the effective luminous flux range becomes stray light when reflected by the exit surface 33B of the mirror 34 or the condenser lens 33. When this stray light passes through the separator mask 36 and the separator lens 37 and reaches the AF sensor 38, the focus detection accuracy is significantly lowered, which becomes a problem.

In order to solve this problem, by satisfying the following conditional expression (1), the stray light can be blocked by the separator mask 36 and prevented from reaching the AF sensor 38. In FIG. 3, this conditional expression (1) is satisfied.
1.1 α<θ<85° (1)

  On the other hand, FIG. 4 shows a state in which the angle θ is below the lower limit of the conditional expression (1) (in particular, the state where the angle θ is equal to the angle α). In this case, a part of the light flux reflected by the lower end of the mirror 35 is reflected again by the mirror 34 to become stray light, which passes through the separator mask 36 and the separator lens 37 and reaches the AF sensor 38. Specifically, in the configuration shown in FIG. 4, the angle formed by the dotted line showing the lower effective light flux range reflected by the mirror 35 and the reflecting surface 34A of the mirror 34 is small and easy to approach. Therefore, the reflection angle of the stray light reflected by the mirror 34 also becomes small, and it becomes difficult to block the stray light with the separator mask 36.

  Further, FIG. 5 shows a state when the angle θ exceeds the upper limit of the conditional expression (1) (particularly, a state where the angle θ is 90°). In this case, a part of the light flux reflected by the upper end of the mirror 35 is reflected by the exit surface 33B of the condenser lens 33 to become stray light, which passes through the separator mask 36 and the separator lens 37 and reaches the AF sensor 38. There is. In the configuration shown in FIG. 5, the angle formed by the dotted line showing the upper effective light flux range reflected by the mirror 35 and the exit surface 33B of the condenser lens 33 is small and easy to approach. Therefore, the reflection angle of the stray light reflected by the exit surface 33B of the condenser lens 33 also becomes small, and it becomes difficult to block the stray light with the separator mask 36.

  Here, as shown in FIGS. 1 and 2, the housing 32 is provided with a stray light shielding wall 32F that rises substantially parallel to the optical axis P4 in the vicinity of the peripheral edge of the emitting surface 33B of the condenser lens 33. By this stray light shielding wall 32F, for example, when the angle θ exceeds the upper limit of the conditional expression (1) as shown in FIG. It is possible to reliably block stray light attempting to enter.

1 camera (imaging device)
10 Finder optical system 11 Finder screen (focus plate)
13 pentaprism 15 eyepiece group 17 cover glass 20 main mirror (quick return mirror)
30 Focus detection unit (focus detection device)
31 sub mirror (first mirror)
31A Reflecting surface 32 Housings 32A, 32B, 32C, 32D, 32E Fixed frame 32F Stray light shielding wall 33 Condenser lens 33A Incident surface 33B Emitting surface 34, 35 Mirror (second mirror, third mirror)
34A, 35A Reflective surface 36 Separator mask 37 Separator lens 37A Lens 38 Autofocus (AF) sensor P1, P2, P3, P4, P5, P6 Optical axis AG1, AG2, AG3, AG4 Angle α, β, γ, θ Angle PL1 Planned image plane (primary image plane)
PL2 image plane (secondary image plane)
PL3, PL4 Virtual plane PL5 Virtual roof surface

Claims (2)

Focus detection including a first mirror, a second mirror, and a third mirror that sequentially reflect the light flux that has passed through the shooting lens, and an AF sensor that the light flux reflected by the third mirror enters, in the order of the optical path from the shooting lens side. A device,
The second mirror is located at a stage subsequent to a planned image forming surface of the taking lens located on the reflection optical axis of the first mirror, and the reflecting surface of the second mirror is the same as that of the first mirror. Being arranged in an inner space of a virtual roof surface formed by a virtual plane including a reflecting surface and a virtual plane including a reflecting surface of the third mirror;
A focus detection device. The focus detection device according to claim 1,
A focus detection device in which a virtual plane including the reflection surface of the third mirror intersects with the reflection surface of the first mirror.

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