JPS60120308A - Automatic focus detector - Google Patents

Abstract

PURPOSE:To reduce the size of an automatic focus detector and to improve the precision by projecting and photodetecting luminous flux by the projecting means and photodetecting means of the automatic focus detector of a single-lens reflex camera through roof prism surfaces of a pentagonal prism. CONSTITUTION:Luminous flux L1 from a light source 15 passes through an area 11b on a roof surface of the pentagonal prism 11 and a cut area 12a of a focal plate 12 from a projection lens 16 and is deflected by a quick-return mirror 13 to illuminate a subject S through an area 14a of a photographic lens 14. Reflected luminous flux L3 from the subject S passes through another area 14b of the lens 14 and is deflected by the mirror 13 and then guided to a photodetection lens 18 and a photodetecting element 19 through the cut 12a and an area 11d of the other roof surface 11c of the prism 11. Whether the image on the photodetecting element 19 is in focus or not is detected from its position, and an unshown controller in a figure moves the lens 14 to put the image in focus when the image is out of focus. Consequently, trouble due to the crossing of the pieces L1 and L2 of luminous flux is prevented and the small-sized device is constituted without altering the structure of the single-lens reflex camera greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an automatic reflex camera using a so-called active method in which light is emitted from the camera side toward a subject and the reflected light is received to detect the focus. The present invention relates to a focus detection device.

Various forms of this type of active automatic focus detection device have been introduced in the past, and an example is the TTL type, which emits and receives light through a photographic lens, as shown in Figure 1. are known. In this system, as shown in FIG. 1(a), the optical axis 01 of the light projecting lens 2 that projects the light from the light source 1 also coincides with the light receiving lens 3 of the light receiving system.
The optical axes 02 of the lenses are also arranged parallel to and eccentrically relative to the optical axis O of the photographing lens 4. The light beam L1 emitted from the light source 1 is primarily imaged by the projecting lens 2 onto a plane F that is conjugate with the film surface, and then the photographic lens 4
The light is projected onto the subject S through the. Conversely, the light beam L2 reflected from the subject S forms a primary image in the vicinity of the above-mentioned surface F via the photographing lens 4, and then forms a secondary image in the vicinity of the sensor 5 by the light receiving lens 3.

If the photographing lens 4 is in focus on the subject S, the light beam L1 is projected onto the center of the subject S as shown in FIG. 1(b), and the reflected light beam L2 is reflected from the photographing lens 4 and the light receiving lens 3, a secondary image is formed on the center of the sensor 5.

In addition, in the out-of-focus state, the light beam L1 shifts from the center of the subject S and moves above or below the center of the subject S, as shown in FIG. 1(a) or (c), depending on the state of rear focus or front focus. Since the light is projected, when the reflected light beam L2 is received by the sensor 5 through the photographing lens 4 and the light receiving lens 3, the light receiving position will also be shifted upward or downward. Therefore, sensor 5
For example, a differential sensor consisting of two light-receiving elements 5a and 5b is used, and the position of the received light beam L2 is detected by comparing the amount of light between the two, thereby determining the in-focus, rear-focus, and front-focus states. It is designed to be determined.

This type of TTL active system emits and receives light through the photographic lens 4, so there is no parallax, the lens can be replaced, and it works effectively even when the subject S has low sensitivity. has advantages. but,
It is necessary to provide both a light projecting means including a light source 1 and a light projecting lens 2, and a light receiving means including a light receiving lens 3 and a sensor 5 on the camera side, and they are extremely small due to optical conditions and manufacturing considerations. Since it is difficult to do so, the space required for its arrangement must be considerably large.

On the other hand, the interior of a single-lens reflex camera that must incorporate these components is densely packed with mechanical, electrical, and optical components, so a large space must be secured to install the light emitting means and light receiving means. This is becoming increasingly difficult as cameras become smaller.

An object of the present invention is to solve these problems by rationally arranging the above-mentioned light emitting and light receiving means so as not to interfere with various components inside the camera, and also so as not to cause deterioration of focus detection performance. It is an object of the present invention to provide an automatic focus detection device, the gist of which is to have a light projecting means including a light source and a light projecting lens, and a light receiving means including a sensor consisting of a photoelectric conversion element and a light receiving lens, and to An automatic focus detection device for a single-lens reflex camera that projects light onto a subject and detects the imaging state of a photographic lens by receiving the reflected light by the light receiving means, the light projecting means and the light receiving means comprising: The pentagonal prism is characterized by being arranged so that light is emitted and received through the roof surface of the pentaprism.

The present invention will be explained in detail below based on the embodiments shown in FIG. 2 and below.

FIG. 2 shows a first embodiment of the present invention.
, the arrangement of the quick return mirror 13 and the photographing lens 14 is the same as before, but the arrangement of the light projecting means 17 consisting of a light source 15 and a light projecting lens 16 and the light receiving means 20 consisting of a light receiving lens 18 and a sensor 19 is different from the conventional example. By the way.

That is, the light beam Ll emitted from the light source 15 is transmitted through the area llb of one roof surface 11a of the pentagonal prism 11 by the projection lens 16, and then is primarily imaged near the center of the focus plate 12, and further focused on the quick return mirror 13. The light is deflected by the lens 14, passes through a part of the area 14a of the photographic lens 14, and is projected onto the subject S. Then, the reflected light flux L2 from the subject S is reflected in the other area 1 of the photographic lens 14.
4b, is reflected by the quick return mirror 13, and is primarily imaged near the focus plate 12, and then passes through the area lid of the other roof surface 11c of the pentaprism 11, and is formed by a photoelectric conversion element by the light receiving lens 18. It is adapted to be guided onto a sensor 19. That is, the light projecting means 17 and the light receiving means 20 are the roof surface 11a of the pentaprism 11,
Light is emitted and received through the ie.

In order to distinguish the projected light flux L1 emitted by the light source 15 and the received light flux L2 to be received by the sensor 19 from the photographing light flux, light of a specific wavelength or wavelength range different from the wavelength range that mainly contributes to photographing, such as infrared light, is used. Correspondingly, at least the emitted and received light beam L1. of the pentaprism 11 is used. The roof surface 11a, 11c region 11b, lid through which t2 passes is a semi-transparent mirror with wavelength selectivity that transmits only light of the specific wavelength or wavelength range and reflects light of a wavelength range that mainly contributes to photographing. It has become.

In general, in the TTL active type, when the emitted and received light beams intersect on a boundary surface with different refractive indexes, scattered light is generated by reflection at the boundary surface, and the scattered light is directed onto the sensor along the path of the received light beam. may enter the device and cause malfunction.

In order to avoid such a situation, in the embodiment shown in FIG. 2, the transmitted and received light beam L1. L2 is separated by passing through different regions 14a and 14b in the photographing lens 14, so that scattered light is less likely to occur. Furthermore, in this embodiment, since both the emitted and received light beams L1 and L2 form secondary images near the focusing plate 12, there is a risk that they will intersect and produce similar scattered light, causing malfunctions. In order to avoid this, an idea is taken to cut out the area of the focus plate 12 through which the projected and received light beams L1 and L2 pass, or at least the area 12a through which the projected light beam L1 passes, to make it transparent.

FIG. 3 shows a second embodiment of the present invention, and the drawing shows only the pentagonal prism 11 equipped with a light projecting means 17 and a light receiving means 20, and the other parts are the same as in FIG. It has been omitted for this reason. In the case of FIG. 3, the roof surface 11a of the pentagonal prism 11, the light beam L1.
The projected light beam L1 is made to enter the pentaprism 11 in the area through which L2 passes, and the received light beam L2 is made to enter the pentaprism 1.
In this example, transmission type prism members 21 and 22 are provided as optical members for emitting light from the light source 1 .

In this case as well, the roof surfaces 11 a, 11 of the pentaprism ll
This embodiment is similar to the first embodiment in that the region through which the emitted and received light beams L1 and L2 of c are transmitted is the wavelength-selective semi-transparent mirror described above. However, in this second embodiment, since the light is projected and received through the prism members 21 and 22, the aberration caused by the refraction of the transmitted and received light beams L1 and L2 at the roof surfaces 11a and llc of the pentagonal prism 11 is reduced. This also has the effect of preventing total reflection that may occur when the received light beam L2 exits the roof surface 11c.

FIG. 4 is a partial view similar to FIG. 3 showing the third embodiment, and in this case, the roof surfaces 11a and l of the pentagonal prism 11 are shown.
The prism members 23 and 24 provided on the ie each have at least one reflective surface, and the emitted and received light beams L1 and L
It is designed to deflect the direction of 2. If such reflective prism members 23 and 24 are used, the light projecting means 17 and the light receiving means 20 can be connected to the pentagonal prism 11 (7) as shown in the figure.
) It can be arranged along the roof surfaces 11a and 11c, and the upward bulk caused by the protrusion of the light projecting and light receiving means 17 and 20 can be reduced.

FIG. 5 shows a fourth embodiment, and only shows the pentaprism 11 and prism members 25 and 26 provided on its roof surface 11a and lie. In this embodiment, the upper end surfaces 25a and 26b of the prism members 25 and 26 are curved to have a lens function, so that they can be used as the light emitting and receiving lenses as they are, or as a part of the light emitting and receiving lenses. This is intended to simplify the configuration of the light receiving lenses 16 and 17, save space, and reduce costs.

In the case of FIG. 5, the transmission type prism member 2 shown in FIG.
Although the end surfaces of 1.22 are made into lenses, the end surfaces of reflective prism members 23 and 24 shown in FIG. 4 may be made into lenses. Furthermore, in the embodiment shown in FIG. 4, it is also possible to provide a lens effect by providing a curvature on the reflective surface.

1. As explained above, the automatic focus detection device according to the present invention has the following effects.

(1) Light projecting and light receiving means for focus detection can be provided without significantly changing the structure of a conventional single-lens reflex camera.

(2) Since the upper part of the pentaprism does not interfere with other mechanisms of the camera, the focal length and size of the light emitting/receiving lens can be set relatively freely.

(3) The optical distance from the temporary imaging plane near the focusing plate of the emitted and received light flux to the emitted and received light lens can be shortened compared to other configurations, so compare the bright emitted and received lenses. It can be realized with a small diameter.

(4) The light emitting and light receiving means can be integrated into the same protective member as the pentaprism section together with the pentaprism or its attached finder optical system, and by replacing only the pentaprism section. Cameras that do not have an autofocus function can also autofocus.

2 (5) Since the transmitted and received light beams can be separated, reflected and scattered light of the projected light beam can be prevented from reaching the sensor, thereby preventing malfunctions.

(6) The same malfunctions as mentioned above can be easily prevented by simply making a hole in the center of the focusing plate where the transmitted and received beams intersect and making it transparent. It is possible.

[Brief explanation of the drawing]

Figure 1 (a), (b), and (c) are conventional TTL
An optical layout diagram showing the principle of an active type automatic focus detection device, FIG. 2 and the following shows an embodiment of the automatic focus detection device according to the present invention, FIG. FIG. 2 is a perspective view of a pentaprism section of another embodiment. Code 11 is a pentaprism, lla and lie are roof surfaces,
-12 is a focusing plate, 13 is a quick return mirror, 14
15 is a photographing lens, 15 is a light source, 16 is a light projecting lens, 17 is a light projecting means, 18 is a light receiving lens, 19 is a sensor, 20 is a light receiving means, and 21 to 26 are prism members.

Claims (1)

[Claims] 1. A light projecting device including a light source and a light projecting lens, and a light receiving device including a sensor including a photoelectric conversion element and a light receiving lens, and projects light from the light projecting device to a subject. , an automatic focus detection device for a twin-lens reflex camera that detects the imaging state of a photographing lens by receiving the reflected light by the light receiving means, the light projecting means and the light receiving means being passed through the roof surface of the pentaprism. An automatic focus detection device characterized by being arranged to project and receive light. 2. On the roof surface of the pentagonal prism, there is an optical member for allowing the projected light beam from the light projecting means to enter the pentagonal prism, and an optical member for causing the received light beam to be received by the light receiving means to exit from the pentagonal prism. An automatic focus detection device according to claim 1, further comprising an optical member. 3. The automatic focus detection device according to claim 1, wherein the light source emits light of a specific wavelength or wavelength range different from a wavelength range that mainly contributes to photographing. 4. The area on the roof surface of the pentaprism through which the emitted and received light flux passes is semi-transparent with wavelength selectivity that mainly transmits only light of the specific wavelength or wavelength range. The automatic focus detection device described in . 5. The automatic focus detection device according to claim 2, wherein the optical member provided on the roof surface of the pentagonal prism is a transmission type prism member. 8. The automatic focus detection device according to claim 2, wherein the optical member provided on the roof surface of the pentagonal prism is a reflective prism member. ? , the projected light flux emitted by the light projecting means and the received light flux to be received by the light receiving means are primarily imaged near the focus plate of the camera, and at least a portion of the focus plate through which the projected light flux passes is cut out. The automatic focus detection device according to scope 1. 8. The automatic focus detection device according to claims 5 and 6, wherein the end face of the prism member provided on the roof surface of the pentaprism is given a curvature that acts as a lens. 9. The automatic focus detection device according to claim 6, wherein the reflective surface of the reflective prism member is a curved surface that acts as a lens. 10. The automatic focus detection according to claim 1, wherein the light projecting means and the light receiving means are housed in the same protective member together with the pentaprism, and are configured to be removably attached to the camera body as a single unit. Device.