JPS58106511A - Focusing detecting optical system - Google Patents

Abstract

PURPOSE:To make a focusing optical system small-sized in an image shifting system which has used a secondary image-forming system, by providing a relay image-forming system for reducing an image on a prearranged image-forming surface and forming an image on a photoelectric element train. CONSTITUTION:On a prearranged image-forming surface of a photographic lens, or its conjugate position, a field lens 13 is provided, and luminous fluxes la, lb from the photographic lens pass through an opening 11 of a mask plate 12 and form an image on the field lens 13, the luminous fluxes which have passed through the field lens 13 are reflected by a prism 14, advance to secondary image-forming lenses 16a, 16b from the opening of the second mask plate 15, also are reflected by a prism 17, and form an image on CCD line sensors 18a, 18b. The secondary image-forming lenses 16a, 16b reduce an image in the slit 11 of the prearranged image-forming surface, to about 1/2 and form an image on the line sensors 18a, 18b, therefore, as for the licenser, the shortest one in its length can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical system for detecting focus using an imaging light beam from a photographing lens in a -eye reflex camera or the like.

Conventionally, this type of focus state detection device is broadly classified into two types: a method that detects blurring of an imaging light beam, and a method that detects a shift between two images using a special optical system. In the latter image shift detection method, a so-called secondary imaging method in which an image formed on a plane conjugate to a planned image formation plane such as a film surface is guided to a sensor by a relay imaging system and image shift is detected is used, for example, as disclosed in Japanese Patent Laid-Open No. 55 -118019, JP 55-124112, JP 55-1
Various proposals have been made, such as in Publication No. 5533.1. However, compared to the former blur detection method, the image shift detection method using the secondary imaging method requires a larger overall optical system, and -
It has not yet been possible to incorporate this into a camera with high space utilization efficiency, such as an eye-flex camera.

The device shown in Fig. 1 is a focus detection optical system disclosed in Japanese Patent Application Laid-Open No. 55-155308, and the entire light splitter including the sensor package is 10 mm x 10 mm x
It is housed within a space of approximately 5 mm. In this optical system, an imaging light beam ρ (only the rays on the optical axis are shown) from an imaging lens (not shown) passes through a quick return mirror 1 whose part is a half mirror or a minute part is a transmission surface, and then passes through a submirror. 2 and is deflected downward by the light splitting element 3
incident on . This light splitting element 3 divides the imaging light beam ρ into three parts, which enter three CCD line sensors 4a, 4b, and 4C while having a mutual optical path length difference. Here, the central line sensor 4b is located at a position conjugate to the intended imaging plane, that is, the film plane. Therefore, the line sensor 4a receives images at three different positions in the optical axis direction of the imaging light beam, in front of the planned image plane, and the line sensor 4C at the rear, and evaluates the degree of blurring of the image at each position. The image sensor is used to perform comparison processing and find the in-focus position.

When incorporating such a focus detection optical system into a single-lens reflex camera, the easiest place to install it is below the quick return mirror box.

In the blur detection method, since image information is detected at the planned focal plane and two points before and after it, the optical path length along the optical axis becomes somewhat longer, but the longer optical axis must be deflected laterally. Bye. For example, FIG. 2 shows an image shift detection method using a secondary imaging method disclosed in Japanese Unexamined Patent Publication No. 55-118019. A part of the light beam ρ that has passed through the photographing lens 6 passes through the quick return mirror 1 and is reflected downward by the submirror 2, passes through the field lens 7, and is laterally deflected by the reflection mirror 8. The deflected light flux passes through a pair of relay lenses 9 and reaches a photoelectric element 10. As described above, since the secondary imaging method requires at least two stages of imaging optical systems, a normal method has been used. Therefore, miniaturization is quite difficult.

The purpose of the present invention is to miniaturize the focusing optical system in the image shift method using the secondary imaging method, use a shorter line sensor without sacrificing accuracy, and simplify the implementation of the camera. The purpose is to provide an optical system for focus detection, the gist of which is to provide a field lens at a predetermined image formation plane of a photographing lens or a position conjugate to the predetermined image formation plane, and to detect an image formed on or near the field lens. , in a focusing device that is guided onto a photoelectric element array by at least one pair of relay imaging systems and determines the in-focus state from the output signals of the two series of photoelectric element arrays, the relay imaging system is configured to This method is characterized in that the above image is reduced in size and formed on the photoelectric element array.

The present invention will be explained in detail based on the embodiment shown in FIG. 3 and below.

In general, in image shift detection systems, in order to reduce the length of the entire system, either a reduction system or an expansion system is selected as the secondary imaging system. However, when a magnifying system is used, the required length of the line sensor increases, making it unsuitable as a compact system. Also, while keeping the length of the entire system constant,
Using an enlargement system causes problems in mounting on the camera.

Fig. 3 is a developed view of the focus detection optical system using a 1-magnification secondary imaging system, where A is the pupil position of the photographing lens, B is the intended imaging plane, and C is the secondary imaging lens. is the plane on which D is placed, and D is the position of the line sensor surface. If the total length a+b of the secondary imaging system is constant, and the secondary imaging lens placed on the 0 plane is an enlargement system, then a
Must be <b. Then, the image of the pupil of the photographic lens on surface A by the field lens placed on surface B becomes C.
smaller than that on the surface. In other words, the imaging magnification of the pupil by the field lens becomes smaller, which requires stricter accuracy in the assembly position of the secondary imaging lens. Furthermore, the amount of deviation Δ of the optical axis of the secondary imaging lens becomes smaller, making it difficult to process the secondary imaging lens. Therefore, the present invention realizes a compact optical system by making the secondary imaging system a reduction system.

FIG. 4 is a configuration diagram of the secondary imaging system, in which a first mask plate 12 having a slit 11, a field lens 13, a first mask plate 12 having a slit 11, a field lens 13, etc. , a first triangular prism 14 that deflects the optical path, a second mask plate 15 having an aperture, and a first triangular prism 14 that deflects the optical path. Second
secondary imaging lenses 16a, 16b, and a second lens for deflecting the optical path.
A sensor board 19 having a triangular prism 17 and first and second CCD line sensors 18a and 18b is arranged. The first mask plate 12 is located near the intended imaging plane,
The length of the slit 11 is about 4 mm. Luminous flux ρa, β
b is imaged onto the field lens 13 via the first mask plate, and this field lens 13 is designed to form images of the secondary imaging lenses 16a and 16b onto the photographing lens. The light beam that has passed through the field lens 13 is reflected and deflected by the metal reflective surface 20 of the first triangular prism 14, and then enters the secondary imaging lenses 16a and 16b into a light beam ρa.
, ρb, and is further reflected by the reflecting surface 21 of the second triangular prism 17 to form the CCD line sensors 18a, 18b.
Form an image on top. The secondary imaging lenses 16a and 16b are designed to reduce the image within the slit 11 on the intended imaging plane to approximately 1/2 and form the image on the line sensors 18a and 18b. Therefore, the length of each line sensor is approximately 2 mm, which is the length of the slit 11 divided into two, and the total length of both is 4++
It only requires around u++, and it becomes possible to use a short line sensor.

FIG. 5 is a developed optical system related to the secondary imaging system of FIG. 4. The length of the slit 11 of the first mask plate 12 is Wl,
The deviation of the optical axis of the second secondary imaging lens 16a from the optical axis of the field lens 13 is ×2, and the second line sensor 18
If the distance between the center of b and the optical axis of the field lens 13 is Xd, and the length of the second line sensor 18b is Wd, then Wd= (b/a) *Wi - * a *
(1) Xd=X2 fist(a+b)/az(2). Since the smaller the gap between the line sensors 18a and 18b, the more efficient the sensor is used and the more compact the system is, it is ideal if Xd=Wd/2. (1
), From equation (2), x2 in this case is X2=b・W
i/(2(a+b)) +1(3).

In Figure 5, Wi = 4mm, field lens 13
and the distance 111a between the secondary imaging lenses 16a and 16b is 10
mm, and if the distance gb between the secondary imaging L/7 lenses 16a, 16b and the line sensors 18a, 18b is 5 mm, then X2=0
．． It becomes 667mm. The total length of the secondary imaging system at this time is a
+b=15 mm, resulting in an extremely compact optical system. In addition, the focal length of the secondary imaging lenses 16a and 16b is 3.33 mm) 6. In particular, as shown in FIG.
．． By bending at 17, a practical size for mounting the camera can be obtained. Further, if the condition of equation (3) is satisfied at this time, the line sensors 18a and 18b may be connected without any gap, which is extremely convenient for mounting. In FIG. 4, the relationship between the second mask plate 15 having an opening and the first and second secondary imaging lenses 16a, 16b is shown in FIG. 6 when viewed from a direction perpendicular to the mask plate 15. It is as shown. In this FIG. 6, the secondary imaging lenses 18a and 1
6b is in contact with the boundary line S. On the second mask plate 15, there is a circular opening 2 formed by combining semicircular openings 22a and 22b.
2 is provided. The diameter d of the aperture 22 is set to be large enough to sufficiently transmit the light through the pupil of the photographic lens when the aperture 22 is back-projected toward the photographic lens. By the way, the brightness of the photographic lens is F5°6, and the distance from the exit pupil position A to the imaging plane B in Fig. 3 is 70 mm.
When the air-equivalent optical path length from the field lens 13 to the first mask plate 15 in FIG. 4 is 10 mm, and the focal length of the field lens 13 is 8.75 mm, the second Since the image diameter on the mask plate 15 is 1.79 mm, the opening 2 on the mask plate 15 is
It is calculated that the diameter d of 2 is preferably about 1.5+++m.

Generally, the diameter d of the aperture 22 is d (exit pupil diameter of the photographic lens x imaging magnification of the field lens 13), but in reality, the focal length and F number of the lens used in a single-lens reflex camera are There are many, and the diameter d can be determined from the diameter of the farthest exit pupil with the largest F number. In terms of brightness on the line sensor 18a, 18b surface, it is best to make the diameter of the aperture 22 formed by the apertures 22a, 22b correspond to F5.6 when using Fl, 4 photographing lenses. I have too much leeway, so
It is desirable that the aperture 22 has a variable aperture. still,
In FIG. 6, two symmetrical secondary imaging lenses 16a,
The length of the boundary line S in contact with the mask plate 16b may be equal to or larger than the diameter d of the opening 22 on the mask plate 15.

Further, the shape of the opening 22 may be a rectangular opening inscribed in a semicircle. The reason why the size of the aperture 22 is made smaller than the image formed by the field lens 13 at the exit pupil of the photographing lens is because the secondary imaging lens 16 is
When the boundary line S between a and 16b or the boundary line between the opening 22 on the second mask plate 15 deviates from the optical axis of the photographic lens, the line sensors 18a and 18b in FIG. This is because the brightness of the images differs. , ``In Fig. 4, the reflective surface 2 of the triangular prism 14.17
0.21 is the outermost part of the imaging light beam ρ if the reflection surface is made of a metal coating, or if the spread of the imaging light in the cross-sectional view at the end of the quick return mirror 1 and the submirror 2 is set to about F4. The angle that the light ray makes with the optical axis of the photographing lens, that is, the half angle of the light beam at F4 is 7.1°. Here, reflective surface 2
In order to totally reflect the luminous flux ρ at 0, as shown in FIG. When θ≦right angle - half angle of imaging light beam - total reflection angle, it is sufficient that θ is smaller than (90'-7, 1° - θt) to provide a reflective coating on the reflective surface 20. There will be no need. By the way, when the prism 14 is made of acrylic material, the refractive index n of the acrylic material is 1.4.
9, and the total reflection angle θt is sinθt = 1/n
is 42.2°, and it is sufficient if θ is 40.7',
Similarly, the second triangular prism 17 may have a total reflection surface without a reflective coating. .

FIG. 8 shows another embodiment, which is almost the same as the embodiment shown in FIG. 4, except that the field lens 13 and the first triangular prism 14 in FIG. It becomes. Prism lens 2 with this shape
3 can be manufactured in large quantities at low cost by injection molding, and by reducing the number of parts, the number of assembly and adjustment steps can be reduced, which is extremely effective.

FIG. 9 is a cross-sectional view of an optical system according to yet another embodiment,
In addition to the first prism lens 23 in FIG. 8, a pair of first and second secondary imaging lenses 16a, 16b and a second
is integrated with the triangular prism 17 to form the second prism lens 24. In addition, the secondary imaging lens Lea, 16
b may be integrated with the second triangular prism 17 in this way, but may also be provided on the exit surface of the first triangular prism 14, or its power may be transferred to the first triangular prism 17. Second triangular prism 14
．． You may have 17 minutes.

Furthermore, in the embodiment shown in FIG. 10, secondary imaging lenses 16a and 16b are added to the first prism lens 23 in FIG. 9 and integrally molded to form a third prism lens 25. The second mask plate 15 is placed behind this prism lens 25 and the first mask plate 15 is held by the sensor package 26.
, the luminous fluxes ρa and ρb are made incident on the second line sensors 18a and 18b via an infrared absorbing glass 27. Note that 28 is a holder that holds the prism lens 25.

In each of the above embodiments, the secondary imaging system is a 1/2 reduction imaging system, but it is of course possible to use a reduction system other than 1/2. For example, in order to reduce the size of the optical system while being easy to assemble and without reducing the focus detection ability, it is appropriate for the reduction ratio of the secondary imaging system to be about 1/4 to 3/4. Approximately 1/2 is suitable. But 1/ml1! Small type (m
>1), the width of each element sensor of the line sensor is
At the planned imaging plane, the number is multiplied by m, and the pitch at which images are sampled becomes correspondingly larger. In order to prevent this, a line sensor with a correspondingly fine pitch may be used.

As explained in the many embodiments above, the focus detection optical system according to the present invention is an optical system for a focus detection device using an image shift detection method, which conventionally had a thick optical system and was thought to be difficult to incorporate into a camera. The system can be made smaller by making the secondary imaging system a reduced system. Furthermore, if the lens and prism are integrally molded, it becomes possible to further reduce the size, make adjustment easier, and provide the device at a lower cost. In terms of size, the whole thing is approximately 10mm wide x 15mm wide x 10m thick.
m, and an extremely compact optical system for a secondary imaging type focus detection device can be realized.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the main parts of the blur detection method, Fig. 2 is a block diagram of an image shift detection method using a secondary imaging method, and Fig. 3 and subsequent figures are implementations of the focus detection optical system according to the present invention. Figure 3 is an explanatory diagram of the optical system, Figure 4 is a configuration diagram of a secondary imaging system optical system, Figure 5 is a developed optical path diagram of the optical system, and Figure 6 is an aperture. 7 to 10 are diagrams showing the relationship between the lens and the secondary imaging lens, and FIGS. 7 to 1O are configuration diagrams of other embodiments. 11 is a first mask plate, 12 is a slit, 13 is a field lens, 14.17 is a triangular prism, 15 is a second mask plate, 16a and tab are secondary imaging lenses, 18
a and 18b are line sensors, 19 is a sensor substrate, 22 is an aperture, 22a and 22b are apertures, and 23, 24, and 25 are prism lenses. Patent applicant Canon Co., Ltd. Figure 3, r''i is JP-A-58-106511 (6), Figure 6 (4°. 1), 15■ 16b Figure 8, Figure 10, Figure 79-

Claims (1)

[Claims] 1. A field lens is provided at the intended imaging plane of the photographing lens or at a position conjugate to the intended imaging plane, and an image formed on or near the field lens is formed by at least one pair of relay imaging systems. In a focusing device that guides the photoelectric element onto an array of photoelectric elements and determines the in-focus state from the output signals of the two series of photoelectric element arrays, the relay imaging system reduces the image on the planned imaging plane and focuses the image on the photoelectric element array. An optical system for focus detection characterized by forming an image on an array of elements. 2. A field-limiting slit is provided on the field lens, and the imaging light after passing through the field lens is deflected by a triangular prism in a direction approximately perpendicular to the optical axis of the field lens, and a pair of straight boundaries are formed. 2. The focus detection optical system according to claim 1, wherein the optical system is adapted to lead to the relay imaging system. 3. The focus detection optical system according to claim 1, wherein the magnification of the relay imaging system is 1/2 or less.