JPS61295523A - Focus detector - Google Patents

Abstract

PURPOSE:To obtain a compact focus detecting circuit which suits to a single-lens reflex camera and is free from the influence of flare and ghost due to reflection between surfaces of a photographic lens in active AF mode by forming images of entrance pupils of secondary image forming lenses for passive AF and active AF at the exit pupil position of the photographic lens. CONSTITUTION:A microcomputer 41 drives a motor 43 by a lens driving circuit 42 by processing the output of a focus detecting circuit 40, and adjusts the focus of the photographic lens 1. A light measuring circuit 45 measures the brightness of a subject and outputs a signal when the brightness is lower a constant level. When this signal is outputted to the microcomputer 41, the microcomputer 41 enters the active AF mode and makes itself ready to turn on an LED. Then when the active AF mode is entered, the microcomputer corrects focus detection by referring to information stored in a ROM 46. In this case, a stop plate 8 passes only marginal light distant from the optical axis of the photographic lens.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention detects a focus state using light emitted from a light projecting means and reflected from a subject and external light, and then detects a focus position. The present invention relates to a focus detection device.

(Prior Art and its Problems) In general, an important element required for a focus detection device for an eye reflex camera is the ability to adapt to various interchangeable lenses having different open F-numbers and focal lengths.

It is also important to be able to perform focus detection regardless of the brightness of the outside world.

The applicant has proposed a focus detection method that enables focus detection by incorporating an auxiliary lighting device into a strobe and projecting light toward the subject when the outside world is dark (Japanese Patent Application No. 59-261194). and patent application 1986-7686
issue).

FIG. 8(a) shows this focus detection method.

In FIG. 8(a), 51 is a camera body, 52 is a photographic lens, and a subject image is transferred to a focus detection module 5.
3 and automatically performs focus detection and focus adjustment.

The range defined by Su and Si that is symmetrical with respect to the optical axis OA is the focus detection area.

An auxiliary illumination optical system 5 is provided in the strobe 54 that can be attached to this camera, and when it is dark such as at night, illumination light is projected from this auxiliary illumination optical system 55 onto the subject, and the reflected light is used to detect focus. It is configured to do this.

The illumination light is arranged at a distance B away from the optical axis OA of the photographic lens and inclined at an angle θ, and emits light having a spread defined by Ru and R1. OB is the optical axis of illumination light.

In such a focus detection system, as shown in FIG. 8(b), the illumination light illuminates the focus detection area from an angle corresponding to the distance B between the illumination optical system and the focus detection optical system. Illuminable distance range (in Fig. 8(b), L
There is a natural limit to the range shown in the figure from min to L max. If this distance range that can be illuminated is lengthened, the irradiation angle of the illumination light must be widened accordingly, but this has the disadvantage that the subject distance at which focus can be detected becomes shorter. Another major limitation is that focus detection cannot be performed when the strobe is not carried.

On the other hand, Japanese Patent Application Laid-Open No. 54-155832 discloses that a lighting device is built into the camera body, and light is projected onto the subject side through a predetermined limited cross section of the photographic lens, and the light reflected from the subject is It has been disclosed that the light passes through another limited cross section of the photographic lens and is received by a light receiving element to perform focus detection. In this case, the projected light rays are reflected between the surfaces of the photographic lens, causing flare and ghost, so it is important to take countermeasures against this.

On the other hand, Japanese Patent Application Laid-Open No. 57-22210 discloses that the projection light from the light projection means is projected to the outside through a part of the photographic lens,
The light reflected by the subject and returned is received by the photoelectric light receiving means through another area of the photographic lens,
By setting the light emitting optical axis and the light receiving optical axis so that they are not symmetrical on the principal plane of the photographing lens with respect to the intersection of the principal plane and the photographing lens optical axis, inter-plane reflection of the photographing lens can be prevented. The optical system is also shown. However, none of these is suitable for compact storage in a limited space like an eye reflex camera.

Another point to consider when applying this method to single-lens reflex cameras that use various interchangeable lenses is that ghosts and flares may become point symmetrical with respect to the optical axis of the photographic lens due to changes in the configuration or extension amount of the photographic lens. This means that the area in which it will become will change. In addition, in the active automatic focus detection method (hereinafter simply referred to as active AP), which projects light onto the subject from the camera side and uses the reflected light to adjust the focus, the distance at which the focus can be adjusted is Due to its natural limitations, it cannot adequately support photographic lenses with long focal lengths.Passive automatic detection, which has an unlimited detection range, relies on external light to adjust the focus without projecting a projection light for focus detection. It would be wise to consider using it in combination with a focus detection method (hereinafter referred to as passive AP).

Furthermore, in either method, in order to effectively utilize the functions of an eye reflex camera, it is necessary to have the ability to fully adapt to a variety of interchangeable lenses with different aperture f-numbers and focal lengths. In this case, the light-receiving optical axis must face an area extremely close to the photographing lens optical axis.However, if this arrangement is used, as can be understood from the above, flare and ghosts will be prevented during active AF. become more susceptible.

The present invention has been made to solve the above-mentioned problems, and is a compact camera suitable for an eye reflex camera that combines an active AF method and a passive AP method.
Another object of the present invention is to provide a focus detection device b'i that eliminates the influence of flare and ghost caused by inter-plane reflection of the photographing lens that occurs during active ΔF.

(Means for solving the problem) Therefore, in the present invention, a lens system is arranged near the intended image formation point of the photographing lens, and the light transmitted through this lens system is transmitted to the secondary imaging lens for passive AF. , and a temporary diaphragm that allows ambient light to pass through are respectively incident on the secondary imaging lens for active AP, which are arranged in close proximity, and during passive AF, two images are formed by the light rays that pass through the two apertures of the photographing lens. Focus detection is performed by measuring the correlation of active A.
The camera is characterized in that, at F, focus detection is performed by detecting the position of the image of the projected light flux reflected from the subject.

That is, the present invention arranges a lens system near the intended imaging plane of the photographing lens, and arranges a secondary imaging lens for passive AF and a secondary imaging lens for active AP behind it. , for the above passive AP and active AF
The image of the entrance pupil of the secondary imaging lens for active AF is formed at the exit pupil position of the photographing lens, resulting in a compact configuration. A diaphragm plate that only allows light to pass through is arranged to prevent flare and ghost from entering the focus detection means.

(Function) In the present invention, the light projecting means projects light onto the subject from the rear of the photographic lens with the optical axis of the photographic lens removed. A lens system disposed near the intended image formation plane of the photographic lens forms an image of the entrance pupil of the secondary imaging lens for passive AF and active AF at the exit pupil position of the photographic lens. During active AF, the aperture plate allows only peripheral light away from the optical axis of the photographic lens to pass through, and blocks flare and ghosts from entering the light receiving element.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a single-lens reflex camera equipped with a passive focus detection device and an active focus detection device, which is an embodiment of the present invention.

In Fig. 1, l is an exchangeable photographing lens, and 2 is a reflex mirror, which reflects the light that has passed through the photographic lens l toward the finder optical system (not shown), and also transmits some of the light. It also leads to the focus detection optical system S. 3 is a reflecting mirror for that purpose.

The focus detection optical system S will be explained below. 4 is a mask placed near a surface conjugate with the film surface, and 5 is a field lens placed immediately behind the mask.

This field lens 5 serves to form an image of the entrance pupil (calibrated aperture) of a secondary imaging lens 9, which will be described later, into the exit pupil of the photographing lens l. Reference numeral 6 denotes a total reflection mirror for deflecting the direction of the light beam transmitted through the field lens 5. A beam splitter 7 has a semi-transparent surface 7a and a total reflection surface 7b. The semi-transparent surface 7a is configured to transmit visible light and reflect infrared light. 8 is the diaphragm temporary, and the second
As shown in Figure (a), two aperture apertures 8a for passive AF have a roughly elliptical shape.

8b are formed with an interval a left and right, and below these diaphragm apertures 8a and 8b, two diaphragm apertures 8c and 8d for active AP, which also have an elliptical shape, are formed with an interval a left and right. It is formed.

These diaphragm apertures 8a and 8b for passive AF and diaphragm apertures 8c and 8d for active AP have a size b of diaphragm aperture 8a and 8b for passive AF, and diaphragm apertures 8c and 8d for active AF.
If the size of the aperture apertures 8C and 8d is C, then C>b
The lens is configured so that during active AF, the lens focuses on the larger pupil of the photographing lens I than during passive AF.

This is to increase the amount of light that enters the light receiving element during active AP and to lengthen the distance at which focus can be detected. However, in this case, if the photographing lens 1 has a large open I2 value and is dark, a portion of the light rays incident on the diaphragm apertures 8c and 8d may be rejected by the pupil of the photographing lens l. By the way, in passive AF, focus is detected by taking the correlation (phase difference) between two images, but as described later, active AP uses a secondary imaging lens 9.
Since the position of the LED image created by the LED image c (see Fig. 2(b)) is simply detected by the two light receiving elements 10b and 1Oc (see Fig. 2(c)), the above-mentioned problem occurs. Even if this happens, it will not affect focus adjustment in any way.

Reference numeral 9 denotes a secondary imaging lens provided immediately after the two-leg diaphragm 8, and as shown in FIG. A secondary imaging lens 9c is integrally molded. The secondary imaging lens 9a for pan-focus AF converts the light beam transmitted through the aperture aperture 8a into a light receiving element array IOa shown in FIG. 2(C).
The secondary imaging lens 9b similarly images the light beam transmitted through the diaphragm aperture 8b onto the light receiving element array lQa.

The secondary imaging lens 9C for active AF has an aperture aperture of 8
The light beams transmitted through the light receiving elements 10b and 8d are imaged onto the light receiving elements 10b and IOc.

The light receiving element [Oa of the focus detection light receiving element IO is a light receiving element for Pannob AF, and the light receiving elements IOb and IOc are light receiving elements for active AF.

The light-receiving element lOa for the pump ΔF is constituted by a light-receiving element array such as CCl) in order to calculate the elephant H] function. The light receiving elements lOb and IOc for active AF are
L I”: In order to detect the position of the D image,
), the apertures 8c and 8d are arranged in a direction perpendicular to the direction in which the apertures 8c and 8d are arranged.

11 is a total reflection mirror placed behind the photographing lens 1;
The EDI 2 is arranged so that the light projected from the EDI 2 passes through a position G of a planned imaging plane on the optical axis of the photographic lens 1, and forms an angle inclined with respect to the optical axis OC of the photographic lens 1. I2
13 is an LED as a light source for projection, 13 is a projection lens, 14
is a mask, and the light emitted from the LEDI 2 passes through the reflex mirror 2, is reflected and deflected by the total reflection mirror 11, passes through the photographic lens 1, and is projected toward the subject.

The total reflection mirror 11 is linked to the reflex mirror 2, and is retracted from the photographing optical path in conjunction with the movement of the reflex mirror 2 from the finder observation state to the photographing state. Further, +5°1G is a light shielding member.

FIG. 3(a) depicts only the active AP optical system in order to explain the principle and operation of the active AP.

Components that are the same as those in FIG. 1 are designated by the same reference numerals.

Now, assuming that the object 0 is in a position conjugate to the film F, the light projected from the LED t2 is collected by the projection lens I3, passes through the photographing lens I, and is projected onto the object O. As shown above, since the projected light is set to pass through the intersection G (see Figure 1) between the optical axis OC of the photographing lens and the planned imaging plane, the optical axis O of the photographic lens is
It is projected at an angle that intersects C.

The light beam reflected by the object O passes through the photographic lens 1 and then forms an image on the planned imaging plane F at the position oc of the forward axis of the photographic lens. This image is formed between the light receiving element 10b and IOc by the field lens 5 and the secondary imaging lens 9c. Therefore, the output of the light receiving element 1°b and the output of IOc are equal.

On the other hand, when subject 0 is at position P, the projected light forms an image on the subject plane at a distance of I4 from the photographing lens optical axis Oc. After passing through I, an image is formed 4° behind the intended image formation plane, at a distance fi'/h from the optical axis of the photographing lens. This image is formed by the light receiving element T-I by the field lens 5 and the secondary imaging lens 9C.
Image is formed on the OC. Therefore, the output of the light receiving element 10c is greater than the output of the light receiving element 10b.

In this way, the output of the light receiving element 10b and the light receiving element 10
The position of the object O can be known by comparing the output of the image signal C with the output of the image signal C.

Next, the relationship between the projected light flux and the received light flux at the pupil plane 2 of the photographing lens I will be explained.

In FIG. 13(b), 20 and 21 are images of the aperture apertures 8c and 8d formed by the field lens 5 on the pupil plane of the photographing lens l.

On the other hand, 22 is an image of the projected light flux of the LEDI 2 on the pupil plane, which passes through a place that is distanced and eccentric from the optical axis center. The shaded area is the area where flare and ghost occur due to inter-plane reflection of the photographic lens 1 of the projected light flux, and the aperture apertures 8c and 8d are set and arranged so as to exclude this area. By adopting such a diaphragm aperture shape, the influence of flare and ghost can be effectively removed. Further, there is an effect of minimizing a decrease in the light intensity incident on the light receiving element 10b and IOd.

On the other hand, the principle of passive AP is to detect the correlated position of two images created by the subject light beams that have passed through the first and second parts of the photographic lens l that sandwich the optical axis of the photographic lens l. It measures distance. In FIG. 4, the light-receiving element 1 of the so-called front bin fsR31a, in which the image of the object to be focused is formed ahead of the planned focal plane.
Re-imaging 32a and 33a in the area 0a are mutually aligned with the optical axis OC.
, and on the contrary, the re-imaging 32b of the rear-focused image 31b
, 33b move away from each other from the optical axis OC. In the case of focusing, the distance between two mutually corresponding points of re-imaging 32C and 33C of the image 31c has a specific size determined from the configuration of the optical system. Therefore, by converting the light distribution pattern of the image on the light-receiving element 10a into an electrical signal and determining their relative positional relationship, the distance to the object to be zeroed can be determined by combining the bins I and I. .

FIG. 5 is a block diagram showing the focus detection device.

In FIG. 5, 40 is a focus detection circuit, 41 is a microcomputer (hereinafter abbreviated as microcomputer),
The output of the focus detection circuit 40 is calculated and the lens drive circuit 42
The motor 43 is driven to adjust the focus of the photographic lens 1. 45 is a photometric circuit that measures the brightness of the subject and outputs a signal when the brightness is below a certain level. When this signal is output to the microcomputer 41, the microcomputer 41 activates A
Enter F mode and prepare to emit LED light. 4
This is a light projecting optical system including 4 beams and ED. Reference numeral 46 denotes a ROM provided within the photographic lens I, in which various information regarding the photographic lens is stored.

When entering active AF mode, the microcomputer 41
Focus detection is corrected by referring to the chromatic aberration information stored in 46. - Figure 6 shows the relationship between the chromatic aberration of the photographic lens 1 and the wavelength.

As shown in FIG. 7, the vertical axis represents the amount of defocus ΔIf (normally taken with reference to the 589 nm d-line) transmitted through the photographic lens 1, and the horizontal axis represents the wavelength. For example, LEDI2 Assuming that the emission wavelength of is 800 nm, when the chromatic aberration curve of the photographic lens I is (I), the amount of defocus ΔIR becomes ΔIR2, which is the correction amount.The chromatic aberration curves (II) and (II+) are , this is a case where there is dispersion variation in the glass constituting the photographic lens 1, and in this case, the correction amount is 8IR, or ΔIR,
becomes. In general, there is some variation in the dispersion value of glass, so in lenses with a large number of lenses, such as zoom lenses, the variation in bipedal ΔI R can also be
Occurs when it becomes about zm. Therefore, it is desirable that the hlf positive amount ΔIn be adjusted by η for each photographing lens 1. Or, as shown in the graph, for one type of shooting and one lens; nine ΔIR values (ΔIR,, ΔrR2, ΔIf
13), and which Δ
(2) You may decide whether to use the R value or store it in the ROM 46.

(Effects of the Invention) As is clear from the detailed description above, the present invention has the following effects:
The image of the entrance pupil of the secondary imaging lens for BANB ΔF and active AF is formed at the exit pupil position of the photographing lens, and an aperture plate is arranged in the vicinity of the secondary imaging lens for active AP to Since only the light enters the light receiving element, it is possible to obtain a focus detection device that is compact and suitable for clothing reflex cameras, and that eliminates the effects of flare and ghosts caused by inter-plane reflection of the photographic lens during active AF. .

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a camera equipped with a focus detection device according to the present invention, Fig. 2(a), Fig. 2(b), and Fig. 2(
c) is a plan view of the diaphragm plate, secondary imaging lens and light receiving element, respectively, and Figure 3(a) is the active A of the camera in Figure 1.
Figure 153 (b) is an explanatory diagram showing the relationship between the projected light flux and the received light flux on the pupil plane of the photographing lens. Figure 4 is the operation of the camera in Figure 1 during passive AF. An explanatory diagram of the principle, Fig. 5 is a block diagram of the focus detection circuit, Fig. 6 is an explanatory diagram showing the relationship between the photographing lens and chromatic aberration, and Fig. 7 is an explanatory diagram showing the relationship between the photographing lens and chromatic aberration.
The figure is an illustration of the focus shift of the photographing lens due to chromatic aberration.
Figures 8 (, ) and 58 (1) are explanations of the focus detection nostem using a conventional TTL interchangeable lens camera equipped with a focus detection device, a strobe with a built-in auxiliary illumination device, and the illumination distance range using the auxiliary illumination device, respectively. It is a diagram. 7...Beam splitter (7a...semi-transparent surface, 7b
... total reflection surface), 8 ... aperture plate (8a, 8b ... aperture aperture for passive AP, 8c, 8d ... aperture aperture for active AP), 9 ... secondary imaging lens (9a, 9b... Secondary imaging lens for "Passive AI", 9c... Secondary imaging lens for active AF), 10... Light receiving element (10a... Light receiving element for passive AF, IOb, lOc...active AF light receiving element),
II... Total reflection mirror, 12... LED. 13... Light projection lens, 40... Focus detection circuit, 4
1...Microcomputer.

Claims (1)

[Claims] (1) Active automatic focusing that has a light projecting means that projects light from the rear of the photographic lens off the optical axis of the photographic lens, and detects the focus based on the light emitted from the light projecting means and reflected from the subject. This is a focus detection device that performs detection and passive automatic focus detection that detects the focus using external light. The light enters a secondary imaging lens for passive automatic focus detection, and a secondary imaging lens for active automatic focus detection in which a diaphragm plate that allows peripheral light to pass are arranged in close proximity. Focus detection is performed by measuring the correlation between two images formed by light rays passing through the two apertures of the photographic lens, while active automatic focus detection detects the position of the image of the projected light beam reflected from the subject. What is claimed is: 1. A focus detection device characterized in that focus detection is performed using