JPS5968711A - Detector for focusing position - Google Patents

Abstract

PURPOSE:To obtain always a signal for detecting the focusing of a photographing lens having a long focal length with simple constitution by stopping down the luminous flux which is made incident to a photodetector for detecting focusing according to the focal length of the lens. CONSTITUTION:When the focal length of a photographing lens 2 is changed, the signal in of a moving command corresponding to the focal length is outputted, and a pair of shielding members 12-1, 12-2 slide a sub-mirror 11, thereby opening and closing the same. When the signal ps for detecting the position of the member 12-1 and the signal in of the moving command coincide roughly, the positions of a pair of the mebers 12-1, 12-2 are determined. The luminous flux which is made incident to the photodetector is thus stopped down. More specifically, the device is so arranged that the luminous flux 1 incident to the focusing detector is adequately stopped down according to the case when the focal length of the lens 2 changes such as with a telephotolens. The focusing detection signal is thus always obtd. with the simple constitution with the photographing lens having a long focal length.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a focus position detection device, particularly for a back-eye camera.

Conventionally, as shown in FIG. 1, a focus position detection device suitable for a camera has been used to detect a predetermined image formation plane (3), and to detect each image formation state before and after the image formation plane. There is a method that includes a total of three light receivers (4t, 5°) for detection, and compares the contrast of the subject light based on the output signals of these light receivers to determine the in-focus state. In FIG. 1, (1) is a light beam of an object, and (2) is a photographic lens, and the lens (2) converges the light beam (1) onto a predetermined imaging plane (3).

FIG. 2 shows a light splitter (
8), in which (7) is a submirror provided behind the quick return mirror (not shown);
(9-/, war 2) is a half mirror constituting the light splitter (8), and (9-3) is a total reflection mirror. (10-
/, 10-2, 70-3) is a light receiver group consisting of a line-shaped sensor such as a CCD array, and these light receiver groups (10-/, 10-x: 1O-3) are They are placed on the front and in front and behind each side.

The above-mentioned focus detection device was disclosed in Japanese Patent Application Laid-Open No. 55-7, No. 330.
g, each receiver (10-/, 10
-2, /0-3) are electrically processed to obtain a contrast value corresponding to the defocus amount as shown in FIG. In the figure, the horizontal axis indicates the amount of extension of the photographic lens (2),
The vertical axis represents each light receiver C70-/.

10-2 and 10-3>, the contrast of the luminous flux (2) at each light receiver position is shown.

And each photoreceiver (10-/, 10-λ.

1O-3), the contrast value obtained from the curve (F, , F2゜F
3) Changes as shown below. That is, each photoreceiver (10-/.

/θ-λ, 10-3>, a higher contrast value was detected as the focus position of the light beam (1) moved to each receiver position, and the focus position of the light beam (1) and the receiver position coincided. In doing so, each receiver detects the peak of the contrast value. Therefore, by comparing the above contrast values, the direction of movement of the lens (2) can be determined, and the lens (2) can be moved accordingly to reach the in-focus position when the light receiver 10-2 detects the peak of the contrast value. .

However, as shown in Fig. 3, although it is possible to know the amount of lens extension and the direction of movement of the lens (2), if the lens (2) is in area B, the relationship between each light receiver position and the focus position of the light beam can be determined. Since the deviation becomes very large, the contrast values detected by each light receiver become very small, making it impossible to compare the respective contrast values and making it impossible to determine the moving direction of the lens (2). Especially when attempting to automatically move the lens (2) to the focusing position using a motor, etc., if contrast values cannot be compared,
This was a serious problem as the motor would become inoperable.

As shown in Figure 9, this problem is solved by various interchangeable lenses. is the difference from the focus position of the lens in a close-up state, that is, the amount of focus movement (V, ~V4
) are different, so if the focal length (0) of the photographic lens is short, the range of the photographic lens will fall within the range shown in Figure 3; however, if the focal length (f) of the photographic lens is long, The extension range of the lens deviates to the region (Bl) in FIG.

Therefore, in order to solve the above problem, the planned imaging plane (3
) The above photoreceiver (11,
Some cameras are equipped with an in-focus signal so that a focus signal can be obtained even if the focus is significantly out of focus. However, in this case, the light splitter (8) must be made larger or have a more complicated structure in order to guide the light beam (1), which is the subject light, to a place far away from the intended image plane (3). ) Also, the receiver (10-/,
In addition to 10-2 and 10-3), it is also possible to add one more receiver, but this would also increase cost and require modification of the light splitter (8). It wasn't a very good method.

The present invention provides a focus position detection method that allows a signal for focus detection to be always obtained even for a photographic lens with a long focal length without modifying the light splitter or changing the light receiver as described above. The aim is to provide equipment.

Examples according to the present invention will be described below.

FIG. S shows a first embodiment. In the figure, (2) is a photographing lens, and (11) is a sub-mirror, which are placed behind a quick return mirror (not shown). The light splitter (8) divides the luminous flux (1) of the subject into the intended image forming plane (3) and the light receivers (10-7, 10-), which are approximately equidistant from each other in front and behind it, 10
-3) Lead to a group. (4/) is a variable resistor, and when a telephoto lens, etc. is attached, the resistor is connected to the pin @ of the lens.
3) The movable contact ('#) moves and the telephoto lens @
A movement command signal (1n) is output that takes into account the focal length of the lens. In addition, instead of the pin (lA3), depending on the focal length of the telephoto lens (dial),
The movable contact (■) may be moved by sliding.

(IIA) is also a variable resistor, and its movable contact ('',
Z'7) is fixed to one of the shielding members Cl2-/, /2-s), and slides as the shielding members (/, 2-/) move, changing the position of the shielding member. The signal corresponding to (
ps).

(K) is a differential amplifier, which inputs the movement command signal (j-n) and the position detection signal (ps), respectively.
A rotation signal (rv) for rotating the motor (4'q) in forward and reverse directions is output. A pair of worms (not shown), which are threaded in opposite directions to each other, are interlocked with the rotating gear (7) of the motor (llwo), and a pair of worms (not shown) are connected to the rotating gear (7)), and a pair of worms (not shown) are connected to the rotating gear (7). The motor (lI
9), the light member (/2-/, /, 2=,
2) It is designed to open and close.

In the above configuration, when the telephoto lens (in) is attached and the focal length of the photographing lens (2) changes, a movement command signal (in) corresponding to the focal length is output, and as a result, the motor (l19) is rotated, and the seven pairs of optical members (/, ! -/ , /2-2) are aligned with the sub-mirror 0.
1) Slide to open and close. And Shiyahikari member (/
2-/ ) When the position detection signal (ps) and the movement command signal (1n) almost match, the output of the differential amplifier IIg becomes a low level, and the rotation of the motor (kura) is stopped. , /The position of the pair of edge light members (/2-/:/2-.2) is determined. This narrows down the light flux that enters the light receiver.

That is, the /pair of optical members (/, 2-/, /2-2> is
When the focal length of the photographic lens (2) changes due to a telephoto lens or the like, its position is automatically switched and the light flux t+1 entering the focus detector is appropriately narrowed down. In addition,
Of course, when the focal length of the lens changes, the /pair of lenses and the optical member (/2-7./2-2> may be manually moved).

Figure 4 is a curve similar to Figure 3, and (C) in the figure shows the extension range of a lens with a short focal length, and the range in which focus detection is possible from infinity to close range with respect to the extension amount. (A)
It's in. In addition, (D) shows the extension range of a lens with a long focal length, and depending on the extension amount, the focus detection range (A) may extend beyond the focus detection range (B).
).

Therefore, when a lens with a long focal length is attached, the effective reflecting part (//-/) of the sub-mirror 01) is 2-.
If the light flux (1) entering the focus detector is narrowed down by limiting 2), the depth of focus will become deeper and the amount of blur will be reduced, so that the light beam detected by each light receiver will be detected as shown in Figure 7. The contrast value is expressed by the curve (Fl'.

F2', F3'), and even if the amount of extension of the photographic lens falls within the region CB), the output signal can be discriminated and focus detection can be performed.

In addition, when the light receiver (10-/, 10-s, 1O-3) is a line sensor, the contrast value detected by the line sensor increases by narrowing the luminous flux i11 in the direction in which the line sensor is arranged. do. Moreover, since it is possible to suppress a decrease in the amount of light compared to stopping down the entire image, it is very effective for shooting low-luminance subjects.

Figure S shows a second embodiment of the present invention, in which (+3) is a submirror, and (/Il-/, /l-3) is a liquid crystal, which becomes a diffusion surface when a voltage is applied, for example. If no voltage is applied, it becomes a totally reflective surface. (/1l-2) is the mirror portion of total reflection. When power is applied to the liquid crystal (/4-/, /1l-3), the mirror part (/l-, 2) of the submirror 0 boils down to each light receiver (10-/, 10-λ).

1O-3), and a part of Mira (/1
-2) only.

FIG. 9 shows a third embodiment of the present invention, in which a movable mask (/&-115-□2) restricts the light flux (1) entering the focus detection device.
) is provided inside the photographic lens (2),
In the figure, the mask enters the photographing optical path and each light receiver (1
0-/, 10-2.1O-3), the luminous flux m is restricted in the line direction.

Note that the diaphragm mechanism shown in the above embodiment may have a wide range of corresponding focal lengths, and may be configured to operate for each zone. That is, for example, f = 3 Q ran or less, f = 700
The aperture mechanism may have three stages of aperture depending on the focal length, such as f=200 to 200 mm and f=200 to 300 f.

In addition, in the embodiments shown in S, g, and 7, if the aperture position is other than the aperture plane that determines the FNO of the photographing lens or its vicinity, when the aperture is stopped down, each light receiver The amount of light at both ends of the line may decrease. As a result, the information at the line ends of each light receiver is not information about the original object, so it is necessary to electrically cut off the information at the line ends or provide an aperture that covers only the line ends.

On the other hand, in FIG. 9, a movable mask (/, ff-115
-, 2) can be replaced, for example, with a liquid crystal mask that is transparent when no voltage is applied and becomes opaque when a voltage is applied, or it is also possible to use an aperture that determines the FNO of the photographic lens. Of course, the aperture may also be used as the aperture that determines the FNO of the photographic lens.

As described above, the present invention provides a camera with interchangeable lenses.
This device narrows down the light flux that enters the focus detection receiver according to the focal length of the lens attached to the camera.Even if the lens attached to the camera has a long focal length, the focus position of the subject light and With an extremely simple configuration, it is possible to prevent a situation where the detection position of the light receiver is greatly misaligned and in-focus detection becomes impossible.

In addition, by restricting the light flux to the line direction of the receiver, it is possible to minimize the decrease in the amount of light entering the receiver, thereby minimizing the decrease in focus detection ability in the case of low-brightness subjects. can.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a conventional focusing position detection device, and Figure 2 is a schematic diagram of a conventional focusing position detection device.
A schematic diagram of the case where the above-mentioned focusing position detection device is incorporated into an eye lens, FIG. 9 is a graph illustrating the relationship between the focal length of the lens and the amount of focus movement, and FIG. 9 is a graph according to the present invention. It is a graph showing the relationship between focus position detection and production. /: Light flux, 2=Photographing lens. 3: (planned) focal plane. Dat5+6: 10-810-2, 70-3: Photoreceiver (photodetector). 7.2-/, /2-2: (Movable) blocking member. /ku/, /'l-2: Liquid crystal. /Left-/,/,! ;-, 2: Movable mask. Patent applicant: Canon Co., Ltd. Agent: Tadashi Wakabayashi Light receiver A1
(From 2, 71 Donore 4 pieces) Torajinto fJ Fig. 3 Fig. 4

Claims (1)

[Claims] +11 A light-receiving means for detecting the sharpness of an image using light from a lens, and means for narrowing down the incident light entering the light-receiving means according to the focal length of the lens. Features a focus position detection device. (2) The focusing position detection device according to claim (1), wherein the light receiving means is a line sensor.The light receiving means is a line sensor. (3) The aperture means is characterized in that the subject light is constricted in one direction of the line sensor.
The focusing position detection device described in ).