JP2000338394A - Focus detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a contrast component possessed by an object from being restricted, so that a range-finding result with respect to an object with low contrast can be obtained in a focus detector using a TTL phase difference system, such as a single lens reflex camera. SOLUTION: This focus detector is constituted so that an image on a scheduled image forming surface of an objective lens is separated into plural images and image-formed again by using an image re-forming optical system, and the moving amount of the image formed again on an area sensor 4 for photoelectric conversion is changed in a specified direction in accordance with the focusing condition of the objective lens. In this case, the image re-forming optical system is constituted so that four image re-forming lenses 3 are arrayed in a rectangular state centering an optical axis inside a planar surface perpendicular to the optical axis Z, and the image re-forming lenses adjacent to each other are arranged symmetrically with a horizontal axis or a perpendicular axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection device using a TTL phase difference method, such as a single-lens reflex camera, and more particularly, to a focus detection device that is hardly restricted by a contrast component of a subject.

[0002]

2. Description of the Related Art A conventional passive-type automatic focus detecting device is configured to detect a defocus amount of a photographing lens from a luminance distribution of a subject in only one specific direction. Therefore, focus detection cannot be performed on a subject having no luminance distribution in a direction detectable by the focus detection device.

In order to compensate for the above-mentioned drawbacks and to enable detection of the focus adjustment state of the photographic lens regardless of the appearance or pattern of the subject, Japanese Patent Application Laid-Open No. Sho 62-95511 discloses a photographic lens. An image on the predetermined focal plane is separated and re-imaged into two images using a secondary imaging system, and a relative interval between the two images is changed in a predetermined direction according to a focus adjustment state of the photographing lens. The focus adjustment state of the photographing lens is detected based on a change in output signals of a pair of photoelectric conversion units arranged to receive each of the two images.

[0004]

In a conventional focus detection device using a TTL phase difference method using a line sensor,
Consisting of a pair of re-imaging lenses and a corresponding pair of sensors, focus information can only be obtained from a subject that has a contrast component perpendicular to the re-imaging lens division direction. There was a case.

In the method of separating and re-imaging into two images, cross-shaped line sensors are arranged in the horizontal and vertical directions, and signals obtained from the four images separated and recombined are:
Since they are independent of each other, signal integration processing was not possible. As a result, it is difficult to obtain distance measurement results for low-contrast subjects, and as a result, the optical sensitivity of the automatic focus detection system depends on the sensitivity of the sensor and has a limit. Could not.

[0006] An object of the present invention is to provide a T-lens reflex camera and the like.
It is an object of the present invention to provide a focus detection device using a TL phase difference method, which is hardly restricted by a contrast component of a subject and can obtain a distance measurement result even for a subject having a low contrast.

[0007]

In order to achieve the above-mentioned object, a focus detection apparatus according to the present invention separates and reconstructs an image on a predetermined imaging plane of an objective lens into a plurality of images by using a re-imaging optical system. Statue and
In a focus detection device configured such that a moving amount of an image re-imaged on an area sensor for photoelectric conversion changes in a predetermined direction according to a focus adjustment state of an objective lens, the re-imaging optical system includes an optical system. Four re-imaging lenses are arranged in a plane perpendicular to the axis so that four re-imaging lenses are squarely arranged around the optical axis, and adjacent re-imaging lenses are arranged symmetrically with respect to the horizontal axis or the vertical axis. Features.

In the above-mentioned focus detecting device, the square arrangement of the re-imaging lenses is a square arrangement.

In the above-mentioned focus detection apparatus, signals from two pairs of images in the horizontal or vertical direction among the images re-imaged on the area sensor are integrated.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a focus detection device according to the present invention will be described with reference to the drawings. FIG.
In the focus detection optical system according to the present invention, when the focus detection optical system is incorporated in a single-lens reflex camera, an objective lens is arranged in front of the optical system. In the figure, reference numeral 1 denotes a planned imaging plane position of an objective lens, 2 denotes a condenser lens, 3 denotes a re-imaging lens body, 4 denotes an area sensor, and a photoelectric conversion device such as a CMOS. Here, Z is the optical axis of the imaging system. The aerial image of the subject formed by the taking lens at the predetermined imaging plane position 1 of the objective lens is formed of four re-imaging lenses 3a, 3b, 3 constituting the re-imaging lens body 3.
By c and 3d, re-imaging is performed on each corresponding pixel column of the area sensor 4.

FIG. 2 is a diagram showing an arrangement of the re-imaging lens body 3. The re-imaging lens body 3 has four planes having the same radius of curvature in a plane perpendicular to the optical axis Z. Convex lens 3
a, 3b, 3c and 3d. Each lens is squarely arranged around the optical axis in a plane perpendicular to the optical axis, and adjacent re-imaging lenses are symmetrically arranged on the horizontal axis X or the vertical axis Y. The distance between the optical axes of each lens is the lens 3a
The distance A between 3c and 3b3d is the same distance A, and the lens 3a3
The interval B is the same as the interval B between 3c3d. Where A = B
In the case of, the square array corresponds to the square array.

FIG. 3 shows the area sensor 4 at the time of defocusing.
FIG. 3 is a diagram for explaining image movement on a surface, and includes a re-imaging lens 3a,
In each of the first to fourth quadrants 4a, 4b, 4c, 4d of the area sensor 4 corresponding to 3b, 3c, 3d, an image corresponding to each lens is formed in an oblique direction toward the center of the optical axis. The image is moved in the illustrated predetermined direction according to the focus adjustment state.

The re-imaging lenses 3a, 3b, 3c, 3d
The four images formed on the area sensor 4 surface by
These four images usually have substantially the same shape. Focusing information from an image by the lenses 3a and 3b in FIG.
Focusing information by c and 3d is also substantially the same.

For example, when measuring the distance of an object having a contrast component parallel to the Y-axis direction, lenses 3a and 3b and lenses 3c and 3 capable of detecting the image movement amount Dx in the X direction.
What is necessary is just to perform in combination of d, and the ranging result from each is obtained. By comparing these two distance measurement results relatively, a more reliable distance measurement system can be provided.

Further, as shown in FIG. 4, lenses 3a,
By integrating the signal from each image by the lens 3b and the signal from each image by the lenses 3c and 3d, it is possible to improve the apparent sensor sensitivity, and it is possible to measure the distance even for an object having low contrast. Information can be obtained.

Similarly, for the image movement amount Dy in the Y direction, the combination of the lenses 3a and 3c and the lenses 3b and 3d may be considered, and two distance measurement results are obtained in the same manner as described above. What is necessary is just to perform the integration process. As described above, Dx and Dy can be detected twice in a double manner, and focus detection with higher accuracy can be performed.

The area sensor 4 is a CMOS sensor which can read out a signal for each pixel and can read out an image signal at an arbitrary position. The area sensor 4 independently detects the image movement amount Dy in the y direction and the image movement amount Dx in the x direction, and the pixel rows 4a and 4b.
The focus adjustment of the objective lens is performed so that the image movement amount Dx in the x direction and the image movement amount Dy in the y direction of 4a and 4c have the same value.

In practice, however, the relationship between the defocus amount and the deviation amount between Dx and Dy is obtained by an experiment, stored in the CPU, and enables quick distance measurement. The combination of the two images can be compared by 4a, 4b and 4a, 4c or 4b, 4d or 4c, 4d and 4c, 4a or 4b, 4b.
In addition to d, a more accurate combination such as 4a, 4d and 4a, 4d may be used.

[0019]

As described above, according to the structure of the present invention, focus information can be obtained even for a subject having a contrast parallel to both the X-axis and the Y-axis and a subject having a low contrast. Focus detection with high accuracy becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a focus detection optical system of the present invention.

FIG. 2 is a diagram showing an arrangement configuration of a re-imaging lens body.

FIG. 3 is a diagram illustrating movement of an image on an area sensor surface during defocusing.

FIG. 4 is a diagram for explaining integration of a signal from each image.

[Explanation of symbols]

 1 Planned imaging plane position of objective lens 2 Condenser lens 3 Re-imaging lens body 4 Area sensor Z Optical axis of imaging system

Claims (3)

[Claims] An image on a predetermined imaging plane of an objective lens is separated and re-imaged into a plurality of images using a re-imaging optical system, and the re-imaged image is formed on an area sensor for photoelectric conversion. In a focus detection device configured such that a movement amount changes in a predetermined direction according to a focus adjustment state of an objective lens, the re-imaging optical system includes four re-imaging lenses in a plane perpendicular to an optical axis. Are arranged in a square around the optical axis, and adjacent re-imaging lenses are arranged symmetrically with respect to a horizontal axis or a vertical axis. 2. The focus detecting device according to claim 1, wherein the re-imaging lens has a square array in a square array. 3. The focus detection device according to claim 1, wherein signals from two pairs of images in a horizontal or vertical direction among the images re-imaged on the area sensor are integrated. .