JPS59101610A - Focusing detecting device - Google Patents

Abstract

PURPOSE:To detect exactly a focused position by providing a phase plate in the vicinity of a photodetector train face, correcting a distortion, and making an image forming face coincide exactly with the photodetector train face, in a device for detecting a focused position of an image forming lens. CONSTITUTION:Photodetectors 5A, 5B, 6A and 6B are vertical to a paper surface, are arrayed in parallel to each other and are on the same plane 7. An image forming face 8 of two split luminous fluxes generates a step difference between the two luminous fluxes concerned by a phase plate 4, and also generates a distortion by an aberration, etc. generated generally in a luminous flux splitting means. For instance, in case when photodetector trains 5, 6 are parallel and consist of plural trains, and a distortion of the image forming face 8 is regarded as almost uniform in the direction of the photodetector train, a phase plate 9 is constituted of a face which is uniform in the direction of the photodetector train and whose direction is changed discontinuously, the distortion of the image forming face is nearly corrected only on each photodetector, and an image forming face 10 is obtained. Also, it is not always necessary that the phase plate 9 covers all the photodetector trains, and as a matter of course, the distortion of the image forming face 10 can be corrected in the same way by covering only a part of the photodetector trains.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on a focus detection device using a beam splitting means that effectively splits a beam into two wavefronts in the pupil of an imaging lens using a lens, prism, reflecting mirror, or the like. be. FIG. 1 shows an embodiment in which the beam splitting means is configured by a lens. In the figure, optical image information of three beams divided by two sets of light-receiving element array groups 5 and 6 are detected and compared with each other. The purpose is to detect the focal position of the imaging lens 1. In addition, in FIG. 1, the light receiving element array 5A.

5B, 6A, 6]3 are arranged perpendicular to the paper surface and parallel to each other.

By the way, the photodetector array is often formed on a single semiconductor substrate, so in this case all the photodetectors are on the same plane 7.
It's on top of. On the other hand, the imaging plane 8 of the three beams divided as shown in FIG. A plane parallel to the light receiving element surface 7 is not necessarily formed. For this reason, as shown in Fig. 1, the image formation plane of the three beams and the light receiving element surface accurately match (each part of the image formation plane of the three beams and the corresponding light receiving surface of the light receiving element array group). Therefore, the focusing position detection performance deteriorates. Figure 2 shows a patented phase plate 9, which corrects such distortion of the image plane 8 and correctly aligns the image plane with the plane of the light receiving element array, thereby detecting an accurate focus position, on the plane of the light receiving element array. This is an embodiment of the present invention provided in close proximity. In addition, Fig. 2 shows the phase plate 9.
In this example, the image forming surface is formed by a smooth curved surface so that the image forming surface coincides with the surface of the array of light receiving elements, but a pond structure may be used as long as it has the same effect on light detection. For example, if the light-receiving element array consists of multiple parallel rows and the distortion of the imaging plane 8 can be considered to be uniform in the direction of the light-receiving element array, there is only one row of light-receiving elements in the direction of the light-receiving element array, as shown in Figure 3. The phase plate 9 is a surface whose direction changes discontinuously.
may be configured such that the distortion of the image plane is corrected only on each light receiving element. Furthermore, it is of course not necessary for the phase plate 9 to cover the entire array of light-receiving elements; it is of course possible to cover only some of the arrays of light-receiving elements to similarly correct the distortion of the imaging plane 9. be.

Although Fig. f51 shows an example in which the beam splitter is composed of a lens, it is
7-027179), the present invention has similar effects even when using a beam splitting means having another configuration as shown in FIG.

[Brief explanation of drawings]

FIG. 1 shows an example of a focus detection device and shows how the image plane 8 is distorted. FIG. 2 shows one embodiment of the present invention in which the distortion of the imaging plane 8 is corrected by a phase plate 9, and FIG. 3 shows another embodiment of the present invention in which the phase plate 9 is configured with a surface whose direction changes discontinuously. This is an example. DESCRIPTION OF SYMBOLS 1... Imaging lens, 2, 3... Lens constituting a beam splitter, 4... Phase plate, 5, 6... Light receiving element array group, 5A, 5B... Light receiving element array group 6A, 6B... Light receiving element arrays forming light receiving element array group 6; 7... Light receiving element array surface; ...Phase plate according to the present invention, 1
0...imaging plane corrected by the present invention. Patent applicant Takeomi Suzuki

Claims (1)

[Claims] A beam splitting means consisting of a lens, a prism, a reflecting mirror, etc. effectively divides the beam into two wavefronts at the pupil of the imaging lens, and the optical images of the two divided beams are detected and evaluated by the corresponding light receiving element array groups. In the apparatus for detecting the focal position of the imaging lens by correcting the distortion of the imaging plane in the two-split luminous flux caused by the luminous flux splitting means, the optical image is correctly focused on the light receiving element array surface. What is claimed is: 1. A focus detection device comprising a phase plate provided close to a light-receiving element array surface.