JPS60192909A - Single-lens reflex camera with focus detection system - Google Patents

Abstract

PURPOSE:To obtain a single-lens reflex camera provided with a compact focusing detecting system of high focusing accuracy by using space around a penta roof prism. CONSTITUTION:After forming an image near the focusing screen 3 of the first image-forming plane of a photographing lens, luminous flux from an object passes through a penta roof prism 4, and taken out from a luminous flux take- out port 4R' of the penta roof prism 4, and splited into two luminous fluxes by a light splitting prism 5, and led on photodetecting elements 9a, 9b by a secondary image-forming lenses 6a, 6b through reflection prisms 7a, 7b and total reflection mirrors 8a, 8b. As the secondary image-forming lenses are provided in a space of subject side of the penta roof prism, the distance between the first image-forming plane and the secondary image-forming lenses can be set properly. Accordingly, specified image-forming magnification can be obtained and accuracy of focusing can be heightened by this optical arrangement.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a single-lens reflex camera having a focus detection system, and particularly to a so-called 'I'TL type focus detection system that performs focus detection using an imaging light beam from a photographic lens. This invention relates to a single-lens 7-lens camera.

A focus detection system conventionally used in single-lens reflex cameras refocuses the object image formed on the first imaging surface into two object images behind the imaging lens, which is the first imaging surface. A secondary imaging system for imaging is arranged, and a light receiving element consisting of a plurality of charge conversion elements is arranged at the second imaging plane position where the object image is formed by the secondary imaging system. A so-called secondary imaging type focus detection system, in which the relative positional relationship is detected by a light receiving element to detect the focus of the photographing lens, has been proposed, for example, in Japanese Patent Application Laid-Open No. 52-95221.

When applying this focus detection system to a single-lens 7-lens camera, the conventional methods were to house the focus detection system at the bottom of the camera via a small mirror placed immediately after the quick return mirror, and to use a half prism near the focus plate. A method was used in which the laser beam was arranged and housed on the exit surface side of the pentagonal roof prism.

In general, in a focus detection system using a secondary imaging method, it is necessary to re-image the object image at a predetermined imaging magnification while maintaining good imaging performance. It is necessary to secure a certain distance to the image plane.

For this reason, the method of storing the camera at the bottom of the camera increases the size of the bottom of the camera in order to ensure a predetermined optical path length, and the method of placing it on the exit side of the pentagonal roof prism requires storing the secondary imaging system near the eyepiece. Therefore, there was a tendency for the area near the eyepiece to become larger.

SUMMARY OF THE INVENTION An object of the present invention is to provide a single-lens, 7-lens camera having a focus detection system that can make the entire camera compact despite using a secondary imaging type focus detection system.

The main feature of a single-lens 7-lens camera equipped with a focus detection system to achieve the object of the present invention is that the object image formed on the image forming surface of the photographic lens is re-focused into two object images behind the image forming surface of the photographing lens. A secondary imaging system for imaging is arranged, a light receiving element each consisting of a plurality of elements is arranged at a position where an object image is formed by the secondary imaging system, and the relative positional relationship between the two object images is determined. In a single-lens reflex camera having a focus detection system that detects the focus of the photographing lens by detecting it with the light receiving element, a light flux extraction port is provided on the object side reflection surface of the penta roof prism, and the secondary imaging system A secondary imaging lens is disposed in a space on the object side of the penta-roof prism, and after extracting a light flux for focus detection from the light flux that has passed through the photographic lens through the light flux extraction port, the secondary imaging lens is This is because the light was guided. In particular, in the present invention, the pupil plane of the photographing lens is divided into pupils by a secondary imaging system,
The relative positional relationship between the two object images formed by the respective light beams on the divided pupil planes is detected using a light receiving element.

Next, embodiments of the present invention will be described with reference to each drawing.

FIG. 1 is an explanatory diagram of an optical system of a focus detection system using a conventional secondary imaging method. In the figure, 31 is the first imaging plane by the photographing lens, and 6a1 and 6b1 are the 2nd imaging plane as the secondary imaging system.
It is a second imaging lens, and re-images the object image formed on the first imaging surface 31 onto the light receiving elements 9a and 9b, respectively. When the imaging position of the object image in the optical axis S direction changes around the first imaging plane 31, the imaging position of the object image changes in the direction perpendicular to the optical axis S. This change is detected by the light receiving elements 9a and 9b. Detection is performed to detect the focus of the photographic lens.

Fig. 1 (N indicates when the object image is formed on the first image forming plane 61 of the planned image forming plane, indicating that the photographic lens is in the focused state. Fig. 1 (B) shows that the object image is When the image is focused on point P, it is the so-called front focus, and at this time, the object image moves in the direction of the arrow on the light receiving elements 9a and 9b compared to the case in FIG. 1(A). ) is when the object image is focused on point Q, which is the so-called rear bin, and at this time the light receiving elements 9a and 9b
The object image on the surface moves in the opposite direction compared to that in FIG. 1(B). Therefore, by detecting the relative positional relationship between the object images at this time using the light receiving elements 9a and 9b, it is possible to determine the in-focus state of the photographic lens. This is because the secondary imaging lenses 6 & 1, 6b extract light beams from different pupil positions of the photographing lens and perform so-called pupil division, so that the in-focus state can be determined. At this time, when the magnification of the secondary imaging system is constant, the amount of movement, that is, the shift, of the two object images is from the first imaging surface 61 to the light receiving elements 9a1 and 9b.
, is proportional to the distance @L, so in order to improve the focusing accuracy, it is necessary to increase the distance to some extent.

FIG. 2 is a schematic diagram of an optical system according to an embodiment of the present invention. In the figure, 1 is a photographing lens, 2 is a quick return mirror, and 3 is a focusing plate, a portion of which is a transparent or semi-transparent surface. Reference numeral 4 denotes a penta-roof prism, and 4R denotes an object-side reflecting surface of the penta-roof prism, which is partially provided with a light beam extraction port 4R/ for allowing a portion of the light beam that has passed through the photographic lens 1 to pass therethrough. 5 is a beam splitting prism, 6a and 6b are secondary imaging lenses of the secondary imaging system, 7a and 7b are reflective prisms, and 8
Reference numerals a and 8b denote total reflection mirrors, 9a and 9b light receiving elements each consisting of a plurality of photoelectric conversion elements, and 10 an eyepiece lens.

In the figure, the light beam from the object forms an image near the focusing plate 3, which is the first imaging surface of the photographic lens 1, and then passes through the penta-roof prism 4.
R/, is split into two beams by a light splitting prism 5, and is then passed through reflecting prisms 7a, 7b and total reflection mirrors 8a, 8b by secondary imaging lenses 6a, 6b, and then onto light receiving elements 9a, 9b. be guided.

In the present invention, since the secondary imaging lens is arranged in the space on the object side of the pentagonal roof prism, it is possible to
The distance to the secondary imaging lens and the distance from the secondary imaging lens to the light receiving element can be set appropriately, resulting in an optical arrangement that can obtain a predetermined imaging magnification and improve focusing accuracy. There is.

As described above, in the present invention, by effectively utilizing the space on the subject side of the penta-roof prism, the distance from the first image forming plane to the light receiving element can be increased, so that focusing accuracy can be improved. Since the space on the subject side of the pentagonal roof prism is utilized, it is possible to prevent the camera from becoming sacred due to the use of a focus detection system.

FIG. 3 is a plan view of a portion of FIG. 1, showing the central light beam of the secondary imaging system from the roof surface of the pentagonal roof prism 4. FIG. As is clear from the figure, the pen image system has a long optical path length to improve focusing accuracy.

FIG. 4 is a partial explanatory diagram of another embodiment of the present invention.

The embodiment shown in the figure differs from the embodiment shown in FIG. 2 in that two light-receiving elements 12a and 12b are arranged in the space on the subject side of the pentagonal roof prism 4, and the rest is completely the same. 2
Although the optical path length of the secondary imaging system is somewhat shortened, this is an advantageous configuration for making the camera more compact.

In the present invention, the light beam extraction port of the pentagonal roof prism 4 may be fully transparent or semi-transparent, or the prisms may be bonded together so that the light beam is vertically emitted.

As described above, according to the present invention, by effectively using the space around the pentagonal roof prism, it is possible to achieve a single-lens reflex camera having a compact focus detection system with good focusing accuracy.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an optical system of a focus detection system using a conventional secondary imaging method, FIG. 2 is a schematic diagram of an optical system according to an embodiment of the present invention, and FIG. 6 is a partial diagram of FIG. The plan view, FIG. 4, is a partial explanatory diagram of another embodiment of the present invention. In the figure, 1 is the photographing lens, 2 is the quick return mirror, 6 is the focusing plate, 4 is the Pentazino 1 prism, 4R' is the light flux extraction port, 4R is the subject reflection surface of the Pentazino 1 prism, 5 is the light flux splitting prism, and 6 to 6b is a secondary imaging lens, 7a17b is a reflection prism, and 8a. 8b is a mirror, and 9a, 9b, 12a, and 12b are light receiving elements. Figure 1 Three boxes of flutes

Claims (2)

[Claims] (1) A secondary imaging system for re-imaging the object image formed on the imaging surface into two object images is arranged behind the imaging surface of the photographic lens, and the secondary imaging system A light-receiving element each consisting of a plurality of elements is arranged at a position where an image is formed, and
In a single-lens reflex camera having a focus detection system that detects the focus of the photographic lens by detecting the relative positional relationship between two object images using the light receiving element, a light beam extraction port is provided on the subject side reflective surface of the penta roof prism. and placing the secondary imaging lens of the secondary imaging thread in the subject-side space of the pentagonal roof prism, and extracting a light flux for focus detection from the light flux that has passed through the photographing lens through the light flux extraction port. , A single-lens reflex camera having a focus detection system, characterized in that light is guided to the secondary imaging system. (2) The light receiving element is arranged on the exit surface side of the penta roof prism, and receives the light beam from the secondary imaging system via the penta roof prism. A single-lens 7-lens camera having a focus detection system as described in 1.