JPS6350822A - Movable mirror device for single-lens reflex camera - Google Patents

Abstract

PURPOSE:To guide part of photographic luminous flux efficiently to a focus detection system arranged at the bottom part of a camera by specifying the shape of a reflection optical member arranged behind a movable mirror. CONSTITUTION:While the photographic luminous flux 22 is reflected by a movable mirror 23 to a finder system, part of the photographic luminous flux 22 is transmitted through a translucent surface 24 and guided to the focus detection system 28 through the reflection optical member 26. At this time, the shape of the prism body of the reflection optical member 26 is so specified that the length of the optical path from the translucent part 24 to an image picked-up body 32 is equal to the length of the optical path from the translucent part 24 to the focus detection system 28 through the reflection optical member 26. Consequently, the distance from the translucent part 24 to the focus detection system 28 is increased by a quantity corresponding to the length of the optical path of the prism body to facilitate the arrangement of the focus detection system 28 off the photographic luminous flux at the bottom part of the main camera body.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a movable mirror device for a single-lens reflex camera, and in particular to a movable mirror device in which a reflective optical member having a reflective surface is fixed to a part of the movable mirror, or Place it behind the non-hit
A single-lens reflex camera that is capable of efficiently and accurately reflecting a light beam that has passed through a semi-transparent surface provided on a part of a movable mirror in a predetermined direction, such as a focus detection device or a photometry device, using a reflective optical member when in the shadow. The present invention relates to a movable mirror device suitable for, for example, an electronic camera with a relatively small screen size.

(Prior Art) Conventionally, in single-lens reflex cameras, a movable mirror has been placed behind the photographic lens to reflect the shadow light flux to the finder system. Among these, in Japanese Patent Application Laid-Open No. 60-60611, as shown in Figure 2, a semi-transparent surface is provided on one side of a movable mirror, and an auxiliary mirror is provided on the other side, so that part of the photographic light beam passes through the semi-transparent surface. The light beam is reflected by an auxiliary mirror to automatic focus detection means, photometry means, etc. provided at the bottom of the camera.

That is, in FIG. 2, 1 is a camera body such as a photographic camera or an electronic camera, and 2 is a movable mirror that reflects a photographing light beam toward a finder system above. 3 is a holding frame for the movable mirror 2; 4 is a rotating shaft of the holding frame 3; and 5 is a stopper which restricts rotation of the holding frame 3 in order to determine the position of the movable mirror 2.

A semi-transparent surface is provided in the center of the movable mirror 2,
The light flux that has passed through the semi-transparent surface is reflected by an auxiliary mirror 6, which is a reflective optical member provided on the movable mirror 2, toward an automatic focus detection device 7 provided at the bottom of the camera.

By the way, the screen size of recent so-called electronic cameras is about 100% smaller than that of single-lens reflex cameras for 35 mm film. For this reason, the focal length of the photographic lens is often shorter than that of a single-lens reflex camera for 35 mm film. For this reason, a movable mirror provided behind the photographic lens is located near an image pickup body such as a CCD. Also, since many electronic cameras use an image pickup body such as a COD, various photographic optical components such as a crystal plate, an infrared cut filter, a cover glass, and a color filter are placed between the movable mirror and the image pickup body. It consists of

For this reason, when performing automatic focus detection, for example, by using the reflected light flux that passes through the semi-transparent part of the movable mirror and is reflected by a conventional auxiliary mirror provided on the image plane side of the movable mirror, out of the photographic light flux. Since the optical path length of the focus detection system is shorter than the optical path length from the movable mirror to the imaging body, it becomes spatially very difficult to arrange the focus detection device so as not to block the photographing light beam.

Further, after the photographing lens for an electronic camera passes through various photographic optical members such as filters, aberrations are corrected to obtain the best optical performance. For this reason, the optical performance of the object image differs between the photographing system and the focus detection system that does not use optical members, which causes a decrease in focus detection accuracy, especially when performing focus detection using the imaging performance of the object image. It's coming.

(Problems to be Solved by the Invention) When the present invention performs focus detection, for example, using a reflective member provided behind the movable mirror or a part of the movable mirror, a portion of the photographing light beam is directed to the focus detection system. An object of the present invention is to provide a movable mirror device for a single-lens reflex camera, which is particularly suitable for an electronic camera, and which efficiently guides light and easily obtains optical performance similar to that of a photographing system.

(Means for solving the problem) A semi-transparent part is provided in a part of a movable mirror that reflects the photographing light flux that has passed through the photographic lens in the direction of photographing, and a part of the photographic light flux that has passed through the semi-transparent part is provided. a reflective optical member for reflecting the image in the direction of the photographing direction, the reflective optical member having a shape such that the optical path length of the reflective optical member is approximately equal to the total optical path length of the photographing optical members disposed closer to the image plane than the movable mirror. and arranged on the image plane side of the movable mirror.

(Embodiment) FIG. 1 is a schematic diagram of an optical system of an embodiment when the present invention is applied to an electronic camera. In the figure, 20 is a photographing lens, 21 is an optical axis of the photographing lens 20, 22 is a photographing light beam, 2
3 is a movable mirror, 24 is a semi-transparent part provided on a part of the movable mirror 23, and 26 is a reflective optical member, which is constructed by providing a reflective surface on a part of a prism body, and is fixed to the movable mirror 23. ing. 28 is a focus detection system installed at the bottom of the camera, 29
30 is a shutter unit, 31 is a cover glass, 32 is an imaging body,
33 is a package for the imaging body 32. 34 is a prism of a finder system, and 35 is an eyepiece lens.

In this embodiment, the photographing light flux 22 is reflected by the movable mirror 23 to the finder system, and a part of the WL shadow light flux 22 is transmitted through the semi-transparent surface 24 and guided to the focus detection system 28 via the reflective optical member 26. There is. At this time, the semi-transparent part 24
The shape of the prism body of the reflective optical member 26 is specified so that the optical path length from the to the imaging body 32 and the optical path length from the semi-transparent part 24 to the focus detection system 28 via the reflective optical member 26 are equal to each other. There is.

This increases the distance from the semi-transparent part 24 to the focus detection system 28 by an amount corresponding to the optical path length of the prism body, making it easy to arrange the focus detection system 28 outside the photographing light beam at the bottom of the camera body.

In addition, in the case of 66 Kinotsu, the aberrations generated in the prism body of the reflective optical member 26 and the crystal plate disposed in front of the imaging body 32,
The shape of the prism body of the reflective optical member 26 is configured so that the aberrations generated in the overall photographic optical member such as the infrared cut filter are approximately equal.

That is, the aberrations of the photographing lens are corrected taking into consideration the state when a plane parallel plate is placed in a converging light beam, and in particular, the aberrations are corrected taking into account the influence of spherical aberration. Therefore, when obtaining an object image, unless a parallel plane plate is used, aberrations will be overcorrected.

Therefore, in this embodiment, by configuring the prism body as described above, the focus detection system is optically in the same imaging state as the imaging system, and the optical performance of the object image obtained by the focus detection system is improved. I'm trying.

This aims to improve the detection granularity when performing focus detection using an object image.

In this embodiment, the semi-transmissive portion 24 may be constructed of a semi-transmissive surface or a plurality of minute reflective surfaces divided in terms of area.

Further, the reflective optical member 26 may be arranged independently without being fixedly attached to the movable mirror 23, and may be retracted from the photographing optical path during photographing.

(Effects of the Invention) According to the present invention, by specifying the shape of the reflective optical member placed behind the movable mirror as described above, a part of the photographing light beam is efficiently guided to the focus detection system placed at the bottom of the camera. In addition, it is possible to guide an object image with almost the same optical performance as the 1M> U2 system to the focus detection system, increasing focus detection accuracy when performing focus detection using the object image. A movable mirror device for a single-lens reflex camera can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention applied to an electronic camera, and FIG. 2 is a schematic diagram of a portion of a movable mirror device of a conventional single-lens reflex camera. In the figure, 20 is a photographing lens, 23 is a movable mirror, 24 is a semi-transmissive section, 26 is a reflective optical member, 28 is a focus detection system, 32 is an imaging body, 29 is a parallel plane plate, and 30 is a shutter unit.

Claims (1)

[Claims] A semi-transparent part is provided in a part of the movable mirror that reflects the photographic light flux that has passed through the photographic lens in a direction other than the photographic system, and a part of the photographic light flux that has passed through the semi-transparent part is reflected in a direction other than the photographic system. The reflective optical member is constructed in such a shape that the optical path length of the reflective optical member is approximately equal to the total optical path length of the photographing optical members arranged on the image plane side of the movable mirror, and A movable mirror device for a single-lens reflex camera, characterized in that the mirror device is arranged in a.