JPS59101613A - Optical system having focus detecting device - Google Patents

Abstract

PURPOSE:To form a compact optical system having an active type focus detecting device of a TTL method by leading a reflected luminous flux to a photodetector through a light transfer member. CONSTITUTION:A reflected luminous flux from an object passes through a focusing lens 1, passes through a photodetecting lens 4, and is made incident to one end face of a light transfer member 8 placed at a position conjugate with a prearranged image forming face of the focusing lens 1. The light transfer member 8 consists of at least two light guides, a glass rod, etc. The other end face of the light transfer member 8 is placed in the vicinity of a photodetecting face of a photodetector 5 so that a luminous flux led by the light guide 8A is made incident to an area A of the photodetector face, and a luminous flux led by the light guide 8B is made incident to an area B. According to this constitution, it is not required to place the photodetector 5 in the vicinity of an image field side of the focusing lens 1, therefore, a photodetecting system can be placed in a cam ring as shown in the figure by use of its space, and a lens barrel can be made small-sized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical system having a focus detection device applied to optical equipment such as still cameras and ZEDEO cameras. It has a so-called active automatic focus detection device that detects the focus detection state of the optical system with respect to an object by projecting a light beam and photoelectrically detecting the reflected light by a photoelectric receiver placed on the optical system side. It is related to optical systems.

One method of an active automatic focus detection device is to use the light beam that has passed through the imaging optical system. They tend to become larger.

FIG. 1 shows an example of the configuration of the optical arrangement of the above-mentioned TTL method. In the figure, 1 is a focusing lens, 2.6 is a total reflection mirror, 4 is a light-receiving lens, 5 is a light-receiving element such as OCD or SPC, and 6 is an optical system for dipping magnification (in the case of a zoom lens) The projection light beam emitted from the light emitter disposed at a position equivalent to the center of the optical axis of the image plane is projected onto the object through a predetermined area on or off the optical axis of the focusing lens 1. projected onto a surface. Of the light beams reflected on the object surface, the light beams that pass through other predetermined areas of the focusing lens 1 pass through the mirror 2°, the light receiving lens 4, and then reach the optical axis center of the expected image plane of the focusing lens 1. The light enters the light receiving element 5 provided at an equivalent position.

Then, by detecting the position of the center of gravity of the light flux of the incident spot of the light flux on the surface of the light-receiving confectionery 50 at this time, focus detection of the focal length lens 10 is performed.

In FIG. 1, the center of gravity of the light beam of the incident spot is at the light receiving element 50.
The optical system is arranged so that the focusing lens 1 is in the front bin if it is below the optical axis center on the surface, the rear bin if it is above the center, and the focusing state if it is in the center.

One method for detecting the movement of the center of gravity of the incident spot is to divide the light-receiving element surface into two regions A and B, upper and lower, with the center of the optical axis as the boundary. Then, by detecting the differential output from the light-receiving element obtained from the area A and the 82 areas, the front bin and the rear bin of the focusing lens 1 are determined based on the polarity.

Judging whether to combine bins, etc.

This tends to lead to an increase in the size of the optical system.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the tendency for optical systems to become larger and to provide a compact optical system having an active focus detection device using the TTL method.

The technical means for achieving the above object is characterized by arranging one end of a light transmitting member such as an optical fiber or a glass rod having the function of transmitting the energy intensity of light at the position where the light receiving element is disposed in the above-mentioned optical system, and placing one end of the glass rod at the other end. The first step is to arrange a light receiving element.

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

FIG. 2 is a schematic diagram of an optical system according to an embodiment of the present invention.

A light beam emitted from a light emitter placed on a part of the intended image forming plane of a focusing lens 1 (not shown) passes through the focusing lens 1 and is projected onto an object.0 A light beam reflected from the object passes through the focusing lens 1 as M'. 1 through the light receiving lens 4,
The zero light transmitting member 8, which is incident on one end face of the light transmitting member 8 disposed at a position common to the expected imaging plane of the focusing lens 1, is composed of at least two light guides, a glass rod, or the like. For example, when the light transmission member 8 is composed of two light guides, one end surface 8 of the light guide is placed above the center of the optical axis of the imaging optical system as the boundary.
A, and another end surface 8B is arranged below. In order to improve detection accuracy, it is preferable that the boundary surface at this time be formed by a straight line. The other end face of these light transmitting members 8 is placed near the light receiving surface of the light receiving element 5, and the light flux guided by the light guide 8A is directed to the area A of the light receiving element surface.
The light beam guided by the light guide 8B is arranged so as to be incident on the area B.

In such a configuration, the same focus detection operation as in the fourth conventional example shown in FIG. 1 is performed.

That is, by detecting the differential output obtained from the two areas A and B on the surface of the light receiving element 5, the in-focus state of the subject can be determined from the polarity thereof.

In the construction example of this embodiment, it is not necessary to arrange the light receiving element 5 close to the image field side of the focusing lens 1, so the light receiving system can be arranged inside the cam ring using that space as shown in the figure. The light-receiving element 5 can be installed at any position, but for example, if it is installed in a part of the relay where there is plenty of space inside the lens barrel, it can reduce the size of the lens barrel. This is preferable because it does not cause an increase in size.

FIG. 6 shows a schematic diagram of the optical system of the second embodiment of the invention. 5A and 5B are light receiving elements arranged at different positions. The light beams guided by the light guides 8A and 8B enter the light receiving elements 5A and 5B, respectively. In such a configuration, the in-focus state can be detected by comparing the outputs of the light receiving elements 5A and 5B. If two light receiving elements are provided as in this example, a differential type structure in which one light receiving element surface is divided into two can be used, or a CO
Since there is no need to divide the region D into two, a light receiving element with a simpler structure and lower cost can be used.

In the above embodiment, two light guides are used as the light transmission member 8, but when six or more light guides are used, for example, when there are six light guides, the output of the light receiver guided by the central light guide is When the focus state is maximum, it can be determined that the in-focus state is in-focus, and when the output from the light receiver guided by either the left or right light guide is the maximum, it can be determined that the in-focus state is in-focus. When there are six or more light guides, the in-focus state can be detected in the same way.

Furthermore, the light emitting device that emits a beam of light to be projected onto the object side does not necessarily have to be placed on the intended imaging plane for focusing; for example, in the case of a zoom lens, it may be a variator behind the focusing lens, a conven-1=-J-i or a relay lens, etc. It may be placed at any position behind the This also applies to the light receiver.

The emitter and receiver do not necessarily need to be placed at positions that are aligned with the optical axis on the intended image-forming plane of the optical system, but rather at a specific point on the intended image-forming plane and at a position common to that point. They may be arranged individually.

As explained above, according to the invention, by directing the reflected light beam that has passed through an imaging optical system such as a focusing lens to the light receiving element via the light transmission member, the arrangement position of the light receiving element can be freely determined. This makes it possible to realize an optical system having a compact focus detection device.

Furthermore, by guiding the light beams to at least two light receiving elements through the light transmission member, the focus detection device can be constructed using light receiving elements that have a simple structure and are inexpensive.

[Brief explanation of drawings]

FIG. 1 is an optical layout diagram of an active focus detection device for a conventional TTL method. FIG. 2 is a schematic diagram showing an embodiment of the invention; FIG. 6 is a schematic diagram showing a second embodiment of the invention. In the figure, 1 is a focusing lens; 2. Ro is full-back, and Q is a light transmission member.

Claims (1)

[Claims] (1) A light emitter and a photoelectric receiver are arranged at two positions that are conjugate to the planned image plane of the imaging optical system, which is adjustable along the optical axis, and the light emitter is connected to the imaging optical system. After projecting a beam of light to the object side through the object, the reflected light reflected by the object and incident on the imaging optical system is detected by the photoelectric receiver,
In a focus detection device that detects the focusing state of the imaging optical system with respect to the object based on the output of the photoelectric receiver at this time, the reflected light is transmitted to the photoelectric receiver via a photoconductive member. An optical system having a focus detection device characterized by guiding light. Q) An optical system having a focus detection device according to claim 1, wherein the light conductive member is constituted by two light guides.