JPS59185304A - Optical system for range-finding of camera - Google Patents

Abstract

PURPOSE:To omit a beam splitter and to manufacture the titled optical system easily and economically by providing a photographing optical system using a full reflecting prism and a range-finding light source projecting the light of a specific wavelength range. CONSTITUTION:The photographing optical path of the photographing optical system is refracted downwards by the full reflecting prism 11 arranged next to the front-group 10 of the photographing optical system and an image is formed by the rear-group 12 of the photographing optical system on an image pickup surface of an image pickup tube 13 for instance. An auxiliary prism 15 is arranged on the back of the full reflecting surface 14 of the full reflecting prism 11 and a projection lens 16 and a range-finding light source 17 are successively arranged on the back of the auxiliary prism 15. On the other hand, a photodetecting lens 18 and a photodetecting element 19 are arranged on the external part of the photographing optical system. Said constitution makes it possible to omit a beam splitter and to manufacture the optical system easily and economically.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distance measuring optical system for a general still camera or a video camera, and particularly for a camera having a total reflection prism in the photographing optical system.

In a typical camera object distance detection device, for example, an infrared diode or infrared semiconductor laser is used as a light source to project light toward the object, and the object distance is detected by the output of a light receiving element that receives the reflected light. . Most of these are so-called external distance measuring methods in which light is emitted and received from outside the photographic optical system, but recently, in order to achieve more accurate distance measurement, the entire or part of the photographic optical system is used as a light emitting or receiving optical system. A so-called TTL method has been proposed.

In this TTL system, a beam splitter is inserted into the photographing optical system to separate the photographing light and the ranging light. As shown in FIG. 1, this beam splitter is generally constructed by bonding two prisms 1.2 with an adhesive 3 and depositing a multilayer film 4 on one of the bonded surfaces to create a so-called half mirror of the intensity splitting type. Alternatively, it is configured as a wavelength region dividing type gicroic mirror. Such a beam splitter 1±,
There are many manufacturing difficulties such as vapor deposition of the multilayer film 4 and bonding of both prisms, and the disadvantage is that the cost is high.Moreover, it also has the problem of wood quality, which adversely affects the brightness and color characteristics of the photographing light.

SUMMARY OF THE INVENTION In order to eliminate such drawbacks, an object of the present invention is to provide an easy-to-manufacture distance measuring optical system for a camera that utilizes the wavelength characteristics of a total reflection prism in a photographing optical system without using a beam splitter. The gist of the system includes a photographing optical system using a total reflection prism and a distance measuring light source that emits light in a specific wavelength range, and the photographing light beam is totally reflected on the total reflection surface of the total reflection prism, The distance measuring light beam emitted from the distance measuring light source is characterized in that the angular relationship is set so that the distance measuring light beam is refracted and transmitted through the total reflection surface.

The present invention will be explained in detail below based on the embodiment of the video camera shown in FIGS. 2 and 3.

In FIG. 2, the photographing optical path is refracted downward by a total reflection prism 11 disposed following the front group 10 of the photographing optical system, and the image formed by the rear group 12 of the photographing optical system is, for example, 13 imaging planes. With this configuration, the storage portion of the image pickup tube 13 can be used as a grip, and a camera using a solid-state image sensor or a regular film can be made compact.

On the other hand, an auxiliary prism 15 is provided behind the total reflection surface 14 of the total reflection prism 11, and a light projecting lens 16 and a distance measuring light source 17 are sequentially arranged behind the auxiliary prism 15. On the other hand,
A light receiving lens 18 and a light receiving element 19 are installed outside the photographing optical system. The angle of the total reflection surface 14 of the total reflection prism 11 is set so as to totally reflect the photographing light beam having spectral sensitivity from the image pickup tube 13, film, etc., and refract and transmit the light emitted from the distance measuring light source 17. ing.

Generally, materials used for prisms, such as glass and plastics, have a large refractive index n at short wavelengths, and a low refractive index n at long wavelengths such as infrared rays. Therefore, if the emission wavelength of the ranging light source 17 is in the infrared region, the incident light is easily refracted and transmitted by the total reflection prism 11 without being totally reflected. In other words, the critical angle θ that causes total internal reflection is the wavelength λ
, when its refractive index is n(λ), θ=5in-1 (1/n (in)), and from this relationship, it can be set so that infrared light is refracted and transmitted through the total reflection surface 14.

Therefore, if the critical angle θ of the total reflection surface 14 is appropriately selected, for example, from 31.34 degrees to 31.80 degrees, the infrared light emitted from the ranging light source 17 will pass through the projection lens 16, It is refracted and transmitted through the auxiliary prism 15 and the total reflection prism 11,
The light can be projected onto the subject through the front group 10 of the photographic optical system, and the reflected light can be received by the light-receiving lens 18 and the light-receiving element 19 to perform distance measurement. In addition, as for the distance measuring method, the light projecting lens 16, the distance measuring light fi 17, and the light receiving lens 1 are used.
8. A method of scanning at least one of the light-receiving elements 19 and detecting the maximum value of the output, or a method of detecting the object distance from the detection position of the object image by using a plurality of line sensors as the light-receiving elements 19. etc. can be applied.

FIG. 3 shows another embodiment of the present invention. Of the light that passes through the front group 10 of the photographing optical system, infrared light is not totally reflected by the total reflection prism 11 but is refracted and transmitted. An example is shown in which a light receiving lens 18 and a light receiving element 19 are arranged on the optical path. In this case, without using the auxiliary prism 15,
The distance measuring light source 17 and the projection lens 18 may be placed outside.

In addition, in addition to the embodiment, for example, the front group 10 of the photographing optical system is used for both light beams for emitting and receiving light for distance measurement, and a total reflection prism 1 is used.
It is also possible to refract and transmit 1. In addition, in a camera that uses an image pickup tube, the finder system can be a so-called electronic viewfinder that displays the video signal from the image pickup tube on a small cathode ray tube. A so-called TTL finder that takes out the finder light from the rear can also be configured. Furthermore, it is also possible to arrange the total reflection prism 11 after the rear group 12 of the photographing optical system, and in this case, the distance measuring light projecting lens 16 and the light receiving lens 18 can be omitted.

As described above, according to the distance measuring optical system for a camera according to the present invention, a total reflection prism is used in the photographing optical system in order to achieve mechanical compactness and improve functionality, and the wavelength selection characteristics of the total reflection prism are favorable. By conveniently refracting and transmitting the distance measuring light beam, the conventionally used beam splitter can be omitted, making manufacturing easy and inexpensive. Further, since the photographing light beam is guided by total reflection without using a beam splitter, the conventional problem of having an adverse effect on the brightness and color characteristics of the photographing light beam can be solved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a beam splitter used in a conventional object distance detection device, FIG. 2 is an optical configuration diagram showing an embodiment of a distance measuring optical system of a camera according to the present invention, and FIG. 3 FIG. 2 is a main part configuration diagram of another embodiment. Reference numeral 10 is the front group of the photographing optical system, 11 is a total reflection prism,
12 is a rear group, 13 is an image pickup tube, 14 is a total reflection surface, 15 is an auxiliary prism, 16 is a projection lens, 17 is a distance measuring light source, 1
8 is a light receiving lens, and 19 is a light receiving element. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1. It has a photographing optical system using a total reflection prism and a distance measuring light source that emits light in a specific wavelength range, and the photographing light beam is totally reflected by the total reflection surface of the total reflection prism. A ranging optical system for a camera, characterized in that an angular relationship is set such that a ranging light beam emitted from a ranging light source is refracted and transmitted through a total reflection surface. 2. The distance measuring optical system for a camera according to claim 1, wherein infrared light is used in the wavelength range of the distance measuring light source. 3. The distance measuring optical system for a camera according to claim 1, wherein an auxiliary prism is interposed between the total reflection prism and the light projecting lens of the distance measuring light source.