JPS61233713A - Optical system with focus detecting means of two systems - Google Patents

Abstract

PURPOSE:To allow one lens system to function for focus detection on both active and passive bases by arranging the 1st optical splitter on part of an optical path and a lens system and the 2nd splitter in a branched optical path, and arranging focus detecting means of two active and passive systems behind the 2nd optical splitter. CONSTITUTION:When an object side is bright or when the object is relatively at a distance, luminous flux split by the 1st optical splitter 2 is passed through the lens system 6 to form an image and the majority of luminous flux within the visible range is reflected by the 2nd optical splitter 7 to form an object image on the surface of the 1st photodetection part 8; and the image formation state is measured to perform focus detection. When the subject side is dark or when the subject is at a short distance, luminous flux is emitted by a light source 9. The majority of infrared luminous flux of the light emitted by the light source is passed through the 2nd optical splitter 7 and projected on the object side through part 1 of a photography system. Luminous flux reflected by the object side is guided to the surface of the 2nd photodetection part 11 by a lens 10 for photodetection and the position of the reflected luminous flux is detected to perform the focus detection.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an optical system having two types of focus detection means suitable for photographic cameras, cine cameras, video cameras, etc.
In particular, a so-called passive focus detection means performs focus detection by measuring the state of image formation of a subject image by an optical system, and a camera side emits invisible light such as ultraviolet light or infrared light to the subject side. The present invention relates to an optical system having two types of focus detection means, a so-called active focus detection means that performs focus detection by receiving a reflected light beam.

(Prior Art) Conventionally, two types of focus detection methods have been used in photographic cameras, cine cameras, video cameras, and the like.

One is a passive method proposed in, for example, Japanese Patent Application Laid-open No. 54-159259, and the other is an active method proposed in, for example, Japanese Patent Application Laid-Open No. 57-154206.

Among these, the passive method detects the focus by detecting the state of the object image formed by the optical system using a detection means installed in a part of the camera. It has the advantage of focus detection. However, when the subject is dark or the contrast of the subject is low, there is a drawback that the focus detection accuracy decreases.

On the other hand, the active method detects focus by projecting, for example, an infrared beam from the camera side toward the subject and receiving the reflected beam from the subject, even when the subject is dark or the contrast of the subject is low. However, it has the advantage of being able to perform focus detection with high precision. however,
When the subject is far away, there is a drawback that the reflected light flux decreases and the focus detection accuracy decreases.

Therefore, a method may be considered in which focus detection is performed by appropriately selecting and using both passive and active focus detection means. However, if both types of focus detection means are simply combined, the entire camera becomes large and difficult to use, and it is also difficult to effectively utilize both the luminous flux from the subject side and the luminous flux projected from the camera side. It becomes difficult to perform highly accurate focus detection with both methods.

(Objective of the present invention) The present invention comprises two types of focus detection means, a passive type and an active type, in a part of an optical system by sharing some of the optical elements, thereby simplifying the entire device and achieving both. It is an object of the present invention to provide an optical system having two types of focus detection means, which enables highly accurate focus detection by effectively utilizing the luminous flux in the system.

(Main features of the present invention) A first light splitter for splitting a part of the photographing light flux is arranged in a part of the optical path of the optical system, and at least A lens system having one lens is arranged, a second light splitter is arranged behind the lens system to split the passing light beam into two regions, a visible region and an invisible region, and the second light splitter splits the light flux. In the optical path of the visible region of the two luminous fluxes! @1 focus detection means is arranged, and a second focus detection means which uses a different focus detection method from the first focus detection means is arranged in the optical path of the invisible region.

Other features of the invention are described in the Examples.

(Example) FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention.

In the figure, 1 is a front group or a variable magnification unit which is a part of the optical system, 2 is a first optical system, and 3 is a first reflecting surface provided on the first light splitter 2.

The #11 reflective surface has spectral characteristics, for example, as shown in Figure 2, and is a semi-transparent reflective surface with low reflectance in the visible region (e.g. wavelength 400-700 nm), and in the invisible region, e.g. infrared region (e.g. It is composed of a dielectric multilayer film with wavelength selectivity that has high reflectance at wavelengths of 700 to 1000 nm). 4 is an imaging lens arranged as necessary; 5 is an image forming surface such as a film surface or an image sensor; and 6 is a lens system for transmitting and receiving light in both passive and active focus detection. It forms part of the optical system. 7 is a second light splitter. The second light splitter 7 is coated with a wavelength-selective dielectric multilayer film having spectral characteristics such as high reflectance in the visible region and high transmittance in the infrared region, as shown in FIG. ing. 8 is a first light receiving section for passive method;
For example, it is made up of a plurality of light receiving elements. Reference numeral 9 denotes a light source, which is composed of, for example, a light emitting diode or a semiconductor laser.
Lens; placed near the focal point of $6. 10 is a light-receiving lens, and 11 is a second light-receiving section for active type.

In this embodiment, when the subject side is bright and the subject is relatively far away, the illuminance on the subject side is measured manually or by a light receiving means (not shown) placed on the camera side, and the first light receiving section 8 is automatically activated. is configured to do so.

At this time, among the photographing light fluxes from the subject that have passed through part 1 of the optical system, the first light splitter 2 reflects a relatively small amount of light fluxes in the visible range, and most of the light fluxes in the infrared range. The light beam in the visible range that has passed through the first light splitter 2 forms a subject image on the imaging plane 5 via the imaging lens 4. On the other hand, the luminous flux split by the first light splitter 2 is 1%
The second light splitter 7 reflects most of the luminous flux in the visible region to form an object image on the surface of the first light receiving section 8. Then, by measuring the imaging state of the subject image formed on the surface of the first light receiving section 8, focus detection is performed using, for example, the method proposed in Japanese Patent Application Laid-open No. 159259/1983. .

In this way, in this embodiment, the first. #! The two-beam spectral division spectral characteristics are #I2. Second. By setting as shown in
High-precision focus detection is performed using a passive method by effectively utilizing the luminous flux from the subject.

On the other hand, when the subject side is dark or the subject distance is short, the light source 9 and the second light receiving section 11 are configured to operate manually or automatically by a light receiving means (not shown).

Then, a light beam is emitted from the light source 9 by pressing the shutter release button or by pressing a button provided on the camera body. Of the luminous flux emitted from the light source, the second
Most of the infrared region passes through the light splitter 7.

The light flux in the infrared region that has passed through the second light splitter 7 is subjected to an imaging action by the lens system 6, and is reflected by the first light splitter 2, which has a high reflectance in the infrared region, to form an image in the photographing system. The light passes through part 1 and is projected toward the subject. Then, the light beam reflected from the subject side is passed through the light receiving lens 10 to a second
The light is guided onto the surface of the light receiving section 11.

Then, by detecting the position of the reflected light beam from the subject guided onto the second light receiving section 11 surface, for example,
Focus detection is performed using a method proposed in Japanese Patent No. 7-154206 and the like.

In this way, in this embodiment, by effectively using the infrared light beam emitted from the light source 9 without wasting it, highly accurate focus detection is performed in an active manner. Further, by performing both passive and active focus detection by sharing one lens system 6 and second light splitter 7, the overall size of the apparatus is reduced. That is, in this embodiment, the entire apparatus is simplified by using the lens system 6 for imaging in the passive method and for projecting a light beam in the active method. In addition, in the active method focus detection, the second light splitter 7 and the first light receiving section 8
A Kamisuke lens system may be placed between the two to change the range of distance measurement or to improve the accuracy of distance measurement.

In addition, the above-mentioned 1. The spectral characteristics of the second light splitter may be varied depending on the purpose, for example, by increasing the reflectance of the first light splitter in the visible region for a bright optical system.

The second light splitter 7 is configured so that the spectral characteristics of the visible region and the invisible infrared region are reversed, and the light source 9 and the first light receiving section 8
It may be configured by replacing the .

In addition, the light source 9 and the second light receiving section 11 are interchanged, and invisible ultraviolet light or infrared light is projected toward the subject from outside the optical system, and the reflected light flux from the subject is received via the optical system. You may also do this.

In this case, it is preferable to move the projecting lens or the light source in a direction perpendicular to the optical axis in conjunction with the focus section of the optical system to reduce parallax.

The lens system 6 and the imaging lens 4 may be composed of the same lens. When the optical system is a zoom lens, between the variable power unit and the imaging lens or between the final lens and the imaging surface, and when the optical system is a single focal length lens system, the final lens and the imaging surface. It is preferable to arrange the first light splitter between the two and the first light splitter in order to downsize the entire device.

(Effects of the present invention) According to the present invention, the first light splitter is disposed in a part of the optical path of the optical system, and the lens system and the second light splitter are disposed in the optical path branched by the first light splitter. Furthermore, by arranging two types of focus detection means, an active type and a light receiving type, behind the second beam splitter, one lens thread can be used for both types of focus detection, thereby achieving effective use of the luminous flux and achieving high precision. It is possible to achieve an optical system having two types of focus detection means, which enables focus detection of 100% and reduces the size of the entire device.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, FIG.
FIG. 3 shows the first embodiment according to the present invention. This is a spectral characteristic of the second light splitter. In the figure, 1 is a part of the optical system, 2 is the first light splitter, and 6 is the first light splitter.
reflective surface, 4 is an imaging lens, 5 is an imaging surface, 6 is a lens system,
7 is a second light splitter, 8 is a first light receiving section, 9 is a light source, 10 is a light receiving lens, and 11 is a second light receiving section.

Claims (3)

[Claims] (1) A first light splitter for splitting a part of the photographing light flux is arranged in a part of the optical path of the optical system, and at least one lens is placed in the optical path of the light flux split by the first light splitter. A second light splitter is arranged behind the lens system to divide the passing light flux into two regions, a visible region and an invisible region, and the two light fluxes divided by the second light splitter are arranged. A first focus detection means is arranged in the optical path of the visible region, and a second focus detection means which uses a different focus detection method from the first focus detection means is arranged in the optical path of the invisible region. An optical system with two types of focus detection means. (2) The first focus detection means includes a first light receiving element, and the second focus detection means is configured to receive a light beam emitted from a light source or a light source disposed near the optical system and reflected from the subject. An optical system having two types of focus detection means according to claim 1, further comprising a second light receiving element. (3) An optical system having two types of focus detection means according to claim 2, characterized in that an auxiliary lens system is disposed in at least one of the first or second focus detection means.