JPS61138221A - Focus detector - Google Patents

Abstract

PURPOSE:To make possible satisfactory photographing even if a dichroic mirror is disposed in a photographic optical path by providing a reflecting mirror of which the IR reflectivity decreases with a decrease in the distance from the central part to part of the photographing system. CONSTITUTION:At least either of a light projecting means 10 or photodetecting means 12 is provided to a part of the inside of the photographing system and the projection or detection of the light is executed via the reflecting mirror 5a constituted in such a manner as to allow mainly the transmission of the visible light and to decrease the IR reflectivity with an increase in the distance from the central part for reflecting IR ligxt in a focus detector which detects the focus of the photographing system by projecting the luminous flux from the means 10 to a subject side and detecting the luminous flux reflected from the subject side by the means 12.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device, and more particularly, to a focus detection device that projects a luminous flux from a light projecting means to a subject side through a part of a photographing system or from a subject side through a part of a photographing system. 1111 TTL where the focus of the photographing system is detected by receiving the reflected light flux
This article relates to an active focus detection device based on the above-mentioned method.

The conventional active focus detection device was released in Japanese Patent Application Laid-open No. 56-1.
This is because it was proposed in Publication No. 65126, etc. In most active focus detection devices, the light source of the camera 91m has a light projecting means for projecting a light beam mainly composed of infrared light toward the subject, and a light receiving means for receiving the reflected light beam from the subject. Each of these facilities is set up independently from the photography system or by sharing a part of the photography system. The light projecting means or the light receiving means mainly transmits or receives light toward the subject via a reflective surface, such as a dichroic mirror, that transmits visible light and reflects infrared light. Using invisible infrared light flux for focus detection in this way does not have any effect even when the subject is human intelligence, and allows for good photography without reducing the visible light range. There is. In many cases, dichroic mirrors used for focus detection are constructed using multilayer films so that they have high transmittance in the visible range and high reflectance in the infrared range. However, the multilayer film has characteristics that vary greatly depending on the incident angle of the light beam. Therefore, if a dichroic mirror is placed in the photographing light beam, the screen may be colored due to different spectral characteristics depending on the position of the photographing light beam passing through the dichroic mirror.

The present invention uses a new dichroic mirror that does not affect the photographing surface, such as color unevenness, to create a focal point that enables good photographing even when seven iK dichroic mirrors for projecting or receiving light are placed in the photographing optical path. The purpose is to provide a detection device.

The main feature of the focus detection device for achieving the object of the present invention is that the light beam from the light projecting means is projected onto the subject side, and the reflected light beam from the subject side is received by the light receiving means. In the focus detection device, at least one of the light projecting means and the light receiving means is provided in a part of the photographing system, and the infrared light reflectance increases as the distance from the center of the camera mainly transmits visible light and reflects infrared light. This is due to the fact that light is emitted or received through a reflecting mirror configured to reduce the amount of light.

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

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention. In the same figure, l is a focusing lens, 2 and 4 are zoom lenses, 3 is an aperture, 5 is a prism with a dichroic surface 5a, 7 is a rotating mirror, 8 is a photosensitive surface, 13 is a focusing surface,
14 is a pentaprism, and the intestine is an eyepiece. 9 is a lens for projecting light, and 10 is a light source that mainly emits infrared light.

11 is a light receiving lens, 12 is a light receiving element and focusing lens 1
It is possible to move in the direction of the arrow in conjunction with.

In this IM, an infrared beam from a light source 10 is collected by a projection lens 9 and reflected by a dichroic surface 5a, and then converted into an imaging system having variable magnification systems 2 and 4 and a focusing lens 1. The light is projected toward the subject. and focusing lens 1
□ The light-receiving lens 11 transfers the reflected light flux from the subject to the light-receiving element 12.
The focus of the photographing system is detected by detecting the position of the reflected light beam on the surface of the light receiving element 12. Regarding such a focus detection method, please refer to Japanese Patent Application Laid-Open No. 58-1710.
This is proposed in Publication No. 25. That is, as shown in FIG. 2, two light-receiving surfaces 14a are
, 12b moves in the direction of the arrow to receive the reflected light flux from the subject [17]. At this time, as shown in Fig. 3(b) K, there are 12 light-receiving surfaces of 5FC2,
The structure is such that when the reflected light beam 17m is located between the light receiving surfaces 12b and 12b, the output signals from both light receiving surfaces are equal, and the #1 distance is completed, that is, the focus detection of the photographing system is completed.

As shown in Fig. 3 (1) or Fig. 3 (e) K, when the reflected light beam is biased towards one of the light receiving surfaces 12m and 12b, the output signals from the light receiving surfaces 12m and 1211 will be different, so if you keep it It is determined that it is a bottle or a rear bottle. In addition, the focus detection system of this embodiment may be one that specifically detects the focus by simply detecting the strength or weakness of the reflected light beam, and can be applied to any active focus detection device.

FIG. 4 shows the dichroic surface 5 shown in FIG. 1 according to the present invention.
6 is a plan view of an embodiment of &. In the figure, 5a is a dichroic surface, and 5b is a simple transmission surface.

The dichroic surface 5a is configured so that its area decreases toward the periphery of the reflective surface 5-1, that is, the reflectance decreases. This causes the aperture 3 of the imaging system to be narrowed down. Then, the light beam that forms an image on the photosensitive surface 8 is divided into a light beam that passes through the dichroic surface 5a and a light beam that does not pass through the dichroic surface 5a, resulting in color unevenness within the screen. For this reason, in this embodiment, the reflectance of the dichroic surface of the portion where light is incident at a large angle is configured to be low, thereby reducing the influence of differences in incident angles.

That is, since the spectral characteristics vary depending on the angle of incidence of the light beam on the dichroic surface, the influence of the reflection characteristics on the dichroic surface is made to decrease toward the periphery of the reflective surface.

For example, FIG. 5 shows a line of spectral characteristics depending on the incident angle of the dichroic surface. In the same figure, the angle of incidence is 35[, 45 degrees,
The spectral characteristics of three cases of 55 liters are shown.

In the figure, the spectral characteristics are set so that visible light is transmitted through the dichroic surface and infrared light is reflected so that the dichroic surface has an optimal shape when the incident angle is 45 degrees. At this time, the angle of incidence is 3
5, the amount of transmitted light is blue component (wave & 400~50
0 nm), the color is more yellowish, and ff
If the angle of incidence on i is 55[deg.], the color development will be more greenish with less blue and red components (wavelength 600~Too!Lm).

FIG. 6 schematically shows the color unevenness within the screen at this time, as compared to when the subject is white. In the same figure, W indicates white, cover indicates yellowish white, and GW indicates greenish white.

Such color unevenness within the screen can be reduced by configuring the dike quick surface so that the reflectance decreases toward the periphery, as in the case of Honjitsu 11F4, to reduce the influence of light flux incident at angles other than the standard incidence angle. It can be reduced by filtration.

Incidentally, in the pattern of the Dichroic surface on the reflective surface 5-1 in this embodiment, the reflectance of the dichroic surface decreases as the incident angle of the photographing light beam deviates from the reference incident angle. That is, any shape may be used as long as the shape reduces the influence of reflection, such as concentric circles or a grid pattern.

Furthermore, in the vocal point detection device of this embodiment, the light emitting means and the light receiving means may be interchanged, and both the light emitting means and the light receiving means may emit or receive light through a part of the photographing system. It may be configured as follows.

As described above, according to the present invention, the aperture of the photographing system can be made small by using a dichroic mirror in a part of the photographing system, which is shaped so that the reflectance decreases in terms of area as it goes toward the periphery for projecting or receiving light. It is advantageous to be able to achieve a focus detection arrangement that can reduce color blemishes that occur within the screen.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, FIG.
3 is an explanatory diagram of the principle of focus detection, FIG. 4 is an explanatory diagram of an embodiment of the dichroic surface according to the present invention, FIG. 5 is an explanatory diagram of the spectral characteristics of a conventional dichroic surface, and FIG. 6 is an explanatory diagram of the spectral characteristics of a conventional dichroic surface. This is an explanatory diagram of color unevenness within the iai plane due to nine light beams passing through a conventional dichroic surface. In the figure, 5a is a dichroic surface, 5 is a prism, 9 is a light projecting lens, IO is a light source, 11 is a light receiving lens, 12 is a light receiving element, and 12a and 12b are light receiving surfaces.

Claims (1)

[Claims] In a focus detection device that detects the focus of a photographing system by projecting a light beam from a light projecting means toward a subject and receiving a reflected light flux from the subject by a light receiving means, at least one of the light projecting means or the light receiving means is provided. Light is emitted or received through a reflector provided in a part of the imaging system that is configured so that it mainly transmits visible light and reflects infrared light as it moves away from the center of the camera. Features a focus detection device.