JPS627028A - Optical system having fodus detecting device - Google Patents

Abstract

PURPOSE:To observe a fine finder image even when a strong semiconductor laser light source is used by arranging an optical member for interrupting the incidence of infrared light flux on a part of a finder system. CONSTITUTION:The optical member 9 such as an optical filter for interrupting the incidence of infrared light flux upon an observing position 8 for a finder image is arranged on a part fo othe finder system 7. A part of the infrared light flux radiated from a light source 6 is reflected by the 1st optical divider 2 or the len surface of the pregroup 1 and returned to the finder system as infrared flare or infrared goast, so taht the finder image is colored with red and the picture quality may be reduced. However, these deterioration can be prevented by arranging the optical member 9. Thereby, a fine finder image can be obtained in an optical system having a TTL type active focus detector by using a semiconductor laser with a strong output.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical system having a focus detection device; The present invention relates to an optical system having a so-called TTL type active focus detection device that detects the focus of the optical system by receiving reflected light flux from the subject side using a light receiving means.

(Prior Art) A conventional TTL type optical system having an active focus detection device has been proposed, for example, in Japanese Patent Laid-Open No. 57-154206. In general, in an active focus detection device, a light projecting means for projecting a light beam from the camera side to the subject side and a light receiving means for receiving the reflected light beam from the subject are each independent of the optical system or share a part of the optical system. installed. Active focus detection devices are capable of good focus detection even when the subject is dark or has low contrast, and the TTL method in particular has advantages such as no variation during focus detection. It has advantages.

In many cases, the light emitting means is a light source that emits infrared light that is hardly noticeable to the naked eye, is insensitive to the photosensitive surface, and is TTL type. □ Even if it is a TTL method, it does not reduce the amount of photographic light in the visible range. is being used.

However, if the infrared light beam is projected toward the subject through a part of the optical system, the infrared light beam reflected by the lens surface in the optical system will enter the viewfinder system, enter the observer's naked eye, and have a negative effect on the viewfinder. Image quality may be degraded. In particular, when using a light source such as an infrared semiconductor laser that emits a large amount of light and has good light condensing properties to enable distance measurement to distant objects, the viewfinder image becomes reddish, making it very difficult to observe. It may happen.

(Problems to be Solved by the Invention) The present invention solves problems caused by infrared flare, infrared ghost, etc. caused by reflection on the lens surface in the optical system when a powerful light source such as an infrared semiconductor laser is used as a light projecting means. The purpose of the present invention is to provide an optical system having a focus detection device that prevents deterioration in the image quality of a finder image and enables good observation of the finder image at all times.

(Means for solving the problem) An infrared light flux is projected from a light projecting means to a subject side via a part of an optical system, and a reflected light flux from the subject side is arranged in a part of the optical system, or In an optical system having a focus detection device that detects the focus of the optical system by receiving light with a light receiving means disposed near the optical system, a part of the finder system of the optical system is provided with a focus detection device located at a finder image observation position. An optical member is provided to prevent infrared light beams from entering.

Other features of the invention are described in conjunction with the examples.

(Embodiment) FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention. In the figure, 1 is the front group of the optical system, 2 is the first light splitter that splits the photographing light beam into two and guides the divided light beams toward the photosensitive surface 4 and the finder system 7, and 3 is the rear of the optical system. It is a group. Reference numeral 5 denotes a second light splitter, which is composed of a reflecting mirror that reflects the visible range and transmits the infrared range, and reflects a part of the photographing light beam split by the first light splitter 2 to the finder system 7. .

8 is the observation position of the finder image. Reference numeral 9 denotes an optical member provided in a part of the finder system 7, which is composed of an optical filter or the like having a characteristic of preventing infrared light flux from entering the observation position 8 of the finder image. Reference numeral 6 denotes a light source consisting of an infrared semiconductor laser or the like that emits an infrared light beam, which constitutes a part of the light projecting means, 10 a light receiving lens that receives the reflected light beam from the object, and 11 a light receiving element.

In this embodiment, the infrared light flux emitted from the lights W and 6 passes through the second light splitter 5, is reflected by the first light splitter 2, and then is sent to the subject side by the front group 1 of the optical system as a spot image. It is projected as. Then, the reflected light flux from the object is formed as a spot image on the surface of the light receiving element 11 by the light receiving lens 10, and the focus of the optical system is detected using the position of the spot image formed on the surface of the light receiving element 11. ing.

On the other hand, a part of the infrared light beam emitted from the light source 6 is reflected by the first light splitter 2 and the lens surface in the front group 1 of the optical system, and returns to the finder system 7 as an infrared flare or an infrared ghost. may enter the finder observation position 8.

As a result, the viewfinder image becomes reddish and the image quality deteriorates. Therefore, in this embodiment, an optical member 9 is disposed in a part of the finder system 7 to prevent infrared flare and infrared ghost from entering the finder image observation position, thereby preventing deterioration of the image quality of the finder image and facilitating the observation of the finder image. It is well maintained.

FIG. 2 is a schematic diagram of an optical system according to another embodiment of the present invention.
It is □. In this figure, the same elements as those shown in FIG. 1 are given the same reference numerals. In the figure, 21 is the Luns group.
22 is a second lens group having a variable power section. 23 is the third
Lens group, 24 is a first light splitter, 26 is a light projecting lens, 2
7 is a total reflection mirror.

In this embodiment, the infrared light beam emitted from the light source 6 is projected as a spot image toward the subject by the lens group 21 through the projection lens 26 and a reflecting surface provided on a part of the first light splitter 24. are doing. Similarly to the embodiment shown in FIG. 1, the light beam reflected from the subject side is focused by the light receiving lens 10 on the surface of the light receiving element 11 as a spot image.

On the other hand, the photographing light beam is split into two parts by a second light splitter 25 and guided to the photosensitive surface 4 and the finder system 7, respectively.

In this embodiment as well, the light source 6 is similar to the embodiment shown in FIG.
A part of the infrared light beam emitted from the lens is reflected by the first light splitter 24, the lens surface of the lens group 21, etc., and enters the finder system 7 as an infrared flare or an infrared ghost, which impairs the image quality of the finder image. may reduce the Therefore, by arranging an optical member 9 in a part of the finder system, infrared light beams are prevented from entering the finder image observation position 8, thereby preventing deterioration of the image quality of the finder image.

In this embodiment, the optical member may be either a solid filter or a dielectric multilayer filter. Furthermore, instead of using an optical member, a vapor-deposited film that absorbs infrared light or does not transmit infrared light may be applied to some lens surfaces in the finder system, and a total reflection mirror 27 shown in FIG. The object of the present invention can also be achieved by applying a deposited film with low light reflectance. In this embodiment, the light receiving lens 10 and the light receiving element 11 may receive light through a part of the optical system.

(Effects of the Invention) According to the present invention, in an optical system using a TTL method and having an active focus detection device, when a light source such as a semiconductor laser having a strong output is used as a light projecting means, the optical system Achieved an optical system with a focus detection device that prevents the image quality of the viewfinder image from deteriorating due to infrared flare and infrared ghost caused by reflections on the lens surface, and enables good viewfinder image observation. can do.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are each a schematic diagram of an optical system according to an embodiment of the present invention. In the figure, 1 is the front group of the optical system, 2.24 is the first light splitter, 5.25 is the second light splitter, 6 is the light source, 7 is the finder system, 8 is the finder image observation position, 9 is the optical member , 10 is a light receiving lens, 11 is a light receiving element, 4 is a photosensitive surface, 2
6 is a projection lens %27 is a total reflection mirror.

Claims (2)

[Claims] (1) An infrared light flux is projected from the light projecting means to the subject side through a part of the optical system, and the reflected light flux from the subject side is arranged in a part of the optical system or in the vicinity of the optical system. In an optical system having a focus detection device that detects the focus of the optical system by receiving the light with a light receiving means, the infrared light beam is incident on a part of the finder system of the optical system at the finder image observation position. An optical system having a focus detection device, characterized in that it is provided with an optical member for preventing. (2) An optical system having a focus detection device according to claim 1, wherein the light projecting means includes an infrared semiconductor laser.