JPS6165213A - Optical system for automatic focusing - Google Patents

Abstract

PURPOSE:To increase the accuracy of forming, and widen the range measurable area of automatic focusing and improve the accuracy of range measurement by allowing either of lens systems for projection and photodetection to include a lens made of synthetic resin having a high refractive index, and interposing a ultraviolet-light and visible-light cutting filter at an object side. CONSTITUTION:An image of an object 9 picked up by the photographic system 1 of a camera is formed on a film and the photosensitive surface 2 of an image pickup element. Infrared projection luminous flux from an infrared-light emitting element 3 arranged outside a photographic system is projected upon the object 9 through a projection lens system 4 and the ultraviolet-light and visible-light cutting filter 7 and its reflected light is image-formed on a photodetecting element 6. When the photodetecting element 6 consists of two differential type elements 6A and 6B, the photodetecting element 6 is scanned until the output is zero, and the whole or part of the photographic system 1 is moved associatively with said scanning to attain automatic focusing operation. Consequently, the range measurement area of the automatic focusing is widened and the accuracy is improved, so yellow changing of the lens and a defect in outer appearance such as black dust are prevented.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to autofocus for cameras, particularly for autofocus that emits infrared light and receives all of the reflected light from the subject to detect the distance to the subject. This relates to the configuration of the optical system.

[Background of the invention]

Conventionally, this type of autofocus optical system has generally used an aspherical lens made of methyl methacrylate resin as a light emitting or light receiving lens in order to achieve high performance at low cost. For example, an example of this is disclosed in Japanese Patent Laid-Open No. 55-101915.

However, as the aperture of the camera/)e becomes larger and the zoom ratio becomes larger, it is required to increase the detection distance of the auto 7A-scatter, that is, the reachable distance of the infrared light. Possible ways to do this include using a highly efficient infrared light emitting element or increasing the current flowing through the infrared light source, but the former would dramatically increase the cost, and the latter would increase power consumption. Further, there are problems such as a shortened lifespan of the light emitting element. Another method is to reduce the F number of the light emitting or receiving lens, but methyl methacrylate has a refractive index of 1.492.
Because of this low value, when this lens is compared to a six-aperture lens, the amount of aberration increases, it does not satisfy the required performance of autofocus, causes a decrease in N degree, and the difference between the center wall thickness and the peripheral wall thickness becomes large. , molding accuracy deteriorates. So, let the light shine!
It is preferable to use a material with a high refractive index for the light-receiving lens, both from the viewpoint of aberrations and from the viewpoint of minimizing the difference in wall thickness.

However, when a glass material is used as the high refractive index material, the cost of an aspherical surface becomes extremely high. On the other hand, when using synthetic resin with a high refractive index, there are many disadvantages inherent to the material.For example, when exposed to ultraviolet light, absorption of short wavelength light increases and yellowing occurs.
e) Styrene and copolymers of acrylonitrile and styrene have a remarkable llX orientation. Polycargonate also has this tendency, but another problem is the black dust generated inside during molding. In other words, polycargonate has poor fluidity, so high-temperature molding is necessary to fully improve the facetability, but since polycargonate contains benzene rings in its composition, it carbonizes during high-temperature molding, leaving a black inside. Foreign matter occurs. Although this black dust is minute and does not cause any actual damage to the imaging performance, it is heavy in appearance.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional examples, and to make it possible to increase the diameter of the light emitting or light receiving lens and to improve the molding accuracy by using a high refractive index synthetic resin, thereby increasing the distance measurement range of autofocus. To provide an autofocus optical system for a camera that can improve magnification and distance measurement, and avoid problems such as yellowing and black spots on the lens.

[Summary of the invention]

In the autofocus optical system of the present invention, at least one of the lens systems for projecting infrared light onto a subject and the lens system for receiving reflected light from the subject includes a high refractive index synthetic resin lens, In addition, ultraviolet and visible light power is applied to the subject side of at least one lens system through a filter. It is characterized by being i.

[Embodiments of the invention]

An embodiment of the present invention will be described according to the drawings. In FIG. 1, an image of a subject 9 produced by a photographing system 1 of a camera is formed on a photosensitive surface 2 of a film or an imaging probe.

An infrared light beam from an infrared light emitting element 3 disposed outside the photographing system, such as an infrared light emitting diode or an infrared semiconductor radar, is passed through a light projection lens ice 4 through an ultraviolet and visible light cut filter 7t to a subject 9. The reflected light is imaged by an ultraviolet and visible light cut filter 8 and a light receiving lens system 5) on a light receiving element 6, for example, a silicon photodiode. The light-receiving element 6 is a differential type probe 6A with two probes as shown in the figure.
, 6B, autofocus can be achieved by scanning the light receiving element 6 to a position where its output becomes zero and moving the entire photographing system 1 or a part thereof in conjunction with the scanning. Since the principle of such auto7 orcus is well known, it will not be described in detail here.

In an embodiment with such a configuration, at least one of the light emitting lens system and the light receiving lens system 4.6 is made of a synthetic resin having a higher υ refractive index than conventional methyl methacrylate for the purpose of aberration correction and molding accuracy. Use it as a material. Regarding the above-mentioned problems such as yellowing due to ultraviolet irradiation and black dust during molding regarding high refractive index polystyrene, copolymer of acrylonitrile and styrene, polycarbonate, etc., in this embodiment, the above-mentioned filter 7.8 is Since it is an ultraviolet and visible light cut filter, it blocks ultraviolet rays from the outside and prevents yellowing.Also, since the internal light emitting and receiving lenses cannot be seen through the filter, black dust does not become an obstruction point, and synthetic resin As a general property, those with a high refractive index tend to have high dispersion and a large amount of dust chromatic aberration, but if the autofocus light source 3 has a narrow infrared spectral distribution, chromatic aberration will not be a problem. No.

Although the above embodiment has a configuration in which an autofocus optical system is provided outside the photographing system, the present invention uses a TTL method in which part or all of the photographing system is shared by both the infrared light projecting system and the light receiving system, or a light projecting system. Alternatively, it can also be applied to a half-TTL system in which this is shared for one side of light reception. Also, the members that perform scanning at the time of Al1 distance are a light projecting lens, a light receiving lens, and a light source.

At least one of the light receiving elements can be used.

Furthermore, in addition to the above-mentioned method of using differential output as a method of detecting received infrared light for autofocus, a method of detecting the maximum output using a light-receiving element is also possible.

[Purpose of the invention]

As explained above, according to the present invention, by using a high refractive index synthetic resin as the material for the light emitting/receiving lens for autofocus using infrared light, this can be made into a large-diameter, high-performance lens. , it is possible to expand the range of autofocus and improve inspection, as well as the power of ultraviolet and visible light.

Since the filter is used in front of the light emitting/receiving lens, it is possible to prevent yellowing of the lens and appearance defects such as black dust.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention. 1... Photography system, 3... Infrared light source, 4...
... Light emitting lens, 5... Light receiving lens, 6...
・Photodetector, 7.8... Ultraviolet and visible light cut filter, 9...
·subject. Figure 1

Claims (1)

[Claims] 1. Projecting infrared light onto a subject via a light projecting lens system, receiving the reflected light from the subject through a light receiving lens to a light receiving element, and detecting the subject distance from its output. In an autofocus optical system of a camera, at least one of the light emitting lens system and the light receiving lens system includes a high refractive index synthetic resin lens, and the at least one lens system has a lens on the subject side that emits ultraviolet and visible light. An autofocus optical system characterized by interposing a cut filter. 2. The autofocus optical system according to claim 1, wherein the high refractive index synthetic resin has a refractive index Nd>1.55.