JPS6173935A - Camera equipped with ttl viewfinder and automatic focusing optical system - Google Patents

Abstract

PURPOSE:To improve the brightness of a viewfinder and the light utilization efficiency of automatic focusing by using a light splitter whose transmissivity and reflectivity are specific. CONSTITUTION:Subject reflected light passed through a zoom photographic lens 1 is split into two by a beam splitter 1 which has equal reflectivity and transmissivity to visible light and reflects infrared light completely, and the transmitted light becomes photographic light. Reflected light, on the other hand, is split by a beam splitter which transmits visible light completely and reflects infrared light completely; the reflected light becomes automatic focus infrared optical system light and the transmitted light becomes viewfinder optical system light. Thus, the brightness of the viewfinder and the light utilization efficiency of automatic focusing are improved by the simple constitution which uses the two beam splitters.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The undiscovered invention is a TTL optical finder and a TTL autofocus optical system, particularly an active auto 7 first system that projects infrared light onto a subject and receives the reflected light. The present invention relates to a camera equipped with a scrap optical system.

[Background of the invention]

Conventionally, photometric optics in cameras have a structure in which -7 mirrors are further placed in the TTL finder light beam that is split from the shooting light beam by -7 mirrors to guide a part of the finder light to a photometric element for secondary light. The system is known. A TTL autofocus optical system in which the infrared light source or infrared light receiving element for active autofocus is arranged in place of this photometric element can be easily conceived. However, since such an optical system passes through the half mirror twice, the viewfinder is not dark and the autofocus efficiency is poor. On the other hand, in place of the TTL finder, video cameras often use an electronic knee finder (EVF') that displays an image on a CRT (cathode ray tube) using electrical signals from an image sensor. Although the brightness of the eye/goo and the efficiency of autofocus are high, it has the disadvantages of increased power consumption and weight, which goes against the demands of Needy for smaller size, lighter weight, and lower power consumption.

[Purpose of the invention]

An object of the present invention is to provide a camera which is equipped with a combination of a TTL active autofocus optical system that uses infrared light and a TTL finder optical system, and which has extremely high finder brightness and autofocus light utilization efficiency.

[Summary of the invention]

According to the present invention, a first light splitter that transmits and reflects visible light and substantially completely reflects infrared light is disposed in the photographing optical system, and the first light splitter that transmits and reflects visible light and substantially completely reflects infrared light is provided. A second light splitter that substantially completely transmits visible light and substantially completely reflects infrared light is disposed in the split optical path, and includes a photographing optical system and the first and second light splitters. The visible light that has passed through is treated as inner light, and on the other hand, infrared light is projected onto the subject via the photographing optical system and the first and second light splitters, and the infrared light is reflected from the subject. Provided is a camera equipped with a TTL 7 optical system and an autofocus optical system, characterized in that the camera performs at least one of the following:

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention applied to a camera having a photographing lens as a zoom lens.

The present embodiment will be described by taking as an example an autofocus optical system in which infrared light reflected from an object onto which infrared light is projected is received by an infrared light receiving element through a photographing lens. Hereinafter, the term autofocus will be abbreviated as Ar. The light beam that has passed through the zoom section l is sent to the light splitter 2 with a rhythm of -77''.
The light splitting surface 2' separates the photographic light flux from the viewfinder and A.
It is divided into a light beam for r. The photographing light beam passes through the aperture 3 and the imaging lens system 4, and forms an image on the film surface or the image sensor surface F. On the other hand, the light beam reflected by the light splitting surface 2' passes through the objective lens 5 for the finder and Ar, and is separated by the second light splitter 6 into an optical path for Ar and an optical path for the finder. A light-receiving auxiliary lens 7 is disposed in the Ar optical path after reflection by the light splitter 6, and an infrared light-receiving element 8 is disposed approximately at the focal point of the AF light-receiving optical system made up of elements 1-7. On the other hand, in the finder optical path that has passed through the light splitter 6, a focusing plate 9 is placed on the primary focusing plane, and then, after the optical path is bent by a total reflection mirror 10, a secondary focusing lens 11 is used for image erecting. An erect image is formed on the surface 12 and observed by the eyepiece 13.

Now, it is assumed that the light splitters 2 and 6 split the intensity of light of any wavelength at the same ratio, for example, transmit 50% of light of any wavelength and reflect 50% of it, and cover the entire luminous flux. Assuming that it is a -7 mirror, 25 beams of human light from the photographing lens reach the Ar system and the finder system, respectively. However, it is desirable that the 7-blade indexer receives as much visible light as possible to make it bright, and that the AF optical system receives as much strong infrared light as possible to further increase the above-mentioned delivery efficiency. For this purpose, regarding the AF optical system, in cameras that do not use an optical 7-blade indexer, the light splitter 2 may be a dichroic mirror that completely transmits visible light and completely reflects infrared light. This makes viewfinder observation impossible for cameras equipped with a TTL optical finder. Furthermore, if the A11'' light and the 7-inner light are extracted from the photographing light beam using separate half prisms, the efficiency of each light beam reaching the light beam can be increased, but this requires two ^-Fuderisms in the photographic optical system, and it also takes up space. The above is also not preferable.In particular, in order to avoid affecting the 7-inner and MU F even when the iris 3 is squeezed, it is necessary to place two -5-7 de IJ f in front of the iris. Therefore, the distance from the first surface of the lens to the aperture diaphragm increases, which is not preferable because it increases the overall length and also causes an increase in the diameter of the front lens.

Therefore, in the embodiment of the present invention, by appropriately selecting the optical characteristics of the light splitters 2 and 6 shown in FIG. This makes it possible to increase the efficiency of light reaching the optical system and the utilization efficiency of TB light. That is, the light splitter 2 is configured so that it divides the intensity of visible light of any wavelength at the same ratio, and has a characteristic of almost completely reflecting infrared light. Such a light splitter can be realized by using a multilayer film structure that combines a so-called nof mirror structure and a visible light/infrared light guichroic mirror structure. On the other hand, the light splitter 6 is a gicroic mirror that almost completely reflects infrared light and almost completely transmits visible light. As a result, the above-mentioned utilization efficiency can be greatly increased.

For example, the light splitter 2 transmits 50 pixels of visible light, and 50 pixels of visible light.
The light splitter 6 has ideal characteristics of 100% reflection for infrared light, while the light splitter 6 has 100% reflection for visible light.
Assuming that 50% of the visible light incident on the photographic lens reaches the focusing system, and 50% of the visible light incident on the photographic lens reaches the AF optical system, 50% of the visible light incident on the photographic lens reaches the AF optical system. 100% of the results will be reached. Therefore, compared to a case where both are light splitters with characteristics of 50% transmission and 50% reflection for light of any wavelength, the finder system can achieve twice the efficiency and the AF system can achieve four times the efficiency. The above comparison is based on ideal characteristics, but the comparison based on actual design data shows that although the efficiency is extremely high, ordinary infrared light receiving elements are also sensitive to visible light, so AP
'In order to improve the S/N ratio of the signal, visible light power and a filter are used together, but in this embodiment, the light splitter 6 has this effect, so the visible light cut filter can be omitted.

The above embodiment describes the general configuration when the finder is a secondary imaging system, and specifically, it is possible to change the arrangement according to the layout of the camera, or to add a field lens or field mask. It is possible. Furthermore, a light splitter 6 may be placed in front of the objective lens 5. Light receiving auxiliary lens 7
It is also possible to omit this depending on the performance required for AF.

The AF optical system composed of elements 1 to 7 is preferably coated with other means to reduce the loss of the amount of infrared light as much as possible. The infrared light projection system to the subject may be placed outside the photographic optical system.

In addition to the above-mentioned embodiment, an infrared light receiving element 8 is shown in FIG.
It is also possible to implement an embodiment in which an infrared light projection system for AF' is constructed in which the infrared light source is replaced with an infrared light source, and the infrared light emitted from the light source follows the optical path opposite to the above and is projected onto the subject. In this case, the effect of improving the infrared light projection efficiency of the light source can be obtained. It is also possible to implement an embodiment in which an infrared light source is arranged in the vicinity of the infrared light receiving element 8 in FIG. This results in the effect of improving the efficiency of both the emission and reception of infrared light for AF.

Note that the present invention is also applicable to a camera having a TTL finder system for observing primary imaging.

〔Effect of the invention〕

According to the present invention, Iif, TTL optical finder and T
It simultaneously realizes a TL infrared active AF' optical system, and has the effect of making the 7-blade index brighter and improving the transmission efficiency of infrared light of the AF' optical system, improving the performance of AF' cameras (including video cameras). It can contribute to improvement, size reduction, weight reduction, and power saving.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention. 1.4...Zoom photographing lens 2...Barf grism 6...Half mirror 7,
8...AF infrared receiving system 9...Primary focus plane 12
...Secondary focus plane

Claims (1)

[Claims] disposing a first light splitter that transmits and reflects visible light and substantially completely reflects infrared light in the photographing optical system;
A second light splitter that substantially completely transmits visible light and substantially completely reflects infrared light is disposed in the optical path divided by reflection from the first light splitter, and includes a photographing optical system and 1st above
The visible light that has passed through the optical system and the second light splitter is used as finder light, and the infrared light is projected onto and from the subject via the photographic optical system and the first and second light splitters. A camera equipped with a TTL viewfinder and an autofocus optical system, which performs at least one of receiving reflected infrared light.