JPS6173938A - Camera equipped with ttl viewfinder and automatic focus optical system - Google Patents

Abstract

PURPOSE:To improve the brightness of a viewfinder and the light utilization efficiency of automatic focusing with simple constitution by using two beam splitters which have specific optical characteristics. 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 reflected light is split by a beam splitter 6 which transmits visible light completely and reflects infrared light completely; the reflected light is automatic focusing light and the transmitted light is light to viewfinder. 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 present invention relates to a TTL optical finder and a TTL auto7 orcus optical system, particularly an optical system for active autofocus that projects infrared light onto a subject and receives the reflected light. The present invention relates to a turtle 2 equipped with the following.

[Background of the invention]

2. Description of the Related Art Conventionally, in a camera, an optical system is known in which a distance measuring means such as a micro prism is further arranged in a TTL finder light beam that is split from a photographing light beam by a half mirror. It is easy to arrange an active autofocus optical system in place of this distance measuring means. However, in such an optical system, the light passes through the half mirror twice, so
The viewfinder is also dark and the autofocus doesn't use infrared light efficiently. On the other hand, in video cameras, etc., instead of TTL 7-inder, the image is captured by electrical signals from the image sensor.
An electronic viewfinder (EVF) that displays on a T (Plaquen tube) is often used, and in this case, the brightness of the viewfinder and autofocus efficiency are high, but it has the disadvantages of increased power consumption and weight. shed lightweight,
This goes against Needy's demand for lower power consumption.

[Purpose of BI4] The purpose of the present invention is to provide a camera 2 that is equipped with a combination of a TTL active autofocus optical system that uses infrared light and a TTL finder optical system, and that has extremely high finder brightness and autofocus light utilization efficiency. is to provide.

[Summary of the invention]

According to the present invention, a first light splitter that transmits and reflects visible light and substantially completely transmits infrared light is disposed in the photographing optical system, and the first light splitter transmits and reflects visible light and substantially completely transmits infrared light. 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 the 7-inner light is treated as 7inder light, and the infrared light that is reflected from the subject is projected onto the subject via the photographic optical system and the first and second light splitters. A camera is provided that includes a TTL 7 indexer and an autofocus optical system that performs at least one of receiving light.

[Embodiments of the invention]

FIG. 1 shows an embodiment in which the present invention is applied to a camera using a zoom lens as a photographing lens. This embodiment takes as an example an autofocus optical system as a TTL infrared receiving system that receives infrared light reflected from an object onto which infrared light is projected.

Hereinafter, autofocus' will be abbreviated as υ゛. The light beam passing through the zoom section 1 is transmitted to the light splitting surface 2' of the light splitter 2,
It is divided into a light beam for photographing and a light beam for the finder and AF. The photographing light beam reflected by the light splitting surface 2' passes through the aperture 3 and the imaging lens system 4 to the υ film surface or image sensor surface F.
K image is formed. On the other hand, the light beam transmitted through the light splitting surface 2' passes through the objective lens 5 for the finder and i, and is separated by the second light splitting surface 6 into a spot light path and a finder light path. An auxiliary light-receiving lens is disposed in the optical path for post-mortem propagation reflecting off the light splitting surface 6, and an infrared light-receiving element 8 is disposed approximately at the focal point of the AF light optical system composed of elements 1 to 7. On the other hand, a focusing plate 9 is arranged on the primary focusing surface of the 7-eye/goo optical path that has passed through the light splitting surface 6, and then an erecting image is connected to the secondary focusing surface 11 with an image erecting lens 10, and this is the eyepiece. It is observed by 12.

Now, these light splitting surfaces 2' and 6 split the intensity of light of any wavelength at the same ratio, for example, 50% of light of any wavelength is transmitted and reflected for 50 meters, and it covers the entire luminous flux. Assuming that there are 7 mirrors, 25% of the light incident on the photographing lens reaches the AF system and finder system, respectively. However, it is desirable to make the finder as bright as possible and to allow as much infrared light as possible to reach the optical system, so it is desirable to further increase this efficiency. For this purpose, for cameras that do not use an optical viewfinder, the AF optical system must be replaced with a light splitter 2 that has the characteristics of completely reflecting visible light and completely transmitting infrared light.
-, but this will make viewfinder observation impossible on devices equipped with an optical viewfinder. Furthermore, if the AF light and finder light are extracted from the photographing light flux using separate half mirrors, the efficiency of each light beam reaching the light beam can be increased, but this requires two light splitters, which is undesirable in terms of space and cost. In order to not affect the viewfinder and i system even when stopping down υ3, it is necessary to place these two light splitters before the aperture, so the first lens
This is not desirable because the distance from the surface to the crest increases, which 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 setting the optical characteristics of the light splitters 2 and 6, only a single light splitter 2 is provided in the photographing optical path, and the viewfinder optical system and the AF optical system can be combined. This made it possible to increase the light arrival rate, that is, the light usage efficiency. That is, the light splitter 2 is configured to divide the intensity of visible light at the same ratio for all wavelengths, and to have a characteristic of almost completely transmitting infrared light. Such a light splitter has a so-called) 1-7 mirror configuration,
This can be realized by using a multilayer film structure that combines the structures of visible light and infrared light.

On the other hand, the light splitter 6 is a gicchroic mirror that almost completely reflects infrared light and almost completely transmits visible light.

This allows the efficiency to be greatly increased.

For example, the light splitter 2 transmits 50 pixels of visible light, and 50 pixels of visible light.
% reflection and 100% transmission for infrared light, while the light splitter 6 has ideal characteristics of 100% transmission for visible light.
Assuming ideal characteristics of % transmission and 100% reflection of infrared light, the finder system will absorb 5% of the light incident on the photographic lens.
0% is reached, and the AP optical system reaches 100%. Therefore, compared to a case where both mirrors are constructed of half mirrors that transmit 50% and reflect 50% of light of any wavelength, the efficiency of the finder system is twice as high, and the efficiency of the AF system is four times as high. Although the above comparison is based on ideal characteristics, the efficiency can be extremely high even when compared on an actual designed rotor. Since a normal infrared light receiving element is sensitive to visible light, a visible light cut filter is also used in order to improve the S/N of the signal, 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 system is a secondary imaging system, and specifically, the arrangement is changed according to the layout of the camera, and a field lens and field mask are added. is possible. It is also possible to arrange the light splitter 6 and the AP optical systems 7 to 8 in front of the objective lens 5.

It is also possible to omit the light-receiving auxiliary lens 7 depending on the required performance for i. It is preferable that the i-optical system composed of elements 1 to 7 is coated with other means to reduce the loss of infrared light as much as possible. In the embodiments described above, the infrared projection system may be placed outside the photographing optical system.

In addition to the above-mentioned embodiment, an infrared light receiving element 8 is shown in FIG.
It is also possible to construct an infrared projection system for AF in which the infrared light source is replaced with an infrared light source and the infrared light emitted from the infrared light follows the optical path opposite to that described above and is projected onto the subject.1 In this case, The effect of improving the efficiency of projecting infrared light from 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. AF
This results in the effect of improving the efficiency of both emitting and receiving infrared light.

〔Effect of the invention〕

As explained above, according to the present invention, a camera is equipped with a TTL optical finder and a TTL infrared active AF optical system at the same time, and the finder is bright and U
The infrared light usage efficiency of the optical system is improved, and it is possible to contribute to improving the performance of cameras (including video cameras), making them smaller and lighter, and saving power.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention. 1.4...Photographing lens system, 2...Light splitter, 3...
・Aperture, 6... Light splitter, 7.8...
・AF infrared receiving system, 9...Primary focus plane, 11...Secondary imaging plane,
12...Finder eyepiece. Figure 1

Claims (1)

[Claims] disposing a first light splitter that transmits and reflects visible light and substantially completely transmits 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 split optical path resulting from transmission by 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 finder and an autofocus optical system, characterized by receiving at least one of reflected infrared light.