JPH0260165B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical system for a single-lens reflex camera capable of detecting focus.

In conventional single-lens reflex cameras, the light transmitted through the photographic lens is guided to the eyepiece through an optical system for viewfinder observation, which consists of a quick return mirror, a pentaprism, an eyepiece, etc. A focus detection system that splits a light beam with a beam splitter placed between the return mirror and the pentaprism, that is, within the finder optical system, and includes a filter that cuts out light outside the visible range (for example, infrared light) from the split light beam. There is one that guides the light onto a photoelectric conversion element via an optical system. A device in which a filter is placed immediately in front of a photoelectric conversion element as described above has been proposed in Japanese Patent Application No. 55-38804 (Japanese Patent Application Laid-Open No. 55-130524). Such filters have the characteristic of cutting infrared light in order to eliminate the influence of infrared aberration on focus detection, but if this infrared light cutting characteristic is made too strong, it will adversely affect focus detection. There is a risk that the amount of light necessary for proper operation may also decrease. Furthermore, since photoelectric conversion elements are generally formed to be more sensitive to infrared light than to visible light, the filter completely cuts out light in the infrared region as described above. This is considered to be inconvenient.

Therefore, even if the infrared cut filter placed just before the photoelectric conversion element cuts out light outside the visible range, it is necessary to cut out light in the infrared light range to a certain extent so that the infrared aberration does not adversely affect focus detection. It is considered desirable to have a structure that allows the light to pass through and guide a sufficient amount of light for focus detection processing onto the photoelectric conversion element. In the conventional device described above, the filter is provided in the focus detection optical system, so the photographing lens,
quick return mirror, beam splitter,
Out of the light guided to the photoelectric conversion element via the focus detection optical system, non-visible light can be cut out, and the light that is guided from the eyepiece to the photoelectric conversion element via the eyepiece, pentaprism, beam splitter, and focus detection optical system can be cut out. It is also possible to cut out light outside the visible range of the so-called reverse incident light that is guided to the sensor. However, in this conventional device, it is thought that the filter in the focus detection optical system transmits some light in the infrared region, and if only the transmitted light from the photographic lens is incident, the focus detection is due to infrared aberration. However, when reverse incident light enters from the eyepiece side, it reaches the photoelectric conversion element for focus detection, although this reverse incident light itself is stray light that does not contribute to focus detection. Therefore, even if a filter is provided, there is a problem in that as the amount of reversely incident light increases, focus detection becomes impossible or the focus detection accuracy decreases significantly.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and to provide a single-lens reflex camera capable of detecting focus, which can sufficiently eliminate the influence of light outside the visible range among reversely incident light.

In order to achieve the above object, the present invention provides a filter for cutting out light outside the visible range in the optical system for viewfinder observation, and the reverse incident light is transmitted between the filter provided in the optical system for viewfinder observation and the optical system for focus detection. The positional relationship between the two filters was determined so that the photoelectric conversion means was reached through the filter provided in the system.

Embodiments of the present invention will be described below with reference to the accompanying drawings. In Fig. 1, light from a subject Q is transmitted through a photographing lens 12, a quick return mirror 1, a finder screen 2, a condenser lens 3, a beam splitter 4, a pentaprism 10, an eyepiece 11, and long wavelength light (outside the visible range). (e.g., a part of infrared light) is guided to the eyepiece (not specifically shown) through a filter 14 that cuts out the light (for example, a part of infrared light). The optical system from the quick return mirror 1 to the eyepiece constitutes an optical system for viewfinder observation. A portion of the viewfinder observation light is branched to the side where the eyepiece 11 is located by a semi-transparent mirror 4a provided in the beam splitter 4, and the branched luminous flux is passed through a filter 5 that cuts out long wavelength light similarly to the filter 14. is guided to the light distribution means 6 via. The light distribution means 6 distributes the light beam split by the beam splitter 4 into two light beams Pa'' and Pb''. One light beam Pa'' is guided onto a photoelectric conversion element 9a via a focus detection lens 7a and a reflecting mirror 8a.
The other luminous flux Pb'' passes through the focus detection lens 7b and the reflecting mirror 8b to the photoelectric conversion element 9 as described above.
b. The optical system that guides the light split by the beam splitter 4 to the photoelectric conversion elements 9a and 9b constitutes an optical system for focus detection.

The finder screen 2 is placed at a position conjugate with the film surface (not shown), and the focus detection optical system is configured to reimage the light transmitted through the finder screen 2 on photoelectric elements 9a and 9b. There is. In this embodiment, after the light emitted from the subject Q is split by the beam splitter 4, the light fluxes Pa' and Pb' corresponding to the light fluxes Pa and Pb transmitted through different areas 12a and 12b in the pupil of the photographic lens 12 are used. are distributed by the light distribution means 6, and the luminous flux corresponding to the luminous flux Pa is
Pa'' onto the photoelectric element 9a, the luminous flux corresponding to the luminous flux Pb
Pb'' is guided onto the photoelectric element 9b, respectively. Therefore, when the photographing lens 12 moves in the front-back direction, the optical images on the photoelectric elements 9a and 9b move on these elements 9a and 9b, and the image on the element 9a and When the image on element 9b reaches a predetermined positional relationship, each element 9a, 9b
It can be detected from the photoelectric output that the photographic lens 12 is in the in-focus position. The light distribution means 6, the detection lenses 7a and 7b, and the reflecting mirrors 8a and 8b are part of the eyepiece system 1.
A light beam Pa'' from the reflecting mirror 8a to the photoelectric conversion element 9a and a light beam Pb'' from the reflecting mirror 8b to the photoelectric conversion element 9b are guided upward through both sides of the eyepiece lens system 11, respectively. The optical system (part of the finder optical system) and the focus detection optical system extending from the beam splitter 4 to the eyepiece are each independently shielded from light. Photography lens 1
The light that has passed through the filter 2 is partially split by the beam splitter 4 and reaches the photoelectric conversion elements 9a and 9b via the focus detection optical system, but after passing through the filter 5, it is guided onto the elements 9a and 9b. So,
Light with long wavelengths outside the visible range is filtered out by this filter 5, and the photoelectric conversion elements 9a and 9b react to this light to prevent errors in focus detection. in particular,
This filter 5 is as shown in FIG.
It is configured to gradually cut out light in the visible range around 600 nm to light in the infrared range around 850 nm, and then completely cut out light in the infrared range after that. In this way, the filter 5 transmits a certain amount of light in the infrared region to the extent that infrared aberration does not adversely affect focus detection, and emits a sufficient amount of light for focus detection onto the photoelectric conversion elements 9a and 9b. configured to lead. Note that the photoelectric conversion elements 9a,
9b has a characteristic of not reacting to light with a short wavelength outside the visible range. Therefore, focus detection can be performed mainly by sensing light in the visible range. Furthermore, it goes without saying that the filter 5 can be omitted if a photoelectric conversion element that does not react to light outside the visible range (long wavelength and short wavelength light) is used. There is a risk that the reverse incident light 15 from the eyepiece (not shown) will be guided onto the photoelectric conversion elements 9a and 9b via the filter 14, the eyepiece 11, the pentaprism 10, the beam splitter 4, and the focus detection optical system. be. However, the reverse incident light from the eyepiece lens 11 is transmitted to the photoelectric conversion elements 9a and 9.
Even in the event that the beam is guided upward, the infrared cut filter 14 is placed in the optical path from the eyepiece to the beam splitter 4, as shown in FIG. Most of the light passes through the two filters 14 and 5 to the photoelectric conversion elements 9a,
9b is not affected. Filter 14
The stronger the long-wavelength cutting performance, the better; however, it must not exhibit significant coloring or interference colors that are obnoxious to the eyes when observed through a viewfinder eyepiece (not shown). Since the reversely incident light from the eyepiece does not contribute to focus detection at all, it is desirable that the filter 14 has the same or slightly stronger long wavelength cutting performance as the filter 5. Figure 2 shows filters 5 and 1 used in this example.
4 shows the long wavelength cut characteristic.

In addition, in the embodiment described above, the filter 5,
Needless to say, if the light distribution means 6, the detection lenses 7a, 7b, and the reflecting mirrors 8a, 8b are housed in one unit, adjustment will be easier. Further, if necessary, the photoelectric conversion elements 9a and 9b may also be housed in this unit.

Further, in addition to placing a filter behind or in front of the eyepiece 11, the eyepiece 11 or a part thereof may be formed of filter glass, and such filter glass has slightly lower weather resistance than ordinary glass. Taking this into consideration, it may be configured such that it is sandwiched in the eyepiece lens 11 in the shape of a sandwich. Furthermore, if it is formed as a filter by thin film deposition, it may be attached not only to the eyepiece lens 11 but also to any entrance/exit surface or reflective surface of the pentaprism. Also, beam splitter 4
Alternatively, the semi-transparent film 4a may be provided with a property of cutting long wavelength light, especially with respect to obliquely incident light, so that the semi-transparent film 4
It is also possible to form a multilayer film or a composite film, taking into account the effects of colored polarized light on the a part. Furthermore, direct transmission of light through each member of the eyepiece lens 11, pentaprism 10, and beam splitter 4,
A thin film is formed on surfaces that contribute to reflection to cut out the longer wavelengths of flare light that enters at various angles. It is also useful to apply a coating that absorbs long wavelengths well. In the embodiment shown in FIG. 1, the photoelectric detection optical system receives the beam split by the beam splitter located behind the finder screen 2, but the movable reflector 1 located in front of the finder screen 2 receives the light beam split by the beam splitter located behind the finder screen 2. A single-lens reflex camera in which the part 1a is semi-transparent, and the light beam passing through it is guided to a photoelectric conversion element 9' via a photoelectric focus detection optical system 7' on the bottom of the camera body using a reflective optical system 16. It goes without saying that the present invention can also be applied to Lexus cameras in order to reduce the adverse effects of reversely incident light from the viewfinder (see FIG. 3). In FIG. 3, a filter 5' corresponds to the filter 5 in FIG. 1, and a filter 14' corresponds to the filter 14. A movable reflector 1 serves as a beam splitter. The characteristics of filter 5' are shown in FIG.

According to the present invention, infrared light from the transmitted light from the photographing lens is cut by the first filter disposed between the beam splitter and the photoelectric receiving means or by the photoelectric receiving means itself; The infrared light from the reversely incident light entering from the viewfinder eyepiece is filtered out by a second filter before reaching the beam splitter, and then filtered by a first filter disposed between the beam splitter and the photoelectric receiving means. The infrared light is doubly cut by the filter or the photoelectric receiving means itself.

As a result, in the present invention, since the infrared cut is performed twice for the back incident light that does not contribute to focus detection at all, the back incident light from the viewfinder eyepiece and especially the infrared light in the back incident light is cut off twice. It is possible to sufficiently remove the influence of light and achieve the effect of enabling more accurate focus detection.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a first embodiment of the invention, FIG. 2 is a characteristic diagram of a filter, and FIG. 3 is an optical path diagram showing a second embodiment of the invention. Explanation of symbols of main parts, beam splitter...
...4, 1a, first filter...5, 5', optical system for viewfinder observation...1, 2, 3, 10,
11. Optical system for focus detection...6, 7a, 7b,
8a, 8b, 7', 16, photoelectric conversion means...9a,
9b, 9', Photographing lens...12, Second filter...14, 14', Light incident from the eyepiece...
...15.

Claims (1)

[Scope of Claims] 1. A finer observation optical system that guides transmitted light from a photographic lens to an eyepiece, a beam splitter that is disposed within the optical path of the observation optical system and that splits a beam of the transmitted light; It has a focus detection optical system that guides the light beam split by the beam splitter, and a photoelectric light receiving means that receives the transmitted light of the photographing lens guided by the focus detecting optical system, and the photoelectric light receiving means In a single-lens reflex camera capable of photoelectrically detecting the focus of the photographing lens from the output, the photoelectric light receiving means transmits a part of the light in the infrared region between the beam splitter and the photoelectric light receiving means. It is provided so as to limit part of the light in the infrared region by disposing a first filter to cut out the light or by its own characteristics, and mainly detect visible light contained in the light transmitted through the photographic lens, In the optical path from the eyepiece to the beam splitter, there is a lens for cutting a part of the infrared light that is incident reversely from the eyepiece and reaches the photoelectric receiving means via the beam splitter. An optical system for a single-lens reflex camera capable of focus detection, characterized in that two filters are provided.