JPH0141963B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active type focus detection optical system suitably used in a compact camera using a lens shutter.

Conventionally, in a focus detection device such as a lens shutter camera, a light beam emitted from a light source 1 such as an LED is transmitted to an object (not shown) through a projection optical system 2, as shown in FIG. The basic method is a so-called baseline length distance measuring method in which distance information to the object is obtained from the light beam l ₂ that is emitted as l ₁ , reflected by an object, and returned to the light receiving optical system 3 . Here, in order to increase the intensity of the light returning to the light receiving optical system 3 and to reduce the spot diameter generated on the photoelectric conversion element surface 4 on the optical axis C2 of the light receiving optical system 3, the light flux l ₁ is parallel. It is preferable that the light flux be close to the luminous flux. The incident angle θ of the light flux l ₂ reflected from the object and incident on the light receiving optical system 3 changes depending on the distance to the object, and for example, the angle of incidence θ with respect to the optical axis C2 of the light receiving optical system 3 changes. The spot S formed on the photoelectric conversion element surface 4 installed above is deviated from the optical axis C2 of the light receiving optical system 3 by a distance δ.

In FIG. 1, the distance to an object (not shown) on the extension of the optical axis C1 of the light emitting optical system 2 is D, and the distance between the optical axis C1 of the light emitting optical system 2 and the optical axis C2 of the light receiving optical system 3 is D. The distance is the baseline length L, the focal length of the light receiving optical system 3 is f,
As mentioned above, if the distance from the position of the optical axis C2 on the focal plane corresponding to the imaging position of an object at infinity to the center of the spot S of the reflected light from the object is δ, then
From the geometrical positional relationship, D/L=f/δ, that is, δ=f·L/D...(1) is obtained.

Therefore, the longer the focal length f of the light-receiving optical system or the longer the base line length L, the greater the movement distance δ and the higher the distance detection sensitivity.

This means that the photoelectric conversion elements 5a and 5a shown in FIG.
Intensity distribution I of reflected light from an object at a distance D from the imaging position P of the object at infinity on the surfaces 5b and 5c
If the distance δ to the center position Q is constant, the optical axis C1 of the light emitting optical system 2 and the light receiving optical system 3
This means that it is proportional to the distance between the optical axis C2 and the base line length L. The meaning of this base line length L is not necessarily limited to the distance between the optical axis C1 of the light emitting optical system 2 and the optical axis C2 of the light receiving optical system 3, but also the aperture center of gravity of the light emitting optical system 2 and the light receiving optical system 3. It may be an interval. Generally, the base line length L is the opening center of gravity interval,
As shown in FIG. 1, in many optical systems, the aperture center spacing and the optical axis spacing are usually the same.

In view of the above-mentioned facts, an object of the present invention is to provide a light emitting optical system that utilizes a finder optical system, deforms the aperture of the convex lens of the light receiving optical system, and deflects the convergent light flux passing through the convex lens asymmetrically to the optical axis, thereby creating an empty space. The objective is to provide a focus detection optical system suitable for a compact camera that effectively uses the space by installing other mechanisms in the space. In a focus detection optical system comprising a light projection optical system that projects a light beam toward the subject, and a light reception optical system that forms an image and receives the reflected light beam reflected from the subject, the light projection optical system includes: A concave mirror that transmits visible light and reflects infrared light is arranged at an intermediate position between the negative lens and the positive lens of a finder system consisting of a group of lenses having negative refractive power and positive refractive power from the subject side, and the concave mirror and the negative lens is configured to project an infrared beam from the light source toward the subject, and the center of gravity of the aperture shape of the light receiving optical system is deviated from the optical axis of the light receiving optical system. That is.

Figure 3 is a diagram of the principle of the present invention, and 10 is an LED
A light source that emits infrared light is generally preferred. Reference numeral 11 denotes a light projecting optical system, in which a light source 10 is arranged on the optical axis C1, and forms an image of the light source 10 as a parallel light beam _l1 at an appropriate position in the subject space. A light-receiving optical system 12 is arranged in this light-emitting optical system 11 at a distance B, and the light-receiving optical system 12 is connected to the light-emitting optical system 1 with its optical axis C2 remaining.
It is an eccentric lens with a notched end on the first side, and it connects the optical axis C1 of the light projecting optical system 11 and the light receiving optical system 12.
The distance between the aperture and the center of gravity G2, that is, the length corresponding to the base line length is L, similar to the optical axis distance in FIG.
The aperture width of the light receiving optical system 12 is, for example, a length A as shown in FIG. To further simplify the explanation, it is assumed that the respective aperture shapes of the light projecting optical system 11 and the light receiving optical system 12 have biaxial symmetry with respect to the optical axis C1 and the aperture center of gravity G2. Further, at a focal position behind the light receiving optical system 12, a light receiving element surface 13 consisting of a plurality of photoelectric conversion elements is placed on the back of the light receiving optical system 12.
The light-receiving optical system 12 parallel to the surface direction of the
are arranged substantially aligned with the optical axis C2.

Here, the distance between the optical axes C1 and C2 of the light emitting optical system 11 and the light receiving optical system 12 is L-(A/2),
When substituted into L in the above equation (1), δ becomes smaller, and the sensitivity appears to decrease. However, as mentioned above, L in equation (1) is the distance between the centers of gravity of the apertures, and there is no difference in the distance detection sensitivity of the autofocus device shown in the principle diagram shown in FIG. 3 and in FIG. 1.

This is because the distance to the object is D, and the light receiving element surface 1
Light receiving optical system 1 from the center Q of the reflected light spot on 3
2's optical axis C2 is δ', then δ'={L-(A/2)}・(f/D) +(1/2)・{A(d'-f)・(D -f)}/
(f・D) = {(2L−A)・f}/(2D)+A・f/
This is because (2f・D)=f・L/D=δ. Note that in the above formula, d' is the object distance D
It is the distance to the image plane by the light receiving optical system 12 for the distance, and has the following relationship: 1/D+1/d'=1/f (3).

By the way, if the light-receiving optical system 12 has an aperture that is symmetrical about the optical axis like the light-receiving optical system 3 shown in FIG. In this case, the straight line becomes the optical axis, and there is a light ray _l3 that is close to or in contact with the outer shell 14 of the cartridge chamber or spool chamber. However, according to the principle diagram shown in FIG. 3, the deflected light receiving optical system 12 is used to avoid the outer shell 14 of the patrone chamber or spool chamber after the reflected light beam _l2 from the object passes through the light receiving optical system 12. Since it converges to the side, the above-mentioned inconvenience does not occur, and the base line length L is maintained.
A space is obtained in which the cartridge chamber 15 can be placed obliquely behind the light receiving optical system 12.

Next, we will discuss examples that effectively utilize the spatial margin created based on the principle diagram in Figure 3, as shown in Figures 5 and 6.
This will be explained using figures.

FIG. 5 shows the first embodiment, in which the projection optical system is also used as an Arvada-type finder, and a concave lens 19 serving as an objective lens and a convex lens 20 serving as an eyepiece are the basic components of this type of finder. be. A light transmitting block 21 made of transparent glass or synthetic resin is arranged on the optical axis C1 between the concave lens 19 and the concave lens 20, and inside this block 21, visible light is transmitted and infrared light is reflected. A concave mirror 22 is provided obliquely. The concave mirror 22 is preferably a spheroidal mirror, and the infrared light emitted from the light source 10 placed on the side of the light transmission block 21 is
The light is converged by the concave mirror 22, passes through the concave lens 19, and is emitted as a substantially parallel light beam _l1 . In addition, the light receiving optical system 1 installed in parallel with the light emitting optical system
2 is an eccentric lens as explained in Fig. 3;
The reflected light _l2 from the object passes through the light-receiving optical system 12 and is converged on the optical axis C2 side, so that the space obliquely behind the light-receiving optical system 12 can be used as the outer shell 14 of the cartridge chamber or spool chamber.

FIG. 6 shows a second embodiment, in which the space obtained on the side of the light receiving optical system 12 of the light transmitting block 21 is effectively utilized, and the light receiving optical system is the same as that shown in FIG. The positions of the optical axis C2 of the light-receiving optical system 16 and the center of gravity G2 of the aperture have a relationship opposite to that of the first embodiment. Furthermore, the light beam l ₂ after passing through the light receiving optical system 16 is deflected by a reflecting mirror 23 placed obliquely with respect to the optical axis C2, and is made to enter the light receiving element surface 17.

Now, in FIG. 6, if the aperture width of the light receiving optical system 16 is 10 mm and the focal length is 20 mm, the focal length of the light receiving optical system 16 can be extended to about 23 mm to 25 mm. This extension improves the distance detection sensitivity, as is clear from equation (1).

Therefore, the area occupied by the focus detection optical system according to these embodiments is determined by the focal length f of the light receiving optical system, and
The area required is the product of the width W including the light emitting optical system and the light receiving optical system, and furthermore, other mechanisms or mechanisms that can improve the focusing function can be housed within this area. .

Note that the polarization of the receiving optical system is done in the straight line direction connecting the light emitting optical system and the receiving optical system, but there is no problem if it is carried out in a direction perpendicular to this direction, that is, in a direction perpendicular to the plane of the paper. .

As explained above, the focus detection optical system according to the present invention utilizes the surplus space created by using a deflection optical system in which the center of gravity of the aperture and the optical axis are shifted in the light receiving optical system. A focus detection optical system with higher distance detection sensitivity can be housed in the space occupied by the conventional focusing device, or a focus detection optical system with the same distance detection sensitivity can be installed in a narrower space than the conventional one. It becomes possible to store the system. In addition, since a part of the viewfinder optical system is shared as the floodlight lens of the floodlight optical system, space utilization efficiency is dramatically improved, making it ideal for use in intermediate-grade lens shutter cameras, which have recently become more compact. It can be used as a focus detection optical system.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional active baseline length method focusing detection optical system, FIG. 2 is an explanatory diagram of the light intensity distribution on the photoelectric conversion element of FIG. 1, and FIG. 4 is a front view of the aperture of the optical system, FIG. 5 is a block diagram of the first embodiment, and FIG. 6 is a block diagram of the second embodiment. . Reference numeral 10 is a light source, 11 is a projection optical system, 12,1
6 is a light receiving optical system, 13 and 17 are light receiving element surfaces, 19
20 is a concave lens, 20 is a convex lens, 21 is a light transmitting block, 22 is a concave mirror, _l1 is a projected light beam, _l2 is a received light beam, C1 and C2 are optical axes, and G2 is a center of gravity.

Claims (1)

[Claims] 1 Focus detection optics consisting of a light projecting optical system that projects the light beam from a light source that emits infrared light toward the subject, and a light receiving optical system that forms an image of the reflected light beam reflected from the subject and receives the light. In the system, the projection optical system transmits visible light and emits infrared light to an intermediate position between the negative lens and the positive lens of the finder system, which is composed of a lens group having negative refractive power and positive refractive power, from the object side. A concave mirror that reflects the light is arranged, and the concave mirror and the negative lens are configured to project the infrared light flux from the light source toward the subject, and the center of gravity of the aperture shape of the light receiving optical system is A focus detection optical system characterized by being deviated from the optical axis.