JP2534789B2 - Focus detection optical system - Google Patents

Description

The present invention relates to a focus detection optical system used in cameras, video cameras, still video cameras and the like.

[Conventional technology]

Focusing is detected by projecting infrared light onto the subject and receiving the reflected light with multiple optical systems with parallax to detect focus, or receiving the subject image itself with multiple optical systems with parallax. In the passive type focus detection optical system for performing the above, a large number of optical systems other than the taking lens system are conventionally known, and as a representative one, for example, the one described in JP-A-55-149007. There is.

It is constructed as shown in FIG. 7, and in the figure,
Reference numeral 1 is a positive lens that forms a reference image, 2 is a first reflection surface (reflection coat surface) that forms a reference image, and 3 is a second reflection surface (reflection coat surface) that forms a reference image. The two prisms 8 are integrally formed. Reference numeral 4 is a positive lens that forms a comparative image, 5 is a first reflective surface (reflective coating surface) that forms a comparative image, and 6 is a second reflective surface (reflective coating surface) that forms a comparative image. The two prisms 9 are integrally formed. Reference numeral 7 is a photoelectric conversion element such as a photo array or a PSD for receiving a reference image and a comparison image for photoelectric conversion, and the same thing can be achieved regardless of which of the two formed images is the reference image or the comparison image. . Since this is a passive type, the two images are formed on the photoelectric conversion element 7 by the light flux having parallax passing through different optical paths from the same object point on the subject, and the two images are changed depending on the distance to the subject. Distance detection is performed by detecting the changing interval between these two images.

Further, in the case of the active type, the reference image optical system is a projection optical system for projecting a spot on the subject, and the position of the reflected spot image formed on the light receiving surface of the photoelectric conversion element 7 of the comparative image optical system is determined. The distance is measured by detecting it. Therefore, in FIG. 7, a light emitting element for projecting light is placed at an arbitrary position P on the photoelectric conversion element 7. Even in this case, the same thing can be said if the light emitting element is placed in either the reference image optical system or the comparative image optical system.

[Problems to be Solved by the Invention]

8 and 9 are enlarged views of either the reference image optical system or the comparative image optical system of the focus detection optical system shown in FIG.

In both figures, a and b are rays from the object to be focused, a is an upper ray and b is a lower ray. Also, O
Is the optical axis. c is stray light that causes a ghost, and in the figure, as a representative example, it is incident at a position 3 mm above the optical axis O with respect to the virtual surface S placed on the apex of the entrance surface of the positive lens 4 (1). It shows a ray on the meridian plane that is incident at an angle of 89 °. Reference numeral 10 is an exit surface of the prism 9 (8), and 7a is a light receiving surface of the photoelectric conversion element 7, and in the case of FIG. 8, it is a joint for fixing the photoelectric conversion element 7 between them and preventing foreign matter from entering. Agent
11 is filled, and in the case of FIG. 9, nothing is filled between the two to form an air layer. Therefore, in the case of FIG.
The stray light c enters the prism 9 (8) from the positive lens 4 (1) and then does not enter the first reflecting surface 5 (2) and the second reflecting surface 6 (3) but directly exits from the exit surface 10. The light reaches the light receiving surface 7a. In the case of FIG. 9, the stray light c enters the prism 9 (8) from the positive lens 4 (1), is totally reflected by the exit surface 10, and is then reflected by the second reflection surface 6 (3). To reach the light receiving surface 7a. As described above, in each case, there is a drawback that stray light c from a subject other than the subject to be focused reaches the light receiving surface 7a and causes erroneous distance measurement. SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a focus detection optical system that prevents erroneous distance measurement even if stray light enters the prism.

[Means and Actions for Solving the Problems]

A focus detection optical system according to the present invention includes a focusing lens having a positive refracting power, a plurality of reflecting surfaces, and a light receiving element that receives the object image formed by the focusing lens and the reflecting surfaces on the light receiving surface. The first and second imaging optical systems are provided, and focus detection is performed by the relative positional relationship between the object image formed by the first imaging optical system and the object image formed by the second imaging optical system. In the focus detection optical system to be performed, at least the final reflecting surface of the plurality of reflecting surfaces is formed by a prism member in which a surface including a light emitting area of a light beam forming an object image is opposed to the light receiving surface of the light receiving element, The surface including the non-effective optical path area that is almost adjacent to the exit area of the prism member is separated from the light receiving surface of the light receiving element by an arbitrary distance, and the surface including the non-effective optical path area is formed at a position facing the light receiving surface. The non-effective optical path area To is characterized by being configured by at least one of the light diffusion surface and the light absorbing material coated surface of the non-effective optical path region in order to prevent stray light incident on the light-receiving surface of the light receiving element.

Further, the focus detection optical system according to the present invention is characterized in that the exit area of the prism member is adjacent to the ineffective optical path area in the same plane.

Further, in the focus detection optical system according to the present invention, not only the non-effective optical path area that is substantially adjacent to the exit area of the prism member, but also the surface that does not include the optical path of the light flux forming the object image is also used as the non-effective optical path area. It is characterized in that it is constituted by at least one of a diffusing surface and a light absorbing substance coated surface.

Here, the non-effective optical path area means an area other than the effective optical path range that is adjacent to the exit area of the prism surface through which the light flux from the subject to be focused passes and that is in a facing relationship with the light receiving surface.

That is, FIGS. 1 and 2 show the case where the bonding agent 11 is filled between the emission surface 10 and the light receiving surface 7a, and the emission surface 10 and the light receiving surface 7a, respectively.
2 shows a structure for preventing stray light in the case of an air layer between the light diffusion surface 12 and the light absorbing material at a portion AB of the exit surface 10 through which the light flux from the object to be focused does not pass. Since the coating surface 13 is used, the stray light c is blocked by the surface 12 or 13 and does not reach the light receiving surface 7a. Therefore, erroneous distance measurement does not occur.

Needless to say, the portion AB may be used as the light diffusing surface 12 and the light absorbing material coated surface 13.

〔Example〕

Hereinafter, the present invention will be described in detail based on the illustrated embodiment by assigning the same reference numerals to the same members as those in the conventional example.

FIG. 3 is a perspective view of one embodiment, and FIGS. 4 (a), (b),
3 (c) and 3 (d) respectively show the above embodiment in FIG.
It is a view from the direction of a, b, c, d, and is a view other than the effective optical path area shown in white, that is, the non-effective optical path area shown by the shaded area is all a light diffusion surface or a light absorber coating. Or a light diffusing surface and a light absorber coating portion.

Further, FIG. 5 shows the surface spacing and the angle of the reflecting surface of the two image forming optical systems of this embodiment, and the shape and size of the white background portion, that is, the effective optical path region when viewed from the respective arrow directions. here,
The unit of dimensions is mm.

Numerical data regarding the positive lens 4 (1) are as follows.

Radius of curvature of incident surface R = 3.87576 Aspherical coefficient P = 0.378637 E = −0.106781 × 10 ⁻² F = 0.901748 × 10 ⁻³ G = −0.243196 × 10 ⁻³ H = 0.235946 × 10 ⁻⁴ Aspherical formula However, the z-axis is the optical axis.

Refractive index of the prism part n _d = 1.49216 n _c = 1.48957 n _e = 1.494 n _F = 1.49413 NA = 0.24, f = 7.9, image height = 0.2 Therefore, according to this embodiment, the stray light is in the non-effective optical path region. Since it is shielded by the light diffusing surface or the light absorbing agent application portion, it does not reach the light receiving surface 7a of the photoelectric conversion element 7, and therefore erroneous distance measurement does not occur.

Incidentally, the focus detection optical system according to the present invention is generally used as a non-TTL type optical system different from the taking lens, but it is not always necessary.
It may be used as an L type. That is, as shown in FIG. 6, the beam splitter 18 is arranged at the afocal portion of the photographing lens composed of the focus group 14, the variable power group 15, the compensator group 16 and the relay group 17 so that the beam splitter 18 is placed in a direction different from the film direction. The optical path may be divided and the focus detection optical system may be arranged via the mirror 19.

〔The invention's effect〕

As described above, the focus detection optical system according to the present invention is not affected by stray light, and thus has an important practical advantage that erroneous distance measurement does not occur, that is, accurate focus detection can be performed.

[Brief description of drawings]

1 and 2 are views showing a stray light prevention structure in the case of a bonding agent and an air layer between the exit surface and the photoelectric conversion element light receiving surface in the focus detection optical system according to the present invention, respectively. 3 is a perspective view of one embodiment, FIG. 4 (a),
3 (b), (c), and (d) are views of the above embodiment seen from the directions of arrows a, b, c, and d in FIG. 3, and FIG. FIG. 6 is a diagram showing the surface spacing of the imaging optical system, the angle of the reflecting surface, and the shape and size of the effective optical path region when viewed from the respective arrow directions. FIG. 6 is a diagram showing an application example of the focus detection optical system of the present invention. FIG. 7 shows a conventional example, and FIGS. 8 and 9 show a bonding agent between the exit surface and the photoelectric conversion element surface in either the reference image optical system or the comparative image optical system of the conventional example. FIG. 3 is an enlarged view of a case and an air layer. 1,4 …… Positive lens, 2,5 …… First reflecting surface, 3,6 …… Second reflecting surface, 7 …… Photoelectric conversion element, 7a …… Light receiving surface, 8,9 …… Prism, 10… … Ejection surface, 11 …… Binder, 12 …… Light diffusion surface, 13 …… Light absorbing material coated surface.

Claims (3)

(57) [Claims] 1. A first and a second comprising: an imaging lens having a positive refractive power, a plurality of reflecting surfaces, and a light receiving element for receiving an object image formed by the imaging lens and the reflecting surface on a light receiving surface. Focusing optical system, the object image formed by the first imaging optical system is subjected to focus detection by relative positional relationship with the object image formed by the second imaging optical system. In the focus detection optical system, at least the final reflection surface of the plurality of reflection surfaces is formed by a prism member in which a surface including an emission region of a light flux forming the object image faces a light reception surface of the light receiving element. A surface including a non-effective optical path area that is substantially adjacent to the exit area of the prism member is separated from the light receiving surface of the light receiving element by an arbitrary distance, and a surface including the non-effective optical path area is the light receiving surface. Shaped in opposite positions In order to prevent stray light entering the light receiving surface of the light receiving element through the non-effective optical path area, the non-effective optical path area is constituted by at least one of a light diffusion surface and a light absorbing material coating surface. Focus detection optics. 2. The focus detection optical system according to claim 1, wherein the exit area of the prism member is adjacent to the non-effective optical path area in the same plane. 3. A non-effective optical path region that is substantially adjacent to the exit region of the prism member, and a surface that does not include the optical path of a light beam that forms the object image other than the non-effective optical path region is also a non-effective optical path region. The focus detection optical system according to claim 1 or 2, wherein the focus detection optical system is configured by at least one of the substance application surfaces.