JPS6240410A - Optical system having focus detecting device - Google Patents

Abstract

PURPOSE:To simplify mechanism and to make focus detection possible with high accuracy by constituting focus group of a photographing system of a lens group of negative refracting power, and at the same time, using a reflection mirror partially for focus detection and making focus detection by moving the focus section of the photographing section and an element for focus detection in a body. CONSTITUTION:When a focus group is constituted of a lens group of negative refracting power, and the distance between a projection lens and a light source or the distance between a photodetecting lens and a photodetecting element is S, focal length of a lens group for focusing is (f), and A (Anot equal to 1) is constant, focus detection is made constituting to satisfy L.S=A.f<2>. In this way, error in range finding when the distance of an object changed can be portioned out to plus side and minus side within the depth of focus, and accuracy of focus detection can be improved. For instance, as the focus group 61 is of negative refracting power, front side focus position F is positioned more image face side that front side principal point position H61, the position F and position H62 can be conformed easily, and the whole optical system can be constituted as a photographing system of a camera, etc. in well-balanced form.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an optical system having a focus detection device suitable for photographic cameras, video cameras, etc. The present invention relates to an optical system having a so-called active focus detection device that detects the focus of a photographing system by receiving a reflected light beam from an object using a light receiving means.

(Prior Art) Recently, active focus detection devices have been widely used not only in lens shutter cameras but also in single-lens reflex cameras, video cameras, and the like. Among these, an optical system having an active focus detection device using the principle of triangular distance measurement is disclosed in Japanese Patent Application Laid-Open No. 58-88, for example.
This method has been proposed in JP-A No. 0608, Japanese Unexamined Patent Publication No. 59-201007, and the like.

FIGS. 1 and 2 are schematic diagrams of a typical active focus detection optical system that utilizes the principle of conventional triangular distance measurement. 1st
In the figure, a light beam from a light source 12 is projected to a subject 13 through a light projecting lens 11, and a reflected light beam from the subject 13 is received by a light receiving lens 14 at a light receiving section 15 made up of a plurality of light receiving elements. .

The distance to the subject 13 is measured by detecting the position of the reflected light beam formed on the light receiving section 15. Since this focus detection method uses a plurality of light receiving elements, the signal processing of the light receiving means and the accompanying electric circuit tend to become complicated.

In FIG. 2, a light beam from the light [26] is projected to the subject 22 side through a part of the photographing system 21, and the reflected light beam from the subject 22 side is received by the light receiving section 24 consisting of two light receiving elements. .

At this time, the light receiving section 24 is linked with the focusing lens group 25 to scan in the direction of the arrow so that the outputs from the two light receiving elements are equal, or the difference in output is below a certain value, so that the photographing system Focus detection is performed. Although this focus detection method requires relatively simple signal processing and electric circuitry, it is necessary to move the amount of extension of the focusing lens group 25 and the light receiving section 24 in a predetermined relationship.

For this reason, the interlocking structure of the cam mechanism, drive method, etc. becomes complicated, and highly accurate focus detection tends to become difficult.

(Problems to be Solved by the Invention) An object of the present invention is to provide an optical system having a focus detection device using triangular distance measurement that has a simple configuration and is capable of highly accurate focus detection.

A further object of the present invention is to obtain a patent application filed in 1983 by the applicant.
The present invention further improves the focus detection device according to No. 0-31033, and provides an optical system having a focus detection device that enables high-granularity focus detection from objects at infinity to objects at short distances.

(Means for Solving the Problem) When detecting the focus of a photographing system by using a light projecting means and a light receiving means for focus detection arranged apart from each other by a baseline length, the light projecting means or the light receiving means The optical path of one of the means is bent through a reflecting mirror, the one element for focus detection is disposed on this bent optical path, and the focus adjustment lens group of the photographing system is a lens group with negative refractive power. The distance between the light projecting lens of the light projecting means and the light source or the distance between the light receiving lens of the light receiving means and the light receiving element is set to S, and the focal point of the focusing lens group is moved integrally with the one element. Distance f,
The configuration is such that when A (A≠1) is a constant, L-5=A-f2 is satisfied. Other features of the invention are described in the Examples.

(Embodiment) FIG. 3 is a schematic diagram of an optical system of an embodiment of the focus detection device proposed by the present applicant in Japanese Patent Application No. 60-31033. Adjustment lens group (hereinafter referred to as "focus group").

32 is a light-receiving lens, 33 is a reflecting mirror, and 34 is a light-receiving section disposed on the rake surface of the light-receiving lens 32, which is attached to a part of the lens barrel 35. In the figure, the light receiving section 34 and the focus section 31 are integrally extended together with the lens m cylinder 35 to perform focus detection. Although the light projecting means is not shown in the figure, the light projecting means is configured to project light toward the subject through a part of the photographing system 30.

Next, in order to explain the optical properties, a schematic diagram of the optical system shown in FIG. 3 in which the reflecting mirror 33 is omitted and the light source of the light projecting means (not shown) is placed substantially on the optical axis of the photographing system 30. A diagram is shown in FIG. In FIG. 4, 41 is a light source, 42 is a focus group that is part of the photographing system, F is a front focal position of the focus group, 43 is an object at a finite distance, 44 is a light receiving lens, and 45 is a light receiving section. X is the distance between the object 43 and the focal position F, H
441Ha4' are the front and rear principal point positions of the light receiving lens 44, L is the base line length, l is the distance between the object 43 and the principal point position H44 in the direction parallel to the optical axis of the imaging system, and S is the principal point position H44
The distance between .degree. Note that the distance @D is the light receiving part 3 in Fig. 3.
This corresponds to the scanning distance from the infinite distance object No. 4 to the focusing position of the finite distance object, that is, the moving distance of the lens barrel 35.

In FIG. 4, according to the principle of triangular distance measurement, D=L-5/l (]). Further, the imaging relationship of the focus group 42 is as shown in FIG. In the same figure, 51 is the focus group, H5□+
H51° is the front and rear principal point positions of the focus group, respectively.
F and F' are the front and rear focal positions of the focus group, O is the object, and O'' is the imaging position. If the focal length of the focus group 51 is f and the distance is set as shown in FIG. 5, x'=f2/X (2) is obtained from the so-called Newton's formula. In the focus detection device shown in FIG. 3, the formula D=X'
It is characterized in that the focus group 31 and the light receiving section 34 are moved integrally by setting each element as shown in FIG. That is, L-3/]=f2/X ---
---Each element is set so as to satisfy (3). Here, if C is a constant, L-3=Cf2 1 =CX. Since l and X differ only in the measurement point of the distance to the object, C=1, and equation (3) becomes as follows. Here, the equation LS=f2 is a condition that can be set as a value unique to the device. The formula t=X corresponds to making the front focal position F of the focus group and the front principal point position H44 of the light receiving lens coincide with each other in the optical axis direction of the WL132 system. That is, this corresponds to configuring so that the straight line connecting the position F and the position H44 is orthogonal to the photographing optical axis. However, l = come. The distance measurement error at this time increases as the object distance becomes closer.

The purpose of the present invention is to enable highly accurate focus detection over the entire range from objects at infinity to objects at short distances, while downsizing the entire optical system to facilitate handling. The group is composed of a lens group with negative refractive power, so that 1=x in equation (4) is satisfied for an intermediate distance object, and at the same time, L-S=A is used instead of L-S=f2 in equation (4).
It is characterized in that it is configured to satisfy f2 (A<1) and performs focus detection. This allows distance measurement errors when the object distance changes to be divided into positive and negative sides within the depth of focus, improving focus detection accuracy.

FIG. 6 is a schematic view of the main parts of an embodiment of the present invention, omitting the light projecting means having a light projecting lens and a light source. In the same figure, 61 is a focus group with negative refractive power, 62 is a light receiving lens, 63 is a light receiving section, and 64 is a reflecting mirror. In this embodiment, since the focus group 61 has negative refractive power, the front focus position F
is located closer to the image plane than the front principal point position HGI, so the position F and the position H62 can be easily matched. As a result, the light-receiving means having the light-receiving lens 62 and the light-receiving section 63 can be placed behind the photographing EL, so that the entire optical system can be configured as a photographing system such as a camera with good balance. For example, as shown in FIG. 7, the focus group 71
If the front focal position F and the front principal point position H7□ of the light-receiving lens 72 are made to coincide with each other as in this embodiment, the light-receiving means will protrude toward the object side than the photographing system. For this reason, when the entire optical system is configured as a camera, it results in an unbalanced arrangement.

Next, FIG. 8 shows a schematic diagram of an embodiment in which the present invention is incorporated into an actual photographing system. In the figure, reference numeral 81 indicates a light source 81 that emits infrared light.
7, the light is reflected by a reflective mirror 82 that reflects infrared light and transmits visible light, and is projected to the subject side through a part of the photographing system. 83 is a focus group with negative refractive power, and the focus group 83 is used to focus the front focal position F of the focus group 83 and the front principal point position H84 of the light receiving lens 84 to a finite object distance.
so that they match when unrolled, and further set the constant A mentioned above to A = 0.996 so that L - S = 0.996
By setting each element such as f2, it is possible to reduce the distance measurement error when adjusting the focus on a close object. For example, in this embodiment, the distance measurement error on the focal plane is reduced from 0.2 mm to ±0.01 mm. FIG. 9 is a diagram showing the state at this time obtained by paraxial theoretical calculation.

In the figure, the horizontal axis represents the distance 1lIX from the front focal position of the focus group to the object, and the vertical axis represents the amount of defocus when the focal length of the focus group is 100 mm.

FIGS. 10(A) and 10(B) are schematic diagrams of an embodiment of an optical member 10 in which a light-receiving lens and a reflecting mirror according to the present invention are integrated. In the figure, 101 is a refractive surface corresponding to a light-receiving lens, 102 is a reflecting mirror, and 103 is a light-receiving section. Especially in the diagram
In (B), three reflecting surfaces are provided and the position of the light receiving section 103 is arbitrarily changed. It is preferable to integrally mold the optical section 10 of this embodiment using plastic or the like, since manufacturing is facilitated.

In the above embodiments, the light flux from the light source of the light projecting means is projected onto the subject through a part of the photographing system, and the reflected light flux from the subject is received by the light receiving means arranged outside the photographing system. However, in the present invention, the light projecting means and the light receiving means may be replaced as shown in FIG. Alternatively, both the light projecting means and the light receiving means may be arranged through a part of the photographing system. 111.121 in Figures 11 and 12
is a light source, 112, 122 are projecting lenses, 113, 12
3 is a focus group, 114 and 124 are light receiving sections, and 125 is a light receiving lens.

(Effects of the Invention) According to the present invention, the focus group of the photographing system is composed of a lens group with negative refractive power, and a reflecting mirror is used as a part of the focus detection part, and the focus part of the photographing system and the focus detection part are combined. By integrally moving the elements to perform focus detection, it is possible to achieve an optical system that is mechanically simplified and has a focus detection device that can perform focus detection with high accuracy.

[Brief explanation of the drawing]

Figures 1 and 2 are schematic diagrams of a conventional active type optical system for focus detection, and Figures 3, 4, and 5 are schematic diagrams of an optical system for focus detection previously proposed by the applicant. 6 is a schematic diagram of an optical system according to an embodiment of the present invention, FIG. 7 is an explanatory diagram for comparison with the optical system of FIG. 6, and FIG. 8 is a schematic diagram of an optical system of an embodiment of the present invention. FIG. 9 is an explanatory diagram of distance measurement accuracy in the present invention. FIGS. 11 and 12 are explanatory diagrams of other embodiments of the present invention, and FIG. 10 is a part of the present invention. It is an explanatory view of another example. In the figure, 31.61 and 71.83 are focus groups, 34.6
3.85 is the light receiving part, 32, 62.84 is the light receiving lens, 3
3, 64.86 is the reflecting mirror, F is the front focal position of the focus group, H6□, H84 is the front principal point position of the light receiving lens, 8
1 is a light source, and L is a baseline length.

Claims (1)

[Claims] (1) When detecting the focus of an imaging system using a light projecting means and a light receiving means for focus detection, which are arranged with a baseline length L apart, the optical path of one of the light projecting means or the light receiving means is reflected. It is bent through a mirror, and the one element for focus detection is arranged on this bent optical path, and the focus adjustment lens group of the imaging system is composed of a lens group with negative refractive power, and the element is integrated with the one element. At the same time, the distance between the light projecting lens of the light projecting means and the light source or the distance between the light receiving lens and the light receiving element of the light receiving means is set to S, the focal length of the focusing lens group is set to f, and A (A≠1). ) is a constant, L・S=A・f^
An optical system having a focus detection device, characterized in that it is configured to satisfy the following.