JPS6239809A - Focus detecting device - Google Patents

Abstract

PURPOSE:To execute effectively automatic forcing of a reflex telephone lens, extending to a lens of a small F-number, by forming a shape of the inside peripheral part and the outside peripheral part of a pupil of a separated optical system, to a concentric circular arc centering around an optical axis of a photographic lens. CONSTITUTION:A pair of pupils E, E of an image re-formation lens projected to a reflecting pupil of a reflex telephone lens consisting of the outside periphery U and the inside periphery L are placed between the outside periphery U and the inside periphery L. Both the outside periphery EO and the inside periphery EI of the pupils E, E are concentric circular arcs centering around the center of the optical axis. Also, the upper and the lower peripheries ES, ES of the pupil E are divided by parallel lines of a line symmetry, and the upper and the lower length of the pupil E becomes roughly equal to a diameter of the inside periphery L.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a focus detection device for detecting the focus of a photographic lens by receiving light transmitted through a photographic lens.

(Prior art) Various focus detection devices are known, one of which is a condenser lens placed near or behind the expected focal plane of a photographic lens, and a pair of condenser lenses arranged symmetrically on the optical axis behind the nuclear condenser lens. There is a camera that detects the focus of the photographing lens by arranging two imaging lenses and comparing two images of the intended focal plane formed by the solid imaging lenses. Third
The figure shows the basic optical system of such a focus detection device, where TL is a photographing lens, Lo is a condenser lens, and L, I, and 2 are imaging lenses, respectively. The solid imaging lenses Ll and L2 are arranged symmetrically with respect to the optical axis X of the photographing lens TL, and the optical axes of the solid imaging lenses L+ and I-2 are parallel to the optical axis X, respectively. There is.

Furthermore, a light flux limiting mask M is installed in front of the imaging lenses L, L2. F is the photographing lens, TL is the planned focal plane,
PR is the imaging plane of the solid imaging lens.

With this configuration, when the projection lens is in focus on a single object, its image A is formed on the predetermined focal plane F, and the image A is further formed on the first focal plane F by the imaging lens I,1°I,x.
Image A8. A second image A2 is formed. When the photographing lens TL is in the rear focus state, the image B of the subject is formed behind the focused image A, and furthermore, the image B1. The second image B2 is formed by the imaging lenses LL and L2, respectively.
First image A1 when focused. The second image A is formed at a position farther away from the second image A in the direction perpendicular to the optical axis X. Conversely, when the front is in focus, the image C of the subject is formed by the photographing lens TL in front of the image A when in focus, and both the first image C1 and the second image C2 are exposed to less light than when in focus. It is formed near the axis X. While moving the photographing lens TL in the optical axis direction, the focused positions of the first image and the second image are detected using the output values of a pair of photoelectric converters (not shown) arranged on the imaging plane PR, and the focusing is performed. Can distinguish between focused and out of focus.

(Problems to be Solved by the Invention) The focus detection device described above has been used for a refractive type photographic lens. However, the reflective telephoto lens (fourth
(An example is shown in the figure) cannot be used as is.

Reflective telephoto lenses have the following advantages over refractive lenses, and are desired to be capable of automatic focus detection.

(a) The number of lenses is small and the cost is low.

(b) Due to reflection, the overall length can be shortened and it can be made lighter.

(C) Due to reflection, the influence of chromatic dispersion of glass is small, and chromatic aberration is much smaller than that of refractive lenses.

However, in a reflective telephoto lens, no light enters from the center of the lens at the exit pupil. As shown in Fig. 5, since the light near the optical axis X is blocked, the shape of the exit pupil is
This is an annular region shown as having an outer circumference U and an inner circumference. Therefore, the influence of vignetting on focus detection is large, and it is even more desirable to match the position of the projected pupil of the re-imaging lens with the position of the exit pupil.

6 to 8 show the shape of the pupil E of a conventional re-imaging lens projected onto the exit pupil of the photographing lens. @E is inside the outer shape U of the exit pupil of the photographic lens. In FIG. 6 (see Japanese Patent Application Laid-Open No. 60-32013), the outer periphery of the pupils E and E of the re-imaging lens has a shape corresponding to the outer shape of the pupil U of the photographing lens, while the pupils E and E The inner periphery is approximately symmetrical to the outer periphery, and is elliptical in this figure. In FIG. 7 (see Japanese Patent Application Laid-open No. 56-130725), the outer circumference and inner circumference of the pupils E and E of the re-imaging lens are:
It is a straight line that is symmetrical to the center line, and the upper and lower circumferences are
It is a circular arc, and the length in the vertical direction in the figure is longer than the width in the horizontal direction. In addition, in FIG. 8 (see U.S. Pat. No. 4-370,551),
The outer periphery of the pupils E, E of the re-imaging lens has a shape corresponding to the outer shape of the pupil U of the photographing lens, but the inner periphery is a straight line. 6th
Regarding any of the pupils E shown in the figures to Fig. 8, there is no mention of the inner circumference of the exit pupil that occurs when a reflective telephoto lens is used.

An object of the present invention is to provide a focus detection device that can be used in reflective telephoto lenses.

(Means for Solving the Problems) 41 The focus detection device according to the present invention includes a condenser lens arranged near or behind the expected focal plane of the photographic lens, and a pair of optical axis symmetrical lenses arranged behind the condenser lens. In a focus detection device that detects the focus of a photographing lens by arranging an image separation optical system, separating the images, and comparing them with each other, the shapes of the inner and outer peripheries of the pupil of the separation optical system are It is characterized by a concentric arc shape centered on the optical axis.

(Function) Since the shape of the exit pupil of a reflective telephoto lens is similar to the shape of the pupil of the separation optical system, focus detection can be performed accurately with a reflective telephoto lens, and furthermore, distance measurement can be performed correctly even with lenses with a small F number. .

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In focus detection for a reflective telephoto lens, the shape of the exit pupil of the automatic focus is used as the shape of the exit pupil of the reflective telephoto lens (5th
It is desirable to make it similar to the figure).

Figure 1 shows the reflex pupil of a reflective telephoto lens (outer circumference U and inner circumference ■7).
A pair of pupils E and E of the re-imaging lens projected onto
The shape in this example is shown. Pupils E and E are arranged between the outer circumference U and the inner circumference. Hitomi E.

The outer circumference Eo and inner circumference El of E are both concentric circular arcs centered on the optical axis center. Also, the pupil E'-lower circumference E3.
E3 is divided by line-symmetric parallel lines, and the lower length of the pupil E is approximately equal to the diameter of the inner circumference.

”-The shape of the pupil of the imaging lens is actually determined by the mask placed in front of it.

Therefore, by changing the aperture shape of this mask by electrical control, it is possible to increase versatility by making it compatible with various types of photographic lenses. Specifically, the re-imaging lens L1. The light flux regulating mask M (see Figure 3) installed in front of L2 is composed of an electro-optical element, and as shown in Figure 2, the pupil E, E is adjusted between the refractive lens and the reflective telephoto lens. Allow the shape to change. If a refractive lens is to be used, the inner periphery El' of the pupil E is configured symmetrically with the outer periphery E□, as in FIG. When corresponding to a reflective telephoto lens, is made to have the same shape as shown in FIG. 1, that is, an arc El concentric with the outer circumference EQ.

The outer periphery E□ and the inner periphery EI of the pupils E, E may be accurate concentric circular arcs, or, for example, the circular arcs may be linearly approximated to improve workability (as disclosed in Japanese Patent Application Laid-Open No. 1986-
(See Publication No. 32013).

(Effects of the Invention) A focus detection device that can be used for a reflective telephoto lens can be provided.

By using a mask shape that is effective for reflective telephoto lenses, automatic focusing of reflective telephoto lenses can be performed effectively even for lenses with small F-numbers.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a pupil of a re-imaging lens projected onto a reflection pupil of a reflective telephoto lens according to an embodiment of the present invention. FIG. 2 is a diagram showing the shape of a mask made of an electro-optical element according to another embodiment of the present invention. FIG. 3 is a diagram showing an optical system of an automatic focusing device using a conventional separation optical system. =7= Figure 4 is a diagram of a reflective telephoto lens. FIG. 5 is a diagram of the exit pupil of a reflective telephoto lens. FIGS. 6 to 8 are diagrams showing the shape of the pupil E of a conventional re-imaging lens projected onto the exit pupil of the photographing lens. TL...Photographing lens, M...Light flux limiting mask,
M,, M, mask, Lo condenser lens, I,
+, L2...imaging lens, E, E...pupil. Patent applicant Minolta Camera Co., Ltd. Representative
Person Patent attorney Aoyama Aoyama and 2 others Figure 1
Figure 6

Claims (2)

[Claims] (1) A condenser lens is placed near or behind the planned focal plane of the photographic lens, and a pair of image separation optical systems are placed behind the condenser lens symmetrically with respect to the optical axis to separate the images and compare them with each other. A focus detection device for detecting the focus of a photographic lens by: a focus detection device characterized in that the shape of the inner circumference and the outer circumference of the pupil of the separation optical system are concentric arcs centered on the optical axis of the photographic lens. . (2) The focus detection device according to claim 1, wherein the focus detection device is configured to be able to change the formation of the pupil of the separation optical system.