JPS60256115A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To make a lens unit compact by splitting light by a half-mirror and reflecting the light by a concave mirror, and passing the light through the half- mirror again and guiding it to a photosensor for focus adjustment. CONSTITUTION:The light split upward by the half-mirror block 7 arranged in front of the stop 5 of a photographic optical system is reflected totally and converged by a concave mirror 11 to travel downward, and the light is passed through the half-mirror 7 again to reach the photosensor 9 for focus adjustment. Therefore, the space from the half-mirror to the photosensor for focus adjustment which is required by the lens barrel of the optical system is used in common to the space that the half-mirror 7 occupies, and the lens unit for a camera including the automatic focus adjusting device is reduced in size and also made compact.

Description

[Detailed Description of the Invention] The present invention provides a still camera, a video camera, etc.
The present invention relates to a so-called TTL passive automatic focus adjustment device that receives light from a subject with a photographic optical system and uses a portion of its output to adjust focus.

Most photographic optical systems used in recent video cameras and the like are so-called zoom lenses of a variable focal length type. This type of zoom lens is generally composed of four lens groups shown as 1 to 4 in FIG. That is, a focus adjustment lens l that contributes to focus adjustment, a variable power lens 2 for setting magnification, a correction lens 3 that corrects focal fluctuations (f), and an imaging system that forms an image on the imaging surface. It is composed of four groups of lenses 4. Note that 5 is an aperture, and 6 is a photographing optical sensor.

When incorporating optical focusing into such a zoom lens, behind the afocal correction system lens 3,
A light splitting member made of a half mirror or the like tilted at 45 degrees with respect to the optical axis is installed to split a portion of the photographing light and guide it to the finder optical system. Also, in the same photographic optical system, T
Even when incorporating a TL passive type automatic focus adjustment device, the second
As shown in the figure, the complementary IF system becomes afocal.
A half-mirror block 7 consisting of a half-mirror that shines at 45 degrees with respect to the optical axis is placed behind the camera, and a part of the photographing light is divided and guided to an optical system 8 for adjusting the Hjjj point. Generally, a sensor 91- forms a ¥ image.

In this case, the focus adjustment optical sensor 9 has the following constraints with respect to the photographing optical sensor 6, which is composed of, for example, an image pickup tube or a solid-state image sensor. First, even when using the grazing method as the focus adjustment method,
Even when using the brush type sharpness detection method, the optical system is generally used in a state where it is fully opened or at a constant aperture ratio close to that of 11, so a very large dynamic range is required in terms of optical energy. Second, with any focus adjustment method,
A special optical system is disposed in front of the light 7L conversion section of the optical sensor, and a photoelectric conversion section must be disposed correspondingly.

Due to such constraints, it is difficult to extremely miniaturize a module including the above-mentioned special optical system of the focusing optical sensor. On the other hand, photographic optical sensors, whether they are image pickup tubes or solid-state image sensors, are becoming smaller in shape as new photosensitive physical properties and h-formulas are developed.
j conversion) 411'ilj;There's one in there.

In this way, recently, optical sensors for photography have been gradually becoming smaller and smaller, but since the power of the optical sensor for focus adjustment cannot be made proportionally smaller, the focus The size of adjustment optical sensors tends to increase.

Next, the question of what proportion of the focal point 11 and adrenal gland areas in the photographic area, or in other words, the focus adjustment field of view ratio, should be determined depends on the conditions of the subject, the photographer's photographic technique, and even personal preference. For example, the optimum ratio is 1/3 of the entire screen in both the horizontal and vertical directions (if there is an A, then the point of the photographing optical system is The focal point of the focusing system compared to &l#
! It is necessary to set the distance considerably large.

To give an example of an ear body, for example, by combining an image pickup tube with a horizontal width of 8 mm and a 6 mm optical sensor for adjusting the searing temperature,
In order to set a focus adjustment field of view ratio of 3, it is necessary to make the focal length of the focus adjustment system 2.25 times the focus distance 1/Ij of the photographing optical system. As can be understood from this example, it is inevitable that the lens barrel of the focusing optical system after the half mirror will be quite long.

In order to improve this problem, in reality, as shown in Figure 3, the optical path of the focusing optical system is bent by a total reflection mirror lO to make it more compact, but the volume is small. is not. Furthermore, when considering lens exchange, if a screw mount such as C-mount i, which is used in current ENG cameras, is used, the bent lens barrel may protrude behind the flange of the mount. The problem is that there is a restriction that it must not be done.

As described above, in the prior art, the TTL passive type automatic focus adjustment device is not so compact as compared to the external measurement type automatic focus adjustment device.

An object of the present invention is to provide an automatic focus adjustment device that improves the problems of such conventional devices and makes a camera lens unit more compact. A light splitting member that splits a part of the light, a concave mirror that reflects the light split by the light splitting member back to the light splitting member, and a light that is reflected by the concave mirror and passes through the light splitting member again. The invention is characterized by comprising a focus adjustment optical sensor placed at a receiving position.

The present invention will be explained in detail based on the embodiment shown in FIG. 4 and below. Note that the symbols 1 to 9 indicate the same members as in FIGS. 1 to 3.

FIG. 4 shows an embodiment of the present invention, in which a half-mirror block 7 having a half-mirror surface 7a inclined by 450F with respect to the photographing optical axis is located at the afocal part of the photographing optical system and at the aperture 5. It is placed in front. However, the light that is split by the half mirror surface 7a and directed toward the force is totally reflected by the concave mirror 11, and is folded in the direction toward the side while one beam of light S is emitted.
Pass through the half mirror block 7 again and move to 1, ′, ζ
The light reaches the adjustment optical sensor 9.

FIG. 5 shows another 'i' embodiment of the present invention, in which case a special half mirror block 7 that integrates the concave mirror 11 and half mirror block h7 of FIG. The end portion is spherically curved 411- and this is used as a reflective surface 11a.

By using the half mirror block 7 having the concave reflective surface 11a in this way, the number of parts can be reduced and the adjustment process can be simplified.
・Profit of −5 is obtained.

In addition, if the concave mirror ll is made aspherical, the focus adjustment P
This provides advantages such as simplification of the complementary +1 optical system. Furthermore, if the central part of the half mirror surface 7a is made into a transparent part, the light reflected by the four-sided mirror 11 will mainly pass through this transparent part, and the light weight obtained by the optical sensor 9 will increase. Detection 11 is good even for subjects with lower illuminance.

As explained above, the autofocus 1.5 and adjustment device according to the present invention reflects the light divided by the half mirror by the gate +ru mirror, and then allows it to pass through the inner half mirror to adjust the focus. Since the configuration is such that the light reaches the light sensor 9, from the conventional half mirror; 1. (Section 1.1: The space required for the gate of the optical system up to the optical sensor for adjustment,
It is possible to have a lens occupied by a half-mirror, and is advantageous because it is popular for downsizing and compactness of camera lens units equipped with automatic suspension, I-J, and adjustment devices.

[Brief explanation of the drawing]

1 to 3 show the configuration IA of a zoom optical system for explaining a conventional automatic focus adjustment device H, 1, and the configuration IA of a zoom optical system for explaining a conventional automatic focus adjustment device H, 1; Small example,
FIG. 4 is a diagram showing the optical arrangement thereof. FIG. 5 is a diagram showing the configuration of another embodiment. Numerals 1 to 4 are zoom optical system lenses, 6 is a photo sensor for photographing, 7 is a half mirror block, and 7a1 is a half mirror.
surface, 7b is a transparent portion, 9 is a focal adrenal optical sensor, 11
is a concave mirror, and lla is a reflective surface. Patent applicant Canon Co., Ltd. 1 Figure 1 Figure 4 Figure 1 Figure 5-961

Claims (1)

[Scope of Claims] 1. A light splitting member installed in a shooting optical system that splits a part of the shooting light, and a concave mirror that reflects the light split by the light splitting member back to the light splitting member. An automatic focus adjustment device comprising: a focus adjustment optical sensor disposed at a position to receive light reflected by the concave mirror and passed through the light splitting member again. 2. The automatic focus adjustment device according to claim 1, wherein the light splitting member and the concave mirror are formed into an integral block. 3. The automatic focus adjustment device according to claim 1, wherein the concave mirror has an aspherical surface.