JP2007079058A - Lens device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adjust sensitivity in focusing by varying a focal distance for focusing corresponding to service circumstances when detecting focusing by branching incident luminous flux in an image-formation optical system. <P>SOLUTION: The lens device has: a branching optical system 2 provided in an optical path on an image side of a focus moving group 1; a focusing detection optical system 4 detecting a focusing state by using branched luminous flux from the branching optical system 2; an arithmetic means 7 performing focusing arithmetic operation, based on information from the focusing detection optical system 4; and a driving means 8 driving the focus moving group 1 according to output from the arithmetic means 7. The focal distance of the focusing detection optical system 4 is made variable. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lens apparatus that has a branching optical system in an optical path and performs autofocus using a branched light beam.

  Various autofocus (AF) techniques have been proposed in the past for photographing devices such as still cameras and video cameras. In particular, lenses that have a branch optical system in the optical path and a focus detection optical system in the branch optical path. An imaging apparatus is known from Patent Documents 1 and 2. In addition, Patent Document 3 proposes an imaging apparatus in which a range for distance measurement in autofocus, that is, a distance measurement frame is variable.

JP-A-9-274130 JP 2002-365517 A JP 7-46455 A

  However, as in Patent Documents 1 and 2, an imaging system that has a branching optical system in the optical path in the imaging optical system, detects the in-focus state by the branched light flux, and performs autofocus, is necessary for detecting the in-focus state. Light amount is reduced by branching a large amount of light from the imaging side. In order to accurately detect the in-focus state, it is sufficient to secure a large amount of light to be guided to the detection system, but since the amount of light on the imaging side is reduced by that amount, the image will eventually become quite dark, It is necessary to suppress the amount of light necessary for detection in the in-focus state as much as possible.

  Also, in the actual imaging state, the depth of focus changes due to changes in the focal length and F value on the imaging side, so the accuracy required for detection changes, and stable autofocus detection accuracy may not be ensured. .

  Furthermore, depending on changes in shooting conditions, such as dark subjects, it may be desirable to prioritize the amount of light on the shooting side rather than focusing accuracy. However, with the conventional technology, the reflectance of the branching optical system in the optical path is always constant, so shooting It is difficult to change the amount of light on the photographing side according to the change in the situation.

  On the other hand, for example, if the focal length of the detection system is shortened, the detection image becomes brighter and the amount of light to be branched can be suppressed. Accuracy will be reduced. Conversely, if the focal length of the detection system is made longer, the sensitivity of the amount of movement of the image to be detected can be increased, but the detection image becomes dark and a large amount of light to be branched is required.

  As described above, in the prior art, the antifocal length of the branching optical system in the optical path is always constant, so that it is impossible to change the sensitivity of the amount of movement of the image to be detected in accordance with the change in the photographing condition.

  An object of the present invention is to solve the above-described problems and provide a lens device that performs focus detection by branching an incident light beam into an imaging optical system.

  In order to achieve the above object, the technical feature of the lens apparatus according to the present invention is that a focusing state is obtained by using a beam splitting unit disposed in the optical path on the image side of the focus lens and a split beam from the beam splitting unit. A focus detection means for detecting the focus lens; a calculation means for calculating a movement amount of the focus lens based on a detection result of the focus detection means; a drive means for driving the focus lens based on an output of the calculation means; And the focus detection means has a focus detection optical system having a variable focal length.

  According to the lens device of the present invention, the focal length of the focus detection optical system that detects the in-focus state using the light beam from the branching optical system is variable, so that it should be detected according to changes in the shooting situation. It is possible to cope with changing the sensitivity of the moving amount of the image. In addition, even when detection accuracy is required, by increasing the focal length of the detection system without making the detection image dark, the sensitivity of the amount of movement of the image to be detected can be increased. The amount of light to be branched to the detection system can be suppressed. Since the amount of light on the imaging side can be increased accordingly, a bright image is finally obtained.

  The present invention will be described in detail based on the embodiments shown in the drawings.

  FIG. 1 shows a basic configuration diagram of an autofocus optical system, in which at least one branch optical system 2 and imaging means 3 are provided in an optical path on the image side of a focus moving group 1 composed of one lens or a plurality of lenses. Has been placed. In the branching direction of the branching optical system 2, a focusing detection optical system 4 for detecting a focused state is arranged, and the focusing detection optical system 4 includes a lens 5 and a sensor 6. The output of the focus detection optical system 4 is connected to the calculation means 7, and the output of the calculation means 7 is connected to the drive means 8 for moving the focus movement group 1.

  Then, by moving the position of the lens 5, the focus detection optical system 4 has a variable focal length, and changes the sensitivity of the amount of movement of the image to be detected according to the change in the photographing situation. It is possible.

  For example, in the case of normal shooting that does not require much focus detection accuracy, the focal length of the focus detection optical system 4 is shortened so that the detection image is brightened. The amount of light to be branched can be suppressed. And since the light quantity of the imaging means 3 can be increased by that much, a bright image can be finally obtained.

  On the other hand, even when focus detection accuracy is necessary in relation to the shooting situation, the focal length of the focus detection optical system 4 is increased to make the detection image longer, without darkening the detection image. The sensitivity of the amount of movement can be increased.

  Thereby, since the light quantity in the imaging means 3 does not change, the brightness of the image finally does not change, and it becomes possible to suppress the light quantity necessary for detection in the in-focus state.

  In the autofocus optical system shown in FIG. 2, at least one moving lens group 9 is built in the focus detection optical system 4 so as to move in the optical axis direction.

  The focal length of the focus detection optical system 4 can be varied by moving the moving lens group 9 on the optical axis. This makes the focal length variable by the same principle as that of a normal zoom lens or varifocal lens.

  In the autofocus optical system in FIG. 3, at least one moving lens group 10 is inserted into or retracted from the optical axis in the focus detection optical system 4, and this focal length is switched.

  This makes the focal length variable by the same principle as that of a front, rear, and built-in type converter lens attached to a normal imaging lens.

  The imaging optical system applied to the present invention has no problem whether it is a variable magnification system or a constant magnification system.

  In addition, the lens apparatus including the focus movement group 1, the branching optical system 2, the focus detection optical system 4, the calculation unit 7, and the driving unit 8 of the autofocus optical system of the above-described embodiment is used as the imaging unit including the imaging unit 3. The imaging device can be configured by connecting to each other.

1 is a basic configuration diagram of an autofocus optical system. It is a block diagram which enabled the magnification change of the focal distance of a focus detection optical system. It is a block diagram which enabled switching of the focal distance of the focus detection optical system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Focus movement group 2 Branching optical system 3 Imaging means 4 Focus detection optical system 7 Arithmetic means 8 Drive means 9, 10 Moving lens group

Claims (4)

  Based on the light beam branching means arranged in the optical path on the image side of the focus lens, the focus detection means for detecting the in-focus state using the branched light flux from the light beam branching means, and the detection result of the focus detection means And a driving means for driving the focus lens based on an output of the calculation means, and the focus detection means has a variable focal length. A lens apparatus having an optical system.   The lens apparatus according to claim 1, wherein a focal length of the focus detection optical system is variable by moving a moving lens in the focus detection optical system on an optical axis.   The lens apparatus according to claim 1, wherein a focal length of the focus detection optical system is variable by inserting or retracting a moving lens in the focus detection optical system on an optical axis.   An imaging apparatus comprising: the lens apparatus according to claim 1; and a camera to which the lens apparatus is connected.

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