JPS59113A - Automatic focal point adjusting device of ttl photometry system - Google Patents

Abstract

PURPOSE:To make the constitution compact and reduce the manufacturing cost of the titled adjsting device, by correcting the moving amount setting element of a focus ring in accordance with the image point moving amount of an object caused by the variable power of a zoom lens and setting the moving amount of the focus ring. CONSTITUTION:An object image having the same focal point as an image formed on an image pickup device 50 is formed on a focal plane Z2 by beam splitters D1 and D2. The object image is caught by a focal point detecting element 61 and the defocus amount DELTAp which is the sum of the deviated amount of focal point DELTAs and the moving amount of image point DELTAl, is detected. Moreover, an automatic focal point adjustment controlling section 60 corresponds to the zoom information N of a zoom ring 20 and the manification (m) and focal length (fe) of a variable power lens group E corrected in accordance with the moving amount of image point DELTAl are stored in the microcomputer of the controlling section 60. Then, the moving amount DELTAx of a focus ring 10 is set based on the relation from the detected value. Therefore, the constitution can be made compact and the manufacturing cost can be reduced in such a way.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus adjustment device for an optical device such as a video camera equipped with a zoom lens using the so-called TTL photometry method, which measures the light of a subject image that has passed through the zoom lens.

Conventionally, zoom lenses attached to this type of optical equipment have been designed with great care, from design to processing and assembly, to prevent the image point from shifting, especially when changing the magnification. The zoom lens was very expensive.

However, as mentioned above, in the case of a zoom lens used in an optical device with a built-in automatic focusing device using the TTL method, it is possible to compensate for image point movement to some extent by adjusting the amount of movement of the focus lens group for automatic focusing. above is possible.

The present invention has been devised in view of the above, and the present invention corrects the movement of the image point of a subject image caused by the displacement of the zoom lens by moving a focus ring that supports a focus lens group during automatic focus adjustment. In other words, the focus detection element detects the defocus amount of the subject image passing through the zoom lens, and moves the focus ring of the zoom lens in accordance with the defocus amount. In an automatic focus adjustment device that performs automatic focus adjustment, a movement amount setting element for setting a movement amount of the focus ring is appropriately corrected according to an amount of movement of an image point of the subject that occurs as the zoom lens changes magnification. The present invention provides an automatic focus adjustment device for an optical device that sets the amount of movement of the focus ring.

Hereinafter, the present invention will be described in further detail based on an embodiment of an automatic focusing device for a zoom lens according to the present invention shown in the accompanying drawings.

In the figure, A is a focus lens (fOcllθ6]θng) group that uses a front group extension method and has a distance adjustment function, and is supported by a focus ring (10). Further, the focus ring (10) is provided with a distance ring (11) inscribed with a simple distance number to display the distance from the camera to the subject to obtain the focus state. If you know the distance to the focus ring (
As long as the distance ring (11) is manually rotated to match the distance of the distance ring (11) with the index, an in-focus state can almost be obtained. Further, a gear (90) that rotates by receiving the driving force of a focusing motor (80) that is driven and controlled by a signal output from an automatic focus adjustment control section (60) is meshed with the focus ring (10). However, a second gear portion (12) for driving the focus ring (10) is provided. B is a variator lens that moves greatly to change the focal length.
s) group, which is slidably supported in the cam groove (31) of the fixed ring (60) and can be moved along the cam groove (21) provided in the zoom ring (20) to change the magnification. do. Further, the zoom ring (20) is provided with zoom information (N) of the zoom lens corresponding to the focal length, etc. that is changed during zooming to obtain a zoom effect. D is a relay system that does not participate in zooming, but is fixedly supported by a fixed ring (30) and has the role of combining the subject images with a predetermined size and brightness.
nθ) group, and the master lens! At ff (D), a diaphragm of a diaphragm device controlled by a semi-transparent mirror (1)+) and a servo motor (70) is provided centered on the optical axis. 40id: For example, in a video camera body, the focus lens group (A) described above,
And, the focal plane of the Zoono lens (Z) constituted by the variable power lens group (F2) consisting of the variator lens group (B) (!: the compensator lens group (C) and the master lens group (D)) zl) and the imaging device (5
0: For example, an image pickup tube, solid-state imaging device, etc.) is installed and performs photoelectric conversion processing on the subject image. Therefore, the subject image separated by the beam splitter (1)K has exactly the same focus as the image formed on the imaging device (50) by the second beam splitter (D2). An image is formed on a second focal plane (Z2), the subject image is captured by a focus detection element (61) provided in the automatic focus adjustment control section (60), and the amount of focus shift (ΔS) of the subject image is determined. The automatic focus adjustment control unit (60) detects the defocus amount (Δp=Δp−ΔS+Δt”) that can occur from the image point movement amount (Δt) caused by the magnification change at that time. The focus state of the subject image captured by the device (50) is indirectly detected.

Further, the automatic focus adjustment control section (60) simultaneously detects the defocus amount (Δp) including the image point movement amount (Δt) and controls the zoom ring (20) with a resistor, a gray code, etc. The provided zoom information (l) is read and set in advance to correspond to the zoom information (N), and the value is appropriately corrected and set according to the image point movement amount (Δt). Magnification (m) and focal length (fe)
For example, the image point movement amount (Δt
), the magnification (m) and focal length (fe) of the variable magnification lens group (E) are detected together with the defocus amount (Δp), and the microcomputer is programmed based on the relational expression m(mIfe〒Δp). etc. to set the amount of movement (ΔX) of the focus ring (10). Historically, the automatic focus adjustment control section (60) drives and controls the focusing motor (80) in an appropriate direction, extends the focus ring (10) by ΔX, and moves the focus lens group (A) so that the subject image is always on the focal plane. (Zl) and performs automatic focus adjustment.

In the embodiment described above, the variator lens group (B
) Compensator lens (compnnna, tor ) that corrects the image point shift that may occur with the change in magnification
, ens ) groups are eliminated to form a zoom lens optical system. However, in cases where the amount of image point movement due to magnification changes significantly, the compensator lens group can be supported and configured to be fixed or movable more easily than in conventional systems, so that the amount of image point movement cannot be corrected to some extent. By processing the amount of image point movement that cannot be corrected in accordance with the above-described embodiment, automatic focus adjustment can be easily and reliably performed. Further, an element for setting the amount of movement of the focus ring, such as the defocus amount, the magnification and focal length of the variable power lens group, is referred to as a movement amount setting element.

As described above, according to the present invention, the movement amount setting element is appropriately corrected in advance according to the image point movement amount that occurs due to zooming,
Moreover, in addition to being compatible with the zoom information of the zoom lens, during automatic focus adjustment, the zoom information is read and the corrected movement amount setting element is detected and processed, so that the movement of the focus ring of the zoom lens can be adjusted. Compared to conventional zoom lenses that correct image point movement by skillfully displacing the lens optical system, lens design and lens processing are much easier, and the manufacturing cost of zoom lenses is lower. In addition, it is possible to provide a compact zoom lens, and it is also possible to perform accurate automatic focus adjustment even in a mechanical zoom lens rather than a rigid optical one. Has excellent effects.

[Brief explanation of drawings]

The drawing shows an embodiment of the automatic focus adjustment device for a zoom lens according to the present invention. In the drawing, A: focus lens group, B: router lens group, 1) master lens group. , E...variable magnification lens fiL N...
・Zoom information, z...zoom lens, 10...focus ring, 20...zoom EJJ, 30...fixed ring,
40... Optical equipment main body, 50... Imaging ring (chair, 60... Automatic focus adjustment control unit, 70... Servo motor, 80... Force/ring motor.

Claims (2)

[Claims] (1) Automatic focusing in which the focus detection element detects the defocus amount of the subject image that has passed through the zoom lens, and moves the focus ring of the zoom lens according to the defocus amount to adjust the autofocus. In the adjustment device, the movement amount of the focus ring is set by appropriately correcting the movement amount setting element of the focus ring according to the amount of movement of the image point of the subject that occurs as the zoom lens changes magnification. An automatic focus adjustment device using a T T TJ photometry method, characterized in that: (2) The TTL photometry automatic focus adjustment device 0 according to claim 1, wherein the movement amount setting elements are the defocus amount, the magnification of the variable magnification lens group, and the focal length.