Photography – Having variable focal length of camera objective – Having focus operation
Reexamination Certificate
2000-06-20
2001-07-17
Gray, David M. (Department: 2851)
Photography
Having variable focal length of camera objective
Having focus operation
C396S080000, C396S085000, C396S087000
Reexamination Certificate
active
06263163
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a focal length detector of a camera having a zoom lens.
2. Description of the Related Art
A focal length detector of a camera having a zoom lens which is provided therein with a code plate, having predetermined code patterns, and a brush, whose sliding contacts are in sliding electrical contact with the code plate to detect the focal length of the zoom lens, is known. In this known type of focal length detector, the brush and the code plate move relative to each other during zooming according to the movement of a moving barrel of the zoom lens so that the focal length of the zoom lens is detected by detecting a combination of electrically-connected or disconnected code patterns (electrical-connection indication signals or zoom code data) via the brush. For instance, in cameras having a zoom lens whose moving barrel or barrels are driven to retract from a wide-angle extremity to even a housed position in the camera body when power of the camera is switched OFF, the housed position, the wide-angle extremity, the telephoto extremity and intermediate positions (different focal-length positions) between the wide-angle extremity and the telephoto extremity of a moving barrel of the zoom lens are each detected. In such cameras, the detectable number of the focal lengths between the wide-angle extremity and the telephoto extremity can be increased to substantially an infinite number in theory by counting two-bit repetitive patterns. However, in practice, the detectable number of the focal lengths is limited by the size of terminals of the code plate and the amount of relative movement between the code plate and the brush. In the case of a focal length detector in which one particular sliding contact of the brush and a corresponding particular conductive pattern of the code plate which remain in contact with each other are used as terminals for ground, the code plate needs to be provided with at least three conductive patterns including the aforementioned conductive pattern (i.e., two conductive patterns in the form of a two-bit repetitive pattern and a pattern for ground), or the brush needs to be provided with at least three sliding contacts including the aforementioned sliding contact, in order to obtain two-bit repetitive codes. In order to detect specific focal length positions such as the housed position, the wide-angle extremity and the telephoto extremity, the code plate further needs to be provided with at least one more conductive pattern or the brush further needs to be provided with at least one more sliding contact to obtain electrical-connection indication signals or zoom code data that are different from the aforementioned two-bit repetitive codes. Therefore, in such a focal length detector, the code plate or the brush needs to be provided with at least four conductive patterns or at least four sliding contacts, respectively, which are to be electrically connected to a focal length detecting circuit (a control circuit) of the camera. In such a conventional focal length detector, regardless of which of the code plate and the brush is electrically connected to the focal length detecting circuit, the brush is generally provided with four sliding contacts. However, from a view point of miniaturizing the camera including the focal length detector, preferably the number of sliding contacts of the brush is as small as possible.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a focal length detector of a camera having a zoom lens, wherein the focal length detector is designed so small that it can be advantageously used to miniaturize the camera.
To achieve the former object mentioned above, according to an aspect of the present invention, a focal length detector of a camera having a zoom lens is provided, the focal length detector having a code plate and a brush which contacts with the code plate, the code plate and the brush being moved relative to each other according to a variation of the focal length of the zoom lens, and the focal length detector has a focal-length detecting circuit. The brush includes three sliding contacts which are electrically connected to one another. The code plate includes three code patterns and a ground pattern which are insulated from one another to be electrically connected to the focal-length detecting circuit. The ground pattern remains in contact with a specific sliding contact of the three sliding contacts regardless of the relative position of the code plate and the brush. The three code patterns come into contact with the remaining two of the three sliding contacts in predetermined combinations when the code plate and the brush are moved relative to each other.
According to this structure, since the brush needs to be provided with only three sliding contacts, specifically the width of the brush in a direction perpendicular to the direction of relative movement between the brush and the code plate can be made small, which is advantageous to miniaturize the camera. Still more, electrical-connection indication signals or zoom code data necessary to detect the focal length of the zoom lens can be obtained if only the brush and the code plate are provided with two sliding contacts and three conductive patterns, respectively, in addition to a particular sliding contact of the brush and a corresponding particular conductive pattern of the code plate for ground, so that the focal length detector can be designed small and compact without sacrificing the performance thereof, as compared with a conventional focal length detector.
Preferably, two of the three code patterns are formed on two contacting portions which are defined on the code plate to correspond to the remaining two of the three sliding contacts, respectively, and the remaining one of the three code patterns are formed to extend over the two contacting portions.
Preferably, two of the three code patterns are formed as two repetitive-pattern detecting terminals for detecting intermediate focal lengths between a wide-angle extremity and a telephoto extremity of the zoom lens, and the remaining one of the three code patterns is formed as a specific-code detecting terminal for detecting specific focal length positions of the zoom lens.
Preferably, the specific-code detecting terminal is electrically connected to the ground pattern via the brush when the zoom lens is at each of the wide-angle extremity and the telephoto extremity, and wherein one of the two repetitive-pattern detecting terminals and the specific-code detecting terminal are electrically connected to the ground pattern via the brush when the zoom lens is at a housed position behind the wide-angle extremity.
In an embodiment, one of the two repetitive-pattern detecting terminals, which is electrically connected with the ground pattern together with the specific-code detecting terminal when the zoom lens is at the housed position, is formed to extend over two contacting portions which are defined on the code plate to correspond to the remaining two of the three sliding contacts, respectively, and the specific-code detecting terminal and the other of the two repetitive-pattern detecting terminals are formed on the two contacting portions, respectively.
Preferably, the focal length detector further includes a zoom motor which is controlled to rotate forwardly and reversely to drive the zoom lens to vary the focal length; a zoom motor detector which detects a direction of driving of the zoom motor; and a position detecting device for determining whether the zoom lens is at one of a first focal length position and a second focal length position by referring to the direction of driving of the zoom motor when a common signal generated when the zoom lens is at one of the first focal length position and the second focal length position is detected via the three code patterns and the ground pattern.
In an embodiment, the common signal is detected at each of a wide-angle extremity and a telephoto extremity.
Preferably,
Nomura Hiroshi
Sasaki Takamitsu
Asahi Kogyo Kabushiki Kaisha
Blackman Rochelle
Gray David M.
Greenblum & Bernstein P.L.C.
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