1. Field of the Invention
The present invention relates to an optical filter used for an image-pickup device and an image-pickup apparatus using the image-pickup device.
2. Description of the Related Art
A single lens reflex type digital camera provided with a finder apparatus and a lens which is a photographic optical system replaceable for the camera body is being commercialized in recent years. With this digital camera, a user mounts desired lenses in the camera body, and can thereby selectively use a plurality of types of lenses for the single camera body. Furthermore, the camera body incorporates various mechanical mechanisms such as a shutter mechanism and a diaphragm mechanism.
In such a single-lens reflex digital camera whose lens is replaceable, dust may enter the camera body from outside when the lens is removed from the camera body. Furthermore, through operations of the various mechanical mechanisms, dust such as abrasion powder may be produced from members making up the mechanisms. When such dust is stuck to, for example, the image-pickup surface of an image-pickup element or the surface of an optical member (cover member) disposed in front thereof, images or so-called shadows of dust may be imaged onto an image captured by the digital camera, which may cause image quality to degrade.
Therefore, there is a proposal of a first conventional technique for providing a dust-proofing member for sealing and protecting the image-pickup surface of an image-pickup element, vibrating the dust-proofing member using a vibration device and thereby removing dust or the like stuck to the surface of this dust-proofing member (see e.g., Japanese Laid-Open Patent Publication (Kokai) No. 2002-204379).
Furthermore, when dust enters a space between the cover member of the image-pickup element and an optical filter arranged in front of the cover member, the digital camera needs to be disassembled to remove the dust. For this reason, a dust-proofing structure is conventionally provided which prevents dust from entering the space by blocking off the space between the cover member of the image-pickup element and the optical filter.
However, the above described dust-proofing structure is intended to prevent dust from entering the space between the cover member of the image-pickup element and the optical filter, and not intended to prevent dust from sticking to the incidence surface of the optical filter (hereinafter referred to as “the surface of the optical filter”). Therefore, dust may sometimes stick to the surface of the optical filter. Here, when the optical filter is arranged in the vicinity of the position of a focal plane, images of the dust stuck to the surface thereof is imaged onto the image-pickup device as shadows, thus causing degradation of image quality.
Furthermore, there is also a proposal of a structure whereby the surface of the cover member of the image-pickup element or the surface of the optical filter is cleaned with a wiper (see e.g., Japanese Laid-Open Patent Publication (Kokai) No. 2003-005254). This makes it possible to remove dust stuck to the surface of the cover member of the image-pickup element or the surface of the optical filter without removing the lens and without disassembling the digital camera.
However, dust stuck to the surface of the cover member of the image-pickup element or the surface of the optical filter may be sometimes hard like metallic powder. In this case, when the wiper slides along the surface of the cover member or the surface of the optical filter, this dust may damage the surface of the cover member or the surface of the optical filter.
Therefore, a configuration whereby the cover member or the optical filter is vibrated to remove dust stuck to the surface without damaging the surface of the cover member of the image-pickup element or the surface of the optical filter is proposed as a second conventional technique (see, e.g., Japanese Laid-Open Patent Publication (Kokai) No. 2004-032191). That is, this configuration is intended to vibrate the cover member or the optical filter using a vibration device and remove dust stuck to the surface thereof through vibration of the cover member or the optical filter.
However, adopting the above described mechanism (dust removing mechanism) which removes dust stuck to the surface of the dust-proofing member in a single-lens reflex digital camera according to the above described first conventional technique results in an addition of many mechanical parts. This is not desirable for a single-lens reflex digital camera whose size is required to be decreased from the standpoint of mounting space.
Furthermore, since the above described dust removing mechanism is arranged between the shutter mechanism and the image-pickup device, a space required for the mounting of the dust removing mechanism must be reserved between the shutter mechanism and the image-pickup device and the distance between the shutter mechanism and the image-pickup device needs to be extended more than the distance necessary for an image-pickup process. However, it is preferable to make the distance between the shutter mechanism and the image-pickup device as short as possible from the standpoint of the shutter efficiency. Therefore, when the above described dust removing mechanism is added to the digital camera, the distance between the shutter mechanism and the image-pickup device is necessarily extended and the shutter efficiency degrades.
Furthermore, when the vibration device according to the above described second conventional technique vibrates the cover member or the optical filter, vibration of the cover member of the image-pickup element or the optical filter propagates to the member which fixes the cover member or the optical filter. As a result, there is a possibility that the cover member of the image-pickup element or the optical filter may be detached from the member which fixes the cover member or the optical filter.