1. Field of the Invention
The present invention relates generally to a lens barrel provided with a rotation operation member and having drip-proofness.
2. Description of the Related Art
Recently, image pickup apparatuses, such as digital cameras and video cameras, have been put to practical use and have been widespread which are configured to be capable of sequentially performing photoelectric conversion of an optical image formed by an image pickup optical system, using a photoelectric conversion device (hereinafter referred to as an image pickup device), such as a CCD (charge coupled device) type image sensor and a CMOS (complementary metal oxide semiconductor) type image sensor, storing an image signal acquired thereby into a storage medium as image data in a predetermined form (for example, digital image data indicating a still image or a movie), and displaying the still image or the movie on the basis of the digital image data on an image display apparatus such as an LCD (liquid crystal display) device and an OEL (organic electro-luminescence) display device. Furthermore, among image pickup apparatuses of this kind, those having dust-proofness and drip-proofness realized by providing a sealing structure between an exterior and an interior have been widespread.
Further, among conventional image pickup apparatuses, those provided with an image pickup optical system configured to have variable magnifications, a so-called zoom optical system, have been widespread. A lens barrel including such an image pickup optical system having variable magnifications (a zoom optical system) (hereinafter referred to as a zoom lens barrel) is configured with a plurality of cylindrical members, and a variable magnification function is realized by relatively extending and contracting each cylindrical member in an optical axis direction. Furthermore, recently, there is a tendency that a variable magnification rate of the zoom optical system is more and more increased.
Generally, in a zoom lens barrel, when a zooming operation or the like is performed, each cylindrical member relatively moves forward or backward in an optical axis direction, and, therefore, an internal volume at a time of being contracted and an internal volume at a time of being extended are significantly different from each other. Therefore, for example, in a lens barrel with a watertight structure, when a zooming operation causing change in the internal volume is performed, a heavy load accompanying the zooming operation or the like is imposed on the cylindrical members and sealing members because the structure is such that entrance and exit of air between inside and outside of the cylindrical members are difficult. Therefore, various devices for, even for a lens barrel with a watertight structure, securing entrance and exit of air between the inside and outside of the cylindrical members by a zooming operation or the like to provide air permeability and preventing entrance and exit of water drops and the like to secure drip-proofness have been proposed, for example, by Japanese Patent Application Laid-Open Publication No. 2007-47411 and Japanese Patent No. 4035402.
A lens barrel disclosed by Japanese Patent Application Laid-Open Publication No. 2007-47411 is configured by providing an air hole passing between internal and external spaces in a partial area of a fixed barrel, arranging a sheet member having air permeability and drip-proofness so as to cover the air hole, and providing an exterior member so as to cover the sheet member.
A lens barrel disclosed by Japanese Patent No. 4035402 is configured by using cam grooves or hole portions used to fix lenses as air holes and sticking drip-proof sheet members so as to cover the hole portions.