Abstract: A zoom lens mechanism includes a switching lens group frame supporting a first sub-lens group frame and a second sub-lens group frame which support first and second sub-sub-lens groups, respectively; a lens group shift mechanism for causing the first and second sub-lens group frames to linearly move to a mutually close position or a mutually distant position, with respect to the optical axis direction, in accordance with relative rotation between the first sub-lens group frame and the second sub-lens group frame; and a focusing mechanism which integrally moves the first sub-lens group frame and the second sub-lens group frame in the optical axis direction while maintaining a distance therebetween after the first and the second sub-lens group frames are moved to one of the mutually close position and the mutually distant position by the lens group shift mechanism.

Abstract: A flexible tube for an endoscope which has excellent insertion operability is disclosed. The flexible tube includes and an elongated flexible tubular body constructed from a core body having a hollow space and an outer cover which is provided over the outer periphery of the core body and formed into a laminated structure having a plurality of layers. The tubular body is formed with a plurality of easily bendable portions which are provided in a spaced apart manner along the longitudinal direction thereof, each of these easily bendable portion being adapted to bend locally with a smaller curvature radius when the flexible tube is bent in one direction. The average interval between the adjacent easily bendable portions is preferably in the range 50-400 mm. The easily bendable portions is formed by locally changing the flexural rigidity of the outer cover.

Abstract: A diffractive-refractive achromatic lens that has a positive resultant power includes a refractive lens system and a positive diffractive grating. The refractive lens system is provided with a positive lens having relatively small dispersion, a negative lens having relatively large dispersion and an additional refractive lens. The additional refractive lens is a positive lens. The refractive lens system exhibits longitudinal chromatic aberration that is substantially proportional to wavelength such that the back focus of the refractive lens system decreases as the wavelength becomes shorter. The positive diffractive grating corrects the longitudinal chromatic aberration of the refractive lens system. The condition 0.005<f/fD<0.2 is satisfied where f is the focal length of the entire lens system, and fD is the focal length of said positive diffractive grating.

Abstract: A selectable assembling device of a zoom lens barrel includes a stationary barrel having a female helicoid, and linear guide grooves spaced at 120 degree intervals; a cam ring including bottomed cam grooves; a linear guide barrel provided with linear guide projections and linear guide slots spaced at 120 degree intervals; and a plurality of lens frames provided with sliding projections spaced at 120 degree intervals, which are engaged in the linear guide slots of the linear guide barrel, each of the sliding projections including a cam follower which is fitted in a corresponding bottomed cam groove of the cam ring. Upon assembly, a relative angular position of assembly for the cam ring and the linear guide barrel can be selected from among three circumferential positions spaced at 120 degree intervals. A device for guiding a flexible circuit board is also provided.

Abstract: A zoom lens includes a cam barrel having first and second cam grooves formed on an inner peripheral surface thereof; and first and second lens frames having first and second cam followers, respectively engaged with the first and the second cam grooves. The cam dead end of the first cam groove and the second cam follower insertion opening of the second cam groove are formed at the same circumferential position. Upon assembly, the first cam follower is inserted into the first leading section via a first cam follower insertion opening, and the second cam follower is inserted into the second leading section via a second cam follower insertion opening.