Camera with a variable focus lens device

#The present invention relates to cameras which have a variable focus lens device such as a zoom lens device and an autofocusing device. The invention more particularly relates to a lens position detecting device for detecting the position of a zoomed photographing lens in order to detect the focal length of the lens, and a structure for supporting a flare preventing mask for preventing, through the zooming operation, undesirable flare from being caused by light entering the photographing lens, as well as a structure for retaining a front lens group constituting the compound photographing lens.

#In recent years, cameras have been popularly used in many applications which are fitted with a variable focus lens device that is designed to enable any photographer to readily take good photographs without the need to interchange the component lenses. Typical examples of such variable focus lens devices are so-called focus switching devices which allow the focal length of the photographing lens to be switched between a long focal length (telephoto position) and a short focal length (wide-angle position), and a zoom lens device which is capable of continuously changing the focal length of the photographing lens. These cameras fitted with variable focus lens devices also have structure for moving the component lenses along the optical axis in order to properly change the focal length as required. Furthermore, many of the above-mentioned types of cameras can automatically focus on an object to be photographed, such as by the photographer depressing the release button halfway while pointing the camera at the object. This function is known as an autofocusing function and services greatly to facilitate the photographer's focusing operation.

#In variable focus lens devices, a front lens group and a rear lens group, constituting the compound photographing lens, are retained in a movable lens mount. The variable focus lens device can change the focal length while maintaining a predetermined optical relation between the front and rear lens groups, by advancing or retracting the movable lens mount in relation to a fixed lens mount along the optical axis and also advancing or retracting the rear lens group with respect to the movable lens mount along the optical axis in accordance with the advance or retraction of the movable lens mount. The autofocusing device is designed to move, upon release of the shutter and prior to an exposure operation, a focusing lens from a reference position to an in-focus position on the basis of the distance to an object that is detected by a distance measuring circuit.

#FIG. 1 is a schematic cross-sectional view of a camera with a variable lens device according to the present invention, taken along a vertical plane containing the optical axis, and having a lens position detecting device, in which the photographing lens is in the short focus or wide angle position;

#FIG. 2 is a view similar to FIG. 1 but in which the photographing lens is in the long focus or telephoto position;

#FIG. 3 is a rear view of essential parts of the camera body illustrating the power transmitting system for performing zooming operations;

#FIG. 1 is a cross-sectional view of a zoom lens device for a camera which is in its short focus or wide-angle position, taken along a vertical plane containing the optical axis S. A lens position detecting device is also shown in FIG. 1. FIG. 2 is a cross-sectional view of the zoom lens device which is in its long focus or telephoto position. The zoom lens device is mainly made up of a fixed lens mount 11 fixed to a camera body 10, an intermediate lens mount member 12 as a driving lens mount rotatably accommodated in the fixed lens mount 11, a movable lens mount 13 accommodated in the intermediate lens mount 12, and a key plate 16 for guiding the movement of the movable lens mount 13. A front lens group 14 is retained in the front portion of the movable lens mount 13, while a rear lens group 15 is supported in the rear portion of the movable lens mount 13 so as to be movable with respect to the movable lens mount 13 along the optical axis S. The movement of the rear lens group 15 with respect to the movable lens mount 13 is by a predetermined amount in order to vary the focal length of the zoom lens device while maintaining a predetermined optical relation with the front lens group 14. An opening formed about the optical axis S of the camera body 10 constitutes the aperture 10a of the camera.

#A helicoid 11a is formed in the inner peripheral surface of the fixed lens mount 11, and an outer helicoid 12a is formed in the outer peripheral surface of the intermediate lens mount 12. When the intermediate lens mount 12 is accommodated in the fixed lens mount 11, the helicoid 11 a is in meshed engagement with the helicoid 12a. An inner helicoid 12b is formed in the inner peripheral surface of the intermediate lens mount 12, and a helicoid 13a is formed in the outer peripheral surface of the movable lens mount 13. When the movable lens mount 13 is accommodated in the intermediate lens mount 12, the inner helicoid 12b is in meshed engagement with the helicoid 13a. The key plate 16 extends into the intermediate lens mount 12 and the movable lens mount 13 from the rear end portion of the intermediate lens mount 12. Rollers 17 provided within the movable lens mount 13 are in engagement with opposite sides of the key plate 16. A bracket 34 having a guide portion 34a on a lower portion thereof is fixed to the rear end portion of the movable lens mount 13, and the rollers 17 are supported in such a manner as to be rotatable about downwardly directed shaft pins 35 secured in the guide portion 34a.

#The front lens group 14 is held by a lens holder 36. The lens holder 36 is of barrel shape suitable for holding the front lens group 14 and has, at its front end, a flange portion 36a which extends radially outwardly. The movable lens mount 13 has, at its front end, a flange portion 13b which extends radially inwardly. When the lens holder 36 is inserted into the movable lens mount 13 from the front thereof, the flange portion 36a is brought into engagement with the flange portion 13b, whereby the optical axis of the rear lens group 15 is automatically brought into alignment with the optical axis of the front lens group 14.