1. Field of the Invention
This invention generally relates to a lens barrel and more particularly, to a lens barrel that has a light shielding (namely, intercepting or blocking) portion for preventing light rays from being incident through an opening between barrels which are adapted to move relatively in a direction of an optical axis and/or in a direction of rotation thereof.
2. Related Art Statement
A camera provided with zooming and collapsing functions has a lens barrel consisting of a plurality of barrels such as a lens cylinder, a linearly (or rectilinearly) movable (or moving) cylinder, a rotary (or rotating) cylinder and a stationary (or fixed) cylinder. Such a type of camera realizes (or implements) the aforementioned zooming and collapsing functions by relatively displacing the aforesaid barrels or displacing the aforementioned barrels relative to an outer cover for a camera main body in a direction of an optical axis and/or in a direction of rotation thereof.
In the aforementioned lens barrel, small gaps are provided between the barrels facing each other and between the barrel and the outer cover for the camera main body, respectively, so as to reduce a drive (or driving) load at the time of relatively displacing the barrels. If adequate measures are not taken to block light at the gaps, there is caused a defect in that unnecessary external (or extraneous) light enters directly the main unit of a camera or indirectly therein (after undergoing secondary reflection or scattering) and then reaches a film surface and thus a film is exposed to the light.
Therefore, there has been made various propositions for preventing external light from entering the camera main body through the aforementioned gaps. For example, in Japanese Unexamined Utility Model Publication No. 5-61711 Official Gazette, there has been proposed the following light shielding device for use in a camera.
Namely, as shown in FIG. 10, the aforesaid light shielding device has a light shielding member 103 formed by sticking (or putting) a ring-like synthetic resin sheet member 103a, whose inside (or inner) diameter is less than the outside (or outer) diameter of a movable cylinder 101 for holding a (picture) taking lens, onto a ring-like light shielding (or intercepting) sheet base plate 103b. Further, the aforesaid light shielding member 103 is fixed to a front cover 102 of the camera main body. Then, the aforementioned sheet member 103a is pressure-connected (or pressure-contacted) to and is brought into surface contact with the aforementioned movable cylinder 101. Thus, external light is prevented from entering the camera main body through the gap between the movable cylinder 101 and the front cover 102 thereof.
There have been employed light shielding devices, most of which have the configuration as above described.
Meanwhile, the light shielding device for use in a camera, which is proposed in the aforesaid Japanese Unexamined Utility Model Publication No. 5-61711 Official Gazette, is a mechanism by which the shielding of light is achieved by bringing only a single elastic (or resilient) light shielding means (corresponding to the sheet member 103a in the aforementioned example of the device) into surface contact with the surface of the inner wall of the movable cylinder. However, the light shielding device of such a configuration has encountered problems that the surface contact is unstable in the case where the aforesaid movable cylinder is eccentric with respect to an optical axis and that thus the complete light shielding performance cannot be obtained.
On the other hand, in recent years, there have been increasing demands for miniaturization of a camera. This exerts an influence on barrels. Further, when miniaturizing the barrels, there arises a necessity for miniaturizing a light shielding device incorporated in a camera.
However, when miniaturizing the aforementioned light shielding device, there is a fear that the following drawbacks, especially, deterioration in light-shielding performance may be caused.
To begin with, drawbacks caused in the case of reducing the size in a direction (namely, in a radial direction), which is perpendicular to an optical axis, of the aforementioned elastic light shielding means will be described hereinbelow.
First, in the case where it is intended that the miniaturization is achieved by reducing the outside diameter of a supporting member (corresponding to the light shielding sheet base plate 103b) for the elastic light shielding means (corresponding to the sheet member 103a), the mounting strength of the aforesaid sheet member decreases. Thus, the contact of the aforesaid sheet member with the movable cylinder 101 becomes unstable. Consequently, there is caused a drawback in that the complete light shielding performance cannot be obtained.
Namely, when reducing the outside diameter of the aforesaid supporting member, the stiffness (or rigidity) of the aforesaid supporting member itself decreases. The relative displacement between the barrels causes deformation of the supporting member, which receives a force exerted in a direction of an optical axis, into a cone-like (or conical-spring-like) form. Thus, an amount of lap in the sheet member decreases. Consequently, there is caused a drawback in that unnecessary light enters the camera main body.
Second, in the case where it is intended that the miniaturization is attained by reducing the inside diameter of the aforementioned supporting member without changing the thickness in the radial direction thereof and by further cutting a lap portion of the aforementioned supporting member, the amount of the remaining lap may be small according to the quantity of the cut lap. In this case, owing to the eccentricity of the barrel (namely, the movable cylinder), there is caused a drawback in that external light is liable to leak into the camera main body.
Moreover, the curvature of a bending (or bent) portion of the sheet member decreases. Thus, there is caused another drawback in that a load imposed on the barrel increases. Namely, even if the sheet member is formed in such a manner as to be thin to some extent, a rather large load is produced between the barrel and the sheet member, with the result that the drive load between the barrels increases.
Next, drawbacks caused in the case of reducing the size in the direction of the optical axis (or the optical axis direction) of the aforementioned elastic light shielding means will be described hereunder.
First, in the case where it is intended that an amount of lap in a portion in the optical axis direction of the aforementioned sheet member 103a, at which the sheet member 103 is in contact with the movable cylinder 101, is reduced, there is caused a drawback in that external light is liable to leak into the camera main body, similarly as in the aforementioned case. Further, the curvature of a bending portion of the sheet member decreases. Thus, similarly as in the aforementioned case, there is caused another drawback in that a load imposed on the barrel increases.
Second, in the case where it is intended that the miniaturization is achieved by reducing the sheet thickness of the sheet member, the light blocking quality of the aforesaid sheet member itself is degraded. Namely, in the case where the sheet member is formed in such a manner that the sheet thickness thereof is small, external light is transmitted by the sheet member when the external light impinges directly on the sheet member. In addition, when light rays are transmitted by the sheet member, the light rays are scattered. Thus, there is caused a drawback in that a wide range of a film surface is exposed to the light rays having been incident in a camera.
Third, in the case where it is intended that the miniaturization is attained by reducing the thickness of the supporting member for supporting the sheet member, the stiffness of the sheet member is degraded. Thus, the contact of the sheet member with the movable cylinder becomes unstable. Consequently, similarly as in the aforementioned case, there is caused another drawback in that the complete light shielding performance cannot be obtained.