1. Field of the Invention
The present invention relates to a lens barrier mechanism for use in a camera, openably and closably attached at a front side of a taking lens for protecting the taking lens.
2. Description of the Prior Art
A lens barrier mechanism of this type is disclosed by the present applicant in Japanese Laid-open Patent Application No. H4-34709. In this prior art lens barrier mechanism, as shown in FIG. 1, two barrier blades 3' arranged on the same level and a driver ring 4' for driving the blades 3' are arranged to overlap each other on a substantially disk-shaped base member 1' having an aperture 10' at its center. The barrier blades 3' and the driver ring 4' are held between a lens barrel (not shown) and the base member 1'.
A first spring 5' is arranged between the driver ring 4' and each of the barrier blades 3'. The driver ring 4' is rotated until the first springs 5' are overcharged so that the two barrier blades 3' are pressed against each other, thereby closing the barrier blades 3' tight enough to substantially completely prevent dust from coming into the lens barrel at a collapsed position.
To prevent the aperture 10' of the base member 1' from being inadvertently closed during photographing, a second spring 6' is arranged between the driver ring 4' and the base member 1' to always push the driver ring 4' in a direction to open the barrier blades 3'.
Moreover, in another prior art, a presser plate is provided as a means for holding the two barrier blades 3' and the driver ring 4' to overlap each other. The barrier blades 3' and the driver ring 4' are held between the presser plate and the base member 1'.
In the above-described prior art lens barrier mechanisms, however, since the two barriers 3' are separately driven by receiving a rotation force from the driver ring 4', the first spring 5' should be provided between the driver ring 4' and each of the blades 3'. Thus, in the prior art mechanisms, two first springs 5' arranged between the driver ring 4 and the barrier blades 3' and one second spring 6, i.e. a total of three springs are required.
In addition, since these springs have to be extension springs, under present circumstances, it cannot be helped to use coiled springs occupying considerable space. For this reason, the prior art mechanisms in which the coiled springs are incorporated to lie on the base member 1' is inevitably large in dimension along the optical axis, which makes it impossible to reduce the size of the barrier mechanism. A mechanism requiring the presser plate like the latter prior art mechanism is of great bulk with a greater thickness because of the thickness of the presser plate.