A closure mechanism, such as a shutter in a camera, in which a closure member (11) having a arcuate portion (12) is arranged to roll on a support member (19) to cause a part (20) of the closure member to move across an aperture (4) thereby providing a movable barrier permitting selective communication of the aperture with spaces on opposite sides of the closure member. When used in a camera, the closure member (11) is accommodated in an enclosure of which one wall (10) includes the aperture, which may be a fibre optic plate (4). The closure member is movable between two extreme positions; in one position a mirror (15) carried by the closure member optically couples the aperture with a viewing system (16,17) and in the other position it blocks the viewing system while a film (5) is located adjacent the aperture by a mechanism (21,22) actuated in synchronism with the closure member.
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