| 摘要 |
<p>In single-lens reflex cameras a movable minor (1) is disposed between the lens (13) and the film (14). This minor deflects, in a view finding position (1), the light rays onto a focusing screen (15) viewfinder and can be retracted by tilting into a shot taking position (1"). This must be done so as to avoid a fuzzy image caused by the shock of the minor against the camera frame. A retraction of the mirror free from vibrations is obtained by accelerating it with the help of a torque spring (4) which is placed between the minor (1) and a movable balancing mass (2) added to the mirror and braking it by means of a brake (21, 22, 23) disposed on the movable parts. The minor position at every moment of its displacement is determined by cogwheels (16, 17, 18, 19) linked to the minor, to the balancing mass, respectively to a supplementary pin (20). Through the rotation of the pin (20) the minor can be disposed into a view finding position after the taking of photographs and be held in this position by locking this axis. The unlocking allows the minor to tilt into the view finding position. The unbalance resulting from the displacement of the minor and the balancing mass can be reduced by providing some counterweights (11, 12) or by disposing the masses of the minor and of the balancing mass symmetrically with respect to the rotation axis at the centre of the displacement. A corresponding disposition for the minor with a virtual mirror with a virtual rotation axis (for instance a pivoting mirror) is also described. </p> |
