Device for moving slides vertically in projectors

The device is provided with a lever which is pivotally mounted at one end and is urged in the downward direction by a spring, a slide-carrying shoe being attached at the free end of the lever. The lever has an upwardly curving centre portion which rests on a roller mounted on a disc driven at half-speed by a motor. The device also comprises a slide guide consisting of two prismatic rails, one of which is stationary, while the other is secured to a carriage mounted displaceably in the plane of the slide and capable of being pulled towards the stationary rail by means of a spring. There is a coupling pin on the carriage which is engaged with a control cam provided on the lever-driving disc, the said cam being designed in a manner such that the movable prismatic rail is pulled back only during the downward movement of the slide shoe which moves between the prismatic rails, the said slide being otherwise pressed against the stationary rail under the action of the spring. In its lowermost position, the slide shoe may rest upon a stop which is vertically adjustable in order to be able to set the slide accurately in relation to the optical axis. The stop for the slide shoe is preferably mounted at the end of a double-ended, spring-loaded lever, the setting of which is adjusted by means of a screw.