Abstract: The optical unit comprises a frame (1), a subrame (3), and objective holder (5) having an objective (7) for concentrating the radiation beam so as to form a radiation spot. First connecting means (11) movably connect the objective holder to the subrame, which first connecting means allow focussing movements of the objective and counteract other movements. Second connecting means (9) movably connect the subframe to the frame, which second connecting means allow radial tracking movements of the objective and counteract other movements. Electrically controllable first focussing means (19), connected to the frame and electrically controllable second focussing means (21) connected to the objective holder cooperate with each other to produce the focussing movements.

Abstract: A device having a pivotal cover, such as a magnetic tape cassette, for covering one or more front openings between the front edges of two major walls which extend generally parallel away from the opening. The cover has flanges by which it is connected at the sides of the device, through a pivot pin and a straight slot, on the pivot axis, and another pin which engages a circular segment slot. The circular segment slot has a recessed portion which the other pin engages when the cover is closed. The cover must be moved in a direction away from both major walls, to an unlatched position, before it can be pivoted to an open position adjacent one or the other of the major walls.

Abstract: The cover of a cassette such as a magnetic tape cassette is pivoted in either of two opposite directions to open positions about a single axis. To latch the cover, adjacent each side wall of the cassette there is a cover flange having a circular slot concentric with the pivot axis, the slots in the two flanges extending in opposite directions and overlapping at ends which, in the closed cover position, are aligned with latching projections on the cassette housing. By moving one latching projection out of its slot, the cover is free to pivot in the direction in which the other projection engages the slot at its end. In a flip-over reversible cassette, one unlatching member on the apparatus will engage the correct latching projection, depress and release it, so as to permit the cover to open only the correct direction. When the cover is fully opened, the projection may be permitted to be reinserted, into a recess provided for that purpose.

Abstract: A magnetic-tape cassette has a front opening (7) which when the cassette is not in use is covered by a pivotal front cover (20) and a sliding plate (9) which is situated on the outside of the cassette housing (1) adjacent the bottom wall (2) thereof. In the closed position the sliding plate covers the front opening (7) at the bottom and a part of the magnetic tape (18a) which extends across said opening. The top wall (3) of the housing is imperforate and is contiguous with the front cover in the closed position of the cover. In the closed position the sliding plate (9) extends from the front of the cassette housing (1) beyond openings (4) in the bottom wall (2) to cover these openings. The sliding plate is formed with two apertures (15) which expose the openings (4) in the open position of the sliding plate (9).