English: Basic mechanical principles of present-day fluoroscopes. 1, x-ray tube heavily shielded to contain unwanted radiation, at the same time permitting useful beam to emerge by way of a small window fitted with filters of aluminum to reduce the effect of radiation on patient's skin; 2, heavy sheet-lead shutters to modify size of x-ray beam; 3, transparent lead impregnated glass to protect observer against excessive exposure; 4, rigid arm to which both tube and screen are attached. Counterbalanced and fitted with ball-bearing rollers, entire assembly is freely movable, side to side and up and down, on supporting framework. Fluoroscopes are built in vertical, horizontal and tilting types.