a.  To tighten the focussing controls of the coarse focus knob, the ring must be turned in an  anti-clockwise direction, as indicated by the arrow. To loosen it, the ring must be turned  clockwise. 2.  Adjusting the stage stopper.  a.  Loosen the stage stopper screw (Fig. 6) with a 2mm hexagonal key.  b. Focus on the sample using only the fine focus knob (20) with firstly the 4X objective (4),  and 10X objective.  c. Tighten the stage stopper screw until tight enough for the stage (8) not to move  upwards. The 40X and 100X (optional) objectives incorporate security measure in that the lens tip retracts to avoid damage to the front of the lens should it come into contact with the slide. An additional measure of security consists of an adjustable stopper on the ascending  movement of the stage. The stopper comes pre-adjusted by the manufacturer for standard  slides with cover slips 0.17mm thick. For observing other types of samples, however, it may  become necessary to readjust the stage stopper. -11-  Stage stopper  screw  Coarse focus  tension control  Condenser  focussing  control  Fig. 6 