condenser housing. By properly adjusting the condenser, you can greatly improve the clarity  of the specimen A  filter holder  may be attached to the bottom of the condenser. It usually  contains a blue filter. The Light Source:  Your microscope has an  illuminator  built into the base of the microscope  and controlled by an on/off switch. You can control the amount of light entering the specimen  by adjusting the diaphragm. You can also control the light intensity by adjusting the voltage of  a transformer attached to the illuminator. Use low or medium voltage settings for most  microscopic observations. You will need a higher setting when using the oil-immersion lens. Some compound microscopes have an attached  mirror  instead of a built-in illuminator. The mirror is usually concave on 1 side and flat on the other. The flat side of the mirror is usually  used with the scanning and low-power objectives. The concave mirror is used with the higher  power objectives. The light source for the mirror is usually a lamp; natural light can be used but  it is not preferred because its intensity is too variable.  You can focus your microscope by using the  coarse  and  fine adjustment knobs ;  these raise or lower either the body tube or the stage, depending on the type of microscope  you are using. Try this with the low-power objective in position, about 1/4 inch above the  stage. Rotate the coarse adjustment knob 1/4 turn clockwise while watching the low-power  objective. Do the same with the fine adjustment knob. Before using your microscope, thoroughly clean the oculars and objectives with lens  paper. Use a circular cleaning motion to avoid scratching the lens. When using the microscope,  keep your eyelashes from touching the ocular:because oil from your lashes will adhere to the  oculars and smear them. (Students should avoid wearing mascara in microscopy labs.) Thoroughly clean the stage and microscope slides to prevent damage to the microscope. USING A COMPOUND MICROSCOPE: Focusing 1. Clean the oculars and objectives using lens paper. 2. Cut out a letter "e" from a newspaper or other printed page. Clean a microscope slide and  prepare a wet mount of the letter, using the procedure described below.  3. Put the scanning (4x) objective in position, and then place the slide on the stage in its normal  viewing position. Add a drop of  water to a slide. Place the specimen in the water. Place the edge of a coverslip on the slide so that it touches  the edge of the water. Slowly lower the coverslip to prevent forming and trapping air bubble