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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. 

## USING A COMPOUND MICROSCOPE: 

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. 

## 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. 

<img src='content_image/769570.jpg'>

3. Put the scanning (4x) objective in position, and then place the slide on the stage in its normal viewing position. 

