Microscope Review

MICROSCOPE REVIEW

A. MICROSCOPE PARTS AND THEIR FUNCTION

Throughout this course you will be using a microscope to study both the external and internal structures of a variety of organisms. The light microscope will enable you to observe structures up to one thousand times smaller than those visible to the naked eye.

A labeled illustration of the parts of your microscope is included on the following page (figure 1-A). The important parts of your microscope are:

OCULAR the lens system closest to the eye that magnifies the image ten times - 10X

OBJECTIVE the lens attached to the circular nosepiece that performs the initial magnification. There are three objectives on the nosepiece:

scanning lens - 4X low power lens - 10X high power lens - 40X

Some microscopes have a fourth lens that magnifies 100X and is used with oil. This lens requires careful cleaning after each use to remove the oil. USE ONLY LENS CLEANER AND LENS PAPER TO CLEAN THE LENSES.

COARSE FOCUS KNOB allows vertical movement of the stage so the specimen can be positioned under the objective to produce an image.

FINE FOCUS KNOB brings the image into sharper focus.

STAGE a platform with an opening that permits the beam of light to pass through the specimen on a glass slide.

DIAPHRAGM a disk with a variable opening that regulates the diameter of the light beam from the lamp below.

CONDENSER a combination of lenses that focus light from the lamp onto the specimen.

viii FIGURE 1-A. PARTS OF THE MICROSCOPE

B. TOTAL MAGNIFICATION

To calculate total magnification of a specimen being viewed, multiply the ocular lens magnification (10X) by the objective lens magnification (4X, 10X, 40X, or 100X).

Total Magnification = (Ocular lens magnification) x (Objective lens magnification)

Example: Total Magnification = (10X) x (40X) = 400X, a 400-fold magnification

ix C. CARE AND USE OF THE MICROSCOPE

The microscope is a very expensive instrument with very delicate adjustments. It must be handled with care and respect at all times. Always follow the precautions listed below:

i. Only lens paper should be used to clean the lenses. Other papers, including KimWipes, will scratch the lenses.

ii. When moving the microscope from one place to another, always hold it upright and carry using two hands, using one hand to support the bottom of the microscope.

iii. First locate the object to be studied under scanning power and focus with the coarse and fine focus knobs. Center the object within the field and then turn to higher magnifications if desired. Use only the fine focus on higher powers.

iv. Never use the coarse focus knob under higher powers—only under scanning power.

v. Never focus downward. This means that you should move the stage away (down) from the objective rather than toward (up) to the objective. If you were to focus upward, it is possible for you to break the objective or its lenses.

vi. If your microscope is not working properly, notify your instructor. Do not attempt to fix it yourself.

vii. When not using your microscope, turn of its light.

viii. Remove slides (put them away) and set the scanning objective in place before putting the microscope away. Make sure the stage is clean and the lenses are dry. If an oil immersion objective was used, be sure to clean it with lens cleaner and lens paper before storing the microscope.

ix. Do not transfer oculars or objectives from one microscope to another.

To use the microscope:

1. Rotate the nosepiece until the scanning objective clicks into position. Make sure there is sufficient light passing through the diaphragm opening in the stage. However, too much light will wash out the image altogether.

2. Place the slide on the stage. Center the slide so that the light passes through the spot where you think the specimen is located.

3. Use the coarse focus to bring the stage as close to the objective as the knob allows. Then, looking through the ocular, use the coarse focus to move the stage away from the objective. An image should come into focus. 4. Use the fine focus to produce a sharper image. After centering the specimen in the field of view, switch to the 10X objective. Only the fine focus should now be used to obtain a sharp image. If higher magnification is needed, again make sure the specimen is centered in the field of view before changing objectives.