3.2: Lab Procedures - Operating a Microscope

General Operating Procedure Guidelines

The following step-by-step operating procedure should be carefully observed:

1. Plug in and turn on the in-base illuminator.
2. Raise the nosepiece using the coarse adjustment knob. This provides greater access to the stage when the slide is in position.
3. Rotate the nosepiece so that the 10 times objective is in operating position. You should feel a definite position stop for the objective. Turn the nosepiece clockwise and counter-clockwise until you are familiar with this position stop.
4. Open the iris diaphragm approximately half way.
5. Place the slide in the stage slide holder securely. Be sure the slide has the specimen side up. Roughly center the specimen over the light coming from the condenser.
6. Move the microscope condenser by means of the condenser rack and pinion knob until the top of the condenser is approximately the thickness of a piece of paper beneath the slide.
7. Lower the objective using the coarse control knob until it reaches a stop. Do not force the knob. The stop should be obvious if you are moving the controls gently. Again, become familiar with the feel of the position stop.
8. View through the eyepieces and without disturbing the coarse adjustment setting, slowly rotate the fine adjustment knob in the appropriate direction until the specimen detail is in sharpest possible focus.
9. Adjust the interpupillary distance between the two eyepieces by sliding the eyepiece plates in or out.
10. Once the specimen detail is in sharp focus using the 4 times (scanning) objective, it is then possible to rotate the nosepiece to other objectives without changing the position of the coarse adjustment knob. Very little refocusing with the fine adjustment is required, it will be in focus with all of the lenses (parfocal).
11. Make certain that the portion of the specimen you wish to view is exactly centered in the field of the low-power objective. This is necessary because the microscopic field of view is smaller under high magnification than under low magnification.
12. Remember that the iris diaphragm setting must be changed whenever a different objective is used. As magnification increases the condenser iris diaphragm is opened as required. With these microscopes you are effectively increasing the light reaching the higher power objective. Adjustment of the condenser iris diaphragm results in proper contrast for viewing specimens under varying magnifications.
13. Try the highest magnification, the l00 times - oil immersion objective. To focus with the oil immersion lens, proceed in the following manner:
    • Revolve the nosepiece so that there is no objective directly over the specimen. This allows enough space so that a drop of immersion oil may be placed on the specimen.
    • Place one drop of immersion oil in the center of the circle of light formed on the specimen slide.
    • Turn the nosepiece until the 100 times objective snaps into place. The objective should be in the oil but must not touch the slide.
    • Rotate the fine adjustment knob to obtain a sharp focus of the specimen.
14. Note: Make sure the immersion oil has been cleaned from the lens with lens cleaner fluid before returning the microscope to the storage space.