The purpose of the compound microscope is to magnify the structural components of a thin specimen. The magnification is calculated by multiplying the magnifying power of the objective lens by that of the ocular lens. The maximum magnifying power is about 1200x. Because of the wavelength of visible light, the limit of resolution of the light microscope is about 0.2mm.

If you are not totally secure with the use and function of the light microscope, read the following material and view "Use of the Light Microscope", Volume 1 of the Histology Videotape Series by David Moran. This 26 - volume collection is an excellent preparation for the weekly histology laboratory sessions. The collection is on room reserve (ask at front desk to borrow earphones and videotape for viewing these tapes in the library).

1. Make sure that chair and microscope heights are properly adjusted. Do not hunch over the microscope. Backaches may result from improper posture during prolonged use of the scope.

2. KEEP THE MICROSCOPE LENSES CLEAN. You will not be using the oil immersion lens until spring (in microbiology), but you should be aware of the cleaning procedures to be used after the use of oil. Wipe oil from the oil immersion objective, 100x (and from any other lens in need of cleaning). USE CLEAN LENS PAPER ONLY ON LENSES. Clean lenses immediately after use. Leaving oil on the lens may allow oil to seep behind and harden on the inside of the lens.

If oil has been deposited on a high - dry (40x) lens, clear it with a piece of lens paper slightly moistened with lens cleaner and then with dry lens paper. Avoid soaking the lens with lens cleaner, as this may loosen the cement with which the lens has been mounted.

3. When studying a slide, work from lowest to highest magnification. First examine the section with the naked eye to get an idea of the gross structure of the section, then use the scanning lens (4x). Study the tissue section methodically at increasing magnifications. Use the 10x lens (low power) to get a magnification of 100x, then the 40x lenses (high power) for 400x.

5. We will not use immersion oil for histology (we will however use it for microbiology in the spring). There are two main reasons for not being able to bring an object into focus with the oil immersion lens. a) The coverslip plus mounting medium and the specimen itself may be too thick to permit use of the oil immmersion lens. b) The slide has been turned upside down. Do not try to force an object into view! The oil immersion lens (100x) magnifies a thousand-fold.

6. The illumination must be corrected for each specimen. You can adjust the light source, the iris diaphragm, or the height of the condenser. When studying living, unstained material, it may be advantageous to restrict the light levels. Remember, the higher the magnification, the more light is required. Keep light levels low for low power to protect your vision.

7. Kohler Illumination (for your information only; our gray Nikons do not need this manipulation).

A microscope lamp consists of a bulb (usually with a coil or ribbon filament, or an arc lamp of some kind), a condensing field lens, and a field diaphragm after it. If the lens is moved so that the lamp filament is focused at a considerable distance from the field lens, the latter will appear to an eye placed at the focal point to be uniformly bright over its surface. The purpose of Kohler illumination, then, is to image that lens surface by means of the microscope's condenser in the object plane in order to provide an evenly illuminated field. There are two steps involved

First, focus the field lens so that an image of the filament comes to lie on the iris diaphragm of the condenser. Second, the microscope condenser is moved back and forth until the contracted field diaphragm is imaged in the field. Be sure that this image is centered. For best results, the field diaphragm is then opened to slightly more than the width of the field. Opening it further introduces "stray light" which decreases the contrast of the image.

8. Try to look through your binocular scope with both eyes open; squinting with one eye closed will lead to a headache. Remember, the lower the magnification, the lower the light level necessary. As you increase magnification, increase the light level. You can also raise or lower the condenser lens (under the stage area) using the condenser knob. You may also use the diaphragm (shutter) on the condenser lens to lower or increase light (this is useful in increasing contrast when viewing unstained materials).

9. Before you put your microscope in your locker, be sure you have removed the slide from the stage. If yor lens is dirty (or if you have used immersion oil), clean the lenses with lens paper only. Store your microscope with the lowest power objective lens in place. Carry your scope upright (ocular lenses are not screwed in) to your locker with two hands and place it carefully in the locker without bumping the ocular against the top of the locker compartment.