A microscope is a tool that enables us to see objects and organisms that are invisible to the naked eye. Microscopes use a series of two or more lenses to magnify an illuminated image. Magnification is a measure of how big an object looks to your eye compared to “life size.” Microscopes also enhance the resolution of an image. Resolution is the ability to distinguish between two objects that are close together. Resolution can be increased using immersion oil. All microscopes have three basic components: 1) magnifying lenses; 2) a means of focusing; and, 3) a source of illumination (light). A compound microscope uses two lenses to view an object. The ocular (eyepiece) is at the top of the microscope and contains a lens with the ability to magnify objects 10 times (10x) life size. The objective lenses are small cylinders located on the revolving nosepiece. Each objective has a different magnification (10x, 40x, 100x). The total magnifying power of the lenses is calculated by multiplying the magnification of the ocular (10x) by the magnification of the objective (10-100x). Table 4.1 Parts and Functions of a Light Microscope Part Main switch Light intensity knob Eyepiece Field of view Interpupillary distance adjustment Diopter adjustment ring Condenser Aperture iris diaphragm knob Stage Specimen holder Y-axis knob x-axis knob Revolving nosepiece Objectives: 4x,10x,40x,100x oil Coarse focus adjustment knob Fine focus adjustment knob Adjusts the light intensity Contains viewing lenses (10x) Circular illuminated area seen through the eyepieces Adjusts to match distance between student’s eyes Adjusts focuses for student’s individual eyesight Channels light through specimen and objective lens Opens/closes amount of light passing through the specimen Resting surface for the specimen slide Holds specimen slide in place on stage Front and back movement of the specimen holder Right and left movement of the specimen holder Rotates (black ridged band) and positions objective lenses Allows magnification of specimen Locates specimen and focuses under 10X objective lens Focuses specimen under 40x and 100x oil objective lenses
Controls power (on/off) to the scope
Handling the Microscope 1. Use two hands to transport the microscope. Place one hand under the base at the front of the microscope and the other hand under the handle on the rear of the arm (Figure 2.1).
Figure 4.1 Moving and Handling a Microscope 2. Once the microscope is on the lab bench, connect the power cord to the microscope and plug it into an outlet. 3. Using Figure 2.2 as a guide, locate and identify each ocular and objective lens. Record the magnification of each lens and the total magnification. Total magnification is calculated by multiplying the magnification of the ocular (10x) by the magnification of the objective (10x, 40x, 400x).
10x objective lens 40x objective lens 100x objective lens with oil
Figure 4.2. Parts of a Microscope 4-3
Figure 4.3. Microscope Controls
1. Turn on microscope using the power switch located on the right hand side of the microscope frame. 2. Use the light intensity knob to adjust brightness. 3. Locate the nosepiece and rotate the 4x objective into place above the stage. 4. Place condenser in the highest position. 5. Open specimen holder arm, insert slide, and then carefully close arm. 6. Center the specimen directly over the light source using the Xaxis and Y-axis knobs. 7. Move stage to its highest position using the coarse focus adjustment knob. Slowly lower stage using the coarse adjustment knob until specimen appears in field of view. 8. Use the fine adjustment knob to bring specimen into sharp focus. Avoid using the coarse adjustment knob with higher magnification lenses as they can easily break the slide.
9. Adjust light intensity using the iris diaphragm...