3. Procedures for Examining a Mixed Culture of MicroorganismsGREEN RIVER COMMUNITY COLLEGE IDS Unit 1 DPM IDS Microscope Lab 1 Instructions (page 1) MICROSCOPE LAB 1 THE MICROSCOPE The microscope is one of the principal tools of the biologist. Without the microscope, many of the great discoveries of biology would never have been made. The light compound microscope, illustrated in Figure 1, is the type of microscope most commonly used. Proper, comfortable use of the instrument demands practice. The practice afforded you in this exercise depends upon familiarity with the parts of the microscope and with their interactions. MAGNIFICATION AND RESOLUTION In using the microscope it is important to know how much you are magnifying an object. To compute the total magnification of any specimen being viewed multiply the power of the eye piece (ocular lens) by the power of the objective lens being used. For example, if the eye piece magnifies 10X and the objective lens magnifies 40X, then 10 x 40 gives a total magnification of 400X. The compound microscope has certain limitations. Although the level of magnification is almost limitless, the resolution (or resolving power) is not. Resolution is the ability to discriminate two objects close together as being separate. The human eye can resolve objects about 100 µm apart. The compound microscope has a resolution of 0.2 µm under ideal conditions. Objects closer than 0.2 µm are seen as a single fused image. Resolving power is determined by the amount and physical properties of the visible light that enters the microscope. In general, the greater the amount of light delivered to the objective lens, the greater the resolution. The size of the objective lens aperture (opening) decreases with increasing magnification, allowing less light to enter the objective lens. Thus, you will probably find it necessary to increase the light intensity at the higher magnifications. DEPTH PERCEPTION AND THE MICROSCOPE Any microscopic object viewed has depth as well as length and width. While the lens of your eye fully adjusts to focus on an object being viewed and provides you with a three dimensional interpretation, the lenses of a microscope are focused mechanically and can only “see” in two dimensions (length and width). For example, if the specimen you are examining has three layers of cells, you will only be able to focus on one cell layer at a time. In order to perceive the relative depth of your specimen use the fine adjustment to focus through the different planes (the three cell layers) individually to build a three dimensional picture or interpretation of your specimen.GREEN RIVER COMMUNITY COLLEGE IDS Unit 1 DPM IDS Microscope Lab 1 Instructions (page 2) THE FIELD OF VIEW: A CIRCLE When you view an object under the microscope you will observe that it lies inside a circular field of view. Each different magnification has a different sized field of view. If you determine the diameter of the field of view you can estimate the size of an object seen in that field. As you increase the magnification, the field of view (and diameter) gets proportionately smaller. As a consequence, a critter that appears small under scanning power may appear large under high power. The actual size of the critter did not change, only the space in which you placed it for viewing. CARE OF THE MICROSCOPE Your microscope is an expensive instrument that must be given proper care. Always follow these general instructions when using a microscope. 1. Always carry the microscope with both hands, one hand under the base, and the other on the arm. When getting ready to put the microscope away, always return it to the low-power or scanning-power setting. 2. When setting the microscope on a table, always keep it away from the edge. It is generally best to clear your lab table of items that are not being used. 3. The lenses of the microscope cost almost as much as all of the other parts together. Never clean them with anything other than lens paper. 4. Please report any microscope damage or irregularity in its operation at the beginning of the period so that the repair costs will not be charged to you. You are responsible for the microscope while you are using it. Low-power field of view diameter is 1.8 mm ≠≠≠≠ 2 mm Ruler (mm)GREEN RIVER COMMUNITY COLLEGE IDS Unit 1 DPM IDS Microscope Lab 1 Instructions (page 3) SETTING UP & VIEWING OBJECTS THROUGH THE MICROSCOPE 1. Place the low-power objective in position if it is not so fixed. In changing from one objective to another, you will hear a click when the objective is set in proper position. Make certain that the lenses are clean. 2. Check preliminary lighting a. Turn on the substage light. b. Position the condenser as high as it will go by turning the substage adjustment. This provides for a maximum of light. c. Open the iris diaphragm by means of the lever beneath the condenser, which is below the stage of the microscope. 3. Place the slide for viewing a. Make certain that the lower-power objective is in place. b. Lower the stage (away from the objective) with the coarse adjustment. c. Place a properly prepared slide (see below) on the stage and secure with the stage clips or mechanical stage depending upon which is present on your microscope. d. Place the slide with the object directly above the brightly illuminated substage condenser. 4. Focus: Proper focusing technique a. Viewing the stage from the side, use the coarse adjustment knob to raise the stage until the stop is reached that will prevent further movement of the stage. b. Looking through the eye piece, or ocular, lower the stage slowly by turning the coarse adjustment knob counter-clockwise until the object is in focus. c. Use the fine adjustment to bring the object into sharp focus. d. If necessary readjust the amount and intensity of light for comfortable viewing. 5. Increasing Magnification: Switching from Low to High Power a. First, be sure your slide is focused under low-power. b. Leave the slide where it is and switch to high-power. Watch from the side to make sure that the objective lens does not touch the slide. The object should be in focus. NOTE: Most microscopes are “parfocal”; that is, the slide should be in focus (or nearly so) when you switch from low-power to high-power. If you have properly focused your