THE MICROSCOPE OBJECTIVE/RATIONALE The use of microscopes is an integral part of the laboratory setting. The student will care for a compound microscope and use all of the objectives. TEKS 1A, 1B, 1C TAKS ELA 1, 3, 4 Mathematics 1, 10 Science 1, 2 National Science Education Standards A9-12; E9-12; G9-12 National Health Care Skills Standards .01, .04, .07 National Curriculum Standards for School Mathematics S1; S2; S4 KEY POINTS I. Introduction a. Compound microscopes contain a number of lenses, usually 10x in the eyepiece and 10x, 40 or 45x, and 100x (immersion oil) lenses in the objectives. The microscope magnification is calculated by multiplying the eyepiece magnification by the objective magnification. For example: 10x (eyepiece) x 100x (objective) = 1000x The specimen is therefore magnified 1000 times the normal eyesight. b. Definitions 1. Resolution: the microscopes’ ability to distinguish between two points that are close together. The resolving power is expressed in length. 2. Oil immersion objective: this objective uses immersion oil to allow light to pass through it the same way light passes through the glass slide. The oil decreases the bending of the light rays allowing more light to pass directly to the specimen. 3. Binocular: a microscope with two eyepieces as opposed to one eyepiece. Most hospital laboratories use binocular microscopes. II. Components of the Microscope a. eyepiece b. arm c. base d. binocular tube e. revolving nosepiece f. objective lens g. mechanical stage h. stage clips i. iris diaphragm j. coarse adjustment knob k. fine adjustment knob l. lamp m. bulb n. on/off switch III. The Microscope a. Lower the stage to its lowest position using the coarse focusing knob. Always start with the 10x power objective. b. Place the slide on the stage and place the stage clips on top of the slide to hold the slide in place. c. Use the coarse adjustment knob to focus on the slide, and then use the fine adjustment knob until the object is in sharp focus. d. Adjust the light intensity by raising and lowering the condenser to give the best image. e. After focusing with the 10x objective, rotate the 40x objective into the position over the slide. Use only the fine adjustment knob to obtain a sharp image. f. Rotate the objectives so that there is not a lens directly over the slide. Place one drop of the immersion oil on the slide. Slowly rotate the 100x objective into position over the slide. g. USE ONLY the fine adjustment knob to focus on the specimen slide. Adjustment of light intensity may be necessary. h. To change slides during the investigation, follow steps a through g. i. At the conclusion of the laboratory investigation, lower the stage to the lowest position. Clean all lenses and place the 10x objective in position. j. Wrap the cord around the arm of the microscope and replace the dust cover. IV. Care of the Microscope a. The microscope should always be carried by the base and the arm. b. The microscope cord should be wrapped around the arm of the microscope. c. The microscope should always be covered with a dust cover to prevent dust buildup on the lenses. ACTIVITIES I. Complete the Microscope Exercise.