We will be using a compound light microscope in this lab to view various cells and tissues. It is very important that you learn to use the microscope correctly, and can efficiently get images into the proper focus for study. Know the following parts of the microscope and the function of each part. 2-2
Know the following functions of the microscope parts. PART FUNCTION Arm Used to carry the microscope; located between the body tube and the base Base Supports the microscope; used to carry the microscope Body tube (Head) Supports the objective lens system and the ocular lens; directs light toward the ocular lens Coarse focus (adjustment) Brings the specimen into focus by raising or lowering the stage; never use the coarse focus on high power! Condenser Substage lens that concentrates light on the specimen; the condenser control knob will raise and lower the condenser to vary the light; the best position for the condenser is just below the opening in the stage Fine focus (adjustment) Used for final focusing (fine-tuning the image) Iris diaphragm Regulates the amount of light that passes through the stage; located at the base of the condenser Objective lenses Magnify the specimen for viewing; scanning lens (red ring) magnifies 4X, low power lens (yellow ring) magnifies 10X, high power lens (blue ring) magnifies 40X, oil immersion lens (white ring) magnifies 100X Ocular lens (eyepiece) The lens (or lenses) you look through; magnifies the specimen 10X; monocular microscopes have one ocular lens, binocular microscopes have two ocular lens Revolving nosepiece Contains the objective lenses; use nosepiece to rotate the correct objective lens into place over the opening in the stage Stage Flat platform where the slide is placed for viewing Stage clips Hold the slide in place; two knobs below the stage control the precise movement of the specimen on a mechanical stage Substage light Light source; a light dimmer dial on the base varies the intensity of the light source 2-3
Use and Care of a Compound Microscope 1. Always use both hands when transporting the microscope. Place one hand on the arm and the other hand under the base. Make sure the cord is not hanging down so you don’t trip over it. 2. Carefully place the microscope on your work table. 3. Carefully remove the dust cover and set it aside. 4. Place the cord behind the microscope then plug it into the outlet. Be very careful not to trip over the cord or pull on it. 5. Once you have the microscope plugged in, sit down and find the light switch. The light switch on your microscope is located on the side of the base (see microscope picture above). Turn on the light switch and adjust the intensity of the light with the light dimmer dial (see microscope picture above). 6. Turn and “lock” the scanning lens (4X objective) in place above the opening in the stage. If the lens is in the correct place, you should see a bright circle of light when you look through the eyepiece. This circle of light is your field of view. 7. Without looking through the eyepiece, lower the stage completely and carefully place the microscope slide on the microscope stage with the specimen on the slide directly over the opening in the stage. If your microscope has stage clips, secure the slide under the stage clips. If your microscope has a mechanical stage, turn the control knobs (below one side of the stage) to position the specimen directly over the opening in the stage. 8. While looking through the eyepiece, carefully turn the coarse adjustment knob to raise the stage until the specimen comes into view. 9. Use the fine adjustment knob for final focusing of the image. 10. Since the scanning lens allows you to see a larger portion of your slide in less detail, you may need to increase your magnification. To switch to the next magnification, carefully turn the revolving nosepiece until the low power lens (10X objective) is locked in place. 11. Your compound light microscope is parfocal. If your image was in proper focus before you changed the objective lens, you should only have to do minimal focusing to get the image in focus with the new objective. You should only have to use the fine focus knob on low power to get the image in proper focus. 12. If you need to increase your magnification to the high power lens (40X objective), simply turn the revolving nosepiece until the 40X objective is locked in place. Make sure your image is in proper focus on low power before switching to the high power objective. 2-4