Transcript
Laboratory 2 Microscope Use
Goals: Demonstrate proper use of the microscope and identify the parts of the microscope. Microscopes are used to magnify, or increase the visual size, of images allowing us to see things too small for the naked eye. The microscopes we will be using are compound microscopes, meaning that there are two different magnifying lenses. One of these lenses in the objective and the magnification power can be found on the outside of the objective. The other lens is in the eyepieces and magnifies at 10X. The total magnification of the image is determined by multiplying the eyepiece lens magnification by the objective lens magnification. •
1. Setting up the Microscope: 1. Always use two hands: one underneath the base and one on the arm, when carrying the microscope. Be gentle when picking up or setting down the microscope. 2. Make sure the microscope the eyepieces (oculars), condenser lens, and light source is dust-‐free. Use lens paper if cleaning is necessary. 3. Verify that the lowest power objective (4X, red) is selected. 4. Move iris diaphragm lever to the left and use the condenser lens knob to raise the condenser lens to the highest position possible. 5. Place slide on stage and use mechanical stage control to position the tissue under the objective. Setting ocular distance and ocular focusing: Failure to follow these steps can result in headaches and dizziness, not to mention an unclear image of the slide. 6. Turn on the microscope and use the rheostat dial to adjust the light to a level that is comfortable for your eyes. 7. Adjust the distance between the two eyepieces until you see one clear circle when looking through them. If you see two circles, push the eyepieces together until you see just one. If you see a blurry circle, widen the eyepieces more. Record your setting for future reference: ______________. 8. Adjust the ocular focus by first rotating both eyepieces until they are as close to the headpiece as possible. Then with your left eye closed, focus the slide using the coarse then fine focus. Now close you right eye. Focus the slide by ADJUSTING THE EYEPIECE, not the focus adjustment knobs. Steps 1-8 should be followed every time you use the microscope.
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2. Viewing the Slides: Note: Slides should always have coverslips. The prepared slides in the class have them glued on. For any student prepared slides, ensure that you use a coverslip. 9. Scan the slide on the 4X objective. This corresponds to 40X magnification. ALWAYS look at any slide on this magnification first even if you ultimately draw it on a higher magnification. It helps you get 12
orientated to the tissue and gives a different perspective. Place the region that you want to see more clearly in the middle of the visual area. 10. Look at the slide on the 10X objective. ALWAYS look at this magnification before proceeding higher. The lenses are parfocal, meaning that you should only need to adjust the fine focus. 11. Finally, look at the slide through the 40X objective. Only the fine focus knob should be necessary to bring it into focus. 12. If you wish to use the 100X objective, you should have the image focused at 40X, then move the objective to the slide, place a drop of oil on the slide before moving the 100X objective into place. Do NOT use another objective until you have cleaned the oil off of both the slide and the objective using lens paper and cleaner located in the cabinet with the microscope. Adjusting the condenser lens: 13. For scanning and low power viewing, the condenser should be at its highest setting. To sharpen the image of a higher power view, lower the condenser using the condenser adjustment knob. Controlling light levels: 14. The rheostat can be used to control the light level. The iris diaphragm controls how much light passes through the slide to the objective. Compare and contrast how these two methods of controlling the light effect the image.
3. Storage of the Microscope: 15. Remove the slide. 16. Clean any residue or stains from the objectives with lens paper, and if necessary, lens cleaner. If you used oil immersion, use lens paper to clean the oil from the 100X objective. Wipe the eye pieces and the stage. 17. Put the 4X objective into place. 18. Center the mechanical stage so that none of the gearing is over the side. Wrap and Velcro the power cord. 19. Move the mechanical stage to its highest position. 20. Return the microscope (see step 1 for carrying instructions) to the cabinet with the arm facing you.
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4. Troubleshooting: “The light doesn’t work” • If you are working at a table in the center of the lab, ensure that the worktable is plugged in – the worktables should be plugged into overhead electrical outlets. If your table is not plugged in, it won’t have power. • If you are working at one of the workstations on the side of the lab, try a different outlet – the outlet you are using may be faulty. • Ensure that your power cord is properly inserted into the base. The power cords are removable and sometimes come loose. • Ensure that the rheostat is not dialed all the way down. • If you have tried all of the above, and the light still does not work, notify your instructor. The lightbulb, power cord, or fuse may need to be replaced. Your instructor may have you use a different microscope for the time being. If your instructor is unable to repair the microscope, the lab technician should be notified. “I cannot see anything.” • Ensure that the scanning (4x, red) objective is fully locked into place. • Make sure your slide is centered properly and not upside down. • Check the condenser to make sure the iris diaphragm lever is set to the left. If the iris diaphragm is completely closed, insufficient light may be an issue. • You will need to use the coarse adjustment knob to raise the stage so that the slide is quite close to the objective before an image can be seen. “The image is blurry.” • First, make sure you followed all of the focusing steps described in steps 2 through 11. • CLEAN EVERYTHING. Clean the ocular lenses, the light source, the condenser lens, the objective, and the slide. DO NOT REMOVE ANYTHING. You should be able to clean the objective without removing it. Make sure the slide is not upside down! • If you’ve tried all of the above, and the image is still not sharp, please notify your instructor. Your instructor may attempt further cleaning or direct you to put the microscope away and use a different one. The lab technician should be notified in this case.
Attribution of images used in this document: Figure 1: Leica. (2009) [Parts of the Leica CME]. Leica CME microscope manual. Figure 2. Green, PS and Long, G.. (2012). [Uncovered microscope on shelf]. Tacoma Community College.
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Laboratory 2
Name: _______________________________
Microscope Use
Section: _____________
1. Watch this video demonstrating proper microscope use: http://www.tacomacc.edu/upload/files/distancelearning/video/MicroscopeTutPB.html. 2. Watch this video: http://youtu.be/7yTJIMTpT7o. Identify three mistakes Jack Skeleton made while attempting to use the microscope. 3. The image on the right is observed through your right eye and the image on the left with your left eye. How do you fix this?
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4. For each image pair, the image on the left is what the slide should look like and the image on the right is what you see. Describe how you would correct the improper image using the microscope controls. A
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5. For each picture, indicate whether or not the microscope was stored properly. If not, indicate what is wrong.
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