by Teresa Bondora
Using a microscope isn't difficult. With a little precision and practice you'll be a pro in no time. The key is to make small and careful movements as you make your way from larger to smaller. To understand these directions, you'll need to be familiar with the parts of the microscope. Please print the diagram of a microscope before starting this tutorial. Keep in mind that using a microscope is a skill. You may have to stop the procedure and start over several times before you find your specimen. Keep at it, practice makes perfect!
Before you start you'll need to be sure you have a flat surface for your microscope, some cleaning tissues, your slides, and your lab sheet.
Today I am looking at a slide of red blood cells. Animal tissues make excellent slides. Now that you have what you need to get started, let's look at some specifics: To begin, make sure the lenses of the microscope are raised as high as possible and that the lowest magnification is selected. In most microscopes this will be the 4X lens. Never begin with the highest magnification; this is a good way to break slides and scratch the lens.
- I have chosen the slide of red blood cells for several reasons. It's easy to see them on the lowest magnification and when magnified on highest magnification, they are really beautiful.
- To begin, place the slide on the stage and clip it in.
- While looking through the eyepiece, turn the coarse magnification knob away from you, moving the lens closer to the slide. Make sure you don't crank it too fast. It should take you about 10 seconds to make one revolution with this knob.
- The key to finding your specimen is to remember if you are ahead of it or behind it. That is, did you just pass it moving toward it or away from it? While turning, watch for something to "flash" into and then out of your field of vision. As soon as this happens, stop turning. DO NOT turn the knob back to look for it again, let it pass, and stop. From this point on, you will use your fine adjustment knob to locate the specimen and bring it into view.
- The specimen was just passed when we used the coarse knob so we must work our way backward to locate it. If you forget or lose your way, you'll need to start over. This is where most people who are still learning to use the microscope have trouble. Be sure to move very slowly from this point.
- Using the fine adjustment knob, turn the knob toward your body very slowly. You may not make an entire revolution with this knob. It will be easy to pass your specimen with this knob if you turn it too quickly so be sure to move SLOWLY here. If you continue to turn the knob toward you for 2 revolutions without finding your specimen, you have passed it and will need to start over.
- If you see your specimen "flash" through your field of vision again, you are moving too quickly. STOP. Remember that you were moving upward when you passed it so now you must turn the knob more slowly in the downward direction or away from your body.
- Your specimen should come into view and you can use this knob to adjust the focus. If it does not and you lose the specimen, you will need to start over. Once you have it in focus, remove your eye from the eyepiece and look at the microscope. Turn the turret to select the next highest magnification which is usually 10X or 15X.
- At this point you don't know if you are ahead of or behind your image so you will have to turn the fine adjustment knob very slowly in one direction. If the focus seems to get worse, then move in the other direction. Your specimen should come into focus within only one quarter of a revolution of the fine adjustment knob. If you turn the knob a full revolution in either direction and cannot find your specimen, you will need to start over.
- Once you have your specimen in focus, you will change to the highest magnification. In some instances, this lens will be very close to the slide and sometimes it will be so close that you cannot turn this lens into position. See a tutorial on oil immersion if this happens.
- Once you have the highest magnification lens in place, look into the eyepiece. It is very important that you move very slowly, stopping to check how close the lens is moving to the slide. At this point, if you use the coarse adjustment knob you will break the slide and scratch the lens. Also, if you use the fine adjustment knob too quickly you may also run the lens into the slide and break it. Try to focus your image carefully and slowly. At this magnification, the tiniest imperceptible movements make a large difference so practice turning the fine adjustment knob as slowly as you can.
- If you cannot find the specimen at the highest magnification, DO NOT start over. Move back to the middle lens. Use the fine adjustment knob to locate your specimen if possible. Don't worry if you cannot and then have to start over. This is the point where most people, if they will have to begin again, will have to do it. Sometimes scientists who are very good at using microscopes have to start over at this point.
- If you have found and focused your image, congratulations! Enjoy the view!
- When you are finished viewing this specimen, protocol requires that you FIRST turn the lens to the lowest magnification. Second, remove the slide from the stage and third, turn the coarse adjustment knob toward you so that the lens is raised back to the highest position. The reason for this is that if you turn the coarse adjustment knob first, you may hit and break the slide, second, if you try to remove the slide first, you may not have enough room. Lastly, if you forget to turn the lens to the lowest magnification, when you begin the next slide and grab the coarse knob, you will hit the slide with it and break it.
- When you finish with your microscope, remember to turn the lens to the lowest magnification, remove your slide and raise the turret to the highest position. Clean the lenses and stage before storing your microscope.
© Teresa Bondora
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