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How do I correctly observe a specimen?

Found in: Techniques

Before looking at the specimen, we have to make some basic adjustments to the microscope.

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  • Make sure that the light switch of the microscope is turned off and that the light intensity regulator is set to the lowest light position. This is important to extend the life span of the lamp.
  • Make sure that the condenser is raised all the way to the top. There is a knob next to the condenser which you can turn.
  • Now turn the coarse focus knob (the large knob) to lower the stage. We have to do this in order to make sure that the objectives do not crash into the stage.
  • Now rotate the lowest magnification objective into place, if it is not already in place. for most compound microscopes, this is the 4x objective, which is the one marked with a red ring. The stage has already been lowered (step 3), so there should be no danger in crashing the objective into the stage.
  • We can now start observing the slide.

  • Now take a slide and place it on the stage. If your microscope has stage clips, then use the clips to hold down the slide. If you have a mechanical stage, then place the slide all the way into the slide holder. Center the slide. Many people overlook this step. Make sure that the object that you want to look at is right over the hole in the stage. Otherwise you will not be able to see anything.
  • Using the coarse focus knob, raise the stage all the way up. The low power objective is short and it should not crash into the slide. Do not look through the eyepiece just yet, just check that the objective does not touch the slide.
  • Now it is time to look through the eyepiece. You should not see anything meaningful yet. Adjust the light intensity to a comfortable level.
  • While looking through the eyepiece, turn the coarse focus knob into one direction, lowering the stage slowly. Sooner or later a crisp picture should appear.
  • Then move the slide to re-center the image. If the picture does not move, then you have focused on the dust that can be found on the condenser optics. You still need to find the correct focus.
  • When you have a sharp picture, rotate the next higher objective into place. This is in many cases the 10x objective. Make sure that you turn the revolving nos epiece into the right direction. Some people accidentally move the 40x objective into place (which is located on the opposite side). You do not have to worry about crashing the objective into the slide. As long as the image is in focus, you will not crash the objectives.
  • With the higher magnification objectives (10x, 40x, 100x), you must use the fine focus knob only. Turn the fine focus until you see a sharp picture again. You might need to adjust the light intensity. Also carefully open and close the condenser aperture diaphragm to see what happens.
  • With a sharp picture, recenter the image again and switch to a yet higher magnification (40x). Again use the fine focus knob only.
  • When you have finished your observations, rotate the 4x objective back into place and exchange the slide. The image should still be in focus
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