So far, you have learned how to use a microscope at magnifications of X4, X10, and X40. The next step is to learn how to use the X100 lens. Remember that when viewing through this lens, the specimen will appear 1000 times bigger, i.e., if your ocular lens is a X10. We call this lens the oil immersion lens because it uses oil, unlike the others. At this magnification light refraction (bending of light) cases the specimen to appear obscure. Adding oil reduces this refraction, allowing you to see a much clearer image. The X100 lens is manufactured so that it is sealed to prevent oil from entering. However, the other objective lenses are not oil-proof. They will be damaged if you allow oil to get unto them. They are very expensive to clean. If you forget anything in this lab, please don’t forget this – DO NOT GET OIL ON ANY OTHER LENS OTHER THAN THE OIL IMMERSION LENS.

X40 lens. Students often make the mistake of getting oil on this lens

Very often students make the mistake of rotating the X40 lens unto the oil by rotating the nose in the wrong direction. Please don’t do this. Follow the instructions below when using the oil immersion lens

  1. Focus the X4, X10, and then the X40 lens as described in the last lab.
  2. Now rotate the nose in such away that the specimen is between the X40 and X100 lens
  3. Add a drop of oil unto the specimen (only a drop please!)
  4. Move the X100 lens over the specimen. It will appear as if it will hit the slide but it won’t
  5. Use the fine adjustment knob to bring the specimen into focus
  6. If for some reason you can’t see clearly, you can go back to the X10 lens to focus, and then back to the X100 lens again. Do not go back to the X40 as this may get oil on the lens
  7. When you are done looking at the image, use the coarse adjustment knob to back the stage all the way down
  8. Remove the slide
  9. Use a lens wipe to dab the oil from the oil immersion lens. (You do not need to dab the other lens)
  10. To clean the slides, use a Kim wipe to gently pat the slide up and down until it is dry. DO NOT SCRUB, as this may remove specimen

Use lens paper to dab X100 lens when you are done
Lens paper

Microscope slide with immersion oil
Kim wipes
Cleaning slide (Dab only. Do not rub!)

Lab Assessment

  1. Call your Instructor to look at your slide to verify that you have it properly focused (5 points)
  2. Take a picture of the image using your cell phone camera (2 points)
  3. Repeat the above steps for one more specimen (7 points)
Courtney Simons
Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.
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