How to use microscope immersion oil

Looking to get the best out of your oil objectives lens? Then you’ll need to know how to use immersion oil.

Why use immersion oil?

You’ll find that most high magnification objective lenses require immersion oil to reduce the impact of refraction.

Air, like any medium, refracts light to an extent. The air between your objective lens and your specimen is no exception – when the light hits the air, it bends and scatters.

At lower magnifications, the refraction isn’t particularly noticeable, and you can happily use your 4x, 10x and 40x objectives without any problems. But once you reach the higher magnifications, distortion becomes a real issue.

The solution? Replace that air with an oil with the same refractive index as the glass slide and coverslip. This reduces the amount of refraction, giving you a clearer image.

Nikon Immersion Oil 8cc

How to use immersion oil

First, make sure your lens is actually designed for oil immersion. Non-oil objectives are not properly sealed, and the oil will seep inside and damage them.

Once you’re sure you have an oil lens, here’s a general guide to using oil immersion microscopy with a standard compound microscope.

What you’ll need

  • Oil objective lens
  • Immersion oil
  • Coverslips
  • Glass slide
  • Lens paper

Using the oil

  1. Prepare your specimen on your slide. Make sure you use a coverslip.
  1. Put your slide under the microscope and find your specimen using the lower magnification objectives.
  1. Work your way up to the 40x and bring your specimen into focus.
  1. Rotate the 40x lens out of the way, stopping halfway to the 100x (oil) objective.
  1. Place one small drop of immersion oil directly on your coverslip.
  1. Gently swing the 100x oil objective and position it over the slide. Then use the fine focus control to lower the objective lens until it just touches the oil. It’s often best to look at your slide from the side while you do this, so you get a clear view while you’re lowering the objective.
  1. Look down the eyepiece and bring your specimen into focus using the fine focus. (Don’t use the coarse focus – you can easily ram the objective into the slide, damaging your lens.)
  1. Once you’ve finished inspecting your slide, roll the 100x objective out of position and remove the slide. Make absolutely sure that you don’t accidentally roll the 40x lens into the oily slide.
  1. Gently wipe the immersion oil off your oil objective lens using your lens paper.
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